Coupling Agents Treatment of Electro-conductive White Powders Coated with In2O3-Sn Film

In a previous paper the authors reported a novel wet preparation method for electro-conductive white powders homogeneously coated with In2O3-Sn film. Further experiments were performed to obtain insight into aging treatment of the suspension after hydrolysis reaction of the ITO compound, and into coupling agent treatment to stabilize the electro-conductivity of the resulting powders. The electro-conductivity of the final product was greatly improved by aging a suspension of fine powders coated with mixed ITO composition hydroxides for 60 minutes at pH 6.5±0.5 and 343K. Generally, the electro-conductivity of ITO-coated powders deteriorates owing to the influence of atmospheric oxygen. Coupling agent treatment of ITO-coated powders was found to be very effective in averting this effect. The applicability of various coupling agents, both silane type and titanate type, were examined. A coupling agent is an insulator by nature, so the use of excess amounts must be avoided. However, a suitable amount of coupling agent treatment exhibited remarkable effectiveness in improving the electro-conductivity of ITO-coated powders. A silane type coupling agent with a mercapto group was particularly effective. The decay of electro-conductivity over time caused by oxygen can be almost completely averted by use of coupling agent.