Short-range and Medium-range Structural Order in CaO–SiO₂–TiO₂–B₂O₃ Glasses

Abstract

The present study aimed to provide a deep insight of short-range and medium-range structural order for CaO-SiO 2 -TiO 2 -B 2 O 3 glasses. From various prospects, four techniques, FTIR, Raman, XPS and NMR, were simultaneously employed and only the direct evidences indicated from the spectra were used for structural analysis. The FTIR and Raman spectra proved that the main silicon-related units were Q 0 (Si), Q 1 (Si), Q 2 (Si) and Q 3 (Si) and the results of Raman fittings revealed that a B 2 O 3 addition resulted in an increase of Q 1 (Si) and Q 3 (Si) at the cost of Q 0 (Si) and Q 2 (Si), thus inducing an increasing Degree of Polymerization (DOP). An enhanced DOP generally implied a lower abundance of non-bridging oxygen in the networks, which was further demonstrated by the O1s XPS fittings. Additionally, the 11 B NMR spectra indicated that the dominant boron-related groups were BO 3 trigonal comprising ring and non-ring BO 3 as well as BO 4 tetrahedral comprising BO 4 (1B,3Si) and BO 4 (0B,4Si). Furthermore, it was clarified that an increase of B 2 O 3 content promoted the ratios of BO 4 (1B,3Si) to BO 4 (0B,4Si) and BO 4 tetrahedral to BO 3 trigonal, which undoubtedly identified the occurrence of an equilibrium reaction between NBO, BO 4 tetrahedral and BO 3 trigonal in the glass.

Understanding the Relationship Between Structure and Thermophysical Properties of CaO-SiO2-MgO-Al2O3 Molten Slags

“…The structural units related to the SiO 4 tetrahedron are conventionally denoted as Q i (Si) (i = 0, 1, 2, 3, 4), where i represents the number of BOs per coordinated Si atom. In addition, the shoulder at 980 cm À1 , associated with the vibration of Q 2 (Si), [18][19][20][21] gradually decayed with increasing Al 2 O 3 content, which was consistent with the decreasing Si-O-Si bending vibrations at 350 cm À1 . Moreover, the decreasing content of Q 0 (Si) and Q 2 (Si) in the networks also indicated less symmetry stretching vibrations of Si-O in the networks, which is in good agreement with the variation trend of 600 to 800 cm À1 band.…”

“…To further identify the silicate structure quantitatively, the high Raman shift range of 800 to 1100 cm À1 in the Raman spectra could be fitted using four Gaussian functions assigned to the four Q i (Si) units, namely, Q 0 (Si), Q 1 (Si), Q 2 (Si), and Q 3 (Si), which are generally located at~870,~960,~990, and~1050 cm À1 , respectively. [18][19][20][21]26,27] The fitting results of various Raman curves are presented in Figure 5, and these four Gaussian functions are well fitted by the Raman curve, indicating the reasonableness of the present methodology.…”

“…As can be noted, the entire FTIR spectrum could be divided into the following three bands: a band from 400 to 600 cm À1 assigned to the Si-O-Si bending vibrations, a band from 600 to 800 cm À1 assigned to the Si-O symmetry stretching vibrations and a band from 800 to 1200 cm À1 assigned to the stretching vibrations of the AlO 4 and SiO 4 tetrahedrons. [16][17][18] With increasing Al 2 O 3 content, the intensity of the Si-O-Si bending (400 to 600 cm À1 ) and Si-O symmetry (600 to 800 cm À1 ) vibrations was less pronounced due to the relative decrease in the SiO 2 content in the glasses. Furthermore, it was found that the center of 800 to 1200 cm À1 band gradually shifted to the higher wavenumber range, which generally indicated that the degree of polymerization (DOP) of glassy networks increased; in other words, Al 2 O 3 mainly acted as a network former in the present glasses.…”

“…Third, in the high Raman shift range of 800 to 1100 cm À1 , the stretching vibrations of the AlO 4 and SiO 4 tetrahedrons also showed a continuous variation trend overall. The peak at~870 cm À1 , generally related to the vibration of Q 0 (Si), [18][19][20][21] gradually diminished with increasing Al 2 O 3 content, indicating fewer isolated SiO 4 tetrahedrons. The structural units related to the SiO 4 tetrahedron are conventionally denoted as Q i (Si) (i = 0, 1, 2, 3, 4), where i represents the number of BOs per coordinated Si atom.…”

A Review of Fluorine-free Mold Flux Development

“…32 tetrahedral with two bridge oxygen), in which the original Q 0 (Si) and Q 2 (Si) transferred into Q 1 (Si) ([SiO 4 ]-tetrahedral with one bridge oxygen) and Q 3 (Si) ([SiO 4 ]-tetrahedral with three bridge oxygen), resulting in the improvement of the DOP of silicate structure. [33][34][35][36][37] The evolution process of network structure with the addition of B 2 O 3 is shown in Fig. 3.…”