Composite temperature resistance

In the late 1980s, new fully aromatic polyester fibers were iatroduced for use ia composites and stmctural materials (18,19). In general, these materials are thermotropic Hquid crystal polymers that are melt-processible to give fibers with tensile properties and temperature resistance considerably higher than conventional polyester textile fibers. Vectran (Hoechst-Celanese and Kuraray) is a thermotropic Hquid crystal aromatic copolyester fiber composed of -hydroxyben2oic acid [99-96-7] and 6-hydroxy-2-naphthoic acid. Other fully aromatic polyester fiber composites have been iatroduced under various tradenames (19). 

Fabric Composition. The method of fabric manufacture dictates many of the characteristics of the sheet, but intrinsic properties are firmly estabhshed by the base polymer selected. Properties such as fiber density, temperature resistance, chemical and light stabiUty, ease of coloration, surface energies, and others are a function of the base polymer. Thus, because nylon absorbs more moisture than polypropylene, spunbonded fabrics made from nylon are more water absorbent than fabrics of polypropylene. 

Thermosetting unsaturated polyester resins constitute the most common fiber-reinforced composite matrix today. According to the Committee on Resin Statistics of the Society of Plastics Industry (SPl), 454,000 t of unsaturated polyester were used in fiber-reinforced plastics in 1990. These materials are popular because of thek low price, ease of use, and excellent mechanical and chemical resistance properties. Over 227 t of phenoHc resins were used in fiber-reinforced plastics in 1990 (1 3). PhenoHc resins (qv) are used when thek inherent flame retardance, high temperature resistance, or low cost overcome the problems of processing difficulties and lower mechanical properties. 

Reportedly, OjoCdiaHylbispheaol A is an attractive comonomer for bismaleimides because the corresponding copolymer is tough and temperature resistant (41). Toughness, however, is a function of the BMI—diaHylbisphenol A ratio employed. In one study optimized toughness properties were achieved when BMI and diaHylbisphenol were employed at a close to 2 1 molar ratio (42). In Table 9, the mechanical properties of BMI—bis(3-allyl-4-hydroxyphenyl)-7 -diisopropylbenzene resias are provided, showiag optimized properties for the 60/40 BMI—diaHylbisphenol composition. The 0,(9 diaHylbisphenol A is commercially available under the trademark Matrimide 5292. Another bisaHylphenyl compound is available from SheH Chemical Company/Technochemie under the trademark COMPIMIDE 121. 

Corrosion Resistance Possibly of greater importance than physical and mechanical properties is the ability of an alloy s chemical composition to resist the corrosive action of various hot environments. The forms of high-temperature corrosion which have received the greatest attention are oxidation and scaling. 

Select metal or alloy (or non-metallic material) for the particular environmental conditions prevailing (composition, temperature, velocity, etc.) taking into account mechanical and physical properties, availability, method of fabrication and overall cost of structure. Decide whether or not an expensive corrosion-resistant alloy is more economical than a cheaper metal that requires protection and periodic maintenance. 

Epoxy (Amine-Cured) Bisphenol A-based epoxy resins used for composite fabrication are commonly cured with multifunctional primary amines. For optimum chemical resistance these generally require a heat cure or postcure. The cured resin has good chemical resistance, particularly to basic environments, and can have good temperature resistance. 

Ikonopisov284 has conducted a systematic study of breakdown mechanisms in growing anodic oxides. He has enumerated factors significantly affecting the breakdown (nature of the anodized metal, electrolyte composition and resistivity) as well as those of less importance (current density, surface topography, temperature, etc.). By assuming a mechanism of avalanche multiplication of electrons injected into the oxide by the Schottky mechanism, Ikonopisov has correctly predicted the dependence of Ub on electrolyte resistivity and other breakdown features. 

Albany International Research Co. has developed an advanced hollow fiber composite reverse osmosis membrane and module under the name of Quantro II . This composite membrane is comprised of a porous hollow fiber substrate on which has been deposited a rejection barrier capable of fluxes of commercial importance at high rejection of dissolved salts at elevated temperatures. Resistance to active chlorine has been demonstrated. Proprietary processes have been developed for spinning of the fiber, establishment of the rejection barrier and processing of the fiber to prepare modules of commercial size. Prototype modules are currently in field trials against brackish and seawater feed solutions. Applications under consideration for this membrane include brackish and seawater desalination as well as selected industrial concentration processes. 

Resistivity was nearly 10 O-cm and independent of bath composition. Temperature dependence of resisitivity gave an activation energy of 0.95 eV, which was ascribed, based on previous studies, to an acceptor level above the valence band due to Cu impurity. 

Commercial applications have been identified primarily in the electronics industry where requirements for dimensional stability, mechanical properties, and high temperature resistance make these systems attractive in advanced circuit board technology. Other commercial applications include high temperature membranes and filters where these materials offer performance improvements over glass, Kevlar, and graphite composites. Industrial development of these types of materials will most likely be dependent on monomer cost and advances in various product properties requirements. 

A mixture of diatomaceous earth and an asbestos binder is suitable for temperatures up to the range of 1600-1900°F. Johns-Manville Superex is one brand. Since this material is more expensive than 85% magnesia, a composite may be used to save money sufficient thickness of the high temperature resistant material to bring its external surface to below 600°F, finished off with 85% magnesia in appropriate thickness. Table 8.22(c) is one standard specification of this type. 

DATB-HMX Explosive Compositions for High Temperature Resistance and High Energy. They are discussed by B.A.Stott D-A.Sbrocca in conf NAVWEPS Rept 7589 (NOTS TP 2570 (Dec I960)... 

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