High-temperature Synthesis Process Research Articles

FORMATION OF CHROMATED COATINGS ON A PRESS TOOLING IN THE PRODUCTION OF RUBBER PRODUCTS FOR ROCKET AND SPACE TECHNOLOGY

This research analyzes the influence of residual stresses formed as a result of the process of self-propagating high-temperature synthesis on the mechanical properties and durability of structural materials and protective coatings. The main emphasis is placed on the analysis of the relationship between residual stresses and adhesive strength and durability of the obtained coatings. Rubber-based composites may prove to be competitive and eventually replace traditional materials in a number of applications, as there are many advantages to using these materials. For example, rubber-based composites often have a lower density than traditional materials such as metals. This leads to a reduction in the weight of products, which is important in a variety of industries where lightness is a key characteristic. Rubber composites are characterized by cushioning, flexibility, and elasticity, which makes them able to handle dynamic loads and adapt to various forms of deformation without losing structural properties. Research was carried out on parts of press tooling used for manufacturing of rubber-technical products in rocket-space engineering. It was found that residual stresses formed during the SHS process have a significant effect on the adhesion properties of protective coatings. Residual stresses appear after SHS treatment under conditions of thermal self-ignition of SHS charges. At the cooling stage of the SHS process, residual compressive stresses appear as a result of the elastic interaction of the alloyed titanium coating and the structural material, which have different sizes and coefficients of thermal expansion. The maximum values of adhesion strength of titanium coatings on steel 45 were 120-150 MPa when alloyed with aluminum and 180-210 MPa when alloyed with chromium. This research emphasizes the importance of residual stress control for improving the strength and durability of protective coatings obtained under SHS conditions and their possible role in extending the service life of structures and equipment. Additional research in this direction may contribute to process optimization and product quality improvement in the aerospace industry.

Coordination-based synthesis of Fe single-atom anchored nitrogen-doped carbon nanofibrous membrane for CO2 electroreduction with nearly 100 % CO selectivity

Carbon-based materials with single-atom (SA) transition metals coordinated with nitrogen (M-Nx) have attracted extensive attention due to their superior electrochemical CO2 reduction reaction (CO2RR) performance. However, the uncontrolled recombination of metal atoms during the typical high-temperature synthesis process in M-Nx causes deterioration of CO2RR activity. Herein, by using electrospinning, we propose a novel strategy for constructing a highly active and selective SA Fe-modified N-doped porous carbon fiber membrane catalyst (Fe-N-CF). This carbon membrane has an interconnected three-dimensional structure and a hierarchical porous structure, which can not only confine Fe to be single atom as active centers, but also provide a diffusion channel for CO2 molecules. Relying on its special structure and stable mechanical properties, Fe-N-CF is directly used for CO2RR, which presents an excellent selectivity (CO Faradaic efficiency of 97 %) and stability. DFT calculations reveals that the synthesized Fe-N4-C can significantly reduce the energy barrier for intermediate COOH* formation and CO desorption. This work highlights the specific advantages of using electrospinning method to prepare the optimal SA catalysts.

Novel value-add recycling route of industry solid waste for acting as supporting skeleton of NaNO3 phase change materials (PCMs)

This study provided a value-added utilization route for industrial solid waste by converting them into porous ceramics to act as supporting skeleton for PCMs. Steel slag (SS), ferronickel-slag (FNS) and Fly ash (FA) was used as main raw material to prepared anorthite-cordierite (AC) porous ceramics. Five groups of formula with different phase content were designed by adjusting the amount of SS and FNS addition. FactSage 8.0 software was applied to calculate the equilibrium phase composition of AC at high temperature, which provided guidance for the actual high temperature synthesis process. The prepared AC porous ceramics were found to have good mechanical strength and high porosity. Good chemical compatibility between AC and NaNO3 was demonstrated and the infiltration ratio was varied from 42% to 45%. In addition to high thermal storage capacity, AC has been found to help reduce the supercooling of NaNO3 and helps to improve the thermal storage performance. After 100 thermal cycles of melting and freezing, NaNO3/AC C-PCMs could maintained high than 97% of latent heat. Thermal transfer properties of AC were significantly enhanced after molten NaNO3 infiltrated. The thermal conductivity of NaNO3/AC40 C-PCMs at 25 °C reached 1.60 W·(m·K)−1, which is more than three times that of pure NaNO3. The good thermal storage performance of NaNO3/AC C-PCMs makes it potential candidate in high-temperature thermal storage fields like industrial waste heat recovery and solar energy storage. In a word, the application potential of metallurgical slag in the field of energy saving was well demonstrated by this study.

Thermodynamic analysis of production parameters and microstructural evolution in shape memory Ni(50-x)Ti(50)Fe(x) (x = 5, 10) alloy synthesized by combustion synthesis

This study represents an initial effort to produce NiTiFe shape memory alloys via the self-propagating high-temperature synthesis (SHS) process. The synthesis successfully yielded Ni45Ti50Fe5 and Ni40Ti50Fe10 alloys from elemental Ni, Ti, and Fe powders at three distinct preheating temperatures (240, 330, 420 °C). To support empirical findings, thermodynamic analysis using Factsage Thermodynamic Software was employed to correlate reaction propagation behavior with chemical composition. The calculation showed that the addition of 5 at.% Fe to the B2 phase did not hinder reaction self-propagation. This conclusion was supported with the ∆Hf/Cp ratio and transient liquid ratio, computed using the sub-lattice model, which closely resembled that of NiTi. Whereas 10 at.% Fe that synthesized at preheating temperature of 240 °C exhibits struggle, thus an increase in triggering time causes an effect on crystallite size and a decrease in porosity. Empirical results confirmed these findings, albeit influenced by ignition times. An increase in the liquid ratio due to the adiabatic temperature rise can also result in a reduction of NiTi content when the Fe ratio is increased, consequently diminishing the driving force for the reaction. In the sample containing – 5% Fe, the main phase is B2, and the R martensitic phase is also present. Ms is determined to be – 38.7 °C. SEM analyses revealed the presence of Ti2Ni and Ti2Ni3 phases in the upper and lower regions, while the distribution in the middle section is more homogeneous. No martensitic transformation was observed in 10% Fe. Additionally, nanocrystalline regions were detected within the samples by transmission electron microscopy, contributing to a nuanced understanding of their structural properties.Graphic abstract

Boosting decarboxylation of monomethyl adipate coupling to dimethyl sebacate through Pt electrode at high current density

Dimethyl sebacate is an essential organic chemical, yet its conventional high-temperature pyrolytic synthesis process is marked by complexity, energy intensity, environmental pollution, and volatile raw material supplies. Presently, electrochemical synthesis emerges as a promising, environmentally sustainable method for one-step dimethyl sebacate synthesis via anodic decarboxylation coupling with monomethyl adipate. However, the existing process falls short in achieving the desired selectivity and current efficiency, particularly when operating at high current densities, thus impeding its broader industrial adoption. This study, synergizing density functional theory computations with experimental methods, conducts a comprehensive multidimensional analysis of the electrochemical performance at high current densities across four distinct electrode types: Pt plate, RuO2/Ti, PbO2, and graphite electrodes. It underscores the strong electron-orbital hybridization between adsorbed monomethyl adipate and the platinum electrode, resulting in an enhanced propensity for electron transfer at the electrode interface and facilitating the decarboxylation of monomethyl adipate coupling into dimethyl sebacate. Subsequently, through single-factor experiments and response surface methodology, an exhaustive analysis of the various factors influencing the electrolysis process is conducted, including supporting electrolyte, current density, H2O content, neutralization, and monomethyl adipate concentration. The optimal electrolysis operation configuration offers a robust theoretical foundation and technical framework for the large-scale implementation of green, energy-efficient electrochemical synthesis technology for dimethyl sebacate in industrial settings.

Analysis of Stress Distribution of Composites Based on Hydroxyapatite by Finite Element Method

Self-propagating intermediate temperature synthesis (SIS) is a process that utilizes exothermic reactions to initiate and maintain component combustion so as to produce low porosity values and high hardness. It is necessary to know about the heat transfer phenomenon because SIS has a weakness, namely the high exothermic rate and very fast combustion rate which requires a high level of control. In addition, compression or compaction needs to be done because this method is expected to produce a homogeneous particle density distribution. The phenomenon of heat transfer and pressure that occurs in the SIS process is a simplification of the self-propagating high-temperature synthesis (SHS) process, which can be simulated and analyzed using engineering software based on finite element analysis. Stress simulation that occurs with the addition of weight percent titanium 5%, 10% and 20% using a pressure of 171 MPa and produces a normal stress. The heat transfer simulation that occurs uses a temperature of 750 °C, 850 °C, and 950 °C with a processing time of 2 hours with variations in the addition of weight percent titanium 5%, 10%, and 20% which results in an effect on heat flux and temperature distribution. Samples that were given the addition of 20% titanium by weight were given a pressure of 171 MPa to produce a normal stress of-230.44 MPa with the lowest porosity value of 22.63%. Samples processed at 850 °C with the addition of 10% weight percent titanium produced the lowest heat flux value of 0.0027220 W/m2.

Structure and phase composition of SHS composites based on Al–Ti–B system with different Al content

The paper deals with the influence of the Al content in the initial Al–Ti–B system on self-propagating high-temperature synthesis (SHS) processes, structure, and phase composition of synthesized products. It is found that the higher Al content leads to a temperature decrease of exothermic reaction and changes its wavefront propagation from layerwise to spinwise multiple locations. SHS products obtained from the Al–Ti–B system contain titanium diboride (TiB2) and aluminum (Al) phases. The weight content of phases in SHS products depends on the Al content in the initial powder mix and approximately matches the weight content of its components. The higher Al content provides a decrease in the size of the coherent scattering region for detected phases. SHS products obtained from the Al–Ti–B system with 10 wt% Al, consist of separate TiB2 particles coated with aluminum film. The Al content increased up to 30 and 60 wt%, provides the formation of the metal matrix structure. In this case, synthesis products consist of the aluminum matrix with TiB2 particles distributed inside. It is found that the growth in the Al content from 10 to 60 wt% in the initial Al–Ti–B system, results in the size reduction of TiB2 particles in SHS products from 3.37 to 0.41 μm, respectively.

Research on Microstructure, Synthesis Mechanisms, and Residual Stress Evolution of Polycrystalline Diamond Compacts

The microstructure and residual stress of polycrystalline diamond compact (PDC) play crucial roles in the performance of PDCs. Currently, in-depth research is still to be desired on the evolution mechanisms of microstructure and residual stress during high pressure high temperature (HPHT) synthesis process of PDCs. This study systematically investigated the influencing mechanisms of polycrystalline diamond (PCD) layer material design, especially the Co content of the PCD layer, on microstructure and residual stress evolution in PDCs via Raman spectroscopy and finite element micromechanical simulation. The research shows that when the original Co content of the PCD layer is higher than 15 wt.%, the extra Co in the PCD layer will migrate backwards towards the carbide substrate and form Co-enrichment regions at the PCD–carbide substrate interface. As the original Co content of the PCD layer increases from 13 to 20 wt.%, the residual compressive stress of diamond phase at the upper surface center of the PCD layer gradually decreases and transforms into tensile stress. When the original Co content of the PCD layer is as high as 30 wt.%, the residual stress transforms back into significant compressive stress again. The microstructure-based micromechanical simulation at the PCD–carbide substrate interface shows that the Co-enrichment region is the key for the transformation of the residual stress of the diamond phase from tensile stress into significant compressive stress.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ВИДА ФЛЮСА НА СИНТЕЗ ЛИТОГО КОМПОЗИЦИОННОГО МАТЕРИАЛА АМг2-TiC

The results are presented devoted to the study of the influence of flux type on the process of self-propagating high-temperature synthesis (SHS) of titanium carbide in aluminum flux, as well as on the structure and properties of the resulting composite material AMg2-TiC. During the research, the most promising halide salts for use as fluxes were analyzed and selected: Na3AlF6, Na2TiF6, K2TiF6, K1-3AlF4-6 (Nocolok ™ made in Germany). During the experimental synthesis, the most active signs of an exothermic reaction between titanium and carbon powders in the flux were recorded having a flux additive Na2TiF6. Then microstructural, micro X-ray spectral analysis and quantitative X-ray phase analyses were carried out, according to their results it was found out that the most homogeneous distribution in terms of material volume, the maximum content of a high dispersion of carbide phase close to the stoichiometric composition is also observed in samples obtained with the use of Na2TiF6 salt. The synthesized samples of the composite material were assessed according to physical and mechanical characteristics: hardness, porosity and electrical conductivity. It was found out that composite samples with an optimal structure are also characterized by a decrease in porosity by 1.33%, an increase in hardness by 94 MPa and a reduction of electrical conductivity by 0.3 MSm/m compared with samples obtained using other fluxes. According to the results of the studies carried out, Na2TiF6 flux is recommended for use to implement SHS composite AMg2-TiC material.

Rational design of high temperature processed TbVO4/Nb2O5/carbon aerogel photocatalyst for prompt degradation of emerging pollutants

This present study investigates the construction of novel ternary heterojunction photocatalysts using terbium vanadate (TbVO4), niobium pentoxide (Nb2O5), and carbon aerogel (CG), to increase the photocatalytic performances under visible light. The X-ray diffraction (XRD) outcomes confirmed that the TbVO4 and Nb2O5 present themselves in a highly crystalline nature due to the high-temperature synthesis process. The successful combination of carbon aerogel and Nb2O5 into the TbVO4 lattice is further established by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) studies. The UV-DRS results confirmed that the materials comprising of both carbon aerogel and Nb2O5 present an expressive improvement in visible light activity, which leads to a drop-in band gap energy of the ternary TbVO4/Nb2O5/carbon aerogel photocatalyst. The improved charge separation in the ternary system was further confirmed by the electron spin resonance (ESR) and photoluminescence (PL) studies. The experimental results reveal that Nb2O5 and carbon aerogel were successfully incorporated in the TbVO4, increasing its surface area and structural photostability, thereby increasing its photocatalytic performance in the removal of pollutants under visible light. Compared with TbVO4 and Nb2O5, the outcomes illustrate that the TbVO4/Nb2O5/carbon aerogel displays the optimum photocatalytic removal rate and outstanding chemical stability in the removal of sulfamethoxazole. It shows a degradation efficiency of 92.3 in 90 min, which is 5 and 7 times as high as TbVO4 and Nb2O5, respectively. Based on the trapping experiments, h+, OH, and O2− improved the sulfamethoxazole photodegradation process. Finally, a novel, recyclable photocatalyst was made, which underwent a brand-new pathway for the degradation of various emerging pollutants.

Phosphate removal mechanism of a novel magnesium slag-modified coal gasification coarse slag adsorbent

We used magnesium slag (MS) as a calcium source for modifying coal gasification coarse slag (CGCS) in the presence of NaOH to prepare a novel phosphate adsorbent (MS-CGCS). Ca2SiO4 in MS reacts with NaOH during the high-temperature synthesis process, with sodium displacing a part of the calcium content in Ca2SiO4 and entering the mineral lattice to form Na2CaSiO4. Hydroxide ions reacted with calcium in Ca2SiO4 to generate Ca(OH)2 and decomposed into CaO at a high temperature. The two newly formed species participated in the phosphate removal. The MS-CGCS adsorbent showed good phosphate removal performance over a wide pH range, with a maximum phosphate adsorption capacity of 50.14mg/g, which was significantly higher than that of other reported adsorbents. The Langmuir and pseudo-second-order models described the adsorption process well, indicating it being a monolayer and chemisorption process. The main mechanisms of phosphate removal are as follows: electrostatic interaction between the positively charged MS-CGCS and negatively charged phosphate ions; the inner-sphere complexation of oxides of metal, such as magnesium, aluminum, and calcium, with phosphate ions; and the precipitation of phosphate ions with calcium ions. Precipitation contributes to ~ 32% of the phosphate removal. This study provides a new method for the development of phosphate adsorbents while recycling CGCS and MS.

Optimization of coal-to-liquid processes; A way forward towards carbon neutrality, high economic returns and effective resource utilization. Evidences from China

As the world's largest consumer of coal, China is committed to developing a carbon–neutral coal industry. For this purpose, upgrading the carbon emission-intensive coal-chemical industries, such as coal-to-liquids (CTL) is imperative. This study develops a technical–economic framework to model and test four promising CTL upgrading processes. First and second processes involve low-temperature Fischer-Tropsch (FT) synthesis practices with larger gasifiers and air-separating units than the current level. Third, the process combines olefin and fuel co-production practices that utilize low- and high-temperature FT synthesis processes. Finally, the process produces both electricity and fuel by sending the tail gas of the synthesis process to an integrated cycle. Aspen Plus® is used to simulate the chemical processes, and the financial cost accounting model of the American Association of Cost Engineers is utilized to estimate the financial costs accurately. The results show that the upgraded processes can achieve an energy efficiency of more than 48 %, which is 6 % higher than the existing coal-to-oil process. Additionally, the break-even point is 2 %–14.45 % lower than the actual process, reducing carbon emissions by 2.78 %–10.34 %. According to these findings, the upgrade can help China reach its carbon neutrality targets and significantly contribute to global climate change and sustainable development goals.

Spatially resolved measurement of the distribution of solid and liquid Si nanoparticles in plasma synthesis through line-of-sight extinction spectroscopy.

In many high-temperature gas-phase nanoparticle synthesis processes, freshly nucleated particles are liquid and solidify during growth and cooling. This study presents an approach to determine the location of the liquid-to-solid phase transition and the volume fraction and number density of particles of both phases within a gas phase reactor. Spectrally-resolved line-of-sight attenuation (LOSA) measurements are applied to a silicon nanoparticle aerosol generated from monosilane in a microwave plasma reactor. A phantom-based analysis using particle number density, particle size, and temperature distribution from direct numerical simulation (DNS) of the reacting flow indicates that the contributions from the two particle phases can be decoupled under practical conditions, even with noisy data. The approach was applied to analyze spatially and spectrally resolved LOSA measurements from the hot gas flow downstream of the plasma zone where both solid and liquid silicon particles coexist. Extinction spectra were recorded along a line perpendicular to the flow direction by a spectrometer with an electron-multiplying charge-coupled device (EMCCD) camera, and two-dimensional projections were deconvolved to obtain radial extinction coefficient distributions of solid and liquid particles across the cross-section of the flow. Particle number densities of both particle phases were retrieved simultaneously based on the size-dependent extinction cross-sections of the nanoparticles. The particle-size distribution was determined via thermophoretic sampling at the same location with subsequent transmission electron microscopy (TEM) analysis. The particle temperature distribution was determined from the particle's thermal radiation based on line-of-sight emission (LOSE) measurements. The approach for phase-selective data analysis can be transferred to other materials aerosol systems as long as significant differences exist in extinction spectra for the related different particle classes.

Preparation of high-quality FeV50 alloy by an improved SHS-EAH multi-stage process

As the most widely used vanadium intermediate alloy, ferrovanadium is mainly prepared by the self-propagating high-temperature synthesis (SHS) process with the advantages of short process and large heat release. However, there is a trade-off between the amount of reduction agent of Al and the product quality of ferrovanadium, which is caused by the thermodynamic equilibrium limitation of the reduction between Al and vanadium oxides. The reasonable adjustment of the trade-off has become an urgent problem to be solved for the preparation of high-quality ferrovanadium. In the present work, the thermodynamic equilibrium for the reduction limitation using Al as reducing agent has been thoroughly analyzed with the reference to the equilibrium phase diagram. It was found that the theoretical reduction limitation of total vanadium (T.V) in slag was decreased from 4.08 wt.% to wt. 0.86 wt.% when the Al content in alloy reached 2.0 wt.% at 1800 °C. The vanadium in slag was mainly presented in the form of MgV3O8 and coexisting with other phases of MgAl2O4, CaAl2O4, CaAl4O7, CaAl12O19. With the purpose of further decrease the high Al concentration in alloy and vanadium loss in slag, an improved SHS-EAH process was implemented by multi-stage gradient aluminum addition coefficient pattern, the average vanadium content in slag was reduced from 1.82 wt.% to 0.83 wt.%, while the aluminum content in FeV50 alloy was decreased from 1.5 wt.% to 0.4 wt.%. The SHS-EAH process was proved to be a better process with improved yield and quality for the preparation of ferrovanadium.

SHS of highly dispersed powder compositions of nitrides with silicon carbide Review

The application of the process of self-propagating high-temperature synthesis (SHS) to prepare highly dispersed powder nitride-carbide compositions from the most common refractory nitride (Si3N4, AlN, TiN) and carbide (SiC) compounds with a particle size of less than 1 μm is considered. The advantages of composite ceramics over single-phase ceramic materials and such trends of its development as the transition to nanostructured ceramics and the application of in situ processes of direct chemical synthesis of nanoparticles of components in the composite body are described. The attractiveness of the SHS process as one of the promising in situ processes characterized by simplicity and cost-effectiveness, the possibility of obtaining highly dispersed ceramic powders by burning mixtures of inexpensive reagents is shown. Considerable attention is paid to the consideration of the results of the application of azide SHS, based on the use of sodium azide and gasified halide salts as part of mixtures of initial powders of nitrided and carbidized elements during their combustion in nitrogen gas. The review of publications devoted to the application of SHS to obtain highly dispersed composite powders Si3N4–SiC, AlN–SiC and TiN–SiC, promising for use in sintering of the corresponding composite ceramic materials of submicron and nano-sized structure with improved properties, lower brittleness, good machinability, lower sintering temperatures compared with single-phase ceramic materials made of nitrides or carbides as well as for other applications, is presented. The results of the application of azide SHS are presented in detail both in the form of the results of thermodynamic calculations and the results of experimental research of combustion parameters, combustion product structure and composition. The advantages and disadvantages of using the combustion process for the synthesis of nitride compositions with silicon carbide, the causes of the disadvantages and the directions of further research to eliminate them are discussed.

Preparation of low-oxygen Ti powder from TiO2 through combining self-propagating high temperature synthesis and electrodeoxidation

An effective method was reported to prepare low-oxygen Ti powder, which included two experimental steps: the fast conversion of TiO2 to TiOx<1 powder by self-propagating high-temperature synthesis (SHS) process and the generation of low-oxygen Ti powder by electrodeoxidizing TiOx<1 powder at the cathode in molten CaCl2. The key intermediate steps were analyzed by XRD, SEM and electrochemical testing techniques. The results demonstrated that TiOx<1 powder (TiO0.325 and TiO0.97) was generated after acid leaching MgO in SHS products with TiO2/Mg molar ratio of 1:2, and the TiOx<1 powder with 16.3 wt.% oxygen could be transformed into pure titanium powder with 0.121 wt.% oxygen by electrodeoxidation at a constant potential of -3.3 V for 10 h. The electrodeoxidation of TiOx<1 powder in CaCl2 molten salt follows the step-by-step deoxidation mode, and the lattice of TiOx<1 powder after electrodeoxidation shrinks.

Oxide ion conduction and transporting mechanism in the layered perovskite-related material Sr2Nb2O7

Ionic conduction has been well-documented in three typical layered perovskite materials, namely Ruddlesden-Popper-type, Dion-Jacobson-type, and Aurivillius-type. In the present work, the oxide ion conduction was reported in the Sr2Nb2O7 material which also adopts a layered perovskite-related structure but does not fall into any of the above-mentioned three typical structures. The results revealed that the oxide ion conduction originated from the slight reduction of Nb5+ ions during the high-temperature synthesis process, as the sample prepared under a pure oxygen atmosphere showed more than one order of magnitude lower conductivity than the sample prepared under an ambient atmosphere. The bond-valence-based method was applied to investigate the oxide ion migration mechanism, and revealed a two-dimensional pathway within the perovskite slabs. The discovery of this new oxide ion conductor will stimulate extensive exploitation and fundamental research on other layered perovskite-related materials.

Determination of the figurative point trajectory on the phase diagram of NiO lithiation-oxidation process by x-ray diffraction and Compton scattering methods.

The positions of the figurative points on the triangular Gibbs phase diagram for the process of high-temperature synthesis of solid solutions LiyNi2-yO2 were determined for the first time using a combination of x-ray diffraction (XRD) and Compton scattering methods. The trajectory of the figurative point is built according to experimental data for temperatures of 650 and 750 °C. The ratios of the phases in equilibrium are found. It was established that, when the structure goes from rock salt to layered structures, the composition of the reagent mixture changes nonmonotonically: with an increase in the degree of ordering of the solid solution lattice, the sum molecular weight of the solid reagents increases. It has been shown experimentally that the combined use of XRD and Compton scattering makes it possible to carry out physicochemical analysis of the process and predict the final product.

RAY PHASE AND MICROSTRUCTURAL ANALYSIS OFHARDENING COATINGS OBTAINED BYSELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS IN COMBINATION WITH HEATING OFA MIXTURE OF 𝑨𝒍+𝑩𝟐𝑶𝟑BASED ON HIGH-FREQUENCY CURRENT TREATMENT

The paper describes the results of studies of hardening boride coatings obtained during the implementation of the process of self-propagating high-temperature synthesis. These coatings were composite materials based on aluminum oxide and boron. The obtained coatings were subjected to X-ray phase and microstructural analysis, which showed the maincomponents of the resulting compositions and made it possible to assess the thickness and structure of the coating-base metal transition area. The different content of silicon and iron makes it possible to assess the occurrence of surface chemical and metallurgical processes during self-propagating high-temperature synthesis when heating of the base mixture samples on high-frequency current treatment. The expediency of using high-frequency current treatment in combination with the process of self-propagating high-temperature synthesis for better-quality spattering of the hardening coating is shown. The appearance of two areas in the coating with different thickness and structure of the coating is established.

Growth-Promoting Mechanism of Bismuth-Doped Cu(In,Ga)Se2 Solar Cells Fabricated at 400 °C.

The classical high-temperature synthesis process of Cu(In,Ga)Se2 (CIGS) solar cells limits their applications on high-temperature intolerant substrates. In this study, a novel low-temperature (400 °C) fabrication strategy of CIGS solar cells is reported using the bismuth (Bi)-doping method, and its growth-promoting mechanism is systematically studied. Different concentrations of Bi are incorporated into pure chalcopyrite quaternary target sputtered-CIGS films by controlling the thickness of the Bi layer. Bi induces considerable grain growth improvement, and an average of approximately 3% absolute efficiency enhancement is achieved for Bi-doped solar cells in comparison with the Bi-free samples. Solar cells doped with a 50 nm Bi layer yield the highest efficiency of 13.04% (without any antireflective coating) using the low-temperature technology. The copper-bismuth-selenium compounds (Cu-Bi-Se, mainly Cu1.6Bi4.8Se8) are crucial in improving the crystallinity of absorbers during the annealing process. These Bi-containing compounds are conclusively observed at the grain boundaries and top and bottom interfaces of CIGS films. The growth promotion is found to be associated with the superior diffusion capacity of Cu-Bi-Se compounds in CIGS films, and these liquid compounds function as carriers to facilitate crystallization. Bi atoms do not enter the CIGS lattices, and the band gaps (Eg) of absorbers remain unchanged. Bi doping reduces the number of CIGS grain boundaries and increases the copper vacancy content in CIGS films, thereby boosting the carrier concentrations. Cu-Bi-Se compounds in grain boundaries significantly enhance the conductivity of grain boundaries and serve as channels for carrier transport. The valence band, Fermi energy level (EF), and conduction band of Bi-doped CIGS films all move downward. This band shift strengthens the band bending of the CdS/CIGS heterojunction and eventually improves the open circuit voltage (Voc) of solar cells. An effective doping method and a novel mechanism can facilitate the low-temperature preparation of CIGS solar cells.