Investigation of precipitated alumina structures by secondary-ion mass spectrometry and electron paramagnetic resonance spectrometry. Part 2.—Line-broadened electron paramagnetic resonance spectra interpreted via a distribution of spin-matrix parameters

Abstract

Relatively sharp chromium (3+) tracer electron paramagnetic resonance lines observed in alumina powders extracted from a chloride source solution are interpreted in terms of a narrow spread of λ=E/D values within 0.3 ⩽λ⩽ 1/3. This is consistent with regions of extended sheet-growth of pseudo-boehmite, in which the interior octahedra resemble the crystalline boehmite structure (with an estimated value of λ= 1/3). A sulphate source appears to retard this development of crystallinity, and a distribution of values of the spin-matrix parameter λ is invoked to account for the broad structure observed during short-term ageing. Such an interpretation agrees with an independent model for pseudo-boehmitic growth.