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SOME PHYSICOCHEMICAL PROPERTIES OF THE WHITE SEPIOLITE KNOWN AS PIPESTONE FROM ESKIEHR, TURKEY

Müerref Önal^*, Hamza Yilmaz and Yüksel Sarikaya

Department of Chemistry, Faculty of Science, Ankara University, Tandoan, 06100 Ankara, Turkey

^* E-mail address of corresponding author: onal{at}science.ankara.edu.tr

Various physicochemical characteristics of a sepiolite sample from the Eskiehir area, Turkey, were investigated to help in making predictions about possible uses of the material. The sample was examined by chemical analysis (CA), thermal analysis (DTA/TGA), X-ray diffraction (XRD) analysis, particle-size analysis (PSA), linear dilatometry (LD), scanning electron microscopy (SEM), mercury porosimetry (Hg-Por.), and low-temperature nitrogen adsorption/desorption (N₂-AD) techniques. The CA and XRD data indicated that the sepiolite contains only 6% dolomite by mass. The XRD patterns showed that sepiolite anhydride, enstatite, diopside, and opal-CT form upon heating the sepiolite above 600, 800, 900, and 1200°C, respectively. The maximum rate of endothermic changes in the DTA and TGA curves were observed at 82, 287, and 491°C, corresponding to the loss of external, zeolitic, and bound water from the sepiolite, respectively. Dehydroxylation and recrystallization of the sepiolite were fastest at 845°C and 862°C, respectively. The LD curve indicated that the shrinkage began at 800°C and reached 4.0% at 1000°C. The proportion of particles with diameters of <2 µm, and the external surface area of the long-term (24 h) water-treated sepiolite were determined by PSA as 79% by volume, and 8 m²g^–1, respectively. The SEM view revealed discrete bundles of sepiolite fibers of various lengths. The specific surface area found from adsorption data was 316 m²g^–1. The specific micro-, meso-, macro-, and total-pore volumes obtained from the combination of Hg-Por. and N₂-AD results were 0.16, 0.21, 0.45, and 0.82 cm³g^–1, respectively. The average macropore and micro-mesopore radii in the sepiolite were estimated (using the Hg-Por. and N₂-AD data) to be 35 and 2.4 nm, respectively.

Key Words: Porosity • Sepiolite • Surface Area • Thermal Analysis • X-ray Diffraction