Influence of grinding on the texture, microstructure and chemical reactivity of nickel powders
The influence of grinding on the morphology, texture and microstructure of nickel powders has been studied. A series of three samples, the as-received one (NiNG) and those comminuted for 3 min (NiG3) and 30 min (NiG30), have been used. SEM observations have shown that cold-welding, leading to a decrease of particle size, takes place during the comminution process. Analysis of the XRD profiles by means of the Willianson and Hall method seems to demonstrate that the broadening of XRD peaks is produced by the microstrains generated during the milling of nickel powders, rather than by the diminution of crystallite size (coherently diffracting domains). On the other hand, it has been reported that the recrystallization temperature of this material by annealing under vacuum protection decreases on increasing the grinding time. Moreover, the mean XRD peak widths of samples annealed at 300 °C decreases according to the following trend: NiG30<NiG3< NiNG. This behaviour explains why the catalytic activity of these samples towards the dehydrogenation of formic acid in the vapour phase decreases according to the same trend.
KeywordsCrystallite Size Dehydrogenation Nickel Powder Recrystallization Temperature Integral Breadth
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