Dynamics, Structure and Glass Formation of Calcium Aluminate Liquids
Hao Liu, Ruikun Pan, Wenlin Chen, Zhitao Shan, Ang Qiao, Sandro Jahn, James W. E. Drewitt, Louis Hennet, David P. Langstaff, Haizheng Tao, G. Neville Greaves, Yuanzheng Yue
Crystalline calcium-aluminates include the phases essential in the setting of Portland cements developed over the last century. It is only within recent decades, however, that calcium-aluminate melts and glasses have begun to attract attention, bringing new functionalities in photonic and electronic applications. These studies, though, have been limited to compositions close to a deep eutectic from where glasses easily form. With the development of contactless levitation furnaces the glass forming region can now be hugely extended. We have taken advantage of these developments to rationalise, for the first time, melt rheology with structural properties across this expanded compositional range, substantiating this with atomistic simulation. In the process, we have discovered that supercooled calcium-aluminates comprise a new system where fragile-to-strong phase transitions are ubiquitous. Taking this holistic approach, we have quantified the common basis of thermo-physical and structural diversity in this novel glass-forming system, together with its inherent polyamorphism.
We report new time-resolved synchrotron x-ray diffraction (SXRD) measurements to track structural transformations in calcium-aluminate (CaO)x(Al2O3)1-x liquids during glass formation, and review recent progress in neutron diffraction with isotope substitution (NDIS) experiments, combined with aspherical ion model molecular dynamics (AIM-MD) simulations, to identify the atomic-scale configurational constraints on glass-forming ability.
Connecting bond switching to fracture toughness of calcium aluminosilicate glasses
Aalborg University（奥尔堡大学）；The Hong Kong Polytechnic University（香港理工大学）；Shanghai Jiao Tong University（上海交通大学）；Univ Rennes, CNRS, IPR (Institut de Physique de Rennes)（雷恩大学，法国国家科学研究中心，雷恩物理研究所）；CNRS（法国国家科学研究中心）
Phosphate glasses for bioresorbable implants display dissolution rates that vary significantly with composition, however currently their mechanisms of dissolution are not well understood. Based on this systematic study we present new insights into these mechanisms. Two-stage dissolution was observed, with time dependence initially parabolic and later linear, and a two-stage model was developed to describe this behaviour. Dissolution was accelerated by lower Ca concentration in the glass, and lower pH in the dissolution medium. A new dissolution mechanism is proposed, involving an initial stage…
Effect of the nature of alkali and alkaline-earth oxides on the structure and crystallization of an aluminoborosilicate glass developed to immobilize highly concentrated nuclear waste solutions
Using evolutionary crystal structure prediction algorithm USPEX, we showed that at pressures of the Earth's lower mantle CaAl2O4 is the only stable calcium aluminate. At pressures above 7.0 GPa it has the CaFe2O4-type structure and space group Pnma. This phase is one of prime candidate aluminous phases in the lower mantle of the Earth. We show that at low pressures 5CaO * 3Al2O3 (C5A3) with space group Cmc21, CaAl4O7 (C2/c) and CaAl2O4 (P21/m) structures are stable at pressures of up to 2.1, 1.8 and 7.0 GPa respectively. The previously unknown structure of the orthorhombic 'CA-III' phase is al…
Structure and dynamics of Oxide Melts and Glasses : a view from multinuclear and high temperature NMR
固态核磁共振（NMR）实验可以表征氧化物玻璃和熔体的局部结构和动力学。由于新实验的发展，现在不仅可以证明玻璃网络形成者的配位状态的细节，而且还可以表征延伸到几个化学键上的多原子分子图案的性质。我们目前的结果涉及31 P homogeneous实验，允许多达三个磷酸盐单元和27 Al/17 O heterogeneous，允许证明3个氧桥在铝酸盐玻璃和高温熔体的结构的重新讨论组的描述。
Structure and properties of magnesium silicate and borate melts and glasses were investigated by using newly parameterized interaction potentials in molecular dynamics simulations and compared with those of calcium silicate and borate. The competition between the depolymerization of the silica network and the formation of new bonds with modifier ions leads to the enhancement of the elastic moduli with increasing modifier content in alkaline earth silicate glasses. Compared with calcium silicate, the higher elastic moduli of magnesium silicate result from a higher connectivity of the overall gl…
Celitement is a new type of cement that is based on hydraulic calcium-hydrosilicate (hCHS) that possesses a potential for minimizing the ratio C/S from above 3 in OPC down to 1, which significantly reduces the amount of CO$_2$ released during processing. The reaction kinetics of hCHS differs from that of classical clinker phases due to the presence of highly reactive silicate species, which involve silanol groups instead of pure calcium silicates and aluminates and aluminoferrites. In contrast to Portland cement, no calcium hydroxide is formed during hydration, which otherwise regulates the Ca…
Effect of changing the rare earth cation type on the structure and crystallization behavior of an aluminoborosilicate glass
一种铝硼硅酸盐玻璃，含有高量的稀土（RE），其组成为50.68 SiO 2 - 4.25 Al 2 O 3 - 8.50 B 2 O 3 - 12.19 Na 2 O- 4.84 CaO - 3.19 ZrO 2 - 16.35 RE 2 O 3（重量%），目前正在研究用于固定化核废料溶液。在这项工作中，我们要调查的影响，改变稀土阳离子类型的玻璃结构和其结晶行为。为此，一系列的玻璃阐述了RE的性质是不同的镧，镥。在该玻璃系列中，仅观察到对玻璃结构的影响很小。相反，通过不同的热处理对结晶行为的强烈影响是显而易见的。以1 μ/℃/min的速度缓慢冷却熔体，发现含有离子半径接近钙的稀土的样品中磷灰石Ca_2RE_8（SiO_4）_6O_2明显结晶。另一种热处理，包括连续的成核和生长阶段，进行强制结晶的散装和减少任何表面结晶效果，提出证据的存在下，一个强烈的非均匀的第二稀土丰富的硅酸盐相的样品含有低离子半径（从Y到Lu）。
We apply a recently developed optimization scheme to obtain effective potentials for alkali and alkaline-earth aluminosilicate glasses that contains lithium, sodium, potassium, or calcium as modifiers. As input data for the optimization, we used the radial distribution functions of the liquid at high temperature generated by means of ab initio molecular dynamics simulations and density and elastic modulus of glass at room temperature from experiments. The new interaction potentials are able to reproduce reliably the structure and various mechanical and vibrational properties over a wide range …
Biological activity of a SiO2-CaO-P2O5 sol-gel glass highlighted by PIXE-RBS methods
在这项研究中，建议通过一个完整的PIXE表征观察P2 O 5对生物活性玻璃中的磷灰石类层的形成的影响。采用溶胶-凝胶法制备了SiO2-CaO-P2 O 5三元系统玻璃。将玻璃样品浸泡在生物液体中长达10天。表面的变化，其特征在于使用粒子诱导X射线发射（PIXE）与卢瑟福背散射光谱（RBS），这是多元素分析的有效方法。在微米尺度上获得了主量和微量元素的元素图，并揭示了材料的骨结合能力。在相互作用几天后，形成含有镁的富磷酸钙层。我们证明了材料中磷的存在对骨样磷灰石层的形成和形成速率有影响。实际上，与不含P2 O 5的玻璃相比，玻璃/生物流体界面处的Ca/P原子比更接近纯磷灰石的标称值。它将允许在体内改善生物材料和骨之间的化学结合。
