CaTiOs

A number of high temperature processes for the production of titanium carbide from ores have been reported (28,29). The aim is to manufacture a titanium carbide that can subsequently be chlorinated to yield titanium tetrachloride. In one process, a titanium-bearing ore is mixed with an alkah-metal chloride and carbonaceous material and heated to 2000°C to yield, ultimately, a highly pure TiC (28). Production of titanium carbide from ores, eg, ilmenite [12168-52-4], EeTiO, and perovskite [12194-71 -7], CaTiO, has been described (30). A mixture of perovskite and carbon was heated in an arc furnace at ca 2100°C, ground, and then leached with water to decompose the calcium carbide to acetjdene. The TiC was then separated from the aqueous slurry by elutriation. Approximately 72% of the titanium was recovered as the purified product. In the case of ilmenite, it was necessary to reduce the ilmenite carbothermaHy in the presence of lime at ca 1260°C. Molten iron was separated and the remaining CaTiO was then processed as perovskite. 

Corgne A, Wood B (2003) Trace element partitiorring between silicate melt and Ca-perovskites (CaTiOs and CaSi04)— implications for mantle differentiation. Geophys Res Lett 29(19) 1903, doi 10.1029/2001GL014398... 

Figure 8 The elementary cell of the perovskite CaTiO. (a) Common representation ...

The special electric, magnetic, optical, superconductive and catalytic properties of perovskite-typed oxides make this group of materials attracting and widely used. Perovskites were named according to the similarity of their structure with the CaTiOs compoimd. The... 

Titanium occurs in nature in the minerals rutile( Ti02), ilmenite (FeTiOs), geikielite, (MgTiOs) perovskite (CaTiOs) and titanite or sphene (CaTiSi04(0,0H,F)). It also is found in many iron ores. Abundance of titanium in the earth s crust is 0.565%. Titanium has been detected in moon rocks and meteorites. Titanium oxide has been detected in the spectra of M-type stars and interstellar space. 

Ordering of vacancies also plays a key role in selective oxidation catalysis over perovskite-based catalysts such as CaMnOs oxides. CaMnOs has a CaTiOs (AMO3) perovskite structure which is made up of cations coordinated to 12 0 anions. They, in turn, are connected to corner-sharing MoOe octahedra. CaMnOs was used as a model catalyst on a laboratory scale by Thomas et al (1982) in propene oxidation to benzene and 2-methyl propene to paraxylene. In such reactions the compounds are found to undergo reduction to form anion-deficient metastable phases of the type CaMnOs-x where 0 < x < 0.5, forming several distinct phases. 

Figure 1.42 The perovskite crystal structure of CaTiOs. From W. D. Kingery, H. K. Bowen, and D. R. Uhlmann, Introduction to Ceramics. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

Fluid number or name Formula or mix, % Mol wt Normal bp, °C T °C P MPa LFLC, % Safety classifi-catio d n... 

FIGURE 1.44 The perovskite structure of compounds ABX3, such as CaTiOs. Ca, green sphere Ti, silver spheres 0, red spheres. 

FIGURE 10.6 The A-type unit cell of the perovskite structure for compounds ABOs, such as CaTiOs. 

Draw a packing diagram (Chapter 1, Section 1.4.5) of the perovskite A-type cell (CaTiOs/ABOs), determine the number of ABO3 formula units, and describe the coordination geometry around each type of atom. Repeat this procedure for the perovskite B-type unit cell. 

The parent perovskite structure shown in Fig. 10.4 consists of alternating layers of composition AO and BO2, as for example in BaTiOs (23759) and CaTiOs (62149). It is also possible to have several AO layers between each BO2 layer providing each AO layer is sheared by half a unit cell from the adjacent AO layers, as shown for La2Ni04 in Fig. 12.1. This permits a wide range of structures with an even wider range of compositions to be prepared. Which compositions are possible depend on how well the structure can accommodate the bonding requirements of the atoms A and B. 

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