The crystal structure of Li2Al2Si3O10 (high-quartz solid solution)

Li, Chi-Tang

doi:10.1524/zkri.1970.132.16.118

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“…A la vista de los resultados obtenidos y teniendo en cuenta los datos cristalográficos para esta fase en el ICSD (Inorganic Crystal Structure Database) esta relación no es tan directa. La Tabla 3 muestra estos datos para 12 fichas, donde vemos que los parámetros de la celda unidad establecidos para la eucriptita incluso con la misma composición son confusos (11)(12)(13)(14)(15)(16). Este hecho muestra que, aunque los datos obtenidos en alta resolución son buenos, es imposible establecer la estructura en sistemas tan complejos, para el refinamiento de las posiciones de los átomos en la estructura mediante los datos de difracción de Rayos X.…”

Section: Resultados Y Discusiónunclassified

Comportamiento de la eucriptita a alta temperatura mediante estudio in situ por difracción de Rayos X

Moreno¹,

Khainakov²,

Torrecillas³

2012

Bol. Soc. Esp. Ceram. Vidr.

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La eucriptita es un aluminosilicato de litio con peculiares propiedades de expansión térmica: posee expansión negativa, es decir, se contrae con el aumento de la temperatura en una de sus orientaciones cristalográficas. Debido a esta singularidad la eucriptita se utiliza en la fabricación de materiales con coeficiente de expansión térmica (CTE) próximo a cero. Para este trabajo, se han sintetizado dos composiciones de eucriptita solución sólida con contenidos en Li 2 O:Al 2 O 3 :SiO 2 iguales a 1:1:3 y 1:1:2. La síntesis se ha realizado a partir de caolín, carbonato de litio y TEOS o γ-alúmina respectivamente. Los polvos de las dos composiciones de eucriptita se han caracterizado mediante difracción de Rayos X de alta resolución a alta temperatura entre 25 y 1200 ºC. Se ha estudiado el efecto de la temperatura en la estructura y la composición mediante la determinación de los parámetros de red y la estructura cristalina. Los cambios observados se han relacionado con las variaciones del CTE con la temperatura de sinterización de materiales basados en estas composiciones. Palabras clave: eucriptita, cristalinidad, DRX, coeficiente de expansión térmica High temperature behavior of eucryptite by means of in situ X ray diffraction studiesEucryptite is a lithium aluminosilicate with striking thermal expansion properties: it has negative expansion, i. e. it contracts upon heating in one of its crystallographic dimensions. Due to this characteristic, eucryptite is used in the fabrication of very low coefficient of thermal expansion materials. Two different eucryptite solid solution compositions were synthesized in this study with Li 2 O:Al 2 O 3 :SiO 2 contents of 1:1:3 and 1:1:2. The synthesis was prepared using kaolinite, lithium carbonate and TEOS and γ-Al 2 O 3 , respectively. High resolution X Ray diffraction characterization was performed at high temperature for both compositions between 25 and 1200 ºC. The temperature effect on structure and composition was studied by determining cell parameters and crystal structures. The relation between the observed changes and the CTE variations with the sintering temperature of materials based in these compositions was finally determined.Keywords: eucryptite, crystallinity, XRD, coefficient of thermal expansion. Vol 51, 3, 145-150, Mayo-Junio 2012 iSSn 0366-3175. eiSSn 2173-0431. doi: 10.3989/cyv.212012 Boletín de la Sociedad española de Cerámica y Vidrio IntroduccIónEl interés de los aluminosilicatos de litio (LAS) para su uso como material cerámico alcanzó gran importancia a partir de los años cincuenta con los estudios de Roy et al. (1), en los que se establecieron las relaciones de fases y los diagramas de equilibrio para este sistema. Estos diagramas son aún referencia imprescindible en cualquier estudio del sistema LAS. El peculiar comportamiento en la dilatación térmica de los aluminosilicatos de litio es la característica más interesante de este sistema. También a mediados del siglo pasado, ya se estudiaron estas propiedades con detalle(2), acotando zonas en el diagr...

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Section: Resultados Y Discusiónunclassified

Comportamiento de la eucriptita a alta temperatura mediante estudio in situ por difracción de Rayos X

Moreno¹,

Khainakov²,

Torrecillas³

2012

Bol. Soc. Esp. Ceram. Vidr.

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“…Intense Pulsed Neutron Source (IPNS-I) of Argonne National Laboratory.32 The data were accumulated over a total of 41 h, by the detector banks centered at Bragg angles of 150°, 90°, 60°, 30°, 22°, and 14.5°. The sample can was mounted in a Displex refrigerator (Air Products) and during the data acquisition the temperature varied between extremes of 17.0 and 24.5 K, being generally close to 19 K. The data were collected in three separate sections of 4, 21, and 16 h. respectively, but, as there were no significant differences between the separate data sets, they were combined by simple addition for the final stages of structure refinement. The data from the 90°detector banks were used.…”

Section: Newsammentioning

confidence: 99%

“…In Novel Materials and Techniques in Condensed Matter, Crabtree, G., Vashishta, P., Eds. ; Elsevier-North-Holland: New York, 1982; p 311. gallosilicate ABW zeolite at 19 K. (The background of typically 104 counts has been subtracted.) The positions of the contributing reflections are marked by vertical bars.…”

Section: Newsammentioning

confidence: 99%

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Synthesis and structural characterization of a lithium gallosilicate with the zeolite ABW-framework

Newsam¹

1988

J. Phys. Chem.

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445seems that an oblate shape must be ruled out. Table I11 gives the values of the parameters giving the best fits. The electron densities given in the table are obtained from fits. The obtained values must be close to the theoretical ones calculated by using the partial volumes of the codstituents of the core or the polar region of the micelle. It can be observed, on the experimental data, that the maximum located at s i= 0.02 A-' has disappeared. This is due to the decrease of the electron density of the polar region (and thus of the contrast between this region and the water), owing to the location of the alcohol in this region. The axial ratio of the whole particle, for instance, for the most concentrated binary solution, is found to be 4.2 if 2 wt% alcohol is added. This seems to agree with the viscosity measurements: addition of a little amount of alcohol to binary solutions induces a break in the variation of 9. It is reasonable to think that oblate aggregates with small ellipticity must not give such a behavior.For the most concentrated solutions, for which the aggregation number seems to reach a limit, the experimental data can be fitted by using the measured aggregation numbers. Moreover, if one considers that the aggregation number is underestimated, it seems that oblate objects are still incompatible. Indeed, if one overestimates the N value of, for instance, 25%, prolate ellipsoids also give satisfying results.In the studied range of concentration, the axial ratio of the aggregate reaches a value of about 7, which gives a total length of 350 A if the smallest dimension is equal to 50 A. (The volume fraction of micelles here is of the order of 15%.) ConclusionCombination of several experimental techniques, and especially small-angle X-ray scattering and fluorescence probe study, allows us to obtain the size and the shape of the micelles in ternary systems involving alcohol. Although in the binary solutions one cannot affirm whether or not the aggregates are deformed, in ternary systems the oblate shape seems to be ruled out, while prolate ellipsoids lead to self-consistent results. It must be emphasized that it is the knowledge of the aggregation number and the fact that our experiments are mean-resolution experiments (and not low-resolution ones) which allow US to be almost sure that the aggregates are elongated, even in binary systems. The phase diagram of the n-dodecylbetaine is very similar to those obtained with ionic surfactants, alcohol and brine. The trend in the micellar sizes and shapes with the change in alcohol concentration can thus be useful in the study of the structure and the stability of the isotropic and ordered phases found in all these systems.Acknowledgment. This research has received partial financial support from PIRSEM (CNRS) under AIP 2004.The syntheses and characterization of gallo-and aluminogallosilicates with the zeolite ABW framework, LiGaXA1,,SiO4.H20 with x = 0,0.5, and 1.0, are described. The structure of the hydrated gallosilicate, x = 1 .O, has been determined at 19...

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On the assignment of quartz-like LiAlSi2O6 - SiO2 solid solutions in dental lithium silicate glass-ceramics: Virgilite, high quartz, low quartz or stuffed quartz derivatives?

et al. 2022

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The crystal structure of Li₂Al₂Si₃O₁₀ (high-quartz solid solution)

Cited by 4 publications

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Comportamiento de la eucriptita a alta temperatura mediante estudio <i>in situ</i> por difracción de Rayos X

Comportamiento de la eucriptita a alta temperatura mediante estudio <i>in situ</i> por difracción de Rayos X

Synthesis and structural characterization of a lithium gallosilicate with the zeolite ABW-framework

On the assignment of quartz-like LiAlSi2O6 - SiO2 solid solutions in dental lithium silicate glass-ceramics: Virgilite, high quartz, low quartz or stuffed quartz derivatives?

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