Phase Transformation Of Quartz Research Articles

Highly efficient and green separation of iron from complex low-grade polymetallic ore via hydrogen-based mineral phase transformation

The Bayan Obo low - grade polymetallic ore (BOLPO) is a complex polymetallic resource that has accumulated over decades. Conventional mineral processing struggles to meet specifications. In this study, a hydrogen - based mineral phase transformation (HMPT) technique was introduced. Using HMPT at 425 °C for 30 min, CO and H2 in a ratio of 1:3, 20% concentration, and a product grind size below 38 μm with 95% content, an iron concentrate achieved 65.56% grade and 93.68% recovery. x - ray diffraction, x - ray photoelectron spectroscopy and scanning electron microscopy with energy dispersive x - ray spectroscopy analyses showed selective phase transformation of iron to magnetite in BOLPO during HMPT, avoiding excessive wüstite formation, and no phase transformation of quartz, rare earths or fluorite was observed in the products. Vibrating sample magnetometer analysis showed improved magnetic properties, with saturation magnetization increasing from 7.25 A·m2·kg−1 to 47.28 A·m2·kg−1. HMPT selectively separates high - grade iron from low - grade polymetallic ores without compromising the subsequent recovery of rare earths and fluorite in non - magnetic components.

Effects of Elevated Temperatures on the Microstructural, Physico-Mechanical and Elastic Properties of Barakar Sandstone: A Study from One of the World’s Largest Underground Coalmine Fire Region, Jharia, India

Experimental investigations of the effects of elevated temperature on microstructural, mineralogical, physico-mechanical and elastic properties of rocks were carried out to understand the effect of underground coal fire along with thermal damage and failure initiation in Barakar sandstone from the Jharia coalfield, India. Discolouration analysis, petrographic studies, scanning electron microscopy, thermogravimetry, differential thermal analysis and electron probe micro analysis were carried out to understand the microstructural and mineralogical changes in thermally treated samples. The experimental results suggest that the changes in investigated properties follow three characteristic thermal zones: zone I (25–300 °C), zone II (300–500 °C) and zone III (500–800 °C). Among all, zone II is a prominent transition region where a rapid increase in crack density, porosity and thermal damage is observed along with a sharp reduction in seismic wave velocities, uniaxial compressive strength, tensile strength and elastic parameters. Development of thermal stress-induced intergranular and intragranular micro-cracks, evaporation of organic matters, and dehydration and thermal decomposition of minerals are the most conspicuous reasons for the observed changes in this zone. Zone III is characterized by phase transformation of quartz, recrystallization and partial melting of cement and phyllosilicates that filled some of the existing micro-cracks, resulting in a local change of porosity, strength and elastic properties. Developments of different failure modes are observed in different temperature ranges such as simple shear along a single plane in zone I, progressive growth of Y-shaped (double plane) shearing in the zones II and III (400–700 °C) and axial splitting at 800 °C. The results from this study provide comprehensive elaboration of thermal effects on sandstones at a particular temperature range.

Phase Transformations in Quartz used in Silicon and Ferrosilicon Production

Different quartz types are used as raw material for silicon and ferrosilicon production. Upon heating, the quartz will experience phase transformations to other silica polymorphs. In this study the phase transformation from quartz to cristobalite, via an amorphous intermediate state, have been investigated in four different quartz types. Samples of approximately 10g and 100g were heated to 1600 °C and 1700 °C. After cooling, the amount of quartz, cristobalite and amorphous phase were measured using X-ray diffraction. Type F showed the strongest ability to transform from quartz to cristobalite, while type A had the slowest transformation. A model of the transformations was made. The rate constant, k1, for the transformation from quartz to amorphous phase varied between 0.002h-1 and 0.184h-1 at 1600 °C. The activation energy for the transformations were different for the various quartz types. Type A had an activation energy of 600kJ/mol, type F had 500kJ/mol and type D and G had around and below 200kJ/mol. The reasons for the different abilities to transform are discussed, and it is suspected that properties decreasing the crystallinity will increase the ability to transform.

The variation and visualisation of elastic anisotropy in rock-forming minerals

Abstract. All minerals behave elastically; elasticity is a rheological property that controls their ability to support stress, strain, and pressure; controls the nature of acoustic wave propagation; and influences subsequent plastic (i.e. permanent non-reversible) deformation. All minerals are intrinsically anisotropic in their elastic properties – that is, they have directional variations that are related to the configuration of the crystal lattice. This means that the commonly used mechanical elastic properties that relate elastic stress to elastic strain, including Young's modulus (E), Poisson's ratio (ν), shear modulus (G) and linear compressibility (β), are dependent on crystallographic direction. In this paper, we explore the ranges of anisotropy of E, ν, G and β in 86 rock-forming minerals, using previously published data, and show that the range is much wider than commonly assumed. We also explore how these variations (the directionality and the magnitude) are important for fundamental processes in the solid earth, including deformation (mechanical) twinning, coherent phase transformations and brittle failure. We present a new open-source software package (AnisoVis, written in MATLAB), which we use to calculate and visualise directional variations in elastic properties of rock-forming minerals. Following previous work in the fields of chemistry and materials science, we demonstrate that by visualising the variations in elasticity, we discover previously unreported properties of rock-forming minerals. For example, we show previously unreported directions of negative Poisson's ratio and negative linear compressibility, and we show that the existence of these features is more widespread (i.e. present in many more minerals) than previously thought. We illustrate the consequences of intrinsic elastic anisotropy for the elastic normal and shear strains within α-quartz single crystal under different applied stress fields; the role of elastic anisotropy on Dauphiné twinning and the α–β phase transformations in quartz; and stress distributions around voids of different shapes in talc, lizardite, albite, and sanidine. In addition to our specific examples, elastic anisotropy in rock-forming minerals, to the degree that we describe, has significant consequences for seismic (acoustic) anisotropy, for the focal mechanisms of earthquakes in anisotropic source regions (e.g. subducting slabs), for a range of brittle and ductile deformation mechanisms in minerals, and for geobarometry using mineral inclusions.

Changes in the Structure and Properties of Quartz Successively Implanted by Zn and F Ions during Thermal Annealing

The temperature dependences of structural and phase transformations in quartz successively implanted by zinc and fluorine during annealing in nitrogen have been studied. Plates were doped with 64Zn+ ions to a dose of 5 × 1016 cm–2 with an energy of 50 keV and then with 19F+ ions to the same dose but with an energy of 17 keV. After the implantation, individual Zn-containing particles about 100 nm in size were found on the sample surface. These particles decrease in size during annealing (by an order of magnitude after annealing at 800°C). The implantation leads to the formation of radiation-induced point defects and their clusters in the quartz bulk. Radiation-induced defects are gradually annealed during the heat treatment, and the phase of metallic zinc is transformed first to its zinc oxide (ZnO) at 600°C and then to willemite (Zn2SiO4) at 800°C.

Dauphiné twinning and texture memory in polycrystalline quartz. Part 3: texture memory during phase transformation

Samples of quartz-bearing rocks were heated above the a (trigonal)-b (hexagonal) phase transformation of quartz (625-950� C) to explore changes in preferred orientation patterns. Textures were measured both in situ and ex situ with neutron, synchrotron X-ray and electron backscatter diffraction. The trigonal-hexagonal phase transformation does not change the orientation of c- and a-axes, but positive and negative rhombs become equal in the hexagonal b-phase. In naturally deformed quartzites measured by neutron diffraction a perfect texture memory was observed, i.e. crystals returned to the same trigonal orientation they started from, with no evidence of twin boundaries. Samples measured by electron back-scattered diffraction on surfaces show considerable twinning and memory loss after the phase transformation. In experi- mentally deformed quartz rocks, where twinning was induced mechanically before heating, the orientation memory is lost. A mechanical model can explain the memory loss but so far it does not account for the persis- tence of the memory in quartzites. Stresses imposed by neighboring grains remain a likely cause of texture mem- ory in this mineral with a very high elastic anisotropy. If stresses are imposed experimentally the internal stresses are released during the phase transformation and the material returns to its original state prior to deformation. Similarly, on surfaces there are no tractions and thus tex- ture memory is partially lost.

Stable Modulated and Homogeneous Structures of Quartz (SiO 2 ): Analysis of Eigen-Modes Near Phase Transition Points

We obtain a variety of modulated and homogeneous phases of quartz, stable at zero-temperature, by means of relaxational and lattice dynamics calculation. The interatomic interaction is given by the Tsuneyuki pairwise potential. The order of appearance of the phases resembles the experimentally observed order. The essential role of the potential profile is obviated. The kinetics of phase transformations in quartz is illustrated by the analysis of dispersion curves and eigenvectors, which show some peculiarities near transition points.

Shock metamorphism of quartz in nature and experiment: II. Significance in geoscience*

Abstract— The occurrence of shock metamorphosed quartz is the most common petrographic criterion for the identification of terrestrial impact structures and lithologies. Its utility is due to its almost ubiquitous occurrence in terrestrial rocks, its overall stability and the fact that a variety of shock metamorphic effects, occurring over a range of shock pressures, have been well documented. These shock effects have been generally duplicated in shock recovery experiments and, thus, serve as shock pressure barometers. After reviewing the general character of shock effects in quartz, the differences between experimental and natural shock events and their potential effects on the shock metamorphism of quartz are explored. The short pulse lengths in experiments may account for the difficulty in synthesizing the high‐pressure polymorphs, coesite and stishovite, compared to natural occurrences. In addition, post‐shock thermal effects are possible in natural events, which can affect shock altered physical properties, such as refractive index, and cause annealing of shock damage and recrystallization. The orientations of planar microstructures, however, are unaffected by post‐impact thermal events, except if quartz is recrystallized, and provide the best natural shock barometer in terms of utility and occurrence. The nature of planar microstructures, particularly planar deformation features (PDFs), is discussed in some detail and a scheme of variations in orientations with shock pressure is provided. The effect of post‐impact events on PDFs is generally limited to annealing of the original glass lamellae to produce decorated PDFs, resulting from the exsolution of dissolved water during recrystallization. Basal (0001) PDFs differ from other PDF orientations in that they are multiple, mechanical Brazil twins, which are difficult to detect if not partially annealed and decorated. The occurrence and significance of shock metamorphosed quartz and its other phases (namely, coesite, stishovite, diaplectic glass and lechatelierite) are discussed for terrestrial impact structures in both crystalline (non‐porous) and sedimentary (porous) targets. The bulk of past studies have dealt with crystalline targets, where variations in recorded shock pressure in quartz have been used to constrain aspects of the cratering process and to estimate crater dimensions at eroded structures. In sedimentary targets, the effect of pore space results in an inhomogeneous distribution in recorded shock pressure and temperature, which requires a different classification scheme for the variation of recorded shock compared to that in crystalline targets. This is discussed, along with examples of variations in the relative abundances of planar microstructures and their orientations, which are attributed to textural variations in sedimentary target rocks. Examples of the shock metamorphism of quartz in distal ejecta, such as at the K/T boundary, and from nuclear explosions are illustrated and are equivalent to that of known impact structures, except with respect to characteristics that are due to long‐term, post‐shock thermal effects. Finally, the differences between the deformation and phase transformation of quartz by shock and by endogenic, tectonic and volcanic processes are discussed. We confirm previous conclusions that they are completely dissimilar in character, due to the vastly different physical conditions and time scales typical for shock events, compared to tectonic and volcanic events. Well‐characterized and documented shock effects in quartz are unequivocal indicators of impact in the natural environment.

The Radiation Phase Transitions and the Metamict State of Quartz

ABSTRACTA model of radiation induced phase transformations in quartz using the old idea of Weissmann and Nakajama is developed. The kinetics of these phase transitions is described taking into account intermediate phase formation. A model of the final radiation induced metamict state of quartz is suggested. The metamict state consists of amorphized matrix SiO2+X, where x ≈0.15 (radioglass), in which pure silicon precipitates are included.

On the mechanism of the α-β phase transformation of quartz

With a simple geometrical model the atomic displacements at the transition from α- to β -quartz and the eigenvector of the soft mode at the Γ -point are related to a single (order-) parameter. The model is refined by taking into account possible distortions of the SiO 4 tetrahedra. These refinements, together with considerations on the temperature dependence of the order parameter, suggest an increase of π-bond order in the Si-O bond with increasing temperature as the driving mechanism for the phase transition. The model also offers a qualitative understanding of the appearance of diffuse X-ray scattering in the Γ-M direction.

On the mechanism of the α-β phase transformation of quartz

On the mechanism of the α-β phase transformation of quartz

Vacuum sintering of quartz powder and phase transformation of quartz: Y. Moriya, Vacuum, 11 (3), May 1961, 158–172

Vacuum sintering of quartz powder and phase transformation of quartz: Y. Moriya, Vacuum, 11 (3), May 1961, 158–172