Kinetic study of the non-isothermal crystallization process of hematite in ceramic glazes obtained from CRT wastes

Aventurine type crystallization glazes containing hematite (α-Fe2O3) as reddish-brown crystals with golden reflexes are well known for their highly decorative effect. This effect is conditioned by the vitreous matrix composition selected to have a positive influence over the hematite crystallization process producing crystals with suitable shape and size. This paper promote the use of a glass waste—cathode ray tube (CRT) the funnel glass section (15÷60 wt%)—along with the traditional raw materials (borax, boric acid, quartz, and iron oxide) to obtain the aventurine frits. The mixture of CRT waste and raw materials containing 15÷20 % Fe2O3 was melted at a temperature of 1,250 °C with 30 min soaking time. Black granular frits were obtained after pouring the melts in cold water. The glaze slurry was prepared using the obtained frits (95 %) and kaolin (5 %) as suspension material. The crystallization kinetics of the aventurine type glaze has been investigated using the linear integral isoconversional methods described by Kissinger–Akahira–Sunose, Ozawa–Flynn–Wall, Starink and Tang, and also the non-linear integral isoconversional method described by Vyazovkin. The apparent activation energy of the hematite crystallization in the studied aventurine glazes ranges with the crystallized fraction between 190 and 262 kJ mol−1 for the frit with 3.82 % LiF and between 256 and 281 kJ mol−1 for the frit 3.82 % CaF2, respectively.