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SiO2 Content (sio2 + content)
Selected AbstractsOrigin and palaeo-environments of calcareous sediments in the Moshaweng dry valley, southeast BotswanaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2002S. Ringrose Abstract Quaternary sedimentation in the Moshaweng dry valley of southeastern Botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses. Stratigraphic evidence reveals an upper surface (1095 m) containing abundant sil-calcrete, an intermediate surface (1085 m) in which sil-calcrete underlies nodular calcrete and lower (1075 m) surface in which sil-calcrete and nodular calcrete are interbedded. This subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing SiO2 content (and increasing CaCO3 content) with depth from the highest to the lowest surface levels. The calcretes and sil-calcretes represent modifications of pre-existing detrital Kalahari Group sand and basal Kalahari pebbles which thinned over a Karoo bedrock high. Modification took place during wet periods when abundant Ca++ -rich groundwater flowed along the structurally aligned valley system. With the onset of drier conditions, water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m. A major geochemical change resulted in the preferential silicification of the nodular calcrete deposits. Conditions for silica mobilization may be related to drying-induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile. As calcretization and valley formation progressed to lower levels, silica release took place on a diminishing scale. Thermoluminescence dating infers a mid-Pleistocene age for sil-calcrete formation suggesting that valley evolution and original calcrete precipitation are much older. Late stage dissolution of CaCO3 from pre-existing surface calcretes or sil-calcretes led to the formation of pedogenic case-hardened deposits during a time of reduced flow through the Moshaweng system possibly during the upper or late Pleistocene. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effect of the preparation conditions on the permeation of ultrahigh-molecular-weight polyethylene/silicon dioxide hybrid membranesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Nana Li Abstract Porous ultrahigh-molecular-weight polyethylene/SiO2 membranes were prepared by thermally induced phase separation (TIPS) with white mineral oil as the diluent and SiO2 as an additive. Influential factors, including extraction method, SiO2 content, and cooling rate, were investigated. The results suggest that the both porosity and pure water flux of the membranes by extraction of the solvent naphtha in the tension state with alcohol were the best among our research. With increasing SiO2 content, the porosity, pure water flux, and pore diameter increased. However, with excessive SiO2 content, defects formed easily. Moreover, SiO2 improved the pressure resistance of the membranes. The cooling rate directly effected the crystal structure. A slow cooling rate was good for crystal growth and the integration of the diluent. Therefore, the porosity, pure water flux, and bubble-point pore diameter increased with decreasing cooling rate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Epoxy composites reinforced by different size silica nanoparticlesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Cheng-Fang Ou Abstract Three series of epoxy/SiO2 composites, containing 0.3,7 wt % nanosized SiO2 with different specific surface area, were prepared by solution blending. The resulting composites exhibit the higher glass transition temperature (Tg) than that of pure epoxy. The Tg of composite showed a maximum increment of 35.3°C by the addition of 7 wt % A300. The trade name of A300 is Aerosil 300. It is one of the fumed silica nanoparticles products of Degussa. The decomposition temperatures (Td) of composites were always higher than that of pure epoxy and showed a maximum increment of 20.8°C by the addition of 5 wt % A300. The light transmittance of composites was as a function of the SiO2 content and size. The water permeability of composites decreased with increasing SiO2 content and the 7 wt % A300 composite exhibits a maximum decrement percentage of 35.6%. The Tg, Td, storage modulus, and water-vapor barrier property are as a function of the SiO2 content and size. These properties increased as the content of SiO2 increased. The finer SiO2 are more effective in increasing the Tg, Td, and water-vapor barrier property. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Morphology, mechanical properties, and thermal stability of poly(L -lactic acid)/poly(butylene succinate- co -adipate)/silicon dioxide compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009Ruyin Wang Abstract Poly(butylene succinate- co -adipate) (PBSA) and two types of SiO2 (hydrophilic or hydrophobic) were used to modify poly(L -lactic acid) (PLLA). The mechanical properties, rheological and thermal behavior, phase morphology, and thermal stability of PLLA/PBSA/SiO2 composites were investigated. The impact strength, flexural strength, and modulus of PLLA/PBSA blends increased after the addition of hydrophobic SiO2 without decreasing the elongation at break, and the elongation at break monotonically decreased with increasing hydrophilic SiO2 content. The melt elasticity and viscosity of the PLLA/PBSA blend increased with the addition of SiO2. The hydrophilic SiO2 was encapsulated by the dispersed PBSA phase in the composites, which led to the formation of a core,shell structure, whereas the hydrophobic SiO2 was more uniformly dispersed and mainly located in the PLLA matrix, which was desirable for the optimum reinforcement of the PLLA/PBSA blend. The thermogravimetric analysis results show that the addition of the two types of SiO2 increased the initial decomposition temperature and activation energy and consequently retarded the thermal degradation of PLLA/PBSA. The retardation of degradation was prominent with the addition of hydrophobic SiO2. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Indication of Local Phase Separation in Polyimide/Silica Hybrid Polymers,MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2010Antonino Bartolotta Abstract PI/SiO2 hybrid polymers involving the in situ generation of SiO2 particles through the sol/gel route have emerged as promising materials in many fields of modern technology thanks to their unique structural characteristics. In this paper their structural and dynamic properties were investigated by FT-IR and DMTA as a function of SiO2 content. All data consistently highlight a loosening of polymeric structure due to the presence of SiO2 nanoparticles and suggest a silica-induced structural change most probably due to a sub-micrometer scale SiO2 phase separation. Our results demonstrate how the analysis of sub-glass ,-relaxation dynamics can be exploited to investigate sub-micro phase segregation in such materials. [source] Optimizing Melt-Processing Conditions for the Preparation of iPP/Fumed Silica Nanocomposites: Morphology, Mechanical and Gas Permeability PropertiesMACROMOLECULAR REACTION ENGINEERING, Issue 4 2007Alexandros Vassiliou Abstract A series of iPP/SiO2 nanocomposites, containing 1, 2.5, 5, 7.5, and 10 wt.-% fumed silica nanoparticles, were prepared by melt mixing in a twin screw co-rotating extruder. The effect of different extrusion parameters was evaluated. The size of aggregates increased with increase in SiO2 content and repetition of the mixing process improved the filler's dispersion. A similar effect was also exhibited by either increasing the rotor speed or the mixing temperature, with the latter being more pronounced at the ranges studied. The mechanical properties of the prepared nanocomposites were evaluated and various models used to explain the observed enhancements. However, only the three-phase model could provide some correlation with the experimental results. All nanocomposites displayed lower permeability to gases. [source] Mineralogy and petrology of the angrite Northwest Africa 1296METEORITICS & PLANETARY SCIENCE, Issue 3 2005A. Jambon Dendritic olivine (,Fo50) crystallized first in association with anorthite microcrysts (An98,100) forming composite chains separated from one another by intergrown Al-Fe diopside-hedenbergite pyroxenes. In addition, some olivines with lower Mg# and increased CaO (up to 12%) are found between the chains as equant microphenocrysts. Pyroxenes and olivines are both normally zoned from Mg# = 0.52 to less than 0.01 in the rims. Ca-rich olivines are surrounded by, intergrown with, or replaced by subcalcic kirschsteinite. They appear after plagioclase crystallization stopped, at the end of the crystallization sequence. Minor phases are pyrrhotite, F-apatite, and titanomagnetite. Pyroxene is the last silicate phase to grow, interstitial to idiomorphic olivine-kirschsteinite. Numerous small vesicles and some channels are filled with microcristalline carbonate. The mode (vol%) is about 28% olivine, 3% kirschsteinite, 32% anorthite, 34% pyroxene, and 3% of the minor phases,close to that reported previously for D'Orbigny and Sahara (SAH) 99555. The bulk chemical composition of NWA 1296 is similar to D'Orbigny and SAH 99555; NWA 1296 differs by its texture and mineralogy, which are interpreted as resulting from rapid crystallization,an evidence of impact melting. Angrites cannot be produced by partial melting of a CV source because segregation of a "planetary" core is necessary to explain the low FeO/MgO ratio of magnesian olivines. Neither the odd Ca/Al ratio nor the very low SiO2 content can be explained by conventional partial melting scenarios. We suggest that carbonate is the key to angrite genesis. This is supported by the striking similarities with terrestrial melilitites (low SiO2, superchondritic Ca/Al ratio, presence of carbonate). The lack of alkalies could be the result of either loss after impact melting or absence of alkalies in the source. [source] Effects of interactions among polyaniline, camphorsulfonic acid and silica on the structure and properties of their conductive hybridsPOLYMER ENGINEERING & SCIENCE, Issue 3 2008Hsun-Tsing Lee In this work, the effects of interactions among polyaniline (PAn), camphorsulfonic acid (CSA), and silica on the structure and properties of their sol-gel hybrids are investigated. These interactions were revealed by FTIR, UV,vis spectra, and XRD patterns. The interaction between PAn and CSA raises conductivities of the CSA-doped PAn/SiO2 (c-PAn/SiO2) hybrids. Moreover, the hydrogen bonding interaction between c-PAn and silicic acid (precursor of SiO2) leads to a less degree of three-dimensional network structure of the SiO2 component in a hybrid with higher PAn content. In addition, because of the interactions among CSA, Pan, and SiO2, the conductive c-PAn-rich phase distributes uniformly in the hybrid and thermal resistance of the hybrid is enhanced consequently. Besides, the c-PAn/SiO2 hybrid with higher SiO2 content exhibits more significant blue-shift of its polaron band, lower conductivity, and higher thermal resistance. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Preparation and properties of ternary polyimide/SiO2/polydiphenylsiloxane composite filmsPOLYMER INTERNATIONAL, Issue 11 2006Zhenping Shang Abstract A series of novel ternary polyimide/SiO2/polydiphenylsiloxane (PI/SiO2/PDPhS) composite films were prepared through co-hydrolysis and condensation between tetramethoxysilane, diphenyldimethoxysilane (DDS) and aminopropyltriethoxysilane-terminated polyamic acid, using an in situ sol,gel method. The composite films exhibited good optical transparency up to 30 wt% of total content of DDS and SiO2. SEM analysis showed that the PDPhS and SiO2 were well dispersed in the PI matrix without macroscopic separation of the composite films. TGA analysis indicated that the introduction of SiO2 could improve the thermal stability of the composite films. Dynamic mechanical thermal analysis showed that the composite films with low DDS content (5 wt%) had a higher glass transition temperature (Tg) than pure PI matrix. When the content of DDS was above 10 wt%, the Tg of the composite decreased slightly due to the plasticizing effect of flexible PDPhS linkages on the rigid PI chains. The composite films with high SiO2 content exhibited higher values of storage modulus. Tensile measurements also showed that the modulus and tensile strength of the composite films increased with increasing SiO2 content, and the composite films still retained a high elongation at break due the introduction of DDS. The density and water absorption of the composite films were also characterized. Copyright © 2006 Society of Chemical Industry [source] Mass Transfer, Oxygen Isotopic Variation and Gold Precipitation in Epithermal System: A Case Study of the Hishikari Deposit, Southern Kyushu, JapanRESOURCE GEOLOGY, Issue 3 2002Naotatsu SHIKAZONO Abstract: Transportation of various kinds of elements occurred in wall rocks (Quaternary andesites) during the hydrothermal alteration accompanied by the Hishikari epithermal gold mineralization. For example, K2O and MgO contents of wall rocks decrease away from the gold-quartz veins, while (CaO+Na2O) content increases, and SiO2 content is variable near the veins. Hydrothermal alteration zoning and bulk compositional variations in wall rocks suggest that the mixing of hydrothermal solution and acidic groundwater took place an important role as the cause for the hydrothermal alteration and bulk compositional variations. The relationship between dissolved silica concentration and temperature of hydrothermal solution mixed with groundwater is obtained based on precipitation kinetics-fluid flow,mixing model, and the computed results are compared with the distribution of SiO2 minerals (quartz and cristobalite) in the hydrothermal alteration zones. This comparison suggests that the most reasonable flow rate of fluids migrating through hydrothermal alteration zones, and A/M (A: surface area of rocks interacting with fluid, M: mass of fluid) are estimated to be ca. 10 -4.2 m/sec, and ca. 0.10 m2/kg, respectively. The mixing of two fluids (hydrothermal solution and acidic groundwater) can also explain ,18O zoning in the altered country rocks, hydrothermal alteration zoning from K-feldspar through K-mica to kaolinite from the center (veins) to margin, and deposition of gold. [source] A scientific study of Choson white ware: early porcelain from a royal kiln at Kwangju UsanniARCHAEOMETRY, Issue 2 2002C. K. Koh Choo Scientific study of kiln site no. 9 at Usanni, one of the earliest royal Kwangju kiln complexes in operation (from the early 15th to the early 16th century), shows that the technological expertise used to produce white ware was inherited from the celadon technology of the Koryo dynasty. The body material, of low Al2O3 and high SiO2 content, is based on porcelain stone. Such a material, with almost no titanium and a low level of iron, was a rediscovery of the white ware material used earlier at the Sori kiln from the 9th century through to the 11th century. Ash continued to be one of the major ingredients of the glaze, and wares were fired in much the same way as the Koryo celadon, in kilns constructed of mud and rocks and in two steps. The Confucian philosophy and aesthetic of frugality and simplicity adopted from the Ming dynasty onwards by the new government acted as the catalyst for the successful ascent of the new technology. [source] Crustal Composition of China Continent Constrained from Heat Flow Data and Helium Isotope Ratio of Underground FluidACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2010Yang WANG Abstract: Based on conservation of energy principle and heat flow data in China continent, the upper limit of 1.3 ,W/m3 heat production is obtained for continental crust in China. Furthermore, using the data of heat flow and helium isotope ratio of underground fluid, the heat productions of different tectonic units in China continent are estimated in range of 0.58,1.12 ,W/m3 with a median of 0.85 ,W/m3. Accordingly, the contents of U, Th and K2O in China crust are in ranges of 0.83,1.76 ,g/g, 3.16,6.69 ,g/g, and 1.0%,2.12%, respectively. These results indicate that the abundance of radioactive elements in the crust of China continent is much higher than that of Archean crust; and this fact implies China's continental crust is much evolved in chemical composition. Meanwhile, significant lateral variation of crustal composition is also exhibited among different tectonic units in China continent. The crust of eastern China is much enriched in incompatible elements such as U, Th and K than that of western China; and the crust of orogenic belts is more enriched than that of platform regions. It can also be inferred that the crusts of eastern China and orogenic belts are much felsic than those of western China and platform regions, respectively, derived from the positive correlation between the heat production and SiO2 content of bulk crust. This deduction is consistent with the results derived from the crustal seismic velocity data in China. According to the facts of the lower seismic velocity of China than the average value of global crust, and the higher heat production of China continent compared with global crust composition models published by previous studies, it is deduced that the average composition models of global continent crust by Rudnick and Fountain (1995), Rudnick and Gao (2003), Weaver and Tarney (1984), Shaw et al. (1986), and Wedepohl (1995) overestimate the abundance of incompatible elements such as U, Th and K of continental crust. [source] An In Vitro Investigation of Pulmonary Alveolar Macrophage Cytotoxicity Introduced by Fibrous and Grainy Mineral DustsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2006DONG Faqin Abstract, In order to study the damage mechanism of mineral dusts on the pulmonary alveolar macrophage (AM), the changes in their death ratio, malandialdthyde (MDA) content and activities of lactate dehydrogenase (LDH) and superoxide dismutase (SOD) were measured, and the technique of cell culture in vitro was used to investigate the cytotoxicity of six mineral dusts (twelve crystal habits) from twelve mineral deposits. The results show that wollastonite and clinoptilolite have no AM cytotoxicity, while other fibrous and grainy mineral dusts damage pulmonary AM in various degrees. The cytotoxicity of fibrous mineral dusts was greater than that of the grainy ones, and the cytotoxicity of dusts was positively correlated with the active OH content in dusts, but not necessarily so with its SiO2 content. The high pH values produced by dust was unfavorable for the survival of cells and the dusts with low bio-resistance were safe for cells. The content of variable valence elements in dusts might influence their cytotoxicity and the surface charge of dusts was not a stable factor for their toxicity. It is demonstrated that the shape of mineral dusts was one of the factors affecting cytotoxicity, and that the cytotoxicity of mineral dusts depends mainly on their properties. [source] Permian High Ba-Sr Granitoids: Geochemistry, Age and Tectonic Implications of Erlangshan Pluton, Urad Zhongqi, Inner MongoliaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2009Hongling LUO Abstract: Erlangshan Pluton from Urad Zhongqi, central Inner Mongolia, is located in the middle segment of the northern margin of the North China Plate. The rocks consist mainly of diorites with gneissic structure. Petrochemical characteristics reveal that the diorites belong to metaluminous, high-potassium calc-alkaline series, with chemical signatures of I-type granites. They are characterized by low SiO2 contents (56.63%,58.53%) and A/CNK (0.90,0.96), high Al2O3 contents (17.30%,17.96%) and Na2O/K2O ratios (1.20,1.70), enrichment in large ion lithophile elements (LILE, e.g., Ba=556,915 ppm, Sr=463,595 ppm), and relative depletion in high field strength elements (HFSE, e.g., Nb, Ta, Ti) in primitive mantle-normalized spidergram, and right-declined rare earth element patterns with slightly negative Eu anomalies (,Eu=0.72,0.90). They have Sr/Y ratios (20,25) evidently less than Kebu Pluton (49,75) to its east. Sensitive high resolution ion micro-probe U-Pb zircon dating of the diorites has yielded an intrusive age of 270±8 Ma. This leads us to conclude that Erlangshan diorites were formed by mixing between the middle or lower crustal-derived magma and minor mantle-derived mafic magma, followed by fractional crystallization, which was trigged by crustal extension and fault activity in post-collisional setting. [source] | |||||||||||||