Influence of silver on electrochemical and corrosion behaviours of Pb–Ca–Sn–Al grid alloys Part II: A.c. impedance and scanning electron microscopy studies

The influence of silver, in the range of 0.02 to 0.07wt%, on the electrochemical and corrosion properties of Pb–Ca–Sn–Al grid alloy in sulphuric acid solutions at room temperature was investigated by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). EIS was used to study the effect of silver on the surface layer(s) of an electrode under different conditions, while the oxide layers produced on the working electrode surface were examined by SEM. The addition of silver in the alloy inhibits the reactions of Pb to PbSO4 and PbSO4 to PbO2 and produces a more dense oxide layer which could enhance the corrosion resistance of the alloy.     

Surface Graft Copolymerization of Poly(vinylidene fluoride) Film with Simultaneous Lamination to Copper Foil

Surface thermal graft copolymerization with concurrent lamination was carried out between an Ar plasma pretreated poly(vinyh'dene fluoride) (PVDF) film and a copper foil in the presence of a small quantity of a N-containing monomer, such as 4-vinyl pyridine (4-VPN) and acryloyl morpholine (ACMO), under atmospheric conditions and in the complete absence of an added polymerization initiator and system degassing. The adhesion strength, as reported by T-peel strength, was dependent on the argon plasma pretreatment time of the PVDF film, the thermal lamination temperature and the type of monomer. An optimum T-peel adhesion of about 10 N/cm was readily achieved in the Cu/PVDF laminate for grafting and lamination carried out in the presence of 4-VPN. A lower adhesion strength was obtained using ACMO and other N-containing monomers. The chemical compositions of the graft copolymerized and delaminated sample surfaces were studied by X-ray photoelectron spectroscopy (XPS). The failure mode of the Cu/4-VPN/PVDF assembly was a combined adhesional and cohesive failure. The strong adhesion between the Cu foil and the PVDF film arises from the strong charge transfer interaction between Cu and the pyridine ring, as well as the fact that the graft chains are covalently tethered on the PVDF films surfaces as a result of surface graft copolymerization.     

Methanol decomposition to synthesis gas over supported Pd catalysts prepared from synthetic anionic clays

Supported Pd or Rh catalysts were prepared by the solid-phase crystallization method starting from hydrotalcite anionic clay minerals based on [Mg₆Al₂(OH)₁₆CO ₂ ²⁻ ]·4H₂O as the precursors. The precursors were prepared by a coprecipitation method from the raw materials containing Pd²⁺ and various trivalent metal ions which can replace each site of Mg²⁺ and Al³⁺ in the hydrotalcite. Rh³⁺ was also used for preparing the catalyst as comparison. The precursors were then thermally decomposed and reduced to form supported Pd or Rh catalysts and used for the methanol decomposition to synthesis gas. Among the precursors tested, use of Mg–Cr hydrotalcite containing Pd²⁺ resulted in the formation of efficient Pd supported catalysts for the production of synthesis gas by selective decomposition of methanol at low temperature. Although Pd²⁺ cannot well replace the Mg²⁺ site in the hydrotalcite, the Pd supported catalyst (Pd/Mg–Cr) prepared by the solid-phase crystallization method formed highly dispersed Pd metal particles and showed much higher activity than that prepared by the conventional impregnation method. When the precursor was prepared under mild conditions, more fine particles of Pd metal were formed over the catalyst, resulting in high activity. It is likely that the high activity may be due to the highly dispersed and stable Pd metal particles assisted by the role of Cr as the co-catalyst. This revised version was published online in November 2006 with corrections to the Cover Date.     

Sources of Variability and Lower Values in Toughness Measurements of Weld Metals

In this paper, the sources of variability and lower values in toughness measurements of a high-strength low alloy weld metal are investigated by detailed observations of fracture surfaces and the microstructures at crack initiation. The results reveal that the variability of the notch Charpy toughness is related to the location of the cleavage initiation origins. The three factors jointly contribute to give rise to variability and lower value of toughness. That is, (1) the location that the notch is sampled at deposited weld metal or reheated weld metal, (2) the location that a large grain region is appeared on the path ahead of the notch root, (3) the distributed location of the defect or the brittle second-phase particle. When three factors were simultaneously satisfied, the lower value of the Charpy toughness is appeared. The notch is sampled at the largest grain region at deposited weld metal, and the defect or the brittle second-phase particle is close to the notch root and sampled by its high stress field, the lowest Charpy toughness is obtained.     

The Microstructure Evolution of Dual-Phase Pipeline Steel with Plastic Deformation at Different Strain Rates

Tensile properties of the high-deformability dual-phase ferrite-bainite X70 pipeline steel have been investigated at room temperature under the strain rates of 2.5 × 10^?5, 1.25 × 10^?4, 2.5 × 10^?3, and 1.25 × 10^?2 s^?1. The microstructures at different amount of plastic deformation were examined by using scanning and transmission electron microscopy. Generally, the ductility of typical body-centered cubic steels is reduced when its stain rate increases. However, we observed a different ductility dependence on strain rates in the dual-phase X70 pipeline steel. The uniform elongation (UEL%) and elongation to fracture (EL%) at the strain rate of 2.5 × 10^?3 s^?1 increase about 54 and 74%, respectively, compared to those at 2.5 × 10^?5 s^?1. The UEL% and EL% reach to their maximum at the strain rate of 2.5 × 10^?3 s^?1. This phenomenon was explained by the observed grain structures and dislocation configurations. Whether or not the ductility can be enhanced with increasing strain rates depends on the competition between the homogenization of plastic deformation among the microconstituents (ultra-fine ferrite grains, relatively coarse ferrite grains as well as bainite) and the progress of cracks formed as a consequence of localized inconsistent plastic deformation.     

Corrosion Behavior of Cu40Zn in Sulfide-Polluted 3.5% NaCl Solution

The corrosion behavior of a duplex-phase brass Cu40Zn in clean and sulfide-polluted 3.5% NaCl solutions was investigated by conducting electrochemical and gravimetric measurements. The corrosion product films were analyzed by scanning electron microscopy, energy-dispersive spectroscopy and x-ray diffraction. The presence of sulfide shifted the corrosion potential of Cu40Zn toward a more negative value by 100 mV and increased the mass loss rate by a factor of 1.257 compared with the result in the clean solution. The corrosion product film in the clean solution was thin and compact; it mainly consisted of oxides, such as ZnO and Cu₂O. By contrast, the film in the sulfide-polluted solution was thick and porous. It mainly contained sulfides and zinc hydroxide chloride (i.e., Zn₅(OH)₈Cl₂·H₂O). The presence of sulfide ions accelerated the corrosion damage of Cu40Zn by hindering the formation of protective oxides and promoting the formation of a defective film which consisted of sulfides and hydroxide chlorides.     

Failure Behavior of Plasma-Sprayed Yttria-Stabilized Zirconia Thermal Barrier Coatings Under Three-Point Bending Test via Acoustic Emission Technique

In this paper, the failure behavior of plasma-sprayed yttria-stabilized zirconia thermal barrier coatings fabricated by atmospheric plasma spraying (APS-TBCs) under three-point bending (3PB) test has been characterized via acoustic emission (AE) technique. Linear positioning method has been adopted to monitor dynamic failure process of the APS-TBCs under 3PB test. The investigation results indicate that the variation of AE parameters (AE event counts, amplitudes and AE energy) corresponds well with the change of stress–strain curve of the loading processes. The failure mechanism was analyzed based on the characteristics of AE parameters. The distribution of frequency of crack propagation has been obtained. The AE signals came from two aspects: i.e., plastic deformation of substrates, initiation and propagation of the cracks in the coatings. The AE analysis combined with cross-sectional observation has indicated that many critical cracks initiate at the surface of the top-coat. And some main cracks tend to propagate toward the substrate/bond-coat interface. The actual failure mechanism of the APS-TBCs under 3PB test is attributed to the debonding of metallic coating from the substrates and the propagation of the horizontal crack along the substrate/bond-coat interface under the action of flexural moment.     

Microstructural characteristics and mechanical properties of Al–Mg–Si alloy self-reacting friction stir welded joints

The 5?mm thick Al–Mg–Si alloy was self-reacting friction stir welded using the specially designed tool at a constant rotation speed of 400?rev?min^?1 with various welding speeds. Defect-free welds were successfully obtained with welding speeds ranging from 150 to 350?mm?min^?1, while pore defects were formed in the weld nugget zone (WNZ) at a welding speed of 450?mm?min^?1. Band patterns were observed at the advancing side of WNZ. Grain size and distribution of the precipitated phase in different regions of the joints varied depending on the welding speed. The hardness of the weld was obviously lower than that of the base metal, and the lowest hardness location was in the heat affected zone (HAZ). Results of transverse tensile tests indicated that the defective joint fractured in the WNZ with the lowest tensile strength, while the fracture location of the defect-free joints changed to the HAZ.     

Corrosion inhibition by the trace amount of sulphide ion in CO2-saturated brine solutions

By accurately controlling the concentration of sulphide ion in CO₂-saturated solutions, it was demonstrated that the corrosion behaviour of mild steel was sensitive to the trace amount of sulphide ion additions. An obvious inhibition effect on cathodic reactions was observed at an extremely low level of sulphide ion, while a detrimental effect on corrosion was gradually emerged as its dosage increased higher than 0.5?mg?L^?1. These positive and negative synergy effects would be strengthened after immersing for longer time. The sensitivity of CO₂ corrosion to sulphide ion was attributed to the modification of surface properties by the presence of iron sulphides.     

ICP-AES法测定钛合金中钼铌铝铁硅

介绍了用电感耦合等离子体原子发射光谱法(ICP-AES)法测定钛合金中Mo、Nb、Al、Fe、Si元素的方法。样品采用盐酸、氢氟酸和硝酸溶解,考察了钛合金基体和共存元素对待测元素的影响,确定了各待测元素分析线分别为Mo 202.031nm、Nb 269.706nm、Al 394.401nm、Fe 239.562nm、Si 251.611nm。选定的待测元素分析线不受合金基体和共存元素的干扰,通过在校准曲线溶液中进行基体匹配消除基体的影响,通过加入内标控制测量波动,选择了仪器工作参数,进行了标准物质对照试验,试验结果与标准值相符,进行了加入回收试验,回收率在90~110%之间,相对标准偏差小于6%。