کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4995944 | 1459432 | 2017 | 8 صفحه PDF | دانلود رایگان |
- TG and X-ray data are used to evaluate oxidation of nano-Cu and μm-Cu particles.
- Nano-Cu reacts at lower temperatures than μm-Cu, analyzed by shrinking core model.
- Cuâ¥Cu2Oâ¥CuO is diffusion controlled, kinetics and diffusivities are evaluated.
- Diffusivities of nano and μm-Cu match and agree with boundary diffusion of bulk Cu.
- Crystallite growths of the oxides are obtained and analyzed by a nucleation model.
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) = â5.234 cm2 sâ1, E1 = 88.5 kJ/mol, and Log10(Z2d) = â3.873 cm2 sâ1, E2 = 122.7 kJ/mol from the X-ray study for the 20 μm particles. For the 60 nm particles Log10(Z1) = 8.08 sâ1 (1st order reaction), E1 = 89.15 kJ/mol and Log10(Z2d) = â5.09 cm2 sâ1 (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.
Journal: Thermochimica Acta - Volume 654, 10 August 2017, Pages 93-100