Titanium ceramics

In the last decade, some systems, such as the Dionex DX-500, have been manufactured with a flow path using corrosion-resistant materials such as polyetheretherketone (PEEK , ICI Americas Wilmington, DE), rather than the traditional stainless steel. Since stainless steel is prone to corrosion by salts, particularly halides, the introduction of titanium, ceramic, and PEEK was welcomed by those performing chromatography in aqueous systems, particularly in biological applications. PEEK , however, is not useful in applications requiring pressures greater than about 4000 psi. 

Small animals, for which parenteral blood collection is not possible, should be killed with tools made of plastic or ceramic. There are special tools (scissors) made from zirconium, ceramic or titanium ceramic for hair cutting that can also be used for trace analysis. 

TABLE 7.11 RESIN, STEEL, ALLOY, TITANIUM, CERAMIC, RUBBER, NATURAL AND SYNTHETIC FIBER... 

Evans R, Smith I, Munz W D, Williams K J P and Yanwood J 1996 Raman microscopic studies of ceramic coatings based on titanium aluminum nitride ICORS 96 XVth Int. Conf. on Raman Spectroscopy ed S A Asher and P B Stein (New York Wiley) pp 596-7... 

Aqueous hydrogen fluoride of greater than 60% maybe handled in steel up to 38°C, provided velocities are kept low (<0.3 m/s) and iron pickup in the process stream is acceptable. Otherwise, mbber or polytetrafluoroethylene (PTFE) linings are used. For all appHcations, PTFE or PTEE-lined materials are suitable up to the maximum use temperature of 200°C. PTEE is also the material of choice for gasketing. AHoy 20 or Monel is typically used for valve and pump appHcations. Materials unacceptable for use in HE include cast iron, type 400 stainless steel, hardened steels, titanium, glass, and siHcate ceramics. 

Hafnium oxide 30—40 mol % titanium oxide ceramics (qv) exhibit a very low coefficient of thermal expansion over the temperature range of 20—1000°C. A 45—50 mol % titanium oxide ceramic can be heated to over 2800°C with no crystallographic change (48). 

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. 

H. Hucek and M. Wahl, 1990 Handbook ofiInternational Alloy Compositions and Designations, Vol. 1, Titanium, MCIC HB-09, Metals and Ceramics Information Center, BatteUe Columbus Laboratories, Columbus, Ohio, 1990. 

The sol—gel technique has been used mosdy to prepare alumina membranes. Figure 18 shows a cross section of a composite alumina membrane made by sHp coating successive sols with different particle sizes onto a porous ceramic support. SiUca or titanium membranes could also be made by the same principles. Unsupported titanium dioxide membranes with pore sizes of 5 nm or less have been made by the sol—gel process (57). 

Ion implantation is being used to form a thin haid case on matetials othei than steels. Titanium alloys have been successfully implanted with nitiogen. The process has been appHed to ceramics to modify the surface region. 

Use. Titanium dioxide is mainly used in the production of paints and lacquers (55—60%), plastics (15—20%), and paper ( 15%). Other apphcations include the pigmentation of printing inks, mbber, textiles (qv), leather, synthetic fibers, ceramics, white cement, and cosmetics. 

About 100,000 t of titanium dioxide aimuaHy are used as formulation components in the production of glass (qv), ceramics, electroceramics, catalysts, and in the production of mixed-metal oxide pigments. 

Putile Ceramic Pigments. StmcturaHy, aH mtile pigments are derived from the most stable titanium dioxide stmcture, ie, mtile. The crystal stmcture of mtile is very common for AX2-type compounds such as the oxides of four valent metals, eg, Ti, V, Nb, Mo, W, Mn, Ru, Ge, Sn, Pb, and Te as weH as haHdes of divalent elements, eg, fluorides of Mg, Mn, Fe, Co, Ni, and Zn. 

Titanium raw-material utilization can be broken down as illustrated in Figure 9. About 4% of the titanium mined is used as metal, 94% is used as pigment-grade Ti02, and 2% as ore-grade mtile for fluxes and ceramics. In 1995, the estimated U.S. Ti02 pigment production was valued at 2.6 biUion and was produced by five companies at 11 plants in nine states. About 47% was used in paint, 18% in plastics, 24% in paper, and 18% in other misceUaneous appHcations (56). 

Precipitation of a hydrated titanium oxide by mixing aqueous solutions of titanium chloride with alkaU forms the precipitation seeds, which are used to initiate precipitation in the Mecklenburg (50) variant of the sulfate process for the production of pigmentary titanium dioxide. Hydrolysis of aqueous solutions of titanium chloride is also used for the preparation of high purity (>99.999%) titanium dioxide for electroceramic appHcations (see Ceramics). In addition, hydrated titanium dioxide is used as a pure starting material for the manufacture of other titanium compounds. 

Both anatase and mtile are broad band gap semiconductors iu which a fiUed valence band, derived from the O 2p orbitals, is separated from an empty conduction band, derived from the Ti >d orbitals, by a band gap of ca 3 eV. Consequendy the electrical conductivity depends critically on the presence of impurities and defects such as oxygen vacancies (7). For very pure thin films, prepared by vacuum evaporation of titanium metal and then oxidation, conductivities of 10 S/cm have been reported. For both siugle-crystal and ceramic samples, the electrical conductivity depends on both the state of reduction of the and on dopant levels. At 300 K, a maximum conductivity of 1 S/cm has been reported at an oxygen deficiency of... 

---