This study explores a novel method for fabricating Ca-alpha-sialon ceramics using a calcium aluminate oxide eutectic additive. Conventional sintering techniques for Ca-alpha-sialon ceramics employ nitrogen-containing additives to facilitate the Si-N bond substitution mechanism with Al-O and Al-N bonds. In this work, calcium aluminate additives are utilized, leading to the formation of Ca-alpha-sialon ceramics via carbothermal reduction processes and partial nitridation of aluminum oxide. The influence of varying calcium aluminate content (5, 10, 15, 30, and 40 wt%) on the phase composition of Ca-alpha-sialon ceramics, produced by hot pressing at 1650 degrees C in a nitrogen atmosphere, was investigated. Results indicate that increasing the calcium aluminate content leads to the formation of a beta-sialon phase, which subsequently transforms into Ca-alpha-sialon. At 40 wt% calcium aluminate, complete conversion of alpha-Si3N4 to Ca-alpha-sialon is achieved, with significant glassy phase formation at the grain boundaries. The study elucidates the relationship between calcium aluminate content, phase composition, lattice parameters, mechanical properties, oxidation resistance, and thermal expansion of the ceramics.

— Si 3 N 4 /TiN ceramic composites have been prepared by hot pressing in a nitrogen atmosphere using fine Si 3 N 4 and Ti powders and CaO–Al 2 O 3 sintering aids and investigated. The results demonstrate that hot pressing was accompanied by titanium nitridation, yielding titanium nitride with the composition TiN 0.9 . Reaction between silicon nitride and the sintering aid led to the formation of a Ca-α-SiAlON with the composition Ca 0.67 (Si 10 Al 2 )(N 15.3 O 0.7 ). In addition to the major phases, calcium aluminosilicate with the composition Ca 3 Al 2 Si 3 O 12 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/cm 3 and from 17 ± 1.1 to 29.4 ± 0.9 GPa, respectively.

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.

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

Composites have been prepared using nanopowders whose precursors were synthesized by a sol–gel hydrolysis process in 1 M solutions of the ZrOCl2, Al(NO3)3, Yb(NO3)3, and Sr (NO3)2 salts the amount of which corresponded to the basic composition (mol

We employed contact alloying in the range 1000–1860°С to study the reaction specifics between SiC and Al 2 O 3 −( t + m )ZrO 2 (Y 2 O 3 ) oxide composition. Real-time experiments with photographic recording of the changing size and shape of the Al 2 O 3 −( t + m )ZrO 2 (Y 2 O 3 ) sample on a SiC ceramic substrate showed that Al 2 O 3 −( t + m )ZrO 2 (Y 2 O 3 ) 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, Al 2 Y 4 O 9 , and Al 3.21 Si 0.47 were formed in the contact area via redox reactions involving oxide melt, in addition to 6H-SiC, Si and Al 2 O 3 , t -ZrO 2 phases, which are the initial components of the substrate and oxide composition, respectively.

Получены композиты на основе нанопорошков, прекурсоры которых синтезированы гидролизным золь–гель-методом из 1 М растворов солей ZrOCl 2 , Al(NO 3 ) 3, Yb(NO 3 ) 3 , Sr (NO 3 ) 2 , количество которых отвечало базовому составу (мол. %): 50 Al 2 O 3 , 50 – n 3Yb-TZP (тетрагональный диоксид циркония, стабилизированный 3% Yb 2 O 3 ) и модификатор SrO в количестве n = 1, 3 и 6%. Проведено исследование влияния количества модификатора на формирование фазового состава, микроструктуры и механические характеристики композитов. Установлено, что введение модификатора определяет смещение фазового перехода θ-Al 2 O 3 → α-Al 2 O 3 в область более высоких температур. Показано, что в процессе спекания исходных наноразмерных порошков in situ в температурном интервале 1250–1400°C происходит формирование фаз корунда и гексаалюмината стронция. Определено, что введение модификатора свыше 3% повышает закрытую пористость композитов, снижая параметр прочности с 700 до 450 МПа.

The hot press method was used to obtain the SiC composite from different morphology and partial size powder. The starting SiC powder was: 1) fragmentation particle shape industrial charge of silicon carbide obtained by the Acheson method with sintering additive (9 wt.% Y 2 O 3 − Al 2 O 3 ) by Saint Gobain, 2) spherical particles SiC obtained by SHS in a laboratory. Bending strength, critical stress intensity factor, density, and the friction coefficient of samples of the obtained ceramics were determined. It has been established that the properties of ceramics obtained from SHS silicon carbide powder (spherical particles with sizes of 100–400 nm), due to better compaction, were at least 10% higher than samples from Saint Gobain powder: bending strength (400 ± 22 MPa), density (3.23 ± 0.01 g/cm 3 ), critical stress intensity factor (К 1С = 4.8 ± 0.3 MPa∙m 1/2 ), friction coefficient (0.1126 ± 0.0031).

Изучено влияние фторида натрия как спекающей добавки для β-сиалонов на фазовый состав и физико-механические свойства Si 5 AlON 7 и Si 4 Al 2 O 2 N 6 . Показано, что двухстадийный высокотемпературный обжиг β-сиалонов в атмосфере азота с добавлением NaF не приводит к значимым изменениям в фазовом составе образцов. Плотность и микротвердость полученных с добавлением 0.5 и 5.0 мас. % NaF образцов оказываются ниже, чем для образцов без спекающих добавок, однако прочность на изгиб демонстрирует рост на величину до +14.3% для Si 5 AlON 7 при содержании NaF 0.5 мас. % и до +4.9% для Si 4 Al 2 O 2 N 6 при содержании NaF 5.0 мас. %.

SiC materials are obtained by impregnating a porous workpiece consisting of silicon carbide and carbon with liquid silicon. In the composition of the material, at the stage of preparation of charge compositions, up to 18 vol % SiCf is introduced, reinforcing the material and giving it a high level of mechanical characteristics. With an increase in the fiber content (>10 vol % SiCf), the density decreases and the strength of the material decreases; nevertheless, its crack resistance increases. The maximum value of the critical stress intensity factor is recorded for a material containing 15 vol % SiCf–K1C = 6.0 ± 0.2 MPa m1/2

— Si 3 N 4 -based ceramics have been produced by hot pressing in the temperature range 1550–1650°C using α-Si 3 N 4 starting powder and CaO–Al 2 O 3 (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 Si 3 N 4 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.

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

Ceramic samples based on Si3N4 were obtained and studied using a sintering additive in the MnO-TiO2 system of eutectic composition, which was accepted and applied to the surface of silicon nitride by the sol-gel method. Ceramic samples were obtained by hot pressing at 1650 °C and 1750 °C. Phase composition, thermo-physical and mechanical properties were studied. The microstructure of the resulting ceramics was also studied.