scispace - formally typeset
Search or ask a question

Showing papers on "Tridymite published in 1972"


Journal ArticleDOI
TL;DR: In this article, it was suggested that an explanation of the observed metastable formation of cristobalite and tridymite in the stability field of quartz lies in the topology of these silica polymorphs and the resulting energies at the time of formation.
Abstract: It is suggested that an explanation of the observed metastable formation of cristobalite and tridymite in the stability field of quartz lies in the topology of these silica polymorphs and the resulting energies at the time of formation.

67 citations


Book
01 Jan 1972
TL;DR: In this paper, several pieces of fossil wood have been analyzed with X-ray diffraction and were grouped on the basis of mineralogical composition, showing a structure preservation that points to replacement of cell walls by silica.
Abstract: Several pieces of fossil wood have been analyzed with X-ray diffraction and were grouped on the basis of mineralogical composition. Various mineralizations were studied in thin sections and by means of the scanning electron microscope. Wood-opals appear to show a structure preservation that points to replacement of cell walls by silica. The wood-opals are mineralogically characterized as 'disordered tridymite'. Other mineralizations, such as chalcedony, quartz, carbonates, phosphates and iron-oxydes and -hydroxydes show characteristics of filling-in. Various mineralization processes are discussed.

57 citations


Journal ArticleDOI
10 Apr 1972-Nature
TL;DR: In this paper, the nature of the atomic arrangements in glassy solids has been described in several ways, such as: 1) a portion of the material is composed of small regions of crystalline-like order bonded together in essentially random orientations; 2) a few of the shortest interatomic distances correspond throughout the sample to those present in a crystalline phase.
Abstract: THE nature of the atomic arrangements in glassy solids has been described in several ways. In one model1, a portion of the material is pictured as being composed of small regions of crystalline-like order bonded together in essentially random orientations. In another model2, the material is depicted as a random network in which only a few of the shortest interatomic distances correspond throughout the sample to those present in a crystalline phase. Both models picture the glass as a continuous network and differ only in the degree of local atomic ordering.

35 citations


Journal ArticleDOI
TL;DR: In this article, tridymites containing at most 0.016% Na (0.004% Na) were prepared at 1400° C from Na2WO4 fluxes using high purity amorphous silica as starting material.
Abstract: Well ordered tridymites containing atmost 0.016% Na (0.004% Na) were prepared at 1400° C from Na2WO4-(K2WO4-) fluxes using high purity amorphous silica as starting material. No further reduction of these Na-contents was attainable by soxhlet extraction. These tridymites were treated hydrothermally at temperatures between 815 and 950° C and 200 bars H2O. The products obtained were investigated optically as well as by powder X-ray methods and were analyzed for Na-contents: the hydrothermal treatment resulted either in recrystallization of tridymite or transformation into quartz mostly depending on Na-contents. Na-contents below about 0.015% tend to favour recrystallization of tridymite within the quartz field ( 870° C). This may be due to influences of Na-traces either on the kinetics or on the equilibrium temperature of tridymite-quartz transformation.

16 citations


Journal Article

16 citations


01 Jun 1972
TL;DR: In this article, thermogravimetric measurements were made for the oxidation of hot pressed silicon carbide at an oxygen pressure of 150 torr and at temperatures from 1300C to 1600C.
Abstract: : Thermogravimetric measurements were made for the oxidation of hot pressed silicon carbide at an oxygen pressure of 150 torr and at temperatures from 1300C to 1600C. Oxidized samples were then analyzed using X-ray, metallograph, and electron probe techniques. The oxidation rate was found to increase with temperature. The products of oxidation were a carbon oxide and a protective layer of silica. The silica was primarily amorphous with some tridymite or alpha-cristobalite.

13 citations


Journal ArticleDOI
TL;DR: The mobility of silicogenic dust samples was studied by microelectrophoresis, which showed that they differed in surface potential, and a relationship was found between surface potential and severity of tissue damage.
Abstract: Summary The mobility of silicogenic dust samples (cristobalite, erosil, tridymite, silicon dioxide and vitrinite) was studied by microelectrophoresis, which showed that they differed in surface potential. A relationship was found between surface potential and severity of tissue damage.

6 citations


Journal ArticleDOI
TL;DR: In this paper, the electrophoretic mobilities of various types of silica powders were studied in the presence of various metal ions and the metal ion concentration required for charge reversal was measured.

5 citations


Journal ArticleDOI
TL;DR: In this paper, single crystals of phenacite, bromellite, and tridymite were grown from an Li2MoO4-MoO3 flux.
Abstract: Single crystals of phenacite (Be2SiO4), bromellite (BeO), and tridymite (SiO2) were grown from an Li2MoO4-MoO3 flux. Phenacite, with rhombohedral symmetry, grew in three distinct shapes with aspect ratios (length/width) as follows: needles (>3), rods (>1.1 to 1.5), and rhombohedral-faced crystals (=1). The latter grew as single crystals; the others were twinned on the . For most experiments the temperature was held constant at 1165°C and the Li2MoO4/MoO3 ratio at 1/16. The growth mechanism for crystallization was the evaporation of MoO3. The system produced one to three phases, depending on the BeO/SiO2 ratio. Bromellite grew until a BeO/SiO2 ratio of 0.8 was attained. It grew as a hemipyramidal crystal having a short prism with a curved top or as a hexagonal plate. The pyramid- and prism-shaped crystals were twinned, although a few hexagonal plates were single. Tridymite grew in small hexagonal plates when the BeO/SiO2 ratio was less than 1.5. The effect of temperature, nucleation, and flux composition on crystal shape, twinning, and occurrence is discussed.

4 citations


Journal ArticleDOI
TL;DR: In this paper, phase relations in the ternary system ZnONb2O5SiO2 have been determined at liquidus and sub-solidus temperatures.
Abstract: Phase relations in the ternary system ZnONb2O5SiO2 have been determined at liquidus and sub-solidus temperatures. The following compounds have been encountered as primary phases: ZnO, 3ZnO·Nb2O5, α-ZnO·Nb2O5, β-ZnO·Nb2O5, 2ZnO·17Nb2O5, HNb2O5, silica (either as tridymite or as cristobalite) and α-2ZnO·SiO2. No ternary phase has been encountered in this system. Five ternary invariant points have been located, four of which are eutectics, the remaining one being a peritectic. Sub-solidus compatibility relationships have also been determined. This ternary system was studied using hot-stage microscopy, quenching, and X-ray diffraction techniques.

1 citations