The self-heating and shrinkage phenomena during the high-temperature oxidation of porous nickel
There is a spontaneous temperature rise during heating in the range 400–800°C, with a maximum at 500–600°C.
The extent of oxidation of nickel, as assessed by weight gain, does not increase steadily with increasing temperature. A maximum degree of oxidation is observed in the temperature range 650–700°C. At higher temperatures, the degree of oxidation decreases because the pore outlets become blocked by oxides.
The kinetics of oxidation of porous nickel depend on specimen porosity and cross section. As specimen thickness increases, the relative degree of oxidation decreases.
The heating of specimens in air is accompanied by both oxidation and shrinkage, the magnitude of the latter increasing with temperature and porosity. The steady increase of shrinkage with rising temperature is disturbed in the range 700–750°C by intensified oxidation, which leads to a substantial decrease of shrinkage.
The specific features noted in the high-temperature oxidation behavior of porous nickel are likely to be found in the behavior of other porous materials which are subject to oxidation during heating in air.
KeywordsOxidation Porosity Shrinkage Porous Material Maximum Degree
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