DU Zhenbo, GAO Shengxia ,ZENG Renjie

(College of Materials, Xiamen University, Xiamen Fujian 361005, China)

Abstract: The research and development profiles and prospects of lead -free sealing glass ceramics with a high thermal

expansion coefficient (α), low softening temperature (T_f) and high electrical resistivity (ρ) have been reviewed. The possibility of replacing PbO with some oxides (In₂O₃, SnO, Tl₂O₃ or Bi₂O₃), the metal elements of which are near Pb or in its diagonal positions in the periodic table, or of replacing lead-rich system by either common glass forming oxides (e.g. SiO₂, B₂O₃ or P₂O₅) or conditional glass forming oxides (e.g. V₂O₅ or TeO₂), has been intensively discussed, respectively. The ingredients,preparation techniques and properties of the Bi₂O₃-rich system have been fully discussed. It has been concluded that a high α, low T_f, and high ρ could be obtained in a lead-rich system which had been, already, forbidden to be used in domestic appliance by law for its harm to the environment. The lead-free system rich in SiO₂, P₂O₅ or B₂O₃ could not, unfortunately,obtain the required properties at the same time; rich in other common glass forming oxides may be unsuitable for domestic appliance application due to its high cost (e.g. GeO₂), toxicity (e.g. As₂O₃), or being difficult for preparation (Sb₂O₃). The lead freesystem rich in conditional glass forming oxides may be not suitable for domestic appliance application due to its toxicity (e.g. V₂O₅), or high cost (the oxides of Te, Mo or Se); the glass containing Al₂O₃ may be unsuitable for preparing a sealing glass ceramic due to its low α and high T_f; and the glass containing TiO₂ may be unsuitable for preparing a sealing glass ceramic due to its low α and easy crystallization. The lead-free system rich in In₂O₃, SnO or Tl₂O₃ may be restricted either due to their toxicity (e.g. Tl₂O₃), high cost (e.g. In₂O₃) or the difficulty in preparation (SnO); whereas Bi₂O₃-rich system could meet all the requirements as mentioned above, and, therefore, have a bright prospect to be used in for domestic appliance.

Key words: melting point; bismuth trioxide; solder; metal; heater