K-TIG (Keyhole Tungsten Inert Gas) method is a new, emerging welding technology that offers a significant acceleration of the joining process, even for very thick plates. However, its potential for welding of certain materials is still unknown. Particularly challenging are duplex steels as this technology does not allow the use of a filler material, which is crucial for these steels and for weld joint microstructure adjustment. In order to demonstrate the suitability of this technology for single-pass welding of 1.4462 duplex steel detailed studies of the microstructure of the weld joints obtained for different linear energies were carried out and discussed with respect to their mechanical properties. According to the results obtained, the heat-affected zone (HAZ) shows a microstructure similar to the HAZ of duplex steel welded with the traditional TIG multi-pass methods. However, the weld, due to the lack of filler material, had a microstructure different to that typical for duplex steel welded joints and was also characterized by an increased content of ferrite. However, all joints, both in terms of microstructure and mechanical properties, met the requirements of the relevant standards. Moreover, the K-TIG process can be carried out in the linear energy range typical of duplex steel welding, although further optimization is needed. The steel ,8,9. Duphe steel ; respecthe steel . The selK-TIG process is an innovative welding method; it is a variation of the TIG process that enables deep penetration of the arc, while ensuring high productivity and quality of the welding process. Due to the relatively low linear welding energy, this process has been used in the welding of such materials as: titanium and its alloys, zirconium, corrosion-resistant steels, and high-strength carbon steels ,13,14. TAlthough this technology is very promising due to the efficiency of the welding process, it is still not widespread in industrial practice. First studies have shown its suitability for the welding of steel S32101 (lean duplex) ,20,21. NThe aim of this study was to investigate the microstructure of welded joints of duplex steel of 1.4462 grade with a thickness of 10 mm obtained by the K-TIG method at various linear welding energies and to discuss the effect on mechanical properties, including in particular impact toughness at −40 °C. The latter is significant from the viewpoint of the transition temperature to the brittle state, which is related to the permissible negative operating temperature of components made from these steels.A 10 mm thickness plate of 1.4462 grade according to EN 10088-2  was usedφ = 6.4 mm, and the whole system was cooled by a liquid in a closed circuit.The welding process was carried out using the K-TIG method on a HTIG-1000 device  with a welding current adjustment range: 60–1000 A, voltage U0 = 79 V and 100% duty cycle for the maximum welding current. The power source was connected by control cables to a welding head with a tungsten electrode having a diameter of Butt joints were made with full penetration—single-pass; one-side without a backing (BW ss nb), without beveling the joined elements (plates) and without spacing (gap) between them, and without the use of additional welding material . The shielding gas used was: argon—both on the side of the cap and the root of the weld. The preparation of elements for welding at the workplace is shown in Five samples joints were made at the welding stand with variable parameters: welding current (A), arc voltage (V) and welding speeds (mm/s). The welding parameters were selected in such a way as to obtain the widest possible range of the linear welding energy, within the range permissible according the theoretical values specified for welding duplex steels 0.5–2.5 kJ/mm ,5,23. ThU—arc voltage (V),I—welding current (A),sp—welding speed (mm/s).VThe linear welding energy was determined on the basis of the Formula (1), as calculated without the coefficient of thermal efficiency of the welding method k. A detailed explanation for the application of the k-factor is provided in the The energy parameters of the welding process mentioned in Formula (1) can directly influence the linear welding energy. When it is required to use a narrow linear welding energy range, accurate measurement and constant supervision of the energy parameters becomes crucial in obtaining a welded joint with appropriate mechanical properties and corrosion resistance ,25,26.After completion of the welding process, the obtained welds were assessed for the presence of welding non-conformities in accordance with the requirements of EN-ISO 5817 . SamplesIn the sample number 1, a non-compliance defined as incomplete root penetration was observed along the entire length of the joint. The obtained penetration depth of the sample number 1, with the parameters according to The technological parameters adopted for the welding process of sample number 5 were too high for obtaining an acceptable joint (weld). The weld was not obtained along the entire length of the test plate. Due to the excessively high parameters, melting of the edges of the test panels in the area of the plate thickness occurs and the formation of a welding imperfection called burn-through was observed.The samples number 2, 3 and 4 met the assumed quality level “B” in accordance with the requirements of EN ISO 5817 . The tesThe tensile test was performed for transverse samples in accordance with the requirements of ISO 4136 . The tesThe bending test was performed according to standard EN-ISO 5173 . Two typThe Charpy impact test was carried out on the welded joints in accordance with the requirements of ISO 148-1 , with thThe Vickers method was used for the hardness tests with a load of HV10, in accordance with the requirements of ISO 9015-1 . The har2O, 3 g-(NH4)2CuCl4·2H2O, 50 mL-HCl, 15g-FeCl3). The observation was performed using a Nikon EPIPHOT 200 optical microscope  and the NIS-Elements BR software was used for image analysis .Macroscopic tests were carried out in accordance with ISO 17639 , showing4F·HF, 400 mL-HCl, 12 g-K2S2O5, 800 mL-H2O). The examination was performed using a Nikon EPIPHOT 200 optical microscope . Quantitative analyzes of the surface proportions of individual microstructure components were performed using the NIS-Elements BR computer program .Microscopic examination of the welded joints was carried out according to the procedure described in the standard ISO 17639 . The strAnalysis of the chemical composition of the components of the structure of welded joints in particular areas, such as the HAZ and the WM, as well as the examination of the fracture surfaces after the impact test, were performed using a scanning electron microscope. An FE-SEM SU-70 (Field Emission Scanning Electron Microscopy) microscope  was used equipped with an EDS (energy dispersive spectrometry) X-ray microanalysis spectrometer . The SEM-EDS analysis was performed at an accelerating voltage of 15 kV.The test weld joints were made with the technological parameters, which are shown in The geometry of the obtained welds is shown in In general, it can be assumed that if other welding parameters are constant, the width of the face (cap) and the fusion depth (penetration) increases with increasing welding current. At a level of 480 A, it is not possible to obtain a full penetration of the 10 mm thickness plate and there are gas pores in the weld (WM), as shown in This experiment showed that the penetration depth of the welding arc was enhanced with increasing welding current, provided the welding speed was in a safety regime. At a low level of welding current, it was not possible to obtain a complete penetration of the 10 mm thick plate and there were gas pores in the WM. When the intensity of the welding current increased in order to create the “keyhole” effect, no gas pores were observed in the weld and the root obtained the correct shape. However, if the welding current intensity continued to increase to a level of 533–583 A, this upset the equilibrium between the static pressure of the molten metal in the weld pool and its surface tension . This leOn the obtained macrostructures, shown in Using an optical microscope, it was clearly visible with sample numbers 2, 3 and 4 that the microstructure consisted of two phases: austenite (light phase) and ferrite (dark phase). The structure can be considered as austenite fields (islands) against a background of ferritic matrix.The HAZ of the tested welded joints are shown in As shown in No intermetallic phases were detected in either the HAZ  or the WIn the studies of the welding of lean duplex steel , it was SEM analyses were carried out on samples 2, 3 and 4 in the HAZ and the WM. For comparison, the BM for sample number 4 was additionally analyzed. Two components present in the duplex steel were tested: austenite (convex area) and ferrite (flat area), as shown, for example, in The measured values of the Cr, Mo and Ni content in austenite and ferrite grains for all tested samples are presented in However, significant differences were observed for both the HAZ and the WM in the chemical composition of the austenite and ferrite in comparison to the BM, as shown in In the WM, as in the HAZ, the level of chromium content in both phases is balanced, and for all elements their amounts are too high or too low compared with the parent material. As can be seen from the results obtained, both in the case of the HAZ and WM, the amount of basic alloying elements in ferrite and austenite differs from those measured in the base material. This is most likely due to the limited possibility of diffusion of these elements during cooling. It is noteworthy that this effect is independent of the linear welding energy parameter within the range of 2.18–2.50 kJ/mm.The hardness distribution for individual test joints is almost symmetrical. It can be clearly observed that the hardness of the HAZ is similar to the hardness of the WM, and this may be due to the fact that the relative volume of ferrite in these two zones is at a similar level. There is also a tendency for the hardness to increase in the joint with increasing linear welding energy, probably due to a noticeable increase in the ferrite content in the individual zones of the samples number 3 and 4 in relation to the samples number 2 . MoreoveImpact tests were performed using the Charpy method for reduced samples (7.5 mm) at the temperature of −40 °C. 2. Nevertheless, the observed minimum absorbed energy for sample number 3 corresponds to the increased amount of ferrite observed in this sample : at least 480 MPa, the tensile strength (Rm): in the range of 680–840 MPa and the elongation (A): minimum 25%.The detailed results of the tensile test are shown in the Rm) and deterioration of the plasticity parameters (Rp0.2 and A) were observed. This maybe a results of the observation that during the cooling process ferrite was obtained predominantly as a component of the structure, which has greater hardness and lower plasticity compared to austenite.On the other hand, the tensile strength decreased for sample 4 in relation to the value obtained for the base material. It should be emphasized that for this sample in the WM the ferrite content was slightly lower, and the content of Cr, Mo and Ni was the closest to the content measured for the BM. This would suggest that for this sample the cooling process was slow enough for the diffusion processes and phase changes to take place to a noticeable degree.The fracture point of the sample number 4 is shown in The ductility of samples number 2, 3 and 4 was confirmed by a bend test, as shown in Weld joints with full penetration were successfully obtained on a 10 mm thick 1.4462 duplex plates using the single-pass K-TIG method, within a welding energy range of 2.18–2.50 kJ/mm. The microstructure of the weld was significantly different to that obtained during typical welding methods used for these steel grades due to the lack of additional materials , which are not used in the K-TIG method. However, although the welds were characterized by a relatively high ferrite content (67–75%), their mechanical parameters met the requirements for the base material (BM). In particular, it has to be stressed that also the value of the absorbed energy obtained during the impact test at a temperature of −40 °C, in all areas of the welded joint, also met these requirements as well.Limited differences in the distribution of the main alloying elements between austenite and ferrite grains were observed within the range of the linear welding energy studied. This indicates that the cooling rate after welding was too high for both the effective diffusion of the alloying elements and the ferrite-austenite phase transformation.It was observed that the welding current and welding speed significantly affect the geometry of the weld. This applies in particular to obtaining the appropriate shape of the weld cap without undercut and the correct shape of the root, i.e., obtaining a full penetration of the plate.Differences were observed in the amounts of ferrite measured as a function of the linear welding energy in the tested joints compared to the literature data for lean duplex steel. This could not be explained on the basis of the current limited knowledge of the physics underlying the K-TIG welding method. Thus, there is a need for further extensive research on the influence of welding parameters on the microstructure of joints, in order to optimize these joints for practical implementation of this very promising method.


Solid waste silica fume was used to replace fly ash by different ratios to study the early-age hydration reaction and strength formation mechanism of concrete. The change pattern of moisture content in different phases and micro morphological characteristics of concrete at early age were analyzed by low field nuclear magnetic resonance (LF-NMR) and scanning electron microscope (SEM). The results showed that the compressive strength of concrete was enhanced optimally when the replacement ratio of solid waste silica fume was 50%. The results of LF-NMR analysis showed that the water content of modified concrete increased with the increase of solid waste silica fume content. The compressive strength of concrete grew faster within the curing age of 7 d, which means the hydration process of concrete was also faster. The micro morphological characteristics obtained by SEM revealed that the concrete was densest internally when 50% fly ash was replaced by the solid waste silica fume, which was better than the other contents. Silica fume is an ultrafine powder produced during the smelting of ferrosilicon alloy or industrial silicon, and its main component is amorphous silicon dioxide. In 2018, China produced 2 million tons of silica fume, and its utilization rate was less than 60% in that year . Large-sSince the 1990s, silica fume has been utilized in cement, concrete, refractory materials, chemicals, environmental protection and other fields. By studying the role of MgO in the thermal behavior of MgO-silica fume pastes, Li et al.  establisAs a highly effective pozzolanic material, silica fume is the most widely used pozzolan in the field of concrete making. As early as 1982, Norway used silica fume concrete for the construction of the Vonoves Dam . Adding 2 content of the solid waste silica fume used in this paper is 86.3%, while the active ingredient SiO2 content of common silica fume in the market is usually more than 90%. In terms of financial, the solid waste silica fume used in this paper has a lower cost. Predecessors have used a variety of methods to study the process of concrete hydration. However, those studies mainly focused on the hydration products, hydration exotherm, etc. [The physical properties and chemical composition of silica fume are similar to that of fly ash, while silica fume has higher pozzolanic activity than fly ash . The actrm, etc. ,23,24, arm, etc. . In thisIn this study, the cement used was Conch brand P·O 42.5 ordinary Portland cement produced by Liquan Conch Cement Plant in Xianyang City, Shaanxi Province, China, with its physical and mechanical properties as shown in The silica fume originated from the northern part of Shaanxi Province. The Grade I fly ash used was produced by Shaanxi Weihe Power Plant. Using the Bettersize 2600 laser particle size analyzer, the volume-based average particle size of silica fume and fly ash were measured as 12.35 μm and 12.71 μm, respectively. The particle size distribution is presented in 3 and a bulk density of 1480 kg/m3. Limestone with continuous grading between 5 mm and 20 mm was used as coarse aggregate, with an apparent density of 2835 kg/m3 and a bulk density of 1720 kg/m3.Natural river sand with a fineness modulus of 2.66 was used as fine aggregate, with an apparent density of 2630 kg/mThe superplasticizer applied was the Q8086 powder high performance water reducing agent produced by Shaanxi Qinfen Building Materials Co., Ltd.,  with a water reducing rate of 33%, air content of 2.0%, and solid content of 40%. The water reducer comprised 0.5% of the weight of the cementitious material.The water used was ordinary tap water from Xi’an, Shaanxi Province, China.In the experiment, five different composite cementitious material system concretes were prepared, while the external admixture method was used to keep the amount of cement unchanged. The control group without silica fume was designated as group A. In the other four groups, 25%, 50%, 75%, and 100% of fly ash were replaced with silica fume, which were numbered B, C, D, and E, respectively. The water–binder ratio was 0.48, and the mix proportions of concrete were as shown in (1) Prior to preparing the concrete specimens, the raw materials were weighed according to the pre-determined mixing ratios and placed in the test pan. At the same time, the superplasticizer was poured into the water to fully dissolve, the twin-shaft concrete mixer was cleaned, and the mortar with the same water-binder ratio was prepared. The remaining slurry was poured into the wall-hanging slurry in the mixer. Next, coarse aggregate, cement, silica fume, fly ash, and fine aggregate were added in sequence and stirred for 60 s. Finally, the water mixed with superplasticizer was evenly poured into the mixer and stirred for 120 s.(2) After unloading, the slump of fresh concrete was measured according to the Chinese standard “Standard for Test Methods for the Performance of Ordinary Concrete Mixtures” (GB/T50080-2016), and the HC-7L direct-reading concrete air content tester was employed to measure the air content of fresh concrete.(3) The remaining concrete mixture was put into a 100 mm × 100 mm × 100 mm cube mold, placed on a vibrating table for vibrating compaction, and vibrated until the surface continued to produce slurry. Each group of A, B, C, D, E made 28 specimens, totaling 140 specimens.(4) The concrete specimens were demolded 24 h after production, and 25 specimens of each mixing ratio group were naturally cured at a curing temperature of 20 ± 2 °C and relative humidity of 95%. The WAW-1000KN universal testing machine was used to test the compressive strength of concrete cubes with different amounts of substituted silica fume at curing ages of 1 d, 3 d, 7 d, 14 d, and 28 d.2T inversion software. Thus, a spectrum composed of the LF-NMR signal amplitude and relaxation time of different types of water in the concrete test block is obtained [(5) The remaining three specimens in each group of mix proportions were wrapped with a polyethylene film to prevent the entry and evaporation of water, as shown in obtained .In the hardening process of concrete, cement hydration consumes part of the physically bound water, thereby generating chemically bound water. Jehng measured the apparent transverse relaxation time of the chemically bound water in cement paste to be 12 μs . It is g2T spectrum includes three relaxation peaks, which are defined as peak 1, peak 2, and peak 3 from left to right, which correspond to the LF-NMR signals of hydrogen nuclei in adsorbed water, pore water, and free water, respectively [2T spectrum reflects the change in the contents of adsorbed water, pore water and free water in the filler slurry.The ectively . The chax is the total water content, V and A are the volume and signal of the sample, respectively.According to the volume and signal of the sample, a unit volume nuclear magnetic signal can be obtained, as shown in Equation (1). Then, the total water content of the tested sample can be obtained according to the calibration formula in Equation (2) .(1)y=AV(6) The JSM-7610F field emission scanning electron microscope produced by JEOL was utilized to test the surface micromorphology of 28-day-old concrete. Before the test, the sample was sprayed with gold and vacuumed for inspection by the scanning electron microscope imaging system.The working performance of fresh concrete for each mixing ratio is shown in T2 spectra of concrete fluids with different amounts of silica fume substitution at different ages. As seen in the figure, the total water content in the concrete shows a gradual rising trend with the increase of the replacement amount of silica fume. The area of peak 1 shows an increasing trend with more water is adsorbed, indicating that water in the concrete mainly exists in the adsorbed form. The area of peak 2 generally shows an increasing trend with a higher volume of pore water. The area of peak 3 presents a decreasing trend, indicating that the free water in the concrete decreases with the rise of silica fume replacement amount.The graph of different forms of water content and total water content in concrete with different amounts of silica fume replacement is presented in In order to better explore the relationship between the compressive strength of concrete cubes and the change of total water content over time, the least squares method was used for fitting. The correlation equations of the two parameters are as follows:t represents age in days; t; t; a, b, c, and d are constants, and their values are determined by experiment.In the relational equation, The coefficients of the fitting curve equation are shown in It can be seen from the fitting curve that, before 7 days of age, the compressive strength of concrete cubes in each mixture group has a trend of faster growth, while the total moisture content of concrete in each mixture group rapidly decreases. The hydration reaction is the process of converting physically bound water into chemically bound water in concrete . The actFor concrete materials, moisture is not only a guarantee for strength development, but also closely related to performance . In the 2; high-fineness amorphous SiO2 has high pozzolanic activity. The hydration reaction between cement and water yields the hydration product Ca(OH)2, as shown in 2 can quickly undergo a secondary hydration reaction with Ca(OH)2 under the alkaline excitation to form C-S-H gel . Compared with the control group A without silicon powder, the surface of group C is covered by a more irregularly structured C-S-H gel, and the resulting microstructure also denser , the compressive strength of concrete showed a slowed increasing trend. Although the compressive strength of such concrete cubes was higher than that of control group A cubes, it was lower than that of group C. While the D and E groups also contained C-S-H gels, the pores in the surface concrete still existed, and the C group was denser in comparison  at different ages were monitored by LF-NMR. The hydration products of concrete at age of 28 d were analyzed by using SEM. By studying the early-age hydration and strength formation mechanism of silica fume-like solid waste based composite cementitious concrete, the following main conclusions can be drawn:(1) As the amount of solid waste silica fume increased, the slump and expansion of the concrete mixture tended to decrease and its air content firstly decreased and then increased.(2) With the increase of age, the compressive strength of concrete at each replacement ratio of solid waste silica fume showed an increasing trend, which increased faster in the age of 7 d. Besides, the compressive strength of concrete showed an increasing-decreasing-increasing trend with the increase of the amount of solid waste silica fume at each age. The overall comparison showed that the compressive strength of concrete at all ages was enhanced best when the replacement ratio of solid waste silica fume was 50%.(3) With the increase of the amount of solid waste silica fume, the total water content in the concrete showed a general trend of gradual increase. Additionally, with the continuation of hydration reaction, the water content of concrete under each dosage of solid waste silica fume continuously decreased, which was consistent with the change trend of adsorbed water during the curing period. Moreover, the change of the total water content and adsorbed water of concrete under each dosage was more obvious in the age of 7 d, which was shown by the phenomenon that the compressive strength of concrete grew faster in this period.(4) Through the electron microscope analysis, it was found that the concrete was the densest and most effective in improving the internal pore structure when the content of solid waste silica fume was 50% compared to the other contents, and thus its compressive strength was the highest.2 content of solid waste silica fume used in this study is 86.3%. Most studies use high-purity silica fume. In financial terms, the silica fume used in this study has a lower cost, and the cube strength has been greatly improved. In addition, using solid waste silica fume instead of fly ash can greatly increase the early strength of concrete, which also plays an important role in the application of high early-strength concrete engineering.The active ingredient SiO


Objective: The current study aimed to examine the anatomical structure of the hepatic vein of segment IV liver (S4) of the liver using three-dimensional (3D) visualization technology in order to explore the surgical value of the middle hepatic vein (MHV) manipulation and highlight the importance of current research in hepatic surgery.Methods: Between January 2014 and December 2019, 52 patients with abdominal diseases(not including hepatic disease) were selected for multiphasic computed tomography-enhanced scans of the upper abdomen. A 3D visualization system was utilized to display the structural details of the hepatic veins in S4 of their livers. Couinaud's eight-segment classification system was used to denote the liver' sections.Results: The constructed 3D model clearly displayed vascular morphological characteristics and their location in the liver, hepatic artery and vein system, and portal vein system. Of the 52 patients, 43 had an umbilical fissure vein (UFV) (82.7%), 19 had an accessory S4 liver vein (36.5%), 16 had both a UFV (30.8%) and an accessory S4 liver vein, and 6 had neither (11.5%). A total of 79% of the patients with a UFV and 74.2% of those with an accessory S4 liver vein had venous blood returning into the left hepatic vein.Conclusion: 3D visualization technology was used to determine hepatic venous return of S4 hepatic veins and was found to improve the safety of evaluation in hepatic surgery. The middle hepatic vein (MHV) is a very important vein in the liver: it returns the venous blood of segments 5, 6, and 8  (using Couinaud's eight-segment classification system) , and occAt present, three-dimensional (3D) visualization technology can accurately reconstruct the morphological characteristics of each hepatic vascular system. Through rotation, perspective, scaling, and other functions, the positional relationship between each vessel and liver segment can be clearly understood and the origin of each vessel determined. 3D visualization modeling of the liver uses a large number of samples, which reduces the variance of results caused by the limited number of samples in previous anatomical research –13. In tBetween January 2014 and December 2019, 52 patients  were selected for 3D visualization reconstruction in the Peking University First Hospital. All patients with abdominal disease other than a hepatic disease were included. Thus, patients with liver disease were excluded.The study was conducted in accordance with the Helsinki Declaration (as was revised in 2013). The study was approved by Ethics Committee of the Peking University First Hospital  and informed consent was taken from all the patients.Multiphasic enhanced CT examinations of the upper abdomen were arranged for all patients before surgery. The patient took a supine position in the head–foot direction, and the scanning scope ranged from the diaphragmatic top to the umbilicus, with the whole liver included. Scanning parameters: tube voltage 120 kv; automatic tube current modulation technology (120–300 mas); pitch 0.984; layer thickness 5 mm; scanning field of vision 50 cm, matrix 512 × 512. A Siemens dual-source CT scanner  was used. After injection, 20 ml of normal saline was used to flush the tube. The delay time of the scan in the arterial phase was 20–25 s, and that of the venous phase was 55–60 s.After scanning, the images of each phase were reconstructed in layers of 1 mm, with intervals of 1 mm, and uploaded to the image workstation. The original CT data were saved in DICOM format.Clinical Practice Guidelines for Precision Diagnosis and Treatment of Complex Liver Tumor Guided by Three-Dimensional Visualization Technology (version 2019)  for analysis. The original CT data of each phase were segmented and registered by the program. The displayed objects included the liver, the hepatic artery and vein system, and the portal vein system. The liver was segmented according to Couinaud's eight-segment classification system . The homon 2019) .Only the liver S4s with a diameter of more than 3 mm were used as the main vein for analysis. Deputy chief physicians from the hospital's imaging department and surgical department checked the 3D visualization results together, and the final report was issued when both physicians reached a consensus.SPSS v.25 was used for statistical analysis. Continuous variables were represented as mean averages, and classified data were represented as frequency and rate. A descriptive analysis of the constituent ratio was made. The normality of distributions was tested by K-S normal test.Of the 52 patients, 43 (82.7%) had an umbilical fissure vein (UFV). All but one of these cases had S4 branches, accounting for 80.8% of all patients . NineteeOf the 43 patients with a UFV, 34 (79.0%) had blood returning to the left hepatic vein (LHV), four (9.3%) had blood returning to the MHV, and five (11.6%) had blood returning to the LHV–MHV confluence see . Of the With CT and magnetic resonance imaging data and computer image-processing technology, digital 3D visualization technology can analyze, fuse, calculate, segment, and render data. It can also be used to display the bile duct and vascular system separately from the vision intuitively, accurately, and quickly, allowing clinicians to describe and explain the shape and spatial distribution of the bile duct and blood vessels. It can therefore assist in decision making, accurate preoperative diagnosis, individualized surgical planning, and the selection of an appropriate surgical approach .In hepatic surgery, it is crucial to determine the precise location of a tumor before operating, and the control of blood flow in the portal and hepatic veins is an important factor affecting the operation success. The anatomy of the hepatic veins in S4 of the liver plays a role in whether simple removal of the MHV will obstruct blood flow in that segment in patients with right lobular hepatic tumors invading the MHV who cannot undergo a right lobectomy or right hemihepatectomy due to insufficient volume of the residual liver. It is also involved in possible blood flow obstruction in living-donor liver transplantation when the donor liver does not include the MHV. 3D reconstruction of the portal and hepatic veins is therefore of great value in analyzing the morphological features and variations of these veins and can be used when choosing the most appropriate operative plan , 16.In addition to the MHV, the UFV and the accessory S4 liver vein drain the hepatic venous blood in S4 of the liver. Unfortunately, there are very few anatomical studies concerning these two veins, but 3D visualization technology now offers the possibility of a large-sample study of them, thereby improving the safety of hepatectomies and liver transplantations.ligamentum teres hepatisdrains the S3 and S4 hepatic veins (The UFV in the ic veins . Some reIn the present study, anS4 branch was found in 97.7% of all patients with an UFV, which is slightly higher than the reported 93% of previous studies –21. It hThe accessory S4 liver vein is not the S4 branch of the MHV but a hepatic vein running alone in S4 of the liver and eventually flowing into the LHV or the LHV–MHV confluence. In the 3D visualization conducted in the present study, 36.5% of the patients were found to have an accessory S4 liver vein, which suggests that this vein might be common in the general population. The presence of this vein was also not found to be related to gender.In the 52 patients, 16 cases had both UFV and S4, accounting for 30.8%. Six cases had neither. This indicates that MHV ligation will not affect the blood flow in S4 of the liver in most patients—or at least not cause an overall blood-flow disorder in the hepatic veins in the segment.For most patients, the return of the hepatic vein in segment IV of the liver relies on the other hepatic venous return systems in addition to on the MHV. Therefore, ligation of the MHV does not affect the return of blood to segment IV liver.Wing to the maturity and vigorous development of 3D visualization technology, Great progress has been made in the anatomical reconstruction of important hepatic ducts. The anatomy of hepatic vein of segment IV liver scan be accurately and comprehensively analyzed. This analysis provides a reference for the precise hepatectomy of S4 of the liver and can offer sufficient preoperative evaluation for liver transplantation, thereby improving the safety assessment of hepatic surgeryThe original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.QQ: conception and design of the research. JZhan and JZhao: acquisition of data and critical revision of the manuscript for intellectual content. XG and XW: analysis and interpretation of the data. JZhan and QQ: statistical analysis. XG and XW: writing of the manuscript. All authors contributed to the article and approved the submitted version.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.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Incorporation of graphene oxide (GO) and silica fume (SF) to cement composites enhances their mechanical properties if suitable proportional amounts of GO and SF are used. This study presents a simplified approach to determine experimentally the optimum GO and SF contents that should be added to the cementitious mixture to obtain a proper and stable dispersion of GO sheets within the cement matrix. Composite mortar specimens with different GO and SF contents were designed and tested under flexural and compression loading. The phase formation and the microstructure of selected samples were also investigated to give an in-depth interpretation of the test results. The main criterion to determine the GO and SF contents was the ultimate strength required of the GO–cement composite. It was found that there was a composite interaction between the SF and GO contents in the cementitious mixture, which an envelope surface could describe if all other mix design parameters are kept constant. The σ-bond is responsible for the exceptional mechanical properties of the graphene sheet, with a tensile strength of 130 GPa and Young’s modulus close to 1 TPa. At the same time, the weak π-bond makes the graphene sheet available for chemical modification. Commonly, to reduce the hydrophobicity attribute of graphene, it is modified with oxygen-containing functional groups, producing graphene oxide (GO) [Recently, carbon nanomaterials have been widely used to enhance the mechanical properties of cementitious composites ,4,5,6,7.ide (GO) .As with all carbon nanomaterials, the effectiveness of GO in enhancing the mechanical and rheological properties of cement composite is highly affected by the quality of its dispersion in the cement matrix ,17. Alth3S), belite (C2S), aluminate (C3A), and ferrite (C4AF), which increases the concentration of the divalent calcium ions (Ca++) within the cement matrix at the early stages of the hydration process [The second step to improve the GO performance in the cement composite is to overcome the possible re-agglomeration of graphene sheets in the cement matrix. One of the main reasons that would trigger such aggregation is the formation of a very basic medium after the dissolution of cement minerals: alite  has been widely used to produce high-performance cement composites. It physically contributes as a nanofiller to densify the cement matrix, which is positively reflected on both the microstructure and mechanical properties. It also chemically reacts with portlandite (CH), in what is known as the pozzolanic reaction, producing more C-S-H products ,32. SomeTo serve this purpose, 20 cement composite mortar mixes were designed with different GO and SF contents. The composite specimens were tested under flexural and compression loading at the ages of 7 and 28 days to be compared with benchmark samples. Moreover, the composite specimens’ phase formation and microstructure were selectively investigated, using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, to explain how the GO and SF could enhance the mechanical performance of the composite. Finally, a simplified approach was introduced for the efficient design of cementitious composites. The method relates the accumulative specific surface area (SSA) of GO and SF, as a physical property, to mechanical strength enhancement. Therefore, an optimum ratio of GO/SF could be determined. 2/gm and 23.138 m2/gm, respectively. The SSA of GO determined using the low-temperature adsorption of nitrogen (BET method) was 2.973 m2/gm, which is much lower than the theoretical value (≈2418 m2/gm) [2/gm.A 42.5 N ordinary Portland cement (OPC) conforming to the requirements of European Standard Specifications BS EN 1-197/2011  and SF, 8 m2/gm) ,40,41. TThe GO was prepared using Hummer’s method  in Nanot3. All specimens were cast with a filler to binder (cement and SF) ratio of 2.75:1 and a water-to-cement ratio of 0.485. Different percentages of GO were used—namely, 0.03%, 0.05%, 0.07%, and 0.09% of the total weight of binder materials. In 15 mixes out of 20, the SF partially replaced the cement by 5%, 7%, and 9% of the weight. The mix proportions are shown in In this study, a total number of 20 mixes of cement composite mortar were prepared according to ASTM C109/C109-16a . Each miIn specimens in which the SF was used, the SF was first mixed with diluted GO suspension and stirred for 2 min. Then, cement was added into the GO–SF mixture and mixed for an additional 4 min using an automatic mixer with designated speeds and a fixed mixing sequence. Next, the composite mortar was placed in the casting molds and covered with a non-permeable flat surface. After 24 hours, the specimens were removed from molds and then put in water until testing. It should be mentioned that the workability of the composite mixture gradually diminished, while the amounts of both GO and SF gradually increased, and the water-to-cement ratio was kept constant. The maximum reduction in the workability index, measured using the flow table test, was about 16% in specimens with high incorporated ratios of GO and SF such as S9G5, S9G7, and S9G9.® C-20  at the designated rates. The loading rates for the flexural and compression tests were 0.05 kN/S and 2.4 kN/S, respectively. According to ASTM C348-14, a compression test is carried out using portions of prisms broken in flexural just after flexural test to determine the compressive strength. To evaluate the GO/SF possible interaction on enhancing the mechanical behavior of cement composite, flexural and compression tests were carried out at the ages of 7 and 28 days after curing, according to ASTM C348-14 . The macTo investigate the microstructure of the hardened cement composite, the fracture surface of the crushed chunks from the strength tests were prepared and then examined by QUANTA FEG 250 Field Emission Microscope . The SEM imaging was conducted on specific samples representing the low, medium, and high values of accumulative SSA. Samples were prepared on a monocrystalline silicon substrate and coated with a thin layer (5 nm) of gold. Furthermore, XRD was performed on dry ground samples, using the DIANO 2100E X-ray diffractometer  with Cu Kα (λ = 0.15424 nm), to identify the phase formation progression of the selected samples at 7 and 28 days.Different possible reasons may work individually or together, resulting in such negative post-peak behavior: the use of a high amount of SF that may prevent the interactions between GO sheets and hydration products by mechanically separating the GO sheets from the hydration products ,34; the The 28-day flexural strength tests are shown in The compressive strengths of the GO/SF cement composite specimens at seven days are shown in The SEM imaging for the fracture surface of the tested specimens after 28 days of curing could clearly explain the strength results. Selective samples that represent different values for SSA are presented in On the other hand, the addition of SF to the mixture densified the cement matrix, as shown in specimen S5G0, With increasing the SF or GO amount in the mixture as in sample S5G9, the SSA of the additives reached a high value, resulting in a blockage and preventing the completion of the pozzolanic reaction. Unhydrated particles of SF could be easily identified on the magnified fracture surface of sample S5G9, as shown in 2) phase was also present due to the mixture containing sand despite the grinding and sieving of the samples. The XRD spectrums of the GO/SF cement composite at the age of 7 and 28 days are shown in As the GO was added, a prominent peak (001) could be seen in specimen S7G7, which implies that the GO could promote the formation of the portlandite. This provides an opportunity for the SF to combine with portlandite, producing more C-S-H and hence a dense microstructure. The peak intensity of the portlandite lowered as time passed. These results are consistent with previous findings in the literature ,28,49.As shown in (001) and I(101) are the peak intensities of the (001) and (101) crystal planes, and the (101) crystal plane is used as a reference plane. The XRD pattern could determine the effect of incorporating GO and SF on the orientation of the CH at the fracture surface, where the orientation index could indicate the compactness of the hardened composite ,48,50. Gn for GO and SF, as shown in The orientation index was calculated for the selected samples and plotted against the nominal sum of SSAAnother observation indicates that the orientation index continued to decrease as the SSA increased up to a specific limit, after which the orientation index started to rise again. This behavior indicates the existence of an optimum SSA at which a dense matrix could be achieved, and hence a maximum strength enhancement. These results conform to the strength results mentioned above.n for the GO and SF. In this study, the SSAn was determined as follows:The results above clearly imply that the enhancement in the strength of the cement composite could be related to the nominal SSA of the incorporated GO and SF materials. GO) was determined according to the following equation [G is the theoretical SSA of a single graphene sheet (≈2630 m2/gm) [0.737O0.263Hx and η is an efficiency factor accounts for the dispersion quality of GO sheets in the mixture. This factor was calibrated against the experimental results using nonlinear regression and is given as follows:The nominal SSA of GO (SSAequation : SSAGO ≈0 m2/gm) , 12 and terature ,35. opt, as depicted in cmax) is calculated as follows: co is the characteristic strength of the plain mixture, and ∆fc is the enhancement of GO and SF additives. The strength enhancement could be described by an envelope surface, where the enhancement reaches the plateau at an optimum SSAopt to produce a maximum strength enhancement ∆fc of the additives could be evaluated as follows:co on the curve). Having plotted the curve, both the optimum SSAopt and the maximum strength enhancement ∆fc could be evaluated from the curve.The optimum SSAThis approach could be easily followed for a practical engineer to determine the optimum ratios of GO and SF to design a composite mix that exploits the constituent materials’ properties. Firstly, a particular amount of SF could be chosen, and the optimum amount of GO could then be determined. This study investigated the effective use of GO and SF as nanoadditives to cementitious material. In total, 20 composite mortar mixes were prepared and tested under flexural and compression loading, and the fracture surfaces were selectively investigated using SEM and XRD analysis. The results show a positive interaction between both the GO and SF that can enhance the strength of the composite better than adding any of them individually. For instance, when the GO and SF were incorporated into the cement matrix by certain proportional amounts such as 0.03% GO and 5% SF, the compressive strength enhancement could reach up to 43% at seven days. However, the strength enhancements were only 29% and 32% for GO and SF, respectively, if they were incorporated individually. The optimum strength enhancement could be achieved when certain amounts of both GO and SF were added to the cement matrix. At the same time, all other parameters, such as water/binder and binder/filler ratios, were constant. This composite interaction was adversely affected if either the GO or SF percentage increased. Finally, a simplified approach relating the strength enhancement to the nominal SSA of the additives (GO and SF) was presented to determine their optimum ratios.


In order to solve the shortcomings of the traditional curing agent in the treatment of composite heavy-metal-contaminated soil with the solidification and stabilization method, a new type of cementing material A was used as a curing agent, and the Pb, Cd, Cu composite heavy-metal-contaminated soil was artificially prepared to carry out an experimental study on solidification and stabilization (SS) restoration by the mechanical properties test, leaching performance test, and microscopic test. The results show that in the range of test dosage, with the increase in the curing agent content, the unconfined compressive strength of the solidified body increased, and the resistance to deformation was enhanced. From the perspective of leaching characteristics, the new curing agent A had an excellent curing effect on the composite heavy-metal-contaminated soil. To achieve safe disposal, a curing agent content of 10% applies only for the soil heavily contaminated by heavy metals. The curing agent A could significantly reduce the content of acid-extractable heavy metals after solidifying the heavy metal Pb, Cd, and Cu composite contaminated soil and effectively converted it into a residue state. The solidified phase contained hydrated products such as calcium silicate hydrate (CSH) and ettringite (AFt). These hydrated products can inhibit the leaching performance of heavy metal ions through adsorption, encapsulation, and ion exchange. The study provides a feasible method and reference for the solidification, restoration, and resource utilization of heavy-metal-contaminated soil in the subgrade. The characteristics of long-term concealment, accumulation and irreversibility make it difficult to control heavy metal pollution in the land, and the environmental risks are prominent . Heavy-mThe remediation mechanisms of common curing agents of heavy-metal-contaminated soil mainly include adsorption, precipitation, ion exchange, complexation, and oxidation-reduction ,6,7,8. DIn general, a lot of work has been carried out on the remediation of heavy-metal-contaminated soil both at home and abroad. However, research on the serious heavy metal compound pollution problem is conducted less frequently, and for the heavy metal leaching concentration of the solidified body after solidification, it is difficult to meet requirements or the solidification rate is lower. Therefore, this paper intends to solve the problem through a new type of cementitious material. Through artificial simulation of heavy-metal-contaminated soil, a study on S/S repair test was carried out using a new curing agent A. The mechanical properties and leaching performance of the solidified body specimens were tested. The mechanical properties, deformation characteristics and leaching safety of the solidified body were analyzed on a micro level. Additionally, the changes in the internal composition and structure of heavy-metal-contaminated soil before and after solidification were also observed and analyzed. The study provides technical support for the application of solidified and stabilized heavy-metal-contaminated soil in the subgrade.The soil to be tested was taken from Lintong District, Xi’an City 2, Cd(NO3)2, Cu(NO3)2 solution were uniformly sprayed into the soil to make the soil sample reach the pre-set concentration. After deionized water was added, the soil sample was stirred, sealed and cured for 30 days under standard curing conditions until the heavy metal ions and the soil were mixed thoroughly to make heavy-metal-contaminated soil. A certain mass of contaminated soil was crushed, and sieved through the aperture of 2 mm to obtain contaminated soil with a particle size of less than 2 mm. The contaminated soil with a particle size of less than 0.5 mm was prepared using the same method. The soil sample flow is shown in Referring to the soil quality standard , the polIn this test, five curing agent content levels were selected; 5%, 10%, 20%, 30%, and 40%, respectively. First, the prepared contaminated soil sample was fully mixed with the curing agent A according to the ratio determined by the plan and deionized water, respectively, with moisture content of 13%. After being fully stirred in a mixer, the sample was formed immediately to prevent moisture volatilization using single pressing molding method. The solidified body sample was a cylindrical sample with a size of φ50 × 50 mm, and three parallel samples were made in each group of tests. With the help of a mold stripping machine the pressed sample was demolded immediately. After that, the sample was wrapped with a water-retaining film and kept in a curing box for 7 days under 60 °C water-bath thermal curing or standard curing. The two groups of cured sample are shown in The mechanical properties, deformation characteristics and leaching characteristics of the solidified body specimens were tested after being cured. The effects of the dosage of curing agent and the initial pollution concentration on the properties of the solidified body were analyzed, and the minimum dosage of the new curing agent A required for the resource utilization of heavy-metal-contaminated soil was determined.The unconfined compressive strength test was carried out in accordance with the specification “Test Regulations for Inorganic Binder Stabilized Materials for Highway Engineering” (JTG E51-2009), and the WDW-20 universal testing machine  was used for the test. The loading rate during the test was controlled to 2 mm/min. Three parallel samples were tested in each group of experiments, and the results were averaged. The unconfined compressive strength test is shown in This test quantitatively evaluated the heavy metal leaching characteristics of the solidified body. The leaching test was carried out in accordance with Chinese environmental protection standard “Solid Waste Toxicity Leaching Method Sulfuric Acid Nitric Acid Method” (HJ/T300-2007). First, 50–100 g samples were selected to test its water content. The crushed sample particles could pass through a 9.5 mm sieve. Then, 75 g samples were put into a 1 L extraction bottle. According to the water content of the sample and the ratio of liquid to solid of 10:1, the required amount of extractant was calculated (concentrated sulfuric acid: concentrated nitric acid = 2:1) and added into the bottle, which was put in a flip oscillation device for 24 h, with the bottle cap tight. Finally, the filter membrane was installed on the pressure filter to filter and collect leachate, and the concentration of the leachate was examined by the inductively coupled plasma mass spectrometer (ICP-MS) . The test process is shown in (1)Adding 1 mol/L MgCl2 solution to the selected samples and adjusting pH to 7.0, oscillating continuously for 1 h at 25 °C, and centrifuging for 20 min. The supernatant was taken and diluted to 25 mL as the exchangeable solution to be tested.(2)Adding 16 mL of 1 mol/L NaAc solution to the residue in the previous step, adjusting pH to 5.0, followed by continuous oscillation at 25 °C for 8 h. After centrifugation for 20 min, the supernatant was taken and diluted to 25 mL as the carbonate-bound solution.(3)2OH HCl to the residue in the previous step, oscillating intermittently at 96 °C for 4 h and centrifuging for 20 min. The supernatant was taken and diluted to 25 mL as the Fe-Mn oxide bound solution.Adding 16 mL of 25% HAC solution of 0.04 mol/L NH(4)3 and 5 mL of 30% H2O2 to the residue, adjusting the pH value to 2.0, water-bath heating to 85 °C for 2 h and cooling to 25 °C. Then, 5 mL of 20% HNO3 solution of 3.2 mol/L NH4Ac was diluted to 20 mL, oscillated for 30 min and centrifuged for 20 min. The supernatant was taken out and diluted to 25 mL as the organic bound solution.Adding 3 mL of 0.01 mol/L HNO(5)Taking out the residue in the previous step and completely digesting with graphite digester. The solution was canceled as the residual state to be measured.The BCR method was used to determine the content of available heavy metals in contaminated soil samples. The heavy metal elements in the soil usually exist in exchangeable state, carbonate-bound state, Fe-Mn oxide-bound state, organic-bound state and residual state. The experiment process is shown in The solution to be tested and digestion solution extracted in the above five steps were filtered, and the concentrations of Pb, Cd and Cu ions in each step were measured by ICP-MS.X-ray diffraction test is used to analyze the phase of the heavy-metal-contaminated soil before and after solidification. In the test, the powder of the crushed sample which could pass through a 300-mesh sieve was placed in the slot of a glass slide. After the sample flattened and compacted, the slide was placed on the loading table, and the corresponding diffraction intensity at 2θ was collected by X-ray emission and with a certain speed. The crystal content and structure were determined by the diffraction intensity. The higher peak value indicates that the crystal structure was more complete and contained more material components ,15,16.The uncured heavy-metal-contaminated soil used in the XRD test is the heavily contaminated soil, while the solidified body is heavily contaminated soil with 20% curing agent. The X-ray diffractometer  used in this experiment is shown in SEM/EDS tests were conducted to observe the microstructure and mineral composition of soil samples contaminated by heavy metals before and after solidification. Before the test, the soil sample was dried, broken and sieved through 100 mesh, and then the sample powder was sprinkled on the conductive adhesive and adhered to the sample tray table. The sample was sprayed with gold within 12 h before scanning. After that, the processed sample was placed on the sample table, vacuumed, and the image was scanned. The image magnification is 5000 times, and the results obtained by scanning include SEM microstructure images, distribution maps of various elements obtained by EDS, and relevant information of point energy spectrum. The scanning electron microscope equipment  used in this experiment is shown in The variation in unconfined compressive strength of the solidified body with the amount of curing agent is shown in As is shown in It can be seen from The variation in unconfined compressive strength of the solidified body with the initial pollution degree is shown in In For the heavily polluted soil samples, the amount of curing agent increases from 5% to 40%, and the unconfined strength of the solidified body increases by 260%. When the dosage of curing agent is 20%, the unconfined strength is 6.32 MPa, which is higher than the geological landfill standard (5 MPa). When the content of curing agent is 30%, the unconfined strength is 10.12 mpa, which meets the requirements of building material strength (10 MPa). For moderately contaminated soil samples, the content of curing agent increases from 5% to 40%, and the unconfined strength of the cured body increases by 175%. When the content of curing agent is 10%, the unconfined strength is 5.42 MPa, which is higher than the geological landfill standard. According to the standard, when the curing agent content is 30%, the unconfined strength is 11.32 MPa, which meets the strength requirements of building materials. For lightly contaminated soil samples, the content of curing agent increases from 5% to 40%, and the unconfined strength of the cured body increases by 153%. When the content of curing agent is 5%, the unconfined strength is 5.04 MPa, which is higher than the standard. When the curing agent content is 20%, the unconfined strength is 10.07 MPa, which meets the strength requirements of building materials.In summary, as the amount of curing agent increases, the unconfined compressive strength of the solidified body also increases, and the trend of solidified body of the contaminated soil with different initial pollution degrees is consistent. The maximum unconfined compressive strength of the solidified body can reach 13.38 MPa. After the curing agent content exceeds 30%, the unconfined compressive strength will decrease significantly with the increase in curing agent content. Simply adding more curing agent to improve the mechanical properties of the solidified body may not achieve the desired effect. In terms of mechanical properties alone, for heavily polluted soil samples, the content of curing agent must reach 20% to achieve safe disposal. To meet the strength requirements of building materials, the content of curing agent must reach 30%. For moderately contaminated soil samples, the content of curing agent must reach 10% to achieve the purpose of safe disposal, and to meet the strength requirements of building materials, the content of curing agent must also reach 30%. For lightly contaminated soils, the content of curing agent needs to reach 5% to achieve the purpose of safe disposal. To meet the strength requirements of building materials, however, the content of curing agent also needs to reach 20%.50 is usually used to characterize the deformation characteristics of the material. E50 refers to the secant modulus corresponding to 50% of the peak stress, also known as deformation coefficient [50 are obtained to analyze the deformation characteristics of the solidified body of heavy-metal-contaminated soil. Since the solidified body of heavy-metal-contaminated soil is nonlinearly deformed, the deformation modulus is not a constant. The deformation modulus Efficient . TherefoIt can be seen from 50 in 50 and the dosage of curing agent that with the increase in the dosage of curing agent, the deformation modulus E50 has a significant nonlinear increasing trend. When the content of curing agent increases from 5% to 10%, the increasing range of E50 is the largest. With the further increase in the content of curing agent, the increasing range of E50 gradually decreases.It can be seen from the regular curves of curing agent dosage, failure strain and deformation modulus EThe leaching concentration diagram of heavy metals Pb, Cd, and Cu in the solidified body is shown in It can be seen from It can be seen from It can be seen from In summary, it can be seen from the analysis of the leaching performance test results of the optimized solidified soil that with the increase in the amount of curing agent, the leaching concentrations of three heavy metals Pb, Cd and Cu in the solidified soil also decrease, and the trend of solidified soil with different initial pollution degrees is consistent. Only in heavily polluted soil, the leaching concentration of Pb slightly exceeds the limit after leaching test of the solidified body with 5% curing agent, and the leaching concentrations of Cd and Cu in the same group reach the standard. The leaching concentrations of three heavy metals Pb, Cd and Cu decrease with the increase in the amount of curing agent. The decrease in Pb and Cd is relatively significant, while Cu decreases slightly. The leaching concentration of Pb in slightly and moderately polluted soils is lower than the safety limit if the amount of the curing agent is 5% and the leaching concentrations of Pb in three polluted soils are all lower than the safety limit if the dosage is 10%. As for Cd and Cu, the leaching concentrations of the three contaminated soils after solidification are all lower than the safety limit with curing agent of 5%. Therefore, in terms of leaching safety of the solidified body, 10% curing agent is required for the heavily polluted soil to achieve safe disposal, whereas for other contaminated soils, the dosage of curing agent of 5% can be satisfying.The SEM/EDS diagram and distribution diagram of main elements  of heavy-metal-contaminated soil before solidification are shown in In addition, it can be seen from the element distribution diagram that the distribution of heavy metals Pb, Cd, and Cu is significantly different from that of Ca, Fe, and Si. The distribution of elements Pb, Cd, and Cu are distributed throughout the entire image, and the distribution is uniform, without obvious regularity. The distribution of elements Ca, Fe, and Si has obvious regularity, and is related to the distribution of particles. The shape and edge of the distribution are consistent with the shape and edge of the soil particles. It can also be seen that the heavy metals Pb, Cd, Cu have no obvious dependence on mineral elements.The SEM/EDS map and the distribution map of main elements  after solidification of heavy-metal-contaminated soil are shown in After solidification treatment and curing for 7 days, the occurrence forms of Pb, CD and Cu in the solidified body are shown in In the uncured original soil samples, heavy metal Pb mainly presents in the form of F1 (weak acid state), F2 (reducible state) and F3 (oxidizable state) with contents of 28.5%, 39.5%, and 31.1%, respectively. F4  is extremely low, accounting for 0.9%. After solidification, the main forms of Pb in the contaminated soil are F2 (reducible), F3 (oxidizable) and F4 . In addition, with the increase in the amount of curing agent, the content of F1 (weak acid state) gradually decreases, whereas the content of F2 (reducible state) does not change much, and the overall trend is gradually decreasing. The content of F3 (oxidizable state) also changes little, but the overall trend is gradually increasing. The content of F4  increases greatly, which is 36 times higher than that without curing. This shows that with the increase in solidified agent content, Pb in contaminated soil transforms to F3 (oxidizable state) and F4  and tends to be stable.In uncured original soil samples, Cd mainly presents in the form of F1 (weak acid state) and F2 (reducible state) with contents of 43.8% and 34.2%. The content of F3 (oxidizable state) is 18.5% and F4 , 3.5%, is very low. After solidification, the main forms of Cd in contaminated soil are F2 (reducible), F3 (oxidizable) and F4 . In addition, with the addition of curing agent, the content of F1 (weak acid state) decreases rapidly, the content of F4  increases significantly, and the contents of F2 (reducible state) and F3 (oxidizable state) change little. With the increase in the dosage of curing agent, the content of F1 (weak acid state) constantly decreases. When the dosage of curing agent increases from 5% to 40%, the content of F1 (weak acid state) decreases by 85%. The content of F4  increases with the increase in the dosage of curing agent. When the dosage of curing agent increases from 5% to 40%, the content of F4  increases by 40.7%. This indicates that the addition of the curing agent can transform a considerable proportion of active heavy metal Cd in contaminated soil into a relatively stable form.In the uncured original soil samples, Cu mainly presents in the form of F1 (weak acid state), F2 (reducible state)/F3 (oxidizable state) with contents of 28%, 42%, and 25.7%, respectively. F4  is relatively low; 4.3%. After solidification, the main forms of Cu in the contaminated soil are F2 (reducible), F3 (oxidizable) and F4 . In addition, with the addition of curing agent, the content of F1 (weak acid state) decreases rapidly, the content of F4  increases significantly, and the contents of F2 (reducible state) and F3 (oxidizable state) change little. With the increase in the content of curing agent, the content of F1 (weak acid state) decreases. When the content of curing agent increases from 5% to 40%, the content of F1 (weak acid state) decreases by 67.9%; The content of F4  increases with the increase in curing agent dosage. When the dosage of curing agent increases from 5% to 40%, the content of F4  increases by 66.7%, and the contents of F2 (reducible state) and F3 (oxidizable state) change little. However, with the increase in curing agent dosage, F2 (reducible state) decreases while F3 (oxidizable state) increases. This indicates that the addition of curing agent can transform a considerable proportion of active heavy metal Cu in contaminated soil into F3 (oxidizable state) and F4  and tend to be stable.To sum up, it can be seen that the new curing agent A can significantly reduce the content of the weak acid-extractable heavy metals after solidification of Pb, Cd and Cu composite contaminated soil, and effectively transform it into residual state. Increasing the amount of curing agent can further reduce the content of weak acid extraction in the solidified body and improve the content of its residual state. Meanwhile, the content of oxidizable state decreases slightly and the content of reducible state increases slightly.The phase analysis is a qualitative analysis based on the processing of the XRD spectrum. It can determine the mineral composition according to the diffraction angle and peak value of the mineral ,23. The 2 and CaCO3 are the main minerals in the heavy-metal-contaminated soil before solidification, and Pb5O8, CdO2 and CuO of Pb, Cd and Cu as well as other compounds Pb(NO3)OH, Cd(OH)2 and Cd(NO3)2 of Pb, Cd and Cu can be detected in the secondary minerals. It can be seen from 3, and after solidification, the single peak is searched at the same diffraction peak position. It is found that there are a variety of Ca-Cd compounds, Cd-Si compounds and Pb-Si compounds with extreme similarity. It is determined that there should be a stable compound formed by the adsorption and encapsulation of calcium and silicon products produced by the hydration of curing agent on heavy metal ions.New phases such as hydrated calcium silicate (CSH) and ettringite (AFT) can encapsulate the heavy metal ions. Some of them will undergo ion exchange or addition and combine with calcium and silicon ions to from a stable structure, so that lead, cadmium and copper ions can be stabilized in the contaminated soil. When the diffraction angle is 29.4°, the diffraction peak before solidification is CaCO(1)The mechanical properties of the contaminated soil solidified by the new curing agent A are superior, and the maximum unconfined compressive strength is 33.45 MPa, while the minimum is 3.22 MPa. However, simply adding more curing agent to improve the mechanical properties of the solidified body may not achieve the desired effect.(2)50 under compressive load, and the trend of solidified soil with different initial pollution degree is consistent.With the increase in the amount of curing agent, the resistance to deformation of solidified soil is significantly enhanced, which is manifested as the decrease in failure strain and the increase in the deformation modulus E(3)From the aspect of leaching characteristics, the new curing agent has an excellent solidifying effect on the composite heavy-metal-contaminated soil. To achieve the purpose of safe disposal, the dosage of curing agent should reach 10%, which only applies for the heavily polluted soil. For other soils of different pollution degrees, 5% of the dosage is satisfying. This study, however, only discusses the properties of solidified polluted soil which were cured for 7 days, and its long-term environmental safety and mechanical properties need to be further studied.(4)The content of weak acid-extractable heavy metals can be significantly reduced and effectively transformed into residual state by the new curing agent A. Increasing the amount of curing agent can further reduce the content of weak acid extraction form and improve the content of residual form. After solidification, there are hydrated products such as calcium silicate hydrate (CSH) and ettringite (AFT), which can inhibit the leaching performance of heavy metal ions by adsorption, encapsulation and ion exchange.In this work, a new type of cementing material was used as a curing agent, and the Pb, Cd, Cu composite heavy-metal-contaminated soil was artificially prepared to carry out experimental study on solidification, stabilized restoration. The mechanical properties, deformation characteristics and leaching safety of the solidified body were analyzed based on the mechanical properties test, leaching performance test, and microscopic test of the solidified body specimens. The following main conclusions may be drawn from the results of the present study:


Rare earth metals (REM) with magnetic properties find application in the recently developed high-tech industries. Sensor magnetic systems based on neodymium are increasingly in demand in modern engineering and geological surveys due to their favorable combination of properties of magnetic materials based on rare earth metals. One of the problems is to obtain high-quality materials for the production of such magnetic sensors. It should be noted that the high activity of REM does not allow obtaining master alloys and REM-based alloys from metallic materials; it is advisable to use halide compounds. This work discusses a method for producing neodymium fluoride from its oxide. REM fluorides can be obtained by fluorinating the oxides of these metals. Various fluorine-containing compounds or elemental fluorine are usually used as fluorinating reagents, which have their own advantages and disadvantages. The thermodynamic and technological analysis of neodymium fluoride production processes has shown the most acceptable fluorinating agent is ammonium hydrofluoride, which was used in this work. In order to increase the productivity and degree of chemical transformation, it was proposed to perform heating stepwise; i.e., at the initial stage, heat at a speed of 3 degrees per minute, after which the heating speed was reduced to 2 degrees per minute, and finally the speed was reduced to 1 degree per minute. Due to proposed heating mode, the same productivity and yield of chemical transformation were achieved, with an increased efficiency up to 30%, which can significantly reduce the cost of production. The obtained product is used in the production of neodymium-based alloys by metallothermic reduction of a mixture of fluorides. The sensor material obtained in this way is characterized by a low (less than 0.05%) oxygen content. Integrated sensing arrays ;Stability of ratiometric optical thermometry ;Near-infrared thermometry ;Gas sensing and electrochemical properties of rare earth ferrite ;Magnetic and humidity sensing properties of iron oxide nanoparticles ;Magnetic ophthalmic realignment systems ;Room temperature ammonia gas sensors ;Using uniaxial polyvinylidene fluoride-based photoacoustic sensors ;Dielectric properties of sodium and neodymium ;Time-dependent demagnetization of magnets under magnetic fields ;Effect of REO co-dopant on ionic conductivity ;Synergy of neodymium and copper ;Magnetically driven actuators for vector scanning mems mirrors ;Neodymium-doped graphene foam for magnetic sensors ;Non-contact fluorescence intensity ratio thermometer .Sensor magnetic systems based on neodymium, dysprosium and terbium are increasingly in demand in modern engineering and geological surveys due to their favorable combination of properties of magnetic materials based on rare earth metals, which was demonstrated in very recent research. New studies are conducted in the fields of:Basically, they are devoted to the use in ionic form or in the form of compounds such as perovskite or pyrochlore, but there are also studies related to synthesis and use in metal form ,17. An aThese price indices are calculated as the volume of exports of REM and REM compounds from China to all countries in monetary terms divided by the same indicator in physical terms ,23,24,25The relevance of the work is determined by the need to increase the production efficiency and improve the quality, with a constant (from 25 to 40% per year) growth in consumption, of individual rare earths in the form of metals or oxides in the most important industries . The structure of the global consumption of rare earth metals is presented in Rare earth metals with magnetic properties  are of particular interest, as they find application in the recently developed high-tech industries. These include electronics, space technology, electric vehicles, and green energy. Based on this, the authors in  made a f2Fe14B and Sm2Co17 magnets are now widely used in industries and entertainment. Methods of adding, in particular, dysprosium into magnetic alloys to increase the magnetic properties are proposed in [Neodymium, terbium, and dysprosium, which have increased magnetic properties compared to some ferromagnets, are the most popular magnetic materials among the entire range of REM. The Ndposed in ,29. Howeposed in ,31 methotm or FACT-sagetm online). The calculation results assigned to the mole of fluorine are shown in REM fluorides can be obtained by fluorinating the oxides of these metals. Various fluorine-containing compounds or elemental fluorine are usually used as fluorinating reagents. Each of these reagents has its own advantages and disadvantages. For preliminary assessment and selection of the reagent, a thermodynamic analysis of Equations that can occur in the “neodymium oxide—fluorinating reagent” system was performed with the use of special software for thermodynamic equilibrium equations . This mineral is not widely distributed in nature, so elemental fluorine is an expensive reagent and is used for the production of the most valuable products, and where it cannot be replaced, for example, in the production of uranium hexafluoride. In addition, fluorine is one of the most aggressive reagents, which creates certain difficulties in choosing materials and the need to create safe working conditions and reduce environmental pressure on nature.The most effective fluorinating agent is elemental fluorine. Its use is possible across a wide range of temperatures, but it also has certain disadvantages. Elemental fluorine is obtained by electrolysis of a mixture of KF and liquid HF. The melting point of this mixture is 70 °C. HF is produced by the action of sulfuric acid on fluorite 3LnF6 were most reliably identified. Nd and Tb are characterized by the formation of tetrafluorometallates (NH4LnF4), which decompose directly to LnF3. The pressure in the temperature range 478…523 K for NH4NdF4 decomposition is approximated by the equation lgKp = 18,523 − 10,201/T, and the enthalpy of decomposition is 195.3 kJ/mol [Crystal phases of various compositions were found in LnF systems . NH4LnF43 kJ/mol . AnalyziAt higher temperatures, thermal decomposition of the fluorometallates occurs. This position is illustrated by the sequence of reactions by Baykov:For the sequence (7)-(6)-(5) the total reaction is Equation (4).4HF2 is more preferable, since no heat will be expended on the dissociation of ammonium fluoride. The analysis of neodymium fluoride production processes has shown that the most acceptable fluorinating agent is ammonium hydrofluoride (NH4HF2), which was used in this work. The fluorination process begins at low temperatures. Therefore, the rate of temperature rise will be of great importance. The speed must be such that the solid-phase fluorination process has time to pass before the NH4HF2 transition to the gas phase and its decomposition take place.The total Equation for the sequence (8)-(9) is Equation (3). It is not possible to calculate the thermodynamics of the reaction sequences due to the incompleteness of the thermodynamic data base for most of the REM fluorometallates. The data calculated by the additive methods are not representative due to low accuracy. Ammonium fluoride at temperatures above 165–170 °C can only exist at an ammonia pressure greater than 101.3 kPa. The vertical line in 4HF2. As a result of the fluorination reaction, the reaction product will be NdF3 (at 100% fluorination) or a mixture of NdF3 + Nd2O3 . The coefficient (kF) [3 (at 100 % fluorination), g;The temperature can then be raised to the remove surplus of NHent (kF)  was used2O3 and NH4HF2 powders were used as starting materials in a molar ratio of 1:8 (stoichiometric ratio for Equation (8)). The charges were weighted (2 ± 0.2 g) and filled in the crucibles. The crucibles were installed in the cassette, which was loaded into a horizontal tubular furnace with the ability to change the rate of heating and a programmed control with quartz retort. The heat temperature was raised from 25 up to 600 °C, with different heating rate of 3, 2, and 1 degree per minute. During and after the process, the crucibles were sequentially extracted using the calculated time intervals after heating. The determination of the neodymium fluoride yield according to the coefficient (10) was made. At the end of the experiment and the preliminary express evaluation, the sample was sent for X-ray phase analysis.For experiments, neodymium oxide with a purity of 99.5% (2N) with average grain size less 0.8 µm was used, and dry ammonium hydrofluoride with a purity of at least 98.05%. The raw materials NdThe wave X-ray fluorescence spectrometer ARL 9900 WS was used for the analysis. Elemental analysis and phase analysis of the sample were performed.For elemental analysis, the sample was placed in a metal holder with a plastic centering ring. The samples were analyzed in a vacuum. The standardless analysis was carried out according to the program developed for the software Uniquant. The standard Kappa list “AnySample” was used for the calculation, and the calculation was carried out under the assumption of an oxide matrix. The total analysis time of one sample was 18 min, while measurement takes place on 126 analytical lines. Qualitative phase analysis was performed using the ICDD PDF-2 database and the CrystallographicaSearch-Match software package.On the basis of the obtained data, kinetic graphs of the process were constructed.In order to increase productivity and the degree of chemical transformation, it was proposed to perform heating stepwise; i.e., at the initial stage, heat at a speed of 3 degrees per minute, after which the heating speed was reduced to 2 degrees per minute, and at the final stage, the speed was reduced to 1 degree per minute. Heating modes were identified in A series of experiments were conducted to evaluate the correctness of the assumptions. After careful mixing of the components, the suspension in the form of powder was weighed, placed in an aluminum ceramic boat, which in turn was placed in a quartz retort in a tube furnace (Carbolite MTF 12/25/250). The charge heating mode was set according to the specified program . During 4HF2 leads to a higher degree of fluorination.With a different surplus of ammonium hydrofluoride, the yield of fluorination process does not change after 3 h. At this (3 degrees per minute) rate of heating, the solid-phase fluorination reaction does not have time to pass, since part of the fluorinating reagent has time to volatilize or decompose. Surplus of NHCarrying out fluoridation at a rate of temperature rise of 2 and 1 degrees per minute, although it makes the process longer, increases the degree of fluoridation significantly , reachinThermodynamic calculations in the preliminary section and analysis of the kinetic graphs show that ammonium hydrofluoride is an acceptable fluorinating agent.The total graph  was obta4NdF4 into NdF3, and thus obtain anhydrous NdF3. 3 sample.The thermodynamic possibility of obtaining neodymium fluoride using the process of solid-phase low-temperature fluorination was given. The optimal kinetic parameters of the technological process, such as an excess of 10% ammonium fluoride and a heating rate of 1 °C/min to 600 °C, were determined. An excess of ammonium fluoride leads to an increase in the degree of fluorination . Carrying out fluorination at a heating rate of 1 °C/min increases the duration of the process, but at the same time it increases the degree of fluorination. An increase in the duration of the process makes it possible to pass the reaction in the solid-phase region. Carrying out the process at a temperature of 600 °C allows to completely remove the excess ammonium fluoride from the reaction zone, completely convert the intermediate phase of NHBased on a comparison of existing methods, it can be said that the fluorination process using ammonium fluoride as a fluorinating reagent has economic advantages in comparison to methods with gaseous fluorine and hydrogen fluoride reagents, since there is no need to use expensive gaseous fluorine and a large amount (250% of the stoichiometric required amount) of hydrogen fluoride. In addition to the fact that the method turned out to be very cost effective, the method is safer, compared to others, to the environment.3 can be proposed:4HF2 10%;Surplus of NHHeating rate up to 600 °C sequentially reduced,  °C/min;Total process duration 320–360 min.The method of variable heating at different stages (in accordance to reduce the time for the process) was also tested. Analysis of the results shows that the degree of correlation between the theoretical and experimental curves is 98.55%, which indicates that our assumptions are correct. According to the obtained kinetic curve, the activation energy (8461.7 kJ/mol) was determined, and the change in the limiting stage from vaporization to internal diffusion was also established. Thus, based on the results of research on optimizing low-temperature fluorination, the following technological parameters for obtaining NdFDue to proposed heating mode the same productivity and the yield of chemical transformation were achieved, with an increased efficiency up to 30%, which can significantly reduce the cost of production, providing the necessary indicators for competing in the market of REM-based magnetic sensors for geotechnical surveys.A projected increase in the demand for magnetic REM will stimulate research investigations in the field of their production.2O3-fluorinating agent” system, showed that using ammonium hydrofluoride in comparison with F2 and HF allows the process to be carried out at lower temperatures.Thermodynamic analyses of the “NdUsing the previously developed express analysis, kinetic studies of the process of fluorination of neodymium oxide with the production of fluoride suitable for the production of metal were carried out.Surplus of ammonium hydrofluoride: 10% relative to the stoichiometric amount;Heating rate up to 600 °C: sequentially reduced from 3 to 1 °C/min;Degree of fluorination: 99.0–99.8%The following technological parameters for obtaining neodymium fluoride were established:The continuously growing demand for magnetic materials used in geotechnical, optical, and medical sensors leads to the need to find ways to reduce the costs of producing metals and ligatures based on neodymium. One of these methods is low-temperature fluorination, which allows avoiding the use of expensive reagents, reducing the temperature of the process and reducing its duration. Using the least squares method we obtained the output curve of the process, with a high level of confidence, and the correlation coefficient, which definitely indicates the correctness of the chosen methodology and the prospects of the process.