Abstract Silicon nitride-based compositions containing zirconia and ceria additives were prepared by hot pressing in argon atmosphere. The compositions studied can be divided into two groups: (a) with a constant total amount of ZrO2 + CeO2 additive (32 mol.%) within which the CeO2 content was varied from 0 to 6.2 mol.%, and (b) with various contents (10 to 42 mol.%) of ZrO2 + CeO2 additive, the ratio of ZrO2 to CeO2 staying constant at a level of 7.35:1. Phase compositions were determined by X-ray powder diffraction (XRD), while energy-dispersive X-ray microanalysis (EDX) was used for compositional analysis of the ZrO2 grains. The results showed that after sintering the Ce4+ ions were reduced to Ce3+. At low initial ceria concentrations, Si2N2O was formed beside β-Si3N4 and ZrO2 (the majority of which was monoclinic). At higher ceria concentrations, however, Si2N2O disappeared by reaction with ceria and silica to form Ce – N apatite. Nitrogen-containing zirconia phases were not found in the studied compositions, up to 1750 °C.

Zirconia toughened Si3N4 was prepared with addition of CeO2 by applying hot pressing technique. Phase composition, densification, fracture toughness and hardness were investigated as a function of hot pressing temperature and CeO2 content. The absence of nitrogen containing zirconia phase was discussed. Fracture toughness of Si3N4–ZrO2(+CeO2) with 12 mol% of CeO2 in ZrO2 reached 15MPa m1/2. Dominating toughening mechanism according to our data seems to be stress induced microcracking.

Densification during liquid-phase sintering of Si 3 N 4 –TiN was studied in the presence of Y 2 O 3 . The content of TiN was varied from 0–50 mass%. During the densification Y-silicate was formed. The amount of silicate increased with both decreasing fraction of TiN and increasing isothermal heating time. Density, fracture toughness, and electrical resistivity were measured as a function of TiN content. It was found that the density and fracture toughness increased with increasing TiN content. The electrical resistivity drops drastically, from 10 10 mΩ for sintered Si 3 N 4 to 10 −3 mΩ for sintered Si 3 N 4 –TiN composite containing 30 vol% TiN.

For densification of non-oxide ceramic powders high temperatures are needed because of the character of chemical bonding. To enable hot consolidation of non-oxides, additives are used which create conditions for liquid phase sintering. Since the existing liquid phase degrades their properties at high temperatures different methods can be used to eliminate the liquid phase from the system. The possibilities of preparation of single and multi-component ceramics on the basis of Si3N4 and SiC were analyzed, in the presence of additives from SiO2-Al2O3-X(2)O(3) system (X = Y, Sm, Dy, Nd), by applying pressureless sintering and hot pressing procedures. Properties of dense ceramics were discussed in connection with their phase composition and microstructure.

Formation of the phosphate bonding in electrofused MgO by addition of ammonium and Mg phosphates was investigated and formation of amorphous compounds has been found. On heating these compounds undergo almost identical changes what leads to the conclusion that chemical properties of the phosphate anion play essential role in this bonding reaction which does not depend to the same extent on the present cation. In the present work zero shrinkage sintering was observed. However, porosity substructure considerably changed during sintering. Electron microprobe analyses have shown that phosphate compounds concentrate at the grain boundaries. Phosphorus is present in MgO even after heating at 1660°C but it is no more continuously arranged at the boundaries of periclase grains.

In order to follow the interdependence between characteristics of raw materials and properties of low bulk density bricks several sample series on forsterite basis were made. The starting powders we employed in the brick production were dead-burned magnesite and dunite having different physico-chemical properties: impurity content, granulation, crystal structure and other relevant parameters. Using the cold and vibro pressing and sintering techniques bricks of total porosity 44% and 70% were produced. The bricks contained predominantly macropores having various shape: spherical, irregural and elongated. The relationship obtained between powder granulation, mineral and chemical composition and thermal conductivity, gas permeability, thermostability, mechanical and other properties were discussed.

A short description of high-porosity brick production is given. The technology included the preparation of starting materials, forming by extrusion, firing and finishing. The investigation included physical, thermal, structural and microstructural measurements. Apparent brick density ranged from 0.6 to 1.3 g cm−3; the minimum Al2O3 content was 34 — 36%. Micro and macropores distributions were determined and discussed in relation to mechanical and/or heat conductivity properties.