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Devitrification of a frit (glass) based on the oxide system SiO 2 -Al 2 O 3 -ZnO-CaO was studied. The following major crystalline phases were identified: gahnite (ZnAl 2 O 4 ), willemite (Zn 2 SiO 4 ), and a solid solution exhibiting an anorthite structure. A kinetic model was used to fit the experimental results. The model was derived by assuming that a precursor phase with an anorthite crystalline structure devitrified first and subsequently decomposed to form gahnite, while willemite crystallized independently. The proposed model satisfactorily reproduced the amount of gahnite, willemite, and anorthitetype crystals that formed during firing. The equations developed allowed the prediction of the anorthite structure, gahnite, and willemite crystal volume fractions in the resulting glaze as a function of firing temperature and time.

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