An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070292

The paper presents materials on experimental study of pargasite stability. On the example of calcic amphibole, experimental modeling of the processes occurring in the conditions of volcanic hearth at pressures up to 5 kbar was carried out. The phase diagram of pargasite was clarified. The occurring reactions and their parameters are revealed. Based on the experimental data obtained, the stability of pargasite is controlled by three reactions. The first reaction takes place in the area of low water pressure less than 1 kbar – dehydration reaction:Prg = Fo + Sp + Di + Ne + An +H2O. The second reaction takes place in the area of water pressure more than 1.2-1.5 kbar and temperature around 1100°C. Pargasite decomposition is controlled by incongruent melting:Prg = Fo + Sp +{Di+Ne +An}L+H2O. The third reaction takes place in the same pressure range as the previous one, but at lower temperatures ~1050°C. This reaction determines the pargasite liquidus in the melt and is related to the interaction between the amphibole and the coexisting melt:Prg + L= Fo + Sp + Di +{Ne +Pl}L+H2O.Presumably, the activity of the melt silicaaSiO2has the greatest impact on the pargasite liquidus.

Pargasite stability was experimentally studied in IHPV at P_H_2O = 2 kbar and temperatures of 1000 to 1100oC, with equilibrium approached from above and below. Calcic amphibole was used to experimentally model processes that occur in a volcanic chamber at pressures up to 5 kbar. The phase diagram of pargasite has been refined. It has been established that the stability of pargasite is controlled by three reactions. (1) At low water pressures of less than 1 kbar, the dehydration reaction Prg = Fo + Sp + Di + Ne + An + H2O proceeds. (2) At water pressures higher than 1.2–1.5 kbar and a temperature of about 1100°C, the decomposition of pargasite is controlled by its incongruent melting Prg = Fo + Sp + Di + Ne + AnL + H2O. (3) The third reaction Prg + L = Fo + Sp + Di + Ne + PlL + H2O occurs within the same pressure range as the previous one but at lower temperatures of about 1050°C. The reaction controls the pargasite liquidus and is caused by interaction between amphibole and coexisting melt. The liquidus of pargasite seems to most strongly depend on the activity of silica a_SiO_2 in the melt.

The paper presents materials on experimental study of pargasite stability. On the example of calcic amphibole, experimental modeling of the processes occurring in the conditions of volcanic hearth at pressures up to 5 kbar was carried out. The phase diagram of pargasite was clarified. The occurring reactions and their parameters are revealed. Based on the experimental data obtained, the stability of pargasite is controlled by three reactions. The first reaction takes place in the area of low water pressure less than 1 kbar – dehydration reaction:Prg = Fo + Sp + Di + Ne + An +H2O. The second reaction takes place in the area of water pressure more than 1.2-1.5 kbar and temperature around 1100°C. Pargasite decomposition is controlled by incongruent melting:Prg = Fo + Sp +{Di+Ne +An}L+H2O. The third reaction takes place in the same pressure range as the previous one, but at lower temperatures ~1050°C. This reaction determines the pargasite liquidus in the melt and is related to the interaction between the amphibole and the coexisting melt:Prg + L= Fo + Sp + Di +{Ne +Pl}L+H2O.Presumably, the activity of the melt silicaaSiO2has the greatest impact on the pargasite liquidus.

Important problems of magma differentiation, formation of native metals, and ore-forming processes in the Earth’s crust are often related to participation of hydrogen. In this paper, new experimental data on the crystallization of andesite melts at high temperatures (900–1250°C) and hydrogen pressures (10–100 MPa) have been obtained, which clarify the possible role of hydrogen in the processes occurring in andesite melts in the Earth’s crust and during volcanism under strongly reduced conditions ( fO_2 = 10–17–10–18). In the crystallization experiments, it was found out that the compositions of the crystals (pyroxenes and plagioclases) formed in experiments on crystallization of andesite melt under hydrogen pressure closely correspond to the crystal compositions of lava flows of Avacha volcano in Kamchatka. This result can be considered as an experimental confirmation of the participation of hydrogen in the volcanic process.

The immiscibility of a Fe–FeS–C melt into Fe-metal (Mc) and Fe-sulfide (Ms) liquids has been studied in the basalt–Fe–FeS–C system at 4 GPa and 1400°C. The partition (D) and distribution (Kd) coefficients of S, Fe, Co, Ni, Re, Os, and Pt between the Mc and Ms melts are determined. The partition coefficients D served as indicators of the siderophilic and chalcophilic properties of each element, and Kd characterized their interelemental ratios during fractionation. In the Fe–Os–Co–Re series with D > 1, siderophilic properties prevail, which increase with increasing values of the partition coefficients: 1.2–1.5–1.6–12.6. In the Ni–Pt–S series with D < 1, chalcophilic properties prevail, which increase with decreasing D: 0.9–0.6–0.1. The values of the distribution coefficients Kd Re/Os (8.4) and Pt/Os (0.4) indicate the fractionation of Re and Pt relative to Os, with enrichment of rhenium in a metallic melt and platinum in a sulfide melt and a shift in the fractionation of the Re/Os and Pt/Os relations and related systems of 187Re/187Os and 190Pt/186Os isotopes. The genetic relationship of magmatic sulfide mineralization in intrusive of the Upper Norilsk (ore-bearing) and Lower Norilsk (ore-free) types with metal–sulfide immiscibility of sulfide magma is evidenced by the similarity of the Re/Os ratio in the Upper Norilsk intrusive with the ratio in the Ms component, and in the Lower Norilsk intrusive with the Mc component.

Using the original high-gas pressure unit (IHPV), experiments were conducted for the first time on the interaction of iron with methane at a temperature of 900°C and a pressure of 100 MPa. Complex methods (microprobe, Raman spectroscopy, chromatography, mass balance calculations) are used for a thorough analysis of fluid compositions and metallic phases formed in experiments. For the first time, experimental and theoretical quantitative data on the composition of the fluid and the composition of the fluid components dissolved in the metal were obtained. Unlike the previously studied Fe 3 C–H 2 system, in experiments, when Fe reacts with methane, there is an active interaction of carbon formed due to the pyrolysis of methane with iron up to the synthesis of Fe 3 C carbide. The experiments have shown that increasing pressure inhibits significantly hydrogen yield during methane conversion on metallic iron. Carbon saturation of iron with the formation of Fe 3 C is not complete within the entire volume of the metal during 24 h runs at 900°С. Employing molybdenum containers facilitates CH 4 decomposition.

New data on roméite (CaNa)Sb2O6F solubility in the NaF–H2O system of P–Q type have been obtained within a wide range of sodium fluoride concentrations (from 0 to 25 wt

Layered composite materials based on niobium and cermet are produced via the self-propagating high-temperature synthesis of preliminarily structured samples using metal foils (Ti, Nb, Ta, Ni) and reaction tapes (Ti + 1.7B) and (5Ti + 3Si). The reaction tapes for synthesis are produced by rolling powder mixtures. The microstructure, and elemental and phase compositions of the synthesized multilayer composite materials are studied by scanning electron microscopy and X-ray phase analysis. Particular attention is paid to the formation of intermediate layers and surface modification occurring during combustion. The strength characteristics of the synthesized materials are determined according to the three-point loading scheme at temperatures of 1100°C. Analysis of the obtained materials shows that joining in the combustion mode of metal foils and reaction tapes is provided due to reaction diffusion, mutual impregnation, and chemical reactions occurring in the reaction tapes and on the surface of the metal foils. The formation of thin intermediate layers in the form of cermet and eutectic solutions provides the synthesized multilayer materials with good strength properties up to 87 MPa at 1100°C. These results are of interest for the development of structural materials operating under extreme conditions.

Single crystals of Ga-, Ge-, and Ga,Ge-rich (up to 41.42 wt% GeO 2 and 33.95 wt% Ga 2 O 3 or 0.98 apfu (atom per formula unit) Ge and 0.90 apfu Ga) and undoped topazes were grown on natural topaz seeds as a newly overgrown layer up to 5 mm thick. The thermogradient hydrothermal method was used at a temperature range of 600 - 650 degrees C and a pressure of 100 MPa under the condition of reverse temperature solubility factor of silica and alumina in the fluoride solution. The chemical composition and crystal structure of the grown topazes, as well as the distribution of gallium and germanium in the overgrown layer, were investigated by electron microprobe analysis (EMPA), single crystal X-ray diffraction (SCXRD) and Raman spectroscopy. The overgrown layers of Ge-, and Ga,Ge-rich topazes have a zonal distribution of elements, two zones corresponding to topaz Al 2 SiO 4 (F,OH) 2 and krieselite (Al,Ga) 2 GeO 4 (F,OH) 2 compositions are distinguished. The structural and spectroscopic studies show linear dependences of unit cell parameters and Raman shift on germanium and gallium contents and confirm the existence of a complete series of topaz-krieselite solid solution.

The influence of the arrangement of amino acid residues in a pentapeptide on its stability is being studied. A forecast of pentapeptide stability is made using the gradient boosting method, which allows one to evaluate the influence of each feature on the stability of the pentapeptide. Combinations of amino acid arrangements in the pentapeptide have been identified that make a significant contribution to its stability. It has been shown that the useof such combinations reduces the amount of data required to obtain a reliable prediction of pentapeptide stability.

The study is devoted to searching for possibilities to improve the thermal stability of protective silicide coatings on zirconium alloys by reducing the intensity of their diffusion interaction with the base material. The possibilities of forming barrier layers both from molybdenum silicides with a reduced silicon content and from tungsten are experimentally evaluated. The structural and phase state of diffusion pairs subjected to vacuum annealing at temperatures of 1100–1450°C for 3–9 hours are studied by scanning electron microscopy and X-ray spectral microanalysis. It is determined that a 1-μm-thick tungsten barrier layer reduces the degree of diffusion interaction between molybdenum silicides and a zirconium-based alloy. However, in the interaction region, a porous and brittle layer is formed, leading to peeling of the coating. A decrease in the average silicon content in molybdenum silicides can also significantly reduce the degree of their interaction with zirconium alloys, but does not lead to loss of coating adhesion. The features of the microstructure and chemical composition formed as a result of the diffusion interaction of phases are revealed. The effective kinetic parameters of the processes of diffusion interaction and their temperature dependence are determined.

The work is devoted to the experimental study of the possibility to apply a protective silicide coating on an alloy based on zirconium (E110) by atmospheric plasma spraying. Coatings based on the binary eutectic Mo5Si3 + MoSi2 are deposited onto the surface of an E110 alloy sheet. The features of the structure and phase composition of the coatings after deposition and their evolution as a result of isothermal annealing at a temperature of 1300°C are studied. Upon the rapid cooling of silicide particles during coating, nonequilibrium phases are formed. As a result of annealing, the phase composition changes, which corresponds to the phase diagram. The kinetics of the diffusion interaction between the coating and the base material is studied. The possibility of successfully protecting zirconium alloy from oxidation at 1100°C in air by the complex deposition of a coating of molybdenum silicides is shown for the first time. The minimum radius of curvature of the surface of the protected samples is about 1 mm.

WC–Co cemented carbides build one of the important classes of metal matrix composites. We show in this paper that the use of machine vision methods makes it possible to obtain sufficiently informative statistical data on the topology of the interfaces between tungsten carbide grains (WC) and a cobalt matrix (Co). For the first time, the outlines of the regions of the cobalt binder were chosen as a tool for describing the structure of cemented carbides. Numerical processing of micrographs of cross sections of three WC–Co alloys, which differ in the average grain size, was carried out. The distribution density of the angles in the contours of cobalt “lakes” is bimodal. The peaks close to 110° (so-called outcoming angles) correspond to the contacts between the cobalt binder and the WC/WC grain boundaries. The peaks close to 240° (or incoming angles) correspond to the WC “capes” contacting the cobalt “lakes” and are determined by the angles between facets of WC crystallites. The distribution density of the linear dimensions of the regions of the cobalt binder, approximated with ellipses, were also obtained. The distribution density exponentially decreases with the lengths of the semi-axes of the ellipsoid, approximating the area of the cobalt binder. The possible connection between the obtained data on the shape of cobalt areas and the crack trajectories in cemented carbides is discussed.

We report new experimental data on the interaction of igneous melts with hydrogen at temperatures of 1100-1250 & DEG;C and hydrogen pressures of 1-100 MPa in strongly reducing conditions: fO2 = 10-12-10-14. The experiments were conducted using an original high-gas-pressure unit equipped with a unique device that provides long-term experiments at high temperatures and pressures of hydrogen. The experiments used natural samples of igneous rocks: the magnesian basalt of the Northern Breakthrough of the Tolbachik Volcano (Kam chatka) and the andesite of the Avacha Volcano (Kamchatka). On the basis of the experiments, the following features of the process of interaction of hydrogen with igneous melts have been established: (1) Despite the high reduction potential of the H2-igneous melt system, the reactions of hydrogen oxidation and complete reduction of oxides of metals of variable valence in the melt do not go to the end. The cessation of redox reactions in basaltic and andesitic melts is due to the formation of H2O in the melt, which buffers the reduction potential of hydrogen; (2) The initially homogeneous igneous melt becomes heterogeneous: The formed H2O dissolves in the melt and in the fluid phase (at first pure hydrogen), and melts of variable, more acidic composition and small metallic isolations of the liquation structure are formed; (3) The complex process of metal-silicate liquation in magmatic melts when they interact with hydrogen can be carried out at real magma temperatures in nature (& LE;1200 & DEG;C), significantly lower than the corresponding melting points of iron and its alloys with nickel and cobalt; (4) The structure and dimensions of the experimentally established metal isolations are consistent with natural data on the finds of small quantities of native metals, primarily iron and its alloys with nickel and cobalt, in igneous rocks of different compositions and genesis.

This investigation delved into the alterations in the mechanical properties of a TiZrHfMoCrCo high-entropy alloy due to phase transformations induced by high-pressure torsion (HPT). The alloy’s genesis involved levitation melting within an argon atmosphere, presenting two distinct states for analysis: the initial, post-manufacturing state and the state subsequent to HPT treatment. The original alloy featured a composition comprising a singular A2 phase with a bcc lattice and two Laves phases, C15 and C14. The HPT process triggered significant phase modifications: a retention of one C15 Laves phase and decomposition of the bcc phase into two distinct phases exhibiting different bcc lattice parameters. The HPT-induced effect prominently manifests as strong grain refinement. However, scanning electron microscopy (SEM) observations unveiled persistent inhomogeneities at a micron scale both before and after HPT treatment. Thus, grain refinement occurs separately within each of the bcc and Laves phases, visible in the light, dark, and gray areas in SEM images, while mixing does not occur on the scale of several microns. The examination of Ti, Cr, Co, Zr, Mo, and Hf via X-ray absorption spectroscopy (EXAFS) at specific K-edges and L3-edge revealed that the HPT treatment conserves the local atomic environment of metal atoms, albeit with a slight elevation in static disorder. Assessments through microhardness and three-point bending tests demonstrated the material’s inherent hardness and brittleness. The microhardness, standing at a substantial value of 600 HV, displayed negligible augmentation post-HPT. However, the microhardness of individual phases exhibited a notable alteration, nearly doubling in magnitude.

The results of an experimental study of the melting of a graphite-saturated Fe–Fe(CuNi)S–C system at 0.5 GPa and 1150–1250°C with the impurity elements Ag, Au, Re, Pt, Pd, and Rh are presented. A quenched sulfide melt forms the matrix of the sample; at 1150–1200°С, it is represented by the FeNiS pyrrhotite phase (Mss) with inclusions of the FeCuS phase (Iss) anomalously enriched in Cu. At 1250°C, the quenched sulfide melt forms a homogeneous pyrrhotite Ms phase of the Fe(CuNi)S composition. The change of the Ms composition of the quenched sulfide melt with the two-phase Mss + Iss association is considered as evidence of the existence of supraliquidus Mss and Iss stratification of the sulfide Fe–Ni–Cu melt in the range of 1150–1250°C. In result of element fractionation between immiscible Fe–sulfide (Ms) and Fe-metal (Mc) melts, Fe, Ni, Pt, Re, and Au are predominantly concentrated in the metal melt, while Cu and Ag are concentrated in the sulfide melt. The role of the supraliquidus Mss–Iss stratification in the genesis of sulfide mineralization of the Talnakh ore cluster deposits, including pyrrhotite–chalcopyrite “drops” in picritic gabbro–dolerites, as well as pyrrhotite and chalcopyrite types of ores of zonal sulfide deposits, is discussed. The role of Ms and Mc stratification of the Fe–sulfide melt during carbon contamination in the Cu–Pd specialization of magmatic sulfide deposits in the Norilsk region is considered.

The influence of the arrangement of amino acid residues in a pentapeptide on its stability is being studied. A forecast of pentapeptide stability is made using the gradient boosting method, which allows one to evaluate the influence of each feature on the stability of the pentapeptide. Combinations of amino acid arrangements in the pentapeptide have been identified that make a significant contribution to its stability. It has been shown that the use of such combinations reduces the amount of data required to obtain a reliable prediction of pentapeptide stability.