Catalytic dechlorination of polychlorinated biphenyls in soil by palladium-iron bimetallic catalyst

Pd/Fe bimetallic particles were synthesized by chemical deposition and used to dechlorinate 2,2',4,5,5'-pentachlorobiphenyl in soil. Batch experiments demonstrated that the Pd/Fe bimetallic particles could effectively dechlorinate 2,2',4,5,5'-pentachlorobiphenyl. Dechlorination was affected by several factors such as reaction time, Pd loading, the amount of Pd/Fe used, initial soil pH, and 2,2',4,5,5'-pentachlorobiphenyl concentration. The results showed that higher Pd loading, higher dosage of Pd/Fe, lower initial concentration of 2,2',4,5,5'-pentachlorobiphenyl and slightly acid condition were beneficial to the catalytic dechlorination of 2,2',4,5,5'-pentachlorobiphenyl. The degradation of 2,2',4,5,5'-pentachlorobiphenyl, catalyzed by Pd/Fe followed pseudo-first-order kinetics.     

An investigation of the synthesis,consolidation and mechanical behaviour of Al 6061 nanocomposites reinforced by TiC via mechanical alloying

Nanostructured Al 6061–x wt.% TiC (x = 0.5, 1.0, 1.5 and 2.0 wt.%) composites were synthesised by mechanical alloying with a milling time of 30 h. The milled powders were consolidated by cold uniaxial compaction followed by sintering at various temperatures (723, 798 and 873 K). The uniform distribution and dispersion of TiC particles in the Al 6061 matrix was confirmed by characterising these nanocomposite powders by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The mechanical properties, specifically the green compressive strength and hardness, were tested. A maximum hardness of 1180 MPa was obtained for the Al 6061–2 wt.% TiC nanocomposite sintered at 873 K, which was approximately four times higher than that of the Al 6061 microcrystalline material. A maximum green compressive strength of 233 MPa was obtained when 2 wt.% TiC was added. The effect of reinforcement on the densification was studied and reported in terms of the relative density, sinterability, green compressive strength, compressibility and Vickers hardness of the nanocomposites. The compressibility curves of the developed nanocomposite powders were also plotted and investigated using the Heckel, Panelli and Ambrosio Filho and Ge equations.     

Anode behaviors of aluminum antimony synthesized by mechanical alloying for lithium secondary battery

AlSb was synthesized as an anode active material for lithium secondary battery using mechanical alloying (MA). Electrochemical performance was examined on the electrodes of AlSb synthesized with different MA time. The first charge (lithium-insertion) capacity of the AlSb electrodes decreased with increasing the MA time. The discharge capacity on repeating charge-discharge cycle, however, did not show the same dependence. The electrode, consisting of the 20 h MA sample exhibited the longest charge-discharge life cycle, suggesting that there is the optimum degree of internal energy derived from the strain and/or the amorphization due to mechanical alloying. These results were evaluated using ex situ X-ray diffraction and differential scanning calorimetry.     

Statistical modeling of the mechanical alloying process for producing of Al/SiC nanocomposite powders

Mechanical alloying process was modeled by statistical approach for producing of Al/SiC nanocomposite powders. The process variables included two dimensionless variables TV where T and V are milling time and speed, respectively, and P1/P2 where P1 and P2 are balls weight and powders weight, respectively. Responses of the process were crystallite size of the aluminum matrix, lattice strain of the aluminum matrix, and mean particle size of nanocomposite powders. The response variables were obtained by X-ray diffraction patterns (XRD), transmission electron microscopy (TEM), and laser particle size analyzer (LPSA). Two statistical models namely, fixed effects and regression model were developed. Analysis of variance (ANOVA) at 5% levels of significance for fixed effects model and 1% for regression model were performed. Results showed that P1/P2 has a significant effect on the crystallite size, and lattice strain of the aluminum matrix and TV has a significant effect on the crystallite size, and lattice strain of the aluminum matrix as well as mean particle size of nanocomposite powders. ANOVA for regression model showed that the linear effects of TV and P1/P2 variables were significant for crystallite size, lattice strain of the aluminum matrix, and mean particle size of nanocomposite powders. The final regression models were checked and accepted by residual analysis.     

Effect of carbon on the density,microstructure and hardness of alloys formed by mechanical alloying

This work aimed to produce iron-based alloys containing resistant microstructures to improve the mechanical properties of the resulting alloy. The effects of both carbon content and compaction pressure on the microstructure, density and hardness of the alloys were examined. Iron-based alloys with initial carbon contents of 0.5%, 1%, 2% and 3% were produced by powder metallurgy following a process that involved ball milling elemental powders, cold pressing and sintering. The composition, density, microstructure, porosity, hardness and ductility of the alloys depended on both compaction pressure and carbon content. As the carbon content increased, the amount of the resistant microstructure bainite in the alloys also increased, as did their hardness. In contrast, the density and ductility of the alloys decreased with increasing carbon content. This study shows that formation of the resistant microstructure bainite in alloys fabricated by powder metallurgy is influenced by both the initial carbon content of the alloy and compaction pressure during cold pressing.     

Synthesis and characterization of the novel nanostructured NiC carbide obtained by mechanical alloying

In the present work, a comprehensive study of mechanical alloying of Ni-carbon nanotubes (CNT) and Ni-Graphite equiatomic powder mixtures under the same technological modes has provided to reveal the features of using different types of carbon (CNT or graphite) as a charge component. The as-milled powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and magnetometric study. A novel nanoscale fcc NiC monocarbide was synthesized regardless the type of the charge used. According to the XRD study the formation of this phase takes place in two stages. A two-step carbide formation mechanism has been proposed. The associated changes in the nickel lattice, such as changes in the lattice parameter, lattice strain and residual stresses, which led to the formation of NiC monocarbide were also evaluated and discussed. Parameters of the electronic structure of NiC were calculated using the MStudio MindLab 7.0 software package with the experimental data on the crystal structure of the NiC phase obtained as input. Temperature dependencies of magnetic susceptibility of NiC synthesized have been studied up to 950 K. Carbides synthesized were found to be weak ferromagnets at the room temperature and their Curie temperature T_C ranges within 670 – 725 K. The calculated value of the magnetic moment per nickel atom (2.83μ_B) is higher than that of a bulk Ni (1.3μ_B). Likely, the observed increase of μ is caused by the presence of a certain amount of residual single-domain ferromagnetic Ni nanoparticles in the samples synthesized.     

Synthesis and characterization of Zn/Al2O3 nanocomposite by mechanical alloying

In this study, fabrication and characterization of zinc-based metal matrix nanocomposite reinforced by Al₂O₃ particles was investigated. Aluminum and zinc oxide powder mixture was milled in a planetary ball mill in order to produce Zn/Al₂O₃ nanocomposite. The structural evaluation milled and annealed powders studied by X-ray diffraction, SEM observation and hardness measurement. The zinc crystallite size estimated with broadening of XRD peaks by Williamson-Hall formula. The zinc oxide was found to react with Al through a rapid self-sustaining combustion reaction process. As a result a zinc matrix composite reinforced by Al₂O₃ particulate was formed. The microhardness value of produced nanocomposite powder was about 350 HV which was 10–15 times higher than the microhardness of pure zinc (20–30 HV).     

Structural evolution of the Ti70Ni15Al15 powders prepared by mechanical alloying

Amorphization and crystallization behaviors of Ti₇₀Ni₁₅Al₁₅ powders during mechanical alloying (MA) and subsequent heat treatments are studied. Amorphous phase that cannot be obtained in the rapidly quenched ribbon is formed in the powders after MA for 60 h. Upon continuous heating of the amorphous powders in DSC, two exothermic events are observed. The first exothermic event corresponds to the crystallization of the amorphous matrix into a supersaturated α-Ti phase of hexagonal close-packed structure. The growth kinetic of the α-Ti phase is sluggish, resulting in the formation of nanostructured α-Ti matrix. The second exothermic event corresponds to the solid state transformation of the meta-stable α-Ti into the equilibrium phases, Ti₂Ni and Ti₃Al. Using the amorphous powders, Ti-based bulk materials with novel microstructures can be developed for structural applications.     

Role of A2 and A50 process on the oxide dispersion strengthened ferritic alloy fabricated by mechanical alloying

This study has investigated the effects of adding occasion of Stearic Acid (SA) on the characteristics of powder and properties of bulk with nominal composition of Fe–12Cr–2.5 W–0.4Ti–0.3Y₂O₃, which was fabricated by mechanical alloying and vacuum sintering. SA was milling with the powder mixture with 50 h (added before milling, A₅₀) or 2 h (added after 48 h milling, A₂). The resulted showed: SA could inhibit the agglomeration and retard the alloying process. Powders through A₂ process achieved alloying with high powder yield, while the A₅₀ powders presented alloying extent, and the yield of A₀ powder presented low powder yield. SA added in A₅₀ was almost dissolved into the matrix for the long milling duration, but SA added in A₂ was mostly volatilized during heating. A₂ bulk alloy was of better strength for the finer, more uniform grain and second phase and higher density than A₅₀ bulk.     

机械合金化的原理及在磁性材料研究中的应用

介绍了机械合金化的原理和描述机械合金化过程的理论模型。综述了机械合金化在磁性材料研究中的应用，并对目前研究中的存在的问题及发展前景进行了分析。     

Effect of Mo and Ti on the microstructure and microhardness in AlCoFeNiMoTi high entropy alloys prepared by mechanical alloying and conventional sintering

In this investigation, the synthesis of equiatomic AlCoFeNi, AlCoFeNiMo, AlCoFeNiTi, and AlCoFeNiMoTi high entropy alloys, fabricated by mechanical alloying and conventional sintering processes is presented aiming to elucidate the effect of Mo and Ti additions on the properties of the AlCoFeNi base system. X-ray diffraction studies revealed that after 15 h of milling, only BCC and FCC structures were formed. It was also found that by increasing the crystallite size after sintering, phase transformations and composition variations were observed for all the systems studied but BCC and FCC structures prevailed. Further, the addition of the different alloying elements had a significant effect on the microhardness of the HEAs and particularly, the addition of Mo and Ti to form the AlCoFeNiMoTi system presented the highest value of 894 HV0.2. Finally, it was also found that Mo- containing alloys presented considerable porosity.     

The preparation of nanoporous gold electrodes by electrochemical alloying/dealloying process at room temperature and its properties

A novel method of preparing nanoporous gold has been developed: nanoporous gold materials have been prepared on the bulk gold substrates by galvanostatic electrochemical alloying and galvanostatic electrochemical dealloying processes at 0.05 mA in 1 M LiPF₆, EC/DMC(1:1, v/v) solution at room temperature. The result shows that the particle size ranges from 50 nm to 100 nm on the surface of the prepared nanoporous gold by Quanta 200FEG scanning electron microscope. And it is determined that the maximum anodic current for the nanoporous gold electrode is 50 times higher than that of the polished gold electrode in 0.5 M KOH by the cyclic voltammograms.     

The dynamic properties of SiCp/Al composites fabricated by spark plasma sintering with powders prepared by mechanical alloying process

The dynamic compressive properties of SiC particle reinforced pure Al matrix composites, fabricated by spark plasma sintering technique with mixture powders prepared by mechanical alloying process, were tested in this paper. Two different average SiC particle sizes of 12 μm and 45 μm were adopted, and the compressive tests of these composites at strain rates ranging from 800/s to 5200/s were conducted by split Hopkinson pressure bar. The damage mechanism of the SiC_p/Al composites was analyzed through the microstructural observations and high-precision density measurements. Results show that the dynamic properties and damage accumulation of these composites are significantly affected by the particle distribution, size, particle cracking, particle/matrix interface debonding and adiabatic heat softening. The composites containing smaller SiC particles exhibit higher flow stress, lower strain rate sensitivity, and less damage at high strain rate deformation.     

Effect of milling time on the structure,micro-hardness,and thermal behavior of amorphous/nanocrystalline TiNiCu shape memory alloys developed by mechanical alloying

In the present paper, the effect of milling process on the chemical composition, structure, microhardness, and thermal behavior of Ti–41Ni–9Cu compounds developed by mechanical alloying was evaluated. The structural characteristic of the alloyed powders was evaluated by X-ray diffraction (XRD). The chemical composition homogeneity and the powder morphology and size were studied by scanning electron microscopy coupled with electron dispersive X-ray spectroscopy. Moreover, the Vickers micro-indentation hardness of the powders milled for different milling times was determined. Finally, the thermal behavior of the as-milled powders was studied by differential scanning calorimetery. According to the results, at the initial stages of milling (typically 0–12 h), the structure consisted of a Ni solid solution and amorphous phase, and by the milling evolution, nanocrystalline martensite (B19′) and austenite (B2) phases were initially formed from the initial materials and then from the amorphous phase. It was found that by the milling development, the composition uniformity is increased, the inter-layer thickness is reduced, and the powders microhardness is initially increased, then reduced, and afterward re-increased. It was also realized that the thermal behavior of the alloyed powders and the structure of heat treated samples is considerably affected by the milling time.     

Novel pathways for the preparation of silica antireflective films: Improvement in mechanical property

Silica antireflective films by the base catalyzed sol-gel process show poor mechanical property. In this study, silica antireflective films with good mechanical property have been prepared by the acid catalyzed templating sol-gel process. The single-layer film was deposited from an acid-catalyzed silica sol solution with polymer F127 incorporation. The silica sol was first dip deposited onto substrate to form films on both sides of the substrate and then subjected to thermal treatment at 500 °C. After thermal treatment, the abrasion resistant antireflective film was achieved due to the formation of porous structure in the resultant film as a result of decomposing F127. Optical spectroscopic measurement shows that the coated glass with maximum transmittance of 99.5% has been obtained. Nanoindenter measurement shows that the elastic modulus and hardness of films are 16 GPa and 1.3, respectively, which are much better than those films derived from base-catalyzed silica sols. The high transmittance and good mechanical property make such films potential in both military and civil applications.     

MGH956合金TIG焊原位合金化对其组织性能的影响

采用TIG焊对氧化物弥散强化(ODS)高温合金MGH956进行原位合金化焊接.在相同的焊接条件下,填加两种不同的填充材料:与母材化学成分相似的基体填充材料,以及在基体填充材料基础上加入了合金元素Al和Fe2O3的Al-Fe2O3填充材料.通过对比分析两组试样在焊接过程中发生的原位合金化反应机理,及其对焊缝微观组织和力学性能的影响,研究原位合金化反应对ODS合金TIG焊接头组织与性能的影响.结果表明:在填充材料中加入Al和Fe2O3合金元素时,焊缝处的气孔数量明显减少,气孔尺寸也较为减小;焊缝中原位生成了新的增强相颗粒Al2O3、TiC以及YAlO3,同时,基体中的纳米级增强相Al-Y复合氧化物团聚倾向降低.力学性能试验结果表明,填加Al-Fe2O3填充材料时焊缝显微硬度值明显提高,接头抗拉强度达到了578 MPa,为母材强度的80.3%.     

The design of mechanical equipment for the limitation of in-service failure

Mechanical equipment design demands a deep understanding of the inherent failure mechanisms likely to be encountered in service operation. Such understanding can result in the eradication or the limitation of the effects of in-service failures. This aspect of engineering design is examined and a case study example, in which the design of stand-by equipment involved the limitation of fretting corrosion, is used as an illustration of the general principles involved.     

镁含量对MmNi5-x(CoAlMn)x/Mg复合储氢合金吸氢性能的影响

借助扫描电镜、X- ray及吸氢性能测试装置研究了镁含量对机械合金化制备的 Mm Ni5- x ( Co Al Mn) x/Mg纳米晶复合储氢材料的性能的影响。结果表明 ,随着镁含量的增加 ,合金的活化性能表现出差 -好 -差的变化趋势。当镁含量达到50 wt%时 ,材料无法被活化。镁含量对吸氢量也有影响 ,具体表现为 ,随着镁含量的增加 ,材料的吸氢量增加。     

轻质高导电镀银复合粒子的制备研究

采用分散聚合工艺,以聚乙烯吡咯烷酮为分散剂,偶氟二异丁腈为引发剂,无水乙醇为分散介质,制备出粒径2.0μm、表面光滑、分散均匀的聚苯乙烯微球.将其进行表面磺化处理后运用化学镀工艺制备出了具有轻质高导电特性的聚苯乙烯/银复合粒子.对所制备的复合粒子进行了扫描电镜、红外光谱以及体积电阻率的测试.结果表明:所制备的复合粒子包覆均匀、导电性能良好;表面修饰提高了PS微球表面的电负性和亲水性并引入了磺酸基团,对PS微球表面镀银起到了重要作用;另外,随着PdCl2浓度和AgNO3/PS质量比的增加,复合粒子包覆完整性和导电性能都随之增加,最佳体积电阻率为1.61×10 -4Ω·cm.