Comparison of MA Processes and Products from Ni(OH)₂ with Al or Al(OH)₃

Ni(OH)(2) was milled either with Al metal or with Al(OH)(2) particles to compare the process of compounding and the properties of the products. Although the Knight shift, K-27, of Al-27-NMR spectrum of Al(OH)(3) is about 0ppm, it exceeds 10000ppm after milling with Ni(OH)(2) for 12h. This shift increases to above 20000ppm at lower temperature. In metallic Al system, K-27 under the same condition was ca. 1600ppm and slightly decreases with decreasing temperature. In the latter system, the average conduction electron density of metallic Al is reduced by Ni species in the surface oxide layer and reduces the Fermi contact interaction at Al nuclei to change the Knight shift. In contrast, in AI(OH), system, Al(m) species are surrounded by Ni(ll) so that 27K is directly influenced by the local magnetic field of Ni(II). From the viewpoint of materials synthesis, using AI(OH), is more beneficial due to much more homogeneous structure close to that of NiAl2O4. We further elucidated the change in the state of Al by heating the as-milled product to give well-crystallized NiAl2O4.