Powders zirconates

Ardizzone and coworkers [51] developed a hybrid method between colloidal and polymeric methods starting from Si and Zr alkoxides in water-ethanol mixtures, it was employed to obtain both the yellow of praseodymium-doped zirconium silicate powders and the coral of iron-doped zirconium silicate powders (zircon). 

Zirconia, ZrOj, is made from the natural hydrated mineral, or from zircon, a silicate. Silicon carbide and silicon nitride are made by reacting silicon with carbon or nitrogen. Although the basic chemistry is very simple, the processes are complicated by the need for careful quality control, and the goal of producing fine (<1 jiva) powders which, almost always, lead to a better final product. 

PZT (lead zirconate titanate) and PLZT (lead lanthanum zirconate titanate) combine ferroelectic, optical, and electronic properties and are used in optoelectronic and piezoelectric devices. Powders for hot pressing produced by CVD are being investigated. 

An extension of the reduction-chlorination technique described so far, wherein reduction and chlorination occur simultaneously, is a process in which the oxide is first reduced and then chlorinated. This technique is particularly useful for chlorinating minerals which contain silica. The chlorination of silica (Si02) by chlorine, in the presence of carbon, occurs above about 1200 °C. However, the silica present in the silicate minerals readily undergoes chlorination at 800 °C. This reaction is undesirable because large amounts of chlorine are wasted to remove silica as silicon tetrachloride. Silica is, therefore, removed by other methods, as described below, before chlorination. Zircon, a typical silicate mineral, is heated with carbon in an electric furnace to form crude zirconium carbide or carbonitride. During this treatment, the silicon in the mineral escapes as the volatile oxide, silicon monoxide. This vapor, on contact with air, oxidizes to silica, which collects as a fine powder in the furnace off-gas handling system ... 

The mill has also been used to grind industrial minerals and technical ceramics including limestone, lead zirconates, metal powders, fibrous materials, such as paper, wood chips and peat, and chemicals and agricultural products, such as grains and oilseeds. 

To obtain effective materials for catalytic combustion, Arai and co-workers developed a preparation method based on the hydrolysis of the alkoxides of the components.12 This sol-gel method was originally developed to prepare high-purity submicron powders of alkaline or alkaline-earths titanates or zircon-ates.13,14 The method is particularly suitable for low-temperature production of mixed oxides due to the effective mixing of the components at the atomic level that can be obtained in the gel precursor. 

Low temperature synthesis of lead zirconate titanate (PZT) can also be obtained via a microemulsion process [161]. The microemulsion, containing cations of lead zirconium and titanium in the aqueous phase, was coprecipitated as hydroxide precursors by the addition of ammonium solution. Crystalhne tetragonal PZT powders were then obtained by calcining the precursors at a temperature as low as 450 °C in air without forming any intermediate phases. 

Similar investigations of the mechanochemical synthesis of zircon using anhydrous and sol-gel powders of zirconium and silicon oxides as initial reagents were reported in [43,44]. 

The demand for mixed oxide chromatographic-quality stationary phase materials is small and only a few methods that detail their preparation are available in the hterature. There are, however, numerous examples of the preparation of zircon powders and Ref. [4] is an example of such a process. In general, these types of powders are unsuitable for chromatographic stationary phases because their particle sizes are in the submicron range with very broad distributions. The synthesis of mixed oxide supports for chromatographic apphcations can essentially be divided into two types coprecipitation methods and coating methods. 

D. L. Hankey, Calcination Reaction Mechanisms and Kinetics in Lead Zirconate Titanate Powder Compacts, Ph.D. thesis, Pennsylvania State University, 1980. 

Properties White powder. A strong flux in enamels, glazes, and porcelains. It can be used in place of lithium zirconate. 

Tartaj, P. and de Jonghe, L.C., Preparation of nanospherical amorphous zircon powders by a microemulsion-mcdiated process, J. Mater. Chem., 10, 2786, 2000. 

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