Viscosity, fragility, and configurational entropy of melts along the join SiO2-NaAlSiO4
Viscosity, fragility, and configurational entropy of melts along the join SiO2-NaAlSiO4
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沿 SiO2-NaAlSiO4 连接处熔体的粘度、脆性和构型熵
DOI：
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
T. Lenci
中科院分区：
文献类型：
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作者：
M. Toplis;Donald Bruce Dingwell;K. Hess;T. Lenci
采用同心圆柱法和微穿透技术相结合的方法，在1-1012Pa.S(700-1650°C)范围内测量了SiO_2-NaAl_2熔体附近14种熔体的粘度。这些组成包括五个等价线的二氧化硅含量从50%到82摩尔%，从轻微的过碱性到轻微的过铝。由于在高温和低温测量中使用了完全相同的组成，在接近玻璃化转变的温度下测量了较大范围的二氧化硅含量的粘度，并且在恒定二氧化硅含量和可变的碱/铝比下测量了几种组成，因此可以沿着二氧化硅-铝酸钠的连接处精确地对组成进行数据内插，从而大大改善了对体系粘度的温度依赖性的约束。在高温下(1600°C)，粘度和活化能与二氧化硅含量近似成线性函数，但在接近玻璃化转变范围的温度下出现较大的非线性。将脆性定义为玻璃化转变温度(Tg为1012Pa.S等温线)下的粘度曲线在降温标度(Tg/T)上的梯度，发现随着NaAlO2取代SiO_2，脆性呈非线性增加，且SiO_2含量越低，脆性增加越快。粘度数据与文献中提供的热容数据相结合，使用Adam-Gibbs理论估算钠长石、翡翠和霞石玻璃的构型熵。根据Adam-Gibbs参数定义的脆性随组态热容(液体和玻璃态之间的热容差)而增加，但在玻璃化转变处随组态熵的增加而降低。根据独立的相平衡和光谱和量热学证据，表明Al-Si有序度随着SiO_2含量从SiO_2到霞石的减少而增加，根据Al-Si混合对组态熵的模拟表明：(1)熔体组态熵既有阳离子混合的贡献(化学贡献)，也有O网络拓扑的变化(拓扑贡献)的贡献，后者占主导地位。(2)化学贡献来自于四面体的混合，而不是O位。(3)在玻璃化转变处(1012Pa.S等温线)，拓扑贡献几乎没有变化。
Abstract Viscosities of fourteen melts close to the join SiO2-NaAlO2 were measured in the range 1-1012 Pa·s (700-1650 °C) using a combination of concentric cylinder and micropenetration techniques. These compositions cover five isopleths in silica content from 50 to 82 mol% and vary from mildly peralkaline to mildly peraluminous. Greatly improved constraints on the temperature dependence of viscosity in the system SiO2-NaAlO2 result because exactly the same compositions were used for both high- and low-temperature measurements, viscosities over an extended range of silica contents were measured at temperatures close the glass transition, and several compositions at constant silica content and variable alkali/Al ratio were measured, allowing interpolation of data to compositions exactly along the join SiO2-NaAlO2. At high temperature (1600 °C) viscosity and activation energy are shown to be approximately a linear function of silica content, but large nonlinearities occur at temperatures close to the glass transition range. Defining fragility as the gradient of the viscosity curve at the glass transition temperature (Tg taken to be the 1012 Pa·s isokom) on a reduced temperature scale (Tg/T), it is found that the fragility increases in a nonlinear fashion as NaAlO2 is substituted for SiO2, with fragility increasing more rapidly at lower SiO2 contents. The viscosity data are combined with heat capacity data available in the literature to estimate configurational entropies of albite, jadeite, and nepheline glasses using the Adam-Gibbs theory. Fragility, when defined in terms of the Adam- Gibbs parameters, is shown to increase with configurational heat capacity (difference in heat capacity between the liquid and the glassy states) but to decrease with increasing configurational entropy at the glass transition. In the light of independent phase equilibria and spectroscopic and calorimetric evidence that suggests the Al-Si ordering increases as silica content decreases from SiO2 to nepheline, the modeling of configurational entropy in terms of Al-Si mixing suggests the following: (1) Melt configurational entropy has contributions from both cation mixing (chemical contribution), as well as variations in the topology of the O network (topological contribution), of which the latter dominates. (2) The chemical contribution is due to mixing of tetrahedral rather than O sites. (3) At the glass transition (1012 Pa·s isokom) the topological contribution shows little, if any, variation.