Salts chemical resistance

As a rule, the most widespread liquid environments are water solutions of acids, alkalis, and salts. Chemical resistance of RubCon was specified as a change in weight and compressive strength of the samples after their exposure to aggressive liquid environments during a certain period of time. The choice of aggressive environment compositions was based on their prevalence in industrial production. 

Chemical Resistance. Table 2 shows the chemical resistance of PVA fiber (40). The fiber exhibits markedly high resistance to organic solvents, oils, salts, and alkaU. In particular, the fiber has unique resistance to alkaU, and is hence widely used in the form of a paper principally comprising it and as reinforcing material for cement as a replacement of asbestos. 

In many commercial brochures, chemical resistance is indicated as excellent, good, fair, or poor. Although the test method is usually outlined, wide interpretation is possible. Immersion tests are usually described in this manner. Hydrolytic stabiUty is tested by salt-spray cycling or autoclave cycling. 

The most chemical-resistant plastic commercially available today is tetrafluoroethylene or TFE (Teflon). This thermoplastic is practically unaffected by all alkahes and acids except fluorine and chlorine gas at elevated temperatures and molten metals. It retains its properties up to 260°C (500°F). Chlorotrifluoroethylene or CTFE (Kel-F, Plaskon) also possesses excellent corrosion resistance to almost all acids and alkalies up to 180°C (350°F). A Teflon derivative has been developed from the copolymerization of tetrafluoroethylene and hexafluoropropylene. This resin, FEP, has similar properties to TFE except that it is not recommended for continuous exposures at temperatures above 200°C (400°F). Also, FEP can be extruded on conventional extrusion equipment, while TFE parts must be made by comphcated powder-metallurgy techniques. Another version is poly-vinylidene fluoride, or PVF2 (Kynar), which has excellent resistance to alkahes and acids to 150°C (300°F). It can be extruded. A more recent development is a copolymer of CTFE and ethylene (Halar). This material has excellent resistance to strong inorganic acids, bases, and salts up to 150°C. It also can be extruded. 

As previously stated, polyurethanes do not have the degree of chemical resistance enjoyed by the other elastomers. Specially designed chemical resistant polyurethanes are suitable for use in dilute non-oxidative acids and salts, but are not normally suitable for alkalis. They show good resistance to oils and solvents. Maximum temperature of use is usually about 80°C, but this temperature is very dependent on the chemical environment. 

One of the most common impurities in coastal areas which acts in a chemical manner rather than a physical one is salt water. However, with the ever-increasing spread of the chemical industries, and the stepped-up use of gasoline powered vehicles, the problem of chemical degradation are also of interest particularly in inland areas. While plastics in general are corrosion resistant, the multiplicity of chemical agents which can be in the air in industrial atmospheres, plus the chemical nature of the various plastics indicates that it cannot be assumed that all plastics are chemically resistant to all atmospheres. 

Chemical Resistance. TaC oxidizes rapidly in air at 800°C. Otherwise it is one of the most chemically stable carbides. It decarburizes when heated in hydrogen at very high temperatures (3000°C). It does not react with nitrogen up to 2700°C. It reacts at high temperature with Nb, Ta, and Mo. It is stable in nonoxidizing acids, but is attacked easily by HNO3 and HF and by melts of oxidizing salts. 

High chemical resistance to adds, bases, salts, and molten metals. 

Selection of Corrosion-Resistant Materials The concentrated sofutions of acids, alkalies, or salts, salt melts, and the like used as electrolytes in reactors as a rule are highly corrosive, particularly so at elevated temperatures. Hence, the design materials, both metallic and nonmetallic, should have a sufficiently high corrosion and chemical resistance. Low-alloy steels are a universal structural material for reactors with alkaline solutions, whereas for reactors with acidic solutions, high-alloy steels and other expensive materials must be used. Polymers, including highly stable fluoropolymers such as PTFE, become more and more common as structural materials for reactors. Corrosion problems are of particular importance, of course, when materials for nonconsumable electrodes (and especially anodes) are selected, which must be sufficiently stable and at the same time catalytically active. 

Quartz glass (silica), pyrex (borosilicates) and other household and laboratory glasses (boroaluminosilicates) owe their high chemical resistance to the (tetrahedral) network forming properties of Si, B, P and A1 (cf., the borax and phosphate bead tests in qualitative dry reactions on the salts of numerous metals). 

Chemical resistance is generally good to oils and greases, methanol and certain mineral salts. 

Advantages — Inexpensive material moldable into a variety of shapes chemical resistance especially toward salts, acids, and bases. 

Rubber is chemically resistant to most corrosive liquids, gases, salt water, ozone and UV light. These corrosive agents are commonly... 

One final example of the application of onium salt photochemistry in positive resist materials should be mentioned, because it does not include any postexposure acid-catalyzed processes and therefore does not encompass the principle of chemical amplification (79). Interestingly, Newman (79) has determined that onium salts themselves can inhibit the dissolution of novolac in aqueous base and that irradiation of such an onium salt-novolac resist restores the solubility of the resin in developer and leads to a positive-tone image. In this application, the onium salt behaves like diazonaphthoquinone in a typical positive resist. Recently, Ito (80) has reported also the use of onium salts as novolac dissolution inhibitors. 

The tertiary amine salts are claimed to provide epoxy formulations with very good adhesion to metal. The cured resins also show a hydrophobic effect when in contact with water or at high humidities. The strength, toughness, and elongation (4.7 percent) of the cured epoxy resin are very good. However, heat distortion temperature is only in the range of 70 to 80°C, and chemical resistance is relatively poor for an epoxy. The physical properties fall off rapidly with any rise in temperature. 

Cautionl Amine perchlorate salts are potentially explosive and should not be heated to dryness under vacuum. Manipulations should be carried out in a well-ventilated hood, transfers of perchlorate salts carried out with ceramic or glass spatulas, and latex or vinyl gloves and chemical-resistant safety goggles should be worn. 

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