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Low-temperature photoluminescence was employed to investigate the defects of 4H–SiC crystals after high-energy electron irradiation, and the annealing characteristics and dependence of the detecting temperature and irradiation doses were investigated. Results showed that the emission, associated with carbon antisite–vacancy (VCCSi)+ defects was dominant in the electron-irradiated 4H–SiC crystal. With increase in detecting temperature, the emission decreased demonstrating red-shifted, and the full width at half-maximum broadened, which was attributed to the increase in the concentration of carriers arising from thermal activation at high temperature. The emission intensity was the highest value at an irradiation dose of 7.9 × 1018 e/cm2, and then began to decrease. This revealed the lattice damage caused by long-term high-energy irradiation, which reduced the intensity of the defect radiation in the spectrum.

Ceramics with mullite whiskers were prepared from coal fly ash and Al2O3 raw materials, with AlF3 used as an additive. The phase structures and microstructures of the ceramics were identified via X-ray diffraction and scanning electron microscopy, respectively. The results show that pickling of coal fly ash is an effective method for enhancing the flexural strength of ceramics. Sintering temperature and AlF3 addition were also key factors influencing the creation of ideal ceramics. The ceramic made from pickled coal fly ash, 6 wt% AlF3, and sintered at 1200 °C, exhibited the highest flexural strength of 59.1 MPa, and had a bulk density of 1.32 g/cm3 and porosity of 26.8%. The results show that ceramic materials made under these conditions are ideal candidates for manufacturing ceramic proppants for the exploitation of unconventional oil and gas resources.

In petroleum drilling engineering, materials with high strength and rapid degradation are required for degradable fracturing ball applications. In this work, the microstructure, mechanical properties, and corrosion behavior of extruded Mg-3Zn-Y-xCu (x = 0, 1, 3, 5 weight percent) alloys are investigated using optical microscopy, scanning electronic microscopy equipped with energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electronic microscopy, compression tests, electrochemical measurements, and hydrogen evolution tests, to explore their potential as excellent candidate alloys for degradable fracturing ball applications. It is found that the Mg-3Zn-Y alloy is mainly composed of α-Mg, Mg3Zn3Y2, and Mg3Zn6Y phases. After Cu addition, a new MgZnCu phase is formed, while the Mg3Zn3Y2 phase disappears. The Mg-3Zn-Y-3Cu alloy shows the highest compressive strength (473 MPa) and yield strength (402 MPa), mainly attributed to the combined effect of the fine-grain and dispersed precipitation of Mg3Zn6Y and MgZnCu. The corrosion rate of Mg-3Zn-Y-3Cu reaches 0.41 mm day−1 in 3.5 wt.% KCl solution. Consequently, Mg-3Zn-Y-3Cu alloy is a suitable degradable fracturing ball-seat material.

Phase evolution, microstructure, dielectric performance, polarization, breakdown strength as well as energy-storage behaviors for the lead-free niobates glass-ceramics with Sm2O3 were systematically investigated. Two crystallographic structures of tetragonal tungsten bronze and orthorhombic perovskite complex phases were obtained and Sm3+ entered into the crystalline phases. The optimal microstructure of the glass-ceramic was obtained with Sm2O3 of 2 mol%. Both dielectric constant and polarizability were enhanced with increasing Sm2O3. The breakdown strength and energy-storage behaviors of the glass-ceramics were also improved by increased Sm2O3. The highest breakdown field of 21.2 kV/mm, the highest charged (0.74 J/cm3) and discharged energy density (0.45 J/cm3) were obtained in the glass-ceramic with 2 mol% Sm2O3. It is due to the reduced interfacial polarization in this particular composition.

The microstructure and mechanical properties of an as-cast Mg-4.0Sm-1.0Ca alloy were investigated during thermomechanical treatments consisting of hot extrusion, rolling, and aging at 473 K. Mg41Sm5 phases containing Ca and needle-like Mg2Ca phases formed in the Mg matrix, and the average grain size and elongation were 4.2 μm and 27%, respectively, after hot extrusion, which implied an increase in ductility. In addition, after the rolling, the grain size was further refined, and the tensile strength increased to 293 MPa. A new precipitate Mg3Sm was found in the peak-aged Mg-4.0Sm-1.0Ca alloy and this alloy displayed the best mechanical properties, with a peak hardness of 83 HV and ultimate tensile strength of 313 MPa; these properties were attributed to grain refinement strengthening, solid solution strengthening, work hardening, and precipitation strengthening.

Solid wastes coal gangue and magnesium slag were added to prepare low density ceramic proppants at sintering temperatures below 1300 °C. The addition of solid wastes greatly decreases sintering temperature and preparation cost. The morphology and phase composition of the proppants were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the main crystal phases of the proppants are granular corundum and rod-like mullite, and the proppants have better sphericity. Furthermore, the most suitable sintering temperature is 1250 °C, and the resulting ceramics exhibit transgranular fracture. This means that rod-like mullite crystals provide strong toughening and reinforcing effects.

Effects of Sn on microstructures and mechanical properties of Mg–6Al–Ca–0.5Mn magnesium alloy were investigated. With Sn addition, the grain size of Mg–6Al–Ca–0.5Mn–xSn alloy decreases and the volume fraction of Mg2Sn phase increases. The minimum average grain size of Mg–6Al–Ca–0.5Mn–xSn alloy is 15 μm. The distribution of the phase is more dispersive in the Mg matrix. Sn content plays a key role for the inhibition of β-Mg17Al12 phase and the promotion of Mg2Sn phase. However, excessive Sn addition results in the decline of strength and elongation. Tensile results show that the Mg–6Al–Ca–0.5Mn–3Sn alloy exhibits the best mechanical properties, and the ultimate tensile strength, yield strength and elongation of the alloy are 335.9 MPa, 261.1 MPa and 10.9%, respectively. The improved tensile properties are mainly related to grain refinement, solid solution strengthening of Sn and precipitation strengthening of Mg2Sn phase. Fractographic analysis demonstrates that quasi-cleavage fracture is the dominant mechanism of these alloys.

This study investigated the effect of Ca addition on the microstructure and mechanical properties of as-cast Mg-4Sm alloys. The addition of 1.0 wt% Ca led to a significant grain refinement of Mg-4.0Sm alloys owing to the formation of rod-like Mg2Ca phases that acted as active nucleates for the Mg matrix. The as-cast Mg-4.0Sm-1.0Ca alloy showed the smallest grain size at 45 μm. Furthermore, the Mg-4.0Sm-1.0Ca alloy exhibited greater hardness, higher tensile strength, and higher yield tensile strength and elongation than the other two alloys with different Ca contents. These results were attributed to the grain refinement and precipitation strengthening of the Mg2Ca and Mg41Sm5 phases. Microsc. Res. Tech. 79:707-711, 2016. © 2016 Wiley Periodicals, Inc.

The low-cost, low-density ceramic proppants with high breakage resistance were successfully prepared from low-grade bauxite (59.9 wt%Al 2 O 3 ) partially replaced by purple sand via solid state sintering method. The phase evolution and microstructure of the ceramic proppants sintered at different temperatures were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that with the increase of sintering temperature, the crystalline phases were transferred from sillimanite to mullite and corundum, and glass phase was generated. When sintered at the proper temperature of 1440 °C, the close integration of mullite and corundum bonded by the proper liquid phase was observed, and the obtained proppant presents the apparent density of 2.98 g/cm 3 , bulk density of 1.64 g/cm 3 and lowest breakage ratio of 7.8% under 52 MPa closed pressure.

The hot compression deformation behavior and microstructure of as-cast Mg–5.0Sn–1.5Y–0.1Zr alloy were investigated by performing isothermal hot compression tests. The tests were conducted using a thermal mechanical simulator at 250–450 °C and strain rates ranging from 0.002 to 2 s−1, with a maximum deformation strain of 50 %. The effects of the deformation parameters on the microstructure evolution of the Mg–5.0Sn–1.5Y–0.1Zr alloy were discussed. The study revealed the flow behavior and the deformation mechanism of the Mg–5.0Sn–1.5Y–0.1Zr alloy. The dependence of flow stress on temperature and strain rate was described by a hyperbolic sine constitutive equation. Through regression analysis, the activation energy of 223.26 kJ mol−1 for plastic deformation was determined by considering flow stress at a strain rate of 0.2. Microstructure observation showed that dynamic recrystallization occurred extensively along grain boundaries at temperatures higher than 300 °C and strain rates lower than 0.02 s−1. This observation provides a theoretical basis for the manufacture and application of the Mg–5.0Sn–1.5Y–0.1Zr alloy.

The age behaviors, mechanical and corrosion properties of Mg–1.5Mn– x Sn ( x = 1 and 5 wt.%) alloys under three aging conditions have been investigated. The results reveal that both age behaviors and mechanical properties are improved with the increment of Sn. Meanwhile, the mechanical properties of EA (extrusion + artificial aging) state Mg–1.5Mn–5Sn alloy are higher than those of SA (solid solution + artificial aging) state sample, which are mostly attributed to fine grain and high density secondary precipitate. In addition, an accompanying improvement in age hardening response and strength is achieved in ERA (extruded + rolled + aging) state alloy compared with EA state one. The main reasons are related to the formations of a large number of dislocations and deformation twins, which provide effective nucleation sites to form fine β-Mg 2 Sn strengthening precipitates during the following aging process. In addition, compared with EA state sample, a lower corrosion rate of ERA alloy is confirmed by Tafel curves and electrochemical impedance spectroscopy results, which is mainly related to the formation of a thick anodic passivation film on the surface.

A series of Mn48–xTixNi42Sn10 (x = 1, 2, 3, and 4) ferromagnetic shape-memory alloys were prepared by the arc melting method. The results show that the martensitic transition (MT) temperatures and Curie temperature decrease clearly with Ti addition, but no obvious phase transition from weak-magnetic martensite to a ferromagnetic austenite can be observed for x = 4. Under an applied magnetic field of 30 kOe, the peak values of magnetic entropy changes are 26.6, 36.8, and 15.1 J/kg K, for x = 1, 2, and 3, respectively. The reasons for the large magnetic entropy change and adjustable MT temperatures are discussed in this paper.

Highly effective single-crystal ZnO nanorods based P/N heterojunction has been synthesized by a controllable crystal seed-induced hydrothermal vertical growth method, which facilitates the separation of the photogenerated electrons and holes due to its endogenous space charge region and suitable band structure. Therefore, photocatalytic activity for degradation of the toxic pollutants is markedly enhanced.

The influences of Y and Y-rich mischmetal (Ym) additions on microstructural and compressive properties of as-cast Al-13Mg-0.8Mn alloy prepared by vacuum suction casting were investigated in this study. The average secondary dendrite arm spacing (SDAS) was decreased when adding Y and Ym additions. Moreover, the Al2Y and Al2Ym phases formed during the solidification were mainly distributed along the grain boundary. The mechanical results reveal that both Y and Ym additions are effective in increasing the compressive strength and hardness. The values of yield compressive strength, ultimate compressive strength, and Brinell hardness of the as-cast Al-13Mg-0.8Mn-0.8Y alloy are 357 MPa, 510 MPa, and 138, respectively. The improved mechanical properties are mainly attributed to fine SDAS and precipitation strengthening. A typical cleavage fracture mode is observed on the compressive fracture surfaces of the alloys.

This study investigated the effect of Ca addition on the microstructure and mechanical properties of as-cast Mg-4Sm alloys. The addition of 1.0 wt% Ca led to a significant grain refinement of Mg-4.0Sm alloys owing to the formation of rod-like Mg2Ca phases that acted as active nucleates for the Mg matrix. The as-cast Mg-4.0Sm-1.0Ca alloy showed the smallest grain size at 45 μm. Furthermore, the Mg-4.0Sm-1.0Ca alloy exhibited greater hardness, higher tensile strength, and higher yield tensile strength and elongation than the other two alloys with different Ca contents. These results were attributed to the grain refinement and precipitation strengthening of the Mg2Ca and Mg41Sm5 phases. Microsc. Res. Tech. 79:707-711, 2016. © 2016 Wiley Periodicals, Inc.

Magnetoelastic biosensors are an important type of resonant mode based mass-sensing device, for which mass sensitivity is a critical parameter to evaluate their performance. In this work, the effect of concentrated mass position on mass sensitivity (Sm) of a magnetoelastic sensor under different resonance modes was theoretically studied. The effect of magnitude of loading mass on mass sensitivity for the first resonance mode was also studied. The results indicated that mass sensitivity as the function of loading position for all resonance modes was consistent with the law of functionSm=A cos2t. By comparing the mass sensitivity for the sensor attached with concentrated mass and uniform mass, it was found that mass sensitivity was linearly proportional to the sum of the squares of the displacement of each loading point. For the first resonance mode, when the loading position satisfied0≤xc/l<0.3or0.7

Ni55.5Mn21Ga23.5 and Ni54Mn22Ga23Sm1 films were prepared by radio frequency (RF) magnetron sputtering. The effect of Sm dopant on the morphologic and magnetic properties of Ni55.5Mn21Ga23.5 films was investigated. Sm doping can refine the particle size of the films from 100 to 60 nm, and further grain growth is not occurs even after annealing at 1073 K for 3.6 ks. Compared to Ni55.5Mn21Ga23.5 films, Sm-doped Ni54Mn22Ga23Sm1 films are easier to be magnetized and have a lower martensitic transformation temperature. In addition, the Curie temperature can also be adjusted, decreasing from 350 to 325 K after Sm doping. Martensitic transformation is not observed in the Sm-free films, which is close to the Curie temperature in the Sm-doped films, giving rise to the overlap of the structural and magnetic transition temperatures.

Ni53Mn23.8Ga23.2 ribbons were fabricated by melt-spinning and subsequent high vacuum annealing process. The structure and magnetic properties of the as-spun and annealed ribbons were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), and vibrating sample magnetometer. All the samples exhibit an orthorhombic structure of a seven-layered modulation at room temperature. The martensitic and its reverse transformation were clearly observed on all the samples. With increasing annealing temperature, the saturation magnetization increases while the coercivity decreases. It was found that the transformation becomes drastic in the sample annealed at 1073 K. In addition, an in situ observation on the evolution of magnetic domain patterns with temperature was carried out by means of magnetic force microscopy (MFM).

Red long afterglow Sr 3 Al 2 O 6 :Eu 2 + , Dy 3 + (S3A2O-ED) nanopowders have been prepared by using the conventional sol–gel process and the microwave heating technique. XRD confirmed a cubic Sr 3 Al 2 O 6 single phase for the phosphors. The phosphor powders have a rod-like morphology with little aggregation and the nanorods with diameters of about 80 nm and lengths of about 1 μm. The S3A2O-ED phosphors exhibited a broad excitation band chiefly in visible range and a red broad emission band of main peak at 612 nm under the excitation of 473 nm. Especially the S3A2O-ED phosphors prepared in 20 min of heating time at 680 W exhibited the strongest luminescent intensity and longest decay time.

Magnetoelastic sensors as an important type of acoustic wave sensors have shown great promise for a variety of applications. Mass sensitivity is a key parameter to characterize its performance. In this work, the effects of mass load distribution on the mass sensitivity of a magnetoelastic sensor under different resonance modes were theoretically investigated using the modal analysis method. The results show that the mass sensitivity and “nodal point” positions are related to the point displacement, which is determined by the motion patterns. The motion patterns are affected by resonance modes and mass load distribution. Asymmetrical mass load distribution causes the motion patterns lose symmetry and leads to the shift of “nodal point”. The mass sensitivity changing with mass load distribution behaves like a sine wave with decaying amplitude and the minimum mass sensitivity appears at the first valley. This study provides certain theoretical guidance for optimizing the mass sensitivity of a magnetoelastic sensor or other acoustic wave based sensors.

This study focused on optimization method of a ceramic proppant material with both low cost and high performance that met the requirements of Chinese Petroleum and Gas Industry Standard (SY/T 5108-2006). The orthogonal experimental design of L9(34) was employed to study the significance sequence of three factors, including weight ratio of white clay to bauxite, dolomite content and sintering temperature. For the crush resistance, both the range analysis and variance analysis reflected the optimally experimental condition was weight ratio of white clay to bauxite=3/7, dolomite content=3 wt.%, temperature=1350°C. For the bulk density, the most important factor was the sintering temperature, followed by the dolomite content, and then the ratio of white clay to bauxite.

In this work, we propose a novel wireless actuator which is composed of magnetostrictive material/copper bi-layer film. The actuator can be controlled to move like a snake bi-directionally along a pipe by tuning the frequency of external magnetic field near its first order resonant frequency. The governing equation for the actuator is established and the vibration mode shape function is derived. Theoretical analysis shows that motion of the actuator is achieved by asymmetric vibration mode shape, specific vibration bending deformation, and effective net total impacting force. The simulation and experimental results well confirm the theoretical analysis. This work provides contribution to the development of wireless micro robots and autonomous magnetostrictive sensors.