Structural Studies of Dispersoids in Fe–15 wt% Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–5 wt% Ti Model ODS Alloys During Milling and Subsequent Annealing

Oxide dispersion strengthened (ODS) steels have very high thermal stability and creep resistance due to reinforcement of hard and stable nano-sized ceramic dispersoids in metallic matrix which act as barriers to dislocation motion. This study established the role of Ti in the structural evolution of yttria during mechanical milling and subsequent annealing in a Fe–15 wt% Y₂O₃–5 wt% Ti model ODS alloy, using electron microscopy and XRD techniques. The alloy was synthesized in a high energy planetary ball mill in Ar atmosphere by varying the milling durations in the range of 0 (un-milled) to 60 h. The XRD result revealed amorphisation of Y₂O₃/Ti during milling and evolution of YTiO₃ complex oxide upon annealing at 1273 K for 1 h. The electron microscopy studies revealed the refinement of alloy powders from ~50  μm to few nanometers during milling. Electron diffraction analysis and high resolution transmission electron microscopy of 60 h milled as well as and annealed powder showed formation of different types of Y–Ti–O complex oxides such as Y₂Ti₂O₇, Y₂TiO₅ and YTiO₃.     

Studies on Creep Deformation and Rupture Behavior of 316LN SS Multi-Pass Weld Joints Fabricated with Two Different Electrode Sizes

Effect of electrode size on creep deformation and rupture behavior has been assessed by carrying out creep tests at 923 K (650 °C) over the stress range 140 to 225 MPa on 316LN stainless steel weld joints fabricated employing 2.5 and 4 mm diameter electrodes. The multi-pass welding technique not only changes the morphology of delta ferrite from vermicular to globular in the previous weld bead region near to the weld bead interface, but also subjects the region to thermo-mechanical heat treatment to generate appreciable strength gradient. Electron backscatter diffraction analysis revealed significant localized strain gradients in regions adjoining the weld pass interface for the joint fabricated with large electrode size. Larger electrode diameter joint exhibited higher creep rupture strength than the smaller diameter electrode joint. However, both the joints had lower creep rupture strength than the base metal. Failure in the joints was associated with microstructural instability in the fusion zone, and the vermicular delta ferrite zone was more prone to creep cavitation. Larger electrode diameter joint was found to be more resistant to failure caused by creep cavitation than the smaller diameter electrode joint. This has been attributed to the larger strength gradient between the beads and significant separation between the cavity prone vermicular delta ferrite zones which hindered the cavity growth. Close proximity of cavitated zones in smaller electrode joint facilitated their faster coalescence leading to more reduction in creep rupture strength. Failure location in the joints was found to depend on the electrode size and applied stress. The change in failure location has been assessed on performing finite element analysis of stress distribution across the joint on incorporating tensile and creep strengths of different constituents of joints, estimated by ball indentation and impression creep testing techniques.     

电力市场环境下无功功率集中度的评估和分析(英文)

通过测量发电机有效可用的无功功率,已经实现了无功功率集中度的评估.采用基于价值的方法,考虑有功无功负载最大时所需的无功出力,计算有效可用无功功率,进而确定发电机组的无功集中度,最后分析了负荷水平对无功集中度的影响.并以IEEE 24节点可靠性测试系统和印度75节点系统为例,验证了所提出的评估无功集中度方法的可行性.     

Study of microstructure and microtexture of modified 9Cr–1Mo steel subjected to high deformation

The Nb–V modified 9Cr–1Mo ferritic steel is an extremely important structural material in the power industry. Present work is focused on how the microstructure, microchemistry and microtexture of this steel evolve during high degree of deformation, starting from the normalized and tempered condition. While the microstructure and microchemistry are analyzed using analytical transmission electron microscopy, the microtexture analysis is carried out using the electron back-scatter diffraction (EBSD) technique. High degree of cold rolling leads to the formation of forests of dislocations and cellular structure of ferritic matrix. The carbides were found to retain their morphology and chemistry after 88% cold work. Analysis of misorientation angles was used to derive the grain boundary character of the normalized and tempered steel and the deformed steel. Analysis of fiber texture reveals that deformation in the material does not lead to predominance of any particular fiber which is useful from fabrication point of view.     

The effect of dopants on the activity of MoO3/ZSM-5 catalysts for the dehydroaromatisation of methane

The effect of a number of dopants – Co²⁺, Fe³⁺, Al³⁺, Ga³⁺ and P^(V) – on the catalytic activity of MoO₃/ZSM-5 dehydroaromatisation catalysts has been investigated. Promotional effects were observed with Fe³⁺, Al³⁺ and Ga³⁺, whereas P^(V) added in the form of phosphomolybdic acid decreased the benzene formation rate. Doping with Co²⁺ was not observed to produce any promotional effects, aside from an initial high conversion and burst of hydrogen which was short-lived. In the case of iron, although the benzene formation rate was close to that for the non-doped parent catalyst in the early stages, benzene formation was enhanced at longer times on stream and the addition of iron was observed to enhance methane conversion, principally through enhanced coke formation. The addition of gallium was found to produce an enhancement of benzene production in the early stages of reaction, but its principal effect was the reduction of hydrogen producing side reactions associated with the formation of coke. In comparing the effects of metal ion addition, it is notable that the impregnation solutions of Fe³⁺, Al³⁺ and Ga³⁺ are acidic. Possible effects of these dopants such as zeolite dealumination, modification of catalyst acidity and the formation of mixed molybdenum containing phases or re-dispersion of the MoO₃ phase can be advanced as potential explanations for the observed effects.     

Investigation of hydrogen isotope effect on storage properties of Zr–Co–Ni alloys

The deuterium desorption pressure-composition isotherms (PCIs) of ZrCo_1−xNi_x-D₂ (x = 0, 0.1, 0.2 and 0.3) systems were generated in this study in the temperature range of 524–603 K using Sievert's type volumetric apparatus. Thermodynamic parameters like enthalpy and entropy change for deuterium desorption reactions involved in the ZrCo_1−xNi_x-D₂ systems were derived using the equilibrium pressure data of PCIs. In order to interpret the hydrogen isotope effect on the storage behaviour of ZrCo_1−xNi_x alloys, the results obtained in the present study were compared with the earlier reported data on the ZrCo_1−xNi_x-H₂ (x = 0, 0.1, 0.2 and 0.3) systems. This comparison revealed that these alloys show normal hydrogen isotope effect where the equilibrium pressure of D₂ is higher than that of H₂ at all experimental temperatures. Based on these observation, it is expected that at the ITER SDS operating conditions the equilibrium pressure of tritium, deuterium and hydrogen will follow the order: p(T₂) > p(D₂) > p(H₂) for these alloys.     

Quantum dots as enhancer in photocatalytic hydrogen evolution: A review

Advanced energy conversion processes like photochemical and photoelectrochemical water splitting now a day plays a very important role in challenging the present energy crisis of our world. The successful utilization of this process depends on development of highly efficient, more stable, low cost and outstanding environmental benign semiconductor materials. From recent advancements, it is revealed that quantum dots (QDs) are very outstanding and promising material for the mentioned processes due to their favorable physical and chemical characteristics like high absorption co-efficient, quantum confinement effect, thermal, chemical, mechanical and optical stability, high conductivity and recyclability. In this review article, we have clearly explained the importance of QDs in water splitting along with the general mechanism involved in the process. Following that the enhancement of different materials like metal oxides, layered double hydroxides (LDH), carbonaceous materials (g-C₃N₄, benzene and benzene like materials) by QDs have discussed in the field of water splitting.     

Green synthesis of fibrous hierarchical meso-macroporous N doped TiO2 nanophotocatalyst with enhanced photocatalytic H2 production

A new approach to prepare hierarchical and fibrous meso-macroporous N-doped TiO₂ is attempted at room temperature without using templates by the addition of titanium isopropoxide droplets to the ammonia solution. The catalysts are thoroughly characterized by physico-chemical and spectroscopic method to explore the structural, electronic and optical properties. The photocatalytic activities of the catalyst were evaluated with hydrogen generation. NTP catalyst calcined at 400 °C (NTP-400) exhibited 602.7 μmol/3 h H₂ generation from 10 vol.% methanol under visible light. The excellent photocatalytic activity for NTP-400 is attributed to the porous networks existing in our system with uniform N dispersion throughout the catalyst. The hierarchical and fibrous structures allow easy channelization of electron as in the case of nanotubes for effective surface charge transfer. Along with macroporosity, nitrogen incorporation and mesoporosity play some important roles for enhanced photoactivities.