Clay products particles

The morphology of weathered feldspar surfaces, and the nature of the clay products, contradicts the protective-surface-layer hypothesis. The presence of etch pits implies a surface-controlled reaction, rather than a diffusion (transport) controlled reaction. Furthermore, the clay coating could not be "protective" in the sense of limiting diffusion. Finally, Holdren and Berner (11) demonstrated that so-called "parabolic kinetics" of feldspar dissolution were largely due to enhanced dissolution of fine particles. None of these findings, however, addressed the question of the apparent non-stoichiometric release of alkalis, alkaline earths, silica, and aluminum. This question has been approached both directly (e.g., XPS) and indirectly (e.g., material balance from solution data). 

Compatibility The particles must be compatible with the polymeric substrate. Since natural clays are alumino-silicates, they must be prepared or functionalized so that they will be compatible with a polymer. For natural clay products, this process can be quite complex, given the wide chemical variability of different samples, even from the same mine. 

FIG. 5.19 Schematic of the wetting and delamination of inorganic clay particles. (Supplied by and used with the permission of Southern Clay Products.)... 

A confirmed the presence of unintercalated Na -montmorillonite. Nevertheless, surface area measurements and subsequent neutron scattering studies [5] of the silica sol - clay products were indicative of the formation of composite structures in which the sol particles bind to the basal surfaces of the clay aggregates and become stabilized against particle growth through Oswald ripening. 

A popular filler in the SMPC world is Cloisite 30B. In the MMT clay manufactured by Southern Clay Products, the particle size distribution is such that 90% of the particles (dry weight) are of less than 13 pm diameter, while 50% of the particles are less than 6 pm and 10% are less than 2 pm [68], This breakdown makes Cloisite in some sense a nanoclay, but in reality still a microclay. TEM images presented by Schulz et al. [68] did indicate 500 nm particles in Cloisite 30B. Cloisite 30B is, however, comprised of platelets that are approximately 120 nm in diameter and as small as 3 nm thick [69]. Under the correct pre-processing conditions, these platelets can be incorporated into polymer networks to varying degrees of uniformity and success at very different size scales. 

Fig. 9.1 Kaoline particle size, particle size distributions of clay products commonly used for paper filling and coating.

Every ceramic formation process uses binders to hold the system together, to hold the ceramic particles in relative position to each other. Clays use the organic material inherent in the natural clay product. Some casting formulations take advantage of electrostatic forces, van der Waals attractive forces, etc. Some use very stiff binders to retain shape, like polyacrylic disper-sant/binders in slip casting. Some use binders that are mushy when wet but harden during drying. 

The performance of clay-based construction products, e.g., bricks and roofing tiles, can be monitored using thermal methods. The types of raw materials, viz., clay and accessory minerals, and their reactions that occur during the firing process and the durability of clay products can be examined through the application of DTA, TG, TMA, and dilatometric methods. This is particularly important for quality control as physical and chemical behaviors are dependent on the raw material characteristics, e.g., composition, particle size, and morphology. 

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