A systematic approach to fibre glass development

Kölker, Klara; Conradt, Reinhard (Thesis advisor); Roggendorf, Hans (Thesis advisor); Roos, Christian Hans-Georg (Thesis advisor)

Aachen (2017)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2017

Abstract

The theoretical glass development on the basis of thermodynamic data is a powerful tool to estimate physical and chemical properties of a glass before the actual melting process. Replacing the conventional empirical approach by a systematic one offers the opportunity of saving time and costs.In the course of the development of a novel fibre glass composition for reinforcement applications, a new theoretical strategy is introduced. It is based on the constitutional approach to the description of the amorphous state. Since the properties of glass forming systems are closely related to the properties of the phases occurring under equilibrium conditions, it is possible to make accurate predictions about the glassy state utilizing existing thermodynamic data of the crystalline reference system.By means of the thermochemical software FactSageTM constitutional ranges of the glass forming systems CaO-ZnO-Al2O3-SiO2 (CZAS) and CaO-P2O5-Al2O3-SiO2 (CPAS) are identified. In a second step, the oxide compositions and the liquidus temperatures of invariant points within the constitutional sub-systems are calculated. As a final result of this theoretical step, a network describing quaternary invariant points in addition to their melting temperatures and the corresponding saturation lines is derived for each of the glass forming systems.Four suitable oxide compositions for the system CZAS (e, f, g and v) and six for CPAS (5, 6, 7, 12, 13 and 15) are determined according to criteria set by the industrial fibre process; these are a liquidus temperature below 1200 °C, a fibre drawing temperature at the viscosity level log η = 3 (η in dPa·s) of less than 1260 °C and a resulting ΔT = T3 - Tliq of at least 60 K. The selected glasses are melted, processed, and their properties verified by experiment.The compositions are characterized with regards to their glass forming ability, crystallisation tendency, temperature-viscosity profile, fibre drawing ability and product properties such as Young’s modulus, tensile strength and chemical durability.Altogether, the CZAS system can be reduced to two (e and f) and the CPAS system to one oxide composition (13) which are suitable as a basis for commercially produced reinforcement glass fibres. This proves that the introduced strategy is applicable for the prediction of key glass properties and the specific development of basic compositions of multi-component glass forming systems.