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Evolution of SARS-CoV-2 in immunocompromised hosts may result in novel variants with changed properties, but the mode of selection underlying this process remains unclear. While escape from humoral immunity certainly plays a role in intra-host evolution, escape from cellular immunity is poorly understood. Here, we report a case of long-term COVID-19 in an immunocompromised patient with non-Hodgkin’s lymphoma who received treatment with rituximab and lacked neutralizing antibodies. Over the 318 days of the disease, the SARS-CoV-2 genome gained a total of 40 changes, 34 of which were present by the end of the study period. Among the acquired mutations, 12 reduced or prevented binding of known immunogenic SARS-CoV-2 HLA class I antigens, suggesting that virus immunoediting is largely driven by cytotoxic CD8 T cell clones. The two changes with the strongest effect, nsp3:T504A and nsp3:T504P, were experimentally assessed in a cytotoxic assay of the patient's CD8 T cells. Both these changes were associated with immune escape, with a stronger effect observed for nsp3:T504P, the change which ultimately got fixed. Together, these results suggest that CD8 T cell escape may be an underappreciated contributor to SARS-CoV-2 evolution in humans.

The viscous flow and sintering of porous materials that contain 2D defects are analyzed. The analysis relies on the rheological theory of sintering developed by Valerii Skorokhod and on the extended continuum powder model. The behavior of porous materials is considered for the sintering process combined with uniaxial tension. In particular, neutral sintering is addressed and an indirect method to determine the effective Laplace pressure is discussed.

Due to the complex of their physicomechanical and operating characteristics, the composite materials based on thermosetting polymers are extensively used in all branches of Ukrainian industry for the corrosion and wear protection of the equipment and, in particular, as antifriction materials. We propose a model of these composites based on epoxy oligomers and aluminum oxides capable of the evaluation the wear rate of the material without using a friction machine. For this purpose, we apply the similarity theory. According to this theory, in the case where all corresponding dimensionless characteristics of two different processes are identical, these processes are similar. On the basis of the experimental data obtained in analyzing the friction coefficient, the elasticity modulus, and the hardness of epoxy composites, we propose a model for the prediction of the wear characteristics of materials depending on the content of aluminum oxide. The application of this model guarantees the agreement between the results of modeling and the experimental data.

A comparative study was carried out to explore carbon monoxide total columnar amount (CO TC) in background and polluted atmosphere, including the stations of ZSS (Zvenigorod), ZOTTO (Central Siberia), Peterhof, Beijing, and Moscow, during 1998–2014, on the basis of ground- and satellite-based spectroscopic measurements. Interannual variations of CO TC in different regions of Eurasia were obtained from ground-based spectroscopic observations, combined with satellite data from the sensors MOPITT (2001–14), AIRS (2003–14), and IASI MetOp-A (2010–13). A decreasing trend in CO TC (1998–2014) was found at the urban site of Beijing, where CO TC decreased by 1.14%±0.87% yr−1. Meanwhile, at the Moscow site, CO TC decreased remarkably by 3.73%±0.39% yr−1. In the background regions (ZSS, ZOTTO, Peterhof), the reduction was 0.9%–1.7% yr−1 during the same period. Based on the AIRSv6 satellite data for the period 2003–14, a slight decrease (0.4%–0.6% yr−1) of CO TC was detected over the midlatitudes of Eurasia, while a reduction of 0.9%–1.2% yr−1 was found in Southeast Asia. The degree of correlation between the CO TC derived from satellite products (MOPITTv6 Joint, AIRSv6 and IASI MetOp-A) and ground-based measurements was calculated, revealing significant correlation in unpolluted regions. While in polluted areas, IASI MetOp-A and AIRSv6 data underestimated CO TC by a factor of 1.5–2.8. On average, the correlation coefficient between ground- and satellite-based data increased significantly for cases with PBL heights greater than 500 m.

The solubility of molybdenum in Fe–Cu and Fe–Sn melts and the growth kinetics of Mo6Fe7 layer at the molybdenum–melt interface at 1200°C are examined. The solubility of molybdenum in these melts is well described by the following equations: lgCMo = (–3.957 ± 0.176) + (25.77 ± 7.94) XFe –– (143.02 ± 77.92) XFe 2 (Fe–Cu melt) and lgCMo = (–2.783 ± 0.011) + (7.563 ± 0.111) XFe –– (10.844 ± 0.245) XFe 2 (Fe–Sn melt). The melt composition (atomic fractions) in the three-phase Mo–Mo6Fe7–melt equilibrium is established: 6.4 · 10–3 Fe, 1.64 · 10–4 Mo, and Cu being the rest (Fe–Cu melt); 0.046 Fe, 3.48 · 10–3 Mo, and Sn being the rest (Fe–Sn melt). The substantial difference between the growth rate constants in the melts, kFe–Sn >> kFe–Cu, at the same iron activity a Fe is attributed to the effect of admixtures (Cu and Sn) on the growth of the Mo6Fe7 layer. Data on the solubility of molybdenum in Fe–Cu and Fe–Sn melts and the growth kinetics of Mo6Fe7 in these melts are obtained for the first time.

The effect of hydrogen heat treatment on the chemical composition and morphology of aluminum and silicon nitrides powders for producing ceramics with enhanced operation properties is investigated. It is shown that the hydrogen heat treatment leads to decrease in the content of admixture elements, loosening of aggregates of powder particles and, as a consequence, activation in compacting. The resulting ceramics have enhanced mechanical properties, contrary to the samples produced of nitride powders with no hydrogen treatment.

A thermal kinetic model is used to study the processes that occur in the Ni–Al powder reaction system in contact melting. The effect of control parameters on the nature of these processes is examined through a computer experiment. The kinetic dependences and maximum temperatures developing in the system in the synthesis of equiatomic intermetallide (NiAl) are compared for two heat transfer cases: radiation and thermal conductivity.

On 1 July 2017, Valery Skorokhod, a brilliant scientist, an originator of the modern science of materials, Editor-in-Chief of Powder Metallurgy, Director of the Frantsevich Institute for Problems of Materials Science from 2002 to 2015, and Academician of the National Academy of Sciences of Ukraine, passed away. Valery Skorokhod devoted all his active life to studying the properties of materials and developing the scientific foundations of their formation. The modern materials science is a synthesis of knowledge based on very different scientific concepts. One can rarely find an expert who would have mastered this knowledge to the extent Valery Skorokhod did. The range of Skorokhod’s scientific interests was extremely diverse and included virtually all aspects relating to the behavior of materials and associated effects. Despite his busy activities, Valery Skorokhod found time to conduct his own research in seemingly distant areas of science. When Valery Skorokhod departed from life, several studies performed on his own and in collaboration with his colleagues were in their final stage. The Editorial Board of Powder Metallurgy offers some of them to the readers.

A modified continuum model for the sintering of biporous materials is proposed. Along with the viscous flow of the matrix resulting from the sintering potential, the vacancy flow from small to large pores is considered. The capabilities of the modified theory to consider the above phenomena are used to predict and explain the effect of constraints on local porosity increase and instability of the sintering process. Potential ways for using the results obtained are identified.

The structure of Fe–Cu composites after solid-phase and liquid-phase sintering was studied. It is shown that 2–10 wt.% molybdenum additions have an activating effect on the diffusion processes in densification, grain growth, and recrystallization, as well as on the amount and composition of copper and iron solid solutions. Molybdenum additions to 70 wt.% Fe–30 wt.% Cu composites simultaneously influence their strength and ductility properties. With increasing molybdenum content, the solubility of iron in copper decreases, promoting higher ductility of the composites, and the solid solutions of copper and molybdenum in iron preserve their strength characteristics. Solidphase sintering results in fine-grained FeCuMo samples with high relative density (up to 98.8%) and high ductility.

A physically based cloud nucleation parameterization was introduced into an optical properties/radiative transfer module incorporated with the off-line air quality modeling system Regional Atmospheric Modeling System (RAMS)-Models-3 Community Multi Scale Air Quality (CMAQ) to investigate the distribution features of the first indirect radiative effects of sulfate, nitrate, and ammonium-sulfate-nitrate (ASN) over East Asia for the years of 2005, 2010, and 2013. The relationship between aerosol particles and cloud droplet number concentration could be properly described by this parameterization because the simulated cloud fraction and cloud liquid water path were generally reliable compared with Moderate Resolution Imaging Spectroradiometer (MODIS) retrieved data. Simulation results showed that the strong effect of indirect forcing was mainly concentrated in Southeast China, the East China Sea, the Yellow Sea, and the Sea of Japan. The highest indirect radiative forcing of ASN reached −3.47 W m−2 over Southeast China and was obviously larger than the global mean of the indirect forcing of all anthropogenic aerosols. In addition, sulfate provided about half of the contribution to the ASN indirect forcing effect. However, the effect caused by nitrate was weak because the mass burden of nitrate was very low during summer, whereas the cloud fraction was the highest. The analysis indicated that even though the interannual variation of indirect forcing magnitude generally followed the trend of aerosol mass burden from 2005 to 2013, the cloud fraction was an important factor that determined the distribution pattern of indirect forcing. The heaviest aerosol loading in North China did not cause a strong radiative effect because of the low cloud fraction over this region.

The papers focusing on experimental and theoretical studies on sintering kinetics of real powder systems that were published in the 1940s–1950s are analyzed. Two major concepts explaining the nature of the so-called activity shown by metallic powders and some inorganic powders during sintering are addressed in detail. One concept deals with the key role of plastic flow mechanism and the other gives preference to the role of crystal lattice defects formed in powder particles when produced in nonequilibrium conditions. The reasons why neither of the concepts can underlie the physical theory of active sintering, being in full agreement with the experiment, are ascertained.

The solubility of molybdenum in Co–Cu and Co–Sn melts and the growth of Mo 6 Co 7 layer at the molybdenum–melt interface at 1200°C are examined. The solubility of molybdenum in these melts is well described by the equations: lgC Mo = −3.642 + 24.589 ⋅ C Co – 134.787 ⋅ C Co 2 (Co–Cu melt) and lgC Mo = −3.363 + 6.552 ⋅ C Co – 6.284 ⋅ C Co 2 (Co–Sn melt). The melt composition (in atomic fractions) in the three-phase Mo–Mo 6 Co 7 –melt equilibrium is established: C Co = 5.34 ⋅ 10 −3 , C Mo = = 3.05 ⋅ 10 −4 , the rest being Cu (Co–Cu melt); C Co = 0.176, C Mo = 5.7 ⋅ 10 −3 , the rest being Sn (Co–Sn melt). The substantial difference in growth rate constants in the melts (k Co–Sn >> k Co–Cu ) with the same cobalt activity α Co is attributed to the impact of admixtures (Cu and Sn) on the growth of the Mo 6 Co 7 layer. Data on the solubility of molybdenum in Co–Cu and Co–Sn melts and the growth kinetics of Mo 6 Co 7 are obtained for the first time.

Targeted research efforts focusing on the properties and structure of impregnated dispenser cathodes (IDCs) have been monitored. The data are summarized in terms of scale structural hierarchy in inorganic materials to develop principles for controlling their formation in the design of high-emission and long-life IDCs. The performance of IDCs of different types is modeled using the materials science triad ‘chemical composition ↔ structure ↔ properties’ and the concept of structural hierarchical levels in IDCs. Basic structural levels in IDCs are determined: electronic, nanostructured, mesoscopic, microscopic, and macroscopic. Their structural elements are analyzed: electrons, emitter layer, film coating, matrix and emission material, and cathode structure. It is found out that the electronic level is the key one in the hierarchy of IDC structural levels; its effectiveness depends on the nanocrystalline, mesoscopic, and microscopic levels. The principles of structural engineering are developed for the design of high-emission and long-life IDCs and for the control of their formation at nanostructured and microscopic levels by variation in the chemical composition and structure.

The paper overviews experimental and theoretical studies focusing on the sintering of cermet and ceramic bodies conducted and published from 1922 to 1967. Special attention is paid to the generation and evolution of new ideas, elements of the physical theory of sintering, and attempts to use the entire wealth of knowledge in solid-state physics and physical mechanics available in a given time period. Analysis of the accumulated knowledge on sintering phenomena and the actual contribution of individual researchers to this process may promote further improvement of the physical theory of sintering and its advance to applied problems of powder materials. The key role of theoretical physicists, Frenkel, Herring, and Lifshits, in resolving the most complex problems of sintering science is emphasized.

The structure and properties of biogenic hydroxyapatite ceramics for medical applications produced by microwave and conventional sintering at 800, 900, 1000, and 1100°C are studied. It is established that microwave sintering allows a 33 to 50% decrease in the minimum grain size, which can be attributed to the influence of microwaves on the material structure compared to conventional sintering. The bioceramic samples produced by microwave sintering have stable porosity (~40%) and 30–59 MPa compressive strength, being close to that of native bone and 1.6 to 2 times higher than the compressive strength of samples prepared by conventional sintering. In vitro studies have shown that the solubility of bioceramics sintered in a microwave oven in saline is 1.7 to 5.5 times higher than the solubility of samples produced by conventional sintering. Thus, microwave sintering allows obtaining biogenic hydroxyapatite ceramics with improved mechanical and biological properties for filling bone defects in orthopedics and traumatology.

It is shown that porous calcium phosphate ceramics can be produced from monetite and biogenic hydroxyapatite, the starting materials being in the ratios 25 : 75, 50 : 50, and 75 : 25 wt.%. It is established that phase transitions and solid-phase reactions take place during sintering to form polyphosphate ceramics consisting of hydroxyapatite (Ca5(PO4)3(OH)), β-pyrophosphate (β-Ca2P2O7), and β-tricalcium phosphate (β-Ca3(PO4)2), in which β-Ca2P2O7 and Ca5(PO4)3(OH) phases are predominant, depending on starting composition. When the biogenic hydroxyapatite content changes from 25 to 75 wt.%, the grain size decreases and the pore size increases. The ceramics have 40 to 42% porosity with predominant open porosity for all compositions. The ceramics show 32–55 MPa strength, which increases with the amount of biogenic hydroxyapatite in starting composition.

The Cu–W pseudoalloys with 2–10 vol.% of nanosized tungsten particles (30–40 nm) are studied. The bulk samples with relative density up to 99.1–99.6% are produced by shock compaction. The introduction of nanosized tungsten particles increases the pseudoalloy strength to 2.7HCu with insignificant reduction in plasticity (δ = 13%) and conductivity (to δ = 0.875% IACS for the pseudoalloy with 10 vol.% W). The microstructures of the Cu–W pseudoalloys are analyzed.

The sequence of phase transformations in Ti3Sn and Ti2Sn intermetallics during their interaction with hydrogen is studied. The mechanism whereby Ti3Sn hydride phases form is clarified. It is shown that Ti3Sn reacts with hydrogen at 373–1173 K through hydrogen ordering of the initial intermetallic structure, subsequent amorphization, and restructuring during the formation of hydride phases in the following sequence: hcp Ti3Sn → diamond Ti3SnH0.8 → hcp Ti3SnH0.8–0.9 → fcc Ti3SnH0.9–1.0 → bcc Ti3SnH1+x. A new hydride phase, Ti3SnH1+x (bcc, a = 0.538 nm), with high hydrogen capacity compared to the known fcc Ti3SnH hydride, which decomposes when heated to 1073 K, has been found. Destructive hydrogenation of Ti3Sn at 298–1173 K and hydrogen pressures of 1.0–6.0 MPa is not revealed. It is found that intermetallic Ti2Sn reacts with hydrogen through destructive hydrogenation to form a solution of hydrogen in β-titanium, hydride of a face-centered tetragonal solid solution of tin in titanium, and intermetallic Ti5Sn3.

The phase composition, phase growth kinetics, and structures of diffusion zones formed under microwave heating (24 GHz) (MWH) and conventional heating (CH) in two-layer Al2O3–Y2O3 samples are studied by optical and scanning electron microscopy and electron microprobe analysis. Diffusion annealing was conducted at 1700°C for 5 h in vacuum, the heating rate being 10°C/min in all experiments. The diffusion couples included alumina layers, such as coarse-grained polycore or sintered Al2O3–5 vol.% ZrO2 layers, and yttria layers, such as sintered coarse-grained samples or fine Y2O3 powder layers on the Al2O3 surface. It is shown that the phases formed during reactive diffusion do not uniquely correspond to the phase diagram, but depend on the initial structure of contacting layers and the type of heating. This is attributed to the contribution of kinetic factors to the competitive phase growth, particularly to the structural sensitiveness of diffusion coefficients whereby the diffusive phases grow and the stresses appearing when new phases form. It is found that MWH influences the competitive phase growth in the Al2O3–Y2O3 system, which involves both the change in the phase composition of the diffusion zone compared to that formed under CH and the acceleration of phase growth. The maximum effect of the phase growth acceleration under MWH is observed for the YAG phase, which is 30 times as fast as that under CH. It is suggested that the structure of grain boundaries changes and, accordingly, their permeability increases under MWH. The accelerated GB diffusion under MWH promotes the YAG phase growth in both oxides as a result of opposite diffusion flows of Al and Y ions along GBs. Under TH the YAG phase is formed only in Y2O3 oxide because of the unipolar diffusion of Al3+ ions to Y2O3. The validity of the proposed mechanism is confirmed by numerical evaluations.

Within the general framework of nonequilibrium thermodynamics, we develop a synergetic approach to examine, both theoretically and experimentally, nonlinear interactions and self-organization in reactive powder systems. Nonequilibrium physical and chemical powder systems prone to self-organization are described. A general principle behind the formation of dissipative objects acting as materials with nonlinear mechanisms of adaptation is stated. The capabilities of self-organization processes are demonstrated.

The interdiffusion and microstructural evolution of the Cr2O3–Al2O3 (5 vol.% ZrO2) diffusion couple are studied in the temperature range 1600–1800°C under microwave heating (24 Hz) and, for comparison, under traditional heating using electron microprobe analysis and microscopic analysis. It is found that the concentration of chromium is distributed differently in Al2O3 in diffusion zones under microwave and traditional heating. This is due to greater contribution of grain-boundary diffusion to the effective diffusion flux under microwave heating. Bulk diffusion and average grain-boundary diffusion coefficients are calculated. The grain size in the diffusion zone toward Al2O3 is smaller after microwave heating. Traditional heating induces grain growth by recrystallization, whereas two processes, recrystallization and polygonization, are superimposed during microwave heating. The polygonization is due to the generation of dislocations under thermal stresses originating from nonuniform temperature distribution in the diffusion zone with variable concentrations of the components. The calculated bulk and grain-boundary diffusion coefficients can be used to predict the kinetics of various diffusion mass-transfer processes in Al2O3 and Cr2O3 oxides and their mixtures.

The effect of heat treatment on the mechanical properties and microstructure of Fe–30% Cu pseudoalloys doped with 10% Mo is studied. The samples were produced by compacting mechanically alloyed metal powder mixtures and subjecting them to solid-phase sintering (SPS) and liquid-phase sintering (LPS) at 1000 and 1130°C, followed by quenching and tempering. It is shown that doping Fe–Cu pseudoalloys with molybdenum increases the density of the compacts after both SPS and LPS (residual porosity about 1%). The interdiffusion of all the three components promotes the formation of stable heterophase fine-grained microstructure which prevents grain growth and improves the plasticity of the FeCuMo pseudoalloys. Heat treatment increases the strength of FeCuMo and does not affect its high plasticity. The FeCuMo samples produced by SPS and LPS show optimum values of ultimate strength (683–694 MPa and 741–752 MPa), elongation (12.1–12.4% and 8.2–9.4%), and contraction (24.0–25.9% and 12.5–19.7%) after heat treatment.

The paper examines the sequence of structural and phase transformations and the rate of Ti2Co and TiCo interaction with hydrogen. Destructive hydrogenation of Ti2Co is used to produce nondestructive nanostructured titanium hydride composites. Thermodynamic analysis has shown that Ti2Co and TiCo destructive hydrogenation is thermodynamically favored in the temperature range 298–973 K. In the temperature range 773–973 K, Ti2Co interacts with hydrogen by destructive hydrogenation reaction, in which hydrogen is dissolved in the intermetallic compound, titanium is selectively hydrogenated to cubic TiH1.9, and titanium-depleted TiCo and TiCo2 intermetallics are successively formed in accordance with the Ti–Co phase diagram. The rate of Ti2Co destructive hydrogenation is proportional to temperature, hydrogen pressure, and surface area of the starting samples. Compound TiCo is hydrogenated to form a solution of hydrogen in Ti1+yCo, intermetallic TiCo2, and a solution of hydrogen in β-titanium. Nondestructive composites with nanostructured components are synthesized by Ti2Co destructive hydrogenation.

The structural and phase mechanism and the rate of TiCu, Ti3Cu4, and Ti2Cu3 destructive hydrogenation (DH) are studied at 773 K under a hydrogen pressure of 1.0 MPa. The mechanism of destructive hydrogenation of the intermetallics consists in the formation of a hydrogen solid solution, selective hydrogenation of titanium, and subsequent formation of intermediate intermetallics and copper. The destructive hydrogenation products are nondestructive TiH1.9–Cu matrix composites. The rate of TiCu, Ti3Cu4, and Ti2Cu3 destructive hydrogenation is limited by the rates of hydrogen dissociation on the intermetallic surface and the diffusion of titanium hydride. The products of TiCu, Ti3Cu4, and Ti2Cu3 destructive hydrogenation are recombined in vacuum and hydrogen atmosphere.

The paper examines the phase mechanism and rates of TiCu, Ti3Cu4, and Ti2Cu3 interaction with hydrogen in the range 298–573 K at a hydrogen pressure of 1.0 MPa. The thermodynamic potential of TiCu direct and destructive hydrogenation and TiCu decomposition is established. The thermodynamic priority of destructive hydrogenation in the range 298–773 K is revealed. However, x-ray diffraction shows that only direct hydrogenation of TiCu, Ti3Cu4, and Ti2Cu3 proceeds in the range 298–373 K. The intermetallic compounds successively interact at 573 K with hydrogen through the formation of intermetallic hydrides (TiCuH1.19, Ti3Cu4H2.44, and Ti2Cu3H1.32) and their decomposition to titanium hydride and copper. These hydrides form more rapidly than decompose. It is established that mechanical destruction of the material occurs during direct hydrogenation.

The solubility of molybdenum in copper–silicon melts and the kinetics of growth of Mo5Si3 and MoSi2 layers on the molybdenum–melt interface at 1200°C are studied. At 0.20–0.36 at. parts Si, the solubility of molybdenum in the melts is described by the following equation: lgX Mo = –2.587 + + (3.282)X Si. The dependence of the growth rate constants of the Mo5Si3 layer on the activity of silicon in the 9–15 wt.% Si melt is established: kMo–Si = –0.3806 + (65.191) aSi. It is shown that two phases form at 20 wt.% Si: Mo5Si3 and MoSi2. Their thicknesses are 29.8 ± 2.9 μm and 25.7 ± ± 2.8 μm, respectively. The time dependence of the Mo5Si3 layer growth rate in Cu–Si melts is established to obey a parabolic law. The melt composition in three-phase equilibrium Mo–Mo5Si– melt is found to be (at. parts): XSi = 0.147; XMo = 7.86∙10–3; the rest is copper. At 35 wt.% Si, only the MoSi2 phase is formed at the interface.

Approximate methods for calculating the effective elastic moduli of microheterogeneous materials, including multiphase ones, are considered. These methods are based on the analogy between the electrostatic field in dielectrics and the field of elastic stresses and strains in solids. Formulas are derived for the quantitative evaluation, with accuracy sufficient for materials science practices, of the effective elastic moduli of composites with different structures as a function of the elastic moduli, morphology, and volume fraction of the phases. The method is validated by calculating the elastic characteristics of bodies with plane slit-like defects, including powder compacts.

The recombination of Ti3Al from products of destructive hydrogenation (α-TiHx, β-TiHy, TiH1.9(c), TiH2(t), TiAl2, and TiAl3) is studied. It is established that recombined Ti3Al is an ordered alloy with domain structure. The cross-sectional size of domains varies from 70 to 200 nm. The hardness of recombined Ti3Al is 40% higher than that of starting Ti3Al. The materials subjected to destructive hydrogenation and recombination are used for detonation spraying of coatings. The coatings have a small amount of brittle phases and narrow or absent boundaries between individual layers and between the coating and the substrate. The coatings made of hydrogenated powders have twice as strong bonding with the substrate as the coatings made of Ti3Al powder produced by mechanical grinding of ingots.

The paper examines the pressing, sintering, and structure of binary (hydroxyapatite–pyroceram and hydroxyapatite–tricalcium phosphate) powder mixtures. It is shown that the compactibility of these powder mixtures is an additive function and depends on pure components. The sinterability of the HA–TCP mixture obeys the same law. The HA–pyroceram powder mixture is sintered in the presence of a liquid phase whose amount depends on the particle size of HA, as established experimentally. The use of nanosized powder intensifies diffusion even in solid state due to the great interface area and leads to additional crystallization of the amorphous phase.

It is shown that α2-Ti3Al alloy and hydrogen interact at 298–1533 K in accordance with the destructive hydrogenation reaction whose products are titanium hydride and intermetallic compounds rich in aluminum. The structural mechanism of α2-Ti3Al destructive hydrogenation is as follows. Hydrogen dissolves in Ti3Al, thus leading to disordering of its crystalline structure. Then hydrogen interacts with titanium, but not with the disordered alloy, according to the following scheme: α-Ti (hcp) → α-TiHx (hcp) → β-TiHy (bcc) → TiH1.9 (fcc) → TiH2 (bct). Intermetallic compounds rich in aluminum show up when new stoichiometric concentrations of titanium and aluminum form in accordance with the Ti–Al phase diagram. Solid composites with nanosized components result from the destructive hydrogenation of Ti3A at 973 K for 1 and 4 h. Their phase compositions are Ti3Al–(α-TiH–Ti3–xAl) and ((α-Ti–Hx)–(β-Ti-Hy)–TiH1.9 (fcc)–TiH2 (bct))–(Ti3Al–TiAl–TiAl2), respectively.

The kinetics of Ti 2 Cu and γ-TiCu destructive hydrogenation is examined. The research focuses on Ti 2 Cu and γ-TiCu samples in the form of plates, powders, and compacted powders and ingots. It is determined that the hydrogen pressure, temperature, and surface area of the intermetallides proportionally influence the rate of destructive hydrogenation of Ti 2 Cu and γ-TiCu in general and of each component in particular: hydrogen dissociation, hydrogen diffusion, and reaction rates. It is shown that pressure has a greater effect on the maximum hydrogenation rate than temperature. Higher titanium content of the intermetallides, other conditions being equal, increases the rate of the reaction and thus of the destructive hydrogenation. The compaction of Ti 2 Cu and TiCu powders and ingots intensifies the destructive hydrogenation process. This is due to the formation of catalytic juvenile intermetallic surfaces and to additional self-acceleration of surface reactions through autocatalysis. Of all the examined samples, the compacted ingots have the best kinetic characteristics because of the smallest specific fraction of oxidized surface. This conclusion is very important for application of the destructive hydrogenation process.

The paper examines the phase interaction in mechanical mixtures of thermostable hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) powders depending on the annealing temperature, initial composition, and particle size with x-ray interpretation of phase changes. It is established that HA transforms into β-TCP through a dehydration reaction during annealing of the mechanical mixtures of HA and β-TCP powders. The dehydration reaction proceeds through interphase activation in which the limiting stage of nucleation disappears. The phase boundaries in the two-phase HA–TCP mixture are more permeable for water vapors than single-phase boundaries owing to their disordered structure.

The thermodynamic possibility and conditions of Ti2Cu hydrogenation and recombination are assessed. The mechanism of Ti2Cu interaction with hydrogen between 293 and 973 K at pressure 1.0 MPa is studied. The interaction of Ti2Cu with hydrogen is thermodynamically possible in the destructive hydrogenation region over a wide temperature range. X-ray diffraction shows that destructive hydrogenation products are titanium dihydride and copper-rich intermetallic phases and copper depending on reaction conditions. According to the established mechanism of Ti2Cu destructive hydrogenation, hydrogen selectively interacts with titanium leaving Ti2Cu composition as follows: β-TiHy (bct-bcc) → TiH1.92 (fcc). The initial Ti2Cu composition is recombined from destructive hydrogenation products (titanium dihydride and copper) in vacuum and hydrogen. The minimum temperature of Ti2Cu vacuum recombination is 1050 K and ensures complete TiH2 decomposition. The recombination of Ti2Cu in hydrogen can occur at temperatures above 907 K.

An experimental thermokinetic study of reaction sintering reveals that there are various irreversible paths in a nonequilibrium system. When the external temperature is in the contact melting range and the equilibrium condition of the mixture is in the solid-state range, the thermokinetic path is usually exponential with abrupt increase in the temperature and volume of the samples. Active compaction is observed in the case of thermokinetic oscillations