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
Abstract
Part 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 $80\sp\circ$C. The filter cake contained less moisture following rinsing with ethanol than rinsing with water. The CO$\sb3$:Al ratio dropped after one ethanol rinse and remained relatively constant for all further rinses. When rinsed with water the CO$\sb3$:Al ratio in the filter cake decreased as the number of rinses increased. All samples were X-ray amorphous following drying. Samples rinsed in ethanol had a much greater rate of acid neutralization than samples rinsed the same number of times with water and dried at the same temperature. The greater reactivity was attributed to the larger surface area seen in the ethanol rinsed samples.
Degree
Ph.D.
Advisors
Peck, Purdue University.
Subject Area
Pharmacology|Pharmaceuticals|Mineralogy
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