Ceramic commercially available

Several manufacturers of ceramic powders are involved in commercializa tion of hydrothermaHy derived powders. In the United States, Cabot (Boyertown, Peimsylvania) has built a small manufacturing plant and is supplying materials to capacitor manufacturers. Other manufacturers include Sakai Chemical and Euji Titanium in Japan. Sakai Chemical is reportedly producing 1 t/d in its demonstration plant. A comparison of the characteristics of commercially available powders is given in Table 2. 

Other. Insoluble alkaline-earth metal and heavy metal stannates are prepared by the metathetic reaction of a soluble salt of the metal with a soluble alkah—metal stannate. They are used as additives to ceramic dielectric bodies (32). The use of bismuth stannate [12777-45-6] Bi2(Sn02)3 5H20, with barium titanate produces a ceramic capacitor body of uniform dielectric constant over a substantial temperature range (33). Ceramic and dielectric properties of individual stannates are given in Reference 34. Other typical commercially available stannates are barium stannate [12009-18-6] BaSnO calcium stannate [12013 6-6] CaSnO magnesium stannate [12032-29-0], MgSnO and strontium stannate [12143-34-9], SrSnO. ... 

The number of appHcatioas utilizing the ferroelectric respoase of ceramic materials has beeaHmited. Memory products are uader developmeat and are anticipated to be commercially available duting the early to mid-1990s. 

Fibers in which the basic chemical units have been formed by chemical synthesis, followed by fiber formation, are called synthetic fibers. Examples include nylon, carbon, boron fibers, organic fibers, ceramic fibers, and metallic fibers. Among all commercially available fibers, Kevlar fibers exhibit high strength and modulus. (Kevlar is a DuPont trademark for poly [p-phenylene diamine terephthalamide].) It is an aromatic polyamide (aramid) in which at least 85% of the... 

Special characteristics can be developed in individual materials depending on the cations present and their arrangement relative to each other and to the oxygen anions. The most important of these characteristics is low, medium or high reversible thermal expansion. The properties of some commercially available glass-ceramics are summarised in Table 18.6. 

In most cases, glass-ceramics possess good chemical stability and certainly compare favourably in this respect with other ceramic materials. Table 18.7 summarises makers data for chemical attack on commercially available materials. 

Table 18.6 Property data for some commercially available glass-ceramics...

In this connection it must be pointed out that standard samples which have been analysed by a number of skilled analysts are commercially available. These include certain primary standards (sodium oxalate, potassium hydrogenphthalate, arsenic(III) oxide, and benzoic acid) and ores, ceramic materials, irons, steels, steel-making alloys, and non-ferrous alloys. 

Though these materials are thermally very stable and mechanically inert they do only poorly resist mechanical stresses. This drawback can be overcome by reinforcing the monolithic ceramics with fibers. Today SiC-, Si3N4- and siliconcarbonitride fibers are commercially available, which are used in worldwide research activities to develop bulk component parts with composites. 

A variety of piezoelectric transducers have been employed for PAC. Ceramic transducers, usually lead zirconate titanate, are most commonly employed because of their sensitivity, time resolution and commercial availability. However, their acoustic response is often dominated by their own resonance, and so polymeric film detectors, such as polyvinylidenedifluoride, are often used. These piezoelectric materials are non-resonant, but not as sensitive as the ceramic detectors. Again, each detector has its own advantages (and disadvantages).14,15... 

The copyrolysis of 1 wt% dibromotetrafluoro-p-xylylene with commercially available hexafluoro-p-xylene (Aldrich) with metals was examined and it was found that it was indeed possible to prepare films that were spectroscopically indistinguishable from those deposited from dimer. The PA-F films obtained are of excellent quality, having dielectric constants of2.2-2.3 at 1 MHz and dissociation temperatures up to 530°C in N2. A uniformity of better than 10% can be routinely achieved with a 0.5-gm-thick film on a 5-in. silicon wafer with no measurable impurities as determined by XPS. During a typical deposition, the precursor was maintained at 50°C, the reaction zone (a ceramic tube packed with Cu or Ni) was kept at 375-550°C, and the substrate was cooled to -10 to -20°C. The deposited film had an atomic composition, C F 0 = 66 33 1 3 as determined by XPS. Except for 0, no impurities were detected. Within instrumental error, the film is stoichiometric. Poly(tetrafluoro-p-xylylene) has a theoretical composition ofC F = 2 1. Figure 18.2 illustrates the XPS ofthe binding energy... 

Inorganic membranes commercially available today are dominated by porous membranes, particularly porous ceramic membranes which are essentially the side-products of the earlier technical developments in gaseous diffusion for separating uranium isotopes in the U.S. and France. Summarized in Table 3.1 are the porous inorganic membranes presently available in the market (Hsieh 1988). They vary greatly in pore size, support material and module geometry. 

Porous metals have long been commercially available for particulate filtration. They have been used in some cases as microfiltration membranes that can withstand harsh environments, or as porous supports for dynamic membranes. Stainless steel is by far the most widely used porous metal membrane. Other materials include silver, nickel. Monel, Hastelloy and Inconel. Their recommended maximum operating temperatures range from 200 to 650°C. Elepending on the pore diameter which varies from 0.2 to 5 microns, the water permeability of these symmetric membranes can exceed 3000 L/h-m -bar and is similar to that obtained with asymmetric ceramic microfiltration membranes. Due to the relatively high costs of these membranes, their use for microfiltration has not been widespread. 

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