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We have studied the effect of sodium fluoride as a sintering aid for β-sialons on the phase composition and physicomechanical properties of Si5AlON7 and Si4Al2O2N6. Two-step high-temperature firing of the β-sialons in the presence of NaF under a nitrogen atmosphere has been shown to cause no significant changes in the phase composition of the materials. The density and microhardness of the materials prepared using 0.5 and 5.0 wt % NaF are lower than those of the materials prepared without sintering aids, but the bending strength is higher by up to 14.3% in the case of Si5AlON7 prepared using 0.5 wt % NaF and by 4.9% in the case of Si4Al2O2N6 prepared using 5.0 wt % NaF. [ABSTRACT FROM AUTHOR]

Si3N4/TiN ceramic composites have been prepared by hot pressing in a nitrogen atmosphere using fine Si3N4 and Ti powders and CaO–Al2O3 sintering aids and investigated. The results demonstrate that hot pressing was accompanied by titanium nitridation, yielding titanium nitride with the composition TiN0.9. Reaction between silicon nitride and the sintering aid led to the formation of a Ca-α-SiAlON with the composition Ca0.67(Si10Al2)(N15.3O0.7). In addition to the major phases, calcium aluminosilicate with the composition Ca3Al2Si3O12 was identified. Increasing the percentage of titanium nitride in the composites prepared at a temperature of 1650°C led to an increase in their density and Vickers microhardness: from 3.18 ± 0.03 to 4.33 ± 0.03 g/cm3 and from 17 ± 1.1 to 29.4 ± 0.9 GPa, respectively. [ABSTRACT FROM AUTHOR]

We employed contact alloying in the range 1000–1860°С to study the reaction specifics between SiC and Al2O3−(t + m)ZrO2(Y2O3) oxide composition. Real-time experiments with photographic recording of the changing size and shape of the Al2O3−(t + m)ZrO2(Y2O3) sample on a SiC ceramic substrate showed that Al2O3−(t + m)ZrO2(Y2O3) compositions react with the silicon carbide substrate in the range 1720–1860°С to melt and penetrate into (impregnate) the substrate. X-ray powder diffraction patterns were measured for samples taken from the contact area of the oxide composition with SiC directly on the substrate and in a chipped-off <1-mm-deep near-surface layer. ZrС, Al2Y4O9, and Al3.21Si0.47 were formed in the contact area via redox reactions involving oxide melt, in addition to 6H-SiC, Si and Al2O3, t-ZrO2 phases, which are the initial components of the substrate and oxide composition, respectively. [ABSTRACT FROM AUTHOR]

Si3N4-based ceramics have been produced by hot pressing in the temperature range 1550–1650°C using α-Si3N4 starting powder and CaO–Al2O3 (48 : 52 wt %) sintering aids. The powders and the ceramics have been characterized by dilatometry, scanning electron microscopy, and X-ray diffraction, and we have measured the microhardness and density of the ceramic samples. The results demonstrate that the sintering aid reacted with Si3N4 to form Ca-α-SiAlON. At 40 wt % sintering aids, all of the silicon nitride was converted into Ca-α-SiAlON. We have clarified general trends in the effect of the amount of sintering aids on the properties of the ceramic samples. [ABSTRACT FROM AUTHOR]

The preceramic oligomer organomagnesiumoxanealumoxane was synthesized by the co-condensation of organoaluminoxane and magnesium acetylacetonate. Powders of magnesium aluminate spinel (MAS) were obtained by the pyrolysis of the oligomer at 700 and 1250°C. The effect of the pyrolysis temperature on the physicochemical and rheological properties of the powder was studied. With increasing pyrolysis temperature, the particle shape becomes closer to isometric, which leads to a decrease in the limiting length of the linear portion of the compaction curves. A MAS powder containing 3 wt % Sm2O3 was produced to study the effect of the sintering additive. The sintering kinetics was investigated by dilatometry, and the effect of the sintering additive Sm2O3 on the process and the mass-transfer mechanism during the sintering of spinel was estimated. According to the quantitative analysis data, the activation energies for the pure MAS and the MAS doped with Sm2O3 are Q1250 = 481 kJ/mol and QSm2O3 = 775 kJ/mol, respectively. The sintering additive does not affect the mass-transfer mechanism; however, it increases the activation energy by 60%, doubles the shrinkage, and decreases the temperature of the beginning of sintering from 1546 to 1494°C. [ABSTRACT FROM AUTHOR]