Interactions between alumina and high lead glasses for hybrid components

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Abstract
Kinetics of dissolution of alumina substrates in seven compositions of high lead glasses have been studied. The dissolution process is controlled by correlated diffusion of Al and Pb (and/or B), with interdiffusion coefficients D, at 850 °C, 10 min, in the range from 10−10 to 10−6 cm2 s−1, according to the different compositions. Al solubility ranges from about 10% to 20%. The diffusivity and solubility increase by increasing the content of B and Pb. The reactivity of alumina substrates with the glassy component of thick-film resistors greatly affects their microstructure and electrical properties. Some consequences of these interactions have been evidenced: change in electrical resistivity and its dependence on the resistor thickness, changes in the sintering process and grain growth of RuO2 grains, and a catalytic effect on phase transformations of pyrochlore ruthenates in rutile RuO2 in the glassy matrix of resistors. Moreover, it is shown that Al dissolution gives rise to a recession of the buried glass/substrate interface, which can easily be measured. When alumina is concerned, this measurement gives insight of the sum of two processes: aluminum dissolution in the glass layer and grain-boundary diffusion of glass into the substrate itself.

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