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排序方式: 共有735条查询结果,搜索用时 15 毫秒
51.
52.
Santosh Kumar Gupta Brindaban Modak Mohit Tyagi Pampa Modak Kathi Sudarshan 《Journal of the American Ceramic Society》2023,106(2):1102-1112
Speciation of actinide (An) and lanthanide (Ln) in technologically important ceramics is very important from both fundamental as well as technological aspects. The intrinsic structural flexibility of perovskite containing AO6 and BO12 polyhedra makes them suitable and rich hosts for An and Ln. In this work, emphasis was given to deciphering information such as oxidation state, local dopant site, charge compensating defects, excited state kinetics, and so forth in BaHfO3 (BHO) related to dopant uranium (BHO-U) and cerium (BHO-Ce). Several spectroscopic techniques namely, time-resolved photoluminescence (TRPL), positron annihilation lifetime spectra (PALS), and thermoluminescence (TL) spectroscopy coupled with density functional theory (DFT) were employed to probe the same. Ce and U though are distributed at both Ba and Hf sites, Ce prefers the former, while U prefers the latter site. Uranium on the other hand stabilizes as U6+ in the form of octahedral uranate ion giving green emission. PALS suggested the formation of defects in BHO-Ce and BHO-U with oxygen vacancies predominating in the former whereas BHO-U perovskites are loaded with cation vacancies and vacancy clusters. These cation vacancies are responsible for lower TL output in BHO-U. TL measurements also suggested cerium doping leads to a higher density of deeper traps in BHO-Ce compared to uranium doping in BHO-U which is in concurrence with DFT results and may have implications in designing afterglow phosphors based on perovskite. We believe this work would have a long-term impact on exploring the potential of perovskite for nuclear waste host and afterglow phosphors applications. 相似文献
53.
G. V. Kunte Ujwala Ail P. K. Ajikumar A. K. Tyagi S. A. Shivashankar A. M. Umarji 《Bulletin of Materials Science》2011,34(7):1633-1637
A method for the estimation of vapour pressure and partial pressure of subliming compounds under reduced pressure, using rising temperature thermogravimetry, is described in this paper. The method is based on our recently developed procedure to estimate the vapour pressure from ambient pressure thermogravimetric data using Langmuir equation. Using benzoic acid as the calibration standard, vapour pressure-temperature curves are calculated at 80, 160 and 1000 mbar for salicylic acid and vanadyl bis-2,4-pentanedionate, a precursor used for chemical vapour deposition of vanadium oxides. Using a modification of the Langmuir equation, the partial pressure of these materials at different total pressures is also determined as a function of temperature. Such data can be useful for the deposition of multi-metal oxide thin films or doped thin films by chemical vapour deposition (CVD). 相似文献
54.
Reactions of unsaturated polyester resin and 4,4′ diphenyl methane diisocyanate were carried out at different NCO/OH ratios in presence of catalysts to form the hybrid polymer networks. Chain extender (1,4 butanediol) added in the hybrid network (NCO/OH ratio: 0.76) was optimized at a level of ~ 3 wt % only of the polyester resin. The curing of these networks was studied by a rigid body pendulum type (RPT) method in terms of reduced damping ratio and increased frequency. Lack of multiple glass transition temperatures, sharp Tan delta peak, and particulate composite type morphology clearly demonstrated the formation of phase mixed domains in the hybrid networks. The storage modulus and loss modulus master curves obtained by dynamic mechanical analysis indicate that hybrid polymer networks retained higher modulus at lower and intermediate frequencies over the polyester resin showing their superior time‐dependent response. Efficacy of these hybrid network resins was examined as matrices in the jute composites and compared with those of polyester resin and unsaturated polyester–polyurethane interpenetrating network matrices. It is found that the hybrid polymer network matrix composites exhibited superior physicomechanical properties under both dry and boiling water age test. Fractographic evidences such as fiber–matrix adhesion, hackle markings, and fiber breakage also supported their superior behavior over other composite matrices. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
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56.
B.K. Sharma O.S. Tyagi M.K.S. Aloopwan S.D. Bhagat 《Petroleum Science and Technology》2013,31(3-4):249-272
ABSTRACT NMR and FTIR spectroscopic techniques were used to investigate the effect of different solvent extraction schemes on the composition and chemical nature of species of vacuum residues of two Indian crude oils (namely Jodhpur and Heera) extractable into polar (ethyl acetate) and non-polar (n-pentane and n-heptane) solvents. The obtained soluble fractions were found to consist of mainly simple aliphatic and naphthenic ring structures, while insoluble fractions consisted primarily aromatic compounds. The results were used to draw inferences on the relative utility of different extraction schemes to upgrade vacuum residues as feedstocks for secondary conversion processes in petroleum industry. 相似文献
57.
Amreesh Chandra A. K. Tyagi V. Vijaykumar G. D. Mukherjee R. Boehler 《Journal of Electroceramics》2011,26(1-4):191-199
Pressure dependent studies on technologically important ferroelectric material Pb0.70Ca0.30TiO3 show the occurrence of a new hitherto unreported pressure dependent phase transition around 4 GPa. In the pressure range 4–14 GPa, the parent tetragonal (P4mm) phase of Pb0.70Ca0.30TiO3 transforms in to a monoclinic (Cm) phase before attaining its paraelectric cubic (Pm3m) phase around 15 GPa. High pressure Raman studies reveal the presence of a critical pressure above which the ferroelectric phase starts to reappear in the paraelectric phase. This critical pressure is found to be much lower than the critical pressure observed in pure PbTiO3. Possible reasons for this lowering of the critical pressure are presented. 相似文献
58.
R. Tyagi M. Bal M. Singh Satish Mohan T. Haldar A. Naik Premveer Singh M. Husain S. K. Agarwal 《Solar Energy Materials & Solar Cells》2003,76(3):257-261
Hydrogen passivation on MOCVD grown p-GaAs epilayers on Ge substrate have been studied by plasma and catalytic hydrogenation and the results were compared. The conversion efficiency of the GaAs/Ge solar cells was found to increase by 10% after catalytic hydrogenation at AM1.5. This increase in efficiency is probably due to passivation of surface dangling bonds. 相似文献
59.
R. Rajesh M. Hussain Z. H. Zaidi R. K. Tyagi Gaurav Singhal Mainuddin A. L. Dawar M. Endo 《Journal of Infrared, Millimeter and Terahertz Waves》2004,25(9):1361-1382
Chemical oxygen-iodine Laser (COIL) is one of the fast emerging high power laser source for near Infrared (λ=1.315μm) laser generation. The heart of the system is the singlet oxygen generator (SOG) which is a pumping source for this laser. A Jet type SOG with a novel approach was designed and fabricated. Singlet oxygen was taken out of the SOG at an angle of 40° thus avoiding the carry over of droplets, which is one of the major drawbacks of horizontal system. The preliminary results have been reported in our earlier publication. The present paper discusses the performance of this generator for various operational conditions viz. diluent's gas nitrogen / helium, basic hydrogen peroxide composition, generator pressure and gas velocity. Further, conditions for the stable operation from generator as well as chlorine injection point of view have been identified. 相似文献
60.