Browsing by Author "Vickerman, John C"

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Investigation of Precipitated Alumina Structures by Secondary-ion Mass Spectrometry and Electron Paramagnetic Resonance Spectrometry Part 1.—Prediction of Electron Paramagnetic Resonance Conditions for Tracer Ions in Alumina Structures
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (05), 1981) Hare, Alan S; Vickerman, John C
The potential of a tracer electron paramagnetic resonance (e.p.r.) method for distinguishing crystalline regions in a de-solvated alumina gel is assessed in principle. A conventional matrix-diagonalisation procedure is used in order to establish the variation of principal-axis chromium(3+) and iron(3+) e.p.r. conditions as functions of their local structure (represented by the spin-matrix parameters D and E/D) and the external magnetic field. Simplified equations, assuming a crystal field of point electrical charges, provide a basis for estimating λ=E/D from crystallographic data.
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
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1981, 77 (05), 1981) Hare, Alan S; Vickerman, John C
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.