A modified sol-gel process was developed and used to prepare a-Al2O3. Details of this process have been reported previously. In this process, gels are obtained by keeping higher concentration of starting solution. DTA of dried gel shows the presence of aluminium hydroxide and aluminium sulphate but both are amorphous in nature, revealing materials in the collodial state. After calcination of gels at 1250 degrees C for 1 h, a-aluminia powder is formed, which has particle size distribution in the range of 100-200 nm. Sintering behaviour shows that nearly 99% of theoretical density is obtained at 1600 degrees C for 3h of holding time in the uniaxially pressed samples. Alpha alumina bar samples have hardness values and elastic constants close to the theoretical values, which enable them to possess good fracture strength and fracture toughness. The material also resists crack propagation, and fracture toughness increases with the increase in initial crack size. Densification of powder, morphology and mechanical properties obtained are similar to alumina as reported by international standard organization (ISO 6474 and ISO/TC150/SC1).
