Al-Pt intermetallic compounds: HAXPES study.

Intermetallic compounds in the Al-Pt system were systematically studied via hard X-ray photoelectron spectroscopy, focusing on the positions of Pt 4f and Al 2s core levels and valence band features. On one hand, with increasing Al content, the Pt 4f core levels shift towards higher binding energies (BE), revealing the influence of the atomic interactions (chemical bonding) on the electronic state of Pt. On the other hand, the charge transfer from Al to Pt increases with increasing Al content in Al-Pt compounds. These two facts cannot be combined using the standard "chemical shift" approach. Computational analysis reveals that higher negative effective charges of Pt atoms are accompanied by reduced occupancy of Pt 5d orbitals, leading to the limited availability of these electrons for the screening of the 4f core hole and this in turn explains the experimentally observed shift of 4f core levels to higher BE.

Al-Pt compounds catalyzing the oxygen evolution reaction.

Al-Pt compounds have been systematically studied as electrocatalysts for the oxygen evolution reaction (OER). Considering the harsh oxidative conditions of the OER, all Al-Pt compounds undergo modifications during electrochemical experiments. However, the degree of changes strongly depends on the composition and crystal structure of a compound. In contrast to Al-rich compounds (Al4Pt and Al21Pt8), which reveal strong leaching of aluminum, changes in other compounds (Al2Pt, Al3Pt2, rt-AlPt, Al3Pt5, and rt-AlPt3) take place only on the surface or in the near-surface region. Furthermore, surface modification leads to a change in the electronic structure of Pt, giving rise to the in situ formation of catalytically more active surfaces, which are composed of intermetallic compounds, Pt-rich AlxPt1-x phases and Pt oxides. Forming a compromise between sufficient OER activity and stability, Al2Pt and Al3Pt2 can be considered as precursors for OER electrocatalysts.

INITIATING FACTORS OF COMPLICATIONS DEVELOPMENT DURING PROSTHETICS OF TEETH WITH FIXED PROSTHESES.

OBJECTIVE: The aim: Determination of the factors complications occurrence in prosthetics with metal-ceramic prostheses. PATIENTS AND METHODS: Materials andmethods: Clinical, cytological, cytochemical methods and methods of statistical processing of the received data are applied. RESULTS: Results: A number of factors with different degrees of significance have been identified, which in the dynamics of clinical observations of the percentage of absorbed dispersion are decisive in the development of changes in the gums. At the stage of odontopreparation - the 1 factor, with the percentage of absorbed dispersion (12,3%) - preparation. The 2 factor - (11,9%) - traumatic. The 3 factor, periodontal, was slightly less significant (9,8%). In the dynamics of clinical observations for 45 days in the first place was the dissecting factor - (14%). The second most important factor was the vitality of the teeth - (11,5%). The 3 factor remained relatively stable - periodontal (8,5%). In the dynamics of clinical observations after 1 year, a redistribution of significance was noted. The largest percentage of absorbed dispersion covered periodontal factor - (15%). Vitality factor - (11%). Slightly lower, but clinically significant, of (8%) absorbed dispersion, was the preparation factor. CONCLUSION: Conclusions: Statistical analysis of the studied parameters made it possible to determine the key factors for predicting their development and diagnostics, it is important for organizing an increase in the effectiveness of orthopedic prophylactic therapeutic measures at the stages of restoration of dental hard tissues.

Influence of two-hour tourniquets ischemia of limb and acute blood loss on systemic disorders of the body in the reperfusion period (experimental study).

OBJECTIVE: The aim: to find out the effect of a two-hour tourniquets ischemia of the limb and acute blood loss on systemic disorders of the body in the postperfusion period. PATIENTS AND METHODS: Materials and methods: The experiments were performed on 96 nonlinear male rats weighing 200-220 g. All experiments were performed under sodium thiopental anesthesia. In the first experimental group, two-hour tourniquets limb ischemia was simulated. In the second experimental group, acute blood loss was modeled. In the third experimental group, these lesions were combined. In 1 and 2 hours, as well as in 1, 7 and 14 days, the biliary function of the liver was determined in the experimental animals. RESULTS: Results: Two-hour tourniquets ischemia of the limb in the reperfusion period compared with the control was accompanied by a significant decrease in the rate of bile excretion, which reached a minimum value in 3 h - 1 day of the experiment and returned to the control level in 14 days. After the simulation of acute blood loss, the rate disturbance of bile excretion became significantly greater in all observation periods. The complication of acute ischemia-limb reperfusion caused a greater decrease in the rate of bile excretion with a maximum in 1 day of the experiment. Under these conditions, at 1, 7, and 14 days, the indicator was statistically significantly lower than in the other study groups. CONCLUSION: Conclusions: In the case of acute blood loss, complicated by two-hour tourniquets ischemia of the limb, the reperfusion period is accompanied by a summation of the negative impact of blood loss, ischemia and reperfusion of the limb on the functional state of the liver, which is a significant decrease in the rate of bile excretion with a maximum in 1 day, which further increases, but up to 14 days does not reach the level of control.

State characteristics of the problem of oral cavity environmental system.

OBJECTIVE: The aim: Analysis of literary sources with the study of modern views on the problem of the immune status of the oral mucosa. PATIENTS AND METHODS: Materials and methods: The review and analysis of scientific and medical literature for the years 2013-2019, based on Scopus databases, Web of Science, Med Line, The Cochrane Library, EMBASE, Global Health, CyberLeninka, RIC. CONCLUSION: Conclusions: Bacterial wall antigens are able to affect the local immune response of the oral mucosa. In particular, suppression of lymphocytes and macrophages proliferation, alteration of adhesion molecules expression and homing of the immune system cells to the inflammation site, inhibition of cytokine secretion by contact of the immune system cells with gram-positive bacteria is revealed. Therefore, studying the changes in the differentiation of the oral mucosa epithelium and periodontal tissues under the influence of environmental factors is of relevance. The conception of the oral cavity as a complex ecological system has not only theoretical but also practical value. Summarizing the data, we can say that at the current stage of science development the interaction of all structures should be considered, focusing on epitheliocytes of the oral mucosa, as a closing chain, which initiates changes that can affect the condition of the oral cavity and the results of pathological processes treatment of the oral cavity mucous membrane and periodontal tissues.

Al2 Pt for Oxygen Evolution in Water Splitting: A Strategy for Creating Multifunctionality in Electrocatalysis.

The production of hydrogen via water electrolysis is feasible only if effective and stable catalysts for the oxygen evolution reaction (OER) are available. Intermetallic compounds with well-defined crystal and electronic structures as well as particular chemical bonding features are suggested here to act as precursors for new composite materials with attractive catalytic properties. Al2 Pt combines a characteristic inorganic crystal structure (anti-fluorite type) and a strongly polar chemical bonding with the advantage of elemental platinum in terms of stability against dissolution under OER conditions. We describe here the unforeseen performance of a surface nanocomposite architecture resulting from the self-organized transformation of the bulk intermetallic precursor Al2 Pt in OER.

Ca-Ag compounds in ethylene epoxidation reaction.

The ethylene epoxidation is a challenging catalytic process, and development of active and selective catalyst requires profound understanding of its chemical behaviour under reaction conditions. The systematic study on intermetallic compounds in the Ca-Ag system under ethylene epoxidation conditions clearly shows that the character of the oxidation processes on the surface originates from the atomic interactions in the pristine compound. The Ag-rich compounds Ca2Ag7 and CaAg2 undergo oxidation towards fcc Ag and a complex Ca-based support, whereas equiatomic CaAg and the Ca-rich compounds Ca5Ag3 and Ca3Ag in bulk remain stable under harsh ethylene epoxidation conditions. For the latter presence of water vapour in the gas stream leads to noticeable corrosion. Combining the experimental results with the chemical bonding analysis and first-principles calculations, the relationships among the chemical nature of the compounds, their reactivity and catalytic performance towards epoxidation of ethylene are investigated.

Extended Chemical Flexibility of Cubic Anti-Perovskite Lithium Battery Cathode Materials.

Novel bichalcogenides with the general composition (Li2TM)ChO (TM = Mn, Co; Ch = S, Se) were synthesized by single-step solid-state reactions. These compounds possess cubic anti-perovskite crystal structure with Pm3̅ m symmetry; TM and Li are disordered on the crystallographic site 3c. According to Goldschmidt tolerance factor calculations, the available space at the 3c site is too large for Li+ and TM2+ ions. As cathode materials, all title compounds perform less prominent in lithium-ion battery setups in comparison to the already known TM = Fe homologue; e.g., (Li2Co)SO has a charge density of about 70 mAh g-1 at a low charge rate. Nevertheless, the title compounds extend the chemical flexibility of the anti-perovskites, revealing their outstanding chemical optimization potential as lithium battery cathode material.

Anisotropic Reactivity of CaAg under Ethylene Epoxidation Conditions.

The chemical behavior of CaAg as catalyst for ethylene epoxidation was studied using a combination of experimental (X-ray powder diffraction, scanning electron microscopy, thermal analysis and infrared spectroscopy), and quantum chemical techniques as well as real-space chemical bonding analysis. Under oxidative ethylene epoxidation conditions, the CaAg (010) surface possesses an outstanding stability during long-term experiments. It is caused by the formation of an ordered, stable and dense CaO passivation layer with a small amount of embedded Ag atoms. On this way, the (010) surface constitutes a kinetic barrier for further incorporation of oxygen into the subsurface region and thereby prevents  further oxidative decomposition of CaAg. The calculated adsorption energies of the reaction species show strong adsorption of the reaction products that may explain the observed low conversion of ethylene toward ethylene oxide using CaAg as catalyst.

Anti-Perovskite Li-Battery Cathode Materials.

Through single-step solid-state reactions, a series of novel bichalcogenides with the general composition (Li2Fe)ChO (Ch = S, Se, Te) are successfully synthesized. (Li2Fe)ChO (Ch = S, Se) possess cubic anti-perovskite crystal structures, where Fe and Li are completely disordered on a common crystallographic site (3c). According to Goldschmidt calculations, Li+ and Fe2+ are too small for their common atomic position and exhibit large thermal displacements in the crystal structure models, implying high cation mobility. Both compounds (Li2Fe)ChO (Ch = S, Se) were tested as cathode materials against graphite anodes (single cells); They perform outstandingly at very high charge rates (270 mA g-1, 80 cycles) and, at a charge rate of 30 mA g-1, exhibit charge capacities of about 120 mA h g-1. Compared to highly optimized Li1-xCoO2 cathode materials, these novel anti-perovskites are easily produced at cost reductions by up to 95% and, yet, possess a relative specific charge capacity of 75%. Moreover, these iron-based anti-perovskites are comparatively friendly to the environment and (Li2Fe)ChO (Ch = S, Se) melt congruently; the latter is advantageous for manufacturing pure materials in large amounts.

Binary Alkali-Metal Silicon Clathrates by Spark Plasma Sintering: Preparation and Characterization.

The binary intermetallic clathrates K8-xSi46 (x = 0.4; 1.2), Rb6.2Si46, Rb11.5Si136 and Cs7.8Si136 were prepared from M4Si4 (M = K, Rb, Cs) precursors by spark-plasma route (SPS) and structurally characterized by Rietveld refinement of PXRD data. The clathrate-II phase Rb11.5Si136 was synthesized for the first time. Partial crystallographic site occupancy of the alkali metals, particularly for the smaller Si20 dodecahedra, was found in all compounds. SPS preparation of Na24Si136 with different SPS current polarities and tooling were performed in order to investigate the role of the electric field on clathrate formation. The electrical and thermal transport properties of K7.6Si46 and K6.8Si46 in the temperature range 4-700 K were investigated. Our findings demonstrate that SPS is a novel tool for the synthesis of intermetallic clathrate phases that are not easily accessible by conventional synthesis techniques.

Structural evolvement and thermoelectric properties of Cu(3-x)Sn(x)Se3 compounds with diamond-like crystal structures.

Polycrystalline samples of Cu(3-x)Sn(x)Se3 were synthesized in the composition range x = 0.87-1.05. A compositionally induced evolvement from tetragonal via cubic to monoclinic crystal structures is observed, when the composition changes from a Cu-rich to a Sn-rich one. The Cu(3-x)Sn(x)Se3 materials show a metal-to-semiconductor transition with increasing x. Electronic transport properties are governed by the charge-carrier concentration which is well described by a linear dispersion-band model. The lattice component of the thermal conductivity is practically independent of x which is attributed to the opposite influence of the atomic ordering and the inhomogeneous distribution of the Cu-Se or Sn-Se bonds with different polarities in the crystal structure. The highest thermoelectric figure of merit ZT of 0.34 is achieved for x = 1.025 at 700 K.

New monoclinic phase at the composition Cu2SnSe3 and its thermoelectric properties.

A new monoclinic phase (m2) of ternary diamond-like compound Cu2SnSe3 was synthesized by reaction of the elements at 850 K. The crystal structure of m2-Cu2SnSe3 was determined through electron diffraction tomography and refined by full-profile techniques using synchrotron X-ray powder diffraction data (space group Cc, a = 6.9714(2) Å, b = 12.0787(5) Å, c = 13.3935(5) Å, ß = 99.865(5)°, Z = 8). Thermal analysis and annealing experiments suggest that m2-Cu2SnSe3 is a low-temperature phase, while the high-temperature phase has a cubic crystal structure. According to quantum chemical calculations, m2-Cu2SnSe3 is a narrow-gap semiconductor. A study of the chemical bonding, applying the electron localizability approach, reveals covalent polar Cu-Se and Sn-Se interactions in the crystal structure. Thermoelectric properties were measured on a specimen consolidated using spark plasma sintering (SPS), confirming the semiconducting character. The thermoelectric figure of merit ZT reaches a maximum value of 0.33 at 650 K.

Using crystallographic shear to reduce lattice thermal conductivity: high temperature thermoelectric characterization of the spark plasma sintered Magnéli phases WO2.90 and WO2.722.

Engineering of nanoscale structures is a requisite for controlling the electrical and thermal transport in solids, in particular for thermoelectric applications that require a conflicting combination of low thermal conductivity and low electrical resistivity. We report the thermoelectric properties of spark plasma sintered Magnéli phases WO2.90 and WO2.722. The crystallographic shear planes, which are a typical feature of the crystal structures of Magnéli-type metal oxides, lead to a remarkably low thermal conductivity for WO2.90. The figures of merit (ZT = 0.13 at 1100 K for WO2.90 and 0.07 at 1100 K for WO2.722) are relatively high for tungsten-oxygen compounds and metal oxides in general. The electrical resistivity of WO2.722 shows a metallic behaviour with temperature, while WO2.90 has the characteristics of a heavily doped semiconductor. The low thermopower of 80 µV K(-1) at 1100 K for WO2.90 is attributed to its high charge carrier concentration. The enhanced thermoelectric performance for WO2.90 compared to WO2.722 originates from its much lower thermal conductivity, due to the presence of crystallographic shear and dislocations in the crystal structure. Our study is a proof of principle for the development of efficient and low-cost thermoelectric materials based on the use of intrinsically nanostructured materials rather than artificially structured layered systems to reduce lattice thermal conductivity.