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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]

A complex titanium-silicon carbide of the Ti3SiC2 composition was synthesized using various starting components in a high-temperature furnace at 1400°C for 1 h and by subsequent hot pressing at a temperature of 1350°C and a pressure of 30 MPa for 15 min. The content of Ti3SiC2 was calculated by the Rietveld method, with the Ti:Si:TiC ratio reaching 1:1.2:1.8 98.6 vol.% after hot pressing. The microstructure and phase composition of hot-pressed materials, as well as the physical and mechanical characteristics of sintered and hot-pressed Ti3SiC2-based materials, were studied. [ABSTRACT FROM AUTHOR]

Dense materials based on Si3N4 with oxide additives activating sintering were obtained by reaction and liquid-phase sintering and hot pressing. Their physical and mechanical properties were determined. Porous samples were obtained by semi-dry forming of Si3N4 + Si workpieces followed by reactive sintering in a nitrogen atmosphere. The porosity was controlled by decreasing the Si concentration in the initial charge. The thermal conductivity of the materials was highly dependent on porosity and decreased with increasing temperature. The thermal conductivity of hot-pressed materials decreased from 60 W/(m·K) at room temperature to 35 W/(m·K) at 1200°C, at which temperature the weight gain of the samples was 7 × 10–4 kg/m2. The weight gain of the porous materials increased from 4 × 10–3 kg/m2 with a sample porosity of 32% to 6 × 10–3 kg/m2 with 56% porosity. It was shown that an oxygen impurity was the main reason for the decrease in the thermal conductivity of the Si3N4 ceramics. [ABSTRACT FROM AUTHOR]

Ti3SiC2 was synthesized by hot pressing at 1400°С for 15 and 30 min at a pressure of 30 MPa from powder mixtures, mainly from Ti/Si/TiC and Ti/TiSi2/TiC. The amount of the Ti3SiC2 phase synthesized from these mixtures was 94.0 and 95.9 vol %, respectively (1400°С, 30 min). The Ti3SiC2 phase crystallized as elongated grains. The effect of the hot pressing time on the formation of the Ti3SiC2 phase from the starting Ti/Si/TiC powders was determined. The final products contained titanium carbide and a small amount of silicon carbide as intermediate phases (for composites containing the starting silicon carbide powders). An excess of silicon leads to the formation of the largest amount of the Ti3SiC2 phase. [ABSTRACT FROM AUTHOR]