Relationship between granulometric distribution and compressive strength of heat-treated Toarcian-Bajocian gypsum, Tunis
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ORIGINAL PAPER
Relationship between granulometric distribution and compressive strength of heat-treated Toarcian-Bajocian gypsum, Tunisia: implications for casting teeth in molds Fatma Hassaïri-Krid 1 & Mongi Felhi 2 & Nabil Fattah 3 & Ali Tlili 1 Received: 3 November 2018 / Accepted: 31 July 2019 # Saudi Society for Geosciences 2019
Abstract Toarcian-Bajocian gypsum deposits of the Mestaoua formation (southern part of Tunisia) correspond to very thick gypsum layers. The natural gypsum and their heat-treated products were investigated to assess their utilization in dental field (cast plaster into molds for dental prosthesis). XRD data show that the Mestaoua sample (GMes) constituted of gypsum. However, the commercial product (PXETD) is made up of bassanite. Powder X-ray diffraction combined with chemical and infrared analyses reveals that heat-treated GMes samples at different temperatures (200 °C, 220 °C, 240 °C, 260 °C) are dominantly bassanite with minor amounts of anhydrite, particularly, in the samples heated at 240 °C and 260 °C. The data obtained revealed that the sample heated at 220 °C and 240 °C are distinguished by satisfactory values of compressive strength, which are close to the value observed for a commercial product, and are suitable for use in dentistry. The slight decrease in the compressive strength is commonly due to the less abundant water molecules and the two divergent modes of particle distribution, which enhance pore space. Bulk properties of the sample heated at 240 °C are generally appropriate for use as a material to prepare molds in dental fields, as confirmed by the casting of plaster into mold teeth, where teeth revealed clearly steaks and showed even small details. Keywords Gypsum . Bassanite . Mold teeth . Compressive strength . Particle distributions
Introduction Gypsum is found in nature as a compact sedimentary rock. The porosity, which is about 10 to 15%, depends essentially on the microstructure, where the gypsum rock indicated various morphology and crystals. Gypsum rock is easily recognizable in the outcropping. This rock is scratched with nail related to their very low hardness (Rejab et al. 2012; Chaffee et al. 1997). Gypsum is calcium sulfate dihydrate mineral, which is
Editorial handling: Domenico M. Doronzo * Ali Tlili [email protected]; [email protected] 1
Department of Earth Science, Faculty of Science of Sfax, Sfax University, Sfax, Tunisia
2
Department of Geological Engineering, National School of Engineers of Sfax, University of Sfax, Sfax, Tunisia
3
Gafsa Phosphate Company, Research Center Metlaoui 2130, Gafsa, Tunisia
characterized by a large Ca and S contents; their basic chemical formula is CaSO4.2H2O (Siadat and Shahrokhi 2007). The crystal of gypsum mineral is composed of a stack of calcium ions (Ca2+) and sulfate groups (SO42-) of tetrahedral form, linked by double layers of water (Lewry and Williamson 1994; Karni and Karni 1995; Pinheiro and Camarini 2015). This form constitutes the main natural gypsum deposit (Camarini and Pinheiro 2014). The g
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