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91.
92.
Shiva Agarwal M. Teresa A. Reis M. Joana Neiva Correia Jorge M. R. Carvalho 《溶剂提取与离子交换》2013,31(5):536-551
The extraction equilibrium of copper from sulfate media with the aldoxime Acorga M5640 in ShellSol D70 has been investigated. The distribution results were interpreted by taking into account the nonideality of the aqueous phase. The activity of copper and hydrogen ions in the target systems CuSO4/H2SO4/Na2SO4 and CuSO4/H2SO4/Fe2(SO4)3/ZnSO4 were calculated through the speciation of the aqueous solutions and by applying the Pitzer model. The experimental pH values were found in good agreement with the predicted pH values. A model considering the dimerization of the aldoxime extractant was proposed to predict the distribution ratio and the copper loading isotherms. The extraction constant at infinite dilution and the apparent dimerization constant were evaluated from the experimental data and were found to be 103.06 ± 0.07 and 51 ± 9 M?1, respectively, at 25°C. 相似文献
93.
Isabel F. Sáez del Bosque Manuel Martín‐Pastor Sagrario Martínez‐Ramírez María Teresa Blanco‐Varela 《Journal of the American Ceramic Society》2013,96(3):957-965
This study aimed to monitor the effect of temperature and the addition of nanosilica on the nanostructure of the C–S–H gel forming during tricalcium silicate (C3S) hydration. Two types of paste were prepared from a synthesized T1 C3S. The first consisted of a blend of deionized water and C3S at a water/solid ratio of 0.425. In the second, a 90 wt% C3S + 10 wt% of nanosilica blend was mixed with water at a water/solid ratio of 0.7. The pastes were stored in closed containers at 100% RH and 25°C, 40°C, or 65°C. The hydration reaction was detained after 1, 14, 28, or 62 d with acetone, and then pastes were studied by 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR).The main conclusion was that adding nSA expedites C3S hydration at any age or temperature and modifies the structure of the C–S–H gel formed, two types of C–S–H gel appear. At 25°C and 40°C, more orderly, longer chain gels are initially (1 d) obtained as a result of the pozzolanic reaction between nSA and portlandite (CH) (C–S–HII gel formation). Subsequently, ongoing C3S hydration and the concomitant flow of dimers shorten the mean chain length in the gel. 相似文献
94.
Moisés Frías Sagrario Martínez‐Ramírez Teresa Blasco María Frías Rodríguez 《Journal of the American Ceramic Society》2013,96(7):2306-2310
The evolution of the metastable phases in metakaolin/Ca(OH)2 systems cured at high temperatures, remains mostly unknown, newer techniques may now help to establish both the kinetic mechanism of the pozzolanic reaction and the thermodynamic stability of the main hydrated hexagonal phases: Stratlingite (C2ASH8) and tetra calcium aluminate hydrate (C4AH13). For this reason this work examines the kinetics of the pozzolanic reaction in the MK/Ca(OH)2 system over 123 d at 60°C using nuclear magnetic resonance spectroscopy (27Al and 29Si NMR). The results obtained by 27Al and 29Si NMR show that during the first 30 h, the metastable phases C2ASH8 and C4AH13, coexist with the cubic phase (C3ASH6) obtained directly from the pozzolanic reaction. The gel C–S–H is clearly identified after 21 h of reaction, whereas at shorter times the C–S–H bands overlap those with the unreacted metakaolin ones. After 123 d of pozzolanic reaction, the first signs of the cubic phase are detected, a consequence of the conversion reaction of the metastable phases, and a phenomenon not previously identified. 相似文献
95.
Carmen M. Cepeda-Jiménez M. Mercedes Pastor-blas Teresa P. Ferrándiz-Gómez José Miguel Martín-Martínez 《The Journal of Adhesion》2013,89(2-3):135-160
Modifications produced on a vulcanized styrene –butadiene rubber surface by treatment with sulfuric acid were studied and several experimental variables were considered. The treatment of R1 rubber with sulfuric acid produced a noticeable decrease in contact angle which was mainly ascribed to an increase in surface energy due to the formation of sulfonic acid moieties and C?O bonds, and the removal of zinc stearate. The rubber surface swelled and became brittle as a result of the treatment, and when flexed microcracks were created. A rubber surface layer modification was produced with a consequent decrease in tensile strength and elongation-at-break values. The treatment enhanced the T-peel strength of R1 rubber/polyurethane adhesive joints and the locus of failure was cohesive in the rubber. The optimum immersion time in H2SO4 solution was less than 1 min., and the reaction time in air was not found to be critical; the neutralization with ammonium hydroxide and the high concentration of the sulfuric acid (95 wt%) were essential to produce adequate effectiveness of the treatment. 相似文献
96.
97.
Rabie Fath Allah Teresa Ben David González Vanesa Hortelano Oscar Martínez Jose Luis Plaza 《Nanoscale research letters》2013,8(1):162
The effects of low-energy (≤2 kV) Ar+ irradiation on the optical and structural properties of zinc oxide (ZnO) nanowires (NWs) grown by a simple and cost-effective low-temperature technique were investigated. Both photoluminescence spectra from ZnO NW-coated films and cathodoluminescence analysis of individual ZnO NWs demonstrated obvious evidences of ultraviolet/visible luminescent enhancement with respect to irradiation fluence. Annihilation of the thinner ZnO NWs after the ion bombardment was appreciated by means of high-resolution scanning electron microscopy and transmission electron microscopy (TEM), which results in an increasing NW mean diameter for increasing irradiation fluences. Corresponding structural analysis by TEM pointed out not only significant changes in the morphology but also in the microstructure of these NWs, revealing certain radiation-sensitive behavior. The possible mechanisms accounting for the decrease of the deep-level emissions in the NWs with the increasing irradiation fluences are discussed according to their structural modifications. 相似文献
98.
Cláudio Nico Luís Rino Mariana Matos Rui Monteiro Florinda M. Costa Teresa Monteiro Manuel P.F. Graça 《Journal of the European Ceramic Society》2013,33(15-16):3077-3083
Niobium oxides have been reported as an alternative to tantalum, and its oxide, for the production of capacitors, but these materials still require a further and exhaustive study. Understanding the dynamics of the oxidation process from NbO to Nb2O5 is essential to explain and control the properties of a niobium oxide based capacitors. In situ XRD analysis of NbO powders was performed from 100 to 1100 °C, which showed a temperature range where only amorphous phase is present. The capacitor anodes, formed from the same type of NbO powders, were then heat-treated in air from room-temperature (RT) to 550 °C and recorded with a video camera to see the colour shift. The presence of core–shell structures and the increase of the shell thickness/amount with temperature are visible in SEM. Finally, in situ spectroscopy studies were performed, in order to observe the interference spectra which are responsible for the observed colours. 相似文献
99.
100.
Rosa María Tremiño Teresa Real-Herraiz Viviana Letelier José Marcos Ortega 《International Journal of Applied Ceramic Technology》2022,19(4):2135-2147
The objective of this research is to study the effects produced by ternary binders which combine the addition of waste brick powder with fly ash, limestone, ground granulated blast furnace slag or waste glass powder in the microstructure and mechanical properties of mortars. In these ternary binders, the ordinary Portland cement was partially replaced by 10% of waste brick powder and 10% of another of the abovementioned additions. Mortars prepared with ordinary Portland cement without additions were also prepared. The microstructure was characterized with mercury intrusion porosimetry, electrical resistivity, and thermogravimetric analyses. Ultrasonic pulse velocity, compressive and flexural strengths were also determined. Mortars made using ternary binders with two active additions showed higher pore refinement and higher electrical resistivity at 250 days. Furthermore, their compressive strength and ultrasonic pulse velocity were relatively similar or even higher than that noted for reference specimens. 相似文献