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Evolution of porosity and changes in heat treated lepidocrocite
Author(s) -
CORNEJO J.,
HERMOSIN M. C.
Publication year - 1988
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1988.tb01213.x
Subject(s) - lepidocrocite , porosity , materials science , sintering , transmission electron microscopy , adsorption , dehydration , mesoporous material , diffraction , specific surface area , chemical engineering , phase (matter) , mineralogy , crystallography , composite material , chemistry , nanotechnology , optics , biochemistry , physics , engineering , organic chemistry , goethite , catalysis
SUMMARY The thermal decomposition of lepidocrocite in air has been studied by X–ray powder diffraction, IR spectroscopy, transmission electron microscopy and N 2 adsorption isotherms. Three consecutive processes may be differentiated with increasing temperature: (a)<200°C; no structural change is observed, but a surface dehydration gives rise to an increase in surface area besides a change of mesopore shape from cylindrical to slit–shaped, (b)200–300°C; the maghaemite phase is obtained with a high increase in surface area mainly due to the formation of micropores, because of water losses from inner positions that produce lattice disruption, and (c)≥ 350°C; the transformation of maghaemite to haematite takes place decreasing the specific surface area as the temperature increased. At 450°C microporosity is destroyed and a change of slit–shaped to cylindrical mesoporosity is observed. Porosity dissappeared at ≥600°C, mainly due to interparticle sintering which produces well crystallized haematite samples of low surface area.