Effects of alumina sols on the sintering of alpha-alumina ceramics

The effects of two kinds of alumina sols on the densification behavior of sub-micron grain sized alpha-alumina ceramics have been investigated. Composition of the sol-derived gels was investigated by energy dispersive spectra and Fourier transform infrared spectra. Structural evolution of the gels at different temperatures was characterized by a combination of X-ray diffraction and Al-27 magic angle spinning nuclear magnetic resonance spectroscopy. Results showed that the gel containing chlorine and carbon transformed to alpha-alumina at about 950 degrees C, significantly lower than the other gel which transformed at about 1050 degrees C. Density measurements and scanning electron microscopy analyses were used to investigate the sintering of alumina ceramics with or without alumina sols. It was found that the alumina sols had profound effects on the densification of alumina ceramics. The ceramic displayed the best densification behavior when the sol containing chlorine and carbon was added.