Small Amounts Of Silica Research Articles

Maceral composition, coal quality and depositional environments of the middle Permian Ukhaakhudag coal deposit, South Mongolia

The Ukhaakhudag coal deposit is located c. 560 km SSE of the city of Ulaanbaatar in the northeastern sector the South Gobi Basin. The coal-bearing strata is part of the middle Permian Tavantolgoi Formation. This study aims to determine the coal petrographic composition and depositional environments of five coal seams in the lower part of the deposit based on petrographic and chemical analyses of 106 composite samples. Vitrinite ranges from 12 to 64 vol.%, and inertinite varies between 9 and 68 vol.%. Liptinite ranges from 1 to 7 vol.%. Microlithotype analyses indicate that coals are primarily vitrinertite, few coals are classified as trimaceralic microlithotypes duroclarite and clarodurite. The inorganic fraction in the studied coals is mainly composed of clay, small amounts of silica, carbonate, and pyrite minerals. The vitrinite random reflectance values of the samples vary between 0.93-1.16 %. Volatile matter content varies from 26.10 to 41.48 wt.% (dry ash free basis). Ash, moisture, and sulfur contents vary between 11.20-44.76 wt.%, 1.63-6.03 wt.% and 0.49-1.67 wt.%, (air dried basis) respectively. Based on random vitrinite reflectance values and volatile matter content, the studied coals are classified as coking (Ch4), fat (Ch5), 1/3 coking (Ch6), gas fat (Ch7) based on the Mongolian system and medium to high volatile bituminous coal when using the ASTM system. The Gelification Index and Tissue Preservation Index of the studied samples suggest most seams accumulated in wet forest swamps with a high tree density. The Middle Permian peats from this location accumulated in mostly alternate oxic and anoxic mire conditions. The climate was drier during the peat accumulation of Seam 0, but it became warmer, and humidity increased starting from Seam 3 accumulation.

Silica-Milled Paulownia Biochar as Partial Replacement of Carbon Black Filler in Natural Rubber

Carbon black (CB) has been the dominant filler in the tire industry for decades. The demand for this petroleum byproduct is ever increasing, although petroleum markets can be volatile due to geopolitical issues. Finding sustainable, renewable substitutes for CB reduces the dependence on petroleum. Biochar is a renewable source of carbon that was studied as a potential CB replacement filler in styrene–butadiene rubber (SBR) composites, but little has been done in terms of natural rubber (NR). In this work, biochar made from fast-growing Paulownia elongata was co-milled with small amounts of silica in order to reduce the larger particle size typical with biochar respective to CB. The resulting silica-milled Paulownia biochar (PB) was then used to replace CB in natural rubber (NR) composites. By using this method to make natural rubber composites with 30% total filler, half of the CB was fully replaced with silica-milled biochar with very little loss (<6%) of tensile strength, and equal or better elongation and toughness compared to the 100% CB-filled control composite.

Dolomite-illitic rocks (dolillite) – the product of hydrothermal replacement of carbonate rocks in the Holy Cross Mts., Poland – a possible guide to ores

The dolomites altered to dolomite-illitic rocks were found accompanying marcasite-pyrite-hematite mineralization within the Middle Devonian carbonate rocks in the eastern part of the Holy Cross Mts. (Poland) in the fault zones and their close vicinity. The alteration consist of dolomite recrystallization and replacement by illite, accompanied by small amounts of silica, K-feldspars and disseminated pyrite or hematite. The final product of dolomite replacement by illite are massive, dolomite-illitic rocks unevenly distributed within the unaltered dolomites or in fault breccia. They form irregular metric-sized nest-like bodies most often with blurred boundaries, or in some places sharp delineated veins and lenses. Illite crystallinity, demonstrates its hydrothermal origin. Altered rocks are characterized by elevated contents of REE, Rb, and sometimes other trace metal (Zr, Ti, Zn, U, Th, Ba and al.), compared to unaltered dolomites. The enrichment in REE, Zr and Ti implies their mobility in hydrothermal solutions. The lamprophyre intrusions present in the close vicinity may be considered as the probable source of potassium rich hydrothermal fluids. The peculiar features of dolomite-illitic rocks such as: their composition and occurrence close to the sulphide and hematite mineralization, allow supposing, that they may be a guide to deeply seated unknown ore deposits. Normal 0 21 false false false PL X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Standardowy; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:12.0pt; font-family:Arial,sans-serif; mso-bidi-font-family:CG Times 12pt; mso-fareast-language:EN-US;}

A COMPARATIVE STUDY BETWEEN CALCINATION AND LEACHING OF CALCAREOUS PHOSPHATE ORE

Vast tonnages of low-grade calcareous phosphate rocks are found in several areas around the world. These rocks consist mainly of carbonate-apatite and free calcium carbonate with small amounts of silica. Commercial phosphate rock should not contain more than 8% carbonates (about 3.5% CO2) in order to be economical for fertilizer industry.In Egypt, the low calcareous sedimentary phosphate deposits are widely distributed in three main localities, namely, the Eastern desert, the Nile valley and the Western desert. Beneficiation of these ores by calcination, flotation and high intensity magnetic separation was tried by some investigators.Consequently, the aim of this research is to make a comparison between calcination and leaching of calcareous phosphate ore. For this purpose, the major parameters which effect on calcination and leaching processes are studied. Among them are, particle size, heating temperature, duration time and quantity of ore treated with respect to the calcination process, and particle size, acid concentration, solid percent (W/V) and leaching time with respect to the leaching process. Loss on ignition is used for assessment the results in the two methods.Calcination process is still used efficiently for removing free calcium carbonates. Therefore, this study was carried out on low-grade calcareous phosphate ore of Um-Hammad area (Red Sea phosphate) to reduce its calcium carbonates to an acceptable limit. To optimize the process, the influence of the most affecting parameters on the calcined samples was studied. A concentrate of 82.15% weight recovery and 2.98% L.O.I. was obtained under the optimum conditions.Leaching using dilute acetic acid was applied on the same ore to increase its P2O5content and to reduce its calcium carbonates content to the acceptable limit. To optimize the process, The influence of the most affecting parameters on the digested samples was studied.The selected optimum conditions of these parameters produced a phosphate concentrate having 5.01% L.O.I. with 65.6% weight recovery from a leached feed having 15.38% L.O.I.From this comparative study it can be concluded that the calcination process is more reasonable than the leaching process for the beneficiation of the low calcareous phosphate ore of Um-Hammad area.

Proton conductivity of hybrid membranes based on polybenzimidazoles and surface-sulfonated silica

Hybrid membranes based on polybenzimidazole PBI-O-PhT (a polymer based on 3,3′,4,4′‑tetraaminodiphenyl oxide and 3,3‑bis(p‑carboxyphenyl)phthalide) were obtained by casting with silica particles with the surface modified by sulfonic groups. The morphology, thermal stability, proton conductivity under various conditions, and hydrogen permeability of the obtained membranes were investigated. It was shown that modification with small amounts of silica (2–5%) increases the conductivity and practically has no influence on the gas permeability of the hybrid membranes.

Co-milled silica and coppiced wood biochars improve elongation and toughness in styrene-butadiene elastomeric composites while replacing carbon black

Carbon black (CB) is a petroleum by-product with a million ton market in the US tire industry. Finding renewable substitutes for CB reduces dependence on oil and alleviates global warming. Biochar is a renewable source of carbon that has been studied previously as a replacement for CB in styrene-butadiene rubber (SBR) composites. However, biochar typically has lower carbon content, higher ash content, and larger particle size, which are all significant detractors to making biochar a viable drop-replacement for CB. In this study, high carbon and low ash biochars made from fast-growing Paulownia elongata and Populus tremuloides were co-milled with small amounts of silica in order to reduce the particle size, and the biochar/silica blends were then used to partially replace CB in SBR composites. Using this method both Paulownia and poplar biochars were able to replace 30% of the CB filler and improve elongation and toughness with virtually no loss of tensile strength, compared to the 100% CB-filled control composite.

Formation of Aluminum Titanate with Small Additions of MgO and SiO2

The formation of aluminum titanate was investigated by isothermal treatments of samples obtained from equimolar mixtures of alumina and titania, containing small amounts of silica and magnesia. Results of differential thermal analysis and Rietveld refinements of data collected by X-ray powder diffraction (XRPD) showed that additions of silica in amounts used in this work did not influence the formation of aluminum titanate. However, the presence of magnesia favored the formation of aluminum titanate in two steps, first one by incorporating Mg2+ into Al2TiO5 lattice during its initial formation, and the second one by accelerating the Al2TiO5 formation, contributing to large quantities of this phase. MgO doped samples have also developed a more suitable microstructure for stabilizing of Al2TiO5, what make them promising for applications such as thermal barriers, internal combustion engines and support material for catalyst.

Hard-template preparation of Au/CeO2 mesostructured catalysts and their activity for the selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid

Ordered mesoporous CeO2 has been prepared via a hard-template method using SBA-15 as a structure-directing agent. Leaching with NaOH and thermal treatment at 500 °C enabled the removal of the inorganic template, thus resulting in the formation of long-range ordered CeO2. Nevertheless, small amounts of silica were present in the final oxides. The resulting CeO2 samples were used as supports for Au nanoparticles and the prepared catalysts were tested in the selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). Fine tuning of the silica template removal process was necessary to prepare active materials, by maximizing the close contact between the metal and the support, and thus confirming the important role of ceria defects in 5-hydroxymethylfurfural oxidation to 2,5-furandicarboxylic acid.

Influence of alkaline (pH 8.3–12.0) and saline solutions on chemical, mineralogical and physical properties of two different bentonites

AbstractThe interaction of two different bulk bentonites (Na- and Ca-types) with three types of simulated cement waters (pH 9.7, 11.3 and 12.0) and one saline groundwater simulate (pH 8.3) as a reference, was studied in batch reactors at 25°C. The solution pH was monitored in order to keep the pH as steady as possible by replacing the leaching solution with fresh one when needed. After 554 days, one set of parallel samples was removed from the experiment in order to investigate the possible changes in the bentonite materials.The buffering capacity of bentonite was clearly observed, especially at the beginning of the high-pH experiments, as the pH of the leaching solutions decreased quite dramatically due to interaction with bentonite. The solution chemistry results showed a decrease of Ca content in all leachate samples, but especially in pH 12.0 experiments. Small amounts of silica were released throughout the experiment. Both bentonites in pH 12.0 experiments also released detectable amounts of Al, while in the lower pH experiments the levels were below detection limit. These observations were also supported by chemical analyses of the bentonite materials. Only minor changes were detected in the mineralogy, and they were mainly concentrated on experiments at pH 11.3 and pH 12.0. The measured swelling pressure showed an increase in pH 12.0 experiments. The results obtained in this research may facilitate modelling of bentonite interaction with high-pH solutions.

Geological disposal of energy-related waste

The production of waste materials during energy recovery processes is an unavoidable consequence of the need for energy; consequently, safe and efficient disposal or reuse alternatives for these waste materials is essential for sustainable development. For waste streams that must be geologically disposed, the largest volumes of energy related waste include Coal Combustion Products (CCPs) such as fly ash, coal mining wastes, and processed water and drill cuttings from oil and gas exploration, with relatively small amounts of silica resulting from pipe scaling in geothermal energy production. The fate of the vast majority of these energy-related wastes is geologic disposal, which ranges from placement in landfills (lined or unlined) or surface impoundments, to deep injection within geologic units. Applications for productive reuse of energy-related wastes are cost effective alternatives to disposal, and are gaining popularity as sustainability of processing becomes more critical. This review paper examines geologic disposal and reuse of energy-related waste streams within the U.S., and provides insight into fuel-to-waste production ratios, preferred disposal or productive reuse alternatives, and associated geotechnical/environmental considerations.

Improved hydrothermal stability of niobia-supported Pd catalysts

Aqueous-phase reactions at elevated temperatures can cause significant loss of surface area in oxide supports. Addition of a second component can help improve the hydrothermal stability of the support and retain a more open, porous structure. Here we show that small amounts of silica (5 wt%) help improve the activity and stability of Pd/niobia–silica catalysts used for pentanoic acid formation from γ-valerolactone. At the end of the run, the Pd/Nb–Si oxide catalysts showed significantly higher activity than catalysts where the Pd was deposited on commercial niobia (HY-340). Loss of surface area occurred for all of the catalysts; however, surface area loss occurred to lesser extents for the Pd/Nb–Si oxide catalysts. In these samples, the regions that contained more silica retained their porous structure and maintained smaller Pd crystallite sizes after reaction while those areas with depleted silica content transformed into crystalline niobia along with significant metal particle growth. We conclude that addition of silica to niobia not only improves the stability of the support but also helps retain smaller crystallite sizes for the Pd phase, resulting in improved catalytic performance in the bi-functional aqueous-phase conversion of γ-valerolactone into pentanoic acid.

Improving the Microstructural Stability of Nextel™ 610 Alumina Fibers Embedded in a Porous Alumina Matrix

Nextel™ 610 alumina fibers embedded in ceramic matrix composites (CMCs) with a pure alumina matrix show pronounced grain coarsening above 1350°C, which is not observed for stand‐alone fibers under identical conditions. Moreover, a size gradient with small grains in the fiber center and large grains at the fiber periphery occurs. This can be explained in terms of the outward diffusion of silica traces, which normally reduces the fiber grain‐boundary mobility. Silica outdiffusion and the related excessive grain growth can be suppressed if small amounts of silica are added to the alumina matrix in the green state. Aluminosilicate green compositions, on the other hand, result in a lower matrix sinterability, thus leading to inferior mechanical properties of the CMC. In this communication, we present a novel method to design a CMC that combines the key benefits of an alumina matrix (superior strength) with that of an aluminosilicate matrix (superior thermal stability). Small amounts of silica were added to a CMC starting material with a porous alumina matrix via the sol–gel technique. The silica post treatment effectively suppresses grain growth in fibers and matrix. Mechanical testing revealed significant strength retention in case of the silica‐infiltrated CMC.

Interface temperature between solid and liquid corium in severe accident situations: A comprehensive study of characteristic time delay needed for reaching liquidus temperature

Tliquidus was proposed as the interface temperature (Seiler and Froment, 2000), for various severe accident situations for thermalhydraulic steady state. This proposal was made on the basis of the analysis of solidification front stability in thermalhydraulic steady state for volumetrically heated corium pools and was extended to reactor transients with slow solidification rates that are controlled by the longterm decrease in residual power. The conclusions were corroborated by prototypic corium and variable solidification rates obtained by experimental approaches (Dauvois et al., 2000; Journeau et al., 2003) for corium containing small amounts of silica or none at all. When the concentration in silica increases (approximately above 10 wt%), it was concluded from the experiments that a plane-front situation could not be obtained. The present work offers a theoretical approach to the maximum time delay that is necessary for mass transfer and full phase-segregation in volumetrically heated liquid pools bounded by a crust. It is concluded that full segregation is obtained for in-vessel situations within time delays that are shorter or of the same order of magnitude as the characteristic time for the corium pool to form and evolve to a quasi-steady-state situation. The characteristic time delay for mass transfer associated with simulant material experiments is also determined. Phase segregation can also be obtained for corium–concrete interaction, provided that the silica content is less than approximately 10 wt%. However in the latter case, more complex phenomena occur at the interface due to the interaction with sparging gas (such as porous medium formation) which requires a different model approach.

Bioactive glass induced in vitro apatite formation on composite GBR membranes

The aim of this study was to investigate in vitro bioactivity of different thermoplastic biodegradable barrier membranes. Three experimental GBR membranes were fabricated using Poly(epsilon-caprolactone-co-D: ,L-lactide) P(CL/DL-LA) and particulate bioactive glass S53P4 (BAG; granule size 90-315 microm): (A) composite membrane with 60-wt.% of BAG, (B) membrane coated with BAG; and (C) copolymer membrane without BAG. Membranes were immersed in simulated body fluid (SBF), and their surfaces were characterized with SEM, XRD and EDS after 6 and 12 h and after 1, 3, 5, 7, and 14 days. Calcium phosphate (Ca-P) surface formation was observed on both composite membranes (A and B) but not on the copolymer membrane without bioactive glass (C). The Ca-P precipitation appeared to be initiated on the bioactive glass followed by growth of the layer along the polymer surface. In 6-12 h ion dissolution of the bioactive glass led to formation of the silica rich layer on the surface of the exposed glass granules on composite membrane B whereas only small amounts of silica was observed on the polymer surface of the composite membrane A. At 24 h nucleation of Ca-P precipitation was observed, and by 3-5 days membrane surface was covered with a uniform Ca-P layer transforming from amorphous to low crystalline structure. At 7 days composition and structure of the apatite surface resembled the apatite in bone. Once nucleated, the surface topography seemed to have significant effect on the growth of the apatite layer.

Production of cement clinkers from municipal solid waste incineration (MSWI) fly ash

This communication reports the laboratory scale study on the production of cement clinkers from two types of municipal solid waste incineration fly ash (MSW ash) samples. XRD technique was used to monitor the phase formation during the burning of the raw mixes. The amount of trace elements volatilized during clinkerization and hydration, as well as leaching behaviours of the clinkers obtained from optimum compositions, were also evaluated. From the results it is observed that all of the major components of ordinary Portland cement (OPC) clinkers are present in the produced clinkers. Results also show the volatilization of considerable amounts of Na, K, Pb, Zn and Cd during the production of clinkers. However, major parts of the toxic elements remaining in the clinkers appear to be immobilized in the clinkers phases. Hydration studies of the clinkers obtained from optimum compositions show that the clinkers prepared from raw MSW ash are more reactive than the washed MSW ash based clinkers. TG/DTA analyses of the hydrated pastes show the formation of hydration products, which are generally found in OPC and OPC derived cements. The initial study, therefore, shows that more than 44% of MSW ash with the addition of very small amounts of silica and iron oxide can be used to produce cement clinkers. The amount of CaCO 3 necessary to produce clinkers (approximately 50%) is also smaller than the same required for the conventional process (more than 70%).

Silica or fibre glass reinforced composites via photopolymerisation of acrylate systems

Composites based on an acrylate system were cured using UV light in the presence of a radical photoinitiator, with silica powder or glass fibres as reinforcing agents. The presence of small amounts of silica or glass fibres (up to 7 wt-%), did not influence the kinetics of photopolymerisation or the final conversion of the acrylic double bonds. The properties of the materials obtained were found to depend on the type and concentration of the reinforcing agent, and the surface treatment.

Preceramic organoboron–silicon polymers

AbstractSeveral boron‐containing organosilicon polymers were synthesized from a sodium‐coupling reaction of silicon and boron halides with and without alkyl halide in hydrocarbon solvents. The B–Si preceramic polymers were characterized using techniques such as IR, UV, and NMR spectrometry, gel permeation chromatography, elemental analysis, molecular weight measurement, and thermal analyses (TGA, DSC, DTA, and TMA). The chemical structures of the preceramic polymers were postulated based on the analytical results. Black ceramic materials were obtained from the precursor polymers upon thermal degradation at temperatures above 1000°C in an inert atmosphere. The precursor polymers had a ceramic yield of up to 70%. Thermogravimetric analysis of the ceramic material in air at a flow rate of 100 mL/min showed it was stable up to 1000°C with little weight gain or loss. Several methods were used to characterize the ceramic materials: XRD, solid NMR, high‐temperature DTA, elemental analysis, and acid digestion. The analyses indicated that the ceramic materials comprised a mixture of silicon carbide (SiC), silicon borides (SiB4, SiB6), and amorphous Si–B–C ceramics, with small amounts of silica and free silicon.

EXPOSURE OF DIAMOND POLISHERS TO COBALT

Interstitial pulmonary fibrosis due to 'hard metal' exposure is well known, and the presence of cobalt has always been considered as the causative factor. Recently interstitial pulmonary fibrosis has been described in diamond polishing workers. In this study the dust composition in different polisher's workplaces where diamond disks are in use has been determined. Careful investigation showed that the exposure to respirable dust was comparable to that of 'hard metal' workers. The dust consists mainly of iron and cobalt particles and small amounts of silica. No 'hard metals' have been found, and other fibrogenic agents such as beryllium have been excluded. These observations lend support to the hypothesis that crystalline cobalt particles can be responsible for pulmonary fibrosis even in the absence of carbides.

Developments in geothermal energy in Mexico—part thirteen: the operation of surface equipment for geothermal fluid conduction at Cerro Prieto I

At Cerro Prieto I 34.5 PJ e have been generated and 334 million tonnes of geothermal fluid have been produced. The length of the present system of 300 mm (12 in) to 350 mm (14 in) dia. steam pipelines is 24 km. That of the water pipeline system of 200 mm (8 in) to 400 mm (16 in) dia. pipe is 46.5 km. A total of 32 wells, 41 separators, 51 silencers, 7 steam driers, and 290 200 mm (8 in) to 400 mm (16 in) dia. valves are in operation. Corrosion in the pipelines and other surface equipment has not been a serious problem. The principle maintenance problem has been the cleaning of silica scaling and sediments in pipelines, equipment and channels. Frequent maintenance is necessary in order to maintain the capacity of water pipelines, separators and channels. The well liners and in some cases the deposits themselves have been affected by scaling. Even the small amounts of silica that are carried by the separated steam cause scaling of turbine blades, reducing their capacity.

Clay mineralogy of the B horizons of two hydrandepts, a Torrox and a Humitropept in Hawaii

The mineralogy of the clay fractions separated from the B horizons of two Hydrandepts (Hilo and Akaka soils), a Torrox (Molokai soil) and a Humitropept (Kolekole soil) was determined by a combination of methods. The Hydrandept B horizons were characterized by predominance of hydrous non-crystalline alumina and iron oxides associated with considerable amounts of humus and with very small amounts of silica. Allophane, allophane-like constituents and imogolite were present but in minor amounts. Gibbsite, goethite, chlorite and illite were also present as accessory minerals. The Torrox and Humitropept B horizons were characterized by predominance of kaolinite, hematite and goethite. The iron oxide minerals were present as fine particles (40–80 A diameter) often clustered to form larger aggregates. Neither imogolite nor allophane and allophane-like constituents were detected. Considerable amounts of dithionite-citrate soluble Al and humus were, however, present in the Humitropept B horizon, which may reflect the effect of an admixture of volcanic ash to the parent material.