Properties of alumina sol prepared via inorganic route

In this research, alumina sol has been synthesized via an inorganic route using inexpensive starting materials including aluminum nitride, deionized water, ammonia, and nitric acid. A clear, homogenous and stable sol was achieved which converted to a soft gel at 60 °C. The physical and microstructural properties of synthesized sol such as pH, particle size, density, solid content, phase analysis, nature of bounds, and thermal behavior were investigated. The pH of the prepared sol was in the range of 3–4, and the solid content was measured by about 6% at the temperature of 1000 °C. Utilizing the SEM micrographs, the average particle size of the dried and calcined sol at 110 °C and 1000 °C were measured less than 20 nm and 40 nm, respectively. XRD patterns of calcined sol at 200, 600, 1200, and 1400 °C revealed the formation of β-alumina (boehmite), γ-alumina, and α-alumina, respectively. Above the temperature of 1200 °C clear and sharp peaks of α-alumina appeared. Also, TG-DSC patterns confirmed the formation of β phase at 200 °C, boehmite into γ transformation at approximately 450 °C, and the alter of γ into α phase at temperatures above 1000 °C.