Abstract
Dark brown oxyhydroxide films were formed on aluminum, copper, and, ITO glass by cathodic pulse electrolysis in a 0.016mol L-1(NH4)6Mo7O24-0.32molL-1MgSO4 solution of pH 5 at 50°C. The XPS and ICP-AES analyses indicated that the films were composed of mixed valence molybdenum ions of Mo (IV) to Mo (VI), Mg (II) ions, and small amounts of sulfate ions. The MgSO4 is a necessary component in the solution to obtain uniform and adhesive films. The NH4+, Na+ or Zn (II) ions substituted for Mg (II) ions, and acetate, nitrate or phosphate ions substituted for sulfate ions in the solution adversely affected the formation of uniform and adhesive films. Though the decrease of Mg (II) ions in the solution increased the amount of Mo ions in the film, it also showed adverse effects. The films were amorphous by XRD even after drying at 200°C for 12h. Diffuse reflectance spectra of films showed that transmittance is about 15% in the UV-VIS region of 200-700nm in wavelength and increases to 70-80% in the near IR region of 1.5-2μm. Spectrophtometric emissivity measurements at 100°C indicated that emissivity in the IR region of 4-10μm is around 40% and increases drastically to over 90% for wave length longer than 10μm. It indicaates that the film is a selective emitter/absorber for the far IR region. The film also showed electric conductivity.
