Comparison of corrosion and oxygen evolution behaviors between cast and rolled Pb–Ag–Nd anodes

The corrosion and oxygen evolution behaviors of cast and rolled Pb–Ag–Nd anodes were investigated by metalloscopy, environmental scanning electron microscopy, X-ray diffraction analysis, and various electrochemical measurements. The rolled anode exhibits fewer interdendritic boundaries and a dispersed distribution of Pb–Ag eutectic mixtures and Nd-rich phases in its cross-section. This feature inhibits rapid interdendritic corrosion into the metallic substrate along the interdendritic boundary network. In addition, the anodic layer formed on the rolled anode is more stable toward the electrolyte than that formed on the cast anode, reducing the corrosion of the metallic substrate during current interruption. Hence, the rolled anode has a higher corrosion resistance than the cast anode. However, the rolled anode exhibits a slightly higher anodic potential than the cast anode after 72 h of galvanostatic polarization, consistent with the larger charge transfer resistance. This larger charge transfer resistance may result from the oxygen-evolution reactive sites being blocked by the adsorption of more intermediates and oxygen species at the anodic layer/electrolyte interfaces of the rolled anode than at the interfaces of cast anode.     

Influence of chromium on the initial corrosion behavior of low alloy steels in the CO_2–O_2–H_2S–SO_2 wet–dry corrosion environment of cargo oil tankers

The influence of Cr on the initial corrosion behavior of low-alloy steels exposed to a CO2–O2–H2S–SO2 wet–dry corrosion environment was investigated using weight-loss measurements, scanning electron microscopy, N2 adsorption tests, X-ray diffraction analysis, and electrochemical impedance spectroscopy. The results show that the corrosion rate increases with increasing Cr content in samples subjected to corrosion for 21 d. However, the rust grain size decreases, its specific surface area increases, and it becomes more compact and denser with increasing Cr content, which indicates the enhanced protectivity of the rust. The results of charge transfer resistance(Rct) calculations indicate that higher Cr contents can accelerate the corrosion during the first 7 d and promote the formation of the enhanced protective inner rust after 14 d; the formed protective inner rust is responsible for the greater corrosion resistance during long-term exposure.     

Hot ductility behavior of a Fe–0.3C–9Mn–2Al medium Mn steel

The hot ductility of a Fe–0.3C–9Mn–2Al medium Mn steel was investigated using a Gleeble 3800 thermo-mechanical simulator. Hot tensile tests were conducted at different temperatures(600–1300°C) under a constant strain rate of 4 × 10~(-3) s~(-1). The fracture behavior and mechanism of hot ductility evolution were discussed. Results showed that the hot ductility decreased as the temperature was decreased from1000°C. The reduction of area(RA) decreased rapidly in the specimens tested below 700°C, whereas that in the specimen tested at 650°C was lower than 65%. Mixed brittle–ductile fracture feature is reflected by the coexistence of cleavage step, intergranular facet, and dimple at the surface. The fracture belonged to ductile failure in the specimens tested between 720–1000°C. Large and deep dimples could delay crack propagation. The change in average width of the dimples was in positive proportion with the change in RA. The wide austenite–ferrite intercritical temperature range was crucial for the hot ductility of medium Mn steel. The formation of ferrite film on austenite grain boundaries led to strain concentration. Yield point elongation occurred at the austenite–ferrite intercritical temperature range during the hot tensile test.     

Thermodynamic simulation of the effect of slag chemistry on the corrosion behavior of alumina–chromia refractory

The corrosion behavior of alumina–chromia refractory against two kinds of industrial slags (coal slag and iron smelting slag) at 1550°C was investigated via thermodynamic simulations. In the proposed simulation model, the initial slag first attacks the matrix and surface aggregates and subsequently attacks the inner aggregates. The simulation results indicate that the slag chemistry strongly affects the phase formation and corrosion behavior of the refractory brick. Greater amounts of alumina were dissolved and spinel solid phases formed when the brick interacted with iron smelting slag. These phenomena, as well as the calculated lower viscosity, may lead to much deeper penetration than that exhibited by coal slag and to more severe corrosion compared to that induced by coal slag. The thermodynamic calculations well match the experimental observations, demonstrating the efficiency of the proposed simulation model for evaluating the corrosion behavior of alumina–chromia refractory.     

In vitro corrosion behavior of the extruded Mg–4Zn–1Mn alloy in different physiological solutions for biomedical applications

The extruded Mg–4Zn–1Mn alloy was prepared and its in vitro corrosion behavior in different physiological solutions of simulated body fluid(SBF), artificial saliva(AS) and artificial urine(AU) was investigated for biomedical applications. The microstructural characterization by optical microscope(OM), X-ray diffractometer(XRD), scanning electron microscopy(SEM) and energy dispersive X-ray spectrometer(EDS) showed that the alloy with an average grain size of approximate 20 μm was mainly composed ...     

The precipitation strengthening behavior of Cu-rich phase in Nb contained advanced Fe–Cr–Ni type austenitic heat resistant steel for USC power plant application

Copper has been used as a strengthening element in newly developed Fe–Cr–Ni type austenitic heat resistant steel for inducing Cu-rich phase precipitation to meet high temperature strength requirement for 60°C Ultra Super-Critical (USC) coal fired power plants for many years. However, the precipitation behavior and strengthening mechanism of Cu-rich phase in these advanced austenitic heat resistant steels is still unclear. In order to understand the precipitation strengthening behavior of Cu-rich phase and to promote high strength austenitic heat resistant steel development, 18Cr9 NiCuNb steel which is a Cu-added Nb contained advanced Fe–Cr–Ni type austenitic heat resistant steel has been selected for this study to be aged at 650°C till to 10,000 h. Micro-hardness and room temperature tensile test were conducted after long-time aging. SEM,TEM, HRTEM and three dimensional atom probe (3DAP) technology accompanying with thermodynamic calculation have been used to investigate the Cu-rich phase precipitation behavior during 650°C aging. The experimental results showed that Cu atoms can quickly concentrate in clusters at very early precipitation stage to form the fine nano-size Cu-rich ‘‘segregation areas’within less than 1 h at 650°C. With increasing aging time at 650°C Cu atoms continuously concentrate to Cu-rich segregation areas (clusters) and simultaneously other kinds of atoms such as Fe, Cr and Ni diffuse away from Cu-rich segregation areas to austenitic matrix, and finally to complete the transformation from Cu-rich segregation areas to Cu-rich phase. However, there is only Cu atoms concentration but not crystallographic transformation from early stage of Cu-rich clusters forming to the final Cu-rich phase formation. Even the Cu atom becomes the main composed element after 500 h aging at 650°C the Cu-rich phase still keeps coherent relationship with austenitic matrix. According the experimental results in this study, Cu-rich phase precipitation sequence which starts from the Cu atom segregation followed by the Cu diffusing from matrix to segregation areas and Fe, Cr and Ni atoms diffuse out from Cu-rich areas to matrix without crystallographic transformation is proposed. The Cu-rich phase is the most dispersed phase and contributes the most important strengthening effect among all precipitated phases (M23C6, MX and Cu-rich phase). It has been found that Cu-rich phase is very stable and still keeps in nano-size even for 10,000 h aging at 650°C. The unique precipitation strengthening of Cu-rich phase in combination with nano-size Nb-rich MX phase and grain-boundary M23C6carbide contributes excellent strengthening effect to 18Cr9 NiCuNb austenitic heat resistant steel.     

Effects of cupric ions on the corrosion behavior of aluminum alloy 5A02 in ethylene glycol-water solution

The effects of cupric ions on the corrosion behavior of aluminum alloy 5A02 in ethylene glycol-water solutions were studied by potentiodynamic polarization, electrochemical noise (EN), and complementary techniques including scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). A positive corrosion potential and increased corrosion current were observed due to the deposition of copper. The results demonstrate that the main corrosion type was pitting and the increasing cupric ion concentration augmented the pitting density. The pits became larger and deeper as a result of the embedment of copper into the surface of the alloy. Cupric ions were preferentially deposited at the defects around the secondary phase, leading to the formation of Al-Cu microgalvanic couples, which increased the corrosion rate. The corrosion rate gradually reached a stable value as the concentration of cupric ions was increased beyond 10 mmol/L.     

Effect of Ce addition on hot corrosion behaviours of a cast γ′-strengthened Co–Al–W–Mo–Ta–B alloy at 800 ​°C

Hot corrosion behaviours of a novel Co–9Al-4.5W-4.5Mo–2Ta-0.02B alloy doped with 0.01, 0.05, 0.1 and 0.2 ?at% Ce exposed at 800 ?°C in a solution of 75%Na₂SO₄/25%NaCl were investigated. The alloys comprised a coherent γ-Co_SS/γ′-Co₃(Al, W) microstructure (0.01Ce and 0.05Ce alloys) and κ-Co₃(W, Mo) precipitates (0.1Ce and 0.2Ce alloys) at grain boundaries. Hot corrosion kinetics curves demonstrated the parabolic time dependency profile with two stages: the first parabolic stage is within the beginning ～50 ?h corrosion and follows by the second parabolic stage. With an increasing nominal Ce content the weight gain of the alloy significantly decreased from approximately 70.1 ?mg ?cm^?2 (0.01Ce) to 40.8 ?mg ?cm^?2 (0.2Ce) when exposed for 100 ?h. A two-layer corrosion scale formed, and the scale was composed of an outer layer of Co₃O₄ oxide with spinel compounds of CoAl₂O₄, CoWO₄and CoSO₄, and an inner γ/needle-like Co₃W/sulphide layer adhered to the substrate. Heavy spallation of the corrosion scale occurred in the 0.01Ce～0.1Ce alloys, however, spallation was slight in the 0.2Ce alloy. The excellent corrosion resistance of the 0.2Ce alloy could be attributed mainly to the formation of continuous Al₂O₃ lines in the corrosion scale, as well as the prolongation of the incubation period of the corrosion product spallation.     

Corrosion behavior of Mg–Y alloy in NaCl aqueous solution

The corrosion behavior of Mg–(0.25, 2.5, 5, 8 and 15)Y alloys in 3.5wt.% NaCl aqueous solution was investigated. It was found that the degree of corrosion deterioration increased with increasing immersion time up to 2 h. Corrosion modes for the alloys with low and high content of Y element were general corrosion and pitting corrosion, respective ly, and the threshold content for the corrosion mode change was 2.5% for the tested alloys. The experimental results showed that the addition of Y refined the grain of the alloy, and the distribution, i.e., continuous or not, of the Mg24Y5 phases had great effect on the corrosion rate and corrosion mode.     

Co-oxidation of arsenic(Ⅲ) and iron(Ⅱ) ions by pressurized oxygen in acidic solutions

The co-oxidation of As(Ⅲ) and Fe(Ⅱ) in acidic solutions by pressured oxygen was studied under an oxygen pressure between 0.5 and2.0 MPa at a temperature of 150℃. It was confirmed that without Fe(Ⅱ) ions, As(Ⅲ) ions in the solutions are virtually non-oxidizable by pressured oxygen even at a temperature as high as 200℃ and an oxygen pressure up to 2.0 MPa. Fe(Ⅱ) ions in the solutions did have a catalysis effect on the oxidation of As(Ⅲ), possibly attributable to the production of such strong oxidants as hydroxyl free radicals(OH·) and Fe(IV) in the oxidation process of Fe(Ⅱ). The effects of such factors as the initial molar ratio of Fe(Ⅱ)/As(Ⅲ), initial pH value of the solution, oxygen pressure, and the addition of radical scavengers on the oxidation efficiencies of As(Ⅲ) and Fe(Ⅱ) were studied. It was found that the oxidation of As(Ⅲ) was limited in the co-oxidation process due to the accumulation of the As(Ⅲ) oxidation product, As(V), in the solutions.     

Electrochemical behavior and corrosion resistance of IrO_2–ZrO_2 binary oxide coatings for promoting oxygen evolution in sulfuric acid solution

In this study, we prepared Ti/IrO_2–ZrO_2 electrodes with different ZrO_2 contents using zirconium-n-butoxide(C_(16)H_(36)O_4Zr) and chloroiridic acid(H_2IrCl_6) via a sol–gel route. To explore the effect of ZrO_2 content on the surface properties and electrochemical behavior of electrodes, we performed physical characterizations and electrochemical measurements. The obtained results revealed that the binary oxide coating was composed of rutile IrO_2, amorphous ZrO2, and an IrO_2–ZrO_2 solid solution. The IrO_2–ZrO_2 binary oxide coatings exhibited cracked structures with flat regions. A slight incorporation of ZrO_2 promoted the crystallization of the active component IrO_2. However, the crystallization of IrO_2 was hindered when the added ZrO_2 content was greater than 30 at%. The appropriate incorporation of ZrO_2 enhanced the electrocatalytic performance of the pure IrO_2 coating. The Ti/70 at%IrO_2–30 at%ZrO_2 electrode, with its large active surface area, improved electrocatalytic activity, long service lifetime, and especially, lower cost, is the most effective for promoting oxygen evolution in sulfuric acid solution.     

Impoverishment of Soil Nutrients in Gully Erosion Areas in Yuanmou Basin

The impoverishment of soil nutrients of nine gully head areas in Yuanmou Basin is assessed through an integrated evaluation method established on the basis of Fuzzy mathematics and multivariate mathematical theory. Results show that soil erosion of gully erosion area in Yuanmou basin has resulted in severe impoverishment of soil nutrients. All gully head areas are at high leves of impoverishment except for one at middle. By probing into and analyzing the mechanism of impoverishment of soil nutrients, we find that soil erosion has led to impoverishment of soil nutrients in a way of compacting soil, heightening position of obstacle horizon, and reducing the content of organic matter, as well as the direct loss of nutrient elements. Finally, this paper points out that soil and water conservation arming at the prevention of soil erosion is the most effective way against impoverishment of soil nutrients in Yuanmou basin.     

Reconstruction of broken Si–O–Si bonds in iron ore tailings (IOTs) in concrete

This paper reports a study on the reconstruction of broken Si-O-Si bonds in iron ore tailings (IOTs) in concrete. Limestone and IOTs were used to investigate the influence of different types of coarse aggregates on the compressive strengths of concrete samples. The differences in interfacial transition zones (ITZs) between aggregate and paste were analyzed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Meanwhile, X-ray diffraction (XRD) and infrared spectroscopy (IR) were used to study microscopic changes in limestone and IOTs powders in a simple alkaline environment that simulated cement. The results show that the compressive strengths of IOTs concrete or paste are higher than those of limestone concrete or paste under identical conditions. The Ca/Si atom ratios in the ITZs of IOTs concrete samples are lower than those of limestone concrete; the diffraction peak of the calcium silicate phase at 2θ=29.5°, as well as the bands of Si-O bonds shifting to lower wavenumbers, indicates reconstruction of the broken Si-O-Si bonds on the surfaces of IOTs with Ca(OH)₂.     

Fabrication of plain carbon steel/high chromium white cast iron bimetal by a liquid–solid composite casting process

High-chromium white cast iron(HCWCI) is one of the most widely used engineering materials in the mining and cement industries. However, in some components, such as the pulverizer plates of ash mills, the poor machinability of HCWCI creates difficulties. The bimetal casting technique is a suitable method for improving the machinability of HCWCI by joining an easily machined layer of plain carbon steel(PCS) to its hard part. In this study, the possibility of PCS/HCWCI bimetal casting was investigated using sand casting. The investigation was conducted by optical and electron microscopy and non-destructive, impact toughness, and tensile tests. The hardness and chemical composition profiles on both sides of the interface were plotted in this study. The results indicated that a conventional and low-cost casting technique could be a reliable method for producing PCS/HCWCI bimetal. The interfacial microstructure comprised two distinct layers: a very fine, partially spheroidized pearlite layer and a coarse full pearlite layer. Moreover, characterization of the microstructure revealed that the interface was free of defects.     

Prediction of grain structure in direct-chill cast Al–Zn–Mg–Cu billets using cellular automaton-finite element method

A cellular automaton-finite element(CA-FE) model was used to predict the solidification grain structure of permanent mold cast A7086 alloy. In this model, a Gaussian distribution of nucleation sites was adopted, and the Kurz-Giovanola-Trivedi model was extended to a multicomponent Al–Zn–Mg–Cu alloy system to determine the growth kinetics of the dendrite tip. For describing the Gaussian distribution of nucleation sites on the mold surface, an empirical relationship between the initial cooling rat...     

Structure and corrosion resistance of Al–Cu–Fe alloys

The microstructure and electrochemical properties of Al–Cu–Fe alloys with the atomic compositions of Al_(65)Cu_(20)Fe_(15),Al_(78)Cu_7Fe_(15)and Al_(80)Cu_5Fe_(14)Si_1have been studied.The alloys were produced by induction melting of pure elements with copper mold casting.The microstructure of the alloys was analyzed by X-ray diffraction and high-resolution transmission electron microscopy.The formation of quasicrystalline phases in the Al–Cu–Fe alloys was confirmed.The presence of intermetallic phases was observed in the alloys after crystallization in a form of ingots and plates.The electrochemical measurements were conducted in 3.5%NaCl solution.The electronic structure of the alloys was determined by X-ray photoelectron spectroscopy.The post corrosion surface of the samples was checked using a scanning electron microscope equipped with the energydispersive X-ray detector.It was observed that the Al_(65)Cu_(20)Fe_(15)alloy had the highest corrosion resistance.The improved corrosion resistance parameters were noted for the plate samples rather than those in the as-cast state.And the hardness of the Al_(65)Cu_(20)Fe_(15)alloy was significantly higher than the other alloy samples.     

Fe-based amorphous coating prepared using high-velocity oxygen fuel and its corrosion behavior in static lead–bismuth eutectic alloy

The Fe_49.7Cr₁₈Mn_1.9Mo_7.4W_1.6B_15.2C_3.8Si₂ amorphous coating was deposited on T91 steel substrate by using the high-velocity oxygen fuel(HVOF) spray technique to enhance the corrosion resistance of T91 stainless steel in liquid lead–bismuth eutectic(LBE). The corrosion behavior of the T91 steel and coating exposed to oxygen-saturated LBE at 400°C for 500 h was investigated. Results showed that the T91substrate ...     

Classification and Assessment of Freeze-Thaw Erosion in Tibet, China

Based on the analysis of existing relevant research result, a theoretical basis for the defining freeze-thawerosion zones of Qinghai-Tibet Plateau was been put forward, and a equation for calculating the altitude of the lower bound of the freeze-thaw erosion zones of Qinghai-Tibet Plateau was been established in this paper. Moreover, the freeze-thaw erosion zones in Tibet was been identified by using Geographical Information System (GIS) software. Next, based on thecomprehensive analysis of impact factors of freeze-thaw erosion, this paper chooses annul temperature range, slop and vegetation as three indexes, works out the criteria for relative classification of freeze-thaw erosion, and realizes the relative classification of the freeze-thaw erosion in Tibet under the support of GIS software. Then, a synthetic assessment of freeze-thaw erosion in Tibet was been done according to the relative classification result.     

Electroplating of Ni/Co–pumice multilayer nanocomposite coatings: Effect of current density on crystal texture transformations and corrosion behavior

The present paper aims to investigate the influence of the current density in the electroplating process on the microstructure, crystal texture transformations, and corrosion behavior of Ni/Co-pumice multilayer nanocomposite coatings. The Ni/Co-pumice composite coatings were prepared by deposition of Ni, followed by the simultaneous deposition of pumice nanoparticles (NPs) in a Co matrix via an electroplating process at various current densities. Afterward, the morphology, size, topography, and crystal texture of the obtained samples were investigated. Furthermore, electrochemical methods were used to investigate the corrosion behavior of the produced coatings in a solution of 3.5wt% NaCl. The results indicated that increasing the plating current density changed the mechanism of coating growth from the cell state to the column state, increased the coating thickness, roughness, and texture coefficient (TC) of the Co (203) plane, and reduced the amount of pumice NPs incorporated into the Ni/Co-pumice composite. The electrochemical results also indicated that increasing the current density enhanced the corrosion resistance of the Ni/Co-pumice composite.