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Preparation and characterization of whisker and particulate SiC-AI2 O3 ceramic composites
This work involves the preparation and the characterization of SiC particulate-Alz03 and SiC whisker- Alz03 ceramic composites. A new technique was used in order to increase the density of composite. Fine Alz03 and SiC whiskers and particulates were used as a matrix and secondary phase, respectively. Whiskers and particulate were coated with Al-S04-OH precursor by precipitation using urea. In this method, it was important to keep the alumina hydrate in the noncrystalline state at 5.5>pH>8.6. The alumina- hydrate compound was separated from SiC whiskers and particulates when the reaction was continued at high pH (pH>8.7) causing the crystallization of alumina precursor. Alumina hydrate coated SiC whiskers and particulate were used as the starting material for the preparation of SiCw/p reinforced Alz03. Die pressing was used as the most appropriate and cheapest consolidation technique of composite materials. Upon sintering Al-S04OH on the SiC transformed into Alz03 by providing empty spaces for matrix densification in the proposed technique ( shrink- fit idea). Green bodies with SiC whisker and particulate contents in the range of 10 to 40 vol.% were sintered at 14500C for 2h under atmospheric conditions. The densities of sintered composites were measured by using Archimedes method. The density of composites containing 10%, 20%, 30% and 40 vol.% coated SiC particulate and whisker composites changed from 81% to 70% of theoretical density and from 79% to 75% of theoretical density, respectively. The density of coated composites were -22% greater than that of the uncoated composites .The thermal behavior of Al-S04-OH on the SiC was characterized by using TGA, DTA. TGA curves showed that materials are hydrated and dehydroxylization was observed between -700 and 800°C. TGA and DTA curves indicated that desulfurization then occurred at about -950°C. Chemical characterization of the coated SiC whiskers and particulates were obtained by using FTIR spectrometer.The hardness of these composites were measured by usmg Vickers Microhardness Testing Device. Vickers microhardness of the 20vol.% and 30vol.% coated SiCp ,and 20vol.% and 40 vol.% SiCw-Alz03 composites were measured as 10.71, 12.94, 10.89 and 5,96 GPa, respectively and compared with the mechanical properties of the composites manufactured by the conventional methods.