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Thermal decomposition of basic manganous chromate

16 Jan 1982-Thermochimica Acta (Elsevier)-Vol. 52, pp 345-348
About: This article is published in Thermochimica Acta.The article was published on 1982-01-16. The article focuses on the topic(s): Thermal decomposition & Chromate conversion coating.

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Abstract: Temperature-programmed thermal decomposition of γ- and α-manganese oxyhydroxide has been studied between 20 and 670°C under vacuum and under a low pressure (10 Torr) of oxygen. Solid products at various temperatures have been analyzed by X-ray diffractometry. Under vacuum γ-MnOOH decomposed below 400°C to a mixture of Mn5O8, α-Mn3O4, and water according to the reaction scheme: 8MnOOH → Mn5O8 + Mn3O4 + 4H2O. Above this temperature Mn5O8 was converted to α-Mn3O4 as a result of oxygen removal. The vacuum dehydration at 250°C of oxyhydroxide rich in α-MnOOH led to the formation of a new modification of Mn2O3 isostructural with corundum (α-Al2O3). In oxygen both oxyhydroxides decomposed to β-MnO2. γ-MnOOH transformed directly to β-MnO2 while α-MnOOH appeared to transform via corundum-phase Mn2O3 as an intermediate.

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38 citations


Journal ArticleDOI
M.R. Udupa1Institutions (1)
16 Mar 1981-Thermochimica Acta

1 citations