Study On ZnO-B₂O₃-SiO₂Glass Forming Regions And Effects Of Rare Earth On Phase Separation

The borosilicate glass is a widly used optical material, the borosilicate glass with good thermal stability, excellent optical performance, decent machining property and chemical stability is gradually taken seriously by people. ZnO-B2O3-SiO2glass as a important kind of borosilicate glass have been paid great attention to in receng years.In this paper, ZnO-B2O3-SiO2glass was prepared by conventional melting method. Point-by-point method was used to research the glass forming regions; infrared spectrum was applied to study the evolution of the glass structure unit; and finally with the aid of SEM, CLSM, FTIR and XRD, the influence of the rare earth ions on the glass phase separation and crystallization was studied. Conclusions are as follows:Silicon boron oxide structure is the main body of ZnO-B2O3-SiO2glass and ZnO is the intermediate oxide. the glass forming range is: ZnO:25-60mol%, B2O3:0-70mol%, SiO2:0-40mol%. Besides, ZnO-B2O3-SiO2glass forming region is near to the rich boron area and the high content of ZnO, B2O3or SiO2area is difficult to form the glass. Additionally, the central region of ZnO-B2O3-SiO2ternary glass forming region is bulged and trends to B2O3with eutectic point under the influence of eutectic position.In the network structure of ZnO-B2O3-SiO2glass, Zn2+can enter the network structure of B-O-Si glass and form Zn-O-Si and Zn-O-B structure when the content of ZnO is more than25%. When the content of ZnO reaches45%, the hexa-coordinate of Zn2+converts to quadridentate, and then gradually forms the zinc oxygen tetrahedron [ZnO4]. At the same time, the increase of the content of ZnO can also promote the boron oxygen triangle module [BO3] into boron oxygen tetrahedron [BO4]. However, when the content of ZnO increases from45%to65%, with the increase of Zn2+content, the polarization of Zn2+is more significant. While the content of ZnO is more than65%, the polarization of Zn2+causes the glass crystallization and this situation is difficult to form the glass. To sum up, when the content of ZnO is less than55%, the glass structure stability can be promoted; when the content of ZnO is more than55%, the polarization effect of zinc ions can lead to the glass crystallization and reduce the glass structure stability.In ZnO-B2O3-SiO2glass, the rare earth ions play a mainly role in the rich boron phase and the high field strength of rare earth ions can destroy the glass network structure, but promote the formation of [BO3] and non-bridging oxygen, resulting in glass crystallization. On the contrary, Zn2+ions give priority to take free oxygen and promote the accumulation of elements; then the glass crystallization can be improved, the low field strength of rare earth ions can decrease the short-range order range, reduce the glass accumulation degree; then and phase separation can be restrained.