George Y. Onoda

An electrophoretic study of calcium oxalate monohydrate

Abstract The electrophoretic behavior of calcium oxalate monohydrate was analyzed in terms of a simple double-layer model. The experimental results with a variety of electrolytes could be described nearly quantitatively with the Nernst-Gouy-Stern double-layer model if reasonable values were chosen for the adjustable parameters. Specific adsorption of ions was analyzed in relation to their location in the double layer and to the strength of the adsorption bonds.

A comparative appraisal of adsorption of citrate on whewellite seed crystals

Abstract Adsorption of citrate by whewellite was examined with three different techniques: solution depletion, seeded crystal growth inhibition, and microelectrophoresis (zeta potential). Comparison of the results from the three techniques indicates that at the concentrations giving 50% coverage or 50% inhibition, there was reasonable agreement if the adsorbate was assumed to be trivalent citrate.

Streaming potential and noncreeping flow in porous beds

Abstract An experimental investigation of flow rate versus flow pressure relationships shows that a transition from creeping (linear) to noncreeping (nonlinear) flow may occur in some streaming potential experiments on porous beds. Thus, the effect of this transition on streaming potentials of porous beds was studied. It was found that the transition does not cause the streaming potential versus flow pressure curves to deviate from linearity or from intersecting with the origin. Therefore, the use of Smoluchowskis equation is as valid for noncreeping flow conditions as for creeping flow conditions for calculating ζ potentials from streaming potential data. Electrode polarization effects in streaming potential experiments on porous beds are considered. An R-C circuit is used to null out these effects in order to record accurately the true streaming potential values. Finally, a simple cell design and solution flow system is described which allows investigation of flow rate versus flow pressure relationships.

Packing and Sintering Relations for Binary Powders

Mixtures of coarse and fine powders are commonly used for processing refractory bodies. Compared with uniform fine powders, mixtures have higher green densities and less shrinkage when fired. The presence of coarse particles can provide a control for achieving fired bodies with a specific level of porosity. As a filler, the coarse particles may also reduce the cost of the raw material. A major disadvantage of mixtures is the limited strength of the fired body because of the large grains in the microstructure.

An Analysis of Citrate Adsorption on Whewellite

Adsorption at the whewellite-solution interface is important in urolithiasis because it affects rates of crystal growth and aggregation. Adsorption may also affect nucleation and apparent solubility (1). A number of substances in urine are adsorbed on whewellite and affect its growth and aggregation kinetics, so the adsorption process must be understood if we are to understand the kinetics of urolithiasis. It will be shown that Langmuir adsorption theory is not adequate to explain citrate adsorption on whewellite when conditions of pH and calcium ion activity are varied. Consideration of the electric double layer of whewellite in aqueous suspension yields an improved but not perfect description of citrate adsorption on whewellite under these conditions.

Interaction Energies in the Coagulation of Calcium Oxalate Monohydrate

In the present work, Gregorys approximation was used to calculate the Hamaker constant (A131) for the van der Waals interactions between calcium oxalate monohydrate (COM) particles in water. An average value of 1.135 (+/- 0.341) x 10(-20) J for A131 was calculated for COM particles at 37 degrees C in aqueous solutions. Theoretical calculations predicting coagulation behavior based on the calculated A131 are consistent with experimental data.

The Electrical Double Layer at Calcium Oxalate-Water Interfaces

Crystal growth inhibition and aggregation (coagulation) of calcium oxalate monohydrate crystallites are phenomena of interest in the physical chemistry of stone formation. These phenomena are affected by the presence of adsorbed species at the solid-aqueous phase interface. Inhibitors function by adsorbing at the growing interface. Aggregation tendencies depend on the forces of interaction between particles which are modified by the adsorption of ionic species. Because of the importance of interfacial processes, a study was carried out with calcium oxalate in aqueous suspensions to define better the role of various ionic species in solution. The electrophoretic mobility was used as a measure of the electric potential (zeta potential) near the particle surface. Variations in zeta potential were determined as a function of calcium/oxalate ion activities, pH, and the activities of multivalent ions which are known to function as crystal growth inhibitors.