38,423 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
Phase Diagram Study for the PbO-ZnO-CaO-SiO2-"Fe2O3" System in Air with CaO/SiO2 in 1.1 and PbO/(CaO+SiO2) in 2.4 Weight Ratios
No full textAn experimental study on the phase equilibrium and the liquidus isotherms for the PbO-ZnO-CaO-SiO2-"Fe2O3" system with CaO/SiO2 in 1.1 and PbO/(CaO+SiO2) in 2.4 weight ratios, respectively, was carried out in the temperature range 1100-1300ºC (1373-1573 K). High temperature phases were determined by the equilibrium-quenching method. Results are presented in the form of pseudo-ternary sections "Fe2O3"-ZnO-(PbO+CaO+SiO2). X-Ray diffraction (XRD) and SEM-EDS results showed that the phase equilibria in this system are dominated by the high melting temperature spinel and zincite phases. It was observed that if the system is at a temperature below 1300ºC and the total (Fe2O3 + ZnO) is greater than 20 wt%, spinel and/or zincite will be present in the slag system. As an application of the phase diagram, the liquid phase compositions below the liquidus surface were estimated, then their viscosities were calculated using FACTSage software.</div
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
Phase equilibria in the TiO2 rich part of the TiO2-CaO-SiO2-10wt.% Al2O3 system at 1773 K and 1873 K
No full textThe phase equilibria of the TiO2-CaO-SiO2-10wt.%Al2O3 system at the TiO2 rich corner were investigated experimentally by the quenching method with subsequent electron probe microanalysis. The investigations were carried out at 1773 K and 1873K. The isothermal section at 1773 K contains one liquidus region and two solid-liquid coexistence regions, liquid-CaTiO3 and liquid-TiO2. And the isotherms of the CaTiO3 primary phase field and TiO2 primary phase field at 1773 K have been found in the TiO2 rich part. At 1873K, the CaTiO3 primary phase field and its isotherm have been determined. Based on the obtained fundamental data, the phase diagram has been established in the TiO2 rich corner of the TiO2-CaO-SiO2-10wt.%Al2O3 system at 1773 K and 1873 K. From the obtained phase diagram, it can be found that the addition of 10% Al2O3 into TiO2-CaO-SiO2 system enlarges the range of the low-liquidus-temperature slags. The phase equilibria data can provide the foundation for the further full investigations on the crystallization and upgradation of the Ti-bearing slag from direct reduction-smelting processes of vanadium-titanium magnetites. (C) 2016 Elsevier B.V. All rights reserved
Kapsa (Rigida) Cao & Zhang
No full textKey to males of Kapsa (Rigida) Cao & Zhang sgen. n. 1. Anal tube appendage rudimentary, small, not hooked at apex...................... K. apicispina Yang & Zhang sp. nov. - Anal tube appendage well developed, hooked apically (Figs 5 b, 6 b, 8 b, 9 b, 10 e, 11 c, 12 c, 13 c)........................ 2 2. Anal tube appendage curved cephalad in larteral view................................ K. maculata Sohi & Mann, 1992 - Anal tube appendage curved caudad in lateral view (Figs 5 b, 6 b, 8 b, 9 b, 10 e, 11 c, 12 c, 13 c)........................... 3 3. Aedeagus without ventral process near base of shaft (Figs 5 h, 6g, 11 i, 13g)........................................ 4 - Aedeagus with unpaired ventral process near base of shaft (Figs 8 h, 9g, 10 j, 12 i)................................... 7 4. Aedeagal shaft with ventral process near apex (Figs 6 g, 13g)................................................... 5 - Aedeagal shaft without process (Figs 5 h, 11 i)............................................................... 6 5. Paramere forked apically, with apical and basal branch, aedeagal shaft with small thornlike process ventro-apically (Fig. 6 e, g)...................................................................... K. aculeiformis Cao & Zhang sp. nov. - Paramere bifurcated apically, with dorsal and ventral branch, aedeagal shaft with large serrated protrusion ventro-medially (Fig. 13 e, g)................................................................ K. serrata Cao & Zhang sp. nov. 6. Apex of paramere straight, aedeagal shaft expanded in lateral view (Fig. 11 f, i)......... K. imminuta Yang & Zhang sp. nov. - Apex of paramere sinuate, aedeagal shaft not expanded in lateral view (Figs 5 e, f, h).......... K. alba Dworakowska, 1981 7. Ventral process not extended to midlength of aedeagal shaft (Figs 8 h, 9g)......................................... 8 - Ventral process surpassing midlength of aedeagal shaft (Figs 10 j, 12 i)........................................... 10 8. Paramere footlike apically, heel expanded, ventral processes of aedeagus rounded in lateral view (Fig. 9 e, g)...................................................................................... K. explanata Cao & Zhang sp. nov. - Paramere with second extension apically, ventral processes of aedeagus pointed in lateral view (Fig. 8 h, i)............... 9 9. Aedeagal shaft expanded in lateral view, almost straight............................... K. minuta Dworakowska, 1994 - Aedeagal shaft not expanded in lateral view, obviously curved ventrad (Fig. 8 h)........... K. brevis Cao & Zhang sp. nov. 10. Ventral process of aedeagus with broadened and concave apex in caudal view....... K. borealis Dworakowska & Sohi, 1978 - Ventral process of aedeagus pointed apically in caudal view (Figs 10 k, 12 j)....................................... 11 11. Paramere forked apically (Fig. 10 h).............................................. K. furcata Cao & Zhang sp. nov. - Paramere not forked apically (Fig. 12 g)................................................................... 12 12. Aedeagus with base of ventral process broader than that of shaft in lateral view (Fig. 12 i).................................................................................................. K. megaprocessa Cao & Zhang sp. nov. - Aedeagus with base of ventral process slightly narrower than that of shaft in lateral view......................................................................................... K. simlensis Dworakowska, Nagaich & Singh, 1978Published as part of Yang, Meixia, Cao, Yanghui & Zhang, Yalin, 2013, Taxonomic study of the genus Kapsa Dworakowska with a new subgenus, and new combinations and records for Tautoneura Anufriev (Hemiptera: Cicadellidae: Typhlocybinae: Erythroneurini), pp. 117-142 in Zootaxa 3630 (1) on page 128, DOI: 10.11646/zootaxa.3630.1.4, http://zenodo.org/record/22287
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
Performance of Multihop Wireless Links over Generalized-K Fading Channels
No full textThe performance of multihop links is studied in this contribution by both analysis and simulations, when communicating over Generalized-K (KG ) fading channels. The performance metrics considered include symbol error rate (SER), outage probability, level crossing rate (LCR) and average outage duration (AOD). First, the expressions for both the SER and outage probability are derived by approximating the probability density function (PDF) of the end-to-end signal-to-noise ratio (SNR) using an equivalent end-to-end PDF. We show that this equivalent end-to-end PDF is accurate for analyzing the outage probability. Then, the second-order statistics of LCR and AOD of multihop links are analyzed. Finally, the performance of multihop links is investigated either by simulations or by evaluation of the expressions derived. Our performance results show that the analytical expressions obtained can be well justified by the simulation results. The studies show that the KG channel model as well as the expressions derived in this paper are highly efficient for predicting the various types of performance metrics and statistics for design of multihop communication links
Phase equilibria of SiO2–Ce2O3–CaO-25 wt %Al2O3 system at 1673 K–1773 K
No full textThe utilization of rare earth resources, especially secondary resources (e.g., RE-oxide system slag), has been limited by the lack of thermodynamic information. In order to supplement and improve the thermodynamic data related to rare earth, the equilibrium experiments of SiO2–Ce2O3–CaO-25 wt %Al2O3 system phase diagram was carried out at 1673 K and 1773 K by the high-temperature isothermal equilibration/quenching technique in current paper. The composition of seven phase regions were determined by FE-SEM, XRD, EPMA and XRF analysis on the samples obtained by high temperature equilibrium technology at 1673 K and 1773 K, including the primary crystal regions of three compounds (C2AS, 2CaO·SiO2, CaO·2Ce2O3·3SiO2) and three three-phase coexistence regions (L + C2AS + 2CaO·SiO2, L + C2AS + CaO·2Ce2O3·3SiO2, L + CaO·2Ce2O3·3SiO2+CeAl11O18) and a liquid region. The phase relations and isotherms of SiO2–Ce2O3–CaO-25 wt %Al2O3 system obtained in current work are beneficial to the recycling of rare earth resources containing cerium
Effect of CaO content in raw material on the mineral composition of ferric-rich sulfoaluminate clinker
No full textFerric-rich calcium sulfoaluminate (FR-CSA) cement is an eco-friendly cement. Fe2O3 exists in different minerals of FR-CSA clinker, e.g., Ca4Al2Fe2O10 (C4AF), Ca2Fe2O5 (C2F), and Ca4Al6-2xFe2xSO16 (C4A3-xFxS-). The mineral composition depends on the chemical composition of the raw materials and significantly determines the reactivity of FR-CSA cement. To optimize the phase composition of the FR-CSA clinker, chemical reagent raw mixtures with different amounts of CaO were used to prepare the FR-CSA clinker. X-ray diffraction (XRD) analysis, Rietveld quantitative phase analysis (RQPA), Fourier Transform Infrared spectroscopy (FT-IR), and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) were used to identify the mineralogical conditions of the FR-CSA clinker. The results indicated that the amounts of CaO in raw materials greatly affected the iron-bearing phase formation in the FR-CSA clinker. With decreasing CaO content involved in calcination reaction, the amounts of Fe2O3 incorporated in C4A3-xFxS- increased up to 17.72 wt% (where x = 0.36). The findings make it possible to optimize the mineral composition of the FR-CSA clinker by changing the CaO content in raw materials. Furthermore, low CaO content in the raw material is beneficial to the formation of C4A3-xFxS-, which enables the use of solid wastes containing low calcium for producing FR-CSA cement.Accepted author manuscriptMaterials and Environmen
Nitride capacities of CaO-Al2O3-CaF2 melts at 1 773 K
No full textThe nitrogen solubility of CaO-Al2O3-CaF2 was studied at 1 773 K. It was found that nitride capacity increased with increasing CaO content for a given CaF2/Al2O3 ratio, decreased with increasing Al2O3 content for a given CaO/CaF2 ratio, and increases with increasing CaF2 content when the CaO/Al2O3 molar ratio was less than about 2, but became unaffected by CaF2 content when the ratio exceeded about 2. These observations were interpreted that CaO depolymerized the Al2O3 network, allowing for nitrogen to exist as both free and non-bridging nitrides, and that CaF, assisted in depolymerization and hence increased nitrogen solubility, provided that there was a sufficient amount of network to be depolymerized. A diagram of iso-nitride capacity was drawn for the CaO-Al2O3-CaF2 ternary system at 1 773 K, and the nitride capacity was related to the optical basicity of the melt to obtain the following correlation equation:X115sciescopu
- …
