Kinetics of partial dehydroxylation in dioctahedral 2:1 layer clay minerals
-
Victor A. Drits
,
Arkadiusz Derkowski
Abstract
A multi-cycle heating and cooling thermogravimetric (TG) method was used to study the kinetic behavior of partially dehydroxylated illite, aluminoceladonite, and dioctahedral smectite samples. The method consists of consecutive heating cycles separated by intervals of cooling to room temperature, with the maximum cycle temperatures (MCTs) set incrementally higher in each consecutive cycle.
In the studied samples, dehydroxylation of each portion of the initial OH groups follows the kinetics of a homogeneous zero-order reaction in each heating cycle. The activation energies (Ea) were calculated in terms of this model for separate heating cycles of each sample with regression coefficients R2 ≥ 0.999. A zero-order reaction determined at each heating cycle indicates that at each stage of partial dehydroxylation, there is no formation of an intermediate phase and the reaction is probably the direct transformation of the original layers into completely dehydroxylated layers.
The Wyoming montmorillonite and illite consisting of cis-vacant (cv) layers had the highest Ea values (53-55 kcal/mol). In the samples consisting of trans-vacant (tv) layers and having almost the same octahedral cation composition the maximum Ea values varied from 45 to 30 kcal/mol and the Ea of each sample in this group are similar over a wide range of the DT. For the samples consisting of a mixture of cv and tv illite structures, a bimodal distribution of the Ea values exists with increasing MCT and DT. The maximum Ea values for dehydroxylation of the tv and cv illite structures are different.
The activation energies from the tv aluminoceladonite and Otay tv montmorillonite samples have similar maximum Ea values (39.4 to 41.8 kcal/mol), but the variation in Ea with DT has a skewed bell-like distribution that is probably related to a heterogeneous octahedral cation composition of the 2:1 layers.
The Ea values calculated for the mineral structures in this study are compared with those published and the main factors controlling the Ea variation at different stages of the partial dehydroxylation are discussed.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Dana medal lecture: Tilts and tetrahedra: The origin of the anisotropy of feldspars
- Amorphous Materials: Determination of water content in silicate glasses using Raman spectrometry: Implications for the study of explosive volcanism
- Density functional calculations of the enthalpies of formation of rare-earth orthophosphates
- U-Pb ID-TIMS dating applied to U-rich inclusions in garnet
- Wassonite: A new titanium monosulfide mineral in the Yamato 691 enstatite chondrite
- Determination of Mn valence states in mixed-valent manganates by XANES spectroscopy
- The morphology of the reaction front of the dissolutionprecipitation reaction rutile + wollastonite = titanite in time series experiments at 600 °C/400 MPa
- Precipitation of rutile and ilmenite needles in garnet: Implications for extreme metamorphic conditions in the Acadian Orogen, U.S.A.
- The genesis of mantle-derived sapphirine
- Experimental investigation of smectite interaction with metal iron at 80 °C: Structural characterization of newly formed Fe-rich phyllosilicates
- High-pressure study of a natural cancrinite
- Investigation of cation ordering in triclinic sodium birnessite via 23Na MAS NMR spectroscopy
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- Tsilaisite, NaMn3Al6(Si6O18)(BO3)3(OH)3OH, a new mineral species of the tourmaline supergroup from Grotta d’Oggi, San Pietro in Campo, island of Elba, Italy
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- Letter. High-pressure phase transitions in Ca-Mn carbonates (Ca,Mn)CO3 studied by Raman spectroscopy
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