Halloysite nanotube and its firing products: structural characterization of halloysite, metahalloysite, spinel type silicoaluminate and mullite

ANDRINI, L.; TOJA, R. MOREIRA; CONCONI, M.S.; REQUEJO, F.G.; RENDTORFF, N.M.

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA

ELSEVIER SCIENCE BV

Año: 2019 vol. 234 p. 19 - 26

0368-2048

Halloysiteand its heating products demand attention due to its multiple technologicalapplications, and in particular for its natural nanostructure. The purpose ofthis paper is to present a structural characterization of these materials andits firing products up to mullite. To achieve this objective, the techniques ofconventional X-ray diffraction (XRD) and X-ray absorption near-edge structure(XANES) were used, in addition to scanning electron microscopy (SEM), andsimultaneous thermogravimetric and differential thermal analysis (DTA-TG). SEMhas allowed to prove that the nanotubular morphology (acicular) of halloysitewas retained for all temperatures (500, 800, 1100 and 1250 °C). For thetemperatures between 500 and 800 °C the metahalloysite phase was identified.The 1100 °C fired samples presented the spinel aluminosilicate phase. Finally,after high temperature treatments the mullite phase was detected as the onlyaluminum containing crystalline phase accompanied by cristobalite and glassyphase. The XANES spectra confirmed the octahedral aluminum coordination innative halloysite, this coordination was progressively lost with the thermaltreatments giving place to the presence of the four folded coordination. In theintermediate treatments, the so called metahalloysite phase, presented somethree and five coordination slight contributions. Particularly, themetahalloysite Al K XANES spectra were not reported before.