High-temperature environment applications

G. M. Graham, S. J. Dyer, and P. Shone. Potential application of amine methylene phosphonate based inhibitor species in HP/HT (high pres-sure/high temperature) environments for improved carbonate scale... 

On the other hand, since most of these reactions are thermally activated, their kinetics are accelerated by the rise in temperature in an Arrhenius-like manner. Therefore, within a much shorter time scale, the adverse effect of these reactions could become rather significant during the storage or operation of the cells at elevated temperatures. In this sense, the long-term and the thermal stability of electrolytes can actually be considered as two independent issues that are closely intertwined. The study of temperature effects on electrolyte stability is made necessary by the concerns over the aging of electrolytes in lithium-based devices, which in practical applications are expected to tolerate certain high-temperature environments. The ability of an electrolyte to remain operative at elevated temperatures is especially important for applications that are military/space-related or traction-related (e.g., electric or hybrid electric vehicles). On the other hand, elevated tem-... 

A diesel fuel stabilizer containing a blend of amines, polyamines, and alkyl ammonium alkyl phosphate as specified under MIL-S-53021 is recommended for federal diesel fuel oil. This stabilizer is to be used at a treat rate of 25 lb/1,000 barrels. It is not intended for use in routine applications, but for situations where increased stability protection is required. Typical applications include fueled equipment undergoing long-term storage in a warehouse or depot, prepositioned equipment or equipment maintained in a high-temperature environment. 

Both of these copper-based lithium primaries are manufactured as button and bobbin-configured cylindrical cells. Copper oxyphosphate cells find particular application in high temperature environments. 

Use of ceramic materials in high temperature structural applications is often limited by creep resistance. However, several recent studies have shown that composite reinforcement can drastically reduce the creep rates compared to the unreinforced ceramic matrix.12,20,27-31 Most of these studies have been conducted in air, which is a strong oxidizing environment. In a few cases, investigators have attempted to isolate the effects of oxidation from creep by conducting parallel experiments in both air and inert atmospheres.27,28 The following is a description of the salient points made in these investigations. 

Since their mechanical properties are maintained at high temperatures (up to 1700 K), silicon nitride-based materials are attractive for use in high-temperature structural applications in chemically aggressive environments. For example, several properties of a Si3N4-based ceramic (Si3N4-l-SiC+TiN), suitable for ceramic engines, are shown in Table Vm. 

Electro-insulation materials. The retention of dielectric properties in a high-temperature environment, coupled with good corrosion resistance in contact with certain reactive chemicals, suggests excellent possibilities of polybenzimidazole use in electrical insulation and other dielectric applications at high operating temperatures and/or in aggressive chemical environments. Typical applications, hence, can be foimd in special cable and wire insulation, in the manufacture of circuit boards and radomes for supersonic aircraft, as battery and electrolytic cell separators, and as fuel cell frame structural materials. Some recent publications in the patent and technical report literature may serve to illustrate such applications. 

Structural engineering materials Use as structural materials, especially under conditions of ablation or in high-temperature environments, has been one of the prime objectives of polybenzimidazole development ever since Marvel s first publication.This holds to a small extent for molded products and to a predominant extent for laminates. Almost all the polymers evaluated and used in these technical applications are of the type 1. 

H. "Development of the Dilute Oxygen Combustion Burner for High-Temperature Furnace Applications." Paper Presented at the 4th International Conference of Technologies and Combustion for a Clean Environment, Portugal, July 7-10, 1997. 

Figure 1 shows the dynamic moduli as a function of frequency for an HPG-borate gel (0.48 wt % HPG, 3 wt % sodium tetraborate, 2 wt % KGl) at ambient temperature. The moduli show solidlike behavior the storage modulus is independent of frequency and higher than the loss modulus. At 65 G, in Figure 2, the moduli show fiuidlike behavior, and both moduli decrease at low frequency. This thermal melting is characteristic of borate gels and limits their application in high-temperature environments. 

Several publications on the processing of membranes based on these materials could be found in the literature [5-28]. The selection of membrane material for a given application could be divided in to two parts Screening of materials based on bulk properties and screening based on thin film properties. In the former case, intrinsic material properties such as stability and conductivity will decide the outcome of the research work. In the latter case, the defect free formability of thin film will be the deciding part. The method of film formation as well as the quality of the support substrates could become important in this respect. In supported membranes, material stability and membrane performance are very much related. The most important issue - the application of membranes in high temperature environments - is therefore the study of the stmcture of the membrane/material and its correlation with the stability/durability. 

These solid electrolytes do conform to the conditions laid out in Wagner s theory and many important applications cein be foreseen which would require devices based on such solid electrolytes. Some of these applications aire of the open circuit variety such as solid electrolyte emf sensors for high temperature environments where contamination of the electrolyte may be a problem. But many other applications will be of the closed circuit variety and to a large extent this aspect has not been negotiated very rigorously in the traditional theory. Significant extensions of the traditional theory will have to be made before the performance characteristics of fuel cells and high temperature steam hydrolyzers can be successfully analyzed via the theory of mixed conduction in solids. 

Pessimism exists about the ability to fabricate cost effective modules from microporous membranes. Specific concerns include the stability of the membranes (especially for silica membranes in humid, high temperature environments), the ability to produce large uniform membrane areas, the effect of thermal cycling (especially for applications that require operation at elevated temperature), the ability to form tubesheets, and the ultimate cost of manufacture. 

Cyclic nitramines such as RDX or cyclotetra-methylenetetranitramine (HMX) are widely used in military composites such as Composition B (TNT and RDX) and Composition C-4 (US) or PE-4 (British) and in commercial blasting explosives such as Semtex (a Czech-made mining explosive). HMX is present as a by-product in RDX made by the Bach-mann process and has applications in explosives to be used in high-temperature environments. Chemical tests for RDX include the J-Acid and thymol tests. A number of TLC systems for RDX and HMX have been reported. With adequate sample, IR identification of the pure material in a micro-potassium bromide pellet is simple. If a diamond anvil sample holder or microscope attachment is available, excellent spectra of pure samples of milligram size or even of single crystals are easily obtained. When HMX is observed in RDX-based explosives, its concentration may suggest the national origin of the explosive. 

Their physical properties, chemical stability, and resistance to temperatures above 135°C qualify these materials as competitors for sdicone rubber and fluoroelastomers. Applications include hose, tubing, gaskets, and protective covers for use in high-temperature environments. 

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