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2017
Journal Article
Titel
Comparison of kinetics, oxide crystal growth and diffusivities of nano- and micrometer-sized copper particles on oxidation in air
Abstract
The oxidation of nanometer-sized and micrometer-sized copper particles with diameters of 60 nm and 20 mm is investigated in air in the temperature range from 323 to 1273 K, using high-temperature X-ray diffraction and thermal analysis with multiple heating rates. The oxidation of both particle types occurs in two steps to Cu2O and to CuO in a similar way, the nanometer-sized particles at substantially lower temperatures and the two steps separated. The kinetics are investigated for both steps using a least squares fit procedure, comparing three different mechanisms: consecutive reaction steps of 1st order, step one with 1st order followed by a step modeled with Shrinking Core (SC) model and two steps connected with two SC models. The diffusivities with lowest standard deviations are: Log10(Z1d) = −5.234 cm2 s−1, E1 = 88.5 kJ/mol, and Log10(Z2d) = −3.873 cm2 s−1, E2 = 122.7 kJ/mol from the X-ray study for the 20 mm particles. For the 60 nm particles Log10(Z1) = 8.08 s−1 (1st order reaction), E1 = 89.15 kJ/mol and Log10(Z2d) = −5.09 cm2 s−1 (diffusion), E2 = 107.4 kJ/mol are found. These values are within the range of those obtained from copper plates. The crystallite size of the oxide particles begins at about 3-10 nm to be evaluated. It increases on temperature rise to be described by a nucleation mechanism, the kinetics being evaluated.
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