Maro Publications

Silicates

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From *12/10/2013  to 6/21/2012

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“A silicate (SiO44-) is a compound containing a silicon bearing anion.[citation needed] The great majority of silicates are oxides, but hexafluorosilicate ([SiF6]2−) and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other terrestrial planets, rocky moons, and asteroids. Sand, Portland cement, and thousands of minerals are examples of silicates.

Silicate compounds, including the minerals, consist of silicate anions whose charge is balanced by various cations. Myriad silicate anions can exist, and each can form compounds with many different cations. Hence this class of compounds is very large. Both minerals and synthetic materials fit in this class.

In the vast majority of silicates, including silicate minerals, the Si occupies a tetrahedral environment, being surrounded by 4 oxygen centres. In these structures, the chemical bonds to silicon conform to the octet rule. These tetrahedra sometimes occur as isolated SiO44- centres, but most commonly, the tetrahedra are joined together in various ways, such as pairs (Si2O76-) and rings (Si6O1812-). Commonly the silicate anions are chains, double chains, sheets, and three-dimensional frameworks. All such species have negligible solubility in water at normal conditions.

(Wikipedia, Silicates, 6/27/2012)

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“Polymeric materials that are reinforced with insoluble materials such as, for example, fibers or particulate materials are generally referred to as "polymer composites" or simply as "composites". In recent years, one type of composite termed a "nanocomposite" has come into widespread use. By definition, a nanocomposite has a reinforcing material that has one or more dimensions on the order of a nanometer. One type of nanocomposite has an exfoliated layered silicate as the reinforcing material wherein the layered structure is broken up and individual silicate platelets are dispersed throughout the polymeric resin.

Layered silicates are generally composed of stacked silicate platelets. The individual silicate platelets typically have a thickness on the order of about one nanometer and an aspect ratio of at least about 100. The spaces between the silicate platelets are called "gallery spaces". Under the proper conditions, the gallery spaces can be filled with a material such as, for example, a polymer. The material swells the layered silicate, increasing the distance between silicate platelets in a process termed "intercalation". If the layered silicate swells sufficiently such that at least some of the individual silicate platelets are no longer organized into stacks, those individual silicate platelets are said to be "exfoliated".

The degree to which a polymer will intercalate and/or exfoliate a particular layered silicate typically depends on the compatibility of the polymer with the layered silicate. For example, polymers having groups that are compatible with the layered silicates may intercalate and/or exfoliate layered silicates. On the other hand, some polymers such as, for example, non-polar polymers (e.g., polyethylene, polypropylene) may not readily intercalate or exfoliate layered silicates due to a lack of compatibility with the layered silicate.

Useful layered silicates include, for example, natural phyllosilicates, synthetic phyllosilicates, organically modified phyllosilicates (e.g., organoclays), and combinations thereof.

Examples of natural phyllosilicates include smectite and smectite-type clays such as montmorillonite, nontronite, bentonite, beidellite, hectorite, saponite, sauconite, fluorohectorite, stevensite, volkonskoite, magadiite, kenyaite, halloysite, hydrotalcite, and combinations thereof.

Examples of synthetic phyllosilicates include those prepared by hydrothermal processes as disclosed in U.S. Pat. No. 3,252,757 (Granquist); U.S. Pat. No. 3,666,407 (Orlemann); U.S. Pat. No. 3,671,190 (Neumann); U.S. Pat. No. 3,844,978 (Hickson); U.S. Pat. No. 3,844,979 (Hickson); U.S. Pat. No. 3,852,405 (Granquist); and U.S. Pat. No. 3,855,147 (Granquist). Many synthetic phyllosilicates are commercially available; for example, as marketed by Southern Clay Products, Inc., Gonzales, Tex., under the trade designation "LAPONITE". Examples include "LAPONITE B" (a synthetic layered fluorosilicate), "LAPONITE D" (a synthetic layered magnesium silicate), and "LAPONITE RD" (a synthetic layered silicate).

Organoclays are typically smectite or smectite-type clays produced by interacting a clay with one or more suitable intercalants. These intercalants are typically organic compounds, which may be neutral or ionic. Examples of neutral organic intercalants include polar compounds such as amides, esters, lactams, nitriles, ureas, carbonates, phosphates, phosphonates, sulfates, sulfonates, nitro compounds, and the like. Neutral organic intercalants can be monomeric, oligomeric, or polymeric, and may intercalate into the layers of the clay through hydrogen bonding without completely replacing the original charge balancing ions. Suitable ionic intercalants include cationic surfactants such as, for example, onium compounds such as ammonium (primary, secondary, tertiary, and quaternary), phosphonium, or sulfonium derivatives of aliphatic, aromatic or aliphatic amines, phosphines and sulfides. Onium compounds include, for example, quaternary ammonium ions having at least one long chain aliphatic group (e.g., octadecyl, myristyl, or oleyl) bound to the quaternary nitrogen atom. Further details concerning organoclays and methods for their preparation may be found, for example, in U.S. Pat. Nos. 4,469,639 (Thompson et al.); 6,036,765 (Farrow et al.); and 6,521,678 B1 (Chaiko).

A variety of organoclays are available from commercial sources. For example, Southern Clay Products offers various organoclays under the trade designations "CLOISITE" (derived from layered magnesium aluminum silicate) and "CLAYTONE" (derived from natural sodium bentonite) including "CLAYTONE HY", "CLAYTONE AF", "CLOISITE 6A" (modifier concentration of 140 meq/100 g), "CLOISITE 15A" (modifier concentration of 125 meq/100 g), and "CLOISITE 20A" (modifier concentration of 95 meq/100 g). Organoclays are also available commercially from Nanocor, Arlington Heights, Ill., for example, under the trade designation "NANOMER".

Typically, layered silicates exhibit a d-layer spacing that can be determined by well-known techniques such as X-ray diffraction (XRD) and/or transmission electron microscopy (TEM). According to the present invention, the d-layer spacing typically increases as intercalation between individual silicate layers by the deprotected polymer proceeds until the layers become so widely separated that they are considered exfoliated and no d-layer spacing is observable by XRD or TEM.”

[Marx, Nelson and Cernohous, US Patent 8,193,270 (6/5/2012)]

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Interested!!
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(RDC 6/5/2012)

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Roger D. Corneliussen
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Copyright 2012 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen
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* Date of latest addition; date of first entry is 6/27/2012.