Reduced-graphene-oxide-and-strontium-titanate-based double-layered composite: an efficient microwave-absorbing material

Microwave-absorbing materials based on reduced graphene oxide (r-GO)/strontium titanate were prepared by embedding in epoxy matrix. R-GO and strontium titanate were synthesized and characterized before composite fabrication. Microstructures of the constituent elements were studied by scanning electron microscopy and X-ray diffraction (XRD). Microwave absorption capabilities of the composite absorbers were investigated using a Vector Network Analyser in the range 8–12 GHz. A maximum reflection loss of ?7.5 and ?16.4 dB was obtained at 9.3 and 12.08 GHz, respectively, for 2% (w/w) r-GO-loaded epoxy composites. A maximum attenuation of ?12.8 dB at 9.3 GHz was obtained for the strontium titanate/epoxy composite. However, double-layer composite with r-GO/strontium titanate/epoxy composition showed the maximum reflection loss of ?15.1 dB at 9.47 GHz and ?9.65 dB at 12.3 GHz. All the results are discussed in terms of complex permeability and permittivity. The study revealed that intrinsic conductivity and polarization of the r-GO particles and dielectric polarization of the strontium titanate within epoxy matrix contribute to the microwave absorption.     

Environmentally assisted cracking resistance of Al–Cu–Li alloy AA2195 using slow strain rate test in 3.5% NaCl solution

The general corrosion and environmental cracking resistances of Al–Cu–Li alloy AA2195 were investigated in 3.5% NaCl environment and compared with those of another high strength alloy AA2219. The general corrosion resistance of these alloys was examined using immersion corrosion and potentiodynamic polarization tests, while the stress corrosion cracking (SCC) resistance was evaluated by slow strain rate test (SSRT) method. The tested samples were further characterized by SEM–EDS and optical profilometry to study the change in corrosion morphology, elemental content and depth of corrosion attack. The reduction in ductility was used as a parameter to evaluate the SCC susceptibility of the alloys. The results indicated that the corrosion resistance of AA2195 alloy was better than that of AA2219 alloy as it exhibited lower corrosion rate, along with lower pit depth and density. However, the SCC index (?_NaCl/?_air) measured was greater than 0.90, indicating good environmental cracking resistance of both the alloys. Detailed fractography of the failed samples under SEM–EDS, in general, revealed a typical ductile cracking morphology for both the alloys.     

颗粒激发形核在热挤压Al6061/SiCp复合材料再结晶过程中的作用

采用电子背散射衍射技术,研究SiCp增强热挤压A16061铝合金复合材料的织构和微观组织演变.A16061铝合金及其Ni包覆SiCp增强的复合材料织构中都存在强的β纤维,其轴平行于挤压方向.在未用SiCp增强的热挤压A16061铝合金中,除了主要的立方织构001)<100>,在完全再结晶晶粒中也存在部分等轴结构.这种再结晶织构的出现归因于粒径小于5μm的SiCp粒子的形成而产生的粒子激发形核.在这些条件下,低Z(～1012 S-1)值证实了粒子激发形核是再结晶的主导机制之一,且受变形区的形成而非储能的控制.     

Detection of H2S gas at lower operating temperature using sprayed nanostructured In2O3 thin films

Nanostructured indium oxide (In₂O₃) thin films were prepared by spray pyrolysis (SP) technique. X-ray diffraction (XRD) was used to investigate the structural properties and field emission scanning electron microscopy (FESEM) was used to confirm surface morphology of In₂O₃ films. Measurement of electrical conductivity and gas sensing performance were conducted using static gas sensing system. Gas sensing performance was studied at different operating temperature in the range of 25–150 °C for the gas concentration of 500 ppm. The maximum sensitivity (S = 79%) to H ₂ S was found at lower temperature of 50 °C. The quick response (4 s) and fast recovery (8 s) are the main features of this film.     

TOXICOLOGICAL EVALUATION OF GUM KARAYA IN RHESUS MONKEYS

Gum karaya was fed to rhesus monkeys at the 5% level for 18 weeks. Growth pattern, hematological status and histopathological patterns were studied. No toxic effect attributable to gum karaya was observed.     

Experimental Optimization of Jet Self-Priming Centrifugal Pump Based on Orthogonal Design and Grey-Correlational Method

The novel jet self-priming centrifugal pump, as important modern irrigation equipment, is widely used in large-scale irrigation, mine drainage and so on. In order to improve the profile streamline of blade, the inlet shape of impeller was designed as distorted and the outlet shape as cylindrical, which can not only improve the pump efficiency, but also shorten the self-priming time. Further, the novel jet self-priming system was proposed, by employing the jet nozzle and check valve to improve th...     

APPLICATION of ARTIFICIAL NEURAL NETWORKS to INVESTIGATE the DRYING of COOKED RICE

Commercially available neural networks software was applied for prediction of processing parameters with reference to the product quality of the dehydrated cooked rice. These results were verified with experimental data. the experimental results indicate good concurrence with the predicted data. A small capacity vibrofluidized bed drier was used to conduct the experimental studies. the inlet air temperature of 160C to 180C, the inlet air velocity of 3 to 6 ms⁻¹ and the resident time of 5 to 8 min were used in the study. the optimized process parameters were identified. the operation of the neural network model is discussed. the trained model can be applied in a nonlinear model predictive scheme to control the product moisture content.     

Synthesis,growth, optical,mechanical and electrical properties of <Emphasis Type="Italic">L</Emphasis>-lysine <Emphasis Type="Italic">L</Emphasis>-lysinium dichloride nitrate (<Emphasis Type="Italic">L</Emphasis>-LLDN) single crystal

Semi-organic nonlinear optical material, L-lysine L-lysinium dichloride nitrate (2C₆H₁₅N₂O₂⁺_{2}^{+} · H⁺ · NO₃^-_{3}^{-} · 2Cl⁻) was synthesized at room temperature. Single crystals of L-LLDN were grown by slow cooling solution growth technique. The grown crystal was confirmed by powder X-ray diffraction analysis. The crystalline perfection of the grown single crystal was characterized by high-resolution X-ray diffraction (HRXRD) studies. The cut-off wavelength was determined by UV-vis transmission spectral analysis. The frequency doubling of the grown crystal was confirmed by powder second harmonic generation (SHG) measurement. The refractive index and birefringence of the crystal were determined using He–Ne laser source. Mechanical property of the crystal was determined by Vickers hardness tester. The frequency and temperature dependence of dielectric constant (ε _r), dielectric loss (tan δ) and a.c. conductivity (σ _ac) were also measured.     

菱面体畸变的钙钛矿结构多铁性氧化物薄膜畴界精细结构

畴是所有铁性材料的一个共同本质特性,畴及畴界的结构极大影响着材料性能。本文应用高分辨透射电子显微学和定量电子显微学,在原子尺度定量研究了钙钛矿菱面体结构多铁性薄膜BiFeO3的109°畴界的精细结构,包括畴界附近阳离子位移及局部铁电极化分布。结果表明：正是由于畴界附近原子发生微小位移,导致材料能带的变化,带隙减小,从而在绝缘BiFeO3中产生独特的导电性能。这不仅为研究铁电极化反转和磁电效应等科学问题提供关键的定量结构信息,同时也促进相关材料的设计和性能优化。     

Sliding wear characteristics of solid lubricant coating on titanium alloy surface modified by laser texturing and ternary hard coatings

Titanium alloys are poor in wear resistance and it is not suitable under sliding conditions even with lubrication because of its severe adhesive wear tendency. The surface modifications through texturing and surface coating were used to enhance the surface properties of the titanium alloy substrate. Hard and wear resistant coatings such as TiAlN and AlCrN were applied over textured titanium alloy surfaces with chromium as interlayer. To improve the friction and wear resisting performance of hard coatings further, solid lubricant, molybdenum disulphide (MoS2), was deposited on dimples made over hard coatings. Unidirectional sliding wear tests were performed with pin on disc contact geometry, to evaluate the tribological performance of coated substrates. The tests were performed under three different normal loads for a period of 40 min at sliding velocity of 2 m/s. The tribological behaviours of multi-layer coatings such as coating structure, friction coefficient and specific wear rate were investigated and analyzed. The lower friction coefficient of approximately 0.1 was found at the early sliding stage, which reduces the material transfer and increases the wear life. Although, the friction coefficient increased to high values after MoS₂ coating was partially removed, substrate was still protected against wear by underlying hard composite layer.