Stacking structures in pyrophyllite revealed by high-resolution transmission electron microscopy (HRTEM)

Kogure, Toshihiro; Jige, Mayumi; Kameda, J.; Yamagishi, Akihiko; Miyawaki, Ritsuro; Kitagawa, Ryuji

doi:10.2138/am.2006.1997

Cited by 40 publications

(28 citation statements)

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“…The second result is similar to that in pyrophyllite (Kogure et al 2006). In pyrophyllite, interlayer displacement in the same direction as the intralayer shift below and/or above the interlayer region is not favorable owing to the surface corrugation of the pyrophyllite layer.…”

Section: Hrtem Examination Of Stacking Sequences In Talcsupporting

confidence: 71%

“…The peak profi le for the calculated pattern is a pseudo-Voight function with a FWHM of 0.30°. (Kogure et al 2006) where intralayer shift was nearly ordered but interlayer displacement is heavily disordered. This difference between pyrophyllite and talc is probably related to the degree of corrugation of the basal oxygen planes on the surface of the 2:1 layer.…”

Section: Resultsmentioning

confidence: 99%

“…Talc is regarded as one of these phyllosilicates (Veblen and Buseck 1980). However, recently we have successfully determined the stacking structures in phyllosilicates for which it was thought diffi cult to record HRTEM images Inoue 2005a, 2005b;Kogure et al 2006). Because disordered talc possibly has two origins (different intralayer shift and interlayer displacement) for its stacking disorder, HRTEM analysis is critical to distinguish them.…”

Section: Introductionmentioning

confidence: 99%

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Stacking structure in disordered talc: Interpretation of its X-ray diffraction pattern by using pattern simulation and high-resolution transmission electron microscopy

Kogure

2006

American Mineralogist

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Stacking structure in disordered talc, Mg 3 Si 4 O 10 (OH) 2 , has been investigated by using highresolution transmission electron microscopy (HRTEM) and by comparison between experimental and simulated powder X-ray diffraction (XRD) patterns. The talc specimen investigated was massive aggregates of fi ne platy crystals from the Shirakashi mine, Nagasaki-Prefecture, Japan, formed from regional metamorphism. HRTEM observations revealed that the orientation of the 2:1 layer, which is described by the direction of the lateral shift of a/3 from the lower tetrahedral sheet to the upper tetrahedral sheet within the 2:1 layer (intralayer shift), is almost completely disordered. In contrast, lateral displacement between the adjacent tetrahedral sheets across the interlayer region (interlayer displacement) is relatively ordered. The interlayer displacement parallel to the intralayer shift in lower or upper 2:1 layers tends to be avoided.A Gandolfi camera was used to record XRD patterns from a small fragment of the aggregates, to avoid preferred orientation and artifacts in stacking sequence by grinding. XRD patterns were simulated using the DIFFaX program and compared with experimental patterns. The experimental pattern from hk = 02, 11, and 1 -1 reciprocal lattice rows is explained by a mixture of the stacking sequence with almost random directions of intralayer shift and a small amount of 1A dominant stacking sequence. The peak profi les for the refl ections indexed with 20l, 13l, or 1 -3l are reproduced by considering their variance, and a slightly different interlayer displacement from that reported in talc-1A.

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Section: Hrtem Examination Of Stacking Sequences In Talcsupporting

confidence: 71%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Stacking structure in disordered talc: Interpretation of its X-ray diffraction pattern by using pattern simulation and high-resolution transmission electron microscopy

Kogure

2006

American Mineralogist

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“…Their stacking sequences can be more complicated than for normal micas, because the two tetrahedral sheets belonging to different layers across the interlayer can be laterally displaced (in case of normal micas, the displacement cannot occur owing to the potassium ions at the interlayer). The origin of this displacement (termed "interlayer displacement", Kogure et al, 2006a) is the minimization of repulsive forces between the two tetrahedral sheets across the interlayer. Zvyagin et al (1969) suggested using electron-diffraction analyses that this interlayer displacement in pyrophyllite and talc can be almost AEa i /3 (i ¼ 1, 2 or 3) where a i are three vectors connecting the centers of neighboring six-member rings in a tetrahedral sheet, rotated by 120 from each other, similar to the hexagonal crystallographic axes.…”

Section: Resultsmentioning

confidence: 99%

High-resolution TEM and XRD simulation of stacking disorder in 2:1 phyllosilicates

Kogure¹,

Kameda²

2008

Zeitschrift Für Kristallographie - Crystalline Materials

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Stacking disorder is a common phenomenon in phyllosilicates but its nature is difficult to be deduced using conventional diffraction techniques. In contrast, recent investigations using high-resolution transmission electron microscopy (HRTEM) have elucidated the structure of stacking disorder in various phyllosilicates, by directly observing individual layers and stacking sequences. Furthermore, simulations of X-ray or electron diffraction patterns using the information from the HRTEM results can complement the limited analysis area in TEM and quantify the density of the stacking disorder. Although the bonding between adjacent layers is similar, there is a significant difference in the stacking disorder between two counterparts of dioctahedral and trioctahedral 2 : 1 phyllosilicates: pyrophyllite vs. talc and sudoite vs. trioctahedral chlorite. In pyrophyllite and sudoite, stacking disorder is caused mainly by two alternatives of the lateral displacement directions between the two tetrahedral sheets across the interlayer region. On the other hand, rotation of 2 : 1 layer is also an origin of the stacking disorder in talc and trioctahedral chlorite. This difference is explained by the corrugation of basal oxygen planes on the dioctahedral 2 : 1 layer formed by the tetrahedral tilting to enlarge trans-vacant octahedral sites.

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“…Recently Kogure et al (2006) showed that pyrophyllite, previously described as a two-layer monoclinic polytype, in fact has a disordered structure in which two alternative interlayer translations are interstratified between uniformly oriented layers. Each of these translations forms a periodic 1A pyrophyllite structure, but the coexistence of both translations in a single crystal disturbs its structural order.…”

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confidence: 99%

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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Stacking structures in pyrophyllite revealed by high-resolution transmission electron microscopy (HRTEM)

Cited by 40 publications

References 14 publications

Stacking structure in disordered talc: Interpretation of its X-ray diffraction pattern by using pattern simulation and high-resolution transmission electron microscopy

Stacking structure in disordered talc: Interpretation of its X-ray diffraction pattern by using pattern simulation and high-resolution transmission electron microscopy

High-resolution TEM and XRD simulation of stacking disorder in 2:1 phyllosilicates

Kinetics of thermal transformation of partially dehydroxylated pyrophyllite

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