Sintering Mode Research Articles

Sintering mode of a translucent Y-TZP: Effects on its biaxial flexure fatigue strength, surface morphology and translucency.

This investigation evaluated the effect of two sintering modes of a translucent zirconia (Y-TZP) on its surface roughness, topography, phase-transformation (t → m), translucency and biaxial flexure fatigue strength. To do so, 50 Y-TZP discs (Ø=15 mm; thickness=1.2 mm; IPS e.max ZirCAD LT) were prepared and divided into two groups: Standard mode (SM) and Fast mode (FM). Staircase fatigue testing was performed (piston-on-three balls set-up, ISO 6872:2015), as well as surface roughness, profilometry, scanning electron microscopy (SEM-FEG), energy dispersive X-ray spectroscopy (EDX), phase transformation (t → m) using X-ray diffraction analysis (XRD), translucency parameter analysis (TP and TP00 ) and fractography. The results showed no statistical significant differences for roughness parameters (p > 0.05, SM: Ra=0.13 ± 0.02, Rz=1.21 ± 0.26 and RSm=24.91 ± 2.19; FM: Ra=0.14 ± 0.03, Rz=1.32 ± 0.25 and RSm=24.68 ± 2.16) or flexural fatigue strength (SM: 512 (464-560) MPa; FM: 542 (472-611) MPa) between the groups. In addition, similarity in surface morphological features (SEM and profilometry), composition and phases (EDX and XRD) was observed between the firing protocols. Fractography showed that the failure origin occurred on the tensile side. Sintering mode did not affect the TP (F=0.001, p=0.97) and TP00 (F=0.12, p=0.72). Therefore, the fast-sintering mode is suggested as a viable alternative to the standard mode since it does not influence the evaluated surface morphology, microstructure, fatigue strength and translucency of a translucent monolithic zirconia. The fast sintering mode is a viable alternative for zirconia without compromising its topography, microstructure, mechanical performance or translucency.

The Effect of Sintering Temperature on the Phase Composition, Microstructure, and Mechanical Properties of Yttria-Stabilized Zirconia.

It is known that the yttria-stabilized zirconia (YSZ) material has superior thermal, mechanical, and electrical properties. This material is used for manufacturing products and components of air heaters, hydrogen reformers, cracking furnaces, fired heaters, etc. This work is aimed at searching for the optimal sintering mode of YSZ ceramics that provides a high crack growth resistance. Beam specimens of ZrO2 ceramics doped with 6, 7, and 8 mol% Y2O3 (hereinafter: 6YSZ, 7YSZ, and 8YSZ) were prepared using a conventional sintering technique. Four sintering temperatures (1450 °C, 1500 °C, 1550 °C, and 1600 °C) were used for the 6YSZ series and two sintering temperatures (1550 °C and 1600 °C) were used for the 7YSZ and 8YSZ series. The series of sintered specimens were ground and polished to reach a good surface quality. Several mechanical tests of the materials were performed, namely, the microhardness test, fracture toughness test by the indentation method, and single-edge notch beam (SENB) test under three-point bending. Based on XRD analysis, the phase balance (percentages of tetragonal, cubic, and monoclinic ZrO2 phases) of each composition was substantiated. The morphology of the fracture surfaces of specimens after both the fracture toughness tests was studied in relation to the mechanical behavior of the specimens and the microstructure of corresponding materials. SEM-EDX analysis was used for microstructural characterization. It was found that both the yttria percentage and sintering temperature affect the mechanical behavior of the ceramics. Optimal chemical composition and sintering temperature were determined for the studied series of ceramics. The maximum transformation toughening effect was revealed for ZrO2-6 mol% Y2O3 ceramics during indentation. However, in the case of a SENB test, the maximum transformation toughening effect in the crack tip vicinity was found in ZrO2-7 mol% Y2O3 ceramics. The conditions for obtaining YSZ ceramics with high fracture toughness are discussed.

Simulation and Experimental Study of the Multisized Silver Nanoparticles Sintering Process Based on Molecular Dynamics.

Multisized nanoparticles (MPs) are widely employed as electronic materials to form conductive patterns, benefitting from their excellent sintering properties and mechanical reliability. However, due to the lack of effective detection methods for the real-time sintering process, it is difficult to reveal the sintering behavior during the MPs sintering process. In this work, a molecular dynamics method is used to track the trajectory of silver atoms. The melting behavior of a single nanoparticle (SP) is first discussed. The structural evolution of equally sized nanoparticles (EPs) and unequally sized nanoparticles (UPs) during the sintering process is analyzed alongside morphology changes. It is proposed that the UPs sintering process benefits from the wetting behavior of small-sized nanoparticles on the surface of large-sized nanoparticles, and the sintering angle (θ) is proposed as an index to estimate the sintering result of UPs. Based on the works above, three basic sintering modes and one advanced sintering mode in the MP sintering process are analyzed emphatically in this paper, and the roles of different-sized nanoparticles in MPs are concluded from simulation and experimental results. This work provides theoretical support for conductive ink composition design and sintering process optimization.

Research of forming and sintering processes of copper powder blanks for equal channel angular pressing

Copper-based powder materials have found their application in many industries. These include classical powder metallurgy, automotive and aviation industries, microelectronics, instrument engineering, and nanotechnology. In this paper, the processes of forming and sintering copper powders obtained by various methods are considered. The main part of the research was carried out on powders of the PMS-1 brand obtained by electrolysis. Four batches of samples (18 pieces each) were pressed at different pressures. Based on the results of the research, a molding mode was proposed, which should ensure the density of blanks not less than 70 % of the density of compact material. To find the simplest and most rational modes of sintering blanks, the process was carried out in air and in dissociated ammonia. The parameters of the samples were calculated after each technological operation, and the volume shrinkage of the samples was calculated depending on the initial density. Draft tests were carried out. Sediment tests were performed up to a maximum pressure of 400 MPa. Despite the fact that the degree of high-altitude deformation was 37–40 %, none of the samples collapsed during the tests, and no visible cracks were observed. Based on preliminary experiments, the masses and forming modes of rectangular blanks that were used for equal channel angular pressing were calculated. Equal channel angular pressing was performed for two samples parties obtained using different sintering modes. When pressing the first samples party, the lack of the required level of back pressure led to either a complete or significant violation of the material integrity. Before pressing the samples of the second party, a copper sample was previously placed into the channel to create a natural backpressure. It was also possible in principle to carry out the process of equal channel angular pressing of porous sintered workpieces without violating the integrity of the material.

Evaluation of residual stresses in additively produced thermoelastic cylinder. Part I. Thermal fields

The study is aimed at mathematical modeling of non-stationary temperature and stress-strain fields in growing thermoelastic cylinder, which growth is due to the layer-by-layer sintering over its lateral surface. This modeling makes it possible to estimate the reciprocal impact of non-stationary temperature fields, stress-strain state and the scenario of the additive process even in manufacturing of more complicated shapes. The problem is considered in the framework of the theory of thermal stresses with non-linear radiative boundary condition. A distinctive feature of modeling is that the material composition of the body changes over time. Therefore, the mathematical model is represented by the recurrent sequence of initial boundary value problems, formulated for each step of the additive process in different domains with respect to the increments of thermal and stress fields. The domains constitute nested sequence of regions and, together with the sequence of the moments of layer sintering, define the scenario of additive process. Initial values for a step are taken to be equal to the corresponding values at the final moment of previous step. The solution for each step is represented in the form of decomposition over eigenfunctions of differential operator, generated by boundary value problem on this step. Computational modeling of various sintering modes has been carried out. A classification of thermomechanical additive processes, based on the relationship between the characteristic time of the process and the time of thermal relaxation of the attached layer is given. Special attention is paid to non-uniform volume heating, which can be obtained by skin effect during high-frequency induction. Computational simulations based on obtained analytical solution show that auxiliary inductive heating makes it possible to substantially reduce the non-uniformity of the temperature field and thus to reduce the temperature stresses caused by it.

Insight into CO induced degradation mode of Pd/SSZ-13 in NOx adsorption and release: Experiment and modeling

Passive NOx adsorption (PNA) on Pd zeolites is an important technique to remove NOx during the cold start of the engine. However, the stability of Pd zeolites under high concentrations of CO is still challenging in multiple cold starts of an engine. Herein, we illustrate the CO-induced degradation mechanism of Pd zeolite by combining experiments and kinetic models. Pd/SSZ-13 has been used in multicycle processes containing NOx adsorption at low temperature and temperature programmed desorption, which represents the PNA degradation in multiple cold start periods. A kinetic model was developed to describe the NOx storage and degradation behavior of Pd/SSZ-13. Both experimental and modelling observations suggested that two Pd sintering modes are occurring under high CO concentration (4000 ppm), namely Ostwald ripening and particle migration. Apart from the degradation behavior, this model is also adequate for describing multi-cycle NOx storage and release behavior under low CO concentration.

Effect of Modes of Spark Plasma Sintering on the Structure and Properties of Materials of the Ni – Cr – Si – B – C System

Effect of Modes of Spark Plasma Sintering on the Structure and Properties of Materials of the Ni – Cr – Si – B – C System

Production of Nanostructured Boron Carbide Ceramics for Industrial Applications

The optimal modes (temperature, time, pressure force) of spark plasma sintering (SPS) and hot pressing of boron carbide obtained by various methods are determined. The initial powders were obtained from soot and amorphous boron by the mechanochemical synthesis method, by the high-temperature synthesis (SHS) method and by the carbon reduction method. The structure and the properties of SPS sintered and hot-pressed boron carbide blanks were determined. The highest value of the relative density was achieved during SPS sintering of blanks from B4C powders obtained by mechanosynthesis and SHS methods. It was found out the optimal conditions for sintering blanks from B4C powder obtained by mechanosynthesis. The density value reaches 99.0 rel.% at 1500 °C/25 MPa and sintering time of 45 min. For powders obtained by the SHS method, the density of sintered blanks is 98.5 rel.%. at 1800 °C/30 MPa with sintering time of 45 min. The highest value of the relative density was achieved during the hot pressing of blanks from B4C powders obtained by mechanosynthesis.

КЛИНИЧЕСКАЯ АПРОБАЦИЯ ПРИМЕНЕНИЯ МОНОЛИТНЫХ МОСТОВИДНЫХ ЗУБНЫХ ПРОТЕЗОВ ИЗ ПОЛУПРОЗРАЧНОГО ДИОКСИДА ЦИРКОНИЯ «ZICERAM T»

Two-year clinical results of prosthetics with monolithic ceramic bridge-shaped dentures made of three types of translucent zirconium dioxide were studied: "Ziceram T" (Zircon Ceramics, Russia), "CirCad MT" (Ivoclar Vivadent, Liechtenstein), "Upcera ST" (Upcera, China). A total of 23 patients with 38 bridge-shaped dentures with a total of 245 dental units fixed on intraosseous implants (20 prostheses), depulpated teeth (12 prostheses) or vital teeth (6 prostheses) were under dynamic observation. The analysis of clinical results indicates the high quality of the treatment and the absence of functional and aesthetic differences between prostheses made of Russian blanks and foreign analogues. The results of clinical studies have confirmed the correctness of the choice of the final sintering mode of ceramic material based on zirconium dioxide "Ziceram T", it can be recommended for functional and aesthetic prosthetics of full-circuit bridges.

Formation of a fine-grained Si-=SUB=-1-x-=/SUB=-Ge-=SUB=-x-=/SUB=- thermoelectric by spark plasma sintering

The kinetics of diffusion processes occurring during the formation of polycrystalline Si1-xGex nanostructures (x=0.20, 0.35) by spark plasma sintering in the temperature range 20-1200oC was studied for the first time. A mechanism for the formation of a SiGe solid solution is proposed as a result of a comprehensive study of the microstructure and phase composition of samples with particle sizes from 150 nm to 100 μm, together with the analysis of experimental sintering maps. It is based on the phenomenon of mutual diffusion of Si and Ge atoms that occurs during the entire sintering process. For the selected sintering modes, the grain size of the formed SiGe corresponds to the size of the initial powder particles. Keywords: spark plasma sintering, solid solution SiGe, thermoelectric characteristics, figure of merit ZT.

Preparation of Transparent MgAl2O4 Spinel by Pulsed Electric Current Sintering Using Two-step Heating Method

Transparent MgAl2O4 ceramics were fabricated by pulsed electric current sintering (PECS) employing two-step sintering mode. First, nanoscale MgAl2O4 powders were produced by solution combustion synthesis from hydrated nitrate compounds and urea. Subsequently, the synthesized powders were sintered by PECS with a heating rate of 100oC/min under an applied pressure of 100 MPa. The sintering process was conducted according to two-step heating profile. At the first step, the temperature increased to 1050, 1100, and 1150oC, followed by a dwell time of 60 min. The second-step sintering was carried out at 1300, 1350, and 1400oC for 20 min. The transparent ceramics sintered at 1050oC/ 60 min – 1400oC/ 20 min exhibited transmittance over 80% in infrared range. In addition, transparent samples presented a Vickers hardness up to 30 GPa for sintering mode of 1150oC/ 60 min – 1400oC/ 20 min.

Влияние технологии спекания нанопорошков на трещиностойкость тетрагонального диоксида циркония

The effect of various technological conditions of the preparation of samples from ZrO2 ceramics stabilized by various additives of yttrium oxide Y2O3 on the fracture toughness of the material has been investigated. Various modes of sintering of samples obtained by the method of co-deposition of nanopowders of zirconium dioxide ZrO2 and yttrium oxide Y2O3 were performed. An original technique for calculating the critical stress intensity factor from the test data of double cantilever beam specimens with a chevron notch by the wedging method is described. A characteristic feature of the loading diagrams for ceramics based on zirconium dioxide stabilized by additives of yttrium oxide is the presence of a stage of inelastic deformation, which develops without cracking. The mechanism of inelastic deformation is based on the phase transition of the tetragonal modification to the monoclinic modification of the crystal structure. For each mode, the values of fracture toughness characteristics are determined. Ceramics with the composition ZrO2 + 3 mol% Y2O3 (KIc = 6.86 MPa ∙ m1/2) exhibit the maximum crack resistance at a sintering temperature Tsint =1500°C for an hour. Deviation from the composition of 3 mol% Y2O3 reduces the fracture toughness. The increase in fracture toughness is favored by the grinding of the powder in a planetary mill. It is generally accepted that mechanical stresses arising at the top of a growing microcrack cause all round compression stresses, since the phase transformation is accompanied by an increase in the unit cell volume by 4%. This stabilizes the microcrack, slowing down its growth. This point of view was confirmed due to the well-known fact that when zirconium dioxide is cooled from 950°C to room temperature during the t → m transition, microcracks are intensively formed in the bulk of the material. However, when wedging a two-cantilever specimen with a chevron notch, the probability of the formation of compression stresses is small. This is also evidenced by the absence of cracking throughout the inelastic stage of material deformation. In the fine-crystalline structure of zirconium ceramics under loading, favorable conditions arise for the relaxation of shear stresses through the t → m transition.

Армированные одностенными углеродными нанотрубками композиты на основе ZrO2, полученные свободным вакуумным спеканием

The results of a study of sintered composites based on yttria-stabilized zirconia (ZrO2) reinforced with single-walled carbon nanotubes (SWCNTs) are presented in this paper. Mixing of ZrO2 nanopowder with SWCNTs was carried out in ethanol using an ultrasonic bath and a magnetic stirrer. Composite powders with 0.1, 0.5 and 1 wt.% SWCNTs and ZrO2 nanopowder were pressed into compacts at a pressure of 100 MPa, and then they were sintered in a high temperature vacuum furnace for 2 h at a temperature of 1500°C with a heating rate of 300°C / h. Changes in the microstructure, phase composition, and mechanical properties were investigated depending on the SWCNT content in the samples. It was found that in the selected sintering mode, high density samples (99.2 – 97.5 %) were obtained. It was found by scanning electron microscopy that undivided, entangled SWCNT bundles / aggregates and individual nanotubes, which together formed a continuous reinforcing structure, were observed in the microstructure of the composites. Moreover, SWCNTs led to the refinement of the microstructure of composites; the average grain size of composites was 16 % lower than that of ZrO2 ceramics. It was found by X-Ray diffraction that only high temperature modifications of zirconia (cubic and tetragonal) were present in ZrO2 ceramics and composites, and SWCNTs led to a slight decrease in the size of coherent scattering domain. It was found by the Vickers indentation method that the composite based on ZrO2 with 0.5 wt.% SWCNT was optimal in terms of mechanical properties, since it had the highest microhardness (13.6 GPa, which was 6 % higher than that of ZrO2 ceramics) and had a 12 % higher fracture toughness.

Production of corundum armored ceramics

The purpose of this study was to develop the compositions and technology of corundum armored ceramics with high ballistic characteristics based on aluminum oxide with an α-Al2O3 content of more than 99 wt.%. The results of the study of the physicochemical processes of obtaining corundum ceramics modified with complex additives consisting of magnesium - aluminosilicate eutectic mixture and oxides of magnesium, yttrium, titanium, zirconium are presented. The introduction of complex additives into the composition of corundum ceramics provides a significant reduction (100-150°C) of the sintering temperature of the product. In this case, additives of yttrium and zirconium oxides contribute to the formation of a uniform-grained microstructure of ceramics, and in the case of adding titanium oxide, a collective recrystallization of corundum grains is noted. The use of small additives (0.3-0.5 wt.%) of magnesium and yttrium oxides together with a eutectic mixture in the compositions of corundum ceramics based on high-quality alumina contributes to the formation of a uniform-grained, dense structure of the material and giving it a high level of physical and mechanical properties as a result of directional the action of each component of the additive on the physicochemical processes of phase formation of the crystalline matrix. A model idea of the mechanism of action of additives on the formation of the microstructure of ceramics during stage-by-stage heating from 1350 to 1650°C in the sintering mode of products is presented. The developed compositions and technologies of corundum armored ceramics have a production focus and implementation in practice.

Possible nature of electrical conductivity of the corund-graphene composite

The effect of sintering modes on the electrical conductivity of the corundum-graphene composite is investigated. The assumption about the nature of the electrically conductive structure and the conditions of its formation is substantiated.

Effect of thermal and densification processes on reaction and conventional sinterings of a hydrolyzed calcium phosphate phase

Thermal processes resulting in the densification of compacts of an uncalcined powder (UPC) and of the powder calcined at 700 °C for 1 h (CPC), obtained from a hydrolyzed powder with a primary molar ratio of Ca/P = 1:1 obtained by the nitrate synthesis were studied during heating under reaction and conventional sintering modes up to 1100 °C. Due to desorption, decomposition, crystallization and phase transformation processes, the density of the UPC increased stepwise and finally reached 95% of the theoretical density of the formed biphasic HA/β-TCP product with a 52/48 ratio compared to 67% and a 0.55/0.45 ratio in the CPC. Because the annealing time at 1100 °C was negligible (about 1 min), a proper completing sintering to produce high quality ceramics from such UPC phases seems very promising.

Revealing specific features of structure formation in composites based on nanopowders of synthesized zirconium dioxide

Peculiarities of formation of microstructure in composites based on chemically synthesized zirconium nanopowders obtained by the method of decomposition from fluoride salts were considered. Hydrofluoric acid, concentrated nitric acid, aqueous ammonia solution, metallic zirconium, and polyvinyl alcohol were used. It was established that the reduction of porosity in nanopowders in the sintering process is the main problem in the formation of high-density materials. Analysis of various initial nanopowders, their morphology, and features of sintering by the method of hot pressing with direct transmission of electric current was made. Peculiarities of obtaining the composites based on them with the addition of Al2O3 nanopowders applying the electric sintering method were considered. It was shown that the increase in the content of alumina nano additives leads to an increase in strength and crack resistance of the samples due to simultaneous inhibition of abnormal grain growth and formation of a finer structure with a high content of tetragonal phase. The influence of sintering modes on the formation of the microstructure of zirconium nanopowders has been studied for different contents of alumina additives. Electric current promotes the surface activity of nanopowders and its variable value promotes partial fragmentation of agglomerated grains thus affecting the composite structure. Physical-mechanical properties of the obtained samples, optimal compositions of mixtures, and possibilities of improving some parameters were determined. It was found that nanopowders of zirconium dioxide obtained by the method of decomposition from fluoride salts are quite suitable for the production of composite materials with high physical and mechanical properties. They can compete with imported analogs and enable obtaining of crack resistance of 7.8 MPa·m1/2 and strength of 820 MPa.

Structure and Properties of Barium Titanate Lead-Free Piezoceramic Manufactured by Binder Jetting Process.

This article presents the results of manufacturing samples from barium titanate (BaTiO3) lead-free piezoceramics by using the binder jetting additive manufacturing process. An investigation of the manufacturing process steps for two initial powders with different particle size distributions was carried. The influence of the sintering and the particle size distribution of the starting materials on grain size and functional properties was evaluated. Samples from fine unimodal powder compared to coarse multimodal one have 3–4% higher relative density values, as well as a piezoelectric coefficient of 1.55 times higher values (d33 = 183 pC/N and 118 pC/N correspondingly). The influence of binder saturation on sintering modes was demonstrated. Binder jetting with 100% saturation for both powders enables printing samples without delamination and cracking. Sintering at 1400 °C with a dwell time of 6 h forms the highest density samples. The microstructure of sintered samples was characterized with scanning electron microscopy. The possibility of manufacturing parts from functional ceramics using additive manufacturing was demonstrated.

Optimization of Contact Cathode Composition Based on La0.8Sr0.2MnO3±δ for SOFC Stacks

A stack based on planar solid oxide fuel cells (SOFCs) is an assembly of ceramic plates - membrane-electrode assemblies (MEA) and metal current collectors, which play the role of the distribution of gas mixtures over the electrode area, as well as current collection. In order to organize the high-quality current collection it’s necessary to provide a reliable electrical contact between the MEA’s electrodes and contact surfaces of the current collectors. Electrical contact between MEAs’ anode electrode and the collector is achieved by pressing the contact nickel meshes. Metal-based conductive adhesives are also used to reduce the contact resistance at the anode electrode. Despite this in order to ensure contact between the MEA’s cathode electrode and the collector this approach is not applicable due to the rapid oxidation of contact meshes in air atmosphere at high temperatures. In turn, contact pastes based on conductive ceramics do not have such a drawback and make it possible to ensure reliable contact under the conditions of the SOFC cathode chamber.Materials for the contact adhesive for the SOFC cathode chamber must be chemically and thermomechanically compatible with the materials of the SOFC cathode and bipolar plate along with high electrical conductivity. These requirements are met by materials based on lanthanum strontium manganite oxide (LSM) materials, which are widely used as cathode materials for SOFCs. It should be noted that the contact adhesive must also correspond to the limitations of technological processes of SOFC stack manufacturing. SOFC stacks are sealed with glass in a temperature range of 930-950°C, so it’s necessary to use a material that forms a conductive contact at temperatures not higher than 950°C, which is significantly lower than typical sintering temperatures of LSM-based cathode.The synthesis of single-phase highly dispersed powders with the composition of La0.8Sr0.2MnO3±δ (LSM) and (La0.8Sr0.2)0.97MnO3±δ (LSM-d) was carried out by the glycine-nitrate method. After synthesis some of the obtained materials were ball-milled in ethanol using 5 mm ceramic milling bodies at a speed of 600 rpm for 300 and 600 min. A mixture of polyvinyl butyral, toluene, and butanol was used as the basis for the contact paste.Tests of the electrical conductive properties of contact pastes were carried out in air in temperature range of 600-950°C. Samples were kept for 2 hours before cooling at the maximum temperature. Figure shows the results of resistivity measurements: the dashed lines represent the values obtained when the sample was cooled.The maximum values of the resistivity at a temperature of 850°C were obtained for contact adhesive samples based on non-activated stoichiometric (LSM) and A-deficient (LSM-d) powders. Low electrical conductivity can be associated with weak intergranular contact due to the strong agglomeration of the material after synthesis. Grinding for 300 minutes results in a noticeable reduction in the resistivity of the contact adhesive (LSM-300). Change in resistivity after holding at maximum temperature, as well as the change in the slope of the temperature dependence of the resistivity of the adhesive based on LSM-300 indicates the sintering of the contact adhesive powder into a ceramic compact, which is confirmed by SEM results. In turn, holding at a temperature of 950°C of contact adhesive based on LSM-600 (600 min grinding pre-activated) powder does not lead to its sintering.Grinding of the initially single-phase LSM powder results in the appearance of additional reflections in the XRD-spectrum corresponding to the Sr(OH)2 and MnCO3 phases. An increase in the grinding time leads to an increase in the proportion of impurity phases that prevent the contact adhesive from sintering at temperatures <950°C.Thus, the best results were shown by a contact adhesive based on stoichiometric LSM powder, pre-activated by grinding for 300 minutes. Holding at a temperature of 950°C leads to sintering of LSM-300 powder into ceramics, which makes it possible to form a reliable electrical contact under the conditions of the SOFC cathode chamber.We have proposed a method for the manufacture and deposition of a contact cathode composition based on La0.8Sr0.2MnO3±δ. It is shown that the initial powders obtained by the glycine-nitrate method according to the Pechini modification are preliminary prepared. The optimal grinding parameters have been determined. The sintering modes of the contact paste are selected, which are consistent with those for the sealing glass. An experimental SOFC assembly was made using a contact cathode paste. It is shown that the electrochemical characteristics of individual MEAs correspond to the declared ones and the specific power reaches 0.25W/cm2.This work was carried out with financial support from the Russian Scientific Foundation, grant no. 17-79-30071. Figure 1

Degassing and diffusion characteristics of Eu-doped gahnite ZnAl2O4 by kinetic thermodesorption mass spectrometry

The content of water and other gases in crystalline europium-doped zinc aluminate (ZnAl2O4:Eu3+) synthesized in a supercritical water fluid, the temperature regions of their maximum release during vacuum heat treatment, their degassing, kinetic and diffusion characteristics were determined by the kinetic thermodesorption mass spectrometry for the first time. Water and carbon-containing substances (CO2, CO, hydrocarbons CxHy) are the main volatile impurities in ZnAl2O4:Eu3+ crystals. The release of hydrogen and oxygen indicates very complex redox processes in ZnAl2O4:Eu3+ with the participation of vacancy structures and crystal lattice defects. A decrease in the water diffusion coefficients in aluminate materials correlates with an increase in their density. The obtained diffusive characteristics make it possible to calculate the time of material degassing to the required level. Knowledge of the real defectiveness of ZnAl2O4:Eu3+ crystals in relation to the content of water and other gases can be useful in working out the modes of crystal sintering in order to obtain transparent luminescent ceramics.