Individual Cell Layers Research Articles

Deflocculation of Fractionated Montmorillonite by Sodium Polyphosphates

Abstract The gel strength and viscosity of two different suspensions of fractionated montmorillonite clay were measured by using a Stormer viscosimeter and Fann V-G meter. The amount of sodium polyphosphate (sodium hexametaphosphate, sodium tetraphosphate and sodium acid pyrophosphate) adsorbed by the clay particles was determined. A relationship seems to exist between the amount of polyphosphate adsorbed and the nature of the surface, edge or plate, assumed to be the principal sites for selective adsorption. Reduction in viscosity and gel strength was found to be directly related to the adsorption. Both chemical bonding and physical adsorption seem involved in deflocculation. Some indication of the axial ratios of particles of .1- to .04-micron average size is possible through study of the adsorption mechanism. Introduction and Purpose A knowledge of surface areas of clay particles in a suspension and a precise determination of phosphate adsorption should provide a basis for a better understanding of reduction in viscosity and gel strength caused by molecularly dehydrated phosphates. The purpose of this investigation was to study the adsorption of sodium polyphosphates on suspensions of fractionated sodium montmorillonite. Although there is considerable uncertainty regarding details of the structure of montmorillonite, a generally accepted one is that suggested by Hofmann, Endell and Wilm. The structure shown in Fig. 1 is an idealized one, and Marshall has postulated that it is possible for several isomorphous replacements to occur. Thus, aluminum may replace silicon, in which case an exchangeable cation would go along with the aluminum to neutralize what would otherwise be a net negative charge on the structure. There is disagreement among various investigators as to the particle size and shape of montmorillonite clays. Marshall reported the following results for the mean lateral dimensions of a Putnam clay (montmorillonite) - 3,730 A for particles having average diameters ranging from 500 to 1,000 A, and 750 A for those with an average diameter less than 200 A. The latter particles were estimated at 50 A in thickness, which would correspond to a stack of five unit cell layers. On the other hand, Shaw has interpreted micrographs as indicating that particles of montmorillonite are readily broken down to the individual cell layers by dispersion in water.