Nonmetallic materials graphite

Among nonmetallic materials, glass, chemical stoneware, enameled steel, acid-proof brick, carbon, graphite, and wood are resistant to iodine and its solutions under suitable conditions, but carbon and graphite may be subject to attack. Polytetrafluoroethylene withstands Hquid iodine and its vapor up to 200°C although it discolors. Cloth fabrics made of Saran, a vinyHdene chloride polymer, have lasted for several years when used in the filtration of iodine recovered from oil-weU brines (64). 

The construction materials for the plates include most corrosion-resistant metals, usually 304SS, 316SS, titanium, Incoloy 825 , Hastelloy , and others, plus nonmetallic fused graphite, and fluoroplastic Diabon F . Typical gaskets between the plates include nitrile rubber, butyl, and EPDM elastromers, Hypalon and Viton , based on the various manufacturers literature. 

Now let us turn to a brief examination of flotation. Virtually all nonferrous metallic ores are concentrated by the flotation process. Sulfide ores have been studied particularly extensively, although the method has been used with oxides and carbonates as well as such nonmetallic materials as coal, graphite, sulfur, silica, and clay. Something on the order of a billion tons of ore a year are processed in this way. 

The papers read showed that, for application at low temperatures down to 4 K, the most critical properties of nonmetallic materials are their flexibility and resultant mechanical behavior, their coefficients of thermal expansion as compared with that of the inorganic materials with which they are combined, and their thermal conductivity. At present, the leading pol3nneric materials for low-temperature applications are epoxy resins, polypropylene, and polyimide strips and films, and polystyrene and polyurethane based foams. The leading fibers for reinforcement are glass, graphite, boron, and organic polyaramid. 

In the following sections, we look at several nonmetallic materials with applications in modem technology. We begin with a discussion of the different allotropes or forms of carbon—diamond, graphite, and the fullerenes—where research has produced some exciting discoveries (Section 13.4). The fullerenes are recently discovraed molecular forms of the element carbon, in which the carbon atoms form hollow balls and tubes that may make them important as catalysts or possibly as drug-delivay mataials. Diamond shows promise as a material that might supersede silicon in its role as a matmal for sohd-state electronics. Silicon and diamond can act as semiconductors, which we discuss in Section 13.5. We end the chapter with sections on silicon, silica, and silicates (Section 13.6), ceramics (Section 13.7), and finally composites (Section 13.8). 

Another growing field is that of nonmetallic heat exchanger designs which typically are of the shell and tube or coiled-tubing type. The graphite units were previously discussed but numerous other materi- s are available. The materials include Teflon, PVDF, glass, ceramic, and others as the need arises. 

The composite as a unique material normally refers to hybrid or mixed materials between dispersed filler or reinforcemenf in fhe form of fiber, powder, flake, etc. and the continuous matrix. The composite applied to manufacture the plate mainly belongs to the type of nonmefallic composite with both nonmetallic filler and mafrix, alfhough research work on composite plates with metal filler has been carried ouf. This research will not be specifically introduced here because no promising results have been reported so far. The other sandwiched composite plate consists of layered metals and thermal expanded graphite and was developed by Russian scientists [11] however, no technical details were released. 

In brittle nonmetallics (such as porcelain, glass, impregnated graphite, etc.) and some thermosetting resins, the materials show rigid behavior and develop high displacement stresses up to the point of sudden breakage due to overstrain. 

Arc sources are particularly useful for qualitative and semiquantitative analysis of nonmetallic samples, such as soils, plant materials, rocks, and minerals. Excitation times and arc currents are usually adjusted so that complete volatilization of the sample (Kcurs currents of 5 to 30 A for 20 to 200 s are typical. Typically 2 to 50 mg of sample in the form of a powder, small chips, grindings, or hlings, often mixed with a weighed amount of graphite, is packed into the cavity of graphite electrodes. The sample-containing electrode is usually the anode and a second graphite counter electrode is the cathode. 

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