Magnesium silicate, hydrated, from

A second class of silicate mineral called asbestos is a serpentine mineral, chrysotile. It is a magnesium silicate hydrate, Mg6[Si40n(0H)6]H20, with a chemical composition similar to talc, Mg3Si40io(OH)2. There is at least a plausible argument that chrysotile should not have been included with other minerals named asbestos from chemical, health, and legal considerations. There is small doubt that the amphiboles are much more likely to cause difficulties. A study of two cement pipe plants in New Orleans revealed some interesting results. In one... 

Soapstone - A soft powder or stone, basically hydrated magnesium silicate, having a soapy feel, used to dust the surface of un-vulcanized rubber compounds to keep them from sticking together. Similar to talc. 

Magnesium trisilicate hydrate (Mg2Si30s xH20, CAS No. 39365-87-2) is constituted of magnesium oxide and silicon dioxide with varying proportions of water. It should contain not less than 20% of magnesium oxide and not less than 45% of silicon dioxide and can be prepared from sodium silicate and magnesium sulfate. It also occurs in nature as the minerals meerschaum, parasepiolite, and sepiolite. 

Hydrated magnesium silicate (Talc, 3Mg0 4Si02 H20, CAS No. 14807-96-6) is a magnesium silicate commonly referred to as "soapstone". It is obtained from natural sources and may contain a small amount of aluminum silicate. It is composed of MgO (31.7%), Si02 (63.5%), and H2O (4.8%). It is a crystalline nonhygroscopic, odorless, tasteless powder which is practically insoluble in water, dilute mineral acids, dilute solutions of alkali halides, and alkaline hydroxides but is soluble in hot concentrated sulfuric acid. 

Inorganic colorants listed in 21CFR 178.3297 include aluminum, aluminum hydrate, potassium silicate, aluminum silicate, barium sulfate, bentonite, calcium carbonate, calcium silicate, calcium sulfate, carbon black (channel process, prepared by the impingement process from stripped natural gas), chromium oxide green Cr203, cobalt aluminate (with restrictions), diatomaceous earth, iron oxides, kaolin (modified for use in olefin polymers in amounts up to 40%), magnesium oxides, magnesium silicate (talc), sienna, silica, titanium dioxide, titanium dioxide-barium sulfate, ultramarines, zinc carbonate (limited use), zinc chromate (less than 10%), zinc oxide (limited use), and zinc sulfide (less than 10%). 

Thus, water can be stored in silicates and liberated by heating of hydrated silicates. This group of metamorphic rocks includes serpentine (Mg,Fe)3Si205 (OH)4 and tremolite Ca2Mg5Si8022 (OH)2. Serpentine, a basic orthosilicate, is a very common secondary mineral, resulting from a hot water alteration of magnesium silicates (mostly peridotite), present in magma, a process termed serpentinization ... 

Examples of inert or extender fillers include china clay (kaolin), talc, and calcium carbonate. Calcinm carbonate is an important filler, with a particle size of about 1 pm. It is a natural product from sedimentary rocks and is separated into chalk, limestone, and marble. In some cases, the calcium carbonate may be treated to improve interaction with the thermoplastic. Glass spheres are also used as thermoplastic fillers. They may be either solid or hollow, depending on the particular application. Talc is a filler with a lamellar particle shape. It is a namral, hydrated magnesium silicate with good slip properties. Kaolin and mica are also natural materials with lamellar structures. Other fillers include woUastonite, silica, barium sulfate, and metal powders. Carbon black is used as a filler primarily in the rnbber industry, but it also finds application in thermoplastics for conductivity, for UV protection, and as a pigment. Fillers in fiber form are often used in thermoplastics. Types of fibers inclnde cotton, wood flour, fiberglass, and carbon. Table 1.3 shows the fillers and their forms. An overview of some typical fillers and their effect on properties is shown in Table 1.4. Considerable research interest exists for the incorporation of nanoscale fillers into polymers. This aspect will be discussed in later chapters. 

Calcium carbonate is an important filler with a particle size of about 1 p,m. It is a natural product from sedimentary rocks and is separated into chalk, limestone, and marble. In some cases the calcium carbonate may be treated to improve the bonding with the thermoplastic. Glass spheres are also used as thermoplastic fillers. They may be either solid or hollow, depending on the particular application. Talc is an important filler with a lamellar particle shape. It is a natural hydrated magnesium silicate with good slip properties. Kaolin and mica are also natural materials with lamellar stracture. Carbon black is used as a filler primarily in the rubber industry. 

The most frequently available chrysotile asbestos is the fibrous form of serpentine 3Mg0-2Si02 2H20 - hydrated magnesium silicate. The fibres are thin their diameter varies from 0.012 up to 0.03 pm. The fibre length is normally 5 mm, rarely reaching 40 or even 100 mm and there is an empty channel inside a fibre (Hannant 1978). The asbestos fibres are considered as microfibres. 

Talc is the name given to hydrated magnesium silicate, which has the theoretical formula 3Mg0-4Si02 H20 and it occurs in several ores from which talc products can be made. The form of most use in plastic formulations is finely ground talc, which consists of thin platelets. It is considered to be a reinforcing filler in many compound applications, although it can also be described as an extender because of its low cost. 

Kaolin is a naturally occurring hydrated magnesium aluminum silicate (attapulgite), and pectin is an indigestible carbohydrate derived from apples. Both appear to act as absorbents of bacterial toxins and fluid, thereby decreasing stool liquidity and number. They may be useful in acute diarrhea but are seldom used on a chronic basis. A common nonprescription preparation is Kaopectate. The usual dosage is 1.2-1.5 g after each loose bowel movement (maximum 9 g/d). Kaolin-pectin formulations are not absorbed and have no significant adverse effects except constipation. They should not be taken within 2 hours of other medications (which they may bind). 

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