Chemical resistance silicones

Chemical Resistance. Silicon nitride is resistant to oxidation up to 1350°C. It is resistant to most reagents at room temperature. 

Heat and Chemical Resistant Silicone Rubber. Silicones 2. Organic Silicon Chemistry. ChemCases.com Kennesaw State University. http //www.chemcases.com/silicon/sil2cone.htm (accessed on October 26, 2005). 

Paints made from silicone modified resins have excellent weatherability, with good chemical resistance. Silicone copolymers can withstand most severe weather conditions. They are extensively used for coating of steel coils. 

In general, polysulfide sealants resist attack from fuels and water and have good chemical resistance. Polyurethane sealants are especially resistant to alkali exposure. Polyurethane, acrylic, and polychloroprene (neoprene) are all moisture resistant. Both polychloroprene and butyl rubber sealants have good general chemical resistance. Silicones, although expensive, are often the sealant of choice, because they are strongly resistant to moisture and all chemicals. Silicones are also the most resistant sealants to UV and solar radiation. 

Modified alkyd resins In this group one finds styrenated alkyds, vinyl toluenated alkyds, oil-modified vinyl resins, acrylic alkyds, silicone alkyds and polyurethane alkyds. The modifying component usually has a number of effects. It always increases the molecular weight of the alkyd polymer, and may impart hardness, durability, or chemical resistance. It also affects the solubility of the polymer in solvents. 

Silicone polymers having high heat stability and excellent chemical resistance are available. They are very expensive and hence are not commonly found in paint coatings. 

Silicone They have excellent heat resistance up to 260°C (500°F), chemical resistance, good electricals, compatible with human body tissues, etc. and a high cost. There are the room temperature vulcanizing (RTV) types that cure and cross-link at ambient temperatures, catalyzed by moisture in the air. It is a good sealant and excellent for making flexible molds for casting. It is widely used for human implants. 

Beta SiC (PSiC) has good chemical resistance, particularly to oxidation owing to the formation of a thin adherent and protective film of silicon dioxide on the surface. Its characteristics are summarized in Table 9.6. 

The nitrides reviewed here are those which are commonly produced by CVD. They are similar in many respects to the carbides reviewed in Ch. 9. They are hard and wear-resistant and have high melting points and good chemical resistance. They include several of the refractory-metal (interstitial) nitrides and three covalent nitrides those of aluminum, boron, and silicon. Most are important industrial materials and have a number of major applications in cutting and grinding tools, wear surfaces, semiconductors, and others. Their development is proceeding at a rapid pace and CVD is a major factor in their growth. 

The market for silicon nitride is fast growing, particularly in structural and chemical resistance applications and as a thin film in semiconductor devices.P 1... 

An older process to form silicides is siliconizing which is a relatively simple CVD process used to provide oxidation and chemical resistance to refractory metals. The siliconizing reaction uses the substrate itself, (such as Mo or Ti), as the metal source. Silicon diffuses readily in... 

The use of silicone elastomers for high-voltage applications (insulators and cable accessories) requires special formulations. Unusually, stringent requirements for these materials must be met.509,510 Fluorosilicone rubbers, which offer some unique combinations of properties (e.g., chemical resistance and higher temperature stability), have attracted considerable attention and have been reviewed in recent publications.511,512 It was noted that a modification of perfluoroether elastomers with silicone elastomer via hydrosilylation reaction opens the possibility of novel applications.5... 

Current interest in saturated Si-N rings stems primarily from the industrial uses of silicon nitride (and related materials), which is a hard, chemically resistant insulator, and as precursors to silicon-nitrogen polymers (poly-silazanes). The formation and precursor chemistry of these polymers are discussed in Section 10.3.3. 

In general, polycarbonate resins have fair chemical resistance to aqueous solutions of acids or bases, as well as to fats and oils. Chemical attack by amines or ammonium hydroxide occurs, however, and aliphatic and aromatic hydrocarbons promote crazing of stressed molded samples. For these reasons, care must be exercised in the choice of solvents for painting and coating operations. For sheet applications, polycarbonate is commonly coated with a silicone—silicate hardcoat which provides abrasion resistance as well as increased solvent resistance. Coated films are also available. 

Some typical elastomers are natural rubber, which is gathered from trees, SBR rubber, which is used a lot in motorcar tires, neoprene, as in wet suits and oil seals, EPDM, a general purpose rubber, butyl, a heat-resistant rubber with the ability to keep the air in car tires, nitrile for oil seals, silicones for heat resistance, fluoro-elastomers for chemical resistance, and last but not least, polyurethanes, which cover a number of the above fields. Table 1.1 shows some of the advantages of castable polyurethanes over conventional rubbers. 

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