Corrosion resistance of TiO2 films grown on stainless steel by atomic layer deposition

Titanium dioxide (TiO₂) films have been deposited onto stainless steel substrates using atomic layer deposition (ALD) technique. Composition analysis shows that the films shield the substrates entirely. The TiO₂ films are amorphous in structure as characterized by X-ray diffraction. The electrochemical measurements show that the equilibrium corrosion potential positively shifts from − 0.96 eV for bare stainless steel to − 0.63 eV for TiO₂ coated stainless steel, and the corrosion current density decreases from 7.0 × 10^− 7 A/cm² to 6.3 × 10^− 8 A/cm². The corrosion resistance obtained by fitting the impedance spectra also reveals that the TiO₂ films provide good protection for stainless steel against corrosion in sodium chloride solution. The above results indicate that TiO₂ films deposited by ALD are effective in protecting stainless steel from corrosion.     

Improvement in corrosion resistance of CrN coated stainless steel by conformal TiO2 deposition

A conformal titanium dioxide (TiO₂) layer was deposited onto chromium nitride (CrN) coated stainless steel by atomic layer deposition technique, and the electrochemical corrosion test on the CrN single-layer and TiO₂/CrN double-layer coated sample was carried out. The equilibrium corrosion potential of the double-layer coated sample shifted positively compare to that of the single-layer coated one. Moreover, the corrosion current density decreased significantly with the TiO₂ deposition, revealing that better corrosion resistance was obtained after the deposition of the TiO₂ layer. The improvement in corrosion resistance after the TiO₂ deposition was attributed to the blocking of the through-thickness cracks or pinholes in the CrN layer.     

The cracking behavior of anodic films on cast aluminum alloy after heating in the temperature range up to 300 °C

The cracking behavior of sealed anodic films on cast aluminum alloy after heating in the temperature range up to 300 °C was studied and the effects of anodizing temperature, heating temperature and heating rate on cracking behavior were investigated. The results showed that before heating some micro-cracks were present in sealed anodic films on the aluminum alloy tested. After heating between 100 °C and 300 °C, the initial micro-cracks became wider and deeper, and new cracks also may be initiated in the film. As anodizing temperature increased, both the crack density and the crack width increased after heating, which was attributed to increase of the porosity of the anodic films formed at higher temperatures. At higher heating temperature, the cracks obviously got wider, but the crack density remained almost unchanged. Increased heating rate resulted in more cracks in the anodic film, indicating that higher strain rate may promote initiation of the micro-cracks, while cooling rate had little influence on cracking behavior.     

A new type of pilot arc power source used for A．C． plasma arc welding of aluminum alloys

ＡｎｅｗｔｙｐｅｏｆｐｉｌｏｔａｒｃｐｏｗｅｒｓｏｕｒｃｅｕｓｅｄｆｏｒＡ．Ｃ．ｐｌａｓｍａａｒｃｗｅｌｄｉｎｇｏｆａｌｕｍｉｎｕｍａｌｌｏｙｓ￥ＺｈｅｎｇＢｉｎｇ；ＷａｎｇＱｉｌｏｎｇａｎｄＬｉＸｉａ（ＨａｒｂｉｎＩｎｓｔｉｔｕｔｅｏｆＴｅｃｈｎｏ...     

New advances for cast iron welding in China in last decade

ＮｅｗａｄｖａｎｃｅｓｆｏｒｃａｓｔｉｒｏｎｗｅｌｄｉｎｇｉｎＣｈｉｎａｉｎｌａｓｔｄｅｃａｄｅ￥ＳｕｎＤａｑｉａｎ；ＲｅｎＺｈｅｎａｎａｎｄＺｈｏｕＺｈｅｎｆｅｎｇ（ＪｉｌｉｎＵｎｉｖｅｒｓｉｔｙｏｆＴｅｃｈｎｏｌｏｇｙ．Ｃｈａｎｇｃｈｕｎ）Ａｂｓ...     

Effect of tunneling barrier as spacer on exchange coupling of CoFeB/AlOx/Co trilayer structures

Magnetic tunneling junctions (MTJs) have a sandwiched structure, which comprises a top ferromagnetic (FM1) layer, an insulating tunneling layer (spacer), and a bottom ferromagnetic (FM2) layer. Exchange coupling in MTJs has been extensively widely examined because the effect of spacer thickness on the ferromagnetic spin-coupling can be exploited in read-head sensors, spin-valve structures, and magntoresistance random access memories (MRAMs). In this investigation, MTJs were deposited in the sequence, glass/CoFeB(50 Å)/AlO_x(d)/Co(100 Å), where the thickness of the AlO_x layer d = 12, 17, 22, 26 or 30 Å. Saturation magnetization (M_s) results demonstrate that the exchange coupling strength and coercivity (H_c) can be varied considerably by varying the tunneling barrier AlO_x spacer. The X-ray diffraction patterns (XRD) include a main peak from hexagonal close-packed (HCP) Co with a highly (0 0 2) textured structure at 2θ = 44.7°, and AlO_x and CoFeB are amorphous phases. The full width at half maximum (FWHM) of the Co (0 0 2) peak declines as the AlO_x thickness increases, revealing that the Co layer becomes more crystalline. The magnetic results reveal that the magnetic characteristics are related to the Co crystallinity. The exchange coupling strength increases with AlO_x thickness. The coercivity (H_c) also increases, because the Co crystallinity is eliminated.     

Application of the induction plasma to the synthesis of two dimensional steam methane reforming Ni/Al2O3 catalyst

The purpose of the study is to develop a new protocol for preparing supported two dimensional catalysts with high external and low internal surface by combining thermal plasma spraying and thermal plasma chemical vapour deposition (TPCVD) processes. The method was tested for the production of an Al₂O₃ supported Ni catalysts used for methane steam reforming. The deposition of catalytic materials is made in 2 successive steps. The first step deals with alumina powder sprayed by induction plasma spraying (IPS) on a molybdenum substrate. The experimental conditions have been turned towards γ-Al₂O_3. The second stage deals with the deposition of nickel at the nanometric scale on the alumina layer using the thermal plasma chemical vapour deposition method. This last step was focused on the study of the influence of the nozzle type employed for the nickel solution spraying, the reactor internal pressure, the concentration and the flow rate of nickel salts solution, Ni(NO₃)₂·6H₂O, on the catalyst response. The formulations were tested as methane steam reforming catalysts.The results demonstrate that the catalyst morphology depends on plasma projection conditions and show the effectiveness of combining IPS and TPCVD processes for producing catalysts in methane steam reforming.     

The effects of sealing on cracking tendency of anodic films on 2024 aluminum alloy after heating up to 300 °C

The influence of sealing methods on cracking tendency of anodic films on 2024 alloys after heating was studied. The anodic films were sealed by the methods of ambient water, boiling water, nickel fluoride and potassium dichromate, respectively. The results showed that the sealing mechanisms had important effects on initiation of cracks in anodic films during sealing process. The condensation of sealing products resulted in cracking of anodic films during sealing in boiling water, nickel fluoride solution and ambient water. On heating, the thermal stress was released mainly by widening and deepening of the originally initiated cracks during sealing. The cracks may penetrate through the anodic films and have detrimental effect on corrosion resistance of the films. The dichromate sealed anodic film showed an obviously decreased cracking tendency, which was attributed to the lower hydration extent and the opening pores during sealing process. Even after heating, there was no crack observed in the film. The result suggests that an “opening sealing” mode is beneficial to decrease the cracking tendency of anodic films during sealing and heating processes.     

Microstructure development in Cr-Al-Si-N nanocomposites deposited by cathodic arc evaporation

Phase and texture analysis using X-ray diffraction, analysis of the diffraction line broadening, analysis of the lattice parameters and high-resolution transmission electron microscopy were employed to characterize the microstructure development in the Cr-Al-Si-N thin film nanocomposites with a variable [Cr] / ([Al] + [Si]) ratio deposited by cathodic arc evaporation. At the highest chromium contents, a single face centered cubic phase formed in the coatings. Below [Cr] / ([Cr] + [Al] + [Si]) ≈ 0.52, a second crystalline phase developed that was identified as hexagonal AlN. The size of the fcc crystallites decreased with increasing aluminum and silicon contents until it reached 5 nm in the sample with the overall chemical composition Cr_0.40Al_0.52Si_0.08N. The small crystallite size and the presence of two crystalline phases were found to be responsible for a high hardness of the Cr-Al-Si-N nanocomposites. Analysis of the lattice parameters revealed strong crystal anisotropy of the elastic constants in the cubic phase that decreased with increasing aluminum and silicon contents.     

Electroless copper deposition on a pitch-based activated carbon fiber and an application for NO removal

Pitch fibers were prepared from petroleum-derived isotropic pitch precursors using melt-blown spinning. Activated carbon fibers (ACF) were formed from pitch fibers and after stabilization, carbonization and steam thermal activation were then further activated with Pd-Sn catalytic nuclei in a single-step process. The activated ACF were then used as supporters in the specific, electroless deposition of fine copper particles. Field emission scanning electron microscopy-energy dispersive X-ray spectroscopy results showed that the ACF were uniformly coated with nearly pure fine copper particles, and the copper content on the ACF increased with deposition time. The amounts of copper on the ACF and their crystalline characteristics were analyzed using an inductively coupled plasma and a X-ray diffractometry, respectively. With the copper particles-deposited on the ACF, the removal of nitrogen monoxide (NO) for four different deposition times (5, 10, 15 and 20 min) was tested. Experiments on the removal of NO were carried out in a packed bed tubular reactor with various reaction temperatures ranging between 423 and 673 K. For all deposition times, the NO removal efficiency increased with increasing reaction temperature up to 673 K. The NO removal efficiency was the highest when the amount was Cu/ACF = 110 mg/g (deposition time of 5 min), however, decreased at Cu/ACF beyond 110 mg/g (deposition times of 10, 15, 20 min) due to the decreased adsorption as a result of the increased amount of copper.     

GROWTH OF β-SiC BY rf SPUTTERING ON SILICON SUBSTRATES

1. IlltroductiollSili(.oll t.arbide (SiC) llas beell il1vestigated as a nlaterial with great poteIltial il1 high-p()xxer. high teulperature. and high-f1equel1c} devices, sil1ce it has feat[tres of high break-(l()ttll voltage, l1igll satllratioll t.elocit}…     

Evolution of surface chemistry and morphology of oxide scale formed during initial stage oxidation of modified 9Cr–1Mo steel

Initial stage oxidation characteristics of the modified 9Cr–1Mo steel in ambient air at 650 °C have been investigated, for exposure times ranging from 5 to 500 h. Oxygen flux from the gas phase causes high initial oxidation rate, but the growth kinetics do not follow parabolic law. In “as-received” condition, binary oxides of Fe and Cr were found as native oxides. Upon oxidation, segregation of Mn resulted in the formation of MnCr₂O₄ along with FeCr₂O₄ and binary oxides of Fe, Cr and Mn. Thus, the initial oxide scale constitutes multiple oxides with delineated interface, unlikely to have a layered structure.     

Influence of pre-treatment on the surface composition of Al-Zn alloys

The influences of pre-treatments on the composition of Al-Zn alloys, containing 0.6-1.9 at.%Zn, are investigated using scanning and transmission electron microscopies, glow discharge optical emission spectroscopy and ion beam analysis. Alkaline etching, anodic alkaline etching and electropolishing result in zinc enrichments, just beneath the oxide/hydroxide films on the alloy surfaces. The enriched alloy, about 4-5 nm thick, contains zinc in solid-solution with aluminium, up to about 18 at.%. The highest and lowest enrichments are produced by alkaline etching and electropolishing respectively. For a given pre-treatment, the enrichment increases with increase in zinc content of the bulk alloy.     

High temperature carburization behaviour of Mn–Cr–O spinel oxides with varied concentrations of manganese

Mn–Cr–O spinel often formed on austenitic alloys is an oxide phase that could be protective against high temperature carbonaceous attack. In this research, various Mn–Cr–O samples were tested in carburization environments with controlled oxygen partial pressures. The stoichiometric MnCr₂O₄ shows better resistance to carburization and coke formation than the Mn-rich Mn–Cr–O and the Cr-rich Mn–Cr–O samples because of its highest thermodynamic stability as compared with MnO and Cr₂O₃. (Mn,Cr)₇C₃ formed after carburization is catalytic to coke formation, and was found instable at higher levels of H₂O/oxygen and may form volatile phases in the presence of H₂O, leading to a continuous reduction in sample weight.     

Electrochemical behavior of a lead-free Sn–Cu solder alloy in NaCl solution

Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization techniques and an equivalent circuit analysis are used to evaluate the electrochemical corrosion behavior of Sn–Cu alloy samples in a naturally aerated 0.5 M NaCl solution at 25 °C. It has been found that a better electrochemical corrosion resistance is provided by a coarser cellular microstructure array. It has also been found that the corrosion current density (i_corr) is of about a quarter when compared with that of the finest microstructure examined. Such behavior is attributed to both localized strains between the Sn-rich phase and intermetallic (IMC) particles and the cathode/anode area ratios. The effect of copper alloying on i_corr is also discussed.     

Evolution of dissolution processes at the interface of carbon steel corroding in a CO2 environment studied by EIS

The evolution of interfacial phenomena during CO₂ corrosion of C1018 carbon steel was characterized by EIS (Electrochemical Spectroscopy Impedance) and LPR (Linear Polarization Resistance). Turbulent conditions were simulated by a channel flow cell with deoxygenated 3 wt.% NaCl solution at 80 °C and pH 6 during 158 h. EIS helped in the characterization of the dynamic mechanism during the formation of the unprotective porous Fe₃C layer, and subsequent precipitation of the protective FeCO₃ layer inside the cementite. The experimental response of the active states at the interface was characterized by electrical passive elements with constant phase parameter analogs showing good agreement with the experimental results.     

Optimization of transparent conducting oxide ZnO compound thickness in terms of four alloys thermo-physical performance aggregates

ZnO is one of the well-known metal oxide semiconductors, which has been found, in the last four decades, to be very useful as transparent conductors and UV detectors in optoelectronic devices. This binary compound that showed quantum confinement effects in accessible size ranges was elaborated using several techniques. In the present work, the sprayed pyrolysis technique was carried out to prepare undoped ZnO crystals with different controlled thicknesses.Particularly, and parallel to recently performed measurements, a recently proposed range of optimal layer thickness d is validated, through original conjoint morphological-structural-physical investigations.     

PEO protective coatings on inner surface of tubes

Plasma electrolytic oxidation (PEO), also called micro-arc oxidation (MAO) or anode spark deposition (ASD), is a novel technique to produce hard ceramic coatings on metals, such as aluminum, titanium, magnesium (called valve metals) and their alloys. Up to now, many researchers focused on the PEO process for workpieces of regular shapes such as cube, cake or stick samples, etc. But no one paid attention to the irregular samples such as tubular materials. This research emphasized the PEO process of long tubes, especially the way to obtain uniform thickness of ceramic coatings on inner surface of tubes. Furthermore, the PEO kinetic behaviors of aluminum tubes were also investigated. The potential difference between the electrodes indicated a linear relationship with the coating thickness. A central accessory electrode was axially used to eliminate the shielding effect of electric field and was effective to obtain axially uniform coating on the inner surface of the tubes. The combination of hot-dipping aluminum and PEO process to obtain ceramic coating on 45# steel tubes was also performed in this work.     

Liquid-state interfacial reactions in Sn–Zn/Pd couples and phase equilibria of the Sn–Zn–Pd system at 260 °C

This study investigated the effects of Zn contents on the reaction products and microstructural evolution in the liquid/solid Sn–Zn/Pd interfacial reactions at 260 °C. A uniform Pd₂Zn₉ layer was formed at the Sn–9 wt.%Zn/Pd interface. The reaction phase transited from Pd₂Zn₉ to PdSn₄ when the Zn content decreased from 2 wt.% to 1 wt.%. The most striking feature is that the PdSn₄ growth was greatly suppressed with only 0.5 wt.% Zn addition in solders. Additionally, a drastic microstructural evolution was observed in the Sn–1.5 wt.%Zn/Pd reaction. The Pd₂Zn₉ layer was initially formed and then it was detached from the interface due to the decrease in the Zn content. Subsequently, the dominant phase changed to the PdSn₄ phase. Furthermore, a partial isothermal section in the Sn–Zn–Pd ternary system (less than 20 at.%Pd) at 260 °C was experimentally determined. The liquid apex of the liquid + PdSn₄ + Pd₂Zn₉ tie-triangle was located at Sn–2.7 at.%Zn–1.0 at.%Pd. The phase transition from Pd₂Zn₉ to PdSn₄ in the interfacial reactions was in good agreement with the phase equilibria relationship.