Hydrothermal phase transformation of tungsten trioxide and the associated thermodynamic data

Hydrothermal phase stability studies of tungsten trioxide under water vapour pressure showed a monoclinic to tetragonal phase transformation with a nearly pressure independent invariant equilibrium boundary line. The standard thermodynamic data for the tetragonal form of WO3 obtained from the experimental PT points on the equilibrium transformation boundary are: DELTA-G(f)0 = -759.743 kJ/mol., DELTA-H(f)0 = -836.598 kJ/mol., S(f)0 = 82.59 J/mol.deg

P-T Conditions of Metamorphism and Fluid Inclusion Characteristics of the Coorg Granulites, Karnataka

Charnockites and basic granulites occur extensively around Coorg in Western Ghats. Minor metasedimentary rocks like kyanite/sillimanite bearing gneisses and ironstone also occur. A set of late dolerite dykes cross cut all the lithologies. The Coorg granulites record a near-peak metamorphic conditions of 720 to 760-degrees-C at pressures of 7 to 8.6 kb. Charnockites and basic granulites contain high-density (1.07 to 1.09 g/cc) carbonic inclusions. Micro-textures, mineral P-T and fluid inclusion data indicate `'clockwise'' P-T trajectory, pointing to a relatively rapid uplift/erosion of the Coorg granulites

Hydrothermal phase relations in V2O2-H2O system

Hydrothermal phase relations in the vanadium oxide-water system have been studied and the phase diagram for V2O5-H2O is given. The Magneli phases found in between the two stable fields of V2O5 and V3O5 were invariably found with good euhedral morphology. This suggests that oxides of vanadium with a wide range of oxygen stoichiometry can be grown as single crystals using water as a mineralizer

Metamorphic history of Calc-silicate lithologies from the Kambam valley, Tamil Nadu and its bearing on the evolution of the Southern Granulite Terrain

Kambam valley farms an integral part of the Southern Granulite Terrain. The valley represents a deep crustal break hosting high temperature alkaline intrusives and also a carbonatite body. Common rock types encounterd are charnockite and granulite grade calc-silicate and metapelite. Gale-silicate lithologies are interbanded with mafic granulites on cm scale. Wollastonite-scapolite-grandite garnet-clinopyroxene indicate high temperature (900 degrees C). Corroborative high temperatures are recorded from associated metapelites. Textural features such as the formation of coronal garnet and garnet-quartz double rinds at the expense of calcite, scapolite; wollastonite, clinopyroxene suggest a late isobaric cooling at shallower depths. The cooling event was associated with domainal variation in fluid species. Fluid inclusion studies confirm a late carbonic fluid flux consistent with the carbonation reactions that followed. The associated metapelitic lithologies-in the area preserve textural evidence for a rapid high temperature decompression event. The Kambam valley granulites, thus witnessed high temperature metamorphism, rapid decompression and late isobaric cooling. The above metamorphic history is consistent with those reported from other parts of the Southern Granulite Terrain (SGT). Thermal perturbation associated with extensional thinning and alkaline magmatism explain the high temperature metamorphism, decompression and subsequent cooling

Hydrothermal synthesis of Nanosized crystals of diamond under sub-natural conditions

The hydrothermal synthesis of diamond was carried out in the silicon carbide - organic compound system. The organic compounds were expected to dissociate in a closed system to generate C-O-H supercritical fluids, which are known for their high dissolving power and influence on the type of elemental carbon formation, especially in stabilizing the sp3-hybridized carbon. The SEM studies reveal that the bulk portions of the carbon formed are spherical/ovoid shaped particles and in a few cases nanosized crystallites. The micro Raman spectral studies of carbon crystallites reveal that they are having typical spectra of sp3-hybridization, thus clearly demonstrating the formation of nano-sized diamond crystallites under sub-natural conditions. In all the above investigations metal catalysts or the seeded diamond were not used, unlike in earlier attempts on the hydrothermal synthesis of diamond

Garnet-Kyanite Bearing Pelitic and Associated Mafic Granuliters along Jalsoor-Mercara Shear Zone - Evidence for Deep Burial and Later Uplift

Garnet-kyanite-sillimanite bearing pelitic and garnetiferous mafic granulites exposed at several places along the Jalsoor-Mercara and Bavali shear zones preserve evidences of deep burial of atleast 30 km. Estimation of P-T conditions of metamorphism of these granulities give T of 725-800-degrees-C and P of 7 to 8.6 kb. Increase of pressure form core to rim in the garnet-kyanite assemblages and kyanite mantling garnet are the most significant aspects of these lithologies, suggesting long residence in the deep crust and possible thrust tectonics. Moreover, fibrolitic sillimanite overgrowing kyanite in pelites and the development of opx-calcic plag symplectites around garnet in the mafic rocks indicate decompression/uplift, subsequent to crustal thickening. This uplift could be part of a later even unrelated to the burial episode. Significantly, syenite and anorthosite bodies of late Proterozoic age occur along these shear zones indicating that these lineaments were reactivated again in late Proterozoic times

Hydrothermal phase relations in molybdenum oxide–water systems

Molybdenum oxides are important for materials scientists as they show good semiconducting properties. Study of stability relations in molybdenum oxide system is interesting from the point of view of syntheses of pure phases of the oxides or of mixed oxides with other cations. We have studied phase stability in molybdenum oxide-water systems using Tuttle-type pressure vessels. MoO3 on the low-temperature side and MoO2 on the high-temperature side were the stable oxides. A metastable blue phase found between the MoO3 and MoO2 fields was a hydrated nonstoichiometric molybdenum oxide

Well-monocrystallized LaCrO3 particles from a LaCrO4 precursor by supercritical hydrothermal technique

LaCrO3 based materials are currently utilized in a variety of electrical applications at high temperature. However, the morphology of LaCrO3 powder is much less understood as compared to its bulk counterpart. In this work, LaCrO3 powder was synthesized from LaCrO4 precursor by a supercritical hydrothermal technique (SHT). The majority exhibited a pure orthorhombic phase with well-monocrystallized grains of 3–9 μm. This work confirms that dominating faces in LaCrO3 grains are 0 1 0 and 0 1 1 surfaces, which have equivalent surface-energy due to the similarity of their surface structure

Hydrothermal synthesis of polycrystalline carbonates

Polycrystals of orthorhobic carbonates RCO3 (R = Sr, Ba and Pb) were synthesised for the first time using formic acid as mineraliser. The unit cell parameters of this synthetic pure carbonates are: BaCO3:a=5.309, B=8.889, C=6.401; srCO3:a=5.108, B=8.420, C=6.040; PbCO3: A=5.176, B=8.511, C=6.137

Synthesis and characterization of Calcium Aluminum Silicate Hydroxide (CASH) crystals

Minerals whose compositions fall within the CaO-Al2O3-SiO2-H2O (CASH) system are found in a wide variety of metamorphic and igneous rock. Many experimental investigations have been conducted on reaction with the CASH system, but there are many more yet to be studied. Hence phase relations in the CASH system are of great importance in experimental mineralogy. Attempts have been made to synthesize the crystals belonging to these groups (anorthite, zoisite in particular) under hydrothermal treatment of a co-precipitated gel of zoisite Ca2Al3Si3O12(OH), composition at low to medium temperatures (400�600°C) and ambient pressures (1 to 1.5 kb) in the duration of 24 to 136 hours. The obtained run products were identified as Anorthite with minor Quartz, Kyanite and Aluminum oxides phases by X-ray diffraction patterns. The changes in the structural environment can be detected through changes in the energies of OH-vibrations, strong wagging mode of Si-H bond, the stretching mode of Si-C bond, Si-O-Si stretching mode of cyclic trimer, O-H deformation mode, C-O asymmetric stretching and O-H molecule stretching are measured by infrared spectroscopy. SEM shows the growth direction and texture of discrete crystals of anorthite. The chemical composition was obtained by the EDAX