Metals and ceramics

Because membranes appHcable to diverse separation problems are often made by the same general techniques, classification by end use appHcation or preparation method is difficult. The first part of this section is, therefore, organized by membrane stmcture preparation methods are described for symmetrical membranes, asymmetric membranes, ceramic and metal membranes, and Hquid membranes. The production of hollow-fine fiber membranes and membrane modules is then covered. Symmetrical membranes have a uniform stmcture throughout such membranes can be either dense films or microporous. 

Materials used for substrates can be broadly classified into ceramics and metals. Gommonly used ceramics, ie, alumina, aluminum nitride, and beryUia, can be easily incorporated into a hermetic package, ie, a package permanently sealed by fusion or soldering to prevent the transmission of moisture, air, and other gases. 

Cases can be classified as either hermetic or nonhermetic, based on their permeabiUty to moisture. Ceramics and metals are usually used for hermetic cases, whereas plastic materials are used for nonhermetic appHcations. Cases should have good electrical insulation properties. The coefficient of thermal expansion of a particular case should closely match those of the substrate, die, and sealing materials to avoid excessive residual stresses and fatigue damage under thermal cycling loads. Moreover, since cases must provide a path for heat dissipation, high thermal conductivity is also desirable. 

Ceramics and Metals. Among ceramics, the most commonly used material is alumina, which has good electrical resistivity (- 10 H-cm). 

Other Matrix Materials. Advanced materials, eg, stmctural components, in aerospace vehicles also employ ceramics and metals as composite matrices (see Composite materials, ceramic-matrix Metal-matrix composites). 

The forecasts made in 1985 (77) of 8—8.5% worldwide aimual growth have not materialized. The 2 x lOg + /yr engineering plastic production reported for 1985—1986 has remained fairly constant. Whereas some resins such as PET, nylon-6, and nylon-6,6 have continued to experience growth, other resins such as poly(phenylene oxide) have experienced downturns. This is due to successhil inroads from traditional materials (wood, glass, ceramics, and metals) which are experiencing a rebound in appHcations driven by new technology and antiplastics environmental concerns. Also, recycling is likely to impact production of all plastics. 

Catalytic Support Body Monolithic Honeycomb Unit. The terms substrate and brick are also used to describe the high geometric surface area material upon which the active coating material is placed. Monolithic honeycomb catalytic support material comes in both ceramic and metallic form. Both are used in automobile catalysts and each possesses unique properties. A common property is a high geometric surface area which is inert and does not react with the catalytic layer. 

Surface combustion devices are designed for fully premixing the gaseous fuel and air and burning it on a porous radiant surface. The close coupling of the combustion process with the burner surface results in low flame temperatures and, consequently, low NO formation. Surface materials can include ceramic fibers, reticulated ceramics, and metal alloy mats. This approach allows the burner shape to be customized to match the heat transfer profile with the application. 

Ceramics and metals are entirely held together by primary bonds - the ionic and covalent bond in ceramics, and the metallic and covalent bond in metals. These strong, stiff bonds give high moduli. 

According to an early historical overview (Jones 1960), the numerous attempts to understand the sintering process in both ceramics and metals fall into three periods (1) speculative, before 1937 (2) simple, 1937-1948 (3) complex, 1948 onwards. The complex experiments and theories began just at the time when metallurgy underwent its broad-based quantitative revolution (see Chapter 5). 

Ishida H (ed) (1988) Interfaces in polymer, ceramic and metal matrix composites, Elsevier, New York... 

Filtering. This is the final step after purification. Polymers, such as Teflon, are used widely in filters but, because of problems with their outgassing, are being increasingly replaced by ceramic and metal filters. 

Ishida, H., Interfacial Phenomena in Polymer, Ceramic and Metal Matrix Composites, Elsevier New York, 1988. 

The ultimate goal of assemblies of nanoscale MBBs is to create nanostructures with improved properties and functionality heretofore unavailable to conventional materials and devices. As a result, one should be able to alter and engineer materials with desired properties. For example, ceramics and metals produced through controlled consolidation of their MBBs are shown to possess properties substantially improved and different from materials with coarse microstmctures. Such different and improved properties include greater hardness and higher yield strength in the case of metals and better ductility in the case of ceramic materials [102]. 

Ceramic and metal packings are normally dumped into the column wet , to ensure a truly random distribution and prevent damage to the packing. The column is partially filled with water and the packing dumped into the water. A height of water must be kept above the packing at all times. 

Barrier filters have been tested and shown to have potential in gasification demonstration systems. Ceramic and metal candle-type filters were both tested at a commercial demonstration facility at Varnamo, Sweden, that is an integrated... 

Therefore, a team, led by the University of Alaska-Fairbanks, was formed to study these practical issues (75), including the composition of the ceramic membrane, seals that would join the ceramic and metal materials, membrane performance, and development of a ceramic that would resist warping and fracturing at the high temperatures of the conversion process. 

Ivers-Tiffee E, Wersing W, SchieBl M, and Greiner H. Ceramic and Metallic Components for a Planar SOFC. Berichte der Bunsen-Gesellschaftfur Physikalische Chemie 1990 94 978-981. 

AAS has been widely used in Europe to study archaeological ceramics and metals, ranging from Chinese celadons (Pollard and Hatcher 1986) to Roman terra sigillata (Mirti et al. 1990), and from Renin bronzes (Willett and Sayre 2000) and Islamic brasses (Al-Saad 2000) to Chalcolithic and Early Bronze Age copper alloys from ancient Israel (Shalev 1995). ICP-AES, using solution sampling, can potentially provide data on a wider range of elements... 

The electrozone sensing technique, also called the Coulter principle, was originally developed for biomedical applications for counting blood cells. This method counts and sizes particle based on changes in the electrical resistance caused by nonconductive particles suspended in an electrolyte. It presently finds uses in a wide variety of industries, including the food, environmental, coatings, ceramics, and metals industries. 

Castle, J.E. and Watts, J.F. (1988). The study of interfaces in composite materials by surface analytical techniques. In Interfaces in Polymer, Ceramic and Metal Matrix Composites (Proc. ICCI-II) (H. Ishida ed ), Elsevier Seienee, New York, pp. 57-71. 

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