Effect of hydrogen charging on the mechanical properties of advanced high strength steels

The present work investigates the influence of hydrogen on the mechanical properties of four multiphase high strength steels by means of tensile tests on notched samples. This was done by performing mechanical tests on both hydrogen charged and uncharged specimens at a cross-head displacement speed of 5 mm/min. A considerable hydrogen influence was observed, as the ductility dropped by 8–60%. In order to demonstrate the influence of diffusible hydrogen, some parameters in the experimental set-up were varied. After tensile tests, fractography was performed. It was found that hydrogen charging caused a change from ductile to transgranular cleavage failure near the notch with a transition zone to a fracture surface with ductile features near the centre.     

Effect of hydrogen treatment on solidification structures and mechanical properties of TiAl alloys

The effect of hydrogen treatment (HT) on the solidification structures and mechanical properties of Ti-47Al alloys were studied using different contents of hydrogen. Experimental results indicate that together with the refinement of lamellar structure, the grain size of Ti-47Al alloys is reduced. With the hydrogen addition increasing to 1%, the grains of Ti-47Al alloys are refined from 1000 to 100 μm, and the average lamellar spacing of Ti-47Al alloys is decreased by approximately 50%. The hardness, compressive strength and yield stress of Ti-47Al alloys are improved due to the refinement effect of HT on grains and microstructures. The refinement effect of HT on cast TiAl alloys is found to be related to the enhancement of constitutional supercooling induced by hydrogen ahead of the solid-liquid interface.     

机械活化预处理对蔗渣酶解产糖影响的研究

采用机械活化方法对蔗渣进行预处理,研究其对蔗渣酶解产糖的影响。用红外光谱、X-射线衍射和扫描电镜测定预处理前后蔗渣结构及表面形态的变化,并分析其作用机理。研究结果表明,机械活化用于蔗渣预处理,可明显提高预处理后蔗渣的酶解产糖率。酶解时间为48 h时,蔗渣酶解产糖率从未处理时的19.86%提高到59.34%。蔗渣酶解产糖率的提高是由于机械活化处理使得蔗渣纤维素分子间部分氢键发生断裂、结晶度下降、表面有序结构被破坏的所致。     

Effect of multi-wall carbon nanotubes supported palladium addition on hydrogen storage properties of magnesium hydride

To improve the hydrogen storage performance of magnesium hydride, multi-wall carbon nanotubes supported palladium (Pd/MWCNTs) was introduced to the magnesium-based materials. Pd/MWCNTs catalysts with different amounts of Pd (20 wt.%, 40 wt.%, 60 wt.%, 80 wt.%) were synthesized by a solution chemical reduction method. Afterwards, Mg₉₅–Pd_m/MWCNTs_5−m (m = 0, 1, 2, 3, 4, 5) were prepared for the first time by hydriding combustion synthesis (HCS) and mechanical milling (MM). It is determined by X-ray diffraction (XRD) analysis that Pd/MWCNTs can significantly increase the hydrogenation degree of magnesium during the HCS process. The microstructures of the composites obtained by transmission electron microscope (TEM) and field emission scanning electronic microscopy (FESEM) analyses show that Pd nanoparticles are well supported on the surface of carbon nanotubes and the Pd/MWCNTs are dispersed uniformly on the surface of MgH₂ particles. Moreover, it is revealed that there is a synergistic effect of MWCNTs and Pd on the hydrogen storage properties of the composites. The Mg₉₅–Pd₃/MWCNTs₂ shows the optimal hydriding/dehydriding properties, requiring only 100 s to reach its saturated hydrogen absorption capacity of 6.67 wt.% at 473 K, and desorbing 6.66 wt.% hydrogen within 1200 s at 573 K. Additionally, the dehydrogenation activation energy of MgH₂ in this system is decreased to 78.6 kJ/mol H₂, much lower than that of as-received MgH₂.     

Effect of high temperature aging on microstructure and mechanical properties of HR3C heat resistant steel

Abstract

Microstructure and mechanical properties of the HR3C austenite heat resistant steel were investigated after artificial aging at 650°C for time up to 3000 h. The results show that as the aging time increased, the room temperature tensile and impact fracture mechanisms of the HR3C steel change from trans- to intergranular fracture. M₂₃C₆ type carbides and MX type carbonitrides continuously precipitate during aging, leading to the change of the mechanical properties and fracture mode of the steel. Moreover, the dissolution of the coherent twins and the transformation from the incoherent twins to the thermodynamically stable austenite subgrains have great effects on the mechanical properties of the aged steel, too. When increasing the aging time to ≧2000 h, the microstructure and mechanical properties of the steel are nearly constant, indicating a good thermal stability of the HR3C steel at elevated temperature.     

Effects of mechanical milling on hydrogen storage properties of alloy

The hydrogen storage alloy of Ti_0.32Cr_0.43V_0.25 was prepared by arc melting and high energy ball milling. Effects of ball milling were studied for various time periods (30–300 min) at 200 rpm. The hydrogen storage capacity of the alloy decreased with the increase in milling time. The reasons for the drop in the hydrogen storage capacity are twofold: surface contamination of the alloy powder and the microstructural changes. The latter includes the increase in lattice strain, the decrease in crystallite size and the consequent increase in subgrain boundaries. Despite the microstructural changes, the BCC phase of the alloy was maintained and its lattice constant remained nearly the same.     

松子壳热解炭活化特性研究

以松子壳为原料,采用常规热解法得到松子壳炭,利用水蒸气活化的方法制备了微孔率较高的活性炭,并测定其吸附能力。利用红外光谱(FT-IR)、氮气吸脱附曲线、扫描电镜(SEM)对热解炭及相应活性炭进行了表征。最佳活化工艺为活化温度850℃,活化时间60 min,水蒸气流量0.3 g/min。在该条件下松子壳活性炭得率为34%,亚甲基蓝吸附值为186 mg/g,碘吸附值为1 097 mg/g,比表面积为1 094.895 m2/g,平均孔径为3.95nm。微观结构分析表明,热解炭已经具备一定的孔隙结构,活化过程中活化剂能够有效去除堵塞热解炭孔隙的杂质和不定型炭,形成丰富的微孔结构和少量的介孔、大孔。该研究为松子壳活性炭的制备提供了理论依据。     

Phase stability and mechanical properties of niobium dihydride

First-principles calculation shows that the NbH_x phases (1 ≤ x ≤ 2) with face-centered cubic (FCC), orthorhombic (FCO), and tetragonal (FCT) modifications are all energetically favorable with negative heats of formation, while FCC NbH₁ and NbH_1.25 could not be formed due to their mechanical unstableness. It is also revealed that FCT and FCO could coexist in NbH₁ and NbH_1.25, FCC and FCT coexist in NbH_1.5 and NbH_1.75, while only FCC in NbH₂. Calculations also indicate that the magnitude of the elastic moduli of NbH_x phases at each H concentration is as follows: E > B > G, and the G, E, and G/B values of NbH_x phases reach a minimum when x = 1.5. Moreover, electronic structures are discussed to provide a deep understanding of various properties, and the derived results are in good agreement with similar experimental evidence in the literature.     

Effect of Nb2O5 on MgH2 properties during mechanical milling

Recently, it was shown that hydrogen absorption–desorption kinetics in magnesium were improved by milling magnesium hydride (MgH₂) with transition metal oxides. Herein, we investigate the role of the most effective of these oxides, Nb₂O₅ when added in larger volume fraction. The effect of Nb₂O₅ on magnesium crystalline structure, particle size and (ab)desorption properties has been characterised. Moreover, we report that pure MgH₂ can also show fast hydrogen sorption kinetics after a long milling time. The effects of Nb₂O₅ on MgH₂ sorption properties are rationalised in a new approach considering Nb₂O₅ as a dispersing agent, which helps reduce MgH₂ particle size during milling.     

Effect of electron irradiation on the properties of CdTe/CdS solar cells

Polycrystalline CdTe/CdS solar cells are used in space, as well as terrestrial, applications. The results of the studies on the effect of 8 MeV electron irradiation on p-CdTe/n-CdS thin film solar cells prepared by radio frequency (RF) sputtering are presented in this article. Solar cell parameters like short circuit current (I_sc), open circuit voltage (V_oc), fill factor (FF), conversion efficiency (η), saturation current (I_s) and ideality factor (n) have been considered. CdTe thin film solar cells exhibit good stability against electron irradiation up to 100 kGy.     

Microstructural effects on the electrical and mechanical properties of Ni–YSZ cermet for SOFC anode

The electrical and mechanical properties of Ni–YSZ cermet as the anode support of solid oxide fuel cell (SOFC) are determined by the metallic and ceramic components, respectively. We used YSZ and NiO commercial powders of the average particle size from 1 to 10 μm to fabricate Ni–YSZ cermets with different microstructures. The porosity of the cermets was also modified by the amount of carbon black addition. The distribution of each phase of cermets was analyzed with scanning electron microscopy combined with energy dispersive spectroscopy. The electrical conductivity and fracture strength of the Ni–YSZ cermets were investigated and interpreted in a view of percolation phenomena. The finer particles, either NiO or YSZ, were interlinked well by sintering and the electrical and mechanical properties of Ni–YSZ cermets were enhanced by the percolation of Ni and YSZ, respectively.     

Effects of crystallization on the high-temperature mechanical properties of a glass sealant for solid oxide fuel cell

Effects of crystallization on the high-temperature mechanical properties of a newly developed silicate-based glass sealant (GC-9) are investigated for use in planar solid oxide fuel cell (pSOFC). The aged, crystallized GC-9 glass is produced by heat treatment of the original GC-9 glass at 900 °C for 3 h. Not only crystalline phases are formed but the residual glass is also changed in the aged GC-9 glass after the heat treatment. Mechanical properties of the aged GC-9 glass are determined by four-point bending technique at temperature from 25 °C to 750 °C. The glass transition temperature of the given glass is reduced but the softening temperature is increased by such a crystallization heat treatment. The aged GC-9 glass exhibits a greater flexural strength and Young's modulus than the non-aged one at temperature below 650 °C due to the existence of crystalline phases. At temperature of 700 °C and 750 °C, a greater extent of stress relaxation is found in the aged GC-9 glass such that its strength and stiffness are much lower than those of the non-aged one. The changes in the thermal and mechanical properties through the given aging treatment are favorable for application of the GC-9 glass sealant in pSOFC.     

Effect of isothermal aging on the mechanical performance of brazed ceramic/metal joints for planar SOFC-stacks

One of the key requirements for the application of planar solid oxide fuel cells is the hermetical sealing of ceramic and metallic stack-components. Gas tightness and associated mechanical integrity of the sealants are therefore key prerequisites for reliable operation over the lifetime of the stack. To withstand mechanical stresses generated by the differences in thermal expansion of the involved materials as well as non-equilibrium thermal conditions upon heating and cooling, joining with metals rather than brittle glass-ceramics is considered to be advantageous. Hence, as one of the joining possibilities for SOFCs of planar design reactive air brazing of the ceramic cell into a metallic frame has gained increasing interest and proofed its suitability in several mid term full scale stack experiments at Forschungszentrum Jülich.     

Influence of torrefaction on properties of activated carbon obtained from physical activation of pyrolysis char

In this paper, the method of ‘torrefaction–fast pyrolysis–physical activation’ was conducted to investigate the impact of torrefaction on the properties of activated carbon through CO₂ activation. It was found that torrefaction had a significantly positive influence on the quality of activated carbon and 280°C was the optimal torrefaction temperature. The activated carbon obtained under the recommended condition had a higher yield (13.0 ± 0.3% based on dried rice husk) and most developed pore structure (specific surface area of 1090.7 m²/g). The results may be helpful for the potential utilization of high ash content biomass like rice husk.     

Effect of firing temperature on the electrochemical performance of LiMn0.4Fe0.6PO4/C materials prepared by mechanical activation

Carbon-coated LiMn_0.4Fe_0.6PO₄ composites (LiMn_0.4Fe_0.6PO₄/C) were synthesized for use as cathode materials in lithium batteries. The composites were synthesized by a mechanical activation process that consists of high-energy ball milling for 10 h, followed by thermal treatment at different temperatures. The structure, particle size and surface morphology of these cathode active materials were investigated by inductively coupled plasma (ICP) analysis, energy dispersive spectrometry (EDS), high-resolution Raman spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM). The firing temperature was observed to affect morphology, particle size, elemental distribution, structure of the residual carbon, and consequently the electrochemical properties of the composites. LiMn_0.4Fe_0.6PO₄/C synthesized at 600 °C possessed the most desirable properties and it exhibited the best performance when used as cathode in lithium batteries at room temperature. The cell, comprising cathode of this composite, exhibited the initial discharge capacities of 144.5 mAh g⁻¹ (85.0% of theoretical capacity) and 122.0 mAh g⁻¹ (71.8%), respectively, at 0.1 and 1 C-rates. The cathode showed good cycle stability without substantial capacity fade up to 50 cycles.     

Characterization and mechanical properties of high density polyethylene/silane montmorillonite nanocomposites

In order to understand and improve these soft and weak mechanical properties of High Density Polyethylene (HDPE), we add a silane modifier (Nanocor I.31PS) Montmorillonite (MMT) as reinforcement material, then use two kinds of different surfactant: thermoplastic polyolefin elastomers (TPO) or Maleic Anhydride (MA), to join the pieces of HDPE together, making it possess polarization.After that, use a Plastograph-Mixer by the twin-screw mixed method to obtain standard shaped specimens of Polymer-Clay Nanocomposites (PCN) to prepare HDPE/MMT nanocomposites pellets. By adding the different weight percentages (1, 3, 5 wt.%) of MMT, and 2:1 ratio of MA and MMT, the layer distance of MMT and mechanical property of nanocomposites was investigated.The chemical structure and polymer morphology of these as-synthesized PCN specimens were characterized by wide-angle powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, we prepare these experimental specimens in order to probe into its mechanical properties. These tests used are: layer distance of PCN, tensile, impact, shore-hardness, wearing tests, and so on.In addition, use XRD to accomplish the characterization analysis — comparing it to scatter and layer-distance. It is found that adding the MA into the MMT, layer-distance at 5 wt.% MMT increase from 2.11 nm to 3.55 nm; and add the TPO into the MMT, layer-distance at 5 wt.% MMT increase to the 2.66 nm.In the mechanical property, it is found that these specimens grafting with the MA have the following results: In the tensile test, the MMT weight percentage 3 wt.% has the best result, increased by 0.26%. In the shore hardness test, the MMT 3 wt.%, strengthened by 0.62%. In the wearing test, the MMT 3 wt.%, strengthened by 2.6%. Moreover, these specimens graft the TPO have the following results: In the impact test, the MMT 5 wt.% has the best result, increased by 16.96%. In the shore hardness test, the MMT 5 wt.% strengthens by 11.11%.     

Enhancement of surface and bulk mechanical properties of polycarbonate through the incorporation of raw MWNTs — Using the twin-screw extruder mixed technique

In this paper, we present the effects of incorporated multi-walled nanotubes (MWNTs) on a metal surface and the bulk mechanical properties of as-synthesized PC/MWNTs composites that are prepared using the twin-screw extruder mixed technique. MWNTs used for preparing the composites were raw compounds that were not treated with any surface modifications. Transmission Electron Microscopy (TEM) subsequently characterized morphology for the dispersion capability of MWNTs in the PC matrix.     

Influence of injection parameters and mold materials on mechanical properties of ABS in plastic injection molding

This study optimized effect of injection parameters such as melt temperature, packing pressure, cooling time and injection pressure on the mechanical properties of Acrylonitrile–Butadiene–Styrene (ABS) moldings. Mold materials having two different thermal conductivities, 191 W/mK for aluminum 2000 series and 50 W/mK for AISI 1020 at 25 °C were selected to use in experimental studies. Taguchi's L₉(3⁴) orthogonal array design was employed for the experimental plan. Mechanical properties of ABS specimens such as elasticity module, tensile strength and tensile strain at yield, tensile strain at break, flexural modules and izod impact strength (notched) were measured by using some test methods. Signal to noise ratio for mechanical properties of ABS using the Taguchi method was calculated and effect of the parameters on mechanical properties was determined using the analysis of variance. Linear mechanical models were also created by using regression analysis.     

Effect of cathode material on the morphology and photoelectrochemical properties of vertically oriented TiO2 nanotube arrays

We report, for the first time, on the effect of the cathode material in controlling the morphology and properties of TiO₂ nanotube arrays fabricated by electrochemical anodization of Ti foil in both aqueous and ethylene glycol (EG) electrolytes. Some of the alternative less-expensive cathode materials result in TiO₂ nanotube architectures and photoelectrochemical properties similar to or in some cases superior to those obtained using a Pt cathode.