Chemical attack/resistance

More resistant than porcelain to all forms of chemical attack. Resistant up to 1600°C to most acid fluxes Vessels for metallic, alloy, salt and glass melts... 

Carbonaceous materials exhibit excellent thermal conductivity, volume stability, chemical attack resistance, and thermal shock resistance, making them a valuable component for refractory applications. However, they must be properly cooled to assure long-term survivability in metallurgical applications. 

Solid, rubbery silicones likewise retain their plasticity at low temperatures and are resistant to many forms of chemical attack they are now incorporated in paints for resisting damp and for waterproofing. Silicones are also used in moulds to avoid sticking of the casting to the mould. 

Silver has little tendency to formally lose more than one electron its chemistry is therefore almost entirely restricted to the + 1 oxidation state. Silver itself is resistant to chemical attack, though aqueous cyanide ion slowly attacks it, as does sulphur or a sulphide (to give black Ag S). hence the tarnishing of silver by the atmosphere or other sulphur-containing materials. It dissolves in concentrated nitric acid to give a solution of silver(I) nitrate. AgNOj. 

Metallic gold, which is found free in nature, has always been valued for its nobility, i.e. its resistance to chemical attack. This property is to be expected from its position in the electrochemical series. It... 

Electrical. Glasses are used in the electrical and electronic industries as insulators, lamp envelopes, cathode ray tubes, and encapsulators and protectors for microcircuit components, etc. Besides their abiUty to seal to metals and other glasses and to hold a vacuum and resist chemical attack, their electrical properties can be tailored to meet a wide range of needs. Generally, a glass has a high electrical resistivity, a high resistance to dielectric breakdown, and a low power factor and dielectric loss. 

Chemical Properties. Molybdenum has good resistance to chemical attack by mineral acids, provided that oxidizing agents ate not present. The metal also offers excellent resistance to attack by several liquid metals. The approximate temperature limits for molybdenum to be considered for long-time service while in contact with various metals in the hquid state ate as follows ... 

The principal advantage of plastic dmms and liners is their resistance to corrosion. This aspect of their performance requires the lading to be investigated in terms of capacity for chemical attack on the dmm. Stress-cracking tests should be performed in all instances where the compatibiUty of jading and dmm material has not been estabUshed (6). 

Commonly used materials for cable insulation are poly(vinyl chloride) (PVC) compounds, polyamides, polyethylenes, polypropylenes, polyurethanes, and fluoropolymers. PVC compounds possess high dielectric and mechanical strength, flexibiUty, and resistance to flame, water, and abrasion. Polyethylene and polypropylene are used for high speed appHcations that require a low dielectric constant and low loss tangent. At low temperatures, these materials are stiff but bendable without breaking. They are also resistant to moisture, chemical attack, heat, and abrasion. Table 14 gives the mechanical and electrical properties of materials used for cable insulation. 

The platinum-group metals (PGMs), which consist of six elements in Groups 8— 10 (VIII) of the Periodic Table, are often found collectively in nature. They are mthenium, Ru rhodium, Rh and palladium, Pd, atomic numbers 44 to 46, and osmium. Os indium, Ir and platinum, Pt, atomic numbers 76 to 78. Corresponding members of each triad have similar properties, eg, palladium and platinum are both ductile metals and form active catalysts. Rhodium and iridium are both characterized by resistance to oxidation and chemical attack (see Platinum-GROUP metals, compounds). 

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 aUphatic and aromatic hydrocarbons promote crazing of stressed molded samples. Eor these reasons, care must be exercised in the choice of solvents for painting and coating operations. Eor sheet appHcations, polycarbonate is commonly coated with a sihcone—sihcate hardcoat which provides abrasion resistance as well as increased solvent resistance. Coated films are also available. 

Isophthahc (y -phthahc) acid [121 -91 -5] (IPA) is selected to enhance thermal endurance as well as to produce stronger, more resiUent cross-linked plastics that demonstrate improved resistance to chemical attack. TerephthaUc (p-phthaUc) acid [100-21-0] (TA) provides somewhat similar properties as isophthahc acid but is only used in selective formulations due to the limited solubiUty of these polyester polymers in styrene [100-42-5] (see Phthalic acid AND OTHERBENZENEPOLYCARBOXYLIC ACIDS). 

Chemical Durability. The resistance of nontransparent vitreous sihca to chemical attack is slightly less than the resistance of transparent vitreous sihca. This difference results primarily from the higher surface area of the former caused by the presence of a large number of bubbles. Most data in the hterature are on the transparent material. 

It is also not tme that vinyl plastics decompose in landfills and give off vinyl chloride monomer, because like all plastics, vinyl is an extremely stable landfill material. It resists chemical attack and degradation, and is so resistant to the conditions present in landfills that it is often used to make landfill liners. On those occasions when vinyl chloride monomer is detected in landfills, it typically can be traced to the presence of other chemicals and solvents. 

Resistance to Chemicals. Different species of wood vary in their resistance to chemical attack. The significant properties are beheved to be inherent to the wood stmcture, which governs the rate of ingress of the chemical and the composition of the cell wall, which affects the rate of action at the point of contact (56). 

Resistance to chemical attack is generally improved by resin impregnation, which protects the underlying wood and reduces movement of Hquid into the wood. Resistance to acids can be obtained by impregnating with phenoHc resin and to alkaHes by impregnating with furfural resin (see Phenolic RESINs). 

Straight WC—Co tools are not suitable for machining steels that produce long chips because straight grades undergo crater wear from diffusion of WC into the steel chip surface. However, soHd solutions of WC—TiC, WC—TiC—TaC, etc, resist this type of chemical attack. In addition, tantalum carbide can improve thermal-shock resistance. Steel cutting compositions thus typically contain WC—TiC—(Ta,Nb)C—Co. Tantalum carbide is often added as (Ta,Nb)C because the chemical similarity between TaC and NbC makes their separation expensive. 

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