Nano-alumina by gel combustion, its thermal characterization and slurry-based coating on stainless steel surface (Conference Paper)

摘要

Gel combustion method was used to prepare nano-alumina from aluminum nitrate and stoichiometric amount of glycine as fuel. The TG-DTA pattern of the as-prepared powder (combustion product) exhibited exotherms with peaks around 500 and 900 C accompanied with loss of weight of 25 and 5 % attributed to burning away of carbon left behind and decomposition of residual reaction intermediates left behind, respectively. Even though mass stability is attained above 900 C, the DTA exhibited an exotherm around 1,150 C attributed to transformation of gamma to alpha form of alumina. The XRD studies revealed that the powder heated to 900 C was chemically pure nano-crystalline alumina while that heated above 1,150 C was crystalline alpha form. As nano-crystalline powders are sinter-active, the nano-crystalline alumina formed by calcination at 900 C was used to form the coating. A morphological feature of the agglomerates of nano-alumina powders were evaluated using SEM. The powder was de-agglomerated by wet grinding method. The dispersion conditions to form slurry using 900 C calcined powder for slurry-based coating was optimized using zeta-potential studies, and it was found to exhibit a maximum value of -45 mV at a pH of 9. After 8 h of grinding, the median agglomerate size reduced to 2 μm. Rheological studies exhibited desired pseudoplastic behavior in the range of 10-20 vol.% of solid while the slurry with 15 vol.% only form crack free, dense, and adherent coating after heat treatment at 1,150 C. The morphology of the coating was found to be uniform and dense.