Reliable Electrokinetic Characterization Procedures For Ceramic Powders
- PDF / 343,427 Bytes
- 5 Pages / 420.48 x 639 pts Page_size
- 53 Downloads / 236 Views
RELIABLE ELECTROKINETIC CHARACTERIZATION PROCEDURES FOR CERAMIC POWDERS JIUN-FANG WANG, RICHARD E. RIMAN, AND DANIEL J. SHANEFIELD Rutgers University, Department of Ceramics, P.O. Box 909, Piscataway, NJ 08855-0909 ABSTRACT Microelectrophoresis is an important method for measuring surface properties of colloidal materials. In order to obtain reliable measurements, a good reference colloid must be chosen first, and both the behavior of the reference under a variety of measurement conditions and instrumental factors must be established. Polystyrene latex has proven to be a good reference material. Time-dependent, solids-loading, and electrolyte concentration effects are determined below in order to establish reproducible referencing conditions. Using these referencing conditions, surface properties of silicon nitride as a function of aging time and atmosphere are studied. INTRODUCTION Reproducible optimized processing is desired for preparation of defect-free ceramic materials. This can be accomplished by the use of electrostatically stabilized suspensions in forming processes such as slip casting. In order to avoid particle packing defects, it is desirable to process a suspension that is free of agglomerates. Agglomerate-free or stabilized suspensions can be obtained when the surface potential, %V, is maximized (>25 mV). The surface potential can be inferred from calculation of the zeta potential, C, a measurement proportional to the electrophoretic mobility, gt. Thus, measurement of P (defined as the drift velocity divided by the applied electric field) via commercially available microelectrophoresis instrumentation can be used to indicate the optimum conditions for suspension preparation [1]. However, for many ceramic materials, the isoelectric point (IEP), the pH at which gI is zero, is reported instead [2]. From this information, it is understood that, in a suspension free of surfactants or other adsorptive impurities, the surface charge is positive below and negative above the IEP. A common problem encountered in consulting the ceramic colloids literature is the wide range of variability of IEP data for a given material [3]. This variation can be attributed to powder preparation techniques, sample history, suspension preparation methods, and/or equipment used to make the measurement. For silicon nitride powders, for instance, the IEP can range from 3 to 9 depending on the manufacturer and the atmospheric conditions under which it is stored [4]. In addition, microelectrophoresis can be performed with many types of instruments that vary mostly in the manner in which the drift velocity is measured. The relative contribution of this factor to variations in IEP data has not been assessed. Many of the above problems could be solved if a universal reference colloid were selected for calibrating instruments prior to measurement of sample gt and a standard procedure were developed for sample preparation and gt measurement. A good reference colloid should exhibit (a) little sedimentation and agglomeration over the course
Data Loading...
