Differential thermal analysis of titanium enamels

Abstract

Over 30 white and coloured titanium enamels of different origin were tested with a derivatograph. Thermoceram crucibles were used, which enabled the tests to be interrupted when a change was indicated by the DTA curve. The crucible was removed from the derivatograph, and the sample pulverized and studied by X-ray diffraction method. A major difference compared to previous observations was the fact that the exothermic peak indicating the anatase-rutile transformation was also found on the DTA curves of certain anatase-type enamels. With these enamels the temperature relating to the start of the transformation peak was regarded as the critical temperature, as at a temperature below this the enamel was stable, but above it unstable.Some time ago, stannic oxide and antimony oxide were used for opacifying enamels. These opacifying agents were partly melted and partly batched to the system. During melting a part of these oxides dissolved in the enamel, while another part formed a crystalline suspension and produced an opacifying effect. As there is a relatively small difference between the refractive indices of transparent enamels and of these oxides, this type of enamel resulted in a suitable covering only if applied as a thick layer. As a consequence, researchers tried to develop enamels which ensured a perfect covering even in the form of relatively thin layers. This problem was solved by the development of the titanium enamels,