Destructive processes accompanying sulfate corrosion of concrete significantly affect the durability of products and structures based on Portland cement. In the presented study, the long-term effect of sulfate corrosion on the electrical properties of electrically conductive sand concrete was studied. In the course of the study, the following were tested: an electrically conductive composition and a control composition based on plain Portland cement. The analysis of changes in the mineral composition of the samples over the course of time in an aggressive solution was carried out. The results show that during the exposure period of the samples from 28 to 224 days, the absorption of sulfate ions slows down and averages 26% for the control composition and 29% for the electrically conductive composition, of the total volume of absorbed sulfates. At the same time, the course of sulfate corrosion was accompanied by a 6% increase in the density of samples of both compositions, as well as a cyclic change in mechanical strength within 15%. In its turn, the key indicator of the electrical characteristics of the compositions—electrical resistivity—tended to increase throughout the experiment. These results can be recommended for assessing the durability and the nature of the operating conditions of electrical concretes used in aggressive environments. Recent developments in the field of new multifunctional structural materials, such as “Smartconcrete”, led to a paradigm shift in the field of functional loading of building materials and structures towards products with additional functions of self-diagnostics, piezoresistive self-heating, as well as materials with the ability to control electrical properties. In the new context, traditional elements not only perform their basic function, but also include additional properties. For example, sidewalk and road surfaces integrate a resistive heating system for snow melting ,2,3, incThe key indicator characterizing the possibility of giving an additional functional load to materials based on Portland cement is electrical resistivity ,8. This 8 Ωcm for samples dried to constant mass to about 102 Ωcm for water-saturated samples [For traditional concretes, the index ranges from 10 samples . In its  samples .Progress in the use of carbon-containing materials, as well as the use of man-made waste to regulate the structure of mineral matrices, led to the emergence of a number of structuring additives used to ensure stable electrically conductive performance.A review of existing studies shows that the first attempts to regulate the electrical properties of cement matrices were first described in ,11. Ther9 Ωcm [A significant number of experimental and theoretical studies indicate that the degree of electrical conductivity of a composite material based on Portland cement modified with electrically conductive additives is determined by reaching the percolation threshold ,19. Alon9 Ωcm ,20. In v9 Ωcm . The use9 Ωcm ,22, thus9 Ωcm .Analyzing the results of fundamental ,22 and a42− is from 2.5 to 2.7 g/L. This type of mineral matrix corrosion is characterized by certain destruction mechanisms, including chemical reactions between active sulfate ions and hydrates of cement stone, primarily tricalcium aluminate [Sulfate-containing environments are by far one of the most common of the potentially damaging impacts that reduce durability ,26,27. Sluminate , accompaluminate ,27. Someluminate ,30 and sluminate ,32 or prluminate ,34. The luminate ,35. Todaluminate ,36, withTo date, it is established that the rate of corrosion decreases with an increase in the specific resistance of concrete used under normal environmental conditions. At the same time, ambiguous results were obtained for structures used in a hydrosulfate environment ,5,6,22. In studies ,32, the 42−, on the first day of the experiment, the concentration of the aggressive solution does not exceed 0.03–0.04% (300–400 mg/L SO42−). With a sufficiently long test period, the concentration of the aggressive medium levels off and approaches the initial selected value, but this can only be achieved by periodically changing the solution. At the same time, an important aspect is the retention of the concentration of the aggressive environment during the first 28 days of testing by 1–2 orders of magnitude lower than the actual concentrations of the influencing media due to the high probability of distortion of the chemical mechanism of corrosion [To simulate the corrosion process in laboratory conditions, a mode of changing aggressive solutions is required, which, to a certain extent, should take into account the decrease in the corrosion rate with time. In particular, it is obvious that on the first day of contact of the test samples with an aggressive environment, the interaction between them proceeds at a maximum speed; therefore, the concentration of ions in an aggressive environment decreases rapidly and is at a significantly lower level than expected during the experiment. For example, if one is testing the resistance of concrete in a solution containing 500 mg/L SOorrosion . In thisorrosion ,32,33,34orrosion ,41 to usSulfate corrosion today causes significant damage to the economies of countries around the world, and the fight against it requires huge material and technical costs. At the same time, at present, the problem of sulfate corrosion is not given sufficient attention. The flow process, quantitative indicators, and many other issues with the theory of sulfate corrosion of a mineral matrix based on Portland cement and methods for increasing the durability of structural elements of buildings and structures are yet to be sufficiently studied due to their duration and increased labor intensity, which necessitates the improvement of methods for testing the sulfate resistance of mineral matrices.To date, there is a range of methods for accelerated testing of traditional concrete for corrosion resistance ,39. In tThus, the paper presents the results of a study obtained by the potentiometric method, which includes the constant effect of a hydrosulfate medium on the mineral matrix. The results of the influence of the long-term impact of sulfate corrosion on the electrical and mechanical properties, as well as on the change in the microstructure at the later stages of the formation of the mineral matrix, are presented.In the presented study, the compositions of sand concrete are analyzed: a control composition and a composition with an electrically conductive additive introduced in the form of a suspension.Suspension of industrial soot UPC-MIX-1, produced by Novy Dom LLC, is a pigment concentrate, including industrial soot in the amount of 32%. Solid particle size distribution is measured with a laser diffraction analyzer . An anal2—23.22%; Al2O3—5.16%; Fe2O3—4.42%; and SO3—0.47%. In turn, the mineralogical composition of cement is also represented by components in the ratio: C3S—65%; C2S—13%; C3A—4%; and C4AF—18%. Graded quartz sand with fineness modulus Mf = 1.25 was used as a filler, meeting the requirements of GOST 8736-2014; mixing liquid corresponding to GOST 23732-2011.For the manufacture of the compositions, the following were used: Portland cement CEM I 42.5N produced by Novoroscement, OJSC. The chemical composition of cement is a set of components in the following percentage: CaO—66.73%; SiOIn turn, to stabilize the electrically conductive properties, calcium nitrate was introduced into the mixture corresponding to GOST 4142-77 “Calcium nitrate 4-hydrate”, which was previously dissolved in mixing water.2SO4 solution, as well as performing a titrimetric analysis of the solution at control times to assess the rate of absorption of SO42− ions by samples and determine the volume of released calcium hydroxide. In turn, the concentration of ions in the solution is:The potentiometric method was used to study the chemical resistance and evaluate the effect of an aggressive sulfate medium on the properties of the compositions. This method includes recreating hydrosulfate corrosion conditions using a 1% Na2SO4 × 10H2O powder was poured out and stirred in a laboratory vessel for 3–5 min until the salt was completely dissolved.The method of preparing the solution is as follows: in 1 L of distillate at a temperature of 20 ± 1 °C, NaNext, cube samples of 20 × 20 × 20 and 70 × 70 × 70 mm were placed in the obtained solution in a desiccator, which were kept in the solution for 224 days, with control measurements carried out on days 56, 112, and 224 of exposure ,27.2SO4 solution to restore the conditions of an N sulfate medium. Titration was carried out until the color of the indicator changed from crimson to neutral white, after which, the pH was determined. Titration was carried out every day for the first 7 days, every two days until day 14, every three days until day 28, and every 7 days until day 224.To maintain the concentration of sulfate ions in the solution, before titration, the pH was determined on an ST5000-F pH meter (with an ST350 electrode), after which, the solution was titrated with a 5% HWhen the control period was reached, the samples were removed from the solution and subjected to strength tests, mass measurements, electrical resistance measurements, and were examined by a set of physical and chemical analysis tools.The program of the presented study included the preparation of samples of the control and electrically conductive composition; for each composition, samples were made from dough of normal density with dimensions of 70 × 70 × 70 mm and 20 × 20 × 20 mm. Two days after molding, the samples were removed from the mold and placed in water at 20 ± °C until brand strength was reached. Then the samples were removed and placed in the prepared solution. The samples with dimensions of 70 × 70 × 70 mm were used to evaluate the strength and electrical properties.For the correlation analysis of the relationship between the mechanical compressive strength and the volume of released calcium hydroxide and the assessment of the physicochemical properties, the samples of 20 × 20 × 20 mm were used, and these types of samples were also used to determine the change in mass.The combination of small sample sizes and the use of an N sodium sulfate solution made it possible to carry out studies under conditions close to real ones ,28.Compressive Strength of ConcreteThe compressive strength of the samples was determined at the age of 56, 112, and 224 days using a PGM-100MG4-A hydraulic press with a loading rate of 0.5–0.8 MPa/s.Electrical Resistance Measurement Test MethodsTo obtain data for calculating the specific volume resistance of mineral matrices, the probe method was used. The probe method is the introduction of two pin-type copper probes into the sample at a given distance from each other ,36.The MNIPI E7-20 device was used to measure current voltage characteristics. The principle of operation of the device is based on the voltmeter–ammeter method. The operating frequency voltage from the generator is supplied through the measured object to the converter, which generates two sinusoidal voltages , which are converted into digital form. The value of the measured parameters is determined by calculation and displayed on the display in Ohm, Ω.At the same time, based on the data obtained from the device and the geometric parameters of the samples, the electrical resistivity was calculated using the formula ,36:ρ = RMicrostructure Examination of ConcreteTo study the morphological features, chips of samples were taken after 56, 112, and 224 days of exposure in an aggressive environment. The features of the microstructure of the studied composite materials were determined using the scanning electron microscopes Thermo Fisher Scientific Quattro S  and Tescan Mira3 XMU. The Thermo Fisher Scientific Quattro S survey was carried out in low vacuum mode from 20 to 30 kV, without deposition, at a pressure of 50 Pa, with ×5000 magnification steps, while the Tescan Mira3 XMU survey was carried out at 20 kV, with gold sputtering.Thermogravimetry–Dierential Scanning Calorimetry (TG–DSC) Analysis of ConcreteDSC analysis was used to obtain additional information on the phase composition of the studied materials. DSC data were obtained on a TGA/DSC1 instrument from Mettler-Toledo Vostok CJSC in a temperature range from 60 to 1100 °C and at a temperature rise rate of 30 °C/min in air.The study of the process of sulfate corrosion was carried out in a significantly longer period from 56 to 224 days of exposure and is a continuation of work ,40,44. TThe graph presented in The analysis of the results of the titrimetric study was carried out up to 224 days. The period was determined on the basis of the works ,27 and i42− and the electrically conductive composition—32.6 mL SO42−. In turn, for the remaining period, the absorbed volume was 11.4 mL of SO42− for the control composition and the electrically conductive composition was 13.7 mL of SO42−. Thus, the total volume of absorbed SO42- for the entire test period was for the control composition—43.1 mL; and for the electrically conductive composition—46.3 mL.At the initial stage of research on the 28th day of exposure (detailed results are presented in ), the coOn the 224th day of testing, the reactive components of the mineral matrix completely reacted with sulfate ions in the area of the samples, with a depth of 4.5 mm up to 2 cm from the surface, which indicates the transition of the reaction to the diffusion stage.The obtained data on titration and mechanical strength at an early stage of the study (up to 28 days) indicate an active growth of the expansive phase, while due to the filling of micro and macropores, an increase in the density of the samples was noted, which is confirmed by the strength and mass indicators. At the next stage of the study (from 28 to 224 days), a stable growth of the expansive phase was observed, confirmed by an increase in the mass of the samples; the data are presented in In turn, The results of the study of the effect of hydrosulfate corrosion on the electrical properties of the control and electrically conductive compositions, shown in During the impact of sulfate ions on the mineral matrix, the structure of the samples underwent a number of physicochemical changes . An exteThe resulting images visualize the surface morphology of the cleavages of the control and electrically conductive compositions. The structure of the control sample (a) on the 56th day of testing is a polymineral aggregate of set cement, including voids formed during the washing out of calcium hydroxide. Analysis of the morphology of the electrically conductive composition (b) is characterized by the formation of crystalline hydrates of various natures, including tabular calcium hydroaluminates.On the microstructure of the samples after 112 days of testing, the following changes can be observed: (c)—in the structure of the control sample, the formation of microcracks caused by the formation of secondary ettringite  is observed; (d)—the structure of the electrically conductive composition is represented by formations of cubic calcium hydroferrites, as well as polymineral conglomerates of set cement.On the 224th day in the structure of the control sample—(e) the splitting of acicular crystals of ettringite to fibrous crystals with the formation of “two-leaf” is observed; in electron microscopic images of electrically conductive concrete—(f) crystalline hydrates of set cement are observed, including electrical calcium sulfoaluminoferrites in the form of hexagonal crystals and an amorphous phase.A decrease in the concentration of calcium hydroxide, due to its leaching at an early stage of corrosion, at later stages makes it impossible for the formation and existence of polybasic calcium hydroaluminates, which, in turn, prevents and sometimes excludes the possibility of the formation of calcium hydrosulfoaluminates. At a later stage, during the action of sodium sulfate, along with the formation of gypsum, accumulations of well-defined spherulites of calcium hydroaluminate and calcite are presented in a slightly larger amount.To establish the relationship and interpret the causes of changes in physical and mechanical parameters, differential scanning calorimetry was carried out in an oxygen atmosphere. The curves obtained are shown in The mode of constant exposure to an N sodium sulfate solution at the later stages of the experiment showed that in the period from 28 to 224 days, the absorption of sulfate ions slows down and averages 26% for the control and 29% for the electrically conductive compositions of the total volume of absorbed sulfates.Monitoring of the physico-mechanical parameters of the samples during the entire time of exposure to a 1 N sodium sulfate solution showed an increase in the density of the samples, for the control composition—by 6%, for the electrically conductive one—by 6.5%. In turn, the cyclic change in the mechanical strength, on average by 15% for the control and electrically conductive samples, in the period from 56 to 224 days, is a relaxing release of internal stress, followed by compaction of the formed microcracks.The electrical resistivity of the samples has a steady growth trend during the entire experiment, while the growth in the control and electrically conductive compositions has a different character. Thus, the increase in the resistivity of the control composition for the period from 28 to 224 days was 75%, for the electrically conductive composition of 74%, while the final value is 101.3 kOhm cm for the control sample, and for the electrically conductive composition is 37.6 kOhm cm, which indicates a difference in the physicochemical properties of the phase composition of mineral matrices.An analysis of the microstructure of the samples showed that in the control composition, at the later stages of the experiment (from 56 to 224 days), ettringite splits with the formation of “two-leaves”. At the same time, the formation of calcite spherulites and calcium hydroaluminates is observed in the electrically conductive composition, which leads to an increase in the amount of the solid phase, to a cyclic increase in crystallization pressure, and causes a negative effect in the form of a decrease in strength.Differential thermal analysis confirmed the differences between the features of the interaction of compositions with an aggressive environment and a decrease in strength characteristics.Experimental data obtained by analyzing the dynamics of the process of absorption of sulfate ions, microstructure, thermal effects for samples of control, and electrically conductive compositions show the features of the long-term effect of an N sodium sulfate solution on the characteristics of fine-grained concrete under the external influence of sulfates. Based on the laboratory results, the following conclusions can be drawn:The obtained results of the research can be used in preparing recommendations for the development and optimization of the compositions of electrically conductive concrete used in aggressive conditions of hydrosulfate corrosion, it might also be of great importance for choosing the conditions for conducting experimental studies on the process of sulfate corrosion of composite compositions based on Portland cement.


With interest, we read the article by Peric et al. about the frequency and type of autoimmune diseases (AIDs) in a large cohort of Serbian patients with myotonic dystrophy type 2 (DM2) . Their rThe pathogenesis of AIDs in DM2 remains an intriguing question” and “To understand better the autoimmunity in DM2, future studies should also focus on assays to measure B cell and T cell activity and interleukin pathways.” We would like to comment on these statements below based on our previous observations and recent immunological research in DM2.In the conclusion of their article, however, the authors state that “n = 36/125) of AIDs in the Serbian cohort of patients with DM2   depleted zebrafish, CNBP-deficient mice, and human blood samples) revealed important roles of CNBP as a novel transcription regulator of interleukin-12β (IL-12β) gene transcription in macrophages and in IL-12-driven and Th1-mediated immune responses . , 5. in vesponses . Furtheresponses .DM2 is caused by a tetranucleotide (CCTG) repeat expansion in intron 1 of the CNBP gene resulting in both an RNA gain-of-function and a CNBP loss of function. We, therefore, consider the results of the recent immunological studies summarized above very relevant for the observations in the Serbian cohort . The stuIn conclusion, CNBP has recently been identified as a key transcriptional regulator required for activating and maintaining the immune response. This role of CNBP suggests an additional explanation in the pathogenesis of the wide variety of AIDs in DM2.MD wrote the first draft of the manuscript. AT wrote sections of the manuscript. MD, AB, NV, and AT contributed to the manuscript revision and read 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.


In times of pandemic as Covid-19, as in disaster situations, there is an increased risk of Post-Traumatic Stress Disorder, Depression, and Anxiety . The measures taken have affected individual freedoms for the benefit of community health by seeking to reduce the spread of the virus, although the side effects can cause profound damage to society, especially in those most vulnerable populations such as children and adolescents with ADHD.This study aims to assess the psychopathological state and possible consequences of the first wave of the Covid-19 pandemic.This study is part of the Kids Corona, an institutional research project of the Hospital de Sant Joan de Déu and the Fundació de Sant Joan de Déu to provide a social and research response to the Covid-19 Pandemic. To assess the impact of Covid on children and adolescents with ADHD a cross-sectional study was conducted between 20 and 30 July 2020 with a battery of questionnaires. The Child Behavior Checklist (CBCL), the Sleep Disturbance Scale for Children (SDSC), the Screen for Child Anxiety Related Disorders (SCARED), the Children’s Depression Inventory (CDI) were used.70% of children and adolescents aged 7 to 12 years with ADHD had sleep disorders, the 54% had anxiety symptoms and 9% had a depressive disorder.Children and adolescents with ADHD are a vulnerable population to the effects of Covid, with anxiety, depression, and sleep disorders.No significant relationships.


The questions referred to various aspects of the dental care needs of PLWH, together with data on the professional activities of the dentists. After signing the term of informed consent, the dentists were divided into six subgroups according to the time (in years) since completing their bachelor’s degree in dentistry. The data were presented as descriptive statistics and percentages, and then analyzed using the Kappa test. Most  of the dentists were female, the mean age of the dentists was 32.5 years, and a majority (80.2%) were based in the city of Belem; the mean time since graduation was 8.5 years, with 22 (43.1%) having more than 5 years of professional experience, and 31 (60.8%) having graduated from a private dental college. Just over half (51%) of the 51 dentists had completed graduate courses, and the most common dental specialty was orthodontics (19.6%). Most (74.5%) of the dentists work in the private sector, 38 (74.5%) claimed to have already provided oral care to PLWH, and 43 (84.3%) had access to specialist content on the oral care needs of PLWH. In terms of the knowledge of the dentists with regard to the oral care needs of PLWH, four of the ten diagnostic questions obtained more inadequate answers than expected, whereas the final two questions (11–45.1% and 12–31.4%) demonstrated that many of the dentists adopt unnecessary modifications in their oral care protocol for PLWH, due to a fear of contamination. Overall, our results demonstrate a frequent lack of knowledge, especially with regard to the oral healthcare needs of PLWH, which may account for many of the stigmas that persist in the dental care of this vulnerable group.Oral lesions are usually the first sign of HIV infection. The present study aimed to determine the level of the knowledge of dentists on the dental care needs of People Living with HIV (PLWH). This cross-sectional study was conducted between February and May 2021, in the Brazilian state of Pará, during which a total of 51 dentists received an anonymous digital form (Google In the early 1980s, the first cases of Acquired Immunodeficiency Syndrome (AIDS) were recorded around the world, and innumerable reports drew the attention of the scientific and medical community to the high mortality rates in the patients affected by this new pathogen . InitialA few years after this first report, the pathogen was isolated and then classified as the Human Immunodeficiency Virus (HIV) ,6,7. SinEven today, HIV infection is a major public health concern, in particular, in developing nations such as Brazil, where infection rates vary considerably among the country’s different regions, according to data from the Brazilian Ministry of Health (BMH). The 2019 epidemiological bulletin of the BMH showed that the northern region had the second lowest rate of notification of new HIV infections among Brazil’s five regions, with a total of 4948 . Comparisons with the previous bulletins revealed a tendency for linear growth in the HIV/AIDS detection rate ,14,15.It is common for People Living with HIV (PLWH) to present oral manifestations during HIV infection, which may provide systematic criteria for the diagnosis of the acute, chronic, or AIDS phases of the infection, or indicate a possible HIV infection, and also increases the morbidity of PLWH ,12. GiveDentistry courses in Brazil have an extensive curriculum that aims to prepare dental students for the correct treatment of individuals of all kinds . DespiteIn addition to a fear of HIV contamination, published studies have also shown that many dentists and dental students are not well acquainted with the lesions associated with HIV, and that many stigmas associated with this virus persist in these professionals, which unfortunately limit their adoption of the biosafety protocols necessary to satisfy the oral care needs of PLWH, due to a lack of knowledge on HIV contamination, transmission, and replication ,21,22,232, and a population of 8,690,745 inhabitants. It has 144 municipalities, and a Gross Domestic Product (GDP) of R$49.5 billion (approximately US$10 billion), and a per capita GDP of R$7707.The present descriptive and cross-sectional study involved dentists residing in Pará state, northern Brazil, who were surveyed between February and May 2021 . Pará isThe Brazilian Federal Board of Dentistry indicates that approximately 6834 dentists are currently active in Pará, more than half of which  are based in the state capital, the city of Belem. Belem has an estimated population of approximately 1,500,000 inhabitants, that is, less than one fifth of the total population of the state, which indicates a severe imbalance in the distribution of dentists in Pará, and, in turn, the availability of oral care, in particular, for key groups, such as PLWH.The DATASUS/Tabnet platform  was accessed for information on the number of oral health procedures conducted in Pará, and identified 273,326 records for the period between January and July 2021. Unfortunately, this platform does not provide any information on the distribution of these procedures in the state or the groups attended, so there are no systematic data on the oral care of PLWH.The present study was approved by the Research Ethics Committee of the Institute of Biological Sciences at the Federal University of Pará (UFPA), under protocol number 4.606.188. Informed consent was obtained from all the participants that were included in the analyses in this study.A non-probabilistic “snowball” sampling technique was used to invite dentists to participate in the present study . InitialThe digital form used to collect data was distributed using WhatsApp, Facebook, Instagram , and Telegram . Each dentist that received and filled out the digital form was requested to invite three other dentists to participate. This procedure was repeated a number of times until completing the study sample.All participants were informed of the nature of the study, its potential risks and benefits, and were required to sign the digital term of informed consent before being given access to the digital form. The inclusion criteria were: (i) an age of at least 18 years; (ii) graduation from a dentistry course; (iii) active registration in the federal and regional councils of dentistry; (iv) based in Pará state; and (v) with access to the internet. Potential participants who did not sign the informed consent form or did not have stable internet access were excluded from the study. The exclusion criteria were: (i) individuals who moved to other states during the study; (ii) being a dental student or undergraduate; (iii) a lack of internet access; and (iv) any other type of impairment for the completion of the digital form.The dentists were divided into six subgroups according to the time (in years) since completing their bachelor’s degree in dentistry. The groups were formed and organized to categorize the technical level based on the time completing their bachelor’s degree: G1 group: ≤1 year ; G2 group: 2 years; G3 group: 3 years; G4 group: 4 years; G5 group: 5 years; G6 group: >5 years.® Forms Platform , and was distributed through an electronic link in the apps mentioned above. The digital form was composed of four blocks of questions, and the participants could not advance to the next block without filling all the questions in the current block [A digital form was used to collect data in the present study. This form was formatted and administered using the Googlent block .sensu stricto or sensu lato); dental specialty; and professional details, such as their workplace, whether they had already provided oral care to PLWH, or whether they had previous access to specialist content on the oral care needs of this group. Block 4 contained 12 questions on the technical–scientific knowledge of the participant in terms of their knowledge on HIV infection, transmission, and diagnosis, and its clinical signs and symptoms. There were also questions on basic human immunology, dental biosafety, and the clinical examination and management of PLWH patients.Blocks 1 and 2 contained information on the researchers and the objectives, risks, and potential benefits of the study, as well as the consent form . Block 3All of the questions in blocks 3 and 4 have dichotomous or multiple-choice answers, in addition to a section inviting the participant to provide details of their own knowledge on the question. To determine whether the digital form helped the dentists to increase their knowledge on the oral care needs of PLWH, a 0–10 self-reported scale was included at the beginning and the end of the digital form to allow each dentist to evaluate their own knowledge prior to and after answering the form. For analysis, scores of 0–6 were considered to reflect insufficient knowledge, and scores of 7–10 were accepted as sufficient knowledge.All the data collected during the present study were entered into an Excel database , and then converted to BioEstat format. Statistical parameters  were used to describe the characteristics of the sample, in terms of the quantitative and qualitative variables investigated using the digital forms.The level of knowledge of the dentists on the oral care needs of PLWH was assessed using two approaches. The first was to compare the self-reported knowledge scores from the beginning and end of the form, with the total number of adequate answers given to the questions presented in blocks 3 and 4.p < 0.05 significance level). All statistical procedures were run in the BioEstat 5.0 program [The second evaluation compared the self-reported knowledge scores from the beginning of the digital form with those at the end. Between these two moments, all of the dentists answered questions on a range of topics, which would have permitted the emergence of reflections, doubts, and fears, as well as the definition of appropriate resolutions for these various topics related to the oral care needs of PLWH. The effects of this process are reflected in the replicability of the responses of the dentists prior to and following the 10 questions. The difference was evaluated using the Kappa test, which verified the significance of the possible difference between the first and second responses , whereas 18 (35.3%) had no graduate qualifications. The most common dental specialty was orthodontics, practiced by 10 of the dentists (19.6%), followed by dental prosthesis (15.7%), and periodontics (13.7%). The most common workplace was in the private sector (74.5%), followed by the public sector (27.5%), whereas seven (13.7%) of the participants were not working at the time of the study due to the COVID-19 pandemic. Most (74.5%) of the dentists had already provided oral care to PLWH, and 84.3% had access to some type of specialist content on the oral care needs of PLWH.Overall, 26 (51%) of the dentists had taken a graduate course  are summarized in Less than half (47.1%) of the dentists knew which exams are necessary to diagnose HIV, whereas in the DQF space, 14 (58.3%) of the participants that had answered this question correctly raised further questions on HIV test parameters, demonstrating a certain level of doubt. Most (70.6%) of the dentists knew where to refer the patient after a positive HIV diagnosis (question 7), whereas almost half (47.1%) were unsure on the HIV window period. However, only nine (33.3%) of the 27 participants that answered positively described the period correctly in the DQF space.When asked about changes in Personal Protective Equipment (PPE) or biosafety protocols for the oral care of PLWH (question 9), 62.7% responded negatively, although most (78.1%) of these dentists questioned the effectiveness of the basic PPE protocol in the DQF, especially in the context of contact with blood or aerosol during the treatment of PLWH. Just over half (52.9%) were in doubt with regard to the prescription of drugs for PLWH, and in the DQF space, they inquired into the drugs and how to prescribe them.In question 11, 54.9% of the dentists responded negatively to any kind of change during non-invasive dental treatment, even though, in the DQF space, 74.5% of all the dentists, that is, 38 participants, questioned the risk of contamination when coming into contact with saliva or aerosol. In question 12, most of the dentists (68.6%) answered negatively to any kind of change during invasive dental treatment, but once again, many of the participants (43.1%) asked which procedures they should adopt in the case of work accidents in the DQF space.Prior to completing the questionnaire, 32 (62.7%) of the dentists declared they had sufficient knowledge to care for PLWH , whereasIt can be verified through the agreement Kappa test that at the beginning of the associated questionnaire after the 10 specific questions, there was a result of 0.0784, inferring a weak replicability by the kappa value and absence of agreement. Assessing the agreement at the end of the questionnaire after the 10 specific questions, a result of 0.1961 suggests, again, poor replicability of the test application; however, there is agreement, denoting improvement in learning/knowledge about the topic addressed.+ count, leading to manifestations such as oral lesions. A good basic knowledge of HIV is important, not only for healthcare in PLWH, but, in particular, to reduce the stigmas associated with this condition [The present digital study sought to assess the level of the knowledge of dentists with regard to the oral care needs of PLWH in Pará state, northern Brazil. Although the topic is not new—see Menezes et al. , Senna eondition ,31.Infection by HIV can be divided into the acute, asymptomatic, chronic symptomatic, and AIDS phases . It is iSenna et al.  showed tDespite the existence of standard occupational prevention measures such as PPEs, the lack of a national protocol for the oral healthcare of PLWH may contribute to the stigmas, technical ignorance, and misinformation on HIV infection , which mOliveira et al.  evaluateThe results of the present study indicated that the “veteran” dentists (5 or more years since graduating) had more professional and scientific knowledge than newly graduated dentists (no more than 2 years after graduation). However, the veterans tend to take less care with biosafety procedures . Corrêa Though the present study was successful in terms of the data collected, it did suffer from certain limitations, such as the relatively small sample size, its restriction to the state of Pará, the involuntary exclusion of individuals that did not have access to the internet, a possible bias of helpfulness generated by the invited participants, the answers prepared by the researchers, and, in particular, the identification of the need to assess the satisfaction of PLWH with regard to their dental care needs and treatment at both private and public levels.In conclusion, the present study served as the basis for a larger-scale cross-sectional study, and our results demonstrated that the lack of knowledge about oral health care of PLWH will increase stigmas among dentists and prejudice PLWH dental care; therefore, new information and establishment of a national protocol for dental care for PLWH will help dentists to better treat HIV-infected individuals.


The observations obtained by scanning electron microscopy showed that, with the addition of La2O3, the microstructure of AM alloy becomes more uniform and the grains are significantly refined. It is found by friction test that the running-in period is significantly shortened after the addition of La2O3. The coefficient of friction is reduced to a minimum of 0.68. Compared with AM alloys without La2O3, the wear rate of AM alloys with La2O3 is significantly reduced, with a maximum reduction of 38%. Using an optical microscope to observe the surface morphology of the wear scar, it is found that, after adding rare earth oxide, the wear mechanisms changed from adhesive wear and abrasive wear to abrasive wear, with the spalling of hard particles at the same time.Additive Manufacturing (AM) has become increasingly common, and its use in various industries is increasing. However, the microstructure, friction and wear performance of metals made by AM, such as the inexpensive and relatively good-performing iron-chromium alloys, require further investigation. Generally, adding rare earth elements can effectively improve the performance of AM alloys, such as tensile strength, wear resistance, corrosion resistance, creep resistance, etc. This work aims to study the variation of microstructure, friction and wear properties of laser additive manufacturing processed iron-chromium alloys after adding different mass fractions of La Additive manufacturing  is a revolutionary cutting-edge manufacturing technology that combines computer-aided design, material processing and molding technologies . It usesMany scholars have carried out laser additive experimental research on adding modifying elements to titanium alloys, aluminum alloys and other metal materials ,6. Yang 2 on the microstructure and main properties of laser cladding Ni60 on aluminum alloy surface. The results showed that CeO2 can optimize the microstructure of the Ni60 alloy fabricated from laser cladding, improve the uniformity of the grains of the alloy layer and effectively improve the corrosion resistance of the Ni60 alloy. Gu et al. [In addition to the above-mentioned additive elements, rare earths and their oxides are also often used as heterogeneous additive elements to improve the properties of additively manufactured alloys. This is because the fluidity of the molten pool is improved after adding rare earth elements, and the microstructure of the alloy is optimized, so pores and microcracks in the structure can be effectively reduced . Wang etu et al.  and Zhanu et al.  preparedu et al.  showed tu et al.  reported2O3 particles on the microstructure and tensile strength of wire-fed AM TC4 alloys and reported that, as the mass fraction of La2O3 increases, the tensile strength monotonically increases, while the elongation decreases monotonically. Wang et al. [2O3 based on SLM technology. The improvement of mechanical properties such as yield strength was attributed to the synergistic effect of grain refinement strengthening and dislocation strengthening. Chen et al. [Lanthanum oxide, one of the rare earth oxides, is an inorganic compound, usually white powder. It is often used as an added element for material modification and has a wide range of uses. For example, lanthanum oxide can be used in the manufacture of piezoelectric materials, optical glass, etc. It can be used in electroforming electrode materials, which can effectively improve the resistance to galvanic corrosion. Moreover, lanthanum oxide is also often used as a heterogeneous additive element to improve the performance of AM alloys by analyzing existing research. Wang et al.  analyzedg et al.  fabricat2O3 on the strength and wear behavior of Nickle-titanium alloy made by laser direct deposition was investigated by Lu et al. [2O3 can play a role in improving the strength. That is, after adding lanthanum oxide, the grains of the nickel-titanium alloy were refined and the wear resistance was improved. Shi et al. [2O3 addition were 0.63 and 15.79 μm, respectively, which were 3% and 86% lower than those of the 65Mn matrix, respectively. Compared with the other samples, the coating demonstrated the best wear resistance. Zhao et al. [The influence of adding Lau et al. . The resi et al.  investigo et al.  preparedo et al.  fabricatIn summary, adding heterogeneous elements can effectively enhance the microstructure and mechanical properties of additive manufacturing metals. Lanthanum oxide is one of the most commonly used modifier elements for AM alloys. Most of the existing research using lanthanum oxide as an additive element to improve the properties of alloys focus on strength, corrosion resistance, etc., and most of the alloys targeted are titanium alloys, nickel-based alloys and aluminum alloys. Research on improving the wear resistance of AM iron-based alloy is relatively rare.The mining industry has an urgent need for efficient and safe production of fully mechanized mining equipment. Effectively improving the wear resistance of typical parts such as hydraulic supports, sprockets and middle plates of scraper conveyors is of great significance to ensure their service reliability. Therefore, it is urgent to develop an iron-based alloy powder with high wear resistance and low cost for laser additive manufacturing, repair or surface strengthening of key parts of mining equipment. An iron-chromium alloy powder with high corrosion resistance which is inexpensive and can be used in laser additive manufacturing was investigated in our group’s previous work . In thisTherefore, iron-chromium alloys with different mass fractions of lanthanum oxide were fabricated by laser direct deposition. The effect of lanthanum oxide on the microstructure and element distribution was analyzed. The influence of lanthanum oxide content on the friction coefficient and wear rate of AM alloys was analyzed experimentally, and the wear mechanism was analyzed by the wear surface characteristics.2O3 particles is approximately 1 μm–5 μm. Different mass fractions of La2O3 were added, respectively, and iron-chromium alloy powders with La2O3 were produced after 72 h ball milling and mixing. The mass fractions of La2O3 content in the iron-chromium alloy powder were without La2O3 (Specimen-0), 0.5 wt% (Specimen-1), 1.0 wt% (Specimen-2), 1.5 wt% (Specimen-3) and 2.0 wt% (Specimen-4). The microstructure of the iron-chromium alloy powder particles and La2O3 powders is exhibited in The chemical composition of iron-chromium alloy powder is indicated in 3 and H2O in a volume ratio of 1:1:1. A Scanning Electron Microscope  was used to observe the microstructure of AM alloys. Using the method of random sampling in a fixed area to calculate the average value, Image-Pro-Plus6.0 software  was used to measure the average grain size of each specimen, and the average grain size and error value were calculated. Chemical element distribution was tested using the Energy Dispersive Spectrometer .The iron-chromium alloys with rare earth oxide were fabricated by laser direct deposition additive manufacturing at the optimized process parameters, which were reported in our previous work : laser pThe dry sliding friction test was carried out on AM alloy samples using the friction and wear testing machine (UMT-2) at room temperature and without lubrication. A silicon nitride ceramic ball with a diameter of 9.525 mm was used as the counter-grinding pair. During the test, a 15 N vertical load was applied to the surface of the specimens; the sliding speed was 5 mm/s and the total time was 15 min. And coefficient of friction curve was automatically recorded. The microhardness of each specimen was tested using a MH-6 Vickers digital microhardness tester with a load of 10 g and a dwelling time of 5 s. The averaged results of three repeat tests were used in this article. The wear scar profile was observed using a white light interferometer . The scanning resolution of the white light interferometer is 0.01 μm in the Z direction and 0.01 mm in the X and Y directions. The wear volume loss was then estimated using MATLAB using the measured wear scar profile data. The primary wear track volume was estimated as the average cross-sectional area of seven profiles showed by the dash line in The microstructure of AM alloy specimens near the fusion line is shown in 2O3 is 0.5 wt% (Specimen-1), and the number of pores decreases gradually as the mass fraction of La2O3 increases. This shows that the addition of rare earth oxide plays a key role in reducing porosity near the fusion line. The reason is that an appropriate amount of La2O3 can promote gas discharge by improving the convection of the molten pool. The molten pool with less rare earth oxide content has poor fluidity, so the gas molecules inside the alloy layer cannot be discharged within a very short cooling time. In paper [More importantly, the existence of pores can be observed below the fusion line and on the side of the substrate, as shown in the red dash line in In paper , a simil2O3 significantly affects the microstructural characteristics of AM alloys. Whether it is in the coarse-grained region or the fine-grained region, the grains of AM alloy are significantly refined after adding rare earth oxide. That is, as the mass fraction of La2O3 increases, the dendrite size decreases significantly, the number of equiaxed crystals increases and the dendrite gap decreases. As shown in The internal microstructure of AM alloy is divided into a coarse-grained region at the interface between the layers and a fine-grained region in the middle of each layer, as shown in The intergranular energy spectrum analysis of AM alloy was carried out using EDS line scanning, as shown in In order to further analyze the element and phase distribution, quantitative analysis of the AM alloy energy spectrum was carried out using EDS point scanning. 2O3, the grains of AM alloys are significantly refined. The main cause of grain refinement is the addition of La2O3. The La element with a larger atomic radius (RLa = 0.1877 nm) is a surface-active element. It is easy to react with other elements during the laser additive process, such as Cr, C, Si, Ni, etc. Some stable compounds can be generated, such as Cr3NiB, CeFeSi, LaCrO4, LaNi8C2, etc. [2O3 themselves can be used as nuclei for heterogeneous nucleation. The increase in the number of nuclei in the alloy molten pool during the nucleation process helps to promote the nucleation rate and enhance non-spontaneous nucleation [From C2, etc. . During cleation . The mor2O3 mass fractions. As shown in 2O3. When the mass fraction of La2O3 is 2%, the microhardness of the alloy is the highest. Compared to the alloy without lanthanum oxide, the hardness is increased by about 20%. Generally speaking, the strength and hardness of an alloy increase as the grain size decreases. As shown in 2O3. This is the reason why the hardness gradually increases as the content of La2O3 increases.2O3 content, the running-in period is obviously shortened. The friction coefficient of Specimen-3 begins to increase sharply around 42 s, rises slowly after the running-in period and then enters the stable friction stage. The coefficient of friction of Specimen-4 rises rapidly at the beginning of the relative slip and fluctuates greatly after 28 s, then slowly rises. After 200 s, it enters the stable friction stage. Its friction coefficient is 0.68. In general, the smaller the coefficient of friction, the better the wear reduction performance. Therefore, the wear reduction performance of AM alloys increases with increasing La2O3 content. In short, adding lanthanum oxide significantly shortens the running-in period of the alloy samples and makes the samples quickly enter the stable friction stage. This is a significant improvement in the friction properties of the alloy after adding lanthanum oxide. With the increase of lanthanum oxide content, the friction coefficient tends to decrease, but the decrease is not obvious.The coefficient of friction curve of each AM sample automatically recorded by the friction tester is shown in 2O3, the wear scar depth decreases gradually. The maximum depth of Specimen-4 is reduced to 9.3 μm.2O3 increases. The maximum width of the wear scar is 452 mm (Specimen-0), and the minimum width is 372 mm (Specimen-4). The variation trend of wear scar depth is the same as that of wear scar width. As the mass fraction of La2O3 increases, the average depth of the wear scar decreases significantly. The wear scar depth of Specimen-0 reached 7.24 μm, and that of Specimen-4 decreased to 4.99 μm. The change in the wear rate also showed the same trend, that is, the wear rate decreases significantly as the mass fraction of La2O3 increases. Compared with Specimen-0, the wear rate of Specimen-4 is reduced by 38%. Generally speaking, the smaller the wear rate under the same conditions, the better the wear resistance. Therefore, the wear resistance of AM alloy is improved after adding La2O3, and, as the mass fraction of La2O3 increases, the wear resistance improves. It can be seen that the purpose of preparing iron-chromium alloy powder for laser additive manufacturing with high wear resistance is achieved by adding rare earth oxides. The reasons for the improved wear resistance of the alloy and the wear mechanism will be explained in the following paragraphs.In addition, the average width, depth and wear rate of the wear scars (characterized by volume loss) were measured by the profile profiles, as shown in 2O3 (Specimen-0) is much lower than that of the counter-grinding material, the surface material is sheared and transferred by the counter-grinding material during the wear process. Obvious plastic deformation, transfer film and a small amount of grooves morphology can be seen on the surface of the test area, which is shown in In order to reveal the wear mechanism, the wear morphology characteristics of the AM alloy specimens after friction and wear tests were observed by OM, as shown in 2O3, AM alloy specimens produce the morphology shown in 2O3 is mainly abrasive wear. As the mass fraction of La2O3 increases, the depth and width of the groove show a decreasing trend. In addition, pits and microcracks formed after the bulk exfoliation can be observed. Under the fatigue effect of the reciprocating cyclic tangential load and the cutting effect, the surface material is affected by the shear stress on the grinding pair, which leads to the peeling of the binder phase and then causes the block peeling. Therefore, the wear pattern of AM alloy after adding La2O3 also manifests as fatigue spalling of hard particles. The worn surface topography of each sample shown in 2O3 increases, the wear resistance and wear reduction of AM alloy show an increasing trend.After adding La2O3 is the leading cause of the improvement of the wear resistance of AM alloy—this is the fine-grain strengthening effect. When the alloy is subjected to external force, the plastic deformation of the microstructure with finer grains can be dispersed into more grains. As a result, the plastic deformation is more uniform and produces fewer stress concentrations. Therefore, compared with coarse-grained metals, fine-grained metals have a higher ability to locally resist the indentation of hard objects into their surfaces under the same external force. In addition, more grain boundaries after grain refinement make it more difficult for dislocations, especially misaligned dislocations, to transfer to other grains, and disordered grain boundaries make slip more difficult. The finer the microstructure of the alloy—that is, the smaller the grain size—the more the grain boundary will hinder the movement of dislocations, and the more difficult it will be for crack propagation. Grain refinement generally also increases material toughness. Therefore, the increase in strength and toughness caused by grain refinement increases the wear resistance of AM alloy. In paper [Generally, fine-grained metals have higher strength and hardness than coarse-grained metals. Therefore, the grain refinement after adding LaIn paper , laser c2O3 on the microstructure, friction and wear performance and wear mechanism of AM iron-chromium alloy was systematically investigated. The following results were obtained.The effect of adding La(1)2O3, the microstructure of AM alloy becomes more uniform and the grains are significantly refined. La element is the main cause of grain refinement. La element easily reacts with other elements to form some stable compounds during the laser additive process. It can perform slag formation and reduce the content of alloy inclusions. In addition, some of the compounds formed and the La2O3 themselves can be used as nuclei for heterogeneous nucleation. Grain refinement is further promoted.By adding La(2)2O3. The coefficient of friction is reduced. The wear rate has dropped significantly. This shows that the wear reduction and wear resistance of AM alloys have been improved. The increase in the strength and toughness of the alloy caused by grain refinement after the addition of La2O3 is the main reason for the improvement of the wear resistance of the AM alloy.The running-in period is significantly shortened after adding La(3)The wear form of AM alloys after adding rare earth oxide becomes abrasive wear, accompanied by the spalling of hard particles. This is mainly due to the grain refinement strengthening effect after adding rare earth oxide.2O3 on mechanical properties, such as tensile and bending, would be an interesting future research subject.The scope of this research is limited to the influence of lanthanum oxide addition on the microstructure and wear performance of AM alloys. The effect of adding La


In the current study, the yield of gaseous products depends on the decomposition of toxic compounds and methane, because the decomposition of methane also produces H2 and lower hydrocarbons. The percentage yield of H2 increases from 0.43–4.74%. Similarly, the yield of LHC increases from 0.56–7.54% under the same reaction conditions. Hence, input power promoted the decomposition of the toxic compound and enhanced the yield of gaseous products.Methane is the main component of biogas, which could be used as a renewable energy source for electricity, source of heat, and biofuel production after upgrading from biogas. It also contains toxic compounds which cause environmental and human health problems. Therefore, in this work, the removal of a toxic compound (toluene) from methane gas was studied using a dielectric barrier discharge (DBD) reactor. It was observed that the removal of the toxic compound could be achieved from methane carrier gas using a dielectric barrier discharge reactor, and it depends on plasma input power. The maximum removal of the toxic compound was 85.9% at 40 W and 2.86 s. The major gaseous products were H The removal of toluene as a toxic volatile organic compound from methane gas, which is the major component of biogas, is carried out using a non-thermal plasma dielectric barrier discharge reactor. Electrons are produced and accelerated by the electric field, which collide with the molecules and atoms passing through the plasma reactor. Some electrons have sufficient energy to ionize these gas atoms or molecules upon collision. The energy required to dissociate/ionize the background gases is in the range of 5–25 eV.12 It was observed that a sufficient number of high energy electrons are present in a Maxwellian distribution to dissociate/ionize background gas molecules.13 The molecules, ions, and gas atoms remain at modest temperature, whereas electrons in comparison are very hot. It was reported that the input power absorbed by the electrons was very high (i.e. 102–103 times) compared to the heavy particles.14 However, the energy transferred from electrons to heavy particles is small due to the lower mass of the electrons.15In recent years, non-thermal plasma (NTP) has received significant attention in gas cleaning and removal of VOCs due to its simple operation and the ability to handle high and low concentrations of VOCs.via NTP is mostly carried using a dielectric barrier discharge (DBD) due to its ease of operation and the availability of an efficient and economical power supply.16–23 Due to the combined effect of non-equilibrium plasma properties and ease of operation at ambient pressure, DBD reactors are being used for industrial applications.24,25 The ability of the DBD reactor to simple scaling up is also a well-known feature for the commercial applicability of this process.26,27 Moreover, cost-effective and reliable power supplies are also easily available to generate NTP in DBD reactors. The frequency range (1 kHz to 10 MHz) and the pressure range (10–500 kPa) are normally preferred for industrial applications of the DBD reactor.28 Currently, DBD reactors are widely used for a range of industrial applications such as the treatment of pollutants causing anthropogenic emissions into the atmosphere, ozone generation, surface treatment, ultraviolet lamps, mercury-free fluorescent lamps, and large-area flat plasma displays.28,29The treatment of pollutants 30–34 However, in biogas, the major component of gas is CH4, which could be up to 75% depending on the type of feedstock and operating condition of the digester.35 To the best of our knowledge, the removal of the toxic compound using CH4 as a carrier gas in a DBD reactor has not been studied so far. Therefore, it was very important to investigate the removal of toluene using CH4 as a carrier gas to evaluate the performance of NTP. Herein, toluene was chosen as a model compound due to its presence in abundance in biogas. Toluene is also used in many industrial processes.36 The concentration of VOCs was kept higher (33 g Nm−3) than the amount of VOCs present in biogas, leaving operational margin for scaling up into industrial practice.37Recently, many researchers focused on the removal of VOCs using air as a carrier gas.2.38The flow rate of the natural gas was controlled by using a computer-controlled mass flow controller, connected to the gas cylinder . The natural gas was passed through a bubbler filled with toluene to add the vapours.4 and H2, and FID (flame ionization detector) to detect lower hydrocarbons (LHC).The gaseous products were measured by Varian 450-GC provided with a TCD  to monitor CH2.1The decomposition of toluene is defined as:where m > 1The yield of different product was defined as follows:39The energy efficiency and specific input energy (SIE) are calculated using the following formulas:3.3.140,41 These high-energy electrons are responsible to increase the decomposition of VOCs, whereas they can also produce reactive species upon collision with background gas,42–44 which can also contribute to the high conversion of VOCs. Therefore, at high power combined effect of energetic electrons and reactive species may contribute to enhance the decomposition of target compounds. The bond dissociation energy of the –CH3 group in toluene is 3.7 eV,45 which is lesser than the C–C bond between the methyl group and aromatic ring, and bonds present in the aromatic ring.46 Hence, the decomposition of toluene can proceed via the removal of H from the –CH3 group. The abstraction of H from CH3 form the benzyl radicals (4) also produces CH3 and H radicals 3.24 also increases with increasing input power due to the presence of a high number of reactive species at higher input power, which play a vital role in NTP processes.48 However, the effect of power is the same, increases with increasing input power, due to abundant reactive species at high powers. The decomposition of CH4 into CH3 and H by NTP forms a variety of products, and the composition of these products heavily depends on the plasma input power.3.32 increases at higher power, which can also contribute to the formation of LHC. The decomposition of CH4 could also contribute to the production of H2 and LHC. Moreover, it was observed that the impact of energetic electrons generates different radicals such as CH3, CH2, CH, and H. These radicals combine to produce different LHC via reactions 48–503 T of toluene with input power. The value of R2 for linear regression is 0.96, which shows that the decomposition of VOC compounds in the current experiment is first ordered.It has been observed that the reactions involved in NTP are power-dependent. The input power in the DBD reactor is the most important parameter. The input power plays a key role to produce active species, which produces ionization, dissociation, and excitation of background gas to start decomposition reactions. Therefore, it was reported that the reactions involved in NTP are energy-dependent.3.44 and products yield. It can be observed that the decomposition of methane and products yield increase linearly with increasing SIE. The SIE depends on input power and flow rate; however, the flow rate was kept constant in the current study. Due to this reason, SIE is closely related to plasma input power. Previous studies showed that increasing SIE enhanced the decomposition of methane and product yield.52 Overall, the major contributing factor is the input power because SIE only depends on power in this study.4.4 gas, which is the major component of biogas using the DBD reactor. The results show that the removal of VOC could be achieved from CH4 gas by using NTP dielectric barrier discharged reactor. However, the removal of VOC depends on input power. The highest decomposition of toluene at 40 W and 2.86 s was 85.9%. The major gaseous products were H2 and LHC. The effect of input power was the same on the yield of the products as in the case of decomposition efficiency. The decomposition of background gas may be affected due to the formation of methane through the decomposition of toluene, which may occur due to the recombination of CH3 and H radicals. However, it is difficult to measure such an effect due to the presence of methane as the carrier gas. Hence, the NTP dielectric barrier discharged reactor could be employed to remove VOCs from the methane gas.The decomposition of toxic VOC (toluene) has been studied in CHThere are no conflicts to declare.


In the contact explosion of 10 kg TNT, the fragmentation rate of the coated specimen decreased significantly compared with that of the unprotected specimen, realizing the zero fragmentation protection effect on the back-blast face. The maximum deformation area and the main energy absorption area of T26 polyurea under contact explosion is the ring area outside the longitudinal deformation area. The chemical structure of T26 polyurea changed significantly after the explosion; typically the N-H bonds, etc., were broken and the percentage of hydrogen bonding was reduced. T26 polyurea has realized the protection effect of zero fragmentation of large-equivalent contact explosion, which has a high application value for blast mitigation and blast-fragmentation prevention in actual engineering.In order to further study the blast mitigation performance of polyurea and to investigate the protection mechanism and damage characteristics of polyurea-protected structures under contact explosion loads, based on earlier work, this paper investigated the response and energy absorption performance of polyurea under various frequency loads. Qtech T26 blast mitigation polyurea (T26 polyurea) was adopted to protect the reinforced concrete (RC) slab and damage analysis of the post-explosion specimens was carried out at micro and macro levels. The response and energy absorption capacity of the material towards different frequency loads were investigated by dynamic mechanical analysis (DMA). Protective performance of T26 polyurea on RC slab was examined with a 10 kg TNT contact explosion test. Scanning electron microscopy (SEM) was employed to analyze the microscopic fracture morphology of the typical areas of the coating after the explosion. The chemical structure changes of the blast-face coating before and after the explosion were compared by Fourier transform infrared spectroscopy (FTIR). The results show that the glass transition region of T26 polyurea is −40 °C to 10 °C, which is a large temperature range, and the microphase separation of T26 polyurea is low. It is significantly influenced by the ambient temperature and loading frequency. The energy absorption of T26 polyurea is realized through the interaction between the hard and soft segments. When the frequency is between 10 Polyurea is a block copolymer synthesized by the rapid reaction of isocyanates with polyamines , the essThe majority of existing building structures are not designed at the beginning to survive the effects of blast loads ,4. BlastDuring early studies, the hardness and ductility of the polyurea were essential properties in selecting protective coatings to be applied to blast protection. With the intensive research on polyurea, it has been found that due to the special molecular structure of polyurea, the strain-rate sensitivity and energy-absorption capability of polyurea are essential properties in explosion and impact protection . ThroughTherefore, in order to provide blast and impact protection to different substrates in various environments, the mechanical, thermodynamic properties and energy absorption capabilities of polyurea need to be improved in order to obtain polyurea coatings with better protective properties. Tripathi et al.  found thOn the basis of polyurea research, Qtech T26 blast mitigation polyurea (T26 polyurea) was developed through a molecular structure design based on the characteristics of the blast-loading action and the surface characteristics of the substrate. In our earlier work, the mechanical characteristics of T26 polyurea at different strain rates and strain-rate sensitivity have been verified by quasi-static mechanical and dynamic mechanical tests, and it has been demonstrated that T26 polyurea substantially improves the blast resistance of RC slabs through explosive tests and numerical simulations, details of which are given in Reference . Based oT26 polyurea is independently designed and developed by the Institute of Functional Materials of Qingdao University of Technology in accordance with the requirements for concrete protection performance in the field of blast mitigation. The molecular structures of T26 polyurea and its components are shown in PHX-40 proportioner  and AP-2 spray gun  were employed to spray T26 polyurea coating; the reaction volume ratio of A and B components was 1:1; the preheating equipment kept the material reaction temperature at 65 °C; and the spraying pressure was controlled at 2500psi. When T26 polyurea was sprayed into film, the specimen had to be put into an environment of temperature 23 ± 2 °C and relative humidity 60 ± 15% for 7 d, after which the material would be completely cured.The RC slabs adopted double layers of reinforcement, with C40 concrete selected and a thickness of concrete protective cover of 15 mm. The size specification of the RC slabs was 1500 mm × 1500 mm × 300 mm, and the schematic of the test specimen was shown in RC slabs may develop defects such as pinholes due to uneven vibrations during the casting process. These defects, especially pinholes, can damage the integrity of the coating by creating bubbles and bulges during the spraying of the polyurea coating. The edges of RC slabs are highly susceptible to stress concentration during handling, and defects such as cracking and spalling occur, which seriously affect the adhesion of polyurea coating on the concrete surface and reduce the protective performance. Hence, before spraying the specimens, cement of the same strength should be added to the primer, well mixed, and then used to repair the concrete surface defects. To improve the surface roughness of the specimen and remove the mortar attached to the surface, the surface of the specimen should be polished after the repair is completed and the surface dust should be cleaned with an air gun.After the clean-up and repair were completed, the specimen surface was coated with primer  and Shore hardness tester  according to ASTM D412 (Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers-Tension) .DMA of T26 polyurea was performed using the DMA-Q800 . The deformation mode was selected as dual cantilever mode; the temperature range was −90 °C to 90 °C; the temperature rise rate was 3 °C/min; and the sweeping frequencies were 1 Hz, 5 Hz, 10 Hz, 50 Hz and 100 Hz.The basic parameters of the DMA were dynamic modulus and loss factor, whose relationships are defined as follows :(1)E*=E′In this experiment, contact explosion was adopted to verify the blast resistance performance of T26 polyurea. The explosive charges were TNT explosives with the mass of 10 kg. The details of the specimen setup are shown in The fracture mechanism of the specimens was studied by scanning electron microscope (SEM). The damage to the coating surface after the explosion was observed using the JSM-7500F SEM . The imaging was performed using secondary electron signals with the accelerating voltage range of 0.1 kV–30 kV, and the electron gun was a tungsten lamp with a magnification of 25 times to 1,000,000 times, with resolutions of 1.0 nm (15 kV) and 1.4 nm (1 kV), respectively.The specimens obtained in the field were cleaned with ultrapure water and were then dried. After that, the samples were sputtered with gold to form a conductive film to improve image quality and resolution.−1 and a spectral region of 4000–500 cm−1. The surfaces of the samples for measurement were cleaned with ultrapure water before the experiments.The infrared absorption spectra of T26 polyurea before and after the explosion were obtained by using VERTEX 70 FTIR spectrometer  with 32 scans and a resolution of 4 cmThe mechanical properties parameters of T26 polyurea are shown in The basic mechanical properties of the material showed that the tensile strength of T26 polyurea was relatively high while maintaining a high elongation, and the material behaved as a highly elastic and tough material in a quasi-static condition. The tear strength indicated that T26 polyurea had good resistance to stress concentration and the material formed by spraying was relatively dense. From the microstructure analysis, T26 polyurea is a block copolymer with microphase separation, and the hard and soft segments in the material are closely cross-linked, and the content of hard segments in the material is less compared with that of soft segments. Eastmond et al.  concludeThe true stress-strain curve of T26 polyurea /E′(70 °C)) can be used to characterize the temperature sensitivity of the polymer as well as the degree of microphase separation . E′(−30 max), and the corresponding temperature is the glass transition temperature (Tg). The tanδmax and Tg of each experimental frequency of T26 polyurea are shown in max also gradually increases, and the tanδ-frequency curve of T26 polyurea keeps the original linear shift toward the higher temperature, which leads to the increase in Tg. The variation of tanδmax and Tg reveals that the dynamic mechanical properties of T26 polyurea are influenced by the frequency.The loss factor curves calculated according to Equation (2) are shown in 0, ω) = E″ or E′, E is the experimentally obtained data, ω is the angular frequency, T0 is the reference temperature, and T is the experimental temperature. The temperatures here are in absolute scale. The variation curves of E″ and E′ with ω for each different temperature of T26 polyurea in the range from −70 °C to 90 °C were obtained, as shown in Under blast conditions, it is usually associated with blast loads of 400–500 Hz . Therefo0 and are developed by least squares translation along the horizontal axis. The master curve of loss and storage moduli of T26 polyurea is shown in The master curves of E″ and E′ represent the material properties over a wide range of frequencies at T−1 , the loss and storage moduli of the polymer were both in the rising stage. As the temperature remained constant under high strain-rate loading, the material tended to the glassy state. Due to the structural rearrangement of the hard segment of T26 polyurea caused by high strain-rate loading, the energy absorbed by the relative displacement between the soft and hard segments increased, which could efficiently transform the mechanical energy generated by the blast into the internal energy of the coating to be dissipated, thus improving the capacity of energy absorption. In addition, this process was accompanied by the transition from the rubbery state to the glassy state of the material, and the modulus of the material increased with the mechanical strength, which could explain the strain-rate sensitivity of polyurea in terms of dynamic mechanical properties.In accordance with the main curves of E″ and E′, the loss and storage moduli of T26 polyurea were firstly increased and then gradually stabilized with the rise of angular frequency. At 1256–1570 rad·s 2 Hz–106 Hz. As the frequency was greater than 1000 Hz, the tanδ of T26 polyurea stayed above 0.23, and the material could effectively convert energy and give full play to energy dissipation performance. However, there is a limitation to this conclusion. This conclusion cannot be applied to the protective coating of the blast face under near-field explosion since the high temperature generated at the moment of explosion will cause rapid thermal decomposition of the coating in the central area of the blast face.Based on the master curves of E″ and E′, the loss-factor master curve of T26 polyurea (as shown in The shift factor obtained based on the TTS can be fitted with the William-Landel-Ferry (WLF) equation . The fit1 and C2 in the above equation are empirical constants. The C1 and C2 used in the WLF equation at the reference temperature are shown in CThe adjust R-Square of loss and energy storage moduli obtained by fitting the WLF equation are 0.9991 and 0.9947, respectively, and it can be seen from The deformation of the unprotected specimen after the explosion is shown in From the side of the specimen simple support, the side center region developed cracks from the bottom up c,d. The The damage to the specimen protected by T26 polyurea is shown in From the damage details of the specimen, the blast-face coating damage was a quasi-circular notch with a diameter of approximately 41 cm  mechanical property failure mechanism with high temperature; (2) coupled-fracture mechanism with high temperature and impact loading; 3) brittle-fracture mechanism with high-speed loading; (4) tensile-fracture mechanism. For blast-face coatings, mechanical failure mechanism at high temperature is a common drawback of current polymeric protective materials subjected to contact explosion. The instantaneous high temperature generated by the explosion will cause thermal decomposition of the coating surface. In the study of Lyu et al. [ brittle-For back-blast-face coating, the main damage mechanism is a tensile fracture of polyurea, which corresponds to a brittle-fracture mechanism with high-speed loading and tensile-fracture mechanism, but not uniform tensile deformation. The maximum deformation area of the back-blast-face coating is the ring area outside the longitudinal deformation area, namely area 2 in −1, and 1700–1620 cm−1 was attributed to the spectral band of C=O stretching vibration, and the absorption band of C-N stretching vibration was at around 1542 cm−1. The above proved the existence of the urea bond in the material.The central area of the blast-face surface coating was sampled and FTIR infrared spectroscopy was performed. The FTIR spectra of T26 polyurea before and after the explosion are shown in −1 and 3319 cm−1, respectively. The N-H stretching vibration peak weakened significantly after the explosion, indicating that the N-H bond of T26 polyurea was partially broken after the explosion load. Meanwhile, a significant weakening of the C-H stretching vibration absorption band at wavenumber of 3000–2840 cm−1 also occurred, which was probably caused by the side methyl and methylene breakage of C-H bond in the polyether.The FTIR spectra reflected the effect of the explosion on the T26 polyurea at the blast face in terms of the chemical structure, and the absorbance curves of the coating before and after the explosion revealed that the explosion caused changes in the chemical structure of the T26 polyurea. The decrease in the peak signal of the sample spectra after the explosion indicated the breakage of bonds and the loss of a certain group in T26 polyurea. The stretching vibration peaks of N-H before and after the explosion were 3305 cmHydrogen bonds are one of the most important molecular structural features of polyurea and perform a critical role in the morphology and mechanical properties of polyurea . Hydroge−1) before and after the explosion. The hydrogen-bonding degree of the urethane carbonyl group is calculated by Equations (6)–(8) [o, Adiso and Afree represent the area of ordered, disordered and free hydrogen-bonded urea carbonyl, respectively. Xo, Xdiso and Xb denote the percentage of ordered, disordered and free hydrogen bonding. The wavenumber, peak assignment, peak area and percentage of hydrogen bonding of the deconvoluted bands of T26 polyurea before and after the explosion are shown in In the carbonyl region of polyurea, two types of hydrogen bonds are formed, one is a spatially three-dimensional perfect hydrogen bond with two amino groups, and the other is an imperfect hydrogen bond with one amino group. The deconvolution analysis was carried out for the carbonyl region –(8) .(6)Xo=Ao values before and after the explosion were 62.49% and 46.99%, and Xb values were 86.67% and 76.91%, respectively. Comparing with the coating before the explosion, the Xo and Xb values of T26 polyurea after the explosion were remarkably lower, while the Xdiso value was slightly increased. The ordered hydrogen-bonding content of the urea carbonyl group was less than that of T26 polyurea before the explosion. The ordering degree of hard segment is related to the percentage of hydrogen bonding. The blast load will promote the rearrangement and ordering of the hard segments regardless of the temperature change, in which case the percentage of hydrogen bonding will increase. However, the blast-face coating will be subject to high temperature, so that the coating will undergo thermal decomposition and thermal melting, which will result in a decrease in hydrogen bonding. The changes in microscopic morphology and FTIR spectral results are consistent with the discussion here. On the basis of mechanical properties, after the explosion, the coating transforms to a thermomechanically unstable state, and the percentage of hydrogen bonding decreases, which will lower the mechanical properties of the material. Reference [The Xeference  points o(1)The temperature range of the glass transition region of T26 polyurea is significantly larger than that of other types of polymers and has a lower degree of microphase separation. T26 polyurea is significantly affected by temperature and loading frequency, which corroborates the strain-rate sensitivity from the perspective of dynamic thermomechanical properties.(2)2 Hz and 106 Hz, the tanδ of T26 polyurea is between 0.20 and 0.31, so that the material can effectively dissipate energy performance sufficiently. The curve fitted according to the WLF equation is quite close to the shift factor, indicating that the energy absorption of T26 polyurea acts as a unit of motion of the internal chain segments of the molecule, i.e., the interaction between the hard and soft segments.Based on the master curves of loss and storage moduli, and loss factor obtained from the TTS principle, it can be found that when the frequency is between 10(3)The fracture mechanisms of T26 polyurea under contact explosion include a mechanical property failure mechanism with high temperature, a coupled-fracture mechanism with high temperature and impact load, a brittle-fracture mechanism with high-speed load, and a tensile-fracture mechanism. The first two of these fracture mechanisms are consistent with previous experimental and simulation studies , and th(4)The maximum deformation area of the back-blast-face coating under the blast load is the ring area around the longitudinal deformation area, and the deformation is dominated by the tensile damage of the coating in the circular area. This is also the main energy absorption area of the back-blast-face coating.(5)The explosion caused a change in the chemical structure of T26 polyurea on the blast face, and the N-H bonds and so forth were broken and the percentage of hydrogen bonding was reduced. During the explosion, the blast-face coating went into a thermodynamically unstable state, which reduced the mechanical properties of the blast-face coating.(6)Coating with 10 mm T26 polyurea can significantly improve the blast resistance of RC slabs. Under the contact explosion of 10 kg TNT, the fragmentation rate of the coated specimen decreased significantly compared with the unprotected specimen, and the protection effect of zero fragmentation has been achieved on the back-blast side. T26 polyurea is of great value in the application of blast mitigation to engineering structures.Polyurea has tremendous potential to improve the blast resistance of concrete structures, and the application of strengthening and protection of existing structures is currently developing rapidly. However, the damage mechanisms and protection effects of polyureas with different molecular structures under the action of blast loads are highly different. Based on recent research, this paper aims to explain the response characteristics of T26 polyurea at different frequency loads, analyze the protection mechanism of T26 polyurea on RC slab under blast loads, and elaborate the protection mechanism of T26 polyurea at different positions. The main conclusions drawn are as follows:Regarding the quasi-static mechanical properties of T26 polyurea, the mechanical properties did not produce extremely high strength. However, T26 polyurea has a wide glass transition region and high loss factor under the effects of various frequency loadings, especially high frequency. Therefore, it shows that T26 polyurea has good flexibility and energy absorption capability even under high strain-rate loading. That performance should be taken as an essential field of research for polyurea in explosion and impact protection. Subsequent studies will compare the protection performance of highly damped composite coatings on RC slabs under equal thickness conditions by laminating viscoelastic damping materials with T26 polyurea. The coating thickness, different coating ratios, and the optimal coating structure will also be investigated by finite element models.