Coating metal oxide particles via the combustion of deposited polymer precursors

Abstract

Water-swellable chelated polymers were synthesized, starting either from (1) In (III) or In (III) and Sn (II) as central ions and N-trimethoxysilylpropylethylenediamine or ethylenediamine each together with ethylenediaminetetraacetic acid (EDTA) as coordination ligands, or from (2) Ag(I) as the central ion and ethylene glycol (EG) and EDTA as coordination ligands, as follows: The nitrate(s) of the above metal ions together with the corresponding ligands were dissolved in water, and the solution was concentrated by heating to carry out the chelating polymerization. After cooling, the polymer was dried and ground to a fine powder, which was then mixed with a metal oxide powder by grinding in the presence of a small amount of water. A paste was thus obtained, which, after drying, was calcined at 200°C and subsequently at 750°C. The polymer became a sticky gel at 200°C, which adhered to the surface of the metal oxide particles; it was converted to an inorganic coating, In2O3 - SnO2 - SiO2, In2O3 - SnO2, SnO2, or Ag, during the subsequent calcination at 750°C. Two metal oxide powders, namely, the electrically conductive In2O3 and the nonconductive SnO2, were used as substrates. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) indicated that the substrate particles were coated after calcination by a multi-component oxide or silver layer. Temperature-resistant electrically antistatic film could be prepared by using the metal oxide coated In2O3 particles as pigments and polypropylsiloxane as the binder. The Ag-coated SnO2 powder had a conductivity σ = 1.0 × 10-3 S cm-1 at 8.6 vol % Ag, while the mechanically mixed powders of Ag and SnO2 exhibited a conductivity of 2.0 × 10-7 S cm-1 at 16 vol %. © 1998 John Wiley & Sons, Inc.