260,210 research outputs found
Novel sol–gel preparation of (PO)–(CaO)–(NaO)–(TiO) bioresorbable glasses (X = 0.05, 0.1, and 0.15)
No full textQuaternary phosphate-based glasses in the PO–CaO–NaO–TiO system with a fixed PO and CaO content of 40 and 25 mol% respectively have been successfully synthesised via sol–gel method and bulk, transparent samples were obtained. The structure, elemental proportion, and thermal properties of stabilised sol–gel glasses have been characterised using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), P nuclear magnetic resonance (P NMR), titanium K-edge X-ray absorption near-edge structure (XANES), fourier transform infrared (FTIR) spectroscopy, and differential thermal analysis (DTA). The XRD results confirmed the amorphous nature for all stabilized sol–gel derived glasses. The EDX result shows the relatively low loss of phosphorus during the sol–gel process and Ti K-edge XANES confirmed titanium in the glass structure is in mainly six-fold coordination environment. The P NMR and FTIR results revealed that the glass structure consist of mainly Q and Q phosphate units and the Ti cation was acting as a cross-linking between phosphate units. In addition DTA results confirmed a decrease in the glass transition and crystallisation temperature with increasing NaO content. Ion release studies also demonstrated a decrease in degradation rates with increasing TiO content therefore supporting the use of these glasses for biomedical applications that require a degree of control over glass degradation. These sol–gel glasses also offer the potential to incorporate proactive molecules for drug delivery application due to the low synthesis temperature employed
Melt densities in the CaO-FeO-Fe2O3-SiO2 system and the compositional dependence of the partial molar volume of ferric iron in silicate melts
No full textThe densities of 10 melts in the CaO-FeO-Fe2O3-SiO2 system were determined in equilibrium with air, in the temperature range of 1200 to 1550°C, using the double-bob Archimedean technique. Melt compositions range from 6 to 58 wt% SiO2, 14 to 76 wt% Fe2O3 and 10 to 46 wt% CaO. The ferric-ferrous ratios of glasses drop-quenched from loop fusion equilibration experiments were determined by 57Fe Mössbauer spectroscopy.
Melt densities range from 2.689 to 3.618 gm/cm3 with a mean standard deviation from replicate experiments of 0.15%. Least-squares regressions of molar volume versus molar composition have been performed and the root mean squared deviation shows that a linear combination of partial molar volumes for the oxide components (CaO, FeO, Fe2O3 and SiO2) cannot describe the data set within experimental error. Instead, the inclusion of excess terms in CaFe3+ and CaSi (product terms using the oxides) is required to yield a fit that describes the experimental data within error. The nonlinear compositional-dependence of the molar volumes of melts in this system can be explained by structural considerations of the roles of Ca and Fe3+.
The volume behavior of melts in this system is significantly different from that in the Na2O-FeO-Fe2O3-SiO2 system, consistent with the proposal that a proportion of Fe3+ in melts in the CaO-FeO-Fe2O3-SiO2 system is not tetrahedrally-coordinated by oxygen, which is supported by differences in 57Fe Mössbauer spectra of glasses. Specifically, this study confirms that the 57Fe Mössbauer spectra exhibit an area asymmetry and higher values of isomer shift of the ferric doublet that vary systematically with composition and temperature (this study; Dingwell and Virgo, 1987, 1988). These observations are consistent with a number of other lines of evidence (e.g., homogeneous redox equilibria, Dickenson and Hess, 1986; viscosity, Dingwell and Virgo, 1987,1988). Two species of ferric iron, varying in proportions with temperature, composition and redox state, are sufficient to describe the above observations.
The presence of more than one coordination geometry for Fe3+ in low pressure silicate melts has several implications for igneous petrogenesis. The possible effects on compressibility, the pressure dependence of the redox ratio, and redox enthalpy are briefly noted
Process engineering and development of post-combustion CO2 separation from fuels using limestone in CaO-looping cycle
No full textGlobal CO2 emissions produced by energy-related processes, mainly power plants, have increased rapidly in recent decades; and are widely accepted as the dominant contributor to the greenhouse gas (GHG) effect and consequent climate changes. Among countermeasures against the emissions, CO2 capture and storage (CCS) is receiving much attention. Capture of CO2 is the core step of CCS as it contributes around 75% of the overall cost, and may increase the production costs of electricity by over 50%. The reduction in capture costs is one of the most challenging issues in application of CCS to the energy industry. Using limestone in CaO-looping cycles is a promising capture technology to provide a cost-effective separation process to remove CO2 content from power plants operations. Limestone has the advantage of being relatively abundant and cheap, and that has already been widely used as a sorbent for sulphur capture. However, this technology suffers from a critical challenge caused by the decay in the sorbent capture capacity during cyclic carbonation/calcination, which results in the need for more sorbent make-up; hence a reduction in cost efficiency of the technology. The performance of sorbent influenced by several operating and reaction conditions. Therefore, much research involves investigation of influencing factors and different methods to reduce the sorbent deactivation. Cont/d
CaO-SiO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub>-MgO phase diagram
No full textCaO-SiO2-Al2O3-MgO phase diagram, and the MgO/(MgO+Al2O3) is 40wt.%.</p
CaO-SiO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub>-MgO-FeO phase diagram
No full textCaO-SiO2-Al2O3-MgO-FeO phase diagram is from FactSage8.0.</p
Storie cinesi per l’infanzia globale. Uno sguardo al fenomeno Cao Wenxuan
No full textMy contribution aims to provide an overview of the "Cao Wenxuan phenomenon” and its implications for the building of a “China narrative”. First, I will attempt to pinpoint the ideological and intellectual background, as well as the nature of China's editorial policies, which drove the international promotion of the works of the celebrated Chinese author of children's and young adult literature. To do so, I will outline the dynamics of artistic and cultural promotion that led Cao to be identified as the "spokesman" of national children's literature and the ideal candidate for export. I will also briefly touch upon the publishing mechanisms that led to the translation and publication of some of his works, as well as their consecration by the Andersen Prize awarded to Cao in 2016. Secondly - and more importantly -, in order to identity the characteristics and relevance of Cao’s works against the background of China's self-representation strategies addressed to a global audience, I will focus on the image(s) of China that his translated works conjure with regard to the Chinese history, culture, society, and value systems (e.g. views of gender roles, family relationships, institutional education, individual character development). I will specifically investigate the overt and covert ideological implications of the dissemination of Cao’s works in translation and, ultimately, I will seek to assess in which ways and to which extent the national image that Cao’s works convey is embedded in the discourse of self-narration promoted by the Chinese officialdom
Thermochemistry of Heterogeneous CaO–P₂O₅–SiO₂–FeₓO and CaO–P₂O₅–CaF₂–FeₓO Slags
No full textIn steelmaking processes, because of environmental requirements and health considerations, there is a strong incentive to reduce slag volume. The key to meet this requirement is the better understanding of phosphorus removal, which relies on the knowledge of the thermodynamic properties of slags and fluxes used for dephosphorization. In this study, the liquidus compositions of the four-phase assemblages in the quaternary systems of CaO–P₂O₅–SiO₂–FeₓO and CaO–P₂O₅–CaF₂–FeₓO were determined by employing electron probe microanalysis. Measurements were also made on the FeₓO activities by employing an electrochemical technique involving stabilized zirconia electrolyte
Effect of catalyst concentration and simulation of precipitation processes on liquid-phase catalytic oxidation of p-xylene to terephthalic acid
No full textThe influence of catalyst concentration, i.e. cobalt naphthenate, on product distribution
and kinetic constants of the lumped kinetic scheme of liquid-phase p-xylene oxidation
proposed in previous works (cf. Cao et al., 1994a, b) is investigated. The experiments involving
various levels of catalyst concentrations (from 1.67 to 33.3 × 10-4 mol/kgi) are conducted in an
isothermal semi-batch oxidation reactor where both the gas and the liquid phase are well
mixed. The dependence of the kinetic constants of the lumped kinetic scheme on the catalyst
concentration is examined. In addition, the interaction between the chemical reactions of the
lumped kinetic scheme for p-xylene oxidation to terephthalic acid and the precipitation kinetics
of both 4-carboxybenzaldehyde and terephthalic acid is analyzed theoretically. A semi-batch
gas-liquid reactor model which incorporates the description of the above phenomena allows us
to identify their interplay
Functional materials for medical and biological purposes on the system CaO-CaF₂-P₂O₅-H₂O and additives
No full textThe system of CaO-P₂O₅ has been studied, he polymorphism of Ca₃(PO₄)₂ has been verified, he position of binary eutectics and the melting points in them on he Ca₃(PO₄)₂-Ca₄P₂O₉ segment have been determined. A diagram of the state of the CaO-P₂O5 system is constructed. The experimental verification of the calculated data by the high-temperature microscopy method in sity is performed. The regions of primary crystallization of phases in the system Ca₃(PO₄)₂-CaCO₃-Ca(OH)₂-H₂O are refined. The subsolidus structure of the systems CaO-CaF₂-P₂O₅-H₂O and CaO-CaF₂-P₂O₅-H₂O has been studied. The areas promising for the synthesis of materials based on CaO-CaF₂-P₂O₅-H₂O system and additives for the reconstruction of structural defects of the skeleton are established
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