Synthesis of β-sialon from coals or natural graphite

Abstract

The synthesis of β-sialon has been carried out by heat treatment in nitrogen flow of Spanish coals or mineral graphite, both with a high content of mineral matter. The results were compared with those obtained with conventional clay/carbon mixtures. The coals and, especially, the mineral graphite produced a very high yield of β-sialon, with a faster reaction rate than the clay/carbon mixtures due to the more intimate contact among the reactants, with the additional advantage of forming much a lower proportion of vitreous phases. On the other hand, the results show that in the particular case of graphite, the use of high temperatures (even above 1450 °C) does not lead to changes in the crystalline phases of the product, allowing the synthesis to be carried out over a wider temperature range than that used for clay/carbon mixtures. The mechanical properties of the sintered artifacts obtained with the sialon synthesized from natural graphite are superior to those prepared from clay/carbon mixtures and comparable (or even superior) to commercial artifacts manufactured from much more expensive precursors.