PHYSICOCHEMICAL PROPERTIES AND STRUCTURAL ASPECTS OF ALUMINUM HYDROXYCARBONATE GELS
Abstract
The physicochemical properties and structural aspects of aluminum hydroxycarbonate gels were studied. Aluminum hydroxycarbonate gels with different carbonate contents were produced by (1) constant pH precipitations, and by removing the carbonate from commercial aluminum hydroxycarbonate gels by (2) acid addition and (3) purging with nitrogen. These gels were used to study the influence of carbonate upon the zero point of charge of aluminum hydroxycarbonate materials. The constant pH precipitation process and the physicochemical properties and structural aspects of the gels produced by this method were examined. It was postulated that the carbonate of aluminum hydroxycarbonate materials is coordinated by a single bond onto edge aluminum ions by reversible specific adsorption. In general, there was an approximately linear, negative correlation between the zero point of charge and the carbonate content of aluminum hydroxycarbonate gels. Aluminum hydroxycarbonate gels can be mechanical mixtures of particles in various electrochemical states. The nature of the electrochemical forces operative among the particles will greatly affect the gels' rheological and adsorptive properties. An aluminum hydroxycarbonate gel was produced with good acid reactivity and low viscosity (pourable) at concentrations double those that are presently used commercially in the U.S.A. The aluminum hydroxycarbonate gels produced by the constant pH precipitation process were characterized by the following physicochemical properties: structure, composition (carbonate, sodium, chloride, aluminum), electrochemical properties (zero point of charge, gel pH, surface potential), acid reactivity, physicochemical stability, particle size, rheological properties, and cation exchange. A theoretical description of the constant pH precipitation process which explains the experimentally observed physicochemical properties was developed. The pH-stat titrigrams of the aluminum hydroxycarbonate gels were interpreted in terms of the three physicochemical processes that can occur during the titration: proton loading, disaggregation (peptization), and dissolution. The removal of sodium ions from an aluminum hydroxycarbonate gel during the washing procedure was facilitated by exchange with magnesium ions. The magnesium exchange of the gel lowered the sodium content and retarded the loss of acid reactivity.
Degree
Ph.D.
Subject Area
Pharmacology
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.