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Petroleum Geological Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
The feldspathoid silicates resemble feldspar, but have lower silica contents than alkali-aluminum silicates. The group is formed in magma that is rich in alkali and deficient in silica. The group consists of seven types of silicates. The most well-known feldspathoid silicate is leucite.
Effect of heat treatment parameters on the crystallization of feldspathic-based dental glass-ceramics
Published in Journal of Asian Ceramic Societies, 2020
Emre Yalamaç, Mucahit Sutcu, Elif Sıla Ergani
Leucite is a potassium-aluminum-silicate phase and its chemical composition is K2O·Al2O3 · 4SiO2. It is an important crystalline phase in the content of feldspathic glass-ceramic materials and has a high coefficient of expansion (18 × 10−6 1/°C) [11]. Crystallization of the leucite phase takes place by the mechanism of surface nucleation in a glass phase [12]. The bending strength, fracture toughness, elastic modulus and Vickers hardness of the dense leucite (99% relative density) body from the measured mechanical properties are 173 MPa, 2.3 MPa.m1/2, 63 GPa and 5.3 GPa, respectively [13,14]. A leucite-based glass-ceramic composition prepared from a glass generally consists of 66–72 mol% SiO2, 8–11 mol% Al2O3, 9–13 mol% K2O, 0–4 mol% CaO, 1–4 mol% Na2O and 0–3 mol% TiO2 [15]. Some studies on crystallization of leucite-based glass-ceramics have been conducted in the literature. Cattell et al. [16] examined leucite glass-ceramics crystallization by applying different heat treatments with different particle size glassy (amorphous) frit powders. The authors concluded that according to DTA analysis leucite crystallization peak shifted to lower temperature and sharpness of leucite crystal peak increased when the glass powder particle size was reduced. In the study of Chen et al. [17] the microstructure of fine-grained leucite glass-ceramic was optimized by changing nucleation and growth heat treatment parameters in order to increase the flexural strength. After optimization of the crystallization process, fine (0.15 µm2) leucite crystals were formed in the glass matrix with no signs of micro-cracking. As a result, the flexural strengths of the produced glass-ceramics were measured between 220 and 250 MPa. The study by Brodkin et al. [18] involves the production of four different glass-ceramic block compositions containing leucite phases. The objective is to form fine-grained tetragonal or stabilized cubic leucite phases in the glassy phase and distribute them homogeneously. It is reported that leucite makes coarse-grained at high temperatures, making it difficult to process the glass-ceramic. Different amounts of Na2O added potassium feldspar frit mixed with high purity natural leucite crystals to produce leucite-containing glass porcelain. Na2O content in the glass matrix should be taken into account based on leucite crystal transformation temperature which significantly affects the flexural strength of the glass-ceramics [19]. Ban et al. [20] investigated the effect of cooling conditions on the formation and transformation of leucite crystals in three commercial dentin and incisal porcelains. According to their study, they concluded that there is little effect on the microstructural changes of leucite crystals due to the formation of the crystals at a high temperature range.