Method for the preparation of pyrolytic boron nitride-clad double-coated article

摘要

An improvement is proposed in the method for the preparation of a ceramic heater consisting of a substrate of boron nitride, patterned graphite layer thereon as an electric resistance heater element and an overall cladding layer of pyrolytic boron nitride formed on allover the surface after pattern-wise engraving of the graphite layer and the substrate in order to enhance the stability of the cladding layer against crack formation or exfoliation. The improvement is achieved by limiting the depth of engraving not to exceed 200 mu m or chamfering and rounding of the edged and recessed ridge lines formed by engraving so that the cross sectional profile is in a smooth contour having a radius of curvature not smaller than 0.5 mm.