Stability at high temperatures

They lack thermal stability at high temperatures. 

The outstanding characteristics of the noble metals are their exceptional resistance to corrosive attack by a wide range of liquid and gaseous substances, and their stability at high temperatures under conditions where base metals would be rapidly oxidised. This resistance to chemical and oxidative attack arises principally from the Inherently high thermodynamic stability of the noble metals, but in aqueous media under oxidising or anodic conditions a very thin film of adsorbed oxygen or oxide may be formed which can contribute to their corrosion resistance. An exception to this rule, however, is the passivation of silver and silver alloys in hydrochloric or hydrobromic acids by the formation of relatively thick halide films. 

Alloys with iridium Iridium alloys with platinum in all proportions, and alloys containing up to about 40% iridium are workable, although considerably harder than pure platinum. The creep resistance of iridium-platinum alloys is better than that of rhodium-platinum alloys at temperatures below 500°C. Their stability at high temperatures, however, is substantially lower, owing to the higher rate of formation of a volatile iridium oxide. 

For applications having only moderate thermal requirements, thermal decomposition may not be an important consideration. However, if the product requires dimensional stability at high temperatures, it is possible that its service temperature or processing temperature may approach its temperature of decomposition (Tj) (Table 7-12). A plastic s decomposition temperature is largely determined by the elements and their bonding within the molecular structures as well as the characteristics of additives, fillers, and reinforcements that may be in them. 

Among soft organic matrices for electrochemical applications, polysulfone (PSf) appears as a suitable and not very exploited candidate with very attractive properties including a remarkable stability at high temperatures and extreme pH conditions [112]. 

Several proteins from different sources have been shown to maintain stability at high temperatures and NMR studies have been carried out in order to reveal their structures and/or to understand their activity. The most relevant references of a miscellany of thermostable proteins are reported in Table 3. Some of them such as bovine pancreatic trypsin inhibitor (BPTI), thermolysin and lysozyme have been widely studied as model systems in protein science. 

Haselton H. T. and Newton R. C. (1980). Thermodynamics of pyrope-grossular garnets and their stabilities at high temperatures and pressures. J. Geophys. Res., 85 6973-6982. 

Early in our work, we had sought to achieve zeolite stability at high temperatures and in the presence of steam. We sought zeolites that could resist the extreme deactivating conditions of the RCC process. 

Development has been conducted to fabricate SiC-based matrix/Si-C-based fiber composites by polymer infiltration. Nicalon fibers are used, and various polymers such as polysilazanes, polysiloxanes, and polycarbosilanes are used to yield matrices of SiCO, SiNC, and SiC. As with CVI of SiC/SiC composites, carbon acts as an interface layer but does not result in stability at high temperatures. 

For both bacteria, the increase in activity was concomitant with the decrease in the catalyst s stability. At high temperatures, this phenomenon can be explained by thermal denaturation. At low temperatures (lower than 40 °C for R. erythropolis and 30 °C for X. autotrophicus) the drop in activity could be attributed to the accumulation of acid, more rapidly produced at high water activity. 

Graphite with its exceptional strength and thermal stability at high temperatures is a prime candidate material for many aerospace and nuclear applications. Its properties, through process modifications, are tailorable to meet an array of design criteria for survival under extremely harsh environmental operations. 

The resistance of graphite to thermal shock, its stability at high temperatures, and its resistance to corrosion permit its use as self-supporting vessels to contain reactions at elevated temperatures (800—1700°C), eg, self-supporting reaction vessels for the direct chlorination of metal and alkaline-earth oxides. The vulnerability of cemented joints in these applications requires dose tolerance (d=0.10 mm) machining, a feat easily accomplished on graphite with conventional metal machining equipment. 

H. Hammou outlines the thermodynamic concepts and rate processes relevant to solid oxide fuel cells. Recent advances in materials research concerning electrical properties, and stability at high temperatures, are thoroughly reviewed. The most promising hardware developments are described, along with problems to be resolved. 

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