Modeling the X-ray diffraction pattern of opal-CT

Guthrie, George D.; Bish, David L.; Reynolds, Robert C.

doi:10.2138/am-1995-7-823

Cited by 76 publications

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“…[26][27][28][29] Turbostratic disorder, a disorder in which different layers have different rotations with respect to an axis, is commonly found in naturally occurring samples of montmorillonite. 28,29 To reconcile apparent discrepancies between high resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD), 30,31 Guthrie and…”

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Molecular Dynamics Simulations of Turbostratic Dry and Hydrated Montmorillonite with Intercalated Carbon Dioxide

et al. 2014

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Molecular dynamics simulations using classical force fields were carried out to study energetic and structural properties of rotationally disordered clay mineral-water-CO 2 systems at pressure and temperature relevant to geological carbon storage. The simulations show that turbostratic stacking of hydrated Na-and Ca-montmorillonite and hydrated montmorillonite with intercalated carbon dioxide is an energetically demanding process accompanied by an increase in the interlayer spacing. On the other hand, rotational disordering of dry or nearly dry smectite systems can be energetically favorable. The distributions of interlayer species are calculated as a function of the rotational angle between adjacent clay layers.

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Molecular Dynamics Simulations of Turbostratic Dry and Hydrated Montmorillonite with Intercalated Carbon Dioxide

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“…The crystals appear to be anhydrous. These minerals, arising from a low temperature hydrothermal diagenetic process, are generally known as opal-C and opal-CT and are usually partially amorphous with ordered domains consisting of interstratified layers of cristobalite and tridymite with varying degrees of long range order [34]. Diagenesis results in a gradual conversion of tridymite layers to cristobalite with an increase in long range order such that the high angle shoulder disappears and smaller peaks are resolvable, particularly from 41 to 44° 20 (3,4).…”

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confidence: 99%

“…9) [32][33][34][35][36][37][38]. The opal analog phases, whether silicate or A1P0 4 , show only broad features between 19.5° and 24° 20 as well as a broad line between 35° and 36°.…”

Section: Microstructural Analysismentioning

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“…However, error is introduced because the peak broadening is the result of crystalline disorder as well as crystallite size. For this reason, one author [44] has suggested that the peak at 35° would give more accurate results, but the Cerablak data was too noisy to get reasonable values. An interesting feature of paracrystalline silicate opals is their resistance to crystallization above 1000°C.…”

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Investigation of a New Class of Disordered Inorganic Materials

Sambasivan¹,

Steiner²

2001

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“…Es una fase compleja formada por un interestratificado de tridimita y cristobalita con distintos estados estructurales que han sido en la ultima década motivo de diferentes estudios (5,6,7), determinándose incluso sus propiedades eléctricas (8). Por último el ópalo C es escaso y su interés principal estriba en su valor científico en geología por ser marcador durante la diagé-nesis (9).…”

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Caracterización y respuesta al tratamiento térmico de rocas silíceas opalinas

Bustillo¹,

Garcı́a²,

Pérez³

2000

Bol. Soc. Esp. Ceram. Vidr.

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En las rocas opalinas se encuentran diferentes fases de la sílice que son poco conocidas y que ante los tratamientos térmicos responden de forma diferente. Rocas opalinas de diferentes ámbitos sedimentarios e hidrotermales se estudian mediante difracción de rayos X (DRX) y espectrometría de infrarrojos, analizando la respuesta del polvo natural y después de un tratamiento térmico a 1.050ºC durante 24 horas. El objetivo es la diferenciación de las distintas estructuras de la sílice que pueden aparecer en las rocas opalinas, las variaciones que presentan dichas estructuras, y su cambio ante los tratamientos térmicos. En la mayoría de las muestras, la fase silícea encontrada es la denominada ópalo CT. El ópalo CT es un interestratificado de cristobalita y tridimita de estructura compleja que responde, en los análisis de DRX ,con perfiles distintos, principalmente en el intervalo de 19º a 25º 2θ. Se definen tres tipos básicos en este intervalo que se denominan "perfiles ensanchados (E), de hombro (H) y de dos picos (2P)". Estos tipos tienen relación con la proporción de tridimita en el interestratificado (va aumentando desde los perfiles ensanchados a los de dos picos), el tamaño de cristal del ópalo (los ensanchados y los de hombro tienen menor tamaño), y la reactividad ante los calentamientos a 1.050ºC (va siendo progresivamente menor desde los perfiles ensanchados a los de dos picos). Las muestras menos reactivas resultaron ser las que poseían mayor proporción de tridimita en el interestratificado. En espectrometría de infrarrojos, los ópalos CT no manifiestan diferencias importantes entre sí, pero las muestras con perfiles ensanchados y de hombro presentan organizaciones algo distintas y mayor proporción de agua. No se han encontrado variaciones entre las estructuras de los ópalos formados en ambiente hidrotermal y los formados a temperatura ambiental, aunque en algunas muestras hidrotermales aparece ópalo C o una cristobalita α independiente junto al ópalo CT. Durante los tratamientos térmicos tampoco aparecieron diferencias. Palabras clave: ópalo CT, tratamientos térmicos, DRX, espectrometria infrarrojos Characterization of opaline rocks and their behaviour UNDER HIGH temperaturesSeveral silica phases are found in the opaline rocks and they show different behaviours after thermal treatments. Hydrothermal and sedimentary microcrystalline opal rocks were studied by means of X-ray diffraction and infrared absorption techniques. The measurements were carried out firstly on natural powdered samples and later on annealed samples at 1.050ºC for 24 hours. The purpose of this study is to ascertain which silica phases appear and to evaluate what changes take place as a consequence of thermal treatments. Most of the samples are constituted of opal CT. Opal CT is a crystalline stacked sequence of tridymite and cristobalite which displays different X-ray patterns mainly in the interval from 19º to 25º 2θ. Three basic types are defined according to the shape of the patterns in this interval: enlarged profiles (E), shoulder ...

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Modeling the X-ray diffraction pattern of opal-CT

Cited by 76 publications

References 0 publications

Molecular Dynamics Simulations of Turbostratic Dry and Hydrated Montmorillonite with Intercalated Carbon Dioxide

Molecular Dynamics Simulations of Turbostratic Dry and Hydrated Montmorillonite with Intercalated Carbon Dioxide

Investigation of a New Class of Disordered Inorganic Materials

Caracterización y respuesta al tratamiento térmico de rocas silíceas opalinas

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