Dehydroxylation of kaolinite-group minerals: An ESR study

Komusinski, J.; Stoch, L.

doi:10.1007/bf02188856

Cited by 9 publications

(3 citation statements)

References 5 publications

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“…It was expected that kaolin heated below 400 °C would show the same low pozzolanic activity (0.8 Ca(OH) 2 /g) as the kaolin that has not been subjected to thermal treatment. However, it has been reported that even though no major structural changes occur, there is a slight deformation in the octahedral sheets [23], which could possibly explain the pozzolanic values above 0.8 Ca(OH) 2 /g. Only the metakaolin formed at temperature between 350-950 °C had a pozzolanic activity above 1.3 Ca(OH) 2 /g and only these 7 samples were considered to be pozzolanic.…”

Section: For the Fractional Conversion Of The Ratio Between Alo 6 Andmentioning

confidence: 97%

The influence of thermal treatment on properties of kaolin

Erasmus

2016

Hem Ind

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The kinetics of dehydroxylation of South African kaolin revealed that both the inner and the surface hydroxyl groups disappear according to first order kinetics, however, the surface group disappeared faster than the inner groups, showing that diffusion control kinetics is also important. The temperature dependent transformations of the kaolin was measured by means of fractional conversion of the ratios between AlO 6 :AlO 4 and Si-O-Al:Si-O-Si, which showed k obs values 0.0168 s-1 and 0.0089 s-1 for the transformation to the spinel phase and values of 0.0165 s-1 and 0.0156 s-1 for the transformation to mullite respectively. The pozzolanic activities of the kaolin calcined at different temperatures showed a maximum pozzolanic activity when the kaolin is calcined at 650°C and the pozzolanic activity for mullite is even less than for the uncalcined kaolin. XPS revealed that the atomic ratio between Si and Al did not change from kaolin to metakaolin (Si:Al = ca. 1.2) however the mullite showed a atomic ratio of Si:Al = 1.52, implying that some deallumination occurred during calcination at high temperatures.

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Section: For the Fractional Conversion Of The Ratio Between Alo 6 Andmentioning

confidence: 97%

The influence of thermal treatment on properties of kaolin

Erasmus

2016

Hem Ind

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“…Both the X-and Q-band powder spectra (Figs. 5a and 6b) For the structural interpretation of their centres one can in principle follow the argumentations of [20][21][22][23]. However, the most interesting fact results here from the analysis of the Fe 3 § spectra taken from so called metakaolinite samples (see Fig.…”

Section: Dehydration Of Ai(oh)3/fe 3 § and Ale[(oh)4si2os]/fe 3 § (Kamentioning

confidence: 99%

ESR evidence of order/disorder transitions in solids caused by dehydration

Stößer

Scholz

1997

Appl. Magn. Reson.

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ESR spectroscopy was used to study order/disorder phenomena in paramagnetically doped solids. The dehydration process of alurninium fluoride and oxide hydrates and aluminosilicates was examined by ESR in situ measurements as well as using thermoanalytically quenched samples. Two types of amorphous states of solids have been studied: inorganic glasses in the conventional sense and amorphous states of solids which have not passed the liquid state. The complete ESR fine structure pattern of Fe 3 § ions is susceptible with respect to order/disorder processes of the actual host matrix. Dehydration processes bear some model character in this field. A quantitative description of the disorder effects on the Fe 3 § ESR could be given on the basis of a complete spin Hamiltonian using distributions of the fourth order spin coupling parameters.

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“…The effectiveness of chemical methods in removing extra-framework iron, and the ordering of the kaolinite structure on the basis of the intensity ratio of particular Fe 3+ EPR signals, were also investigated then and later (Angel, Hall 1973;Gaite et al 1993;Gaite et al 1997). Polish mineralogists contributed involved research data on the catalytic properties of smectites (Bahranowski et al 1996) and on the purification of clay raw materials contaminated with iron (Komusiñski et al 1981;Komusiñski, Stoch 1984;Bahranowski et al 1993).…”

Section: Introductionmentioning

confidence: 99%

EPR Study of Paramagnetic Defects in Clay Minerals

2007

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EPR Study of Paramagnetic Defects in Clay MineralsRadiation induced defects (RID-s) and transition metal ion impurities were revealed by EPR (Electron Paramagnetic Resonance) spectroscopy in kaolinites from a number of Polish deposits. Arelationship between the intensity of the EPR signals of the RID-s and quantity of radioactive elements was defined in these minerals. In one of the deposits of kaolinites (Wyszonowice) the EPR signal intensity depends on grain size. Other clay minerals studied (illites, montmorillonites) only show weak signals of the RID type.

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Dehydroxylation of kaolinite-group minerals: An ESR study

Cited by 9 publications

References 5 publications

The influence of thermal treatment on properties of kaolin

The influence of thermal treatment on properties of kaolin

ESR evidence of order/disorder transitions in solids caused by dehydration

EPR Study of Paramagnetic Defects in Clay Minerals

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