Corrosion Resistance of Artificial Passive Film and Real Passive Film on Fe-Ti Alloy

The corrosion resistances of Fe₂O₃-TiO₂ artificial passive film and real passive film on the sputter-deposited Fe-Ti alloy films were examined in acid solutions. The Fe₂O₃-TiO₂ films containing less than XTi=0.70 have a spinal structure, the films containing more than XTi=0.70 have an amorphous structure. The dissolution rate of the Fe₂O₂-TiO₂ films in 5 M HCI decreased with an increase in the titanium cationic fraction in the films. The Fe₂O₃TiO₂ films dissolved at cathodic potentials in 1 M H₂SO₄ and 1 M HCl owing to the selective reduction of Fe₂O₃ components in the films. Sputter-deposited Fe-Ti alloy films containing more than 39 at.% Ti passivated anodically in 1 M H₂SO₄ and 1 M HCl. and showed high corrosion resistance. The Fe₂O3TiO₂ artificial passive films have a higher corrosion resistance than real passive films on the sputter-deposited Fe-Ti alloy films in 5 M HCl.     

Influence of cold gas spray parameters on the corrosion resistance of Al-Al2O3 coatings sprayed on carbon steel

ABSTRACT

This work describes the influence of standoff distance (SoD), and gas temperature on the morphology and corrosion resistance of Al-10%Al₂O₃ coatings deposited by cold gas spray (CGS) on carbon steel. The results showed that the standoff distance had little effect on the thickness and microstructure of the coating. However, a 100 °C decrease of the spraying temperature reduced the coating thickness by 300?µm. The use of electrochemical analyses and SEM images showed that all the coatings studied were able to protect the substrate during at least 1300?h of immersion, due to the dense microstructure obtained by CGS.     

Reactive-element effect of electrodeposited Y2O3 oxide films on the oxidation of Fe−25Cr and Fe−25Cr−10Al alloys

Thin Y₂O₃ films were deposited by the electrochemical deposition-pyrolysis process on Fe–25Cr and Fe–25Cr–10Al alloys. The influence of the films on the oxidation behavior of the alloys was studied at 850°C and 1000°C. The results showed that Y₂O₃ films remarkably decreased the oxidation rate of Cr₂O₃-forming alloys and spallation of the scales, but they did not decrease the oxidation rate of the Al₂O₃-forming alloys, although they do reduce the spallation of Al₂O₃ scales. Y₂O₃ films remarkably change the morphology of the scales on both alloys, depending on the oxidation temperatures. These results show that the reactive-element effects of Y₂O₃ films on the Cr₂O₃ formers and Al₂O₃ formers are different.     

Effect of Na2SO4 and Water Vapor on the Corrosion of Ti3SiC2

The corrosion behavior of polycrystalline Ti₃SiC₂ was studied in the presence of Na₂SO₄ deposit and water vapor at 900°C and 1000°C. The mass gain per unit area of the samples superficially coated with Na₂SO₄ exposed to water vapor was slightly lower than that of the samples corroded without water vapor. The microstructure and composition of the scales were investigated by SEM/EDS and XRD. Pores were observed in the corroded sample surfaces. The main corrosion phases on the sample surface were identified by XRD as TiO₂, Na₂Si₂O₅ and Na₂TiO₃. After Ti₃SiC₂ corroded in the presence of the Na₂SO₄ deposit and water vapor, the scale had a three-layer microstructure, which was different from the duplex corrosion scale formed on Ti₃SiC₂ beneath the Na₂SO₄ film without water vapor. Because water vapor penetrated the corrosion layer and then reacted with SiO₂ to form volatile Si(OH)₄, an intermediate porous and TiO₂-enriched layer formed in the corrosion layer.     

The corrosion behavior of Fe-Nb-Al alloys in H2/H2O/H2S atmospheres

The corrosion behavior of eight Fe-Nb-Al ternary alloys was studied over the temperature range 700–980°C in H₂/H₂O/H₂S atmospheres. The corrosion kinetics followed the parabolic rate law for all alloys at all temperatures. The corrosion rates were reduced with increasing Nb content for Fe-x Nb -3Al alloys, the most pronounced reduction occurred as the Nb content increased from 30 to 40 wt.%. The corrosion rate of Fe-30Nb decreased by six orders of magnitude at 700°C and by five orders of magnitude at 800°C or above by the addition of 10 wt.% aluminum. The scales formed on low-Al alloys (3 wt.% Al) were duplex, consisting of an outer layer of iron sulfide (with Al dissolved near the outer-/inner-layer interface) and an inner complex layer of Fe_xNb₂S₄(FeNb₂S₄ or FeNb₃S₆), FeS, Nb₃S₄ (only detected for Nb contents of 30 wt.% or higher) and uncorroded Fe₂Nb. No oxides were detected on the low-Al alloys after corrosion at any temperature. Platinum markers were found to be located at the interface between the inner and outer scales for the low-Al alloys, suggesting that the outer scale grew by the outward transport of cations (Fe and Al) and the inner scale grew by the inward transport of sulfur. The scales formed on high-Al alloys (5 wt.% Al) were complex, consisting primarily of Nb₃S₄, Al₂O₃ and (Fe, Al)_xNb₂S₄, and minor amounts of (Fe, Al)S and uncorroded intermetallics (FeAl and Fe₂Nb). The formation of Nb₃S₄ and Al₂O₃ blocked the transport of iron through the inner scale, resulting in the significant reduction of the corrosion rates.     

The high-temperature corrosion behavior of Fe-Mo-Al alloys in H2/H2O/H2S mixed-gas environments

The corrosion behavior of 11 Fe-Mo-Al ternary alloys was studied over the temperature range 700–980°C in H₂/H₂O/H₂S mixed-gas environments. With the exception of Fe-10Mo-7Al, for which breakaway kinetics were observed at higher temperatures, all alloys followed the parabolic rate law, despite two-stage kinetics which were observed in some cases. A kinetics inversion was observed for alloys containing 7 wt.% Al between 700–800°C. The corrosion rates of Fe-20Mo and Fe-30Mo were found to be reduced by five orders of magnitude at all temperatures by the addition of 9.1 or higher wt.% aluminum. The scales formed on low-Al alloys (5 wt.% Al) were duplex, consisting of an outer layer of iron sulfide (with some dissolved Al) and a complex inner of Al_0.55Mo₂S₄, FeMo₂S₄, Fe_1.25Mo₆S_7.7, FeS, and uncorroded FeAl and Fe₃Mo₂. Platinum markers were always located at the interface between the inner and outer scales for the low-Al alloys, indicating that outer-scale growth was due mainly to outward diffusion of cations (Fe and Al), while the inner scale was formed primarily by the inward flux of sulfur anions. Alloys having intermediate Al contents (7 wt.%) formed scales that consisted of FeS and Al₂O₃. The amount of Al₂O₃ increased with increasing reaction temperature. The high-Al-content alloys (9.1 and 10 wt.%) formed only Al₂O₃ which was responsible for the reduction of the corrosion rates.     

HOPG上ALD沉积Al2O3介电薄膜的生长行为研究

本文采用原子层沉积(ALD)的方法,选择三甲基铝(TMA)和H₂O₂作为反应前驱体,在高定向热解石墨(HOPG)基体上沉积Al₂O₃。系统研究了反应温度和生长周次对Al₂O₃生长行为的影响。研究表明：受HOPG表面饱和成键的影响,Al₂O₃在衬底表面处形核困难,在生长初期主要表现为台阶处择优生长,其形态为线状结构。当沉积100周次Al₂O₃时,其中在沉积温度为50 °C、150 °C和200 °C时呈现为纳米线状结构,而在100 °C时呈现为非连续薄膜。随着生长周次的增加,不同温度下沉积态Al₂O₃都趋于形成连续薄膜,表明其生长行为发生了由三维岛状生长模式向二维平面生长模式的转变。分析认为,生长模式的转变是由纳米线状结构横向生长造成的;横向生长速率主要受生长温度影响。拉曼结果表明：沉积后的石墨烯层结构未受影响,可保留其原有的优越性能。     

Tunneling magnetoresistance in sintered Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> samples diluted with Fe and α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Electric transport and magnetoresistance characteristics were investigated for Fe₃O₄-x Fe(x=0, 10, 20 wt.%) samples and Fe₃O₄-α-Fe₂O₃ samples sintered at 500°C. For composition dependence of Fe₃O₄-x Fe samples, the largest room temperature MR, 3.3% at 10 kOe, was obtained from a Fe₃O₄-10 Fe sample. For the surface heat treatment dependence of Fe₃O₄ powders, the largest room temperature MR, 4% at 10 kOe, was obtained from a Fe₃O₄-α-Fe₂O₃ sample sintered with Fe₃O₄ powders heated at 200°C in air. It was found that these enhanced MR ratios always appear together with the appropriate excess resistance which is regarded as the tunneling barrier. These enhanced MR ratios of Fe₃O₄-10 Fe and Fe₃O₄-α-Fe₂O₃ samples can be explained by the increased interparticle contact sites and the appropriate thickness of α-Fe₂O₃, respectively.     

Effect of Y2O3 additions on the plasticity of sintered Cr2O3

We have carried our constant strain-rate compression tests on polycrystalline Cr₂O₃ and Cr₂O₃ doped with 0.09 wt. % Y₂O₃ to establish whether there exists an effect of Y₂O₃ on the plasticity of Cr₂O₃. This study is motivated by previous work on the oxidation of alloys containing reactive-element additions. In that work, it has been observed that the addition of oxygen-active elements, such as Y to alloys that form Cr₂O₃ or Al₂O₃ oxide layers upon exposure at high temperature, strongly enhances the adhesion of the oxide layer to the base alloy as compared with alloys without reactive-element additions. We have found that at 1200°C (1) chromia exhibits limited plasticity at high temperatures, and (2) the presence of Y in the oxides does not enhance plasticity compared with addition-free oxides.     

The effect of K2SO4 additive in Na2SO4 deposits on low temperature hot corrosion of iron-aluminum alloys

To understand the effect of K₂SO₄ additive in an Na₂SO₄ deposit on low temperature hot corrosion, the corrosion behavior of Fe-Al alloys induced by Na₂SO₄+K₂SO₄ was compared to that by Na₂SO₄ alone, and sulfation of Fe₂O₃ in the presence of either Na₂SO₄ or Na₂SO₄+K₂SO₄ was studied. It was found that K₂SO₄ additive promoted the low temperature hot corrosion, but did not change the corrosion-mechanism. Experimental results refuted the prior suggestions that the accelerated hot corrosion resulted either from the formation of K₃Fe(SO₄)₃ or from the stimulation of sulfation of Fe₃O₃. The earlier formation of the eutectic melt caused the accelerated hot corrosion, or in other words, the K₂SO₄ additive shortened the induction stage of hot corrosion.     

Epitaxial SrRuO3 thin films deposited on SrO buffered-Si(001) substrates for ferroelectric Pb(Zr0.2Ti0.8)O3 thin films

SrRuO₃ thin film electrodes are epitaxially grown on SrO buffered-Si(001) substrates by pulsed laser deposition. The optimum conditions of the SrO buffer layers for epitaxial SrRuO₃ films are a deposition temperature of 700 °C, deposition pressure of 1 × 10^?6 Torr, and thickness of 6 nm. The 100 nm thick-SrRuO₃ bottom electrodes deposited above 650 °C on SrO buffered-Si (001) substrates have a rms (root mean square) roughness of approximately 5.0 Å and a resistivity of 1700 µω-cm, exhibiting an epitaxial relationship. The 100 nm thick-Pb(Zr_0.2Ti_0.8)O₃ thin films deposited at 575 °C have a (00l) preferred orientation and exhibit 2P_r of 40 µC/cm², E_c of 100 kV/cm, and leakage current of about 1 × 10^?7 A/cm² at 1 V. The silicon oxide phase which presents within PZT and SrRuO₃ films, influences the crystallinity of the PZT films and the resistivity of the SrRuO₃ electrodes.     

Microstructure and characterization of La2O3 and CeO2 doped diamond-like carbon nanofilms

Seven kinds of hydrogen-free La₂O₃ and CeO₂ doped DLC films with thickness of 220-280 nm were deposited on Si (100) substrates by unbalanced magnetron sputtering. Nanoparticles with diameter of 20-30 nm are formed on the surface of films. The surface roughness Ra of films is in the range of 1.5-2.0 nm. C, La, Ce and O elements distribute uniformly along the depth direction, and C, La, and Ce elements diffuse into the Si substrate at the interface. X-ray photoelectron spectroscopy confirms that the La₂O₃ and CeO₂ form within the DLC amorphous films, and Raman spectra indicate the obvious amorphous characteristics of DLC films. High-resolution transmission electron microscopy shows the nanocrystallines structure with diameter of 2-3 nm of 16% La₂O₃ and 10% CeO₂ doped DLC films, and Fourier transformation spectroscopy also exhibits the obvious crystalline characteristics. In this work, the microstructure of two kinds of rare earth oxides doped DLC composite films is measured and analyzed.     

Deposition of Al2O3-TiO2 Nanostructured Powders by Atmospheric Plasma Spraying

Al₂O₃-13%TiO₂ coatings were deposited on stainless steel substrates from conventional and nanostructured powders using atmospheric plasma spraying (APS). A complete characterization of the feedstock confirmed its nanostructured nature. Coating microstructures and phase compositions were characterized using SEM, TEM, and XRD techniques. The microstructure comprised two clearly differentiated regions. One region, completely fused, consisted mainly of nanometer-sized grains of γ-Al₂O₃ with dissolved Ti⁺⁴. The other region, partly fused, retained the microstructure of the starting powder and was principally made up of submicrometer-sized grains of α-Al₂O₃, as confirmed by TEM. Coating microhardness as well as tribological behavior were determined. Vickers microhardness values of conventional coatings were in average slightly lower than the values for nanostructured coating. The wear resistance of conventional coatings was shown to be lower than that of nanostructured coatings as a consequence of Ti segregation. A correlation between the final properties, the coating microstructure, and the feedstock characteristics is given.     

基于磁过滤技术的热障涂层表面Al2O3 覆盖层抗CMAS腐蚀性能

为了提高热障涂层（TBC）的抗沉积物（主要成分为CaO、MgO、Al₂O₃和SiO₂,简称CMAS）腐蚀性能,采用磁过滤阴极真空电弧（FCVA）技术在TBC表面上制备了致密的Al₂O₃覆盖层,比较和分析了Al₂O₃改性TBC和沉积态TBC的润湿行为和抗CMAS腐蚀性能。结果表明：使用FCVA技术制备Al₂O₃覆盖层的过程对7%（质量分数）氧化钇稳定的氧化锆（7YSZ）相的结构无明显影响,且经Al₂O₃改性的TBC综合性能均优于沉积态TBC。在1250 ℃、CMAS腐蚀条件下,Al₂O₃覆盖层有效地限制了熔融CMAS在TBC表面上的扩散行为。同时,Al₂O₃填充了7YSZ柱状晶之间的间隔并且阻碍了熔融CMAS的渗透,证明了FCVA可作为一种制备Al₂O₃涂层的新方法以提高TBC的抗CMAS腐蚀性能,且Al₂O₃涂层及其制备过程对TBC的热震性能均无消极影响。     

Mechanical properties of La2O3 doped diamond-like carbon films

Twelve La₂O₃ doped diamond-like carbon (DLC) nanofilms were deposited using unbalanced dual-magnetron sputtering. AFM, XRD, Raman spectroscopy, AES, XPS, TEM, contact surface profiler and nanoindenter were employed to investigate the structure and tribological properties of deposited films. The results show that the La₂O₃ doped DLC films are amorphous. La₂O₃ doping obviously decreases internal stress, and effectively increases the elastic modulus. This results from the dissolving and dissolution of La₂O₃ within the amorphous DLC matrix. Furthermore, the friction coefficient of the doped DLC films decreases, and adhesion strength increases. These are attributed to the lubrication function of La₂O₃ and the formation of transition layer at interface, respectively.     

Effect of O2 on down-hole corrosion during air-assisted steam injection for heavy oil recovery

ABSTRACT

Air-assisted steam injection is used to enhance hydrocarbon recovery from heavy oil reservoirs. During this process, downhole tubular goods are subject to corrosion in a mixed oxygen-carbon dioxide-steam environment at temperature up to around 200°C causing a low-temperature oxidation phenomenon. Here we investigate the influence of the O₂/CO₂ ratio on the corrosion of P110 steel, a grade that is commonly used for oil well casings. Our findings show that corrosion is greatly influenced by the O₂ pressure but hardly at all by the CO₂ pressure. The maximum corrosion rate was in excess of 65?mm per year. However, alkalisation of the injected fluid, which promoted the formation of a protective magnetite scale, was found to greatly reduce corrosion.     

Effects of K2O-Li2O doping on surface and catalytic properties of Fe2O3/Cr2O3 system

The effects of K₂O and Li₂O-doping (0.5, 0.75 and 1.5 mol%) of Fe₂O₃/Cr₂O₃ system on its surface and the catalytic properties were investigated. Pure and differently doped solids were calcined in air at 400-600 °C. The formula of the un-doped calcined solid was 0.85Fe₂O₃:0.15Cr₂O₃. The techniques employed were TGA, DTA, XRD, N₂ adsorption at −196 °C and catalytic oxidation of CO oxidation by O₂ at 200-300 °C. The results revealed that DTA curves of pure mixed solids consisted of one endothermic peak and two exothermic peaks. Pure and doped mixed solids calcined at 400 °C are amorphous in nature and turned to α-Fe₂O₃ upon heating at 500 and 600 °C. K₂O and Li₂O doping conducted at 500 or 600 °C modified the degree of crystallinity and crystallite size of all phases present which consisted of a mixture of nanocrystalline α- and γ-Fe₂O₃ together with K₂FeO₄ and LiFe₅O₈ phases. However, the heavily Li₂O-doped sample consisted only of LiFe₅O₈ phase. The specific surface area of the system investigated decreased to an extent proportional to the amount of K₂O and Li₂O added. On the other hand, the catalytic activity was found to increase by increasing the amount of K₂O and Li₂O added. The maximum increase in the catalytic activity, expressed as the reaction rate constant (k) measured at 200 °C, attained 30.8% and 26.5% for K₂O and Li₂O doping, respectively. The doping process did not modify the activation energy of the catalyzed reaction but rather increased the concentration of the active sites without changing their energetic nature.     

Structural and dielectric properties of Bi2Zn2/3Nb4/3O7 thin films prepared by pulsed laser deposition at low temperature for embedded capacitor applications

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited on Pt/TiO₂/SiO₂/Si(1 0 0) substrates at a room temperature under the oxygen pressure of 1-10 Pa by pulsed laser deposition. Bi₂Zn_2/3Nb_4/3O₇ thin films were then post-annealed below 200 °C in a rapid thermal process furnace in air for 20 min. The dielectric and leakage current properties of Bi₂Zn_2/3Nb_4/3O₇ thin films are strongly influenced by the oxygen pressure during deposition and the post-annealing temperature. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited under 1 Pa oxygen pressure and then post-annealed at a temperature of 150 °C show uniform surface morphologies. Dielectric constant and loss tangent are 57 and 0.005 at 10 kHz, respectively. The high resolution TEM image and the electron diffraction pattern show that nano crystallites exist in the amorphous thin film, which may be the origin of high dielectric constant in the Bi₂Zn_2/3Nb_4/3O₇ thin films deposited at low temperatures. Moreover, Bi₂Zn_2/3Nb_4/3O₇ thin film exhibits the excellent leakage current characteristics with a high breakdown strength and the leakage current density is approximately 1 × 10⁻⁷ A/cm² at an applied bias field of 300 kV/cm. Bi₂Zn_2/3Nb_4/3O₇ thin films are potential materials for embedded capacitor applications.     

Characterisation and oxidation of LVOF sprayed Al2O3–40%TiO2 coating on superni 601 and superni 718 superalloys at 800 and 900°C

Failure of components due to high temperature oxidation is the major degradation mechanism in boiler and gas turbine industries. Superalloys having superior mechanical properties and creep resistance are used in these applications but lack resistance to oxidation under aggressive environments. Protective coatings are used to improve their oxidation resistance in such applications. In the present investigation, Al₂O₃–40%TiO₂ coating was deposited on superni 718 and superni 601 superalloys by low velocity oxy fuel process. The as sprayed coating was characterised for microhardness, surface roughness, scanning electron microscopy and X-ray diffraction analysis. High temperature oxidation behaviour of Al₂O₃–40%TiO₂ coated and uncoated superni 718 and superni 601 superalloys has been evaluated at the elevated temperatures of 800 and 900°C for total duration of 50 cycles under cyclic conditions. Each cycle consisted of keeping the samples for 1 h at the elevated temperature followed by 20 min cooling in ambient air. Al₂O₃–40TiO₂ coating in the as sprayed condition showed the presence of Al₂O₃–TiO₂, α-Al₂O₃, TiO₂ as the main phases. Al₂O₃–40%TiO₂ coating on superni 718 and superni 601 superalloys has shown a lower oxidation rate as compared to those of uncoated superalloys. However, the oxidation rate of the coating was not steady due to the occurrence of spallation/sputtering at various stages. The coating was found adherent on the substrate superalloys throughout the study.     

Protective effect in sulfuric acid media of alumina and ceria oxide layers electrodeposited on stainless steel

The influence of thin layers of Al₂O₃ and Ce₂O₃-CeO₂, electrodeposited on stainless steel OC4004, on the corrosion behaviour of the systems Al₂O₃/SS, Ce₂O₃-CeO₂/SS and Al₂O₃-Ce₂O₃-CeO₂/SS has been studied in sulfuric acid medium. A pronounced stabilizing effect on the passive state of steel and enhancement of its corrosion resistance has been established both for the samples as deposited and for the thermally treated Ce₂O₃-CeO₂/SS systems. In comparison to them the layers of Al₂O₃ have a substantial impact on the corrosion resistance of the Al₂O₃/SS system only in the cases when the system is not subjected to thermal treatment. The consecutive deposition of Al₂O₃ and Ce₂O₃-CeO₂ films on SS gives as a result an outstanding corrosion-protective effect, whereupon the corrosion potential of the system Al₂O₃/Ce₂O₃-CeO₂/SS is shifted in positive direction with ∼ 0.3 V for the samples as deposited and with ∼ 1 V—for the thermally treated samples. The so established favourable effect has been explained by the increased concentration of chromium oxides in the surface passive film, caused by the presence of cerium oxides, as well as by their action as cathode, effective with respect to the reduction corrosion reaction, shifting strongly the potential (at which this reaction is occurring) in positive direction.