Tridymite

About: Tridymite is a research topic. Over the lifetime, 840 publications have been published within this topic receiving 14831 citations.

Characterization of synthetic tridymites by transmission electron microscopy

Abstract: Eight tridymites, synthesized in a variety of ways, have been examined by transmission electron microscopy (TEM). Each sample appeared to be heterogeneous, containing a mixture of low temperature structural forms. Two mqin structure types were identified: one with a pseudohexagonal superlattice, having o: J3ar, 9:2cw and the second with a pseudoorthorhombic C-face centered cell, having a:2J3at, b :2an and wi^th either a multiple c repeat or (001) stacking disorder (where a, and cs are respectively -5A, -8.2A and refer to the high temperature hexagonal sublattice). The former structure seemed to predominate in grains with few (001) stacking faults. In addition, some samples contained regions of considerable (001) disorder intergrown with more highly ordered material on a scale of a few hundred tngstrtims. Diffraction patterns from these grains could not be indexed easily on a known tridymite or cristobalite superlattice and have been tentatively ascribed to mixed (tridymite/ cristobalite) layering. Highlow transformations were inducod by beam heating. The ZJ3asx 2a^x nc' type superstructures could be transformed reversibly to the hex4onal higlt temperature sublattice until radiation damage started to occur. In contrast, the ./3ag x 2c" superlattice gave way to the high temperature hexagonal sublattice on heating but invariably reverted to a 213a, x 2a^ x ncH structure on subsequent cooling. The diversity of superstructures observed in each sample helps to a@ount for differences between the transformation behavior of many synthetic tridymite powders and larger natural or synthetic single crystals. In this context, TEM provides a useful adjunct to X-ray powder diffraction for the characterization of tridymites prepared for other types of experiments.

Flexible Crystal Frameworks.

Abstract: Building upon and complementing recent results on the rigidity theory of periodic bar-and-joint frameworks, this paper studies tetrahedral structures modeled on specific crystalline materials: quartz, cristobalite and tridymite. The general theory predicts at least three infinitesimal degrees-of-freedom. Here, we investigate the actual deformations of these structures. We show that quartz and cristobalite have smooth three-dimensional configuration spaces, but ideal high tridymite is a singular configuration with a six-dimensional tangent space. The topology around this singularity is explicitly described.

Postmortem analyses of salvaged conventional silica bricks from glass production furnaces

Abstract: The microstructure, phase content, and thermal conductivity of salvaged conventional silica bricks from float glass and TV-panel glass production furnaces were examined as a function of position through the brick, and compared with the original, unaltered brick materials. The silica brick from the float glass furnace was in service for approximately 10 years while that for the TV-panel glass furnace was for approximately 6.5 years. The microstructure and phase content in both salvaged bricks showed gradients, from tridymite at the bricks' cold-face ends, to cristobalite at their hot-face end even though both bricks were an initial mixture of tridymite and cristobalite to begin with. The thermal conductivity of both bricks had increased as a consequence of these phase and microstructural changes. A thermal analysis model predicted that such changes would result in an increase in the bricks' cold-face temperature and heat content during service. The initially-produced temperature gradients and environment caused microstructural changes in the silica brick; however, the cause-and-effect relationship between temperature/environment and microstructural changes in the brick likely became mutually reversible once the microstructural changes initiated and the thermal conductivity of the brick started to change as a consequence.