Key Engineering Materials Vols. 645-646

Abstract: In this work, the influences of process parameters including electroplating time, annealing temperature, etchant concentration and dealloying time on the microstructures of nanoporous copper (NPC) were quantitatively evaluated in terms of pore size. Taguchi method was utilized to reduce the number of experiments required for the evaluation. The effect of each parameter variable on the characterization length scale of NPC was quantified and discussed. It was found that the annealing temperature was the most dominant factor influencing the microstructure of NPC and the dealloying time, electroplating time and etchant concentration contributed sequentially weakly to that of NPC.

Abstract: Fe+MnO +Fe2O3+ZnO reaction system was used to prepare Mn-Zn ferrite flake absorbent by self-reactive spray forming technology. Extrinsic enthalpy (H) and adiabatic temperature (Tad) of system were calculated. The formation mechanism and electromagnetic properties of Mn-Zn ferrite flake absorbent were analyzed. The results show that Tad exceeded 1998K, self-propagation reaction can be ignited and products can be melted. The droplets impacted onto copperplate to achieve flake shape. SEM and XRD were used to characterize the morphology and phase of samples. The results show that most of flake absorbent are at 100μm wide and 10μm thick, and they are constituted by pure Mn0.5Zn0.5Fe2O4 phase with spinel crystal structure. Absorption test show that the absorbent has two absorption peaks, the minimum value of reflectivity is at -27dB and the bandwidth lower than -10dB reaches to 3.5GHz. The Mn-Zn ferrite flake absorbent provides with preferable properties, which is potential in the further investigations.

Abstract: Intermolecular interaction of mononitrotoluenes (MNs) plasticizer with 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitrohexahydro-1,3,5-triazine (RDX) was experimentally and theoretically investigated. The basis set superposition error (BSSE) and interaction energy of TNT, RDX and plasticizers were computed at MP2/6-311++G** levels. Compared with the weak E_inter between RDX and TNT (−1.586 kJ/mol), E_inter between the o-nitrotoluene and TNT and RDX can increase to −131.557 kJ/mol and −48.487 kJ/mol, indicating there is strong intermolecular-interaction. SEM imagines also show that mononitrotoluene could form layered deposits in TNT and closely surround RDX crystalline. MD simulation results indicate that tensile modulus of (100) TNT and (100) RDX increases when introducing mononitrotoluene plasticizers separately, which agree with the experimental phenomenon of Brazilian disk test.

Abstract: As one of the significant structural materials used in safe and arming system of MEMS fuze, the research on micro-electroforming process technologies and micro-electroforming nickel’s properties have been a popular field for MEMS area. This paper surveys present domestic and overseas research status of mechanical characterization of electroformed nickel, summarizes and analyzes that changes of the microstructure led by parameters of micro-electroforming process and the external environment make great effects.

Abstract: In this paper, we report a recent experimental observation of the effect of thermal accumulation to the field emission properties of the carbon nanotubes. The carbon nanotubes are grown on Ni by CVD. We compare the field emission characteristics of carbon nanotubes cathodes under DC and pulse mode. Our research shows that the higher current and higher current density could be acquired by suppressing the thermal accumulation. The Fowler-Nordheim plot shows a good linear fit, indicating that the emission current of carbon nanotubes follows Fowler-Nordheim behavior.

Abstract: Porous polyvinylidene fluoride (PVDF) membranes were prepared from PVDF and N-methyl-2-pyrrolidone (NMP) solution system using immersion precipitation phase inversion technique with ammonia as an inert solvent additive. The effects of ammonia amount on pore size, surface morphology, crystallinity, hydrophobic property, oil uptake and water-oil separation performance of the membranes were investigated. It was found that all membranes had an interpenetrating porous structure. The increase of ammonia amount led to significant variations in morphology. Lots of tiny apophysis formed on the membrane surface, pore size deceased, and pore density increased with the increase of ammonia amount. The crystallinity decreased with increasing ammonia amount, and hydrophobic property was improved. The membrane showed high oil uptake and effective separation function of oil-water mixture.

Abstract: Piezoelectric properties of ZnO nanowires orientated along [0001] are investigated via density functional theory (DFT). A new method to calculate the volume of nanowires was proposed, which is crucial to the value of piezoelectric coefficients. Results show that the axial effective piezoelectric coefficients are 29.99 Cm^-2, 25.93 Cm^-2, 22.82 Cm^-2 for ZnO nanowires with diameters of about 0.6 nm, 1.2 nm, 1.8 nm, which are considerably larger than that of the bulk (20.19Cm^-2). It is found that the change in volume during the strain played a dominated role in size effects. This work helps to gain a deeper understanding of the piezoelectric size effects in ZnO nanowires.

Abstract: Multi-jet ejection is the key factor to promote the industrial application of electrospinning technology. Simulation model based on Maxwell theory was built up to investigate the ejection and motion behaviors of multi charged jets. The charge Coulomb repulsive force among adjacent jet was introduced into the simulation model, which enhanced the instability motion and promoted the stretching process of charged jets. The stretching ratio of charged jet increased with the increasing of injection distance, applied voltage, distance between spinneret and collector. But stretching ratio of charged jet decreased with the increasing of distance between charged jets. Stretching ratio in multi-jet electrospinning was larger than that in single-jet electrospinning. The maximal stretching ratio of charged jet was larger than 9000 in the nine jets electrospinning mode. This work provided a good method to investigate the controlling technology of multi-jet electrospinning.

Abstract: SiC films made of different methods may have different mechanical properties, so their mechanical properties need to be determined by mechanical property measurement [1]. Since SiC films have stable chemical properties, it’s very difficult to be etched [2]. This paper introduce a method for SiC films mechanical property testing without processing SiC. Moreover, in view of the lack of square SiC films’ mechanical properties research, this paper also do simulation on it.

Abstract: The polishing process was optimized according to the polishing rate and its consistency of HE slurry with different dilution multiple on the copper wafers, it can be confirmed that: the best pressure value of HE1, HE10, HE20, HE50 type slurries was 6890Pa, the best flow rate value of the preceding three slurries was 300ml/min, the best value of the HE50 slurry was 400ml/min. Through the planarization effects of the slurries with different dilution multiple, it can be obtained that: the initial dishing and erosion heights of the samples were both 1270nm and -500nm, and the two values respectively changed to 539.3nm, -75.7nm and 796.3nm, -191.3nm after being treated by HE1 and HE10 slurries, the step height of the wafer changed from 117nm to 72nm after being treated by HE20 slurry, the step height of the wafer changed from 88nm to 71nm after being treated by HE50 slurry. It was concluded that: the HE slurry shows strong ability for step removal when the slurry is diluted by 1 times and 10 times, the HE slurry also owns high planarization ability when the slurry is diluted by 20 times and 50 times.