Vysokoteplotní fázové transformace kaolinitu v závislosti na krystalinitě

Petr Štursa, Dalibor Všianský, Karel Lang, Lenka Nevřivová, Lukáš Tvrdík, Pavel Kovář, Lucie Keršnerová

Abstrakt

Although kaolinite is one the most important industrial minerals, the processes of its transformation to mullite have not been completely explained so far. The study is focused on kaolinite crystallinity calculation and its effect on high-temperature phases transitions in the series kaolinite-mullite. Samples of purified natural kaolins from several sites were analysed using X-ray diffraction (XRD). Besides the determination of the complex mineral composition, kaolinite crystallite size was calculated from XRD data by the Rietveld method, Scherrer equation and using the Hinckley crystallinity index. Thermal analysis (DSC/TG) was used as the principal approach to examine endothermic and exothermic effects of kaolinite transformations. The course and maximum temperatures of the observed effects were correlated with the original crystallite size of kaolinite. Two samples with different kaolinite crystallinity were also analysed by high-temperature X-ray diffraction (ht-XRD) to study the formation of mullite. Scanning electron microscope (SEM) was used to visualize morphology of kaolinite.

It was found out that the original crystallinity of kaolinite affects all three examined processes-kaolinite dehydroxylation, formation of crystalline phases from metakaolinite and development of mullite crystal structure. Dehydroxylation of samples with higher kaolinite crystallinity takes place at higher temperatures. Similar effect applies for the reaction(-s) at the temperature about 980 °C observed at heat flow curve where crystallization of spinel type phase and mullite with very low crystallinity occurs. Broadening of FWHM of the exothermic effect points to decreasing kaolinite crystallinity. Crystallization of mullite exhibits different dependence on kaolinite crystallinity than the previous processes. The results show that mullite with larger crystallite size develops faster from kaolinite of low crystallinity and vice versa.

Bibliografická citace

Štursa, P., Všianský, D., Lang, K., Nevřivová, L., Tvrdík, L., Kovář, P., & Keršnerová, L. (2020). Vysokoteplotní fázové transformace kaolinitu v závislosti na krystalinitě. Geologické výzkumy na Moravě a ve Slezsku, 27(1-2). doi:https://doi.org/10.5817/GVMS2020-12674

Klíčová slova

kaolinite, crystallinity, Hinckley index, x-ray diffraction, thermal analysis

Plný Text:

HTML

Reference

Zobrazit literaturu Skrýt literaturu

Brindley, G. W., Nakahira, M. (1959) a. The Kaolinite‐Mullite Reaction Series: I, A Survey of Outstanding Problems. – Journal of the American Ceramic Society, 42, 7, 311–314. https://doi.org/10.1111/j.1151–2916.1959.tb14314.x

Brindley, G. W., Nakahira, M. (1959) b. The Kaolinite‐Mullite Reaction Series: II, Metakaolin. – Journal of the American Ceramic Society, 42, 7, 314–318. https://doi.org/10.1111/j.1151–2916.1959.tb14315.x

Brindley, G. W., Nakahira, M. (1959) c. The Kaolinite‐Mullite Reaction Series: III, The High‐Temperature Phases. – Journal of the American Ceramic Society, 42, 7, 319–324. https://doi.org/10.1111/j.1151–2916.1959.tb14316.x

Bellotto, M., Gualtieri, A., Artioli, G., Clark, S. M. (1995). Kinetic study of the kaolinite–mullite reaction sequence. Part I: Kaolinite dehydroxylation. – Physics and chemistry of minerals, 22, 4, 207–217. https://doi.org/10.1007/BF00202253

Chakraborty, A. K. (2014). Phase transformation of kaolinite clay. – Springer India. 346 s. https://doi.org/10.1007/978–81–322–1154–9

Číčel, B., Novák, I., Horváth, I. (1981). Mineralogy and crystallochemistry of clays. – SAV, Bratislava.

Feng, W., Ma, Hongwen. (2004). Thermodynamic analysis and experiments of thermal decomposition for potassium feldspar at intermediate temperatures. – Journal of the Chinese Ceramic Society, 32, 789–799.

Hinckley, D. N. (1962). Variability in “crystallinity” values among the kaolin deposits of the coastal plain of Georgia and South Carolina. – Clays and clay minerals, 11, 1, 229–235. https://doi.org/10.1346/CCMN.1962.0110122

Húlan, T., Trník, A., Medveď, I. (2017). Kinetics of thermal expansion of illite–based ceramics in the dehydroxylation region during heating. – Journal of Thermal Analysis and Calorimetry, 127, 1, 291–298. https://doi.org/10.1007/s10973–016–5873–0

Lee, S., Kim, Y. J., Moon, H. S. (1999). Phase Transformation Sequence from Kaolinite to Mullite Investigated by an Energy‐Filtering Transmission Electron Microscope. – Journal of the American Ceramic Society, 82, 10, 2841–2848. https://doi.org/10.1111/j.1151–2916.1999.tb02165.x

Lee, S., Kim, Y. J., Moon, H. S. (2003). Energy‐Filtering Transmission Electron Microscopy (EF‐TEM) Study of a Modulated Structure in Metakaolinite, Represented by a 14 Å Modulation. – Journal of the American Ceramic Society, 86, 1, 174–176. https://doi.org/10.1111/j.1151–2916.2003.tb03297.x

Murray, H. H. (2006). Structure and composition of the clay minerals and their physical and chemical properties. – Developments in clay science, 2, 7–31. https://doi.org/10.1016/S1572–4352(06)02002–2

Rietveld, H. (1969). A profile refinement method for nuclear and magnetic structures. – Journal of applied Crystallography, 2, 2, 65–71. https://doi.org/10.1107/S0021889869006558

Serrano, F. J., Bastida, J., Amigó, J. M., Sanz, A. (1996). XRD line broadening studies on mullite. – Crystal Research and Technology, 31, 8, 1085–1093. https://doi.org/10.1002/crat.2170310818

Scherrer, P. (1918). Göttinger Nachrichten Math – Phys, 2, 98–100.

Slaughter, M., Keller, W. D. (1959). High temperature phases from impure kaolinite. – American Ceramic Society Bulletin, 38, 12, 702-703.

Varga, G. (2007). The structure of kaolinite and metakaolinite. - Építőanyag, 59, 1, 6-9. https://doi.org/10.14382/epitoanyag-jsbcm.2007.2

https://doi.org/10.5817/GVMS2020-12674