Showing papers on "Tridymite published in 1979"

Heat capacities and inversions in tridymite, cristobalite, and tridymite-cristobalite mixed phases

Abstract: Samples of synthetic tridymite, cristobalite and tridymite-cristobalite mixed phases, examined by differential scanning calorimetry (DSC) from 360 to 770 or 840K, showed distinct peaks in heat capacity (Cp). For \"pure\" tridymite the lambda transition at 390K and two peaks near 436K and 470K, which may also be lambda transitions, appear to correlate respectively with the structural changes from (MC) monoclinic (Cc) to (OP) orthorhombic P2t2t2t, (oP) to (oS) orthorhombic with a non-integral superstructure, and (oS) to (oc) orthorhombic c222' descibed by Nukui et at. (1978) as occurring at 3g3K, 423K, and 463K respectively. It may also be possible to correlate a weak cp effect near 653K with the (oc) to (HP) hexagonal P6/mmc inversion of Nukui et al. The DSC measurements agree with the heat-content measurements by Mosesman and Pitzer (1941) and the dynamic calorimeter data of Shahid and Glasser (1970) for tridymite, although the feature observed in both these studies at 498K was absent in our tridymite sample. This 498K discontinuity probably reflects inversion in cristobalite portions of the \"tridymite\" samples used in the previous studies, as suggested by our DSC examination of tridymite-cristobalite mixed phases. The present Cp data for tridymite above 500K and for cristobalite above 560K agree reasonably well with thi polynomial flts presented by Robie et at. (1978, p.2l7, Zl8).

Magnesian halotrichite from White Island

Abstract: A magnesian halotrichite [(Fe0.63Mg0.37).Al2(SO4)4.22H2O] from a fumarole deposit on the active andesitic volcano of White Island, New Zealand, occurs as the major component in the mixture halotrichite—H2S04-H20—alunogen, with accessory gypsum, alunite, anhydrite, quartz, cristo-balite, and tridymite. Optical, physical, and chemical data are given for the halotrichite. K :Na ratios in the alunite (85K:15Na) and in the solution (28K:72Na) show equilibrium between the salt and solutions.

Binder for chemically resistant concrete and process for producing this binder

Abstract: A binder for a chemically resistant concrete, comprising from 30 to 80% by weight of a finely divided quartz sand having a specific surface area of from 1000 to 5000 cm 2 /g, and from 20 to 70% by weight of at least one of crystalline modifications of silica. The crystalline modification of silica used in the binder is a tridymite and/or cristobalite containing on the surface of their particles from 0.5 to 6 mol percent one of R 2 O, oxides, wherein R is sodium, potassium. A process to produce a binder for a chemically resistant concrete, which comprises mixing quartz sand with at least one of such compounds as sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, said compounds being taken in an amount from 0.7 to 15% by weight. The resultant mixture is heated to 1000°-1550° C. to produce an oxide R 2 O, wherein R is sodium, potassium, and cause said oxide to get bound with the surface of the quartz sand particles. The mixture is treated at this temperature until formation of at least one of such crystalline modifications of silica as cristobalite, tridymite, and then is cooled, crushed and mixed with quartz a finely divided sand having a specific surface area of 1000-5000 cm 2 /g.

A new method for separation of cristobalite and tridymite particles from rocks containing them.

Abstract: To quantify the free silica in a working environment by phosphoric acid method, a few grams of the standard free silica powder is necessary. It is, however, not easy to prepare the amount of the powder in the laboratory because they are usually found in a small phenocryst in some volcanic rocks. A new method for separation of cristobalite and tridymite particles from mother rocks is developed by using hot phosphoric acid with heavy liquid and very effective. It is known that most part of free silica particles survives in a hot phosphoric acid, while silicate particles are dissolved in the acid1)2)3). It is, therefore, expected that the acid residue is formed of the particles of a few sorts of free silica min-erals, and that some of these particles can be separated from the acid residue with the help of heavy liquid4). Present paper shows a new trial on preparation of the cristobalite or tridymite particles from the mother rocks by combination of pho-sphoric acid method and heavy liquid method.