Effect of Aging on Electrophoretic Behavior of Sol-Gel Derived Aluminas
- PDF / 330,796 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 67 Downloads / 126 Views
EFFECT OF AGING ON ELECTROPHORETIC BEHAVIOR OF SOL-GEL DERIVED ALUMINAS Burtrand I. Lee and Larry L. Hench Ceramics Division, Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 ABSTRACT Sample alumina powder prepared with the 3 procedures described by Yoldas [1,2] was suspended in 10- M NaCl and contained in precleaned polypropylene cups with air tight lids. Electrophoretic mobilities of the samples were measured at various pH's using a microelectrophoretic technique. The points of zero charge (PZC) were determined from plots of electrophoretic mobility vs pH of the sample suspensions. The initial values of PZC are 10.6 for y-A1 2 03 and 8.3 for a-A10 3 , T~e corresponding BET surface areas are 206 m27gand 3m /g respectively. Upon aging, the PZC decreased in 2 days and then increased by reaching maximum values of 10.4 for y-A1 2 0 3 and 8.8 for a-A1 2 0 3 in 20 days. Aging of sol-gel derived aluminas and commercial alumina derived by precipitation are compared and differences are discussed. INTRODUCTION Sol-gel methods have been developed [1-41 for the preparation of various phases of alumina which are otherwise difficult to obtain using traditional methods. The alumina sol-gel method is different from traditional methods in several important aspects which may affect the structure of alumina; 1) homogeneity at the molecular level, 2) a possibility of ultimately pure alumina, and 3) low temperature chemical reactions and mixing. Because of these differences, the electrokinetic properties of sol-gel derived alumina may also be different from the properties of alumina prepared by traditional methods. The electrokinetic properties of sol-gel derived aluminas yield important information concerning the surface characteristics of the alumina in a liquid environment. A knowledge of the latter is necessary for scientific control of alumina in dispersions and in producing ceramic composite microstructures. Catone and Matijevic [5] prepared spherical particles of monodispersed aluminum hydrous oxide sol by hydrolysis of Al(OC 4 H ) 3 in aqueous sulfate solution. They showed that the electrophoretic mobirity (EM) at a given S04- concentration increased in a positive direction with aging time in 20 hrs., then the EM decreased up to 30 hrs. of aging at 99°C. No explanations were given for these fluctuations of EM but they suggested that the particle composition may be different than that of sols made from inorganic salt solutions. It is well known that the PZC of metal oxides varies depending on degree of surface hydration, [6,7,14-17] and the method of preparation. Consequently, one of our objectives is to compare the effects of sol-gel vs precipitation methods of preparing alumina on the PZC of the powders. There has been much effort to understand the factors affecting the time dependent variations of PZC of metal oxides, the so called aging effect [7-19]. These studies have shown that aging phenomena of metal oxides can be divided into three general categories: 1) phenomena invo
Data Loading...
