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In situ transformation of amorphous gels into spherical aggregates of kaolinite: A HRTEM study

Published online by Cambridge University Press:  09 July 2018

F. J. Huertas*
Affiliation:
Department of Earth Sciences, Estación Experimental del Zaidín, CSIC, Profesor Albareda 1, 18008 Granada, Spain
S. Fiore
Affiliation:
Laboratory of Geochemistry and Environmental Mineralogy, Istituto di Metodologie per l'Analisi Ambientale, CNR, 85050 Tito Scalo (PZ), Italy
J. Linares
Affiliation:
Department of Earth Sciences, Estación Experimental del Zaidín, CSIC, Profesor Albareda 1, 18008 Granada, Spain
*

Abstract

Initial stages of the gel-to-kaolinite transformation were studied using HRTEM. Spherical aggregates of kaolinite crystals were produced during the synthesis of kaolinite by hydrothermal treatment of Si-Al amorphous gels. Prior to sphere formation, gels transform into pseudospherical domains that have a Si/Al ratio of one and display no SAED pattern. The spherical particles consist of radially arranged sectors of stacks of planar crystallites. Crystals display nonbasal spacings of 4.5, 4.2 and 3.8 Å and a basal spacing of 7.1 Å , the c* axis following the radius of the sphere.

Interpretation of the 3D nanostructure of the spheres is difficult. The c* axis exhibits a radial disposition, but the relative orientation of the a* and b* axes in neighbouring crystallites may produce bent layers or incoherent contacts. In addition, curved layers with a d spacing of 7.4 Å may be attributed to halloysite layers collapsed under microscopy conditions. The disappearance of the spheres during the hydrothermal treatment is probably due to preferential dissolution of either highstress areas near bent layers or non-crystalline material filling crystal boundaries. Dissolution leads to sphere disaggregation and allows the component columnar crystals to continue to grow. Observations of the gel matrix suggest that under our experimental conditions kaolinite crystallizes via an in situ transformation of the gel.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2004

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References

Adamo, P., Violante, P. & Wilson, M.J. (2001) Tubular and spheroidal halloysites in pyroclastic deposits in the area of the Roccamonfina volcano (Southern Italy). Geoderma, 99, 295–316.Google Scholar
Bailey, S. (1990) Halloysite. A critical assessment. Proceedings of the 9’ International Clay Conference, Strasbourg. Sciences Géolgiques, Mémoire, 86, 89–98.Google Scholar
Baronnet, A. & Devouard, B. (1996) Topology and crystal growth on natural chrysotile and polygonal serpentine. Journal of Crystal Growth, 166, 952–960.Google Scholar
Baronnnet, A., Mellini, S. & Devouard, B. (1994) Sectors in polygonal serpentine. A model based in dislocations. Physics and Chemistry of Minerals, 21, 330–343.Google Scholar
Cressey, B. & Zussman, J. (1976) Electron microscopic studies of serpentinites. The Canadian Mineralogist, 14, 307–313.Google Scholar
De Kimpe, C.R., Gastuche, M.C. & Brindley, G.W. (1964) Low-temperature synthesis of kaolin minerals. American Mineralogist, 49, 1–16.Google Scholar
Fiore, S., Huertas, F.J., Huertas, F. & Linares, J. (1995) Morphology of kaolinite crystals synthesized under hydrothermal conditions. Clays and Clay Minerals, 43, 353–360.Google Scholar
González, Jesús|J., Huertas, F.J., Linares, J. & Ruiz Cruz, M.D. (2000) Textural and structural transformations of kaolinites in aqueous solutions at 200°C. Applied Clay Science, 17, 245–263.Google Scholar
Huertas, F.J., Huertas, F. & Linares, J. (1993) Hydrothermal synthesis of kaolinite: method and characterization of synthetic materials. Applied Clay Science 7, 345-356.Google Scholar
Huertas, F.I, Fiore, S. & Linares I (1997) Thermal analysis as a tool for determining and defining spherical kaolinite. Clays and Clay Minerals, 45, 587–590.Google Scholar
Huertas, F.I, Fiore, S., Huertas, F. & Linares, J. (1999) Experimental study of the hydrothermal formation of kaolinite. Chemical Geology, 156, 171190.CrossRefGoogle Scholar
Hughes, C.R., Curtis C, Whiteman I , Heping, S., Whittle, C. & Ireland, B. (1990) Selected applications of analytical electron microscopy in clay mineralogy. Pp. 69-88 in Electron-Optical Methods in Clay Science (Mackinnon, I.D.R. & Mumpton, F.A., editors). CMS Workshop Lectures 2, The Clay Minerals Society, Bloomington, Indiana.Google Scholar
Kawano, M. & Tomita, K. (1995) Experimental study on the formation of clay minerals from obsidian by interaction with acid solution at 150°C and 200°C. Clays and Clay Minerals, 43, 212–222.Google Scholar
Keller, W.D. (1976a) Scan electron micrograph of kaolins collected from diverse environments of origin—I. Clays and Clay Minerals, 24, 107–113.Google Scholar
Keller, W.D. (1976b) Scan electron micrograph of kaolins collected from diverse environments of origin - II. Clays and Clay Minerals, 24, 114–117.Google Scholar
Nagy, K.L. (1995) Dissolution and precipitation kinetics of sheet silicates. Pp. 173—233 in: Chemical Weathering Rates of Silicate Minerals (White, A.F. and Brantley, S.L., editors). Reviews in Mineralogy, 31. Mineralogical Society of America, Washington, D.C.Google Scholar
Peacor, D.R. (1992) Analytical electron microscopy: X-ray microanalysis. Pp. 335—380 in: Minerals and Reactions at the Atomic Scale: Transmission Electron Microscopy (Buseck, P.R., editor). Reviews in Mineralogy, 27. Mineralogical Society of America, Washington, D.C.Google Scholar
Rayner, J.H. (1962) An examination of the rate of formation of kaolinite from a coprecipitated silica gel. Pp. 123—127 in : Collogue sur la Genese et la Synthese des Argilles. CNRS 105, Paris.Google Scholar
Rodrique, L., Poncelet, G. & Herbillon, A. (1972) Importance of the silica substraction process during the hydrothermal kaolinitization of amorphous silico-aluminas. Proceedings of the International Clay Conference, Madrid, pp. 187-198.Google Scholar
Sudo, T. & Yotsumoto, H. (1977) The formation of halloysite tubes from spherulitic halloysite. Clays and Clay Minerals, 25, 155–159.Google Scholar
Sunagawa, I. (1987) Morphology of minerals. Pp. 509—587 in: Morphology of Crystals (Sunagawa, I., editor). Terra Science Publishing Co., Tokyo.Google Scholar
Tazaki, K. (1982) Analytical electron microscopy studies of halloysite formation processes: morphology and composition of halloysite. Proceedings of the International Clay Conference, Italy, 1981. Developments in Sedimentology, 35. Elsevier, Amsterdam, pp. 573—584.Google Scholar
Tomura, S., Shibasaki, Y., Mizuta, H. & Kitamura, M. (1983) Spherical kaolinite: synthesis and mineralogical properties. Clays and Clay Minerals, 31, 413–421.Google Scholar
Tomura, S., Shibasaki, Y., Mizuta, H. & Kitamura, M. (1985) Growth conditions and genesis of spherical and platy kaolinite. Clays and Clay Minerals, 33, 200–206.Google Scholar
Wicks, F.J. & O'Hanley, D.S. (1988) Serpentine minerals: Structures and petrology. Pp. 91—167 in: Hydrous Phyllosilicates (Bailey, S.W., editor). Reviews in Mineralogy, 19. Mineralogical Society of America, Washington, D.C.Google Scholar