Experimental Constraints on the Crystallization of Silica Phases in Silicic Magmas

Low-pressure silica polymorphs, e.g. quartz (Qtz), tridymite (Trd), and cristobalite (Crs), are common in silicic magmas, but the conditions of their formation are still unclear. The stability fields of these polymorphs have been determined in the SiO2, SiO2-H2O, and haplogranite systems, but these simple systems are not directly applicable to silica polymorph crystallization in natural silicic magmas. The present study compiles an experimental database of new and previously-published data documenting the crystallization of silica phases in natural silicic magmas and simple synthetic systems. Silica polymorphs are identified using Raman spectroscopy and their pressure-temperature domains of occurrence and chemical compositions are determined at pressures between 0.1 and 200 MPa, temperatures between 685 to 1200 °C, and under H2O-saturated and H2O-undersaturated conditions. Qtz is the stable silica polymorph at pressures higher than 25-30 MPa, temperatures between ∼700 and 950 °C, and occurs for a narrow range of melt SiO2 contents (∼79-81 wt%). Constraints on Qtz stability derived from simple systems are mutually compatible with, and thus applicable to natural compositions. This is consistent with Qtz compositions being close to ‘pure’ SiO2, both in experiments and nature. In volcanic systems, Qtz crystallization may occur in magmatic reservoirs and deep volcanic conduits. Trd did not crystallized in the experiments conducted as part of this study despite several experiments having been performed in the Trd stability field. This is consistent with results from the literature which show that Trd crystallization is kinetically inhibited in particular relative to Crs. Natural Trd have compositions deviating substantially from ‘pure’ SiO2, so that stability limits determined in simple systems should not be applied directly to natural cases. Crs was encountered at pressures below 20-30 MPa (or H2O contents < ∼1.5 wt%), from sub-solidus (∼800 °C) to near-liquidus (up to 1040 °C), and coexisting with melts having a large range of SiO2 contents (70-81 wt%). The Crs stability field is much larger in natural magmas compared to pure SiO2 systems. Crs is a metastable phase stabilized by components (Al, Na, K; about 3 wt%) present in the silicic melt. In volcanic systems, Crs crystallization may thus be restricted to subsurface manifestations such as lava domes.

Thermophysical Properties of Hybrid Nano Fluids

In this study, the ash from agriculture waste of bamboo leaves was used in the synthesis of silica nano particles followed by leaching and acid treatment. The required ash from agriculture waste (bamboo leaves) is subjected to sintered at 700 degree centigrade for 5 hours to eliminate residues from ash. The obtained powder was treated with 1M NaOH for leaching and then acid- treatment with 0.5 M H2SO4 to precipitate pure SiO2 nano particles powder. The synthesized silica were characterized by XRD, FTIR, SEM, PSA, ZETA POTENSIAL. And the synthesis of CuO-SiO2 hybrid nano fluid from the agriculture waste of silica.

An Investigation of Non-Metallic Inclusions in Different Ferroalloys using Electrolytic Extraction

Ferroalloys are integral constituents of the steelmaking process, since non-metallic inclusions (NMIs) from ferroalloys significantly influence the transformation of inclusions present in liquid steel or they are directly involved in casted steel. In this study, the characteristics of inclusions (such as the number, morphology, size, and composition) in different industrial ferroalloys (FeV, FeMo, FeB, and FeCr) were investigated using the electrolytic extraction (EE) technique. After extraction from the ferroalloy samples and filtration of the solution, the inclusions were investigated on a film filter. The three-dimensional (3D) investigations were conducted using a scanning electron microscopy in combination with energy dispersive spectroscopy (SEM-EDS). The characteristics of inclusions observed in the ferroalloys were compared with previous results and discussed with respect to their possible behaviors in the melt and their effects on the quality of the cast steels. The particle size distributions and floatation distances were plotted for the main inclusion types. The results showed that the most harmful inclusions in the ferroalloys investigated are the following: pure Al2O3 and high Al2O3-containing inclusions in FeV alloys; pure SiO2 and high SiO2-containing inclusions in FeMo alloys; Al2O3 and SiO2-containing inclusions in FeB alloys; and MnO-Cr2O3, Al2O3, and Cr2O3-based inclusions in FeCr alloys.

Petrology and Provenance of Lithic Raw Materials used to knap stone: A Case Study From the Inner Ionian Sea

This paper examines the lithology and raw material provenance of knapped stone artifacts recovered from prehistoric sites on Meganisi in the course of the Inner Ionian Sea Archipelago survey. Research was twofold: in the field to map the geology of the island and collect raw material samples, and in the laboratory to conduct a petrological study using LM, XRD, SEM and ICP-MS techniques. The greater part of the materials used to produce stone tools consists of almost pure SiO2, bedded or nodular cherts mainly of Malm–Turonian and Eocene ages. The cherts were collected by prehistoric knappers from local sources. Patinas present on the artifacts are relatively enriched in calcite material of incomplete silica diagenesis and subsequently a product of late weathering and alteration.

Optimization of SiOx/PET Thin Films Prepared by RF Magnetron Sputtering Technology Based on Orthogonal Experiment

The SiOx thin films were deposited by RF magnetron sputtering physical vapor technology on the substrates of 20μm polyethylene terephthalate（PET）, using a pure SiO2 target. An L15 (33) orthogonal experiment was designed with three factors and three values including deposition time, sputtering power, sputtering pressure. Using OTR test the effect of process parameters were researched. The primary and secondary sequence of the design parameters were acquired by the quadratic multinomial. The result showed that deposition time affected more strongly the OTR of the films than the sputtering pressure, the sputtering power affected least between them. The best SiOx thin films were prepared at a deposition time of 27.9min，a sputtering power of 1825W，a sputtering pressure of 0.3455Pa. The calculated OTR was 0.8387 cc/(m2×day)，which was consistent with the test one.

Single-Layer Silica Anti-Reflective Films Modified with Polytetramethylene Glycol

Single-layer silica films modified with polytetramethylene glycol (PTMEG) were prepared via sol-gel process in the presence of NH4OH as catalyst. Compared with the pure SiO2 coating, the hybrid films possessed higher lased-induced damage threshold (LDT). The characterization results from AFM and TEM indicated that the introduction of PTMEG molecules changes the structure of the colloidal silica matrix, which directly resulted in the improvement of the transparency and LDT.

Nanosized Silicon Carbide Obtained from Rice Husks

Two ways to obtain nanosized silicon carbide (SiC) powders from the products of thermal decomposition of rice hulls and posterior thermal and chemical treatment of SiO2-C precursors are shown in the present paper. The reagents and products were analyzed using BET, DTA, IR, XRD and SEM/TEM. Precursors obtained from rice husks containing pure SiO2 and a controlled SiO2-C ratio were used for the synthesis of SiC. The synthesis of SiC proceeded for 30-45 min in a graphite heater furnace under protective Ar atmosphere at relatively low temperatures (1450oC-1550oC). Nanosized dimensions of reagents obtained from rice husks and their high activity allow obtaining SiC in relatively milder thermal regimes. TEM and XRD analysis revealed synthesis of nanostructured mainly β-SiC with a mean crystallite size of 40-100 nm. Due to their purity and nano-scale properties, the products obtained are appropriate for production of bulk SiC or design of SiC–based ultra high-temperature materials using the methods of powder metallurgy.