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Comparison of kinetics, oxide crystal growth and diffusivities of nano- and micrometer-sized copper particles on oxidation in air

: Eisenreich, Norbert; Schulz, Olga; Koleczko, Andreas; Knapp, Sebastian


Thermochimica acta 654 (2017), S.93-100
ISSN: 0040-6031
Fraunhofer ICT ()

The oxidation of nanometer-sized and micrometer-sized copper particles with diameters of 60 nm and 20 μm 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 μm 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.