Aging at high temperatures

Two propylene oxide elastomers have been commercialized, PO—AGE and ECH—PO—AGE. These polymers show excellent low temperature flexibihty and low gas permeabihty. After compounding, PO—AGE copolymer is highly resiUent, and shows excellent flex life and flexibiUty at extremely low temperatures (ca —65°C). It is slightly better than natural mbber in these characteristics. Resistance to oil, fuels, and solvents is moderate to poor. Wear resistance is also poor. Unlike natural mbber, PO—AGE is ozone resistant and resistant to aging at high temperatures. The properties of compounded ECH—PO—AGE he somewhere between those of ECH—EO copolymer and PO—AGE copolymer (22). As the ECH content of the terpolymer increases, fuel resistance increases while low temperature flexibihty decreases. Heat resistance is similar to ECH—EO fuel resistance is similar to polychloroprene. The uncured mbber is soluble in aromatic solvents and ketones. 

Polycarbonate is blended with a number of polymers including PET, PBT, acrylonitrile-butadiene-styrene terpolymer (ABS) rubber, and styrene-maleic anhydride (SMA) copolymer. The blends have lower costs compared to polycarbonate and, in addition, show some property improvement. PET and PBT impart better chemical resistance and processability, ABS imparts improved processability, and SMA imparts better retention of properties on aging at high temperature. Poly(phenylene oxide) blended with high-impact polystyrene (HIPS) (polybutadiene-gra/f-polystyrene) has improved toughness and processability. The impact strength of polyamides is improved by blending with an ethylene copolymer or ABS rubber. 

Thermal ageing at high temperature of supported silica membranes causes densification of the silica layer, and the higher the temperature, the greater the... 

Polyamide-imides enjoy exceptional thermal stability with a decomposition onset at 500°C and 10% weight loss at 540 C. Long-term aging at high temperatures (250°C) shows only a 80 to 90% drop in tensile strength after 10,000 h (see Fig. 12.19). The UL relative thermal index (RTl) predicts 100,000 h of useful life at temperatiures as high as 220°C. 

All the measurements presented below were performed on PI films deposited on highly doped N" cleaned silicon wafers (resistivity < SxlO Q cm) and aged at high temperature. The time at the beginning of the aging is noted as to. At scheduled times, a part of the specimens were removed from the oven and subjected to non-destructive and destructive tests. The thicknesses noted in the text and labels refer to the initial ones measured at to. 

A second test which is even more discriminating is the so-called "contamination test, in which the rubber is soaked in the fluid for several hours at room temperature and is then subjected to hot air ageing at high temperature. This test simulates the environment of many engine components (e.g. seals, gaskets, hoses, etc.). The main rubbers commonly used in such applications are nitrile rubbers which are not appreciably swelled by hydrocarbon oils and ethylene-propylene (EP) and their ter-polymers (EPDM) which are resistant to the phosphate ester fluids (e.g. Skydrol) used in aircraft hydraulic systems. The following discussion is concerned with the performance of antioxidants under these veiry aggressive conditions. 

The stability of the electrical parameters after ageing at high temperature under power is of prime importance in the selection of die attach adhesives. The test requires a current density of 139.5 A cm applied to five gold-plated Kovar tabs, each tab being adhesively bonded to thin film gold conductors and series bonded with gold wires. The biased test specimens are heated at 150°C in nitrogen for 1000 h, and the electrical resistance of the bonds is measured at 25°C at 200 h intervals. The specification requirement states that the resistance of the five tabs does not increase more than 5%. 

Laves (Fe2Mo type) phases are formed at grain and lath boundaries in FM steels after long-term aging at high temperatures (typically above 500°C). This phase was also observed in irradiated steels [47,78,82], sometimes with modified chemical composition as compared to that measured after thermal aging. 

Two kinds of microstructural evolution are to be expected during selected austenitic steels aging at high temperature ... 

This elastomer is a sulfur-vulcanizable copolymer of propylene oxide and allyl glycidyl ether. Its vulcanizates are particularly attractive for dynamic uses, where high resihence, excellent flex life, and flexibility at extremely low temperatures are required. It performs similarly to NR in these applications, but it also has the added advantages of (1) good resistance to aging at high temperatures, (2) good ozone resistance, and (3) moderate resistance to loss of properties in contact with fuels and/or some solvents. The surfaces of this elastomer should be... 

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