Perovskite deposition

A large deposit of perovskite was found recently in the USA (Powderhom). Perovskite deposits are also known to be found in Russia (Cola Pennisula). There is little information available on research into flotation of perovskite conducted on ores from some Russian deposits [6], These ores are relatively complex and contain a variety of gangue minerals including pyroxene, amphibole, olivine, nepheline, biotite and calcite. 

Most recently, development testwork was performed on a large perovskite deposit (Powderhom) located in the USA. An effective beneficiation process was developed, where a concentrate assaying >50% Ti02 was achieved in the pilot plant confirmation tests [7]. During this development testwork, a number of different collectors were examined at different pH values. Figure 25.5 shows the effect of the different collectors on perovsikte flotation. The most effective collector was phosphoric acid ester modified with either fatty alcohol sulphate or petroleum sulphonate. 

Alifanti, M., Florea, M Cortes-Corberan, V., Endruschat, U., Delmon, B and Pdrvulescu, V.I. (2006) Effect of LaCoOa perovskite deposition on ceria-based supports on total oxidation of VOC. Catal Today, 112 (1-4), 169-173. 

Generally, their poor surface area and low percentage of active metals limit the field of the possible applications however, few applications concern perovskites deposited on a support. Perovskites are often used in oxidation reactions partial or total oxidation of hydrocarbons, oxidation of CO or chlorinated hydrocarbons, where there are possibility of exchange of part of the oxygen of their surfaces with oxygen of the gas phase with vacancies formation. Absorption of NO c in diesel or lean-burn engines has also been described [2-4]. 

Recent applications of e-beam and HF-plasma SNMS have been published in the following areas aerosol particles [3.77], X-ray mirrors [3.78, 3.79], ceramics and hard coatings [3.80-3.84], glasses [3.85], interface reactions [3.86], ion implantations [3.87], molecular beam epitaxy (MBE) layers [3.88], multilayer systems [3.89], ohmic contacts [3.90], organic additives [3.91], perovskite-type and superconducting layers [3.92], steel [3.93, 3.94], surface deposition [3.95], sub-surface diffusion [3.96], sensors [3.97-3.99], soil [3.100], and thermal barrier coatings [3.101]. 

Catalysts include oxides, mixed oxides (perovskites) and zeolites [3]. The latter, transition metal ion-exchanged systems, have been shown to exhibit high activities for the decomposition reaction [4-9]. Most studies deal with Fe-zeolites [5-8,10,11], but also Co- and Cu-systems exhibit high activities [4,5]. Especially ZSM-5 catalysts are quite active [3]. Detailed kinetic studies, and those accounting for the influence of other components that may be present, like O2, H2O, NO and SO2, have hardly been reported. For Fe-zeolites mainly a first order in N2O and a zero order in O2 is reported [7,8], although also a positive influence of O2 has been found [11]. Mechanistic studies mainly concern Fe-systems, too [5,7,8,10]. Generally, the reaction can be described by an oxidation of active sites, followed by a removal of the deposited oxygen, either by N2O itself or by recombination, eqs. (2)-(4). 

Schwartz, R. W. 1997. Chemical solution deposition of perovskite thin films. Chem. Mat. 9 2325-2340. 

Liu, D. D. H. Mevissen, J. P. 1997. Thick layer deposition of lead perovskites using diol-based chemical solution approach. Int. Ferro. 18(l-4) 263-274. 

Extensive research has been carried out mainly on ilmenite and, to a lesser degree, on flotation of rutile and perovskite. Flotation studies have been performed on titanium minerals from both hard rock and fine-grained sand deposits. 

Various metal and metal oxide nanoparticles have been prepared on polymer (sacrificial) templates, with the polymers subsequently removed. Synthesis of nanoparticles inside mesoporus materials such as MCM-41 is an illustrative template synthesis route. In this method, ions adsorbed into the pores can subsequently be oxidized or reduced to nanoparticulate materials (oxides or metals). Such composite materials are particularly attractive as supported catalysts. A classical example of the technique is deposition of 10 nm particles of NiO inside the pore structure of MCM-41 by impregnating the mesoporus material with an aqueous solution of nickel citrate followed by calicination of the composite at 450°C in air [68]. Successful synthesis of nanosized perovskites (ABO3) and spinels (AB2O4), such as LaMnOs and CuMn204, of high surface area have been demonstrated using a porous silica template [69]. 

Mitchell, R. H. 1996. Perovskites a revised classification scheme for an important rare earth element host in alkaline rocks. In Jones, A. P., Wall, F. Williams, C. T. (eds) Rare Earth Minerals, Chemistry, Origin and Ore Deposits. Chapman and Hall, London, 41-76. 

In order to obtain reliable results, magnetostriction should be measured in epitaxial films, free of twins, which are typical for materials of perovskite structure. In the case of films it is not easy, because usually the films are deposited on perovskite substrates, thus presenting difficulties in eliminating twin structures. 

Thin films, to attain enough sensitivity and response time, of oxide materials normally deposited on a substrate are typically used as gas sensors, owing to their surface conductivity variation following surface chemisorption [183,184], Surface adsorption on a Sn02 film deposited on alumina produces a sensitive and selective H2S gas sensor [185]. In addition, a number of perovskite-type compounds are being used as gas sensor materials because of their thermal and chemical stabilities. BaTi03, for example, is used as sensor for C02 [183],... 

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