Papers by Keyword: Aqueous Processing

Abstract: For the production of ceramics containing AlN as a major or minor constituent it is necessary to avoid hydrolysis. To do that, non-aqueous powder processing is required or waterresistant AlN powders must be used. Alternatively, as in the Hydrolysis Assisted Solidification (HAS) process, which exploits the hydrolysis of the AlN for the solidification of the ceramic suspensions, the hydrolysis has to be prevented at room temperature but initiated at elevated temperatures. In this work a systematic study of AlN powder reactivity in water and other aqueous environments is presented. The AlN hydrolysis was investigated by measuring the pH of diluted suspensions and by analysis of the reaction products. The results indicate possible solutions for control of the reaction with water in order to exploit it or to prevent it to enable aqueous AlN powder processing.

Abstract: In this work, two different consolidation techniques were used to obtain AlN samples: slip casting and dry pressing of granules obtained from aqueous suspensions by freeze granulation. The green samples were sintered at a temperature (1750°C) lower than those usually used (>1800°C), using CaF2 and YF3 as sintering aids. The microstructural features were analysed by scanning electron microscopy (SEM) and the crystalline phases formed were identified by X-ray (XRD). Full dense AlN-based ceramics were obtained from both consolidation techniques; however the thermal conductivity values were quite different. The presence of carbon in the samples derived from the freeze granulated powder containing organic processing additives de-waxed in an inert atmosphere revealed to be helpful in the cleaning of oxygen present at the grain boundaries and consequently, for enhancing the thermal conductivity.