Study of the Dehydroxylation–Rehydroxylation of Pyrophyllite

Pérez-Rodríguez, J. L.; Durán, A.; Jiménez, Pilar; Franquelo, M. L.; Perejón, Antonio; Pascual‐Cosp, José; Pérez‐Maqueda, Luis A.

doi:10.1111/j.1551-2916.2010.03750.x

Cited by 17 publications

(24 citation statements)

References 45 publications

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“…The authors found no evidence of any intermediate derivative in the dehydroxylation of pyrophyllite, which is in agreement with the results by Drits et al (2011). Additionally, Pérez-Rodríguez et al (2010) used the isoconversional method to calculate the activation energy for pyrophyllite dehydroxylation reaction. Such a method does not require any assumption regarding the actual kinetic model obeyed by the reaction.…”

supporting

confidence: 82%

“…During rehydroxylation in the cooling phase H 2 O molecules from vapor in the TG furnace are trapped in interlayer sites between 2:1 layers and then migrate into the octahedral sheets and reform OH groups (Drits and McCarty 2007;Pérez-Rodríguez et al 2010). The amount of OH groups reformed during rehydroxylation during the cooling phase in the present experiments [and those by Drits and McCarty (2007)] cannot be compared quantitatively to the results of rehydroxylation obtained by Pérez-Rodríguez et al (2010).…”

Section: Thermal Analysiscontrasting

confidence: 59%

“…The amount of OH groups reformed during rehydroxylation during the cooling phase in the present experiments [and those by Drits and McCarty (2007)] cannot be compared quantitatively to the results of rehydroxylation obtained by Pérez-Rodríguez et al (2010). The experiments by these authors were done in water-saturated conditions where unlimited water was available to the clay structure for OH reconstruction, similar to work by Emmerich et al (1999).…”

Section: Thermal Analysismentioning

confidence: 57%

“…Independently from Drits et al (2011), Pérez-Rodríguez et al (2010 recently showed that pyrophyllite dehydroxylation is a reversible kinetically driven process. The temperature of dehydroxylation and the ability to rehydroxylate are direct functions of crystallite thickness.…”

mentioning

confidence: 98%

“…introDuction Different aspects of the dehydroxylation of pyrophyllite has attracted the attention of many authors (Grim 1968;Heller et al 1962;Frost and Barron, 1984;Brindley and Wardle 1970;Wardle and Brindley 1972;Guggenheim et al1987;Evans and Guggenheim 1988;Guggenheim 1990;Lee and Guggenheim 1981;Zvyagin et al 1969;Fitzgerald et al 1989Fitzgerald et al , 1996MacKenzie et al 1985;Zhang 1997a, 1997b;Kloprogge and Frost 1999;Wang et al 2002;Stackhouse et al 2004;Pérez-Maqueda et al 2004;Sainz-Díaz et al 2004;Molina-Montes et al 2008a, 2008b, 2008cPérez-Rodríguez et al 2010). PyrophylPyrophyllite, Al 2 Si 4 O 10 (OH) 2 , is a dioctahedral layered aluminosilicate mineral consisting of 2:1 layers in which a sheet of octahedral coordinated Al cations is sandwiched between two corner-sharing tetrahedral sheets.…”

mentioning

confidence: 98%

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Kinetics of thermal transformation of partially dehydroxylated pyrophyllite

Drits

Derkowski

McCarty

2011

American Mineralogist

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A multi-cycle heating and cooling thermogravimetric (TG) method was used to study the kinetic behavior of two partially dehydroxylated pyrophyllite samples. In the original state, the S076 sample contains only trans-vacant (tv) layers, whereas in sample S037 tv and cis-vacant (cv) layers are randomly interstratified. The method consists of consecutive heating cycles (rate 2 °C/min) separated by intervals of cooling to room temperature, with the maximum cycle temperature set (MCT) incrementally higher than in each previous cycle.The activation energy (E a ) values were calculated for the S037 and S076 samples for all cycles in terms of a homogeneous zero-order reaction with the regression coefficients r 2 ≥ 0.9997. The S076 sample had E a values that varied from 40 to 42 kcal/mol within a partial dehydroxylation (D T ) range from 19 to 63%. However, at D T values <19% and >63% the E a values are slightly lower at 38-39 kcal/mol and drop below 30 kcal/mol at D T = 90%. A bimodal distribution of the S037 sample E a values exists with increasing MCT and D T . In the first cycles of intense dehydroxylation from tv layers the E a values increase sharply from 34 kcal/mol at D T = 7% to 45 kcal/mol within the MCT interval from 525 to 575 °C and then decrease to 36-38 kcal/mol at the cycles with MCT = 650-700 °C. In the second portion of cycles corresponding to the dehydroxylation of cv layers, the E a values increase from 36-37 kcal/mol at MCT = 700 °C to 44-46 kcal/mol at MCT = 775 °C. These results show that both tv and cv layers require exactly the same energy for dehydroxylation and have similar variation of the E a values with MCT and D T .The pyrophyllite particle size distribution is a major factor that is likely responsible for a broad interval of dehydroxylation temperature. This implies that the lower the temperature, the smaller the particles that can be dehydroxylated. Therefore, the activation energy values at the beginning of the reaction are lower than those at higher degrees of dehydroxylation because of the combination of a slow experimental heating rate and thin crystallites, which both contribute to lower temperatures at which the reaction starts.The decrease in activation energy observed at the end of the dehydroxylation reaction of sample S076, and of the tv layer portion of sample S037 is accompanied by an increase in the "induction" temperature interval during which an accumulation of additional thermal energy decreases the activation energy.The kinetic parameters determined for the samples in this study correspond to a homogeneous reaction and are used to predict a general pattern of the structural transformations of pyrophyllite at different stages during dehydroxylation.

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supporting

confidence: 82%