Yuanming Lai

Glass structure of the CaO–B2O3–SiO2–Al2O3–ZnO glasses system with different Si content

The aim of the present work is to investigate the effects of SiO2 content on the structure of CaO–B2O3–SiO2–Al2O3–ZnO glass using the MAS-NMR, the fourier transform infrared spectrometer and differential scanning calorimetry (DSC). The results showed that the majority of Al existed in fourfold coordination and Zn acted as glass modifier in glass structure. With the increasing of SiO2 content, the relative amount of BIII units decreased while the BIV units increased and the proportion of Si–O–Si bridge oxygen bond in [SiO4] tetrahedrons increased obviously. The DSC curves revealed that the glass transition temperature increased from 732 to 773 °C with the increasing of SiO2 content, indicating that SiO2 generating more bridge oxygen can increase the degree of polymerization of glass structure.

Structural investigation of calcium borosilicate glasses with varying Si/Ca ratios by infrared and Raman spectroscopy

Calcium borosilicate glasses with varying Si/Ca ratios (with constant Si/B value) have been successfully prepared using a normal melt-quench technique. Structural features were investigated through infrared (IR) spectroscopy, Raman spectroscopy and differential thermal analysis (DTA). The IR and Raman spectra showed a Si/Ca ratio-dependent structure of borosilicate, which can provide valuable information to predict the composition and structure relations in the glasses. Conversion of BO3 to BO4 units was driven mainly by the disproportionation reaction between BO3 units and CaO when 0.5 ≤ Si/Ca ≤ 0.7. However, the BO3 units captured the non-bridging oxygens of Q1 units when 1.1 ≤ Si/Ca ≤ 1.3, resulting in the formation of more BO4 and Si–O–Si bonds. Qn (n = 0, 1, 2, 3, 4) notation was used to represent the SiO4 tetrahedral units, where n is the number of bridging oxygen per SiO4 unit. The intermediate phase was presented when 0.7 < Si/Ca < 1.1. Variations in density, glass transition temperature and thermal stability as functions of Si/Ca ratios correspond to the change in BO4, BO3 and SiO4 structural units. The intermediate phase results in maximum density, minimum molar volumes and maximum Tg, which can be expected to be the optimum candidate for applications.

Structure and crystallization behavior of Al containing glasses in the CaO–B2O3–SiO2 system

The aim of the present work is to investigate the effects of Al2O3 content on both the structure and crystallization behavior of CaO–B2O3–SiO2 (CBS) glass composition using NMR, FT-IR and DSC. The density experimental results showed that the density (ρ) of glasses decreased linearly with increasing Al2O3 content, while the molar volume (Vm) of the glasses increased linearly. The NMR revealed that the Al occurred in the forms of AlIV, AlV and AlVI units. With the increasing Al2O3 content, the amount of Al species show little change, the relative amount of BIIIa and BIIIs units increases while the BIV units decrease, and the Q4 structural units increases clearly but the Q3 decreases. Further, crystallization peaks of CBS glasses shift to higher temperatures, indicating that Al2O3 addition can suppress crystallization of CBS glasses.