The Research On The Structure And Properties Of Li₂O-Al₂O₃-SiO₂ With Dopant

Lithium aluminosilicate (LAS) glass-ceramics in the system Li₂O-Al₂O₃-SiO₂,containingβ-spodumene (Li₂O·Al₂O₃·4SiO₂) and/orβ-quartz solid solution, own lowthermal expansion coefficient, good thermal and chemical stability, and so have beenapplied in many fields.β-Spodumene-containing glass-ceramics also have thepotential to meet the dielectric constant and thermal expansion requirements forintegrated circuit substrates.However, due to their high melting temperatures and viscosity in LAS glasses, itmakes them difficulty to be prepared, so additions of fluxes such as B₂O₃, BaO, SrO,alkali oxides and alkali earth oxides have been used in LAS glass-ceramics todecrease the viscosity and melting temperature. But it would induce some problemslike high thermal expansion coefficient and/or loss of transparency, and/or lowmechanical properties at the same time.In the present dissertation, the effects of basic composition, nucleation agents andheat-treatments on the microstructure and properties of LAS glass-ceramics withoutdopants were investigated by XRD, SEM, DTA, IR and Raman. The results show thatthe LAS glass-ceramics have the lower viscosity, the lower melting temperature,reasonable microstructure and excellent properties when (MgO/ZnO) wt% and(TiO₂+ZrO₂) wt% were 3/1 and (2.3+2.0) wt%, respectively. The time ofcrystallization was more important in heat-treatment than other factors.The rare earth oxides were added into LAS glass-ceramics in order to lower theviscosity and improve the properties. The results show that the viscosity and meltingtemperature were lowered with the addition of 0.01 mol La₂O₃, Y₂O₃, CeO₂, Er₂O₃ andGd₂O₃.The viscosity and melting temperature of LAS glass-ceramics decrease with theincrease of yttria addition, but the crystallization temperature and crystallizingactivation energy of the resulting glass increased. And the kinetic and phase structureanalysis indicated that yttria played an important role in adjusting the crystallizationkinetic parameters and controlling the crystal size and crystallinity.The viscosity of specimens decreases with the increase of La₂O₃ addition. The main phase of specimens doped with La₂O₃ was stillβ-quartz s.s. The crystallizationtemperature of the resulting glass was decreased; however, the crystalline and theradius of crystal grain of specimens were increased.The viscosity of LAS glass ceramics doped with Y₂O₃ and CeO₂ was higher thanthose with only one kind of rare earth oxide; however, the melting was improved. Themain phases of specimens were Li_xAl_xSi_1-xO₂ and TiO₂ transformed fromβ-quartz s.s.Increasing the addition of Y₂O₃ and CeO₂, the crystalline of specimens and the radiusof crystal grain decreased and then increased; however, the coefficient of expansion,the elastic module and bending strength increased at all time.