Studies on the Aluminum Porcelain Enamel of the System PbO-SiO₂-V₂O₅

Abstract

This work was undertaken as a part of the research program of development of good opaque porcelain enamels for aluminum alloys. In the present study the efforts were made on the identification of crystalline phases in these enamels. Furthermore, the relation between variety of crystals depositted and chemical durability of the enamel was studied.
The results obtained are summarized as follows:
1) Two kinds of crystalline phases were detected by X-ray diffraction method. One of them was apatite type hexagonal leadsilicovanadate, 5 PbO⋅SiO₂⋅V₂O₅, and another was KBrO₃ type hexagonal phase. Although the exact formula of the latter phase could not be determined, it might be reasonably concluded from many synthetic experiments that the chemical composition corresponds with that of Pb₂SiO₄-x Pb(Na_y⋅K_1-y) VO₄ solid solution.
2) X-ray peak intensities of (00l) reflections of apatite type crystals and of (h00) reflections of KBrO₃ type crystals on the surface of enamels were abnormally strong. Preferred orientation of these crystals might be inferable from the facts mentioned above.
3) Acidity of the frit glazes used might be one of factors determining which phase between the two would be crystallized in enamels. In general, apatite type phases were preferred to crystallize in more acidic enamels, while the KBrO₃ type phases were developed in more basic enamels.
4) Chemical durability of crystalline phases and glass matrix in enamels were compared with each other. It was found from the results of immersion experiments that chemical durability decreases in the following order: glass matrix>apatite type crystalline phase>KBrO₃ type crystalline phase.
5) Good opaque enamels having a nearly pure white tone were established by using a frits contained higher RO₂ components, but in this case, it was necessary to fire at about 600°C.