Selection of the materials

Consider the selection of the material for the mirror backing of a 200-inch (5 m) diameter telescope. We want to identify the material that gives a mirror which will distort by less than the wavelength of light when it is moved, and has minimum weight. We will limit ourselves to these criteria alone for the moment - we will leave the problem of grinding the parabolic shape and getting an optically perfect surface to the development research team. 

The selection of the material suitable for the service depends upon the corrosive nature of the fluid and its bursting characteristics in the pressure range under consideration. For low pressure, a single standard disk of some materials would be too thin to handle and maintain its shape, as well as give a reasonable service life from the corrosion and fatigue standpoints. See section on Selection and Application. 

The dielectric materials interact with the electrical fields and alter the characteristics of the electrical field. In some cases this is desirable and in others it is deleterious to the operation of the system and must be minimized. This is done by both the selection of the material and the configuration of the dielectric. To see how these concepts are applied, an example is presented of one of the major applications of plastics materials, i.e., to insulate wires, and show how a dielectric is designed to meet the service requirements. The specific requirements on a standard wire are ... 

In this case the designer has freedom of choice of both form and dimension as well as in the selection of the materials. Given this freedom, it would be desirable to examine several of the alternatives to see which would provide the best seating at the lowest cost. Obviously, there is no point in doing all of the possibilities so a selection should be made on the basis of anticipated use as well as style requirements. Three types will be analyzed. They are the single curve sheet cantilever mounted from the back, the molded pan supported on four legs, and the structural foam molding which is front supported. 

In the preparation of microporous manganese oxide materials different chemical properties were observed for the microwave and thermal preparations. In the conversion of ethylbenzene to styrene the activity and selectivity of the materials was different [26]. 

There are numerous fireproofing materials available on the marketplace and the selection of the material involved is based on the application and advantages versus disadvantages of each over an economic factor. Usually no single material is ideally suited for a particular application, and an evaluation of the cost, durability, weatherability, and combination of factors is necessary. 

The problem is to minimize the total cost, once produce specifications and the throughput are fixed and the product and feed pumping costs are fixed that is, Cp Cd, and Cb are fixed. After selection of the material of construction, the costs are determined that is, Cp, Cs, Cx are also fixed. 

Selection of the material model is another important factor to be considered. Some programs allow the user to specify plastic moment-rotation curves for beam elements. However, the more rigorous and most widely available method of defining nonlinear material properties is to specify the stress versus strain data, Plastic behavior is approximated at the section level in the former method whereas, the latter method tracks plastic behavior at the individual integration points (fibers) through the thickness of the member. Each method has its advantages and disadvantages. 

Based on this information and additional research, AEA has made the provisional selection of the materials of construction for the SILVER II process systems shown in Table 3-6. This selection of materials should be adequate, assuming that AEA addresses the issue of assuring reliability in achieving leaktight joints after repeated disconnection and reconnection of pip-... 

Once the specification is established, a first pre-selection of the materials having the required minimal properties can be made using the following graphs (see Figures 3.11 to 3.38). For the selected polymer families, one should then refer to the corresponding monographs to determine those that satisfy all the points of the specifications. 

Foreign Porcelain or China Is tho finest and moat valuable description of ware, distinguished from other wares by the composition of the paste from which it is formed, giving a body of a fine, hard, translucent texture. Great cure is exercised in tho selection of the materials to give a colorless mass after firing. Two essentially... 

Whilst carbon and stainless steels are commonly used materials of construction, increasing use is being made of non-metallic and rubber lined equipment. The selection of the material of construction should take into account the cases of the worst process conditions that may occur under foreseeable conditions and should be applied to all components including valves, pipe fittings, instruments and gauges. Both composition (e.g., chlorides, moisture) and temperature deviations can have a significant direct effect on the rate of corrosion. The operator should demonstrate that procedures are in place to ensure that potential deviations in process conditions such as fluid temperature, pressure and composition are identified and assessed in relation to the selection of materials of construction for piping systems. 

According to the specific task, different materials are used for the windows. Typical materials are sapphire, calcium fluoride, zinc selenide, diamond, and normal quartz. The selection of the materials depends on the pressure and, for spectroscpic investigations, also on the wavelength corresponding to the bonds of the species to be analysed. 

Time-resolved X-ray absorption spectra of an activated H5[PV2Moio04o] oxidation catalyst were recorded to determine correlations between the dynamic structure and the catalytic selectivity of the material (Ressler and Timpe, 2007). In addition to experiments carried out under steady-state conditions, time-resolved XAFS measurements at the Mo K-edge were performed under changing reaction conditions (with a time resolution of 30 s per spectrum) (Figure 52). Therefore, the gas-phase composition was isothermally switched from a reducing atmosphere (propene) to an... 

Despite their intrinsic simplicity, the plate-and-frame reactors require accurate selection of the materials, especially when the electrolytic processes are performed in non-aqueous solvents and/or deal with substrates which are currently used as solvents, as in the case of volatile organic chlorides. Special attention should be paid to the selection of the gaskets, for long-term operational stability. Moreover, in the case of the SPE scheme, porous electrodes should be adopted, to allow for optimal contact between electrode, electrolyte and reactants/products. In this case, mass-transfer limitations into the porous structure should be carefully considered. 

After selection of the material, the corrosion scientist must play a role in designing the equipment so that the design is appropriate, and avoids corrosion modes due to inappropriate design. Improper design may result in galvanic corrosion, crevice corrosion,... 

It is virtually an impossible task to list materials suitable for successful operation in every conceivable set of environmental conditions. The choice of material for use in a given environment depends upon the corrosion resistance of the material as the primary factor. The cost of the material is also an important factor in the ultimate selection of the material. 

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