Short-time Oxidation of Alloy 690 in High-temperature and High-pressure Steam and Water

The oxidation behavior of alloy 690 exposed to high-temperature and high-pressure steam and water at 280 ℃ for 1 h was investigated by scanning electron microscopy(SEM),atomic force microscopy(AFM) and X-ray photoelectron spectroscopy(XPS).In high-temperature and high-pressure steam,the oxide film is composed of an outermost Ni-rich hydroxides layer,an intermediate layer of hydroxides and oxides enriched in Cr,an inner oxide layer.The film formed in high-temperature water is similar to that in steam,except for missing the Ni-rich hydroxides layer.Samples with different surface finishes(electropolished,mechanically polished,ground,and as-received) were prepared for comparison.A general increase of the oxide thickness with the degree of surface roughness is observed.The equivalent oxide thicknesses lie in the range of 100-200 nm for the as-received samples,150-250 nm for the samples ground to 400# and 10-20 nm for the samples ground to 1500#,mechanically polished,and electropolished.     

Constitutive modeling of nitrogen-alloyed austenitic stainless steel at low and high strain rates and temperatures

In this paper, microstructures-based constitutive relations are introduced to simulate the thermo-mechanical response of two nitrogen-alloyed austenitic stainless steels; Nitronic-50 and Uranus-B66, under static and dynamic loadings. The simulation of the flow stress is developed based on a combined approach of two different principal mechanisms; the cutting of dislocation forests and the overcoming of Peierls–Nabarro barriers. The experimental observations for Nitronic-50 and Uranus-B66 conducted by Guo and Nemat-Nasser (2006) and Fréchard et al. (2008), respectively, over a wide range of temperatures and strain rates are also utilized in understanding the underlying deformation mechanisms. Results for the two stainless steels reveal that both the initial yielding and strain hardening are strongly dependent on the coupling effect of temperatures and strain rates. The methodology of obtaining the material parameters and their physical interpretation are presented thoroughly. The present model predicts results that compare very well with the experimental data for both stainless steels at initial temperature range of 77–1000 K and strain rates between 0.001 and 8000 s⁻¹. The effect of the physical quantities at the microstructures on the overall flow stress is also investigated. The evolution of dislocation density along with the initial dislocation density contribution plays a crucial role in determining the thermal stresses. It was observed that the thermal yield stress component is more affected by the presence of initial dislocations and decreases with the increase of the originated (initial) dislocation density.     

Water and corrosion resistance of epoxy–acrylic–amine waterborne coatings: Effects of resin molecular weight,polar group and hydrophobic segment

A two-step esterification process is developed for the synthesis of epoxy–acrylic-grafted-copolymer waterborne resins. The effect of synthesis parameters on water and corrosion resistance of the waterborne coatings is investigated. The results reveal that moderate increasing of the resin molecular weight (<8000 Da) and carboxyl content (<27 wt.%) increased the crosslinking property, thereby improved the anticorrosion performance of the coatings. Longer epoxy-octanoic hydrophobic chains can provide stronger shielding effect on the hydrophilic portion of the polymer matrixes. The polar group content in a waterborne resin can be optimized for better anticorrosion performance, whereas the optimal value is coating-specific.     

The influence of chromium content on the electrochemical behavior of weathering steels

To investigate the influence of chromium content on corrosion characteristics of weathering steels, the electrochemical measurements were performed on the steels containing 0–9% Cr (wt.%) in NaHSO₃ aqueous solution. The results indicated that the open circuit potential of these steels shifted to the positive direction remarkably, because the additions of Cr improved the passivation capability of the steels. The corrosion current density of the steels containing more than 7% Cr (wt.%) decreased significantly after pre-rusted treatment, implying the corrosion resistance could be enhanced by the formation of protective goethite rust layer.     

Corrosion behaviour of AM60 magnesium alloys containing Ce or La under thin electrolyte layers. Part 2: Corrosion product and characterization

The corrosion behaviour of AM60 containing Ce or La (AMRE1) under thin electrolyte layers (TEL) in 3.5 wt.% NaCl solution was investigated. The composition and structure of corrosion product was analyzed by XRD, FTIR, SEM and EDS. The results indicated crystal corrosion products were not affected by TEL and the amorphous ones are Mg(OH)₂ and compounds containing CO₃²⁻ in corroded section and only latter one is present in “unaffected” area. The smart map further confirmed the skeleton structure formed due to RE alloying. Moreover corrosion morphologies of AMRE1 alloys exhibited localized corrosion and pit initiation was inhibited by TEL.     

Corrosion behaviour of AM60 magnesium alloys containing Ce or La under thin electrolyte layers. Part 1: Microstructural characterization and electrochemical behaviour

The corrosion behaviour of AM60 containing Ce or La (AMRE1) under thin electrolyte layers (TEL) in 3.5 wt.% NaCl solution was investigated by cathodic polarization and EIS. The results indicated corrosion resistance was enhanced by TEL decrease until 100 μm. There were three kinetic regions in polarization curves of AMRE1, whereas the second region disappeared for AM60. Meanwhile, EIS results showed capacitive loop at LFs for AMRE1 appeared under 200-300 μm thickness. The presence of second regions in polarization curves and capacitive loops at LFs in EIS was attributed to performance of new phases (γ) as indicated in microstructural characterization.     

Hot corrosion properties of composite coatings in the presence of NaCl at 700 and 900 °C

Cyclic hot corrosion tests have been carried out on three coatings (one NiCoCrAlY and two composite coatings) at 700 and 900 °C. The kinetic curves and evolution of microstructure show that the composite coating with a Cr-base interlayer performs best. The Cr₂O₃ scale is more effective to protect the coating at 700 °C than that at 900 °C. The corrosion process is accelerated by NaCl via forming volatile MCl_x and inducing the formation of molten voids in the coating or extra oxidation at the interface of fusant/oxide scale, determined by the temperature and the compositions of the coating.     

Corrosion protection of type 304 stainless steel bipolar plates of proton-exchange membrane fuel cells by doped polyaniline coating

Polyaniline coating doped with dodecylbenzesulfonate anions is electrodeposited galvanostatically on type 304 stainless steel used as bipolar plates of proton-exchange membrane fuel cell from a basic solution of 0.3 M aniline monomer solution containing sodium dodecylbenzesulfonate as a supporting electrolyte. Electrochemical measurements in 1 M H₂SO₄ and in 0.3 M HCl show that the polyaniline coating increases the free corrosion potential of the steel by more than 300 mV and 450 mV, respectively, with a corrosion rate more than two orders of magnitude lower than that of the uncoated steel. Long-term exposure studies show that the coating is highly stable and inhibits the corrosion of the steel effectively.     

高孔率泡沫状MnO_2催化材料的制备及其催化性能

以泡沫海绵为基体材料,采用电镀的方法制备了高孔率泡沫状MnO_2催化材料,测定其孔隙率和比表面积,利用X射线光电子能谱和扫描电镜对MnO_x膜层的组成和形貌进行分析,并通过臭氧催化分解试验评价其催化性能。结果表明,泡沫状MnO_2催化材料具有超大的比表面积,约为29.6 m~2·m~(-3),孔隙率达95%以上,6片高孔率泡沫状MnO_2催化片对臭氧的催化率第9天后仍高达97.75%,具有良好的催化性能。     

Effects of low temperature on the characteristics of tantalum thin films

In this paper the effects of substrate temperature (room temperature – 350 °C) on the phase composition and crystallization orientation of the tantalum thin film deposited by direct current magnetron sputtering in an extremely low power deposition regime are presented. In this experiment, heating the substrates to 350 °C resulted in the growth of the hard and brittle tetragonal crystalline structure (β-Ta). Deposited tantalum has a conical structure with large voided boundaries. Sheet resistance of samples is much larger than for the convenient conductors which decreased with increasing the substrate temperature.