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21.
A. Ravi Shankar U. Kamachi Mudali Vipin Chawla Ramesh Chandra 《Ceramics International》2013,39(5):5175-5184
Hafnium nitride (HfN) is a refractory compound considered to be a suitable material for reaction barriers. The present paper deals with the preparation of HfN thin films by reactive magnetron sputtering on high density (HD) graphite and niobium substrates. Deposition process parameters have been optimised with Si(100) substrate in order to get HfN coating of 3 μm thickness. The optimised parameters were used to deposit HfN on HD graphite and on niobium substrates. The results showed that HfN coating with a thickness of 2.8 μm was successfully deposited on HD graphite and niobium substrates. The presence of HfN was confirmed by glancing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS). XRD studies on HfN coating on Si(100), HD graphite and Nb substrates showed nanocrystalline grains of size 130, 55 and 46 Å, respectively. The surface morphology of HfN coating on HD graphite and niobium by atomic force microscope (AFM) and scanning electron microscope (SEM) showed that nanoparticles are getting agglomerated into clusters. The HfN coating on niobium substrate exhibited good adhesion compared to that on HD graphite as studied by microscratch test. The thermal stress generated in the sputter deposited HfN coating on HD graphite and niobium substrates were calculated by analytical formula for thermal stress. The tensile and highly compressive stresses observed in the HfN coating on niobium and HD graphite, respectively, indicated a lower adhesive strength of the coating on the later than that of the former. 相似文献
22.
Dr. Vipin Kumar Prof. Dr. Eriks Rozners 《Chembiochem : a European journal of chemical biology》2022,23(3):e202100560
2,4-Difluorotoluene is a nonpolar isostere of thymidine that has been used as a powerful mechanistic probe to study the role of hydrogen bonding in nucleic acid recognition and interactions with polymerases. In the present study, we evaluated five fluorinated benzenes as nucleobase analogues in peptide nucleic acids designed for triple helical recognition of double helical RNA. We found that analogues having para and ortho fluorine substitution patterns (as in 2,4-difluorotoluene) selectively stabilized Hoogsteen triplets with U−A base pairs. The results were consistent with attractive electrostatic interactions akin to non-canonical F to H−N and C−H to N hydrogen bonding. The fluorinated nucleobases were not able to stabilize Hoogsteen-like triplets with pyrimidines in either G−C or A−U base pairs. Our results illustrate the ability of fluorine to engage in non-canonical base pairing and provide insights into triple helical recognition of RNA. 相似文献
23.
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
24.
Calcium hexa-aluminate (CaO·6Al2 O3 ) has been prepared from calcium nitrate and aluminum sulfate solutions in the temperature range of 1000°–1400°C. A 0.3 mol/L solution of aluminum sulfate was prepared, and calcium nitrate was dissolved in it in a ratio that produced 6 mol of Al2 (SO4 )3 ·16H2 O for each mole of Ca(NO3 )2 ·4H2 O. It was dried over a hot magnetic stirrer at ∼70°C and fired at 1000°–1400°C for 30–360 min. The phases formed were determined by XRD. It was observed that CaO·Al2 O3 and CaO·2Al2 O3 were also formed as reaction intermediates in the reaction mix of CaO·6Al2 O3 . The kinetics of the formation of CaO·6Al2 O3 have been studied using the phase-boundary-controlled equation 1 − (1 − x )1/3 = K log t and the Arrhenius plot. The activation energy for the low-temperature synthesis of CaO·6Al2 O3 was 40 kJ/mol. 相似文献
25.
Phase‐dependent radiation‐resistant behavior of BaTiO3: An in situ X‐ray diffraction study 下载免费PDF全文
Renu Kumari Pawan Kumar Kulriya Surubala Mishra Vasundhara Kotari Srungarpu N. Achary Avesh K. Tyagi Devesh K. Avasthi 《Journal of the American Ceramic Society》2017,100(9):4263-4269
The radiation‐resistant response of BaTiO3 in the tetragonal and rhombohedral phases on exposure to 100 MeV Ag7+ ion irradiation was investigated by in situ X‐ray diffraction (XRD) at room temperature (300 K) and low temperature (25 K), respectively. This study revealed that the BaTiO3 in rhombohedral phase retained crystallinity up to an ion fluence of 1×1014 ions/cm2, whereas tetragonal phase amorphized at much lower fluence viz. 1×1013 ions/cm2. The in situ XRD along with Raman spectroscopy studies revealed that BaTiO3 in rhombohedral phase is more radiation resistant than that of tetragonal phase. The density functional theory (DFT) calculations confirmed higher bond strength of rhombohedral phase as compared to tetragonal phase, which supported the experimental result of higher radiation stability of rhombohedral phase. The theoretical predictions on high‐temperature phase will be of relevance to the nuclear waste applications. 相似文献
26.
Experimental investigation of particle migration in suspension flow through bifurcating microchannels 下载免费PDF全文
Bhaskar Jyoti Medhi Vipin Agrawal Anugrah Singh 《American Institute of Chemical Engineers》2018,64(6):2293-2307
Experimental measurements of velocity and concentration profiles were carried out to study transport of non‐colloidal suspension in bifurcating micro channels for both diverging and converging flow conditions using a combination of mirco‐particle image velocimetry and particle tracking velocimetry techniques. Migration of particles across the streamline was observed and symmetric velocity and concentration profile in the inlet branch becomes asymmetric in the daughter branches. Further migration of particles toward the center of the channel in the outlet branch make the profiles again symmetric. The evolution of velocity and concentration profiles was observed to be different in the symmetric and asymmetric bifurcation channels. The comparison of the streamlines for the fluid and the particles showed significant deviation near the bifurcation region. This may explain why there is unequal flow and particle partitioning during flow of suspension in asymmetric bifurcating channels as reported in many previous studies. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2293–2307, 2018 相似文献
27.
R. K. Tyagi K. K. Srivastava R. S. Pandey 《Surface Engineering and Applied Electrochemistry》2012,48(1):64-68
The material removal within different machining process can be performed in distinct modalities. One of the modality is based on the effect of impact phenomenon. In this paper theoretical model of non-traditional machining process based on impact phenomenon is discussed. The material is removed from the surface due to the impact of ions. The velocity of ions is equal to the velocity at which the electrostatic ion-cyclotron instability driven by parallel flow velocity shear generated by massive ions takes place. The main ways for the material removal as consequence of the impact phenomenon are the microcracking, microcutting, melting and vaporizing of small quantities from the work-piece surface layer. 相似文献
28.
Gayatri Chauhan Ritu Srivastava Priyanka Tyagi Amit Kumar P.C. Srivastava M.N. Kamalasanan 《Synthetic Metals》2010,160(13-14):1422-1426
The frequency dependent ac conduction mechanism in 4,4′,4″-tris(N-3-methylphenyl-N-phenylamine)triphenylamine (m-MTDATA) has been studied as a function of applied bias and temperature. The Cole–Cole plot shows a slightly depressed semicircle indicating Debye type relaxation. This result has been explained by an equivalent circuit of the device designed as a two parallel resistor and capacitance network in series with contact resistance. The ac conduction studies under dc bias for hole only devices shows an increase in device conductivity with the increase in bias. The variation of bulk resistance with applied bias indicates Space Charge Limited Conduction (SCLC) mechanism for hole conduction. The hole mobility of the material has also been evaluated from SCLC as 8.859 × 10?6 cm2/V s. The temperature dependent impedance studies show two activation energies indicating two different phase of the material with a phase transition at 235 K. 相似文献
29.
Microcellular and nanocellular solid-state polyetherimide (PEI) foams using sub-critical carbon dioxide I. Processing and structure 总被引:1,自引:0,他引:1
In this study we investigate the solid-state batch foaming of polyetherimide (PEI) using sub-critical CO2 as a blowing agent. We report on the gas diffusion for various saturation pressures in this system. Foaming process characterization is reported detailing conditions used to create microcellular and nanocellular PEI foams of 40% and higher relative density. Gas sorption, foaming, and resultant morphologies are analyzed and compared to previously reported results on PEI thin films. It was found that equilibrium gas concentrations for PEI sheet begin to significantly exceed that of films for CO2 pressures above 3 MPa. A large solid-state foaming process window has been identified that allows for the creation of either microcellular or nanocellular structures at comparable density reductions. A transition from micro-scale cells to nano-scale cells was observed at gas concentrations in the range of 94–110 mg CO2/g PEI. Additionally, a hierarchical structure was observed which consisted of nanocellular structures internal to microcells. The PEI–CO2 system offers the unique opportunity to compare and contrast the bulk properties of nanofoams and microfoams. 相似文献
30.
Sathi Rajachandran Nair Ram Dayal Purohit Avesh Kumar Tyagi Pankaj Kumar Sinha Beant Prakash Sharma 《Journal of the American Ceramic Society》2008,91(1):88-91
Ultrafine La(Ca)CrO3 (LCC) powder was prepared through the glycine–nitrate gel combustion process. It was shown for the first time that the use of relatively inexpensive CrO3 as a starting material for chromium has potential for the bulk preparation of sinter-active LCC powder. As-prepared powder, when calcined at 700°C, resulted in LCC along with a small amount of CaCrO4 . The calcined powder was found to be composed of soft agglomerates with a particle size of ≈70–290 nm. The cold pressing and sintering of the calcined powder at 1200°C resulted in the mono-phasic La0.7 Ca0.3 CrO3 with density ≈98% of its theoretical value. This is the lowest sintering temperature ever reported for La0.7 Ca0.3 CrO3 . The conductivity of the sintered La0.7 Ca0.3 CrO3 at 1000°C was found to be ≈57 S/cm in air. The sintering and electrical behavior achieved for La0.7 Ca0.3 CrO3 may find application as an interconnect material for high-temperature solid oxide fuel cells if problems with chemical expansion and poor conductivity in fuel can be overcome. 相似文献