Also, the Cu/SAC257-1Bi/Cu bond had the highest tensile-shear strength and elongation percentage among the alloy solders, which has a tensile-shear strength of about 30% and an elongation percentage of about 38% higher than the base solder joint.A lead-free Sn-2.5Ag-0.7Cu base solder with different weight percentages of bismuth  was used. Thermal properties, microstructure, wettability and mechanical properties were investigated. By decreasing the degree of undercooling, microstructure improved, the eutectic structure become finer and the size of β-Sn and intermetallic compounds decreased. By the addition of bismuth to SAC257 solder, the spreading ratio increased from 80.46% to 85.97, indicating an improvement in wettability. In order to investigate the joint properties, alloy solders were bonded to copper substrate, and the structure of the interface, tensile-shear strength and the fractured surfaces were studied. It was observed that the thickness of the intermetallic compounds of Cu Among the various groups of lead-free solders, the Sn-Ag-Cu (SAC) triple alloy has the highest acceptability4. Due to this fact that these solders are easy to use and have relatively suitable mechanical and physical properties, they are the most widely used alloy solders8; However, there are still many unresolved issues with these solders10. SAC solders with high Ag content (>3 wt.%) have good cyclic thermal properties. However, the formation of a large amount of Ag3Sn intermetallic compound (IMC) results in non-homogeneous stress distribution and reduction of reliability in these solders12. Also, the high silver content has decreased the wettability and has increased the price of these solders. Recently, the SAC solder problems with high percentage of silver have been solved by SAC solders containing low silver content (1–3 wt.%). By reducing the percentage of Ag, despite an increase in elastic compliance and the plastic energy dissipation ability, thermal properties such as thermal fatigue and creep life of SAC solders have been reduced13. Therefore, to improve the properties of these solders, series of investigations have been carried out which show that the properties of SAC solders can be improved by adding a small amount of alloying elements such as Ni, Ti, Sb, Bi, Zn, Ni, Ga. Adding micro-alloying elements can modify the microstructure of SAC solders and it can limit the formation of Ag3Sn intermetallic by affecting the solidification rate15.In recent years, the use of lead-free solders has increased to replace with the common Sn-Pb solderet al.16 studied the effect of Zn on the wettability of Sn-3.8Ag-0.7Cu solder. They have shown an increase in the wettability of the mentioned solder by adding up to 0.8 wt.% Zn, but decreasing at higher percentages. This is due to the oxidation of Zn during soldering that reduces wettability16. Sungkhaphaitoon and Plookphol17 studied the effect of Sb addition on microstructure, mechanical and thermal properties of Sn-3Ag-0.5Cu solder. They reported that with the addition of Sb to the mentioned solder, more homogeneous distribution of IMCs was obtained, and the nature of IMCs changed to Ag3 and Cu65 compounds. Moreover, tensile strength increased and the ductility of the solder was reduced. It is worth to mention that by increasing the concentration of Sb from 0 to 3 wt.%, the melting temperature slightly increased17. El-Daly et al.10 showed that with the addition of bismuth to the SAC157 solder, the eutectic temperature decreases and the microstructure improves, which is a cause of decrease in the degree of undercooling. In addition, the tensile and creep properties of bismuth-containing solders improve as well10.Zhang 18:It can increase or decrease the rate of reaction/growth.It can change the physical properties of the formed phases.It can create additional reactive layers at the interface or even replace reactive products with commonly formed IMCs.Adding alloying elements to the SAC solders have three major effects on the interface reactions and the formation of IMCset al.18 showed that the elements of group (B) have a small effect on the growth of IMCs, while the elements of group (b) have a significant effect. The results showed that the addition of silver and iron, only reduced the diffusion coefficient, while in the case of gold and nickel, the reaction layer changed to 6Sn5 and 6Sn5, respectively, and even in the case of nickel, the curvature of IMC growth did not show any other parabolic behavior with time, indicating a change in the growth mechanism18. Tao et al.19 added Ni and Sb to the Sn-3.8Ag-0.7Cu-3Bi alloy solder. They showed that shear strength increases with the solid solution mechanism of Sb in Sn matrix, and reinforcement of new intermetallic compounds  6Sn5 and Ag319. A. Kantarcıoglu and Y.E. Kalay20 have shown that by adding micro alloying elements, Fe (0.01–0.1 wt%) and Al (0.05 wt%) to the eutectic SAC solder, the microstructure of the solder improved, the formation of Ag3Sn compounds was limited, and the new FeSn2 and Al-Sn-Cu intermetallic compounds were formed in the microstructure. Also, the thickness of the IMCs at the interface was reduced and the shear properties of soldered copper improved20. Developments of adding Bi and other common elements in Sn-Ag-Cu alloy are summarized in Table These elements generally fall into two general categories: (a) Elements that only affect the activity of the elements participating in the interactions of the interface, and these elements do not affect the formation of these phases. These elements generally have no significant solubility in the IMC layer, such as iron and silver. (B) Elements that participate in the interface interactions and have broad solubility in IMCs, such as gold and nickel. T. Laurila In this study, bismuth element was used to improve the properties of SAC solder alloy. Previous studies suggest that a significant reduction in the weight percent of Ag in SAC solders causes problems like an increase in the solidification range. For this reason, Sn-2.5Ag-0.7Cu solder alloy with moderate percentage of Ag was chosen as the base alloy. Therefore, in this study, the physical and mechanical properties of SAC257-xBi solder and their joints were investigated.In this study, the pure elements of tin, silver, copper and bismuth (purity 99.99 wt.%) were used for the synthesis of Sn-2.5Ag-0.7Cu-xBi solder alloys . For this purpose, the pure elements of Sn, Ag, Cu and various Bi percentages were placed in the alumina crucible in an atmospheric furnace at 650 °C. KCl-LiCl (1:1) was used as a flux to prevent molten oxidation and melt vaporization. For homogenization, the melt was kept at this temperature for 1 hour and experienced remelting for three times after the solidification of the alloyed solder. Casting the final melt was carried out in a cylindrical steel mold with a diameter of 4 cm and a height of 1 cm with a cooling rate of 6–8 °C/s. The chemical composition of the alloy solders after solidification is given in Table In order to investigate the microstructure of alloyed solders, the distribution of grains and IMCs before and after alloying, the samples were sectioned in 5 mm * 5 mm dimensions and then cold mounted. Then, the specimens were prepared according to the standard methods of metallography. For etching, a solution of ethanol [96Vol%], hydrochloric acid [2Vol%] and nitric acid [2Vol%] was used and the microstructure of the solder alloys was investigated by a scanning electron microscopy (Philips-Xl30- & FEI-Quanta -EDS Element silicon drift) and optical microscopy (Olympus-BX51M). MIP software was used for analyzing the microstructure images.The DSC test was used to measure the thermal properties of SAC257-xBi solder alloys x = 0, 1, 2.5, 5) in accordance with ASTM D3418/E1356 standard by Pishtaz Engineering Co. model TA-1A instrument. Samples with equivalent weight between 15 to 25 mg were used. The test was carried out in the argon atmosphere in the form of sweep (heating-cooling). The heating rate was 10 °C/min and the maximum temperature reached 300 °C during the DSC test. To determine the wettability of the solder alloys according to Japanese Industrial Standard, , the spreading ratio was calculated. For this purpose, the alloyed solder disks of the same weight (200mgr) containing flux were placed inside a ceramic crucible and melted in the furnace to obtain a spherical state after solidification. After the production of spherical shaped solders, they were placed on the copper substrates with flux (RMA) and according to the temperature program represented in Fig. , 2.5, 5 Tensile test was used to examine the mechanical strength of SAC257-xBi  solder alloys. For this purpose, the sub-size samples were prepared in accordance with Fig. 2 and 300 µm in thickness. In order to remove surface contaminations, the interlayers were washed with alcohol and were stored in the argon atmosphere until bonding process. The RMA flux was used to prevent the base metal and solder alloys against the oxidation during bonding process.In order to investigate the properties of the solder alloy joints, 2 mm copper sheets with a purity of 99.999 wt.% were used as substrate. For deoxidation and reduction of the surface roughness of copper sheets, the specimens were grinded and washed in sulfuric acid solution for 30 minutes. Finally, in order to ensure the absence of fats and other surface contaminants, the samples were washed with alcohol and kept in the neutral atmosphere of argon until they were bonded to maintain surface conditions. The synthesized solder alloy interlayers were cut in 12* 12 mmResistant furnace was used to provide the required temperature for bonding, and bonding temperature program is in accordance with the IEC 60068-2-58 2015 standard, as shown in Fig. In order to investigate the microstructure of the base solder/ base metal interface, a 300 µm solder foil and flux was placed between two copper samples with dimensions of 10 * 10 * 2 mm, and the system experienced temperature cycle in the furnace in accordance with the temperature program given in Fig. In order to determine the average thickness of the IMCs, the MIP image analyzer software was used. Because the thickness of the IMC layer was not uniform throughout the interface, the mean value of the thickness (Y) of IMC was obtained from the Equation , where AThe tensile-shear specimens were prepared in accordance with the ASTM D1002 standard which is provided in Fig. In order to investigate the failure mechanism of the joint, the tensile-shear fractured samples were sectioned, cleaned in ultrasonic bath for 15 minutes to eliminate the surface contaminations and were investigated by FE-SEM.22.To study the thermal behavior of solder alloys during cooling and heating, the DSC test was performed. Figures 25. Another parameter affecting the solidification behavior of the solder and its microstructure is undercooling, which is defined as ΔT = TL − TS, where TL is the temperature at which the melting starts during heating stage, and TS is the solidification temperature during cooling stage. The lower the ΔT, the better the nucleation of solidified phases, which increases the tendency for heterogeneous nucleation and makes the microstructure finer26. According to Fig. 3Sn and β-Sn phases and results in the finer microstructure25.In this study, with the addition of bismuth to the SAC257 base solder, despite the fact that the change in pasty range is small, the melting point decreases from about 219 °C in the SAC257 base solder to 207 °C in the alloy SAC257-5Bi, which indicates the positive effect of bismuth on the melting point. According to Lindemann’s criterion, melting occurs when the second root of the atom displacement in the network exceeds a certain atomic distance. Therefore, it is possible that with the addition of bismuth to the SAC257 solder, and the formation of new Sn-Bi bonds resulting from the reaction between tin and bismuth, the atomic displacement in crystalline network occurs easier and the overall melting temperature of the system decreases3Sn and Cu6Sn5 phases are formed in the β-Sn matrix, which are shown in Fig. 3Sn and Cu6Sn5 intermetallic compounds tends to change from needle to equiaxial shape. Also, due to the decrease in the degree of undercooling, the size of the intermetallic compounds decreases25. On the other hand, the Bi solubility is also limited in Sn, and in the case of more than 1 wt.% Bi, bismuth is deposited separately28, which is visible as white phase in Fig. Figure 3Sn and Cu6Sn5 are formed in the final stages of solidification. But, by adding Bi in the case of SAC257-1Bi, SAC257-2.5Bi, and SAC257-5Bi, the Ag3Sn and Cu6Sn5 intermetallic compounds are formed from the beginning of the solidification process25. Studies have shown that the formation of the β-Sn matrix phase in Sn-based alloys requires high degrees of undercooling11; therefore, in SAC257 solder with a relatively high degree of undercooling, first, the β-Sn phase is formed as the primary solidification product, and then the intermetallic compounds as the secondary phases. Talking about SAC-Bi solder alloys, Bi affects the solidification behavior of solder and reduces the degree of undercooling, which results in the formation of a portion of the intermetallic compounds as the primary solidification products, which act as the heterogeneous nucleation sites. On the other hand, reduction of undercooling limits the growth of β-Sn, and leads to the finer grain structure. Another part of the intermetallic compounds are formed simultaneously during a Sn-Ag-Cu ternary eutectic reaction. Therefore, two types of morphologies of the intermetallic compounds are expected to be observed in the microstructure of the SAC257-Bi alloys25. According to Fig. Figure By calculating the phase fraction in the solder alloys, which is provided in Fig. 30. Therefore, for improving the properties of SAC solders with alloying elements, the alloying elements should be selected in such a way that the wettability of the solder does not decrease and even improves. The spreading ratio is one of the important factors for investigation of the wettability of alloy solders. The results of spreading ratio in different cases are shown in Fig. To achieve a sound solder joint, liquid phase should properly wet the surface of the solid base materials. This means that there should be a special reaction between the liquid solder and the solid surfaces that are supposed to be bonded. The ability of liquid solder for spreading and flow during the soldering process is one of the most important factors for the formation of a suitable bond between solder and the base material31.The variation of the spreading ratio from 2.5 wt.% Bi to 5 wt.% Bi alloy solders is eligible, indicating that more than 2.5 wt.% Bi does not change the wettability. Generally, proper wettability occurs when there is the lowest amount of surface free energy. This means that the surface energy of the solder will be reduced by forming an interface with lower free energy. On the other hand, in order to liquid solder wets and bonds with the base material surface, the external forces (between liquid and the substrate) must overcome the internal forces (liquid interatomic forces). As the molten inner bonds become weaker, wettability can improve. In alloy solders, with the addition of bismuth and the formation of a weaker Sn-Bi bond, instead of Sn-Sn, the wettability can be improved. For this reason, the addition of bismuth to the base solder will increase the wettability33.In terms of classical wettability model, for determining the wettability of molten solder on a solid surface, the competition between the cohesive forces  and adhesive forces (the force between the atoms of the molten solder and the substrate), as well as the molten surface tension, is decisive. Therefore, in order to molten solder wets the substrate, the adhesive forces must overcome the cohesive forces of the molten solder. From the classical wetting point of view, the weaker the cohesive forces of the molten solder, the higher the wettability of the liquid phase on the solid substrate and the lower the wetting angle. As mentioned before, the melting temperature decreases in the solder alloy by adding Bi. Given this, addition of Bi weakens the internal forces (likely to form a weaker Sn-Bi bond instead of Sn-Sn) and therefore, external forces can overcome more than before. In other words, from the classical wetting perspective, by increasing the weight percentage of Bi as the melting point depressant, the spreadability of the liquid phase increases. Bi also has a lower surface tension and, by adding it to the base solder, the overall surface tension of the molten solder is reduced34. As shown in the results of the spreading coefficient, the rate of increase in wettability decreases with increasing Bi weight percent . But by increasing the amount of Bi in the solder alloy, the rate of increase in the wettability decreases and high concentrations of Bi, negatively affects the wettability. The reason for such a behavior can be explained based on the following schematic. Regarding Fig. see Fig. .Figure 1in-situ composites, while fine bismuth precipitates and IMCs are formed in the solder matrix during the cooling stage. Since these precipitates have a suitable chemical bonding with the matrix, their interaction with dislocations, slows their movement, delays the plasticity and increases the strength36.Figure Figure 6Sn537. Due to the limited solubility of Sn and Cu in each other and after dissolution of the copper in a short period of time in liquid phase, the adjacent liquid layer on the substrate at the interface saturates with Cu atoms (dissolved substrate). According to the equilibrium phase diagram, intermetallic compounds on this layer begin to form and generate at the interface by the following reaction40:It is observed that the thickness of the IMCs formed at the interface changes from 4.83 μm in the SAC257 solder to; 4.16, 4.23 and 4.36 µm in 1, 2.5 and 5 wt.% Bi alloy solders, respectively. It can be said that the thickness of IMCs in SAC257-xBi solders has decreased. For example, in the case of SAC257-1Bi alloy solder, the thickness is reduced by about 14% relative to the base solder. The linear and point EDS analyses are used to identify and analyze the interface and matrix phases which are shown in Fig. 6Sn5 interlayer, a very thin interlayer with a darker color compared to Cu6Sn5, is formed between the Cu6Sn5 and the substrate, which can be deduced to be Cu3Sn from EDS results and 3:1 ratio of Cu/Sn. This phase has a super lattice structure with long-range atomic arrangement. Formation of this thin layer is according to the following reaction42:In addition to the Cu3Sn and Cu6Sn5, and in the case of SAC257-5Bi solder alloy, bismuth deposits besides Ag3Sn and Cu6Sn5 have also been observed  represents a soft fracture that occurs from the bulk of the solder. This state occurs when the thickness of the IMC and the strength of the solder matrix are low. Due to the higher strength of IMCs, it is broken down from the solder matrix, (II) this mode occurs when the crack propagates in the boundary of the IMCs and creates a detachment. This mode of failure is more common in tensile mode of tensile-shear test. The smaller the IMCs, the longer the crack propagation and the more the energy absorption. In this mode, mixed fracture (ductile-brittle) occurs, (III) in this mode, which indicates a brittle fracture, the cracks develop inside the IMCs, and the separation of the solder from substrate takes place within the IMCs. Therefore, at the fracture surface, broken IMCs are visible. Mode (III) occurs in a situation where the thickness of the IMCs or the strength of the solder matrix is high48. However, these three scenarios may occur at the same time in a joint due to microstructure changes and variation in the thickness of the IMCs across the interface. According to the fractured surfaces of the SAC257/Cu in Fig. In order to investigate the fracture modes, the fractured surfaces after tensile-shear test were studied and the results are presented in Figs 6Sn5 phase at the surface that means a part of failure is brittle.Figure It was observed that the thermal properties of the SAC257 improve with adding Bi, and the eutectic temperature (melting temperature) was reduced 2 °C per weight percent of Bi element. Degree of undercooling, liquidus and solidus temperatures were decreased as well, while pasty range did not experience significant changes in 1, 2.5 wt.%Bi alloy solders.By adding Bi to the base solder, tensile strength increased by solid solution strengthening mechanism and the formation of fine bismuth precipitates in the matrix. But in high Bi contents (5 wt.%Bi), the tensile strength and elongation percentage decreased due to formation of course Bi-rich precipitates. By considering the spreading ratio in base and alloy solders, Bi has enhanced the wettability of the solder alloys.6Sn5 interfacial IMCs in such a way that IMCs thickness shows a descending trend at first, followed by an ascending trend which is generally thinner than the base solder interfacial IMCs. In the case of SAC257-1Bi joint, the interfacial IMCs is minimum which shows a 14% reduction in the thickness comparing to base solder.Adding bismuth alters the morphology and thickness of CuBy comparing the fracture surfaces of base solder (SAC257) and alloy solders (SAC257-Bi), it was observed that the fracture mechanism changes from IMC control (low reliability) in base solder joint to solder control (ductile fracture) in SAC257-1Bi joint, which is more reliable.Bi white nanosize precipitates were also formed in the matrix during a solid state process due to the reduced solubility of Bi in Sn by reducing the temperature. Therefore, Bi, due to the change in the solidification rate, the growth rate of eutectic phases and the reduction of the eutectic point, makes the microstructure finer.Addition of Bi weakens the internal forces (likely to form a weaker Sn-Bi bond instead of Sn-Sn) and therefore, external forces can overcome more than before. In other words, from the classical wetting perspective, by increasing the weight percentage of Bi as the melting point depressant, the spreadability of the liquid phase increases. Bi also has a lower surface tension and, by adding it to the base solder, the overall surface tension of the molten solder is reduced.In this study, alloying of Pb-free Sn-2.5Ag-0.7Cu solder (containing low Ag content) with Bi was investigated. Bulk and joint (Cu/SAC-xBi/Cu) properties of the solder alloys were studied and the main achievements are summarized below:


A multi-aperture atmospheric pressure plasma processing (APPP) method was proposed to structure the continuous phase plate (CPP). The APPP system was presented and removal investigation showed the removal function of APPP was of a high repeatability and robustness to the small disturbance of gas flows. A mathematical model for the multi-aperture structuring process was established and the simulation analysis indicated the advantages of the proposed method in terms of balancing the efficiency and accuracy of the process. The experimental results showed that multi-aperture APPP has the ability to structure a 30 mm × 30 mm CPP with the accuracy of 163.4 nm peak to valley (PV) and 31.7 nm root mean square (RMS). Continuous phase plates (CPPs) are essential diffractive optical elements in the light path of laser-driven inertial confinement fusion (ICF) systems, such as the National Ignition Facility , Laser MAtmospheric pressure plasma processing (APPP) is a promising technique for the modification, decontamination, and etching of polymers and glasses ,11,12,13The stable and controllable Gaussian-shape removal function makes APPP possible to fabricate structured surfaces with high accuracy and efficiency. Also, multi-aperture processing  is enabled to target different scales of surface features to increase the overall machining efficiency. However, little research has been reported on structuring CPPs with the multi-aperture APPP technique. In this paper, a multi-aperture APPP method was proposed for CPP structuring. The APPP system was first introduced, and its removal characteristics were investigated in two aspects: the repeatability and robustness. Then, a mathematical model for multi-aperture APPP dwell time solution was established and simulation analysis was performed to study the structuring efficiency and accuracy. Finally, the experimental processing was carried out to validate the effectiveness of the proposed multi-aperture APPP to structure CPPs.2, and CF4, was excited in the RF electromagnetic field. The flow rates of gases were controlled by the multichannel mass flow controller.A schematic diagram of the APPP setup is shown in 2) generated by radio frequency power was regarded as a chemical reactor; the reactant gas (CF4) fed into the reactor was decomposed by the collision of plasma electrons into active species [2) to accomplish the nanometric removal process. The balanced chemical reaction equation can be described as The plasma  method and its removal characteristics must be investigated before the fabrication process. In the actual CPP structuring process, the removal function repeatability and its robustness to disturbances were essential, which determined the process convergence and structuring accuracy. APPP removal experiments needed to be carried out. The plasma source was stabilized before the experimental processing. The sample material was fused silica and process parameters are listed in In order to investigate the repeatability of the removal function, five static removal spots were etched using the same process parameters shown in From the results, it can be seen that the maximum deviation of removal depth was about 5%, and the maximum deviation in FWHM was about 3.6%. The Gaussian removal function repeatability of APPP met the requirements for structuring CPPs. In actual processing, small disturbances in gas flow are unavoidable. Thus, it is necessary to study the robustness of the removal function under gas flow disturbances. The experimental parameters shown in 4 and O2 flow, the maximum deviation in the depth direction was about 3.5%, 2.8% and 2.9%, respectively, and the maximum deviation of the FWHM was about 2.9%, 1.2% and 3.6%. This was in the same range as the results from the repeatability experiments, indicating that the removal function of APPP was robust to the small disturbance of gas flows.According to the results, for the small disturbance of He, CFThe APPP structuring process flow chart is illustrated in Due to the complexity of CPP topography, the selection of the removal functions is essential to also meet the structuring capacity and processing efficiency. APPP removal functions with small FWHMs are suitable for structuring topography with small spatial periods. While the processing time might be unaffordable, removal functions with large FWHMs are associated with higher removal rates, but their structuring capacity is limited. For the conventional CCOS dwell time calculation, only a single removal function is considered in each optimization process. Taking both the CPP structuring efficiency and accuracy into account, this study proposed a multi-aperture optimized structuring method, where multiple removal functions were considered, and the corresponding dwell time was simultaneously solved in one optimization process. The mathematical model and the simulation analysis are presented in the following section.For conventional CCOS , the target removal is equal to the convolution between the single removal function and the dwell time . In the d,yd)Q(x can be determined by the Equation (2).The Fourier transform method and the conventional deconvolution method used in the CCOS are be suitable to solve the problem in Equation (1). Therefore, a matrix-based optimization model was established to obtain the dwell time solution for multiple removal functions. As shown in Assuming that the number of removal points is N, and the number of resident points is M, then the removal amount of all the dwell points to the point is as shown in Equation (3).M1, and the number of dwelling points of the second removal function is M2, Equation (1) can be converted into the matrix-based form as follows,Take two different removal functions for the multi-aperture structuring process as an example. Assuming that the number of dwelling points of the first removal function is M1 + M2 > N), the optimal solution of the overdetermined equations is generally needed. According to the two conditions of the minimum of the residue error and the non-negative dwell time, the optimization objective and constraints of the linear equations are as the follows,The solution of the linear equations shown in Equation (4) is the dwell time of the two APPP removal functions involved in the multi-aperture structuring. As the sum of the number of dwell points is larger than the number of removal points , but the structuring efficiency was very low, as the processing time was 340.94 min. When the two removal functions were adopted for combined multi-aperture process, the total processing time was 57.24 min . The PV and RMS values of the residue error were 1.49 × 10−5 μm and 1.11 × 10−6 μm, respectively, showing the advantages of both processing efficiency and accuracy.It can be seen from the simulation results that when the single removal function ①  was used, the total processing time was 5.61 min, but the residue error was high, as the calculated PV value and RMS value were 0.46 μm and 0.055 μm, respectively. When the removal function ②  was used, the residue error was almost zero  and Φ1 mm  diameter electrodes. Other process parameters were adopted to achieve the stable plasma etching process, as listed in The surface figure was then measured by a phase shifting interferometer . The structuring result is shown in In order to structure CPPs with high efficiency and accuracy, a multi-aperture APPP method was investigated with stable and controllable Gaussian-shape removal functions. The APPP system and removal investigation were introduced. The APPP removal function was of high repeatability and robustness to the small disturbance of gas flows. A multi-aperture mathematical model for the dwell time solution was established and the simulation analysis indicated the advantages of the proposed method in terms of balancing the process efficiency and accuracy. The experimental results showed the successful fabrication of a 30 mm × 30 mm CPP with an accuracy of 163.4 nm PV and 31.7 nm RMS, which demonstrates the potential of the multi-aperture APPP to structure complex CPPs.


Characterization of the catalysts was performed by UV-Vis and fluorescence spectroscopy, X-ray diffraction, temperature programed reduction, N2 adsorption, and electron microscopy. The presence of light produced a positive effect in the kinetics of nitrate removal. Higher selectivity toward nitrogen formation was observed under dark condition, while the photo-activated reactions showed higher selectivity for the production of ammonium. The hybrid catalyst containing 20 %wt. of carbon nanotubes shows the best compromise between activity and selectivity. A mechanism for the photocatalytic abatement of nitrate in water in the presence of the hybrid materials was proposed, based in the action of carbon nanotubes as light harvesters, dispersing media for TiO2 particles and as charge carrier facilitators.TiO Nitrate is a naturally occurring ion that is part of the nitrogen cycle, in which nitrogen species are switched between organisms and the environment. The increasing use of inorganic nitrogenous fertilizers, the disposal of wastes  and changes in land use are the main causes accounting for the progressively increasing levels of this pollutant in groundwater supplies. Nitrate ion  and biological denitrification.2 and CO2 are usually used in catalytic reduction reactions, in which H2 serves as reductant and CO2 as buffer  were evaluated as catalysts. Hydrogen and carbon dioxide were used as reducing and pH buffer agents, respectively. The materials were tested under the same experimental conditions, the only difference between the two processes being the introduction of a near-UV to visible light source in the case of the photocatalytic reactions.Following the previous findings, in the present work we explored the synergies between carbon nanotubes (CNT) and titanium dioxide in both catalytic and photocatalytic reduction of nitrate in water. For that purpose, hybrid materials of TiO4 were purchased from Shenzhen Nanoport Co. Ltd . TiO2 and CNT–TiO2 composite catalysts were prepared through an acid-catalyzed sol–gel procedure, as described elsewhere 4 (Aldrich 97%) in ethanol. The solution was magnetically stirred for 30 min, and then nitric acid (Fluka 65%) was added.Multi-walled carbon nanotubes synthesized by catalytic decomposition of CH3H7)4 ethanol solution. The mixture was kept stirring until a homogenous gel was formed. The gel was left aging in air for 5 days. The resulting material was then crushed into a fine powder (particle size < 100 μm). The powders were calcined at 400°C under a flow of N2 for 2 h to obtain TiO2 or CNT–TiO2 hybrid materials. Catalysts were labeled as XCNT–TiO2, where X  corresponds to the weight percentage of CNT in the material.For the composite catalysts preparation, a certain amount of CNT was added to the Ti2, Riedel-de Haen 99%] were added dropwise to TiO2 and CNT-TiO2 materials. In the case of the bimetallic catalyst, the materials were co-impregnated with a solution containing both precursor salts. The palladium and copper contents were fixed at 1%Pd-1%Cu and 1%Pd (weight percentages). After impregnation, the metal-loaded materials were dried in an oven at 100°C for 24 h. Then, the catalysts were heat treated under a nitrogen flow at 200°C for 1 h. At the end of this period, the gas stream was switched to hydrogen for 3 h to promote metals reduction. Finally, the materials were left to cool down to room temperature under a nitrogen flow.The monometallic (Pd) and bimetallic (Pd-Cu) catalysts were prepared by incipient wetness impregnation and co-impregnation, respectively. Briefly, aqueous solutions containing the proper mass of the corresponding salts  was passed through the reactor to remove the dissolved oxygen; CO2 acts as pH buffer (pH = 5.5). A Heraeus TQ 150 medium pressure mercury vapor lamp  was used as radiation source. The lamp was located axially in the reactor and held in a quartz immersion tube. A DURAN® glass jacket was used as water circulating cooling system (temperature maintained at 25°C) and as a filter for cutting-off low wavelength UV lines and letting pass radiation in the near-UV to visible light range (λexc ≥ 365 nm). Before turning illumination on, the solution was magnetically stirred in the dark for 15 min. After that period, 10 mL of a nitrate solution, prepared from NaNO3 (Sigma-Aldrich 99%), was added to the reactor, in order to obtain an initial −1. The first sample was taken out just before the light was turned on, in order to determine the initial nitrate concentration in solution. The catalytic (dark) experiments were carried out under the same experimental conditions, but in the absence of light.The catalytic and photocatalytic experiments were carried out in a glass cylindrical reactor. Initially, 190 mL of deionised water and 100 mg of catalyst were fed into the reactor. When used, a gas mixture of H3OH (45:55). The concentration of Samples were withdrawn regularly from the reactor, and centrifuged before determination of Palladium and copper leaching was assessed after each experiment by atomic absorption spectrometry (UNICAM 939/959), the absence of metals  being confirmed for all the cases.Reproducibility tests were performed for selected experiments, the results being in agreement with a maximum error of about 2.5%. 2, and Pd-Cu/20CNT-TiO2 are displayed in Figure 2 and CNT-TiO2 composites revealed that only anatase phase is present in neat TiO2 and composite catalysts. The XRD patterns of the Pd-Cu loaded CNT–TiO2 materials are very similar to the one of Pd-Cu/TiO2, with the CNT contribution hardly been identified. The Cu and Pd phases were not detected by XRD, which must be related to the low metal percentages (1%wt.). Anatase crystallites of 8.5 nm average size were found for neat TiO2, as determined by the Scherrer equation and confirmed by TEM  of TiO2 and CNT-TiO2 materials are listed in Table 2 and 10CNT–TiO2 composites, showed surface areas lower than the ones estimated through the mass composition of the composites  and even lower than for neat TiO2. These results indicate that the presence of low amounts of CNT induces the formation of big TiO2 crystallite agglomerates, therefore decreasing the surface area of the composite catalyst , the presence of a larger amount of CNT seems to prevent TiO2 particles from agglomerating, thus increasing the surface area, which was even higher than the calculated . This was confirmed by TEM , the values for SBET and SBET, calc were similar. Nevertheless, a further increase on the amount of CNT revealed to have a detrimental effect on the surface area of the resulting composites. A decrease in the SBET in relation to the calculated values of 15 and 40% was observed for 70CNT-TiO2 and 90CNT-TiO2 materials, respectively, which may be attributed to the formation of CNT bundles decreasing the accessible surface area, as could be visualized by TEM for 70CNT-TiO2  agrees fairly well with the nominal percentage, indicating negligible gasification of CNT during the calcination step  spectra were performed for having an insight in the behavior of light-generated electronic species in photocatalysts, since PL emission results from the recombination of electrons and holes. The PL emission spectra of the pure neat TiO2 and CNT-TiO2 composites loaded with 1%Pd and 1%Cu (wt.%) were used for catalytic and photocatalytic reduction of nitrate in aqueous suspensions. Monometallic Pd-TiO2 was used for comparison purposes. H2 and CO2 were continuously added to the reaction media, acting as reducing agent and pH buffer, respectively. The materials were tested under the same experimental conditions, the only difference between the two processes being the introduction of a near-UV to visible light source in the case of the photocatalytic reactions.TiO2 catalyst, the presence of Cu being fundamental for the reaction to occur. Moreover, as expected, it can be observed that the support has a crucial influence on the performance of the bimetallic catalysts.The performances of the different catalysts for the (dark) catalytic reduction process are presented in Figure 2 was the most efficient catalyst in terms of the kinetics of nitrate removal, with total nitrate conversion being achieved at the end of 90 min of reaction. Similar kinetic behavior was observed for nitrate reduction reactions using the composite materials with a CNT load (Y) of 5, 10, and 20%, leading to total nitrate removal at the end of 120 min of reaction. For higher CNT loads, a progressive detrimental effect in the kinetics of nitrate removal has been observed. Nitrate conversions of 95, 79, and 27% have been obtained at the end of 240 min when using composites with Y = 50, 70, and 90%, respectively. For the Pd-Cu/CNT catalyst only 12% nitrate removal was achieved at the end of the catalytic run.In the case of the catalytic reduction process, Pd-Cu/TiOsine qua non condition for nitrate conversion to occur. The composite material with the lowest CNT content (Y = 5%) produced a decrease in the efficiency of nitrate abatement compared to Pd-Cu/TiO2. Yet, a further increase in the CNT load up to Y = 20% lead to a rise in the rate of nitrate removal. For the composites with higher CNT content  a progressive loss in the efficiency toward In general, the presence of light promotes a positive effect in nitrate removal Figure . As in t2 in catalytic nitrate reduction with a decrease in the nitrate conversion with increasing CNT load. Yet, for the photocatalytic process a positive effect was observed using 10CNT-TiO2 and, in particular, 20CNT-TiO2 comparing with the experiments using TiO2 as support. On the other hand, the bimetallic catalyst supported on 20CNT-TiO2 promotes total conversion of nitrate at 60 min of reaction. Reutilization tests were performed using Pd-Cu/20CNT-TiO2 and Pd-Cu/TiO2 under catalytic and photocatalytic conditions. In both cases the results indicate that the performance of the catalysts was maintained within 5% variation over 3 consecutive runs.The conversion of nitrate at 60 min of reaction was calculated in order to get a better understanding of the effect of CNT load in the kinetics of s Figure . It is n2, CNT, and 20CNT-TiO2 catalysts. Residual amounts of 2 was used as catalyst, nitrite is partially transformed into ammonia during the reaction, which is accumulated in the aqueous media. It was found that for the catalytic process, the formation of nitrite and conversion into ammonium is slower than for the photocatalytic process. Also, lower amounts of ammonia were produced in the presence of light, using Pd-Cu/TiO2 and Pd-Cu/CNT, meaning a higher selectivity of the photocatalytic process toward N2 formation.Figure 2 higher amounts of 2 and Pd-Cu/CNT, the use of the metal-loaded 20CNT-TiO2 catalyst under irradiation lead to the formation of higher amounts of ammonia when compared to the catalytic process  catalytic reduction over bimetallic catalysts, using hydrogen as reducing agent, 2, the mechanism generally proposed is based on the role of metal nanoparticles as electron sinks. Since the Fermi levels of noble metals are lower than that of TiO2, the photo-excited electrons can be transferred from the conduction band of the semiconductor to the metal nanoparticles deposited on its surface, being then available for In the case of the photocatalytic process using metal-loaded TiO2 hybrids has been discussed in previous works reporting the use of this type of materials as photocatalysts for environmental applications .Based in our findings, and considering the operation conditions used in this study, the following photocatalytic reaction mechanism is proposed. Since the irradiation source emits in the near UV to visible range, it is expected that TiO2 and also over CNTs  by available electrons, may play a role as reducing mediator  catalytic reactions using CNT-TiO2 and CNT-TiO2 loaded with 1%Pd−1%Cu show high catalytic activity in the dark and under near UV to visible light irradiation, in the presence of H2 and CO2. The presence of light promotes faster 2 formation. In the case of the photocatalytic process, the hybrid materials lead to an increase in the yield of the reduction of +. The efficiency of the hybrid materials depends on the CNT load, the best performing material being that composed by 20 wt.% of carbon nanotubes. In the case of the dark catalytic process, the synergic effect observed by the introduction of CNT in the TiO2 matrix is mainly ascribed to the action of the carbon phase as dispersing medium to metal oxide particles, while under irradiation, CNT produce an increase in the efficiency of charge separation and mobility in the composite material.TiOCS and OS conceived the research work, prepared and characterized the catalysts, performed the activity tests and drafted the manuscript. JÓ, MP, and JF provided the means for the realization of this work and contributed to the interpretation of the experimental results. All authors read and approved the final manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Steel pipes in different engineering applications may fail, leading to numerous environmental disasters. During loading, certain mechanical and chemical phenomena develop inside the pipes and cause them to burst. In this study, the influence of internal pressure on the elastic and plastic behaviour of E355 steel pipes was investigated on small specimens with different wall thicknesses. First, the failure modes of pipes subjected to monotonic loading were assessed, and then the behaviour of specimens subjected to cyclic internal pressure was analysed in terms of variation of radial strain. The strain and stress states of pipes were analysed using the finite element method. The results revealed that the hardening of materials inside the pipes increases the risk of cracking and bursting because of elasticity limits being exceeded, causing entry into the plastic domain. The transition of mechanical behaviour can be observed in the microstructure of steel in cracked areas from the inside to the outside of the pipe. In energy infrastructures, the critical assessment of the bursting pressure of pipelines is very important with regard to their cost-effectiveness, safety and integrity. So, the engineering challenge is to establish the proper dimensions of the external diameter and wall thickness. These dimensions depend on the rate of supply, internal pressure and the mechanical properties of the pipe’s materials. Depending on the location of the pipes , there are several theories regarding the analysis of their elastic–plastic behaviour. Thus, for pipelines installed above the ground, some engineers use Timoshenko and Goodier’s elastic behaviour theory for the purpose of sizing pipes and choosing the material. Other design engineers rely on the theory of elastic–plastic behaviour. Prantdl and Reuss believe that total strain consists of an elastic and a plastic component . NumerouThe experiments on cyclic loads of pipe specimens are scarce in comparison to studies on monotonic behaviour. The cyclic plastic behaviour and the estimation of yield limits and hardening behaviour of metals from pipe structures is very complex, and experimental studies are required in order to cover several aspects. In this paper, the damage models and strains and stresses of steel pipes with different wall thicknesses were assessed after being subjected to high internal pressure in static and cyclic modes. The deformation in the radial direction was determined by measuring the external diameters of samples, before and after the internal pressure was applied. c) of 548 MPa and maximum stress (σr) of 722 MPa. The tested specimens were obtained from honed pipes with dimensions as presented in l) = 2000 mm. To control the experiment, a faucet (6) (type KHB–D/4’’) with a nominal diameter of 6 mm (DN6) and a nominal pressure of 500 bars (PN500) was connected. A supplementary manometer of 1000 bars (7) was attached using a T-shaped connector of 1/4’’ (5). The connection between the manometer and samples was assured by the same type of hydraulic hose (4). At the end of each sample, a metallic cork with gasket was attached (3)  was subjected to the same internal pressure, as provided by a hydraulic oil regime, and pressure from 100 to 1000 bars was measured on the exterior diameter with an electronic calliper (9) in order to observe the elastic–plastic deformation. The experimental setup consisted of an electric pump (8) with the electric current consumption of 4.5 A, working at a 50 Hz frequency and a maximum pressure of 800 bars, which provided the hydraulic oil regime. The pump transmitted the oil under pressure through a hydraulic hose (4) made in conformity with European standards (730 EN 856), having four metallic insertions (4SP) with a nominal diameter of 6 mm (DN6) resisting up to 450 bars and with length (ched (3) . The expWhile testing, the specimens were contained inside a protective pipe to avoid accidents. The damage structure and the microstructure of steel in cracked areas were analysed using a digital microscope. 2). Using similar equipment for monotone loading of samples, in this case, the experimental stand was improved with a pressure-regulating valve, and the pump was set to 400 bars, which was operated by remote control for automatically increasing pressure in the pipe and depressurizing the sample for 30 s/cycle (for the first ten cycles) and 60 s/cycle (in the second stage) over ten cycles  comparison with pipes with β > 1.1. Being of the same material, OL52 (E355), the values of the maximum stresses are close in the two cases, both of which are up to the break stress (722 MPa) and below the yield stress (548 MPa) : pipes with thick walls, characterized by β > 1.1, and thin walls, with β < 1.1. After importing the 3D model in Abaqus, the mechanical properties of steel E355 were used in the pre-processing step. From the point of view of boundary conditions, the “fixed at both ends” condition was applied and the model was loaded with an interior pressure of 80 N/mm548 MPa) . x) are relatively low and approximately equal, regardless of the thickness of the pipe wall. In the radial direction (y = z), the values are equal with regard to the circular section of the pipe being influenced by the wall thickness. Such displacements are approximately two times higher in the circumferential direction for the pipe with wall thickness 2.2 times lower than the thick-walled pipe, as can be seen in Regarding the displacement, it can be seen that in the longitudinal direction (x), the displacements  and experiments, it can be noticed that their differences range between 0.3 and 0.6% . In FiguCrack growth under variable loading has a crucial influence on structural life. The measured exterior diameters for each cycle were recorded in The trend line of radial deformation with increasing cycle number and duration of exposure to internal pressure is presented in In this experimental study, the radial strains of mini honed pipes made from E355 steel were analysed in the elastic and plastic domain with both monotonic and cyclic loading. The monotonic tests were carried out to determine the fracture mode of pipe subjected to internal pressure without the influence of other types of loading. Due to the experimental setup, the internal pressurisation of the pipe led to radial strain with a relatively smaller axial strain (due to Poisson’s effect). The radial deformation depends on the thicknesses of the pipe wall, which in this study, were classified into three types in accordance with the ratio between the outer and inner diameters of the pipe. As mentioned in , for a tThe cyclic tests with a maximum internal pressure around 25% lower than the burst pressure aim to assess the evolution of radial strain. The wall thickness and exterior diameter related to pipe radius play an important role in the high resistance of pipes. The variation of internal pressure in terms of cyclic loading leads to increasing the plastic deformation of pipe and risk of damage. Experiments show that the cyclic plastic characteristics of metallic materials are different from the monotonic ones. However, the behaviour of small pipes subjected to burst pressure depends on many factors, such as the type and intensity of loading, mechanical properties of pipe materials, thickness of wall, temperature, geometry of pipes, and environments.


In this regard, some analyses show a variable number of visits to the oncologist depending upon the stage of the disease, with higher rates at the beginning of treatment (particularly if neoadjuvant protocols are used), lower rates among survivors with controlled disease, and higher rates again toward the end of life.7 thus inducing permanent licensing of new oncology drugs and delivery of associated knowledge, which demands careful analysis by the medical oncologist workforce.In addition to cancer incidence and stage at diagnosis, technologies used for cancer treatment also determine the demand of medical oncology. Currently target and immune therapies represent the highest investment in research and development by pharmaceutical companies,8 Furthermore, the addition of trastuzumab increases treatment adverse effects and modifies the treatment schedule from approximately 8 to 27 sessions during the first year of treatment compared to chemotherapy alone.5 Similarly, systemic therapy combined with other treatment modalities, such as in the case of neoadjuvant and adjuvant protocols or concomitant chemo-radiation, the administration of several lines of treatment, and consolidation with bone marrow transplantation, have also shown better disease control and longer survival for different types of cancer, thus resulting in increased medical oncologist time for cancer care.Moreover, new technologies lead to relevant changes in oncology practice; for instance, trastuzumab combined with cytotoxic drugs for the management of HER2-positive breast cancer patients (approximately 20% of cases) reduces relapse in 50% of cases and increases survival rates.All factors described challenge the planning and supply of medical oncologist workforce, a situation critical to middle-income countries where better access to new cancer care technologies might take place, but the availability of resources to harmonize technology development with cancer care delivery is not a common situation. Hence, in this article, we review supply and demand of the medical oncologist workforce in Colombia using accredited sources of information and international standards.9International standards regarding the medical oncologist workforce are variable; accordingly, while the Royal College of Physicians reports one full-time equivalent medical oncologist per 200 new cancer cases, New Zealand reports 1 per 210 cases , and Australia one per 270 cases.10In the international arena, a publication based on secondary sources found that 24% of 93 countries reported a rate of less than 150 new cancer cases per medical oncologist, 42% reported more than 500 cases, and 29% reported more than 1,000 cases, most of the latter were located in Africa where 7 countries reported not having any oncologist available. In Latin America rates of new cancer cases per oncologist fluctuate from 108 in Uruguay to 667 in Chile; however, all data from the region in the review derive from expert opinion, and consequently, their accuracy and reliability is low.11 Likewise, a verbal report by the Colombian Association of Hematology and Oncology (ACHO for its Spanish acronym), indicates approximately 180 clinical oncologists and 170 hematologists affiliated, the latter comprising hematologists  and hemato-oncologists . Yet, there is no available information on training abroad.In Colombia the National Observatory of Employment for Education reports 177 graduates in clinical oncology (solid tumors) up to 2016, and 153 graduates in hemato-oncology , for a total of 324 specialists in the field of medical oncology .11 LikewKey ObjectiveDoes the medical oncology workforce meet the current demand in Colombia?Knowledge GeneratedColombia is a middle-income country with a growing economy. Available information suggest increased access to oncology care and oncology drugs; however, the medical oncology workforce does not follow the same pattern as represented in a relevant shortage according to international standards .RelevanceProjections based on the number of new medical oncologists graduated per year in the country show a reduced shortage in the next 20 years but not enough to meet the demand. Better planning of the educational offer is highly desirable as well as collection of accurate data on characteristics of oncology practice in the country.1 the rate of full-time equivalent specialists, counting both clinical oncologists and hemato-oncologists, would be 1 per 291 new cancer cases ,er cases . Accordi14 Furthermore, data from the United Kingdom indicate that 63.9% of the specialists rendered their services in more than 1 center, 19% were dedicated to a single type of cancer, 46% to maximum 2 types of cancer, 26% maximum to 3 types of cancer, and 8% were dedicated to more than 4 types of cancer.13 In the United States, the number of oncology centers has decreased while their size has increased and the number of visits per medical oncologist per week has decreased with some variation depending upon the type of practice  and age of the specialist (fewer visits in younger generations).15From a different perspective, Australia reports 1.1 full-time equivalent medical oncologist per 100,000 inhabitants, the United Kingdom 1.3, and the United States 3.5.16 indicating that the number of specialists in clinical oncology (solid tumors) is lower than the number of services officially registered for the medical specialty. The data suggest not only that medical oncologists render their services in several centers as in the United Kingdom, but also that some oncology services may not have a full-time specialist, and in fact, it might be possible that some services do not have any specialist available during several days of the week.In Colombia, by 2016, the National Registry of Health Service Providers (REPS for its Spanish acronym) reported 211 outpatient services in clinical oncology, 85 in hemato-oncology, and 175 in chemotherapy,17 In Europe, the predominant modality of training in medical oncology is a basic medical specialty of 5 years duration and training in internal medicine as part of the academic program.18In the United States, according to the Electronic Residency Application Service (ERAS) of the Association of American Medical Colleges (AAMC), by 2019 there are about 145 training programs in hemato-oncology with a duration of 3 years, offered as a fellowship program after training in internal medicine.11 All of them require preliminary training of 3 years in internal medicine, and their duration is 2 years for training in clinical oncology and hematology, and 3 years for training in hemato-oncology.In Latin America, most countries have at least one training program in medical oncology management of both solid tumors and hematologic malignancies. In Colombia, according to the National Higher Education Information System (SNIES), there is currently 1 training program in clinical oncology, 3 programs in hemato-oncology, and 2 programs in hematology.With 5 to 10 graduates per year from the existing programs in clinical oncology and hemato-oncology, it would take between 15 and 30 years to meet the national demand, without counting retirements and without considering the expected increase in the absolute number of new cancer cases over the period.16Colombia, with 45.5 million inhabitants, would require 450 specialists to obtain 1 full-time equivalent medical oncologist per 100,000 inhabitants, which represents a shortage of approximately 100 medical oncologists . Further19 a figure that drops down to 443 in 2017 with an increase in the average number of oncology services per center .20 Similarly, in the United States a reduction in the number but increase in size of oncology centers has been observed15; however, in Colombia the number of new cases per year by oncology center remains low (between 55 in La Guajira and 309 in Casanare).20By 2012, there were 748 health care centers with oncology services available in the country,15 In Colombia, the number of clinical oncology services (solid tumors) is greater than the number of specialists in this field, thus suggesting a complex dynamic with either low expertise, given the low number of cancer cases per center, or coverage with partial times, and even absence of a specialist during several days of the week in some centers.In the United States reasons related to lifestyle and greater complexity in the management of cancer patients, with the requirement of a more comprehensive approach to the disease, have been linked to the dynamic of oncology services observed.1 and the higher rate of full-time equivalent specialist in the United States compared with other high-income countries, the educational offer seems low in Colombia. Given the different training modalities , it is not possible to make a definite conclusion on the medical oncologist workforce; however, data from official registries (ACHO and SNIES) show a workforce shortage that does not meet international standards, and is having a negative influence on the quality of cancer care. Therefore, the gathering of detailed data through a structured survey among ACHO affiliates would be an asset for planning more effective training in the field in Colombia.Regarding the educational offer, in the United States there is 1 training program in hemato-oncology per 2.2 million inhabitants, whereas in Colombia there is 1 per 11.2 million inhabitants (1 per 7.5 if considering training in hematology). Despite differences in cancer incidence


From the pure-resonant scattering contribution of the Pb2+ cations, and from subsequent analysis of the resonant-invariant, the amount of Pb2+ cations condensed onto the polyanions with respect to the total amount of Pb2+ cations in the solvent was estimated. In order to scrutinize systematic limitations in the determination of the chemical concentrations of resonant scattering counterions in the collapsed phase, Monte Carlo simulations have been performed. The simulations are based on structural confinements at variable size in the range of few nanometers, which represent the collapsed subdomains in the polyanions. These confinements were gradually filled to a high degree of the volume fraction with resonant scattering counterions giving access to a resonant-invariant at a variable degree of filling. The simulations revealed in the limit of small structures a significant underestimation of the true degree of filling of the collapsed subdomains when determining chemical concentrations of Pb2+ cations from the resonant invariant.Anomalous small angle scattering measurements have been applied to diluted solutions of anionic polyacrylates decorated by specifically-interacting Pb The density of charges along a polyelectrolyte chain makes the chain conformation sensitive to electrolytes. The two most efficient strategies to control changes in polyelectrolyte conformation are the screening of electrostatic interactions among charged polymer segments by adding an inert salt  and the Theoretical understanding of the mechanism underlying the impact of specifically-interacting cations has made significant progress. To give but an example, the shape of the anionic polyacrylate coils gradually changes from a coil to a compact sphere with increasing electrostatic discharging via binding of specifically-interacting alkaline earth cations, thereby passing a cascade of transition states. For these transition states cigar-like or pearl necklace structures are discussed. The latter were predicted in analogy to the Rayleigh instability of oil droplets while being electrically charged ,5. Beyon2+] with M2+ equal to Sr2+ or Pb2+ as two examples for the impact of specifically interacting cations on the conformation and solubility of NaPA chains. The specifically interacting M2+ cations form complex bonds with the anionic carboxylate residues, located on every other carbon atom of the polymer backbone. Formation of complex bonds between the anionic groups and the M2+ cations neutralizes electric charges and thereby changes the nature of the respective chain segments. As a consequence, the solubility of the polyelectrolyte is lowered which leads to a significant coil shrinking and eventually causes a precipitation of the respective M2+-salt  = [cm−1] by use of the JUSIFA reference (glassy carbon) standards. The ASAXS sequences covering three energies followed the JUSIFA standard procedures i.e. repeating the whole sequence several times with subsequent averaging /[COO−] ~0.24 (FRM02), and to conclude that the present RI-analysis, which is based on an integral according to Equation (8) up to q = 2 nm−1, has recovered just 11% and 14% of those Pb2+ ions which presumably decorate the NaPA chains and are, thereby, condensed to confinements. Entering into D of 2 < D < 6.4 nm filled with a number of Pb2+ ions representing volume fractions of Pb2+ ions in the confinement between 10 and 25%. The regime of compatible confinement sizes is represented by the grey area in In order to make optimal use of these simulations, with respect to an appropriate evaluation of our quantitative RI-analysis, we adopt the following point of view. If both samples would lie on the phase boundary for Pb-PA in 0.1 M NaNOgiven in  as:[Pb samples  this is 2+ ions in solution are bound by chains, i.e., in case of a significant portion of Pb2+ ions moving freely in solution and, thus, scattering only incoherently the number of Pb2+ ions recovered as being bound to chains by the restricted integral up to 2 nm−1 must be larger than 11%–14%, which in 2+ ions in the confinement larger than ~20%.If, unlike to the just-adopted point of view, not all Pb2+ ions are in the collapsed subdomains while the other 50% are free in solution and not contributing to the small-angle scattering of the collapsed subdomains. Given, now, that 11% and 14% of the ASAXS active species are recovered by RI analysis, 22% and 28% of the counterions have to be in the condensed phase because, per definition, 50% of the Pb2+ ions cannot be detected by ASAXS. Entering with these numbers 2+, because along with the filling by Pb2+ ions additional volume has to be allocated to the hosting polymer segments and, most likely, some volume is also occupied by residual solvent molecules.In order to shed more light on the consequences of the latter, we present a gedankenexperiment. Let us assume that only 50% of the Pb2+ cations have been analyzed by small-angle neutron scattering and anomalous small-angle X-ray scattering experiments in the energy range of the LIII-absorption edge of lead. From the SANS and SAXS measurements, structural information of the organic confinements, which form via condensation of specifically-interacting Pb2+ ions was deduced. This information suggests that the polyacrylate chains host the complex bound Pb2+ ions in collapsed subdomains with a size of 2.6 < R < 3.4 nm where R is the radius of these collapsed pearl-like confinements. Moreover, from the resonant invariant, the amount of Pb2+ ions located in these pearls was determined. Comparison with XANES measurements revealed that the deduced concentration values are smaller by a factor 1/7 to 1/9. It is this point, where significant progress could be achieved with Monte Carlo simulations, which provided an instructive picture of the limitations of the quantitative amount of ASAXS active entities deduced from an integration of the Kratky plot. The simulations revealed estimations of the accessible fraction of the true amount of bound ions, as it depends on the integration limit, the size of the confinements and the degree of filling of the confinements with ASAXS active entities. Applied to our system, the Monte Carlo simulations demonstrate, that if a RI is based on an integral limited to 2 nm−1 and if ASAXS active species are accumulated in confinements of a few nanometers in size, the degree which can be recovered from those accumulated ASAXS active species can show strong variation between a few percent up to 70% depending on the degree of filling. From this findings it was concluded, that the filling degree of bound entities must be between 10% and 25% in order to achieve compatible results when comparing the concentration values obtained from RI-analysis and from XANES. If a significant portion of counterions would not have bound to the polyacrylate chains, our Monte Carlo simulations would have suggested a filling degree in the condensed domains larger than 20%.Diluted solutions of anionic polyacrylates decorated with specifically interacting Pb


The effects of the tension on the mechanical properties and structure of the Kevlar 49 fibers were studied by mechanical testing, wide-angle and small-angle X-ray scattering , and scanning electron microscopy (SEM). The results show that the mechanical properties, crystallinity and orientation of the fiber can be improved when the tension is less than 0.6 cN/dtex, which may be due to the increasing of the mobility of a rigid segment with the help of the plasticization of scCO2 and re-arrangement of macromolecular chain into crystalline and orientation structure under tension. What’s more, the amorphous region also was enhanced by crosslinking reaction of toluene 2,4-diisocyanate (TDI) with the chain end groups of the macromolecules in the amorphous regions. However, a decrease of tenacity was found when the tension was higher than 0.6 cN/dtex, which is because the tension was so high that the microfibril was broken. The results indicated that treating the Kevlar 49 fiber in scCO2 under a suitable tension with TDI as a crosslink agent can simultaneously improve both the tenacity and modulus of the fiber.High modulus aramid fiber, such as Kevlar 49, is conventionally prepared by the heat annealing of high strength aramid fiber under a suitable tension at high temperature, especially higher than 500 °C. This enables the mobility of a rigid molecule chain to be rearranged into a more perfect crystalline or orientation structure under tension. However, annealing decreases the tensile strength, since the thermal degradation of the molecular chain at high temperature cannot be avoided. Kevlar 49 fibers treated in supercritical carbon dioxide (scCO Molla proposed single step process with green scCO2 dyeing while simultaneously functionalization antimicrobial fabrics without environmental pollution [2 as reaction medium to synthesis high molecular weight polycaprolactone-g-glycidyl methacrylate (PCL-g-GMA) [2, which aids in dyeing and improves the crystallinity, were studied, and the rearrangement of polymer chains in the amorphous phase was induced by cold drawing and exposure to scCO2 [2 with glycidyl-POSS to improve the surface adhesion of aramid fiber/epoxy resin [2 by controlling the temperature and tension to improve the mechanical properties or reduced the heat of the cyclic reaction [2, which enhanced the amorphous phase and improved the tensile strength and modulus of the fiber [Supercritical COrization ,16, polyrization  and foamrization ,18,19, crization , and powrization , which arization . ScCO2 hollution . PicchioL-g-GMA) . It has L-g-GMA) ,24,25,26to scCO2 ,28. Luo xy resin . We reporeaction ,30. In ohe fiber . However2 can diffuse into the amorphous region of Kevlar 49 fiber to enable the mobility of rigid segment of macromolecular chain at a lower temperature, which can avoid thermal degradation at high temperature. When tension was applied, the segment chain can be rearranged into a regular structure, which could improve the mechanical properties. In this paper, the influence of the tension applied in scCO2 on the mechanical properties and microstructure of Kevlar 49 fibers was studied.The scCO3. The carbon dioxide, toluene 2,4-diisocyanate (TDI), and acetone used in this study were purchased from Shanghai Chenggong Gases Co., Ltd. , J&K Chemical Ltd. , and Shanghai Ling Feng Chemical Reagent Co., Ltd. , respectively. These chemicals were used without further purification.Kevlar 49 fibers were manufactured by Dupont Co. USA . The yarn is made of 10,012 single filaments with a diameter of 12.7 μm and a specific linear density of 6320 dtex, density of 1.44 g/cm2 with TDI, and the process is reported in our early study [2 and react with the Kevlar 49 fibers. Finally, decompression was slowly conducted. The fibers treated were cleaned with acetone and dried under vacuum at 80 °C for 4 h.Experiments were conducted using scCOly study . After b−1. At least 50 specimens were tested for each sample, and the average values of the tenacity and modulus were calculated. The linear density of fiber was measured by XD-1 vibrating fiber fineness instrument. The unit conversion of Pa and CN/dtex was based on the Equation (1)3, dtex is the average linear density for 10 thousands of meters fibers.The tensile strength and modulus of Kevlar 49 fibers as received and treated were tested by XQ-1A tensile tester  with a gauge length of 10 mm and an extension rate of 10 mm·min2SO4 for 20 s in order to remove the amorphous region. All the samples were coated with a vapor-deposited thin conducting layer of gold to minimize charging.A JSM-5600 LV scanning electron microscope was employed to analyze the surface morphology of fiber which was etched by 85% H2. Temperature ramp measurements were conducted in an inert atmosphere of N2 from 30 to 900 °C at 10 °C·min−1.A DuPont TGA-29 thermogravimetric analyzer  was used to measure the thermal stability of the as-received and treated fibers in scCOWAXS experiments of the fibers were carried out at the SSRF Beamline 16 BL with an X-ray wavelength of 0.124 nm. Small bundles of fibers were vertically mounted onto a sample holder at a sample-to-detector  distance of 120.5 mm.SAXS experiments of the fibers were carried out at the SSRF Beamline 16 BL with an X-ray wavelength of 0.124 nm. Small bundles of fibers were vertically mounted onto a sample holder at a sample-to-detector  distance of 5027.5 mm and calibrated with a chicken collagen standard.The WAXS and SAXS data analyses were carried out using the Xpolar software . The WAXS pattern of the as-received Kevlar fibers is shown in Moreover, the amorphous halo along the equatorial direction indicates the poor intermolecular packing structure of chain segments parallel to the fiber axis.The pattern shape on the equator was sharp along the azimuthal direction. Therefore, the alignment of molecules in the Kevlar49 fiber is parallel to the fiber direction. The bright area will be discussed later, it indicates crystal growth and orientation improvement.cos2φ is the average angle that chains make with the direction, which is the average direction of the orientation of the chains.The (200) and (110) diffractions were used to study the crystallites and size of the Kevlar crystal. Excellent alignment of the (200) lattice fringes, which represent the alignment of Kevlar molecules with respect to the fiber axis, was observed. The degree of orientation of the (200) lattice plane was calculated by Herman’s orientation function, as shown in Equation (2) :(2)f=3coλ is the wave length of the X-ray source (0.124 nm) and β is the full width at the half maximum of the fitted scattering peak at the Bragg angle θ corresponding to the crystal plane (110) and (200).The crystallite sizes (ACS) in the directions perpendicular to of (110) and (200) crystal planes were determined by the Sherrer Equation (3) (3)Lhkl=L, then the width of the streak (obsB) in the reciprocal space is independent of the scattering vector . The effects of both the finite length and orientation can contribute to the width of the equatorial scattering streak. The distribution of the scattering vector can be determined using the Ruland method [Prior to the data analysis, the background scattering was corrected for by subtracting an average 2 s blank image from the sample scattering. Then, these data files were transformed into two-dimensional (2D) data. All data analyses were carried out using the X polar software. A SAXS pattern provides the average cross-sectional size of a cylindrical material that has a scattering power. It is difficult to determine whether the streak-like SAXS pattern originates from the microfibrils, microvoids, or reflections from the fiber surface depending on the angular range. Grubb et al. pointed out that the scattering objects in Kevlar 49 were mainly associated with the microfibrillar structure and not from the void morphology . Dobb etd method ,37.Bobs. The microfibril length (fL) and disorientation width (B) can be obtained using Equation (4)In S2 of the as-received Kevlar49 fibers is linear, as shown in fL and obsB, the data is fitted using a linear least-squares fitting routine. The intercept at s = 0 determines the length of the microfibril, and the slope is related to the microfibril disorientation width.The relationship between 2SO4 for 20 s; some fibrils running parallel to the fiber axis are also observed. Chemical etching techniques have been used to preferentially attack the amorphous regions of the fiber that have a higher chemical activity [2, compared with 2SO4 acid solution.activity . These r2 with TDI, the optimal condition for making high modulus is under tension of 0.6 cN/dtex and when we want to obtain a high tenacity, the best condition is 0.2 cN/dtex. Here, TDI was the crosslinker and a solute in scCO2. It infiltrated into the fiber, and adhered to the fibrillar elements, thus providing a secondary force for improving the mechanical properties. Moreover, the tensile modulus obviously improves because the molecular chains tend to arrange with the help of the plasticization of scCO2 and tension. However, when the tension is too high, owing to the constant pressure and temperature, the tenacity is not obviously improved, especially showed decrease under 0.8 cN/dtex.The mechanical properties of Kevlar fibers treated under various tensions were studied. The change of modulus and tenacity were shown in 2 on the crystal structure and orientation is studied by WAXS. The 2D WAXS patterns and fitting results of Kevlar 49 fibers treated under various tensions are shown in The influence of the treatment tension in scCO2 under tension of 0.6 cN/dtex exhibit narrow equatorial arcs, which imply a higher degree of crystal orientation. The results suggest that at a high temperature and high pressure, tension would promote some strain-induced crystallization, which is responsible for the increased crystallinity and orientation.Obviously, the reflections of the WAXS patterns of Kevlar 49 fibers treated in scCO2 mostly increases with increasing tension, indicating that the crystallites region is perfected. The crystallite sizes of the (110) and (200) planes of fibers increase with tension. However, this does not depend on the tension. A tension less than 0.2 cN/dtex, the size of (110) is increased, which indicated that the crystals growing along this direction were increased under tension. However, as some crystals grow with the reorganization in scCO2, some crystals might be destroyed at a high tension. The increase in the crystal size also indicates the perfection of the crystallites as the crystals grow.The crystallinity of fibers, crystalline orientation and apparent crystal size of the (110) and (200) peaks of the Kevlar 49 fibers are shown in 2 and tension in the amorphous region, the perfection of the crystallization was improved. However, for a treatment at a higher tension than 0.6 cN/dtex, the crystallinity slightly increases, but the crystal size and orientation are not greatly increased. This can be explained as follows. When TDI is added, it impregnates into the defect regions in the interior crystal structures, which disrupts the crystal perfection, and the molecules also infiltrate the amorphous regions for crosslinking reactions. These reactions occur between the molecular chains or microfibrils, forming more networks and increasing the intermolecular force, leading to a decrease in the activity of a chain, which may also inhibit its orientation.With the rearrangement of the molecular structure with the plasticization of scCO2 seems to be the cause for the chain alignment and an increase in the modulus while the number of defects is decreased. Moreover, the increase in the intermolecular force due to crosslinking with TDI could improve the tensile strength. However, the crystallites and orientation at the 0.8 cN/dtex tension was less than at the 0.6 cN/dtex tension, which may be because the higher tension would make fibrils broken and less oriented. The crystallite sizes of the (110) and (210) planes were larger, under a higher tension, which is useful for perfection of the crystallites, so the modulus is larger.As we know, the perfection and orientation of the crystallites are responsible for their mechanical properties . The modfL) and misorientation (obsB) of a microfibril in the direction of the fiber axis were obtained by the Ruland method.SAXS was used to determine the effects of TDI on the fibrillar structure of the Kevlar 49 fibers under various conditions. As discussed in 2 with TDI and without tension, and here are increases in the orientation and correlation length. This result is consistent with the infiltration and crosslinking of a fiber by TDI and the rearrangement of the molecular chains, which will decrease the volume. When the tension is applied, the disorientation of the fibers treated in scCO2 decreased under tension by less than 0.6 cN/dex, indicating an increase in the orientation of the microfibrils. However, the length of a microfibril is slightly lower. This reason is that the microfibrils existing between the loosely connected networks of microfibrillar structures are compressed and oriented with the plasticization of scCO2. In addition, there is a decrease in the misorientation width of the microfibrils in the fibers treated in scCO2 under tension. This may be because the externally applied tensile force will have a stronger effect in the amorphous regions due to their higher mobility since the chains establish a more extended and more densely packed state, decreasing the scattered intensity.The degree of orientation and length of the fibril is listed in As the 0.6 cN/dtex tension was applied, the microfibrillar length was reduced to 733.4 nm, and the orientation was 11.4°, which is slightly larger than that of the as received fibers and could be attributed to the breakage of some molecule chain under tension, resulting more molecule chain end formed. However, the tensile strength is not decreased largely, as the crosslinking reaction of TDI with chain end happened.2 exhibit good mechanical properties. This is because the fibrillar structure plays a significant role in mechanical properties of the Kevlar fibers [2, they are compressed. Moreover, when TDI impregnates into the amorphous regions of a fiber by scCO2, intermolecular crosslinking occurs, and the adhesion between the fibrils increases. The applied tension causes the chains to be arranged more regularly, which would result in crystallization or the perfection of crystallites.From the tensile properties of the fibers, the fibers treated in scCOr fibers ,40. When2 and without tension (b) and that of the as received fiber (a). From the curves of 2 with or without tension are improved at the 550–580 °C. Moreover, at temperatures above 800 °C, the sample mass loss reaches a nearly constant value which corresponds to the carbon ash content of the sample. The residual mass of the fiber treated in scCO2 under a tension of 0.6 cN/dtex is obviously higher than that of untreated fiber and only treated in scCO2 without tension. Thermal degradation of fiber starts from skin to core [2 with TDI, the skin surface and amorphous region were enhanced due to the more regular arrangement of the molecules and the higher crystallinity, which corresponding to the results of 2 under tension, the internal crosslinking reaction between TDI and more hydrogen of the amide bond of the fiber, the intermolecular force improves, resulting in an improved heat resistance and residual mass. Moreover, the residual content of the fiber only treated in scCO2 is lower, which may be because the impurities or the moisture was reduced by the purification of scCO2.We studied the thermal stability of the fibers by thermogravimetric analysis (TGA). From  to core , when th−2 μm in diameter, which, in turn, are comprised of microfibrils, with a diameter of ~100 nm and length of 500–1200 nm. The microfibril was comprised of a large perfectly oriented crystallite phase and irregular amorphous phase. The amorphous phase has a less regular macromolecule with some chain end or defects, which exist between the crystallites or at fibril interfaces. With the help of swelling the scCO2, TDI was dissolved and impregnated the fiber. Crosslinking reaction of TDI with the chain end in the amorphous phase between the interfaces of the fibril will adhere to the fibrillar elements and provide a secondary inter-fibrillar force. With the plasticization of scCO2 and tension, the mobility of rigid segment of macromolecular chain is improved, allowing it to be packed more regularly, and the rearrangement of amorphous region, resulting in the perfection of the crystallization with a higher crystallite, orientation, which is useful for improving the mechanical properties.Based on the results and discussions above, a model of the progress and structure change is shown in 2 under different tensions to improve the mechanical properties. The effects of the tension of scCO2 on the mechanical properties and structure of the Kevlar 49 fibers were studied by mechanical testing, WAXS, SAXS, and SEM. Mechanical testing showed that a suitable tension can simultaneously improve both the strength and modulus of Kevlar49 fiber with the crosslinking reaction of TDI, however, when the tension is higher than 0.6 cN/dtex, the tensile strength is decreased, which may be because the tension that is too high to break some microstructure of the fiber, corresponding to the length of microfibril of SAXS results. As indicated by the results of the measurement of structure from SAXS, the crystallinity of the Kevlar 49 fibers is increased in scCO2, owing to the perfection of crystallites and rearrangement in the amorphous regions. With the plasticization of scCO2 and tension, the mobility of the rigid segment of macromolecular chain in the amorphous region was improved, and the tension can induce alignment of these rigid segments into a more regular structure. What’s more, the amorphous regions can also be enhanced by the crosslinking reaction of TDI in scCO2. The thermal stability of fibers was also be improved as the perfection of structure and improvement of intermolecular force. Owning to the treatment in scCO2 can improve both of the tensile strength and modulus of the aramid fiber, it might be applied to the rigid fiber such as polybenzobisoxazole and polyimide fiber. In addition, there appears to be further scope for the research to improve of compressive strength of the rigid fiber.Kevlar 49 fibers were treated in scCO