Abstract: A system for manufacturing fine-grained SiO powder includes means for heating a mixture of an SiO.sub.2 containing material and an Si and/or C containing material for generating SiO vapor, and for condensing the generated SiO vapor from a gaseous state in the presence of non-oxidizing gas and under substantially low pressure. Preferably, vacuum is maintained at the position where thermal reaction generates SiO vapor. Non-oxidizing gas serves for transferring vapor-state SiO and/or fine-grained SiO powder to an SiO collection chamber. This successfully prevents the SiO from being accumulated within a transfer pipe or duct and thus prevents the pipe or duct from being blocked. Furthermore, substantially low pressure (vacuum) atmosphere encourages SiO vapor generation from the reagent mixture and thus permits a lower heating temperature to cause SiO vapor generation.

Abstract: A hexagonally crystalline boron nitride containing water-soluble boron containing impurity in such a magnitude that amount of boron to be contained in an extract after boiling at 100.degree. C. of pure water is less than or equal to 100 .mu.g/g-BN. In order to purify the boron nitride, a purification process is carried out according to the steps of preparing fine particles of boron nitride powder; dispersing the boron nitride powder in a disperser and stirred for a given period of time for removing water-soluble boron containing impurity; and drying the boron nitride in an atmosphere, in which vapor pressure is maintained lower than or equal to 10 mmHG and/or the process temperature is maintained lower than or equal to 100.degree. C.

Abstract: A hexagonally crystalline boron nitride containing water-soluble boron containing impurities in such a magnitude that the amount of boron contained in an extract after boiling at 100.degree. C. in pure water is less than or equal to 100 .mu.g per gram of boron nitride. In order to purify the boron nitride, a purification process is carried out according to the steps of preparing fine particles of boron nitride powder; dispersing the boron nitride powder in a dispersion medium and stirred for a given period of time for removing water-soluble boron containing impurities; and drying the boron nitride in atmosphere, in which the vapor pressure is maintained lower than or equal to 10 mmHG and/or the process temperature is maintained lower than or equal to 100.degree. C.

Abstract: A method for producing an aluminum nitride powder of superior sinterability of which steps are providing an aqueous boehmite sol having a pH of 1.2 to 4.5, mixing a carbon source material to the sol and drying the mixture. The mixture is sintered in a non-oxidizing atmosphere containing nitrogen or in a nitrogen atmosphere and finally decarbonized to obtain an aluminum nitride powder. The carbon source material is preferably a mixture of an organic carbon source material and a solid carbon powder. A predetermined amount of alpha-alumina may be added to the mixture.

Abstract: In producing zirconia powder by desiliconizing heat treatment of a mixture of zircon powder and a powdery carbon-containing material, optionally with addition of a zirconia stabilizing oxide such as calcia or yttria, in a nonoxidizing atmosphere the conversion of silica into SiO and dissipation of gaseous SiO are promoted and completed by performing the heat treatment under reduced pressure, viz. at a pressure not higher than 0.6 atm. Zirconia powder of very high purity can surely be obtained, even when a large batch of the raw material mixture is treated, by performing the reduced pressure desiliconizing heat treatment in two stages: first at 1200.degree.-1550.degree. C. until almost complete conversion of silica to SiO and then at 1550.degree.-2000.degree. C. The mole ratio of C to SiO.sub.2 in the raw material mixture must be 0.4-2.0. For further enhancement of purity, zirconia powder obtained by the desiliconizing treatment may be subjected to oxidation heat treatment.

Abstract: A hearth structure of an oxygen-bottom-blowing converter comprises hearth bricks including a number of brick row units, each of which is provided with or without one tuyere therein to eliminate thermal stresses otherwise be caused by two tuyeres included in one brick row unit. The hearth bricks preferably include at least one row of bricks not including a tuyere arranged between the brick row units. Bricks around tuyeres are unburned magnesia-carbon or magnesia-dolomite-carbon bricks including an amount of carbon 7-35%, preferably 10-30% or the most preferably 20% by weight and including magnesia or magnesia-dolomite as grains and thicknesses of refractory mortar as joints between the bricks corresponding to 0.5-2.5% of the maximum width of the bricks, thereby improving the durability of the hearth structure and hence the converter.