Study On Preparation And Properties Of SnO₂ Electrode Ceramics Doped With MnO₂, CuO And Sb₂O₃

Dense SnO₂-based electrode ceramics with excellent electrically-conductive property in high temperature and good corrosion resistance to molten glass has extensive application prospect in glass electric-melting industry. SnO₂ electrode products, such as Stannex band and Corhart band, have already been used in the industry; however, combination property of SnO₂ based electrode ceramics still could not satisfy the demand of operating life to the glass melting industry. Furthermore, the references concerning the densification, electrically conductive property and corrosion resistance to molten glass are few, and the mechanisms of densification, electric conductivity and corrosion resistance to molten soda-lime glass are still in dispute.In the present dissertation, SnO₂ based electrode ceramics doped with MnO₂, CuO and Sb₂O₃ were prepared by pressureless sintering. The effects of additives and sintering temperature on densification behavior, electrically conductive performance and corrosion resistance to molten soda-lime glass were studied. The mechanism of densification, electric conductivity and corrosion resistance to molten soda-lime glass were analyzed in detail. The influence of heat treatment in air at 725℃and corrosion by molten soda-lime glass at 1200℃for 100h on resistivity of SnO₂ based ceramics was investigated.Relative density of SnO₂-MnO₂-Sb₂O₃ ceramics decreases with increasing of Sb₂O₃. Densification mechanism of SnO₂ ceramics doped with MnO₂ and Sb₂O₃ contains two points: one is the substitution reaction of Sn⁴⁺ for Mn ions, which promotes sintering; the other is the substitution reaction of Sn⁴⁺ for Sb⁵⁺ ions, which restrains densification of SnO₂-MnO₂-Sb₂O₃ ceramics. Densification mechanism of SnO₂-CuO-Sb₂O₃ ceramics depends on the substitution reaction of Sn⁴⁺ for Sb⁵⁺ ions, which restrains the densification and surface diffusion of rich-Cu liquid phase at grain boundary, which greatly promotes the sintering ability of SnO₂ based ceramics. SnO₂ electrode ceramics simultaneously doped with MnO₂, CuO and Sb₂O₃ integrate the good sintering property of SnO₂-CuO-Sb₂O₃ ceramics in low temperature and of SnO₂-MnO₂-Sb₂O₃ ceramics in high temperature.SnO₂-MnO₂-CuO-Sb₂O₃ ceramics shows the negative characteristic of ln(ρ)-l/T. Electrically conductive property of SnO₂-MnO₂-CuO-Sb₂O₃ electrode ceramics relates closely with the carrier mobility restrained by diffusion of Cu ions on the surface of SnO₂ grains, rich-Cu liquid phase, rich Mn phase at grain boundary and the substitution of Mn ions of low valence in the lattice of SnO₂, and the type and concentration of current carrier determined by Sb⁵⁺/Sb³⁺ ratio.Corrosion rates of SnO₂ based electrode ceramics doped with CuO, MnO₂ and Sb₂O₃ after corrosion in soda-lime glass at 1200℃for 100 hours arrive to 10^-4mm/h. Matrix material-SnO₂ has excellent corrosion resistance to molten soda-lime glass, which is corroded by molten soda-lime glass by diffusion. Sintering aids, namely MnO₂ and CuO, are easily dissolved by molten glass. Molten glass easily enters intergranular pores and corrodes the thick phase layer at grain boundary, but it is very difficult to infiltrate into transgranular pores and to corrode the very thin layer at grain boundary.Optimal compositions of SnO₂ based electrode ceramics with excellently comprehensive property have been obtained as following:(1) 98.5SnO₂-1MnO₂-0.5Sb₂O₃;(2)98SnO₂-0.5MnO₂-0.5CuO-1Sb₂O₃;(3)98SnO₂-0.25MnO₂-0.75CuO-1Sb₂O₃;(3)98SnO₂-1CuO-1Sb₂O₃. Their density, resistivity at room temperature and high temperature, and corrosion rate all arrive to or even exceed the present oversea SnO₂ based electrode products, such as Stannex band and Corhart band.Heat treatment in air at 725℃increases current carrier concentrations and resistivity at 725℃of 98SnO₂-1CuO-1Sb₂O₃ ceramics, decreases resistivity at room temperature and carrier mobility. Corrosion in soda-lime glass at 1200℃for 100 hours reduces resistivity at room temperature of dense SnO₂-MnO₂-CuO-Sb₂O₃ electrode ceramics. 98SnO₂-1CuO-1Sb₂O₃ and 98SnO₂-0.75MnO₂-0.25CuO-1Sb₂O₃ electrode ceramics have excellent stability of resistivity at room temperature.