Material selection specification

Some highly visible public statements have been made by several consumer electronic companies that can be inferred to have a direct impact on their FR material selection. Specific examples include Apple Computer s pledge to completely eliminate the use of PVC and BFRs in its products by the end of 2008. 158 Dell159 and Lenovo160 have publicly stated their intentions to eliminate the use of PVC and BFRs in their products. 

More specifically, data bases are now available which are designed as aids to plastics material selection. One estimate in 1993 was that there were 300-400 systems in the field.Systems vary as to whether they are limited to the products of a particular company, to a particular area of activity and to the depth of coverage over a broad area. 

Because of the multitude of engineering materials and the profusion of material-oriented literature it is not possible to describe specific engineering practices in detail in a single chapter. However, we can outline general criteria for parallel evaluation of various materials that can assist in proper selection. The following is a list of general guidelines that can assist in material selection ... 

Proper material selection for chemical and process equipment is one of the first important problems encountered by the designer. Among the many parameters that must be considered are structural strength specifications, heat resistance, corrosion resistance, physical properties, fabrication characteristics, composition and structure of material and cost. 

The fundamental objective in this section is to describe the factors and procedures to select the right material for a specific structural application. The right stuff for a material, as for a fighter pilot or an astronaut, is a complex combination of characteristics. To select the proper material requires being able to characterize and evaluate various composite materials (or metalsl) and to compare their attractive characteristics with the behavioral features required for a particular structure. Finally, a materials selection example of a space truss design problem will be addressed. 

Selecting an optimal material for a given product must obviously be based on analysis of the requirements to be met. A simplified approach involves comparing the specific service requirements to the potential properties of a plastic. What follows is a simplified but practical material-selection approach. This longhand system is a basis of the fastest computerized databases. 

Some plastics can be worked by many different processes, but others require a specific process (Fig. 10-9). Process selection can take place before material selection, when a range of materials may be available, or made first to meet performance requirements and only then have the applicable process or processes chosen. (Chapter 7, SELECTING PLASTIC and Chapter 8, SELECTING PROCESS) Usually, in the latter situation only one special process can be used to provide the best performance-to-cost advantages. A particular design group may have its own processing capabilities. Unfortunately, some operations use just whatever equipment is available. This situation could either be very unprofitable, limit profitability, or restrict product... 

GE E-seminars (http //www. ge-plastics.com/resins/designsolutiony seminar/) GE s virtual conference center offers the ability to interact with GE Plastics real-time in live on-line conferences. E-Seminar examples include Material Selection, which provides the attendee with the knowledge, skills and competencies to determine how application requirements influence the material specification process and Materials for Single-Use Microwave Food Packaging, which reviews trends in the growing Freezer-to-Microwave Food Packaging industry. 

Comprehensive physicochemical characterization of any raw material is a crucial and multi-phased requirement for the selection and validation of that matter as a constituent of a product or part of the product development process (Morris et al., 1998). Such demand is especially important in the pharmaceutical industry because of the presence of several compounds assembled in a formulation, such as active substances and excipients, which highlights the importance of compatibility among them. Besides, variations in raw materials due to different sources, periods of extraction and various environmental factors may lead to failures in production and/or in the dosage form performance (Morris et al., 1998). Additionally, economic issues are also related to the need for investigating the physicochemical characteristics of raw materials since those features may determine the most adequate and low-cost material for specific procedures and dosage forms. 

The background information that materials selection is based on is derived from a number of sources. In many cases, information as to the corrosion resistance of a material in a specific environment is not available and must be derived experiment ly. It is to this need that the primary remarks of this subsection are addressed. 

As Shown in table 2, a comparative dose of 10 n units of PCP-like activity inhibited 3H-PCP binding in rat brain membranes, but did not inhibit binding of 3 H - d i hydromorphi ne, 3H - D - a 1 a2 - D -1 eu5-enkephalin, 3H-ethylketocyclazocine, 3H-diazepam, or -neurotensin. These results indicate that the active material is specific and selective from PCP receptors, as binding to the mu, delta, and kappa opioid receptors was unaffected, as was binding to benzodiazepine and neurotensin receptors. 

To obtain reliable information it is necessary to identify and characterize each component in the material. To fulfil this aim, methodologies characterized by high selectivity, specificity and sensitivity are required. Mass spectrometry (MS) is one of the most powerful methodologies for identifying, structurally characterizing, and quantitating wide classes of molecules, ranging from small to very big species. 

Although PSA is a batchwise process, by using multiple beds in a sequential manner the overall process is operated in a continuous fashion. Each bed may contain layers of different adsorbent materials selective for specific contaminants in the hydrogen gas stream to be purified. Each bed undergoes a sequence of four basic steps in a PSA cycle adsorption, depressurization, purge at low pressure, and repressurization. This sequence of cyclic operations for each bed is shown schematically for a four-bed PSA process in Figure 8.4 (Yang, 1987 Cassidy, 1980 Miller and Stocker, 1999). 

Judgement sampling involves using knowledge about the material to be sampled, and the reason for sampling, to select specific samples. 

An etch stop is a method that allows for selective removal of a specific material. Selectivity, therefore, is the most important property of an etch stop. It is defined as the etch rate of the faster etching material divided by the etch rate of the slower etching material. 

The resist materials that have emerged from these studies are the first examples of resist materials tailored specifically for use in the microelectronics industry. They are specialty polymers that are produced in very low volumes, and have been developed as a result of research carried out in industrial laboratories. In the following sections, we will examine the chemistry of selected examples of these new systems. 

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