Study of the decomposition of an aqueous metal-chelate gel precursor for (Bi,La)(4)Ti3O12 by means of TGA-FTIR, TGA-MS and HT-DRIFT

Abstract

A (Bi,La)(4)Ti3O12 acetate-citrate gel, prepared from an aqueous solution, was subjected to thermal decomposition in dry air and in inert atmosphere. In order to acquire the insight into its decomposition pathway, several hyphenated thermal analysis techniques were used. The evolved gases were characterized by TGA-MS and TGA-FTIR, while any changes in the solid phase upon heating were detected by means of HT-DRIFT. In dry air, the decomposition consists of four steps, centered at 80, 190, 340 and 455degreesC. After drying of the sample in the first step, the second step is ascribed to the decomposition of ammonium acetate and citrate. Any metal acetates present in the gel would also decompose here. The third step comprises the decomposition/combustion of the citrate ligands. The last step consists of the combustion of all residual organic matter. In the third and fourth step, O-2 plays an important role. XRD has proven that the desired Aurivillius oxide phase forms from the synthesized gel after an appropriate heat treatment in dry air. In inert atmosphere six steps can be distinguished, situated at 70, 200, 330, 420, 590 and 910degreesC. The steps at 70, 200 and 330degreesC correspond to the steps at 80, 190 and 340degreesC in dry air. It is proposed that the steps above 400degreesC correspond to the gradual decomposition of the residual organic matter. It has turned out to be impossible to remove all organic matter from the gel below 700degreesC in inert atmosphere. (C) 2002 Elsevier Science B.V. All rights reserved.