Mixed metal oxides titanates

J. Livingston, Mixed Metal Oxide Titanate Pigments , Ti02 93 Conference, 1993. 

Titanium IV) oxide, T1O2. See titanium dioxide. Dissolves in concentrated alkali hydroxides to give titanates. Mixed metal oxides, many of commercial importance, are formed by TiOj. CaTiOj is perovskite. BaTiOa, per-ovskite related structure, is piezoelectric and is used in transducers in ultrasonic apparatus and gramophone pickups and also as a polishing compound. Other mixed oxides have the il-menite structure (e.g. FeTiOj) and the spinel structure (e.g. MgjTiO ). 

M2Ti04 (M = Mg, Zn, Mn, Fe, Co) have the spinel stmcture (MgAl204, p. 248) which is the third important stmcture type adopted by many mixed metal oxides in this the cations occupy both octahedral and tetrahedral sites in a cep array of oxide ions. Ba2Ti04, although having the same stoichiometry, is unique amongst titanates in that... 

Another major reason for studying mixed metal oxide membranes from double metal alkoxides is the potential for preparing zeolite>like membranes which can exhibit not only separation but also catalytic properties. It has been suggested that combinations of silica and alumina in a membrane could impart properties similar to those of natural and synthetic zeolites [Anderson and Chu, 1993]. Membranes with a pore diameter of 10 to 20 nm and consisting of combinations of titania, alumina and silica have been demonstrated by using a mixture of a meta>titanic acid sol, an alumina sol and silicic acid fine particles followed by calcining at a temperature of 500 to 900 C [Mitsubishi Heavy Ind., 1984d]. 

A considerable number of materials called titanates are known, some of which are of technical importance. Nearly all of them have one of the three major mixed metal oxide structures (page 54), and indeed the names of two of the structures are those of the titanium compounds that were the first found to possess them, namely, FeTi03, Hmenite, and CaTi03, perovskite. Other titanites with the ilmenite structure are MgTiOa, MnTi03, CoTi03... 

Several nanocrystalhne metal oxides have been prepared by the combustion method and the topic has been reviewed by Patil et al. [5]. Combustion of metal hydrazine carboxylates, [e.g. MCjO (N H )J is generally anployed to obtain the nanoparticles of oxides such as y-Fefiy ZnO and NiO. Mixed-metal oxides like cobaltites (MCo O ), ferrites (MFe,0 ), manganites (MMn O ) and titanates (MTiOj) are prepared by the combustion of mixed-metal carboxylate hydrazinates in the temperature range of 165-345 °C [6,7]. Solution combustion synthesis has been used to prepare nanocrystalline oxides such as Al Oj, CeO, ZrO, TiO, ... 

In this chapter we have shown how critical the local structure is to the elucidation of the properties of mixed-ion oxides such as the CMR manganites, ferroelectric titanates, and superconducting cuprates. The effect of local structure is more pronounced for oxides than for free-electron metals since the local structure tends to be better defined in oxides due to their covalent bonding, relatively open structure, and the tendency for charge localization. In metals, on the other hand, small local effects are smeared out because of delocalized charge, strong screening, and densely packed structure. 

Inorganic Titanates. Titanium forms a series of mixed oxide compounds with other metals. Only in one of these, Ba2Ti04, ate there discrete TiOJ ions (99). Compounds of the general formula M" 2Ti02 or M " Ti02 are known as metatitanates those having AU TiO and are called... 

Outside of catalyst preparation, reaction of sucrose with metal nitrates has been used to prepare nanocomposite mixed oxide materials. Wu et al. [46] reported the synthesis of Mg0-Al203 and Y203-Zr02 mixed oxides by reaction of nitrate precursors with sucrose. The resulting powders had smaller particles than those prepared without sucrose. Das [47] used a similar method in the presence of poly vinylalcohol to produce nanocrystalline lead zirconium titanate and metal ferrierites (MFe204, M = Co, Ni, or Zn). The materials prepared using sucrose had smaller crystallites than those made without. Both authors observed an exothermic decomposition of the precursors during calcination. 

The metal has very little commercial use. In elemental form it is a laser source, a portable x-ray source, and as a dopant in garnets. When added to stainless steel, it improves grain refinement, strength, and other properties. Some other applications, particularly in oxides mixed with other rare earths, are as carbon rods for industrial hghting, in titanate insulated capacitors, and as additives to glass. The radioactive isotope ytterbium-169 is used in portable devices to examine defects in thin steel and aluminum. The metal and its compounds are used in fundamental research. 

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