A study of the physical and chemical stability of spray dried aluminum hydroxycarbonate and of drying methods for aluminum hydroxycarbonate gel: Part I. The physical and chemical stability of spray dried aluminum hydroxycarbonate gel. Part II. Drying methods for aluminum hydroxycarbonate gel.

摘要

art I. The physical and chemical stability of spray dried aluminum hydroxycarbonate gel. The physical and chemical stability of amorphous spray dried aluminum hydroxycarbonate gel (SDAHC) was studied at five relative humidities: 0%, 11%, 54%, 84%, and 100%. The moisture content of the SDAHC directly related to the relative humidity. The samples with the highest moisture content showed the greatest changes in physical and chemical properties.;At 84% and 100% relative humidity the X-ray amorphous SDAHC was transformed to a poorly ordered boehmite which dissolved and reprecipitated to form the aluminum hydroxide polymorph bayerite. The moisture content at the surface created an alkaline pH environment that favored bayerite formation. At 100% relative humidity an increase in surface area was seen due to the formation of a large amount of boehmite. Once bayerite formed the surface area decreased. At 84% relative humidity the surface area decreased with the formation of bayerite. A reduction in the rate of acid neutralization accompanied the formation of bayerite at both 84% and 100% relative humidity.;At 0%, 11%, and 54% relative humidity SDAHC remained amorphous. As the moisture content increased in the powder there was a decrease in the surface area and the rate of acid neutralization. This is believed to be due to an increase in the physical aggregation and/or cementation between SDAHC particles.;Part II. Drying methods for aluminum hydroxycarbonate gel. Aluminum hydroxycarbonate gel was rinsed with water or ethanol from one to five times and dried at 25, 50 or