Published online by Cambridge University Press: 06 March 2019
X-ray diffraction analyses were applied to various pure nickel substrates while exposing them to oxygen at temperatures up to 800 °C. Coefficients of thermal expansion (CTE) were calculated from lattice parameters for both the nickel and the growing surface oxides. Behaviors more complex than the case for single phase bulk solids were observed due, in part, to oxidationinduced strains. The CTE values for such dynamic composite systems are not the same as those for the bulk solids. Thus, for example, the CTE values were found to be dependent on substrate metal thickness. In addition, discontinuities in the CTE's of both nickel and NiO occurred at or near their respective second order phase change temperatures.
Research sponsored by the U. S. Department of Energy, Assistant Secretary for Conservation and Renewable Energy, Office of Transportation Technologies, as part of the High Temperature Materials Laboratory User Program under contract DE-AC05-84OR21400, managed by Martin Marietta Energy Systems, Inc