Materials Compatible with and Resistant

Materials Compatible with and Resistant to 72% Perchloric Acid... 

MATERIALS COMPATIBLE WITH AND RESISTANT TO 72% PERCHLORIC ACID... 

Materials compatibility is the resistance of materials of system construction to chemical or physical attack by the propellants or the products of propellant combustion. In addition to destroying the integrity of the pertinent structural member, corrosion of the material by the propellant results in contamination of the propellant with the corrosion products, which in turn deteriorates the propellant s physical and chemical properties. As in storability, materials compatibility is related to usage temperatures, as well as to special materials handling, cleaning, and/or passivation techniques. Although limited materials compatibility of a... 

Resistant to environmental conditions. After deployment, sensors must be resistant to mechanical shocks from waves and be insensitive to, or compensate for, changes in temperature, pressure, salinity, and. biofouling that they will invariably encounter in the ocean environment. Biofouling and corrosion are major problems for instruments that are deployed for long periods of time. Appropriate sensor and instrument design, as well as selection of appropriate materials compatible with such a harsh environment, must be taken into account. 

Specifically for the passivation of temperature sensitive bubble memory devices,these ultrapure materials proved to be of great value. A cure process was optimized to obtain a reliable low temperature cure without affecting the magnetic coercivities of the bubble memory devices. A positive resist process, using a simple development step to pattern via holes in devices has been optimized and successfully used to fabricate devices. The devices fabricated using the the polyimide process have been compared with conventional SiC offers reliable passivations with thinner stress free films for passivations. The fabrications involve simple inexpensive process steps and are compatible with conventional resist processes. The reliability of the imide passivated devices can be considerably enhanced by the use of ultrapure starting materials to preclude harmful ionic mobilities through passivated layers. 

The chemical properties of the polymer are however strongly influenced by the presence of these ester groups. Compared with a hydrocarbon rubber the general effect is to improve the resistance to swelling in oils but to have reduced resistance to hydrolysis. Compatibility with, and adhesion to, polar materials such as leather is increased. 

A final point on technology, although by no means an unimportant one, is the need for the filter, and especially the filter medium, to be materially compatible with the suspension and its components. This requires httle attention in, for example, the filtration of ambient air, but is of vital concern where the gas is hot (as from a furnace), or the hquid is corrosive (as in mineral acid filtration), or the solids are abrasive. Filtration in the nuclear industry especially imposes problems not only of resistance to radiation, but of difficult or impossible access once the filter has been used. 

Long-chain esters of pentaerythritol have been used as pour-point depressants for lubricant products, ranging from fuel oils or diesel fuels to the high performance lubricating oils requited for demanding outiets such as aviation, power turbines, and automobiles. These materials requite superior temperature, viscosity, and aging resistance, and must be compatible with the wide variety of metallic surfaces commonly used in the outiets (79—81). 

Storage. Carbon steel and stainless steel should be used for all equipment in ethylene oxide service. Ethylene oxide attacks most organic materials (including plastics, coatings, and elastomers) however, certain fluoroplastics ate resistant and can be used in gaskets and O-rings. See Reference 9 for a hst of materials that are compatible with ethylene oxide. 

Polymers used for seat and plug seals and internal static seals include PTFE (polytetrafluoroeth ene) and other fluorocarbons, polyethylene, nylon, polyether-ether-ketone, and acetal. Fluorocarbons are often carbon or glass-filled to improve mechanical properties and heat resistance. Temperature and chemical compatibility with the process fluid are the key selec tion criteria. Polymer-lined bearings and guides are used to decrease fric tion, which lessens dead band and reduces actuator force requirements. See Sec. 28, Materials of Construction, for properties. 

Corrosive chemicals and external exposure can cause tank failure. Materials of construction should be chosen so that they are compatible with the chemicals and exposure involved. Welding reduces the corrosion resistance of many alloys, leading to localized attack at the heat-affected zones. This may be prevented by the use of the proper alloys and weld materials, in some cases combined with annealing heat treatment. 

Silicones. Silicones are useful where high temperature resistance or compatibility with silicone components such as molded seals are needed. Silicone firewall insulation materials and silicone gaskets and seals are bonded with silicone rubber adhesives. 

Nonmetallic materials should have the following desirable characteristics low moisture absorption, resistance to microorganisms, stability through temperature range, resistance to flame and arc, freedom from out-gassing, resistance to weathering, and compatibility with other materials. 

One of the most effective methods of preventing corrosion is the selection of the proper metal or alloy for a particular corrosive service. Once the conditions of service and environment have been determined that the equipment must withstand, there are several materials available commercially that can be selected to perform an effective service in a compatible environment. Some of the major problems arise from popular misconceptions for example, the use of stainless steel. Stainless steel is not stainless and is not the most corrosion-resistant material. Compatibility of material with service environment is therefore essential. For example, in a hydrogen sulfide environment, high-strength alloys (i.e., yield strength above 90,000 psi or Rc 20 to 22) should be avoided. In material selection some factors that are important to consider are material s physical and chemical properties, economics and availability. 

In a fully synthetic FR fluid, the fire resistance is due to the chemical nature of the fluid in the others, it is afforded by the presence of water. The other main distinction between the two groups is that the fully synthetic fluids are generally better lubricants and are available for use at operating temperatures up to 150°C (272°F), but are less likely to be compatible with the conventional sealing materials and paints than are water-based products. 

Nitrile rubbers, including fiber-reinforced varieties, are used both as radial shaft-seal materials and as molded packing for reciprocating shafts. They have excellent resistance to a considerable range of chemicals, with the exception of strong acids and alkalis, and are at the same time compatible with petroleum-based lubricants. Their working temperature range is from —1°C to 107°C (30°F to 225°F) continuously and up to 150°C (302°F) intermittently. When used on hard shafts with a surface finish of, at most, 0.00038 mm root mean square (RMS), they have an excellent resistance to abrasion. 

Silicone rubber as a shaft seal and backing material has a number of special applications. It can be used over a temperature range of —60°C to 260°C (—76°F to 500°F) in air or suitable fluids. Its abrasion resistance is good with hard shafts having a 0.000254 mm RMS surface finish. Commercial grades of silicone rubber are compatible with most industrial chemicals up to 260°C (500°F). In lubricating oils, the limiting temperature is 120°C (250°F), but special types have been developed for use up to 200°C (392°F). 

An electrolyte may be characterized by resistance / [Qcm], which is defined as the resistance of the solution between two electrodes at a distance of 1 cm and an area of 1 cm2. The reciprocal value is called the specific conductivity at[Q" cm"1] [5], For comparison the values of k for various materials are given in Fig. 2 Here is a wide spread for different electrolyte solutions. The selection of a suitable, high-conductivity electrolyte solution for an electrochemical cell depends on its compatibility with other components, such as the positive and negative electrodes. 

This section discusses chemical compatibility (resistance) of geosynthetic and natural liner materials with wastes and leachates. Even in a relatively inert environment, certain materials deteriorate over time when exposed to chemicals contained in both hazardous and nonhazardous leachate. It is important to anticipate the kind and quality of the leachate a site will generate and select liner materials accordingly. The chemical resistance of any FML materials, geonets, geotextiles, and pipe should be evaluated before installation.39... 

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