Corrosion and Oxidation Behavior of Zr58Cu22Fe4Co4Al12 Metallic Glass

The pitting corrosion behavior of melt spun ribbon made at a wheel speed of 20 ms in 3.5 wt% NaCl solution and nonisothermal and isothermal oxidation behavior of 2 mm diameter rod samples of newly developed Zr₅₈Cu₂₂Fe₄Co₄Al₁₂ bulk metallic glass have been studied. The pitting corrosion is more on the air side as compared to the wheel side mainly due to the presence of air pockets. The pitted regions are enriched with copper suggesting dealloying effect due to its noble nature. The alloy shows very good oxidation resistance compared to some of the exiting bulk metallic glass forming alloys. The oxidation leads to the formation of mainly tetragonal ZrO₂ with the presence of monoclinic ZrO₂, mixture of CuO and Cu₂O and Al₂O₃. Copper in the alloy oxidized progressively with the appearance of white flowery globule shape which later forms interconnected faceted CuO network.     

Microstructure and corrosion behavior of as-cast and heat-treated Al-4.5 Wt pct Cu-2.0 wt pct Mn alloys

The microstructure and corrosion behavior of as-cast and heat-treated Al-4.5 pct Cu-2.0 pct Mn alloy specimens solidified at various cooling rates were investigated. The equilibrium phases Al₆Mn and θ-Al₂Cu, which are observed in the conventionally solidified alloy in the as-cast condition, were not detected in rapidly solidified (melt-spun) material. Instead, the ternary compound Al₂₀Cu₂Mn₃ was present in addition to the α phase, which was present in all cases. The morphological and kinetic nature of corrosion was investigated metallographically and through potentiostatic techniques in 3.5 wt pct NaCl aqueous solution. Corrosion of the as-cast material was described by two anodic reactions: corrosion of the intermetallic phases and pitting of the α-Al solid solution. The corrosion rate increased with cooling rate from that for the furnace-cooled alloy to that for the copper mold-cast alloy and, subsequently, decreased in the rapidly solidified alloy. In the heat-treated material, corrosion could be described by two anodic reactions: corrosion of Al₂₀Cu₂Mn₃ precipitate particles and pitting of the α-Al matrix. S.M. Skolianos, formerly Graduate Student, Department of Metallurgy, University of Connecticut     

Formation and Thermal Stability of Cu-Based Metallic Glasses with High Glass-Forming Ability

Cu-based Cu-Zr-Al metallic glass samples with diameters of more than 10?mm could be produced in a composition range of 45 to 52 (at. pct) Cu, 41 to 47?at.?pct Zr, and 6 to 10?at.?pct Al by a copper mold casting method. The best glass-forming ability was obtained for the Cu₄₇Zr₄₅Al₈ alloy, and the glassy sample with a diameter of 15?mm was fabricated. The minor addition of Ag or Dy can enhance the glass-forming ability of the Cu₄₇Zr₄₅Al₈ alloy, which decreases the liquidus temperatures, leading to increase in the reduced glass transition temperature. Fully glassy samples with diameters up to 20?mm were obtained for a (Cu_0.47Zr_0.45Al_0.08)₉₈Dy₂ alloy.     

Microstructural characterization of the dispersed phases in Al-Ce-Fe system

Analytical electron microscopy studies were conducted on a rapidly solidified Al-8.8Fe-3.7Ce alloy and arc melted buttons of aluminum rich Al-Fe-Ce alloys to determine the characteristics of the metastable and equilibrium phases. The rapidly solidified alloy consisted of binary and ternary metastable phases in the as-extruded condition. The binary metastable phase was identified to be Al₆Fe, while the ternary metastable phases were identified to be Al₁₀Fe₂Ce and Al₂₀Fe₅Ce. The Al₂₀Fe₅Ce was a decagonal quasicrystal while the Al₁₀Fe₂Ce phase was determined to have an orthorhombic crystal structure belonging to space group Cmmm, Cmm2, or C222. Microscopy studies of RS alloy and cast buttons annealed at 700 K established the equilibrium phases to be Al₁₃Fe₄, Al₄Ce, and an Al₁₃Fe₃Ce ternary phase which was first identified in the present study. The crystal structure of the equilibrium ternary phase was determined to be orthorhombic with a Cmcm or Cmc2 space group. The details of X-ray microanalysis and convergent beam electron diffraction analysis are described.     

Fabrication of wide temperature lanthanum and cerium doped Cu/TNU-9 catalyst with excellent NH3-SCR performance and outstanding SO2+H2O tolerance

The effects of La on the catalytic performance,SO₂ and H2O resistance of Cu-Ce/TNU-9 catalyst were studied in the selective catalytic reduction of NO_x via ammonia(NH₃-SCR).The results show that the La doped Ce-Cu/TNU-9(CCL/T9) catalyst exhibits better SCR performance than Ce-Cu/TNU-9(CC/T9) and Cu/TNU-9(C/T9) in the wide temperature window(200-450 ℃) due to La benefiting from enhancing Cu⁺+Ce⁴⁺?Cu²⁺-+Ce³⁺ to facilitate ...     

The Effect of the Amorphous and Crystalline States on Preferential Corrosion of Hf from a Cu75Hf20Dy05 Alloy

Amorphous solid-solution Cu₇₅Hf₂₀Dy₀₅, which undergoes devitrification without changing composition either locally or globally, was used to examine the effects of structural ordering on corrosion properties in the absence of any accompanying chemical partitioning. Melt spun amorphous Cu₇₅Hf₂₀Dy₀₅ undergoes single-phase devitrification to a Cu₅₁Hf₁₄ phase. The difference in corrosion behavior between these two structures was explored in hydrofluoric acid solutions where preferential dissolution of hafnium occurred. Preferential Hf dissolution occurred more readily in the amorphous alloy compared with its crystalline counterpart. Remaining copper reorganized to form a face-centered cubic (fcc) nanostructure in both conditions, but this process occurred quickly in the amorphous state and more slowly in the crystalline variant. A uniform, nanoporous Cu sponge structure, with a pore diameter of approximately 10?nm, formed after dissolution in the amorphous state. A less uniform, nanoporous structure developed more slowly when occurring from the crystalline state. These differences were traced to the effects of ordering on both dissolution and surface diffusion.     

Diffusion Brazing of Al6061/15 Vol. Pct Al2O3p Using a Cu-Sn Interlayer

Diffusion brazing of Al-6061 alloy containing 15 vol. pct Al₂O₃ particles was attempted using Cu-Sn interlayer. Joint formation was attributed to the solid-state interdiffusion of Cu and Sn followed by eutectic formation and subsequent isothermal solidification. Examination of the joint region using scanning electron microprobe analyzer (EPMA), wavelength dispersive spectroscopy (WDS) and X-ray diffraction (XRD) showed the formation of intermetallic phases such as Al₇Cu₃Mg₃, Mg₂Cu₆Al₅, Cu₃Sn, and Mg₂Sn. The results indicated an increase in joint strength with increasing bonding time giving the highest joint shear strength of 94 MPa at a bonding duration of 3 hours.     

Phase structure and hydrogen storage properties of REMg8.35Ni2.18Al0.21 （RE=La, Ce, Pr, and Nd） hydrogen storage alloys

REMg 8.35Ni2.18Al0.21 (RE=La, Ce, Pr, and Nd) alloys were prepared by induction melting and following annealing. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the alloys were composed of Mg2Ni, (La, Pr, Nd)Mg2Ni, (La, Ce)2Mg17 , (Ce, Pr, Nd)Mg12 and Ce2Ni7 phases. The above phases were disproportioned into Mg2NiH4 , MgH2 and REH x (x=2.51 or 3) phases in hydriding. CeH2.51 phase transformed into CeH2.29 phase in dehydriding, whereas LaH3 , PrH3 and NdH3 phases remained unchanged. The PrMg8.41Ni2.14Al0.20 alloy had the fastest hydriding kinetics and the highest dehydriding plateau pressure while the CeMg8.35Ni2.18Al0.21 alloy presented the best hydriding/dehydriding reversibility. The onset hydrogen desorption temperature of the CeMg8.35Ni2.18Al0.21 hydride decreased remarkably owing to the phase transformation between the CeH2.51 and the CeH2.29 .     

Interdiffusion in copper-base Cu-AI solid solutions

Interdiffusion in couples consisting of pure copper and a Cu-12.2 at. pet A1 alloy has been studied in the temperature range between 977 and 1277 K. Concentration of aluminum was determined by EPMA. The interdiffusion coefficient increased with the atomic fraction of aluminum, N_ai, in solid solution: D₀(m²/s) = 0.43 × 10^-4 and Q (kJ/tool) =194000 — 180000 N_a1 The Kirkendall effect has also been studied in the temperature range from 977 to 1277 K. The markers moved toward the aluminum-rich side. The ratio of the tracer-diffusion coefficient of aluminum, D _* ^Al , to that of copper, D _* ^Cu , at the marker position where N_a1 = 0.073, was estimated at 1.7 to 3.7; this ratio showed a tendency to increase with temperature.     

Effect of Mg and Sr additions on the formation of intermetallics in Al-6 Wt pct Si-3.5 Wt pct Cu-(0.45) to (0.8) Wt pct Fe 319-type alloys

Al-Si alloys are materials that have been developed over the years to meet the increasing demands of the automotive industry for smaller, lighter-weight, high-performance components. An important alloy in this respect is the 319 alloy, wherein silicon and copper are the main alloying elements, and magnesium is often added in automotive versions of the alloy for strengthening purposes. The mechanical properties are also ameliorated by modifying the eutectic silicon structure (strontium being commonly employed) and by reducing the harmful effect of the β-Al₅FeSi iron intermetallic present in the cast structure. Magnesium is also found to refine the silicon structure. The present study was undertaken to investigate the individual and combined roles of Mg and Sr on the morphologies of Si, Mg₂Si, and the iron and copper intermetallics likely to form during the solidification of 319-type alloys at very slow (close to equilibrium) cooling rates. The results show that magnesium leads to the precipitation of Al₈Mg₃FeSi₆, Mg₂Si, and Al₅Mg₈Cu₂Si₆ intermetallics. With a strontium addition, dissolution of a large proportion of the needle-like β-Al₅FeSi intermetallic in the aluminum matrix takes place; no transformation of this phase into any other intermetallics (including the Al₁₅(Fe,Mn)₃Si₂ phase) is observed. When both Mg and Sr are added, the diminution of the β-Al₅FeSi phase is enhanced, through both its dissolution in the aluminum matrix as well as its transformation into Al₈Mg₃FeSi₆. The reactions and phases obtained have been analyzed using thermal analysis, optical microscopy, image analysis, and electron microprobe analysis (EMPA) coupled with energydispersive X-ray (EDX) analysis.     

Interfacial Reaction during Friction Stir Welding of Al and Cu

Commercially pure copper was joined to a 1050 aluminum alloy by friction stir welding. A specific configuration where the tool pin was fully located in the aluminum plate was chosen. In such a situation, there is no mechanical mixing between the two materials, but frictional heating gives rise to a significant thermally activated interdiffusion at the copper/aluminum interface. This gives rise to the formation of defect-free joints where the bonding is achieved by a very thin intermetallic layer at the Cu/Al interface. Nanoscaled grains within this bonding layer were characterized using transmission electron microscopy (TEM). Two phases were identified, namely, Al₂Cu and Al₄Cu₉ phases. The nucleation and growth of these two phases are discussed and compared to the standard reactive interdiffusion reactions between Cu and Al.     

Influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 for NO reduction by CO

In order to investigate the influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 catalyst for NO reduction by CO,two series of catalysts(xCuyMn/Ce and xCu/yMn/Ce) were prepared by co-impregnation and stepwise-impregnation methods,and characterized by means of X-ray diffraction(XRD),Raman spectra,H2-temperature programmed reduction(H2-TPR),in situ diffuse reflectance infrared Fourier transform spectra(in situ DRIFTS) techniques.Furthermore,the catalytic performances of these catalysts were evaluated by NO+CO model reaction.The obtained results indicated that:(1) The catalysts acquired by co-impregnation method exhibited stronger interaction owing to the more sufficient contact among each component of the catalysts compared with the catalysts obtained by stepwise-impregnation method,which was beneficial to the improvement of the reduction behavior;(2) The excellent reduction behavior was conducive to the formation of low valence state copper species(Cu+/Cu0) and more oxygen vacancies(especially the surface synergetic oxygen vacancies(SSOV,Cu+-□-Mn(4–x)+)) during the reaction process,which were beneficial to the adsorption of CO species and the dissociation of NO species,respectively,and further promoted the enhancement of the catalytic performance.Finally,in order to further understand the difference between the catalytic performances of these catalysts prepared by co-impregnation and stepwise-impregnation methods,a possible reaction mechanism(schematic diagram) was tentatively proposed.     

The corrosion of lead anodes in copper electrowinning

The steady-state corrosion rate of 0.4 pct As-10 pct Sb-Pb anodes in H₂SO₄ copper electro-winning electrolytes was studied. The corrosion rate increases markedly with increasing acid strength and current density, although the corrosion per pound of copper electrowon is affected only slightly by current density. Several ions such as Cu⁺², Mg⁺², Al⁺³, SiO₃ ^-2 and Na+ have no effect on the corrosion while Fe+S and Ni+2 ions have moderate inhibiting effects. Strong corrosion inhibition is brought about by introducing small amounts of Co*2 into the solution or by substituting a Ca-Pb alloy for the conventional antimonial lead anodes.     

Alloying evolution and stability of Al65Cu20Ti15 during process of amorphisation by high energy ball milling

Abstract

Mechanical alloying of Al₆₅Cu₂₀Ti₁₅ powder blend has been carried out by high energy vibrating ball mill. The process of amorphisation in the mechanically alloyed Al₆₅Cu₂₀Ti₁₅ powder and the stability of the amorphous phase during ball milling were investigated. Almost completely amorphous powder was achieved after 25 h ball milling. Examination of the microstructural constituents using X-ray diffraction and transmission electron microscopy shows that the amorphisation process was controlled by the transformation of both Al based solid solution and intermetallic compounds (Al₂Cu, Cu₉Al₄ and AlCu₂Ti). However, that prolonging the ball milling time to 30 h led to the appearance of Cu₉Al₄, the Al₆₅Cu₂₀Ti₁₅ composite comprising nanocrystalline and amorphous phases could be stable after 50 h ball milling.     

Identification of precipitate phases in a mechanically alloyed rapidly solidified Al-Fe-Ce alloy

The stable and metastable precipitate phases which form during mechanical alloying of a rapidly solidified (RS) Al-8.4Fe-3.4Ce alloy have been unambiguously identified using X-ray diffraction, transmission electron microscopy (TEM), and energy dispersive spectroscopy techniques. The metastable Al₁₀Fe₂Ce and stable Al₁₃Fe₃Ce and Al₁₃Fe₄ intermetallic phases, with crystal structures and lattice parameters as reported in the literature, have been identified. It is shown that the metastable Al₁₀Fe₂Ce intermetallic phase particles have elongated shapes and their sizes range between 100 and 200 ran and are free of any localized faults, whereas the equilibrium Al₁₃Fe₃Ce and Al₁₃Fe₄ intermetallic phases are equiaxed in shape and have particle sizes ranging from 200 to 500 nm. It is suggested that the presence of the metastable Al₁₀Fe₂Ce in this material is due to its incomplete transformation to the equilibrium Al₁₃Fe₃Ce phase.     

去合金化制备纳米多孔NiCo_2O_4及其超电容性能

采用快速凝固与去合金化相结合的方法制备纳米多孔Ni-Co合金,退火后获得纳米多孔NiCo_2O_4材料,用XRD,SEM和TEM分析多孔NiCo_2O_4的相组成和微观结构,并通过循环伏安、恒电流充放电等方法测试多孔NiCo_2O_4电极的电化学性能。结果表明:前驱体Ni1.7Co3.3Al95合金经去合金化和退火后,可获得由10~15 nm厚的纳米片状骨架与孔径30~80 nm的孔隙共同构成的三维纳米多孔NiCo_2O_4。特殊的三维双连续结构使NiCo_2O_4电极表现出良好的超电容性能,在1 A/g的电流密度下,其比电容达755 F/g;当电流密度增加到20 A/g时,其比容保持率达76.6%,且在4 A/g的电流密度下经1000次循环充放电后,比容保持率达93.9%。     

Catalytic combustion of toluene on Pt/Al2O3 and Pd/Al2O3 catalysts with CeO2,CeO2-Y2O3 and La2O3 as coatings

CeO₂,La₂O₃,and CeO₂-Y₂O₃ oxides were coated on the surface of spherical granular AI₂O₃(3-5 mm)through impregnation method,and proved as better supports of Pd and Pt catalysts.The influences of rare earth metal doping on the adsorption rates of Pd and Pt ions,as well as the catalytic performance,were investigated.Results show that the H₂PtCl₆·6H₂O adsorption rates of the Al     

The oxidation behavior of Ni-Cr-Al-2ThO2 alloys at 1093° and 1204°C

A pack diffusion process has been developed which permits the introduction of nearly 6 wt pct Al into solid solution in the near surface region of TDNiCr (Ni-20 wt pct Cr-2 vol pct ThO₂) and Ni-20Cr. Alumina scales, adherent under cyclic heating and cooling conditions, were produced on TDNiCr-5.86A1 upon exposure to an environment of 1.33 × 10³N/m² (10 torr) or 1.01 × 10⁵N/m² (760 torr) air at temperatures of 1093° and 1204°C. While the same oxidation kinetics were observed in isothermal tests for Ni-14.6Cr-5.86Al as were obtained for the TDNiCr-5.86A1, the dispersion strengthened alloy exhibited superior oxide scale adhesion during cyclic testing. At 1204°C continuous weight gains were observed under all test conditions for TDNiCr-5.86A1, in contrast to the weight loss with time which occurred several hours after exposure of TDNiCr to an oxidizing environment. TDNiCr with an initial aluminum surface concentration of 4.95 wt pct has nearly comparable oxidation resistance to the TDNiCr-5.86Al alloy. Specimens with 4.3 wt pct Al at the surface have inadequate aluminum to form Al₂O₃ scales, and weight losses are observed after 40 h upon exposure of these specimens to 1.01 × 10⁵N/m² (760 torr) air at 1204°C.     

The surface energy of metastable Al3Li precipitates from coarsening kinetics

Small angle X-ray scattering has been used to measure the coarsening kinetics of metastable Al₃Li precipitates in a dilute AlLi binary alloy. The results are compared to previous transmission electron microscopy studies of similar alloys. Lifschitz-Slyozov-Wagner coarsening theory was invoked as a means of obtaining the α/Al₃Li interfacial energy. However, corrections accounting for effects due to finite volume fractions and limited solubility of Li in the precipitate phase are included. The surface energy was found to be ∼0.005J/m², significantly less than previously reported. A possible explanation for the discrepancy is discussed.