Tridymite

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

Alkali-silica reaction—Canadian experience

Abstract: The first case of alkali-silica reaction (ASR) in Canada was discovered in the mid 1950s, by which time most of the investigative techniques currently used had already been developed. Three types of reactive aggregates are recognised in the current Canadian Standards:(1) Alkali-silica reaction, occurring with opal, chert, chalcedony, volcanic glass, cristobalite and tridymite.

Dta and x-ray analysis study of nucleation and crystallization of mgo-al2o3-sio2 glasses containing zro2, tio2, and ceo2

Abstract: Crystallization sequences of glasses with compositions in the tridymite primary phase field of the MgO-Al2O3-SiO2 system were studied by DTA, X-ray diffraction, and other techniques. Crystallization was catalyzed by the addition of 7 wt% of either ZrO2 or TiO2. Up to 10 wt% CeO2 was also added to some glasses. Metastable solid solutions with the high-quartz structure exhibiting varying lattice parameters commonly occurred at low temperatures, transforming into a high cordierite at higher temperatures. Depending on the composition and heat treatment, other phases also appeared, e.g. Ce2Ti2O4 (Si2O7). The rate of crystallization was markedly dependent on the catalyst. Colloidal precipitation of the catalyst accompanied by bulk crystallization of the glass was observed with ZrO2, but no crystalline TiO2 was detected. In the presence of CeO2, TiO2 was a more effective catalyst than ZrO2. Although CeO2 lowered the melting temperatures of the glass-ceramics, it increased the stability of the glasses and inhibited volume nucleation, causing coarse structures to form on crystallization.

Incorporation of impurities in tridymites from a used silica brick

Abstract: The incorporation of impurities in tridymites taken from a used silica brick have been studied by means of a high-resolution microprobe, X-ray fluorescence, X-ray diffractometry, and optical microscopy. The bulk impurity content of the brick changes strongly from the hot zone (4.7 wt%) to the colder part of the brick (7.6 wt%), indicating material transport along the temperature gradient. The transport medium for migration processes is probably a melt occurring in narrow veins between large tridymite crystals at high temperatures. The average impurity contents of homogeneous tridymite single crystals are 0.49 wt% in the hot zone of the brick and 0.81 wt% in the cold zone. Al2O3, TiO2, and Na2O are main impurity constituents; the tridymites do not contain significant amounts of Fe2O3 or CaO. The a parameters of tridymites decrease by about 0.26% from 4.9837 A to 4.9709 A from the hot zone to the cold zone of the brick and the c dimension shows a smaller decrease (0.11 %) from 8.2023 A to 8.1933 A.

Structure and Adsorption Properties of Nenjiang Opal Shale

Abstract: The opal shale is heated up to 600℃ to 1200℃ by heat treatment.The original and heated samples have been characterized by SEM and XRD,and the specific surface area is measured by the BET method.The adsorption capacity of the opal shale is tested by the rhodamine-B solution.The results show that the opal shale is made of microcrystalline tridymite and α-quartz.The specific surface area of the opal shale is up to 82.856 m2/g,increases with the rising temperature and reaches its maximum at 900 ℃.After 900 ℃,the specific surface area of the opal shale declines with the fatherly rising in temperature of heat treatment.The adsorption rate is fast,and the de-colorization rate could exceed 96%.With high adsorption capability,high adsorption rate and high thermal stability,the opal shale has wide application prospects.

AlPO4−ZrO2 catalysts, II. Synthesis, textural properties and crystal structure of systems obtained in ethylene oxide

Abstract: The effects of surface dehydration on textural properties, crystallinity and the structure of AlPO4−ZrO2 (weight ratio AlPO4/ZrO2=3) systems precipitated with ethylene oxide have been studied by N2 adsorption and XRD measurements. The increase in calcination temperature in the range 773–1273 K decreases the textural parameters as a consequence of AlPO4 crystallization to the tridymite form.