Base Materials

Emphasis is placed on the base material, operating conditions, and applicable surface treatments. As can be seen, alternative coating processes/ materials may be recommended for a given material/operating condition combination. Final selection may be based on some of the application and performance requirements listed above and further examined in subsequent sections of this Chapter. 

Base materials for structural parts are conunonly an engineering steel, cast iron, stainless steel (most probably a ferritic or martensitic type), or an aluminum alloy. 

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Installation for Ultrasonic Testing AKV-S is designed for testing of diesel motors pistons. Particularly, this device identifies the areas with cracks and lowered adhesion on interfacial boundary between niresist ring and base material. 

Fisoher J, Heiney P A and Smith A B III 1992 Solid-state ohemistry of fullerene-based materials Accounts. Chem. Res. 25 112... 

Mirkin C A and Caldwell W B 1996 Thin film, fullerene-based materials Tetrahedron 52 5113-30... 

Cagle D W, Kennel S J, Mirzadeh S, Alford J M and Wilson L J 1999 In vivo studies of fullerene-based materials using endohedral metallofullerene radiotraoers Proc. Natl Acad. Sc/. USA 96 5182-7... 

Guth J-L and Kessler H 1999 Synthesis of aluminosilicate zeolites and related silica-based materials Catalysis and Zeolites, Fundamentals and Applications ed J Weitkamp and L Puppe (Berlin Springer) pp 1-52... 

Traa Y, Burger B and Weitkamp J 1999 Zeolite-based materials for the seleotive oatalytio reduotion of NOx with hydrooarbons Microporous Mesoporous Mater. 30 3-41... 

Solid-State Welding. Sohd-state welding comprises a group of welding processes wherein a bond is made between two base materials upon the apphcation of pressure at a temperature below the soHdus of the base materials (Table 1). Interlayers are sometimes used. By joining materials in the sohd state, many of the difficulties of the fusion processes are avoided. 

The largest market for elastomer-based adhesives is that of lamination (see Laminates). Modem office furniture having Formica as a surfacing material is made with an elastomer-based adhesive. Tile adhesives for ceramic or carpet tile are also elastomer-based and usually solvent appHed. Paper adhesives and shoe manufacture also use substantial quantities of mbber-based materials. Solvent-weld adhesives are used to join plastic plumbing and to repair vinyl sheeting. 

Molten Carbonate Fuel Cell. The electrolyte ia the MCFC is usually a combiaation of alkah (Li, Na, K) carbonates retaiaed ia a ceramic matrix of LiA102 particles. The fuel cell operates at 600 to 700°C where the alkah carbonates form a highly conductive molten salt and carbonate ions provide ionic conduction. At the operating temperatures ia MCFCs, Ni-based materials containing chromium (anode) and nickel oxide (cathode) can function as electrode materials, and noble metals are not required. 

Unlike conventional ceramic materials, glass-ceramics are fully densifted with zero porosity. They generally are at least 50% crystalline by volume and often are greater than 90% crystalline Other types of glass-based materials that possess low amounts of crystallinity, such as opals and mby glasses, are classified as glasses and are discussed elsewhere (see Glass). 

Constrained-Layer Treatments. Constrained-layer damping treatments consist of a thin layer (/ m) of viscoelastic material sandwiched between a base material and an outer constraining layer of sheet metal or other stmctural material. Some of these treatments are available with self-adhesives on both sides of the viscoelastic material and act as a bonding agent between the base and constraining layers others have the constraining layer already bonded to the inner layer so they need only be appHed to the base material. 

Urea—formaldehyde use has been greatly restricted because of free formaldehyde (qv) emissions which can cause eye irritation and in some cases serious illness. Some attempts at developing formaldehyde-free urea-based materials are ongoing. 

Since 1971, the overall demand for isocyanates has increased at a compounded rate of 12%. Although this level will not likely be sustained in the future due to the maturation of key appHcation markets, it is probable that additional growth will occur through the year 2000. This trend will likely iaclude a shift in emphasis from TDl to MDl and polymeric MDl-based materials. New growth opportunities in the constmction industry, stmctural appHcations, and growth in the automotive industry exist. Third-world markets are also anticipated to provide growth opportunities. 

Fig. 16. Insulator wall designs (a) peg wall (b) conducting bar wall and (c) segmented bar wall. The gas-side materials are tungsten and tungsten—copper composite, the base material, copper, and the insulators, boron nitride. Slagging grooves are shown.

Traditional textile fabrics are made by weaving or knitting. Nonwoven fabrics are similar to woven and knitted fabrics in that both are planar, inherently flexible, porous stmctures composed of polymer-based materials. The main difference between the two is the manner in which the fabric is made. 

As engineered stmctures, nonwovens can be designed to have appearances, textures, and other aesthetic properties comparable to traditional wovens and knits, and performance and functional properties superior to traditional wovens and knits. Nonwovens are, indeed, a distinct class of fiber-based materials with the characteristics of fabric and many of its useful properties. 

Although beryllium oxide [1304-56-9] is in many ways superior to most commonly used alumina-based ceramics, the principal drawback of beryUia-based ceramics is their toxicity thus they should be handled with care. The thermal conductivity of beryUia is roughly about 10 times that of commonly used alumina-based materials (5). BeryUia [1304-56-9] has a lower dielectric constant, a lower coefficient of thermal expansion, and slightly less strength than alumina. Aluminum nitride materials have begun to appear as alternatives to beryUia. Aluminum nitride [24304-00-5] has a thermal conductivity comparable to that of beryUia, but deteriorates less with temperature the thermal conductivity of aluminum nitride can, theoreticaUy, be raised to over 300 W/(m-K) (6). The dielectric constant of aluminum nitride is comparable to that of alumina, but the coefficient of thermal expansion is lower. 

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