GLASS-MICA COMPOSITIONS AS AN ELECTRIC HEATER SHELL. L.V. Chilikanova, T.I. Shishelova, T.V.Sozinova, A.V.Shcherbakov, Irkutsk Technical University, Irkutsk, Russia

Glass-mica compositions are successfully used as shells for electric heaters. The long service life, mechanical and electric strength of these materials depend on the interaction of Ni-Cr alloy with fusible glass and mica components under working conditions. The data of X-ray diffraction and thermography have shown that upon thermal activation of these substances the processes of metal oxidation, muscovite decomposition, and interaction between the decomposition products and glass are hindered as a result of the reinforcing effect of the silicate medium on the heater metal. The reinforcing film on the mica- composition-metal interface is formed due to the dissolution of spinels (Ni-Cr alloy oxidation products) in the softened glass, that leads to the formation of iron silicate. The oxidation of heater metal starts with the diffusion of iron ions and the formation of ferrospinels. The latter, known for a wide range of homogeneity with many oxides, dissolve the protective solid layer of oxides. The water which is released during dehydration and dehydroxylation of mica and fills intercrystallite pores serves as an oxidant. The established physico-chemical interactions between mica, glass and the products of Ni-Cr alloy oxidation make it possible to find optimal conditions for the production and modification of electric heaters in a shell of glass mica-composition.