Investigation of precipitated alumina structures by secondary-ion mass spectrometry and electron paramagnetic resonance spectrometry. Part 3.—Structure of an alumina coating precipitated on rutile titanium dioxide

Abstract

Deposition of an alumina or alumina–silica coating upon a rutile substrate was achieved satisfactorily in an aqueous precipitation system, which may contain paramagnetic ions co-precipitated at trace levels. Secondary-ion mass spectra of powders extracted during the process are consistent with an independent coating mechanism, i.e. nucleation and growth of the coating occurred at the surface of the rutile particles. The depth distribution of alumina, estimated from secondary-ion mass spectroscopy and etching measurements in the ultimate product, has been confirmed by transmission electron microscopy. Chromium(3+) tracer electron paramagnetic resonance spectra suggest that pseudo-boehmitic sheet growth is well developed in the alumina coating component, even without ageing. Evidence is found in the secondary-ion mass spectra for AlOTi and Al(OH)Ti species, which are plausible structural units in the coating–substrate interfacial region.