Tungsten coatings by chemical solution deposition for ceramic electrodes in fluorescent tubes

In the lighting industry, the concept of ceramic cold cathodes provided with an inside tungsten coating is under consideration to be applied in mercury-free fluorescent lamps for advertising purposes. In this regard, the applicability of chemical solution deposition to fabricate metallic films on the inner surface of alumina tubules was established. The technique involves the preparation of tungsten oxide layers from a peroxotungstic acid precursor solution and their subsequent reduction to tungsten in the presence of hydrogen. Diverse characterisation of the precursor and the intermediates was carried out in order to determine the influence of their properties on the quality of the final coatings. By acquiring the optimum process parameters, highly-conducting tungsten films were obtained. The temperatures allowing for conversion of the oxide to the metal as well as for sintering of the derived tungsten films were observed to be substantially lower than in bulk processes. Electrode prototypes of the described type were accordingly realised and operated successfully in a fluorescent tube test setup, thus proving the feasibility of the hitherto theoretical idea.