چكيده به لاتين
Alpha-phase aluminum oxide, also known as corundum, is one of the most widely used materials in various industries, usually obtained from aluminum hydroxide calcination at temperatures above 1200 °C. With high energy consumption over hours because of calcination step has been an issue and increasing the particle size of the product through this heat is another problem. In this study, seeding, sonication, and microwave techniques were used to overcome these problems, while the behavior of aluminum hydroxide was first investigated by controlling three parameters of precipitation synthesis which are temperature, pH and aging time to maximize the growth of aluminum hydroxide crystals. X-ray diffraction was used to analyze the precipitation of aluminum hydroxide. Seeding technique using nanoparticles of corundum and then sonication after the formation of the precipitate gel were applied. Under microwave waves, the produced precipitate was dried to study the simultaneous effect of these three techniques on reducing calcination temperature. X-ray diffraction and field emission scanning electron microscopy were used to evaluate the results. Simultaneous increase in the temperature, pH and aging time leaded in an increase in the aluminum hydroxide crystallinity and the formation of bohemite phase. Aluminum hydroxide synthesis conditions were assumed to be 85 °C, neutral pH and 24 h of aging. The seeding alone did not significantly decrease the calcination temperature, while with ultrasonication, alpha phase alumina nanoparticles formed at 950 °C. On the other hand, the microwaves slightly increased the calcination temperature and were somehow effective about particle morphology. Evaporation of the residual of aluminum hydroxide synthesis process also resulted in the production of ammonium chloride as by-product.
