Model for the prediction of thermomechanical bulk properties of multicomponent oxide glasses based on a combined quantum mechanical and thermodynamic approach

点击翻译按钮获取中文摘要

The present project is inspired by the motivation to deeply root the understanding of the relation among chemical composition, structure, and thermomechanical properties of glasses in scientific concepts. The objective is the development of a model enabling quantitative exploration of compositional space for areas with outstanding mechanical properties, and its consequent use in materials design. The model shall be directed towards the bulk mechanical bulk properties of multicomponent oxide glasses. It starts from the working hypothesis of equivalency of structural short-range order groupings in such glasses, and the corresponding structures found in the isochemical crystalline states. This hypothesis is well substantiated with respect to thermochemical properties, however, yet unexploited with respect to mechanical properties, in part because of a lack of understanding – or even availability – of fundamental data for the crystals. The envisaged model attemps to establish the wide bridge from single crystals to multicomponent glasses by a combined approach. This is, firstly, a quantum mechanics based ab initio approach; it is directed towards the assessment of crystal structures and properties as well as towards an understanding why certain structures stand out with respect to their properties. This is, secondly, a thermodynamic approach directed towards assessing the differences between one-components glasses and isochemical crystals in terms of phenomenological quantities, and towards the superimposition of such data to the properties of multicomponent glass matrices. Here, “multi” in the sense of the project refers to typically > 5 functional oxide components as found in most industrial glass products. The system MgO-CaO-Al2O3-SiO2-P2O5 is depicted as compositional basis. The experimental work envisaged for this project aims, firstly, at a phenomenological assessment of the differences between selected single crystals and their isochemical counterparts. As these differences are most sensitively reflected by the differences in low-T heat capacities, low-T microcalorimetry shall be performed (external cooperation). The experimental determination of the mechanical bulk properties of one-component glasses serves the same purpose. These properties shall be determined acoustically by impuls excitation technique. The same technique will be applied to extensively verify model predictions for multicomponent matrices. The usefulness of the model for materials design shall be demonstrated at the end of the project for a few cases.