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Use of metastable, dissociated and charged gas species in synthesis: a low pressure analogue of the high pressure technique

Jayadevan, KP and Kumar, NV and Mallya, RM and Jacob, KT (2000) Use of metastable, dissociated and charged gas species in synthesis: a low pressure analogue of the high pressure technique. In: Journal Of Materials Science, 35 (10). pp. 2429-2434.

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Abstract

Oxidation of silver using microwave-induced oxygen plasma and oxygen-ozone gas mixture was studied as a function of temperature and partial pressure. The oxide $Ag_2O$ was formed at temperatures well above its normal decomposition temperature in oxygen plasma at a pressure of 5 Pa. The higher oxide $AgO_{1-x}$ was formed in $O_2+O_3$ gas mixtures at lower temperatures. The oxygen chemical potentials for the oxidation of Ag to $Ag_2O$ , $Ag_2O$ to $AgO_{1-x}$ and AgO to $Ag_2O_3$ were evaluated from thermodynamic data and compared with the experimental results to obtain information on the chemical potential of oxygen in microwave plasma and gases containing ozone. The oxygen potential of the gas phase in microwave plasma operating at a pressure of 5 Pa was found to be in excess of 36 kJ/mol at 750 K. This is equivalent to a pressure of diatomic oxygen gas greater than $3 \times 10^7$ Pa. In the $O_2+O_3$ mixture at ambient pressure containing 5 mole percent $O_3$, the oxygen potential is \sim 112 kJ/mol at 465 K. The equivalent pressure of diatomic oxygen is $\sim 4 \times 10^{17}$ Pa. Thus, metastable species such as $O_3$ or charged species such as $O^-$ present in plasma can be used as a powerful reagent for the syntheses of metastable oxides. Similar techniques can be used for other metastable inorganic solids such as nitrides for functional applications.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Springer.
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 18 Sep 2008 08:26
Last Modified: 19 Sep 2010 04:49
URI: http://eprints.iisc.ernet.in/id/eprint/15873

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