Browsing by Author "Schiffner, Ulrich"

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    Nucleation in a precursor glass for a Li2O-Al2O3-SiO2 glass ceramic Part 1. Nucleation kinetics
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1987) Schiffner, Ulrich; Pannhorst, Wolfgang
    The nucleation of the parent glass of a Li2O-Al2O3-SiO2 glass ceramic is determined. The two-step development method is applied utilizing a specially developed device which allows quantitative determination of nucleation rates despite of the strong tendency for nucleation. The influence of nucleation on the transmission of the glass ceramic is investigated to obtain criteria for optimal nucleation conditions for ceramization of the glass. Nucleation is markedly characterized by non-stationary behaviour. The existence of delay times which depend as well on development temperature as on thermal history of the glass is of great importance for the processing of the glass. The impact of nucleation kinetics on the production of the glass ceramic is explained by means of TTT diagrams.
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    Nucleation in a precursor glass for a Li2O-Al2O3-SiO2 glass ceramic Part 2. Variation of the nucleating agent concentrations
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1987) Schiffner, Ulrich; Pannhorst, Wolfgang
    The influence of nucleating oxide concentration on nucleation in a parent glass of a Li2O-Al2O3-SiO2 glass ceramic is investigated by means of a method described in part 1 of this paper. Furthermore it is investigated to which extent glasses with different concentrations of nucleating agents can be transformed into useable glass ceramics. It is shown that with decreasing concentration of the nucleating agents the nucleation process is slowed down. The data present a basis for improved processing. The study of properties of ceramized glasses with varied concentration of nucleating agents clearly indicates that a reduction in the nucleation tendency can be counteracted by changing the nucleation conditions during ceramizing.