Preparation and properties of β-SiAloN/ZrN nano-composites from ZrO2-coated Si3N4 powder

Abstract

In this study we report on the preparation and properties of ?-SiAlON/ZrN electro-conductive nano-composites from ZrO2-coated Si3N4 powder. The silicon nitride powder was coated with nano-sized zirconia particles by the precipitation of ZrO2 from a zirconium acetate solution using urea as the precipitating agent. For the preparation of sintered ?-SiAlON/ZrN composites two different approaches were used. In the first one the ZrO2-coated Si3N4 powder was mixed with the appropriate sintering additives (Al2O3, Y2O3 and AlN) and reaction sintered, while in the second approach the coated powder was first calcined at 1600?C to prepare ZrN coated Si3N4 powder that was subsequently mixed with the sintering additives and sintered. For comparison, composites with the same composition were also prepared by mixing Si3N4 and ZrO2 powders with sintering additives and sintered. During the thermal treatment and/or sintering of the Si3N4/ZrO2/AlN powder mixtures zirconia reacts with silicon nitride and aluminium nitride to form zirconium nitride. However, during sintering the agglomeration and grain growth of small, nanometric ZrN particles occurs. Despite the fact that the samples were sintered at atmospheric pressure they are dense, have relatively good flexural strengths and are electrically conductive.