Preparation and electrical properties of Mn silicides by reaction of MnCl2 and Si powder

AbstractMn-silicides have been synthesized by reaction between Si powder and MnCl2 vapour. The growth temperature varied from 400 °C to 500 °C. The resultant silicides powders were characterized by X-ray diffraction (XRD). By powder reaction, the silicidation temperature can be decreased to 400 °C. The dominant growth of HMS was obtained at the heating temperature of 500 °C for 36 h. The phase evolution was discussed and compared with bulk reaction. The electrical properties of Mn silicides tablets were measured

Operation and energy management of hybrid AC/DC building microgrid

Microgrid has become a more attractive option in modern power system due to its advantages such as greater stability, lower energy losses and less pollution to the environment. A microgrid is a localized group of distributed generators including renewable energy sources (RESs), energy storage systems (ESSs) and AC/DC loads which are integrated together by either an AC network, DC network or hybrid AC/DC network. However, the intermittency of RES and the high cost of ESS should be carefully considered in the planning and operation stage. A microgrid can operate in a stand-alone or grid tied mode which depends on loads and available power generation from distributed renewable sources and power from bulk power system. Therefore, an optimal energy management system (EMS) for control and operation is very important for future building microgrids. Energy management is the process of tracking and optimizing energy consumption to conserve usage in a building. An energy management can also make sure that the power supply is equal to load demand. There are two main factors which have a great impact on energy management system. One is dynamic pricing of electricity market. Different prices will directly influence the energy management decisions of microgrids. Another is capacity and cost of energy storage system. In this dissertation, based on a typical architecture of hybrid AC/DC microgrids, an energy management system is presented for microgrids. Each part of microgrid is modelled according to its respective output characteristics. In addition to the basic conditions and factors, such as the power flow constraints, the intermittency of renewable energy source and healthy constraints of ESS are also considered in the modelling process. Without loss of generality, some real dataset and reliable and mature model structures are applied. Finally, by applying IPOPT solver in Python, the feasibility of this energy management system is verified. By using this energy management system, the comprehensive operation cost of microgrid has also been reduced to a great extent, which has certain theoretical guiding significance and practical engineering value for the overall economic operation of a microgrid.Master of Science (Power Engineering

Complex Dynamical Behavior in the Shear-Displacement Model for Bulk Metallic Glasses during Plastic Deformation

In this paper, a fresh shear-displacement model is developed for the plastic deformation of the bulk metallic glasses. The multiscale behavior in the shear banding process and the dynamics transition with the parameters are investigated in analytical form. We present a theoretical support for the transition from unstable states to stable states in the experiment by multiscale analysis and the stability analysis. With the small parameter increasing from negative to positive, the stability of the shear slipping displacement system changes, and there is a limit cycle at the transition stage. Meanwhile, the phase diagram and the power spectrum also suggest that there is dynamics transition with the parameter changing. Moreover, the complexity is analyzed for different disturbance parameters, and it is coincident with the fact that the solution is more irregular for larger disturbance. In addition, we find that the amplitude of solution decreases with the temperature decreasing, which is consistent with the experimental results that the amplitude of the serration is smaller and smaller as the temperature decreases

Microstructure-strengthening correlation of 2219 Al alloy subjected to ultrasonic melt treatment, hot rolling and heat treatment

Improving strength while retaining good ductility is crucial for expanding the application of 2219 Al alloy. In this study, refined microstructure, excellent strength and ductility were obtained for the 2219 Al alloy under the combined effects of ultrasonic melt treatment (UMT), hot rolling and T6 heat treatment (HRT6). The mean grain size declined from 664.2 μm to 194.9 μm for the as-cast 2219 Al alloy after 240s UMT, with a refining efficiency of 70.7 %. Meanwhile, the Cu content in Al matrix was increased by 41.7 %, and the area fraction of reticular eutectic structure was accordingly lessened by 64.5 %. The nucleation of θʹʹ/θʹ-Al2Cu phase was actuated owing to the increased Cu content in Al matrix, resulting in more dispersive θʹʹ/θʹ-Al2Cu precipitates in the HRT6 alloy with UMT. Besides, the recrystallization was encouraged because the boundaries of refined as-cast grains provided more favorable nucleation sites, and the increased dispersive θʹʹ/θʹ-Al2Cu precipitates would inhibits the grain boundary merging during HRT6. Thus, the average dimension of the recrystallized grains was decreased to the lowest value of 71.3 μm in the HRT6 alloy with 240s UMT. Meanwhile, the ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) were enhanced to 456.2 MPa, 307.0 MPa and 16.7 %, and precipitation strengthening contributed the most to the YS enhancement. The improved ductility was mainly due to the increased deformation capacity induced by the refined grains and reduced stress concentration caused by the dispersive θʹʹ/θʹ-Al2Cu particles

Effect of the Welding Thermal Cycle on the Microstructure and Mechanical Properties of TiC Cermet HAZ Using the Gleeble Simulator

The effect of heat input on the microstructure and mechanical properties of TiC cermet in MIG welding has been comprehensively investigated by Gleeble simulation. The microstructure, phase composition and shear fracture of TiC cermet were examined by OM (optical microscopy), SEM (scanning electron microscope), TEM (transmission electron microscope) and XRD (X-ray diffraction) analyses. The results show that the heat input has a significant effect on the properties of TiC cermet. With TiC particles and the austenite bonding phase remaining the same, the heat input can effectively improve the toughness of the bonding phase and the structural strength from 219.9 HV0.01 to 380.5 HV0.01 and from 469 MPa to 684 MPa, respectively, as the dislocation density increases while the heat input increases. When the heat input is 3.4 KJ/cm, the shear strength reaches the peak at 684 MPa, with the increase in heat input, the secondary fragmentation of TiC particles increases, and the crack propagation leads to a significant decrease in material strength

Microstructural Evolution and Mechanical Properties of Graphene Oxide-Reinforced Ti6Al4V Matrix Composite Fabricated Using Spark Plasma Sintering

To achieve a further reduction in weight of titanium alloys and to satisfy the increasing demand of energy-saving for aerospace and automotive applications, a graphene oxide nanosheet-reinforced Ti6Al4V (GO/TC4) composite was successfully fabricated using spark plasma sintering (SPS). Contrary to the Widmanstätten microstructure of a monolithic TC4 sample, the microstructure of the composites displayed a typical basket-weave structure in virtue of the introduced residual tensile stress generated from the mismatch of coefficients of thermal expansion (CTE) between GO and TC4 during the phase transformation. Meanwhile, the in situ-formed TiC nanolayer and diffusion layer were identified at the GO–TC4 interface, which is expected to endow a stronger interfacial bonding. As compared with the TC4 sample, the TC4 composite with the addition of 0.27 wt.% GO exhibited a 0.2% yield strength of 921.8 MPa, an ultimate tensile strength of 1040.1 MPa, and an elongation of 5.3%, displaying a better balance of strength and ductility than that of the composite with a higher GO addition (0.54 wt.%). The synergetic strengthening mechanisms such as Orowan strengthening, enhanced dislocation density strengthening, and load transfer were confirmed. Among them, load transfer contributed greatly to the strength of the composites due to improved interfacial bonding between the GO fillers and TC4 matrix