In order to aid the research and development of Al2O3-based materials, a comprehensive study of the structural properties of CaO–Al2O3–SiO2 systems was carried out via Raman and MAS-NMR spectroscopies. The spectral results showed that Raman scattering coefficients of Q2(Al), Q3(Al), Q4(Al), and [AlO6] units calibrated by 27Al MAS-NMR were 1, 0.554, 0.374, and 1.468, respectively. Using these Raman scattering coefficients to quantitatively analyze the aluminum structures, the results showed that CaO could promote the transformation from six-coordinated aluminum to four- and five-coordinated state with simultaneous depolymerization of four-coordinated aluminum. And CaO could exert a stronger depolymerization on [AlO4]-tetrahedrons than [SiO4]-tetrahedrons. Moreover, non-bridging oxygen number per coordinated atom (NBO/T) corresponding to transition of aluminum speciation were acquired. The values of NBO/T of the transformations from coexistences of [AlO6] and [AlO4] to coexistences of [AlO6], [AlO5], and [AlO4] to coexistences of [AlO5] and [AlO4] were 0.94 and 1.38, respectively.

Quantitative insight into aluminum structures in CaO–Al2O3–SiO2 system via Raman and 27Al MAS-NMR spectroscopies

Performance and transition mechanism from acidity to basicity of amphoteric oxides (Al2O3 and B2O3) in SiO2–CaO–Al2O3–B2O3 system: A molecular dynamics study

Al2O3 and B2O3 possess properties of amphoteric oxide, so Al2O3 and B2O3 have many different influences on the structure and properties of silicate melts, while its influence mechanism in atomic scale has not yet been fully understood. Molecular dynamics (MD) simulation was conducted to gain a clear understanding about the influences of Al2O3 and B2O3 on the structure and properties of SiO2-CaO-Al2O3 (SiO2-CaO-B2O3) silicate melts at 1773 K. The results show that when the Al2O3 content is less than 25 wt.%, the Al2O3 in the system is almost acidic in the studied system, and the bridging oxygen content and polymerization degree of the system increase with the increase of Al2O3 content. When the content of Al2O3 exceeds 25 wt.%, part of Al2O3 in the system becomes basic, which makes the bridging oxygen content of the system decrease and the growth rate of polymerization degree decrease. The effect of B2O3 on the network structure of SiO2-CaO-B2O3 (SCB) system is similar to that of Al2O3 in SiO2-CaO-Al2O3 (SCA) system, but the inflection point from acid to basic is lower (21 wt.%) and the basicity is stronger. Moreover, through two suitable viscosity calculation models, combined with experimental data, it shows that the viscosity of SCA system increases with the increase of Al2O3 content, while that of SCB system is just the opposite.

Effects of amphoteric oxide (Al2O3 and B2O3) on the structure and properties of SiO2-CaO melts by molecular dynamics simulation

In this study, the influence of Al2O3 on the viscosity and structure of MnO–SiO2–MgO(–Al2O3) submerged arc welding fluxes was investigated. The results showed that the viscosity initially decreased and subsequently increased with increasing Al2O3 contents from 0 to 25 mass pct, which correlates well with the “V”-shaped variation trend of the activation energy. The enhanced (Q2 + Q3 + Al–O0)/(Q0 + Q1 + Al–O−) ratio indicated the continuous polymerization of the flux structure with higher Al2O3 contents, which was further confirmed by the distribution characteristics of various oxygen species. The variation trend may likely be attributed to the competing effects of the overall weakened bond energy and the enhanced degree of polymerization of the flux structure. 

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Insight into the Viscosity–Structure Relationship of MnO–SiO2–MgO–Al2O3 Fused Submerged Arc Welding Flux

Investigation on the structure and viscosity of BaO-bearing slag melt through molecular dynamics simulation, Raman and 27Al MAS NMR spectra

Amphoteric oxide Al2O3 is generally considered to be acidic or alkaline in different environment. The effects of Al2O3 on the structure and dynamic property of CaO–SiO2–Al2O3 melt were investigated by MD simulation in this work. The results showed that as the content of Al2O3 increased, the contents of the tri-coordinate O and high-coordinate Al increased to balancing charge. When the basicity reaches 1, the viscosity of the melt increases with the addition of Al2O3 and reaches a maximum at 26 mol% of Al2O3. The higher concentration of Al2O3 leads to the relative deficiency of Ca atoms and the increase of tri-coordinate O and five-coordinate Al content, instability of the structure, and increase in DAl and DO. Al2O3 is considered to be acidic and forms network structures in the environment with sufficient alkaline cation. In contrast, Al2O3 becomes alkaline with insufficient basic cations environment, thus providing Oxygen atoms and balancing charge.

Effects of the amphoteric behavior of Al2O3 on the structure and properties of CaO–SiO2–Al2O3 melts by molecular dynamics

Properties and structure of a new non-reactive mold flux for high-Al steel

Al2O3 possess properties of amphoteric oxide, so it plays different network roles in the traditional CaO-Al2O3-based melts, while, its influence mechanism in atomic scale has not yet been fully understood. Molecular dynamics (MD) simulation and MAS NMR Spectrum was conducted to gain a clear understanding about the variation of network structure and Al-Li association on the non-reactive melts structure in different (BaO+CaO)/Al2O3 ratio and temperature. The results show that [AlO4]− tetrahedra serves as the network framework of BaO-CaO-Al2O3-CaF2-Li2O non-reactive melt, and forms the chain and layered spatial network. As the (BaO+CaO)/Al2O3 ratio decreases from 2.0 to 1.7, Al2O3 converts to alkaline first and then to acidic, and the polymerization degree and viscosity of melt increase first and then decrease. In addition, the strength of Al-Li association decreases with the increase of (BaO+CaO)/Al2O3 ratio and temperature, which is conducive to the hop of Li+ between non-bridging oxygen sites and increases the diffusion rate of Li+ in the spatial network. 

Effect of (BaO+CaO)/Al2O3 ratio (1.7∼2.0) on the structure and Al-Li association of BaO-CaO-Al2O3-CaF2-Li2O mold flux

Vertebral compression fractures are more common in the elderly, particularly in postmenopausal women. Most of these people are accompanied by osteoporosis, which can easily lead to spinal deformities and fractures. Once a fracture occurs, the patient would have severe pain response, limited spinal movement, and need to stay in bed for a long time, resulting in a significant decrease in their quality of life. Percutaneous vertebroplasty (PVP) is a minimally invasive spinal surgery that injects bone cement into the diseased vertebrae for therapeutic purposes. It can quickly relieve pain and stabilize the spine. It is widely used in the treatment of vertebral compression fractures and is currently an ideal treatment method. There are many materials of bone cement used in clinical treatment, and each material has unique characteristics. Many scholars would modify the bone cement according to the advantages and disadvantages to make it more suitable for clinical use. In this review, we discuss the clinical application and modification of bone cement.

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Yang Chen

Papers

Effects of the amphoteric behavior of Al2O3 on the structure and properties of CaO–SiO2–Al2O3 melts by molecular dynamics

Properties and structure of a new non-reactive mold flux for high-Al steel

Effect of (BaO+CaO)/Al2O3 ratio (1.7∼2.0) on the structure and Al-Li association of BaO-CaO-Al2O3-CaF2-Li2O mold flux

Application and modification of bone cement in vertebroplasty: A literature review

Amphoteric behavior of component and microstructure feature on CaO-Al2O3-TiO2 ternary melt by molecular dynamics simulation