Low Silicate Research Articles

Optical and spectroscopic investigation on Calcium Borotellurite glass system

In this work, the glass formation in Calcium Borotellurite (CBTx) system and their optical properties were studied. Six glass samples were prepared by melt-quenching technique and the samples obtained are transparent, lightly yellowish, without any visible crystallites. The results showed that TeO2 addition increases the density, the electronic polarizability and, consequently, the refractive index. The increase of electronic polarizability and optical basicity suggest that TeO2 addition increases the non-bridging oxygen (NBO) concentration. The increase of TeO2 shifts the band edge to longer wavelength owing to increase in non-bridging oxygen ions, resulting in a linear decrease of optical energy gap. The addition of TeO2 increases the temperature coefficient of the optical path length (dS/dT) in room temperature, which are comparable to phosphate and lower than Low Silica Calcium Alumino Silicate (LSCAS) glasses. The values of dS/dT present an increase as a function of temperature for all the samples measured. The results suggest that CBTx is a good candidate for rare-earth doping and several optical applications.

The fertile physics of chemical gardens

Many a child has enjoyed watching the gardens grow; many a physicist has puzzled over the transformation of self-organized, nonequilibrium patterns into permanent structures.

The antioxidant properties of Ce-containing bioactive glass nanoparticles explained by Molecular Dynamics simulations

AbstractMolecular dynamics simulations of two glass nanoparticles with composition 25Na2O·25CaO 50SiO2 mol% (Ce-K NP) and 46.1SiO2·24.4Na2O·26.9CaO· 2.6P2O5 mol.% (Ce-BG NP) doped with 3.6 mol% of CeO2 have been carried out in order to explain the enhanced antioxidant properties of the former glass with respect to the latter.The present models show that the different catalase mimetic activity of the two NPs is related to the Ce3+/Ce4+ ratio exposed at their surface. In fact, this ratio is about 3.5 and 13 in the bulk and at the surface of the Ce-BG NP, and 1.0 and 2.1 in the bulk and at the surface of the Ce-K NPs, respectively. Since both oxidation states are necessary for the catalysis of the dismutation reaction of hydrogen peroxides, NPs with a very high Ce3+/Ce4+ ratio possess poorer antioxidant properties.Moreover, our simulations reveal that the already low silicate connectivity found in the bulk glasses examined here is further reduced on the nanoparticle surface, whereas the Na+/Ca2+ ratio rapidly increases. Sodium, calcium and cerium sites in proximity of the surface are found to be under-coordinated, prone to quickly react with water present in physiological environments, thus accelerating the glass biodegradation

Photoluminescence properties of Eu3+-doped low cost zinc silicate based glass ceramics

In this paper, Zn2SiO4:xEu3+ phosphors were synthesized with different concentrations of Eu3+ ions (x=1, 3 and 5wt.%) by using waste bottle glasses as silicate source. The structure, morphology, and luminescent properties of the phosphors were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and photoluminescence (PL) spectroscopy. The XRD analysis revealed that addition of dopant increased the crystallinity of the samples, and then were decreased dramatically when the dopant concentration further to 5wt.%. The FESEM images showed the samples have irregular in shapes while their emission and excitation peak of Zn2SiO4:xEu3+ phosphor was observed at 600 and 400nm, respectively.

Microwave carbothermic reduction roasting of a low grade nickeliferous silicate laterite ore

The known resources of nickel sulphide ores are quickly diminishing and in order to satisfy future nickel demands, nickel laterite deposits are being investigated as an alternative. Currently, expensive leaching and smelting processes are used to process the nickel laterite ores. The objective of the present research was to produce a high grade nickel concentrate via microwave carbothermic reduction roasting followed by magnetic separation. A thermodynamic model was developed for the roasting process in order to determine the optimum experimental conditions. The experimental variables investigated were: microwave energy and argon shrouding for the reduction tests and the magnetic field strength for the concentration stage. The behaviours of nickel and cobalt were studied in the reduction and magnetic separation processes. By optimizing the reducing and magnetic separation conditions, a high grade concentrate containing 9.2% nickel with a nickel recovery of 88.8% was achieved.

Phytoplankton and pigment patterns across frontal zones in the Atlantic sector of the Southern Ocean

Phytoplankton distribution and concentrations of macronutrients and iron were studied in the Polar Frontal Zone (PFZ) and the eastern Weddell Gyre of the Southern Ocean, during austral autumn. HPLC analysis of algal pigments was combined with microscopy observations to assess algal distribution. Patterns of algal distribution were dictated by the frontal systems. Travelling from north to south, four distinctively different algal communities were observed, the composition of which could be explained by variations in nutrients, light climate and grazing pressure. North of the PFZ, low silicate levels (<3μM) were limiting diatom growth, and the algal community was dominated by prasinophytes. Silicate concentrations increased over the PFZ, which coincided with the dominance of diatoms. South of the PFZ, the open waters of the Weddell Gyre are characterised as a high-nutrient low-chlorophyll area. Low iron concentrations (<0.4nM on average) supported an algal community that was dominated by smaller size algae (<20μm). Deep wind-mixed layers (>100m depth) together with low incident irradiance in autumn were likely limiting algal growth. At the Marginal Ice Zone (MIZ), the phytoplankton community consisted mainly of low numbers of flagellates (Chlorophyceae and haptophytes) and high numbers of microzooplankton, indicating phytoplankton control by grazing. The phytoplankton distribution patterns presented here and the relation with potential growth-controlling factors provides more insight in the mechanisms that control carbon fluxes from the atmosphere into the ocean interior.

Proton tunneling in low dimensional cesium silicate LDS-1.

In low dimensional cesium silicate LDS-1 (monoclinic phase of CsHSi2O5), anomalous infrared absorption bands observed at 93, 155, 1210, and 1220 cm(-1) are assigned to the vibrational mode of protons, which contribute to the strong hydrogen bonding between terminal oxygen atoms of silicate chain (O-O distance = 2.45 Å). The integrated absorbance (oscillator strength) for those modes is drastically enhanced at low temperatures. The analysis of integrated absorbance employing two different anharmonic double-minimum potentials makes clear that proton tunneling through the potential barrier yields an energy splitting of the ground state. The absorption bands at 93 and 155 cm(-1), which correspond to the different vibrational modes of protons, are attributed to the optical transition between the splitting levels (excitation from the ground state (n = 0) to the first excited state (n = 1)). Moreover, the absorption bands at 1210 and 1220 cm(-1) are identified as the optical transition from the ground state (n = 0) to the third excited state (n = 3). Weak Coulomb interactions in between the adjacent protons generate two types of vibrational modes: symmetric mode (93 and 1210 cm(-1)) and asymmetric mode (155 and 1220 cm(-1)). The broad absorption at 100-600 cm(-1) reveals an emergence of collective mode due to the vibration of silicate chain coupled not only with the local oscillation of Cs(+) but also with the proton oscillation relevant to the second excited state (n = 2).

Combustion performance and sodium transformation of high-sodium ZhunDong coal during chemical looping combustion with hematite as oxygen carrier

Chemical looping combustion (CLC) of ZhunDong coal (ZD) with hematite as oxygen carrier (OC) is an appropriate solution of how to utilize abundant ZD without severe slagging and fouling problems. At first, the combustion performance of ZD was compared to that of other three types of Chinese coals. Due to the catalytic effect of sodium in ZD, carbon capture efficiency, carbon conversion efficiency, CO2 concentration of fuel reactor and CO2 capture efficiency were all evidently higher than the ones for other types of coals at the same temperature. In addition, no NO2 was detected, and N2O and NO were the sole nitrogen contaminations in CLC of ZD. The high volatile content together with carbon gasification rate for ZD was conducive to the control of nitrogen contamination release. At last, 10h of continuous operation with ZD has been accomplished to evaluate the characteristic of hematite OC and sodium formation in hematite or fly ash. Hematite showed high reactivity in the continuous operation and the porous properties of 5h-hematite was best. High sodium content is the most prominent feature of ZD. Although there are also a large amount of other phases in ZD, due to the better catalytic effect, sodium is inferred to be the main factor accelerating the carbon conversion and improving the porous properties of OC. Moreover, it was found that there was a high melting point sodium aluminosilicate, Na2O·Al2O3·6SiO2 instead of low melting point sodium silicates formed in the CLC fly ash, mitigating the severe slagging and fouling problems.

Solubilização de potássio em misturas de verdete e calcário tratadas termoquimicamente

O Brasil dispõe de reservas de rochas silicáticas potássicas de baixa solubilidade, sendo necessário o desenvolvimento de alternativas de beneficiamento capazes de aumentar sua solubilidade, para o suprimento da demanda desse nutriente na agricultura. Este estudo objetivou a obtenção de novas rotas tecnológicas para a produção de fontes alternativas de potássio, a partir do verdete. Prepararam-se misturas de verdete com calcário, para as quais foram realizados testes de calcinação e solubilização alcalina. O processo de calcinação seguido de resfriamento à temperatura ambiente proporcionou maior disponibilidade de potássio que os outros métodos empregados. Porém, o aumento na proporção de calcário, em relação ao verdete, ocasionou diminuição na solubilidade do potássio. O tratamento calcário:verdete, na proporção 0:100, calcinado por uma hora a 800ºC e tratado com NH4OH, e na proporção 25:75, submetida à calcinação, liberam, proporcionalmente, maior quantidade de potássio que as misturas não calcinadas.

Dielectric, thermal and mechanical properties of zirconium silicate reinforced high density polyethylene composites for antenna applications.

A low cost and low dielectric loss zirconium silicate (ZrSiO4) reinforced HDPE (high-density polyethylene) composite has been developed for antenna applications. The 0-3 type composite is prepared by dispersing ZrSiO4 fillers for various volume fractions (0.1 to 0.5) in the HDPE matrix by the melt mixing process. The composite shows good microwave dielectric properties with a relative permittivity of 5.6 and a dielectric loss of 0.003 at 5 GHz at the maximum filler loading of 0.5 volume fraction. The composite exhibits low water absorption, excellent thermal and mechanical properties. It shows a water absorption of 0.03 wt%, a coefficient of thermal expansion of 70 ppm per °C and a room temperature thermal conductivity of 2.4 W mK(-1). The composite shows a tensile strength of 22 MPa and a microhardness of 13.9 kg mm(-2) for the filler loading of 0.5 volume fraction. The HDPE-ZrSiO4 composites show good dielectric, thermal and mechanical properties suitable for microwave soft substrate applications. A microstrip patch antenna is designed and fabricated using the HDPE-0.5 volume fraction ZrSiO4 substrate and the antenna parameters are investigated.

硫化製錬における非鉄金属とNaのマット－スラグ間の分配

Distribution behaviors of non-ferrous metals of copper, lead, nickel, cobalt and sodium between matte and slag were studied using slags with a composition similar to industrial copper matte smelting of low grade secondary materials. The distribution ratios of copper, lead and nickel increased with the increasing copper concentration in matte, i.e., matte grade. In contrast, those of cobalt and sodium decreased with the increasing matte grade. Two interesting effects of sodium were found out in the present study. One is to reduce copper, lead and nickel concentration in slag; and the other is suppression of lead evaporation from matte. Both effects results in the increasing distribution ratios of copper, nickel and lead; however, sodium has no influence on the distribution ratio of cobalt. The effect of silicate degree, SD, of slags on the concentration of non-ferrous metals in slag was also found out. Distribution ratios of copper, nickel, lead and cobalt in present study, in which the SDs of slags were comparatively low (0.7 ～1.3), were 2 ～4 times higher than those in the previous study using silica-saturated iron silicate slag (SD ≃ 1.5). Variation in copper and nickel concentration in slag with matte grade was also dependent on the SD. These decreased with the increasing matte grade for the slag with low silicate degree. In conclusion, we proposed that the efficient recovery of rare metals, such as nickel and cobalt, in the copper matte smelting of low grade secondary materials is expected when the influences of sodium in secondary materials and a slag with low silicate degree are effectively utilized.

Co-firing of pressed sugar beet pulp with coal in a laboratory-scale fluidised bed combustor

Relatively cheap, poor quality, unprepared biomass materials can be difficult to burn efficiently on a large commercial scale because of their variable composition, relatively low calorific values and high moisture contents. Consequently it is often necessary to co-fire these materials with a hydrocarbon support fuel to ensure stable and efficient combustion. Fluidised bed combustion (FBC) is a promising method for burning mixtures of fuels with widely differing individual characteristics although there is a need for further information on the “optimum” conditions for efficient operation as well as on the proportions of support fuel which should be used in particular applications. This paper is therefore concerned with co-firing of coal with pressed sugar beet pulp, (a solid biomass with an average moisture content of 71%), in a lab scale (<25kW net thermal input) fluidised bed combustor.The project was undertaken in collaboration with British Sugar plc. who operate a large coal-fired fluidised bed, with a nominal thermal rating of 40MW, to generate hot combustion gases for use in subsequent drying applications. The combustion characteristics of different coal and pressed pulp mixtures were investigated over a wide range of operating conditions. For stable combustion the maximum proportion of pulp by mass in the blended fuel was limited to 50%. However under these co-firing conditions a fixed bed temperature can be achieved with 20% lower fluidising air (when compared with coal alone) since evaporation of the moisture in the pressed pulp provides additional cooling of the bed. This reduction in excess air will be beneficial for the output of the full scale plant at British Sugar since at present the flow rate of the fluidising air and hence the amount of coal which can be burnt is limited by high pressure drops in the bed air distributor system. The pressed pulp has relatively low nitrogen levels and hence a further benefit of co-firing is that NOx emissions are reduced by about 25%.Agglomeration of the bed can be a problem when co-firing biomass because of the formation of “sticky” low melting point alkali metal silicate eutectics which result in subsequent adhesion of the ash and sand particles. Consequently, longer term co-firing tests were undertaken with a 50/50 blended fuel by mass. Problems of bed agglomeration were not observed over the duration of these tests and moreover, scanning electron microscopy (SEM) studies indicated that the levels of alkali metals in the ash were relatively low.

Cell and Column Flotation Studies of a Low Grade Siliceous Mine Waste Limestone Sample for Cement Making

Cell and Column Flotation Studies of a Low Grade Siliceous Mine Waste Limestone Sample for Cement Making

Effects of silicon-limitation on growth and morphology of Triparma laevis NIES-2565 (Parmales, Heterokontophyta).

The order Parmales (Heterokontophyta) is a group of small-sized unicellular marine phytoplankton, which is distributed widely from tropical to polar waters. The cells of Parmales are surrounded by a distinctive cell wall, which consists of several siliceous plates fitting edge to edge. Phylogenetic and morphological analyses suggest that Parmales is one of the key organisms for elucidating the evolutionary origin of Bacillariophyceae (diatoms), the most successful heterokontophyta. The effects of silicon-limitation on growth and morphogenesis of plates were studied using a strain of Triparma laevis NIES-2565, which was cultured for the first time in artificial sea water. The cells of T. laevis were surrounded by eight plates when grown with sufficient silicon. However, plate formation became incomplete when cells were cultured in a medium containing low silicate (ca. <10 µM). Cells finally lost almost all plates in a medium containing silicate concentrations lower than ca. 1 µM. However, silicon-limitation did not affect growth rate; cells continued to divide without changing their growth rate, even after all plates were lost. Loss of plates was reversible; when cells without plates were transferred to a medium containing sufficient silicate, regeneration of shield and ventral plates was followed by the formation of girdle and triradiate plates. The results indicate that the response to silicon-limitation of T. laevis is different from that of diatoms, where cell division becomes inhibited under such conditions.

The effect of glass powder on the microstructure of ultra high performance concrete

Glass powder prepared of various types of recycled bottles was used in ultra-high performance concrete (UHPC). Experimental investigation of glass powder as complete replacement for quartz powder and silica fume showed that UHPC with improved micro-structural and compressive strength properties can be prepared. Glass powder milled to micro-scale undergoes low pozzolanic reaction and acts as catalyst accelerating the dissolution of clinker phases and forms low basicity calcium silicate hydrate (C–S–H). These reactions give positive effect on mechanical and microstructural properties of UHPC. Microstructural investigation was made by mercury intrusion porosimetry (MIP), X-ray diffraction (XRD) analysis and by 29Si MAS NMR analysis. Experimental results revealed that additional compressive strength of 40MPa can be gained with combination of glass powder and silica fume.

Using calcium silicate to regulate the physicochemical and biological properties when using β-tricalcium phosphate as bone cement

β-Tricalcium phosphate (β-TCP) is an osteoconductive material. For this research we have combined it with a low degradation calcium silicate (CS) to enhance its bioactive and osteostimulative properties. To check its effectiveness, a series of β-TCP/CS composites with different ratios were prepared to make new bioactive and biodegradable biocomposites for bone repair. Regarding the formation of bone-like apatite, the diametral tensile strength as well as the ion release and weight loss of composites were compared both before and after immersions in simulated body fluid (SBF). In addition, we also examined the behavior of human dental pulp cells (hDPCs) cultured on β-TCP/CS composites. The results show that the apatite deposition ability of the β-TCP/CS composites improves as the CS content is increased. For composites with more than a 60% CS content, the samples become completely covered by a dense bone-like apatite layer. At the end of the immersion period, weight losses of 24%, 32%, 34%, 38%, 41%, and 45% were observed for the composites containing 0%, 20%, 40%, 80%, 80% and 100% β-TCP cements, respectively. In addition, the antibacterial activity of CS/β-TCP composite improves as the CS-content is increased. In vitro cell experiments show that the CS-rich composites promote human dental pulp cell (hDPC) proliferation and differentiation. However, when the CS quantity in the composite is less than 60%, the quantity of cells and osteogenesis protein of hDPCs is stimulated by Si released from the β-TCP/CS composites. The degradation of β-TCP and the osteogenesis of CS give strong reason to believe that these calcium-based composite cements will prove to be effective bone repair materials.

Characterization of Ashes from Different Wood Parts of Norway Spruce Tree

Woody biomass from the forest sector is an abundant resource for renewable energy generation. Conventional woody biomass materials such as timber and stem are normally high quality solid fuels for combustion applications in terms of ash related operational problems. Recently, new raw woody materials such as forest residue are gaining interests for energy production purpose. Forest residue is the remaining fraction after harvest and outtake of the wood timber, including tree tops, branches and barks. Compared to conventional woody biomass, the forest residue has a wide variation of ash content and concentration of ash forming matters. The aim of this work was to characterize and investigate different parts from Norway spruce trees regarding ash content, ash composition and ash melting and slagging behaviors. Different parts from spruce tree were studied in present work including stem wood, bark, branch and twigs. The ash content and ash melting temperature of the four fuel samples were measured through following standard procedures. Concentrations of main ash forming elements were analyzed by an inductively coupled plasma optical emission spectroscopy (ICP-OES). The ashes from stem wood, bark and twigs were further investigated by a scanning electron microscopy equipped with energy dispersive X-Ray analysis (SEM- EDX) and X-Ray diffractometry (XRD). The results showed that the branches and twigs contain higher contents of ash forming matters than that of the stem wood. Chemical compositions of ashes from four parts of the spruce tree are dominated by Ca, K, and Si. The K and Na contents in the branches and twigs are significantly higher than that of stem wood and bark, indicating high tendency of ash melting and slagging. The melting points of ashes from branch and twigs were 100-200 °C lower than those of the ashes from stem wood and bark, respectively. SEM-EDX and XRD analysis, melting of ashes from branch and twigs are mainly attributed to formation and fusion of low temperature melting alkali silicates.

Investigation of additives for preventing ash fouling and sintering during barley straw combustion

Formation of potassium chloride reduces ash sintering temperature and causes fouling deposits in biomass combustion applications. In the present work, the capacity of two mineral additives zeolite 24A and kaolin to capture KCl were investigated. A series of thermogravimetric experiments were carried out to measure fractions of KCl retained in the two additives as function of reaction temperature and heating time. The residues from additive-KCl mixtures after heating treatment were analyzed by X-ray diffractometry (XRD). When heated at 900 °C for 1 h, the overall KCl capturing efficiencies of the two additives were 60% and 45% for zeolite 24A and kaolin respectively, which slightly decreased to 50% and 43% as the heating time increased to 12 h. At 1000 °C, the fractions of KCl captured by zeolite 24A and kaolin significantly decreased from 50% and 40% to 26% and 17%, as the KCl-additive mixtures were heated for 1 and 12 h, respectively. The decrease in of the overall KCl capturing efficiencies is mainly attributed to reduction of surface areas and chemically active compounds of the two additives with increasing temperature and heating time. The XRD analysis results showed that both zeolite 24A and kaolin can react with KCl to form different potassium aluminium silicates. It indicates that chemical reactions play an important role in the overall capturing process. The effects of zeolite 24A and kaolin on sintering behaviors of the barley straw ash were also investigated. The residues from sintering tests were analyzed by a combination of X-Ray diffractometry (XRD) and scanning electron microscopy equipped with energy dispersive X-Ray analysis (SEM-EDX). The barley straw ash melted intensively at elevated temperatures. Together with XRD analysis, the SEM-EDX analysis results revealed that severe melting of the barley straw ash was due to formation and fusion of low temperature melting potassium silicates. Addition of kaolin and zeolite 24A significantly reduced the sintering tendency of the barley straw ash. Upon additive addition, high temperature melting potassium aluminium silicates formed in the barley straw ash as revealed by XRD and SEM-EDX analyses. Formation and presence of the refractory potassium aluminium silicates partly explain the improved sintering behaviors of the ash-additive mixtures.

Regulation of physicochemical properties, osteogenesis activity, and fibroblast growth factor-2 release ability of β-tricalcium phosphate for bone cement by calcium silicate

β-Tricalcium phosphate (β-TCP) is an osteoconductive material. For this research we have combined it with a low degradation calcium silicate (CS) to enhance its bioactive and osteostimulative properties. To check its effectiveness, a series of β-TCP/CS composites with different ratios were prepared to make new bioactive and biodegradable biocomposites for bone repair. Formation of bone-like apatite, the diametral tensile strength, and weight loss of composites were considered before and after immersion in simulated body fluid (SBF). In addition, we also examined the effects of fibroblast growth factor-2 (FGF-2) released from β-TCP/CS composites and in vitro human dental pulp cell (hDPC) and studied its behavior. The results showed that the apatite deposition ability of the β-TCP/CS composites was enhanced as the CS content was increased. For composites with more than 50% CS contents, the samples were completely covered by a dense bone-like apatite layer. At the end of the immersion point, weight losses of 19%, 24%, 33%, 42%, and 51% were observed for the composites containing 0%, 30%, 50%, 70% and 100% β-TCP cements, respectively. In vitro cell experiments show that the CS-rich composites promote human dental pulp cell (hDPC) proliferation and differentiation. However, when the CS quantity in the composite is less than 70%, the amount of cells and osteogenesis protein of hDPCs was stimulated by FGF-2 released from β-TCP/CS composites. The combination of FGF-2 in degradation of β-TCP and osteogenesis of CS gives a strong reason to believe that these calcium-based composite cements may prove to be promising bone repair materials.

Influence of Si species on intergrowth and anisotropic crystal growth of silicalite-1

Silicalite-1 crystals were hydrothermally synthesized from silica gels prepared under different conditions. The influence of the state of Si species in the silica gels and the concentrations of silicate ions and a template agent in the reaction sols on crystal growth of silicalite-1 was examined. The use of silica gels with a high degree of condensation of Si species resulted in the intergrowth of silicalite-1 crystals, whereas a low degree of condensation of Si species led to coffin-shaped crystals. Thus, the degree of condensation of Si species had significant influence on the intergrowth of silicalite-1 crystals. Moreover, at a low silicate concentration, silicalite-1 crystals elongated along the c-axis were obtained. With increasing silicate concentration in the reaction sols, the aspect ratio of silicalite-1 decreased. Furthermore, with decreasing the amount of N(C3H7) 4 + used as a template agent, the silicalite-1 crystals became larger isotropically. Thus, the growth direction of silicalite-1 crystals was dependent on silicate ion concentration in the reaction sols, but not on N(C3H7) 4 + concentration.