Silicate melt formulations

This quasi-lattice formulation of fused salts is known as Temkin s equation. Its application to silicate melts was provided by Richardson (1956), but it is inadequate for the compositional complexity of natural melts, mainly because, in a compositionally complex melt, the types of anions and consequently the entity of the anion matrix vary in a complicated way with composition. 

It can be assumed that the course of the above relationships will also be similar in the Me0-Si02 systems. On the basis of the above facts, the structure of the Me0-Si02 melts can be imagined as a lattice of Si04 tetrahedrons polymerized to a certain degree, where cations are situated in the free spaces between the tetrahedrons. This concept was used by Panek and Dandk (1977) to formulate the thermodynamic model of silicate melts. 

The data which are required, but which are lacking, for a rigorous formulation of the activities of components in natural silicate melts are enthalpies and partial molar enthalpies. Because of this deficiency, it has been assumed that to a first approximation silicate liquids can be adequately treated as S3nranetric, regular solutions (Thompson, 1967). This model has... 

Use of internal mixers offers a direct and environment friendly technique for preparation of nanocomposites. A two-step mixing in an internal mixer followed by addition of curative on a two roll mill for preparation of elastomer-layered silicate nanocomposites [51]. In the study on the effect of processing conditions (mixer type, mixing temperature) and formulations on the properties of EPDM nanocomposites, it has been shown that open two roll mill mixing results in inadequate dispersion of the nanofiller in the elastomer matrix compared to compounding in an internal mixer. Melt compounding with layered silicates has been reported for NR [52], ENR [46], SBR [53], NBR [54], EPDM [55] and PU [56] systems. 

Even after organic modification of the clays, polypropylene does not wet the surface of clays because it is nonpolar. It is necessary to blend in a functionalized polymer such as maleated polypropylene (PP-g-MA) that wets the modified clay surface more readily and is also miscible with the bulk polymer. Okada and coworkers were the first to produce polypropylene layered silicate nanocomposites by melt compounding the modified elay with PP-g-MA and PP. The progress made since then in preparing and characterizing polypropylene layered silicate nanocomposites is reviewed in this chapter. We discuss advances in formulations, preparation methods and characterization then proceed to effects of the dispersion state (intercalated vs. exfoliated) and of silicate loading on crystallinity, mechanical performance and other properties, and end with a summary of progress to date with these composites. All the results presented in this chapter refer to isotactic polypropylene nanocomposites with layered or smectite clays. 

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