Tridymite

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

Particle size effect on the new phase transition in a tridymite compound, CsCoPO4

Abstract: A new phase transition (III–IV) was found at 311 K in CsCoPO4 by DSC measurements. The crystal structure of all the phases, I–IV, in CsCoPO4 was studied by synchrotron-radiation X-ray powder diffraction. The diffractometry revealed that CsCoPO4 had the same crystal structure as that of corresponding phases in CsZnPO4. An extremely large particle size effect was found on III–IV phase transition in CsCoPO4; the phase transition enthalpy decreases with decreasing the particle size around 0.1 mm. Such large particle size effects had been also observed in CsZnPO4. However, no III–IV phase transition was observed in the particle smaller than 0.1 mm of CsZnPO4, while such a critical size was not found in CsCoPO4.

Fibrogenic and Other Biological Effects of Silica

Abstract: Crystalline silica, silicon dioxide (SiO2), has a simple chemical structure but potent biological effects. The structures of different crystalline and amorphous forms of silica and related molecules are reviewed by Heaney and Banfield (1993) and their biological effects are reviewed by Guthrie (1992). The commonest form is quartz, although other tetrahedral crystalline forms of silica (tridymite, crystobalite) have comparable effects. In contrast, stishovite is an octahedral form of crystalline silica, produced under conditions of high temperature and pressure. It is biologically inert, like titanium dioxide (rutile). Silica dust exposure during the mining and smelting of metal ores has long been known to produce pulmonary fibrosis (silicosis or phthisis) and to increase the incidence of tuberculosis (Collis, 1919). In some countries, such as the People’s Republic of China, large numbers of occupationally exposed workers are showing progressive impairment of lung function. It is desirable to clarify the underlying pathogenesis and, if possible, control it.

Dehydration of 2‐methylbutanal to isoprene using aluminium phosphate catalysts

Abstract: The synthesis of isoprene from the dehydration of 2‐methylbutanal is described using aluminium phosphates as catalysts. Two samples of aluminium phosphate are studied prepared from the reaction of phosphoric acid with aluminium chloride or sulphate. The chloride route gives a mixed cristobalite/tridymite AlPO4 and this is shown to be more active than a catalyst containing only the tridymite form of AlPO4 formed from the sulphate route. The AlPO4 catalysts are also shown to be active catalysts for the synthesis of isoprene from 3‐methylbutan‐2‐one, which is the major by‐product formed from the reaction of 2‐methylbutanal. The AlPO4 catalysts are deactivated due to the deposition of coke in addition to loss of phosphorus from the surface. Catalytic activity can be totally restored by a simple calcination procedure at 800°C.