Characterization of TiO2 coatings prepared by a modified electric arc-physical vapour deposition system

TiO₂ thin coatings were prepared, on various substrates, through evaporation of metallic titanium in an oxidizing atmosphere by modified electric arc-physical vapor deposition (EA-PVD). The coatings were characterized chemically (by means of XPS and SIMS) and from the structural point of view (by means of XRD and Raman spectroscopy), in order to understand the factors which lead to homogeneous coatings with high anatase content. The type of substrate is the main parameter that influences the crystal structure of the coatings: when stainless steel is used as substrate the coatings consist essentially of rutile, while on glass substrates coatings containing mainly anatase are obtained. The photocatalytic activity of the samples upon UVA irradiation was tested by using phenol as the target molecule. Phenol in the solution can be photocatalytically and rapidly degraded through the EA-PVD anatase TiO₂ coatings.     

304L stainless steel oxidation in carbon dioxide: An XPS study

From the early beginning of the oxidation of 304L stainless steel in carbon dioxide at 1273 K (1 min, for a weight gain of 0.02 mg cm⁻²), the surface of the alloy was entirely covered by oxides: magnetite Fe₃O₄, chromia Cr₂O₃ and traces of wüstite Fe_1−xO. Later on, for weight gains approaching 1 mg cm⁻², magnetite remained at the outer interface, with traces of hematite (Fe₂O₃), above a thick layer of wüstite Fe_1−xO. Magnetite and wüstite may favour adhesion of thermal plasma protective coatings such as alumina.     

Role of Al2O3 layer in oxidation resistance of Cu-Al dilute alloys pre-annealed in H2 atmospheres

Copper was alloyed with small amounts of Al (0.2, 0.5, 1.0 and 2.0 mass%) to improve the oxidation resistance. Copper (6 N) and the Cu-Al alloys were oxidized at 773-1173 K in 0.1 MPa oxygen atmosphere after hydrogen annealing at 873 K. Continuous very thin Al₂O₃ layers were formed on the surface of all Cu-Al dilute alloys during the hydrogen annealing. Oxidation resistance of Cu-Al alloys was improved especially for Cu-2.0Al at 773-973 K, while it decreases on increasing the oxidation temperature. Cu-Al alloys followed the parabolic rate law at 1173 K, but most of other cases do not at and below 1073 K. Oxidation resistance for Cu-Al alloys was found relevant to the maintenance of the thin Al₂O₃ layer at the Cu₂O/Cu-Al alloy interface.     

Plasma electrolytic oxidation preparation and characterization of SnO2 film

SnO₂ film is firstly prepared by plasma electrolytic oxidation technology in sodium stannate solution. The structure and photocatalytic property of the film are characterized by SEM, XRD and UV-Vis spectrophotometer. Rough and porous netlike film formed on the substrate. The XRD result showed the oxide was pure SnO₂. The absorption edge of the film was determined as 420 nm. Photocatalytic degradation of rhodamine indicated SnO₂ film was an effective photocatalyst.     

Effect of N, C and B interstitial atoms on local bonding structure in mechanically activated TiH2/h-BN, TiH2/C, and TiH2/B mixtures

Mechanically activated TiH₂/h-BN, TiH₂/C and TiH₂/B mixtures was studied by temperature-programmed desorption, X-ray diffraction, transmission electron microscopy and X-ray emission spectroscopy. Ball milling in the presence of additives results in a modification of hydrogen occupation sites. Additional Ti-N, Ti-C or Ti-B bonds from chemical bonding of Ti with interstitial N, C and B atoms, are formed in TiH₂ due to contact of TiH₂ nanoparticles with the respective additive matrix materials. Mixed configurations around Ti atoms with proportional combination of local Ti-H and Ti-N, Ti-C or Ti-B bonds significantly decrease the thermal stability of TiH₂. The effect is most pronounced when boron is the additive.     

H2S/CO2环境中L360钢点蚀行为研究

利用静态挂片失重法研究了含H₂S/CO₂模拟油田水溶液中, 温度及Cl^-浓度对L360管线钢点蚀的影响, 并利用Gumbel第一类近似函数分析了最深蚀孔概率. 结果表明, 在40℃~70℃之间, Cl^-浓度为10 g/L条件下, 点蚀的严重程度随温度增高而增大. 恒定温度下, Cl^-浓度对点蚀发生也有明显的影响, 当Cl^-在10×15 g/L范围时, 腐蚀试样发生明显的点蚀; 当Cl^-浓度大于20 g/L时, 试样主要发生均匀腐蚀, 随着Cl^-浓度的增大, 腐蚀产物膜变得更加疏松, 保护性能下降, 均匀腐蚀速率增大. 最深点蚀分布服从Gumbel第一类近似函数.     

Plasma nitriding of austenitic stainless steel in N2 and N2-H2 dc pulsed discharge

AISI 302/304 austenitic stainless steels have been nitrided in N₂ and N₂-H₂ glow discharge plasmas powered by a high frequency dc pulsed power supply. In a pure nitrogen plasma, no increase in surface hardness from the initial value has been observed. In a N₂-H₂ gas admixture, a 3-4 times increase in hardness has been found, which confirms the necessity of hydrogen gas as a powerful reagent. Grazing incidence X-ray diffraction (GIXRD) shows the presence of three phases of nitride (Fe₃N, Fe₄N and CrN) along with iron oxide (Fe₂O₃). It is found in a N₂ plasma at a sample temperature of 540 °C that at 200 kHz, maximum peak intensity of iron oxide/nitride decreases. In N₂-H₂ plasma treated sample the nitride peak intensity increased in comparison to the intensity in sample nitrided in N₂ plasma. Optical emission spectroscopy (OES) has been used to investigate the active species present during nitriding in the near-cathode region. Emission bands of neutral and ionic molecular species and ionic atomic species of nitrogen have been detected in a nitrogen plasma. In a N₂-H₂ gas admixture, the H_α and H_β lines of Balmer series in addition have been observed. At 20% H₂ addition in nitrogen plasma, a few vibrational state intensities of N₂ and N₂⁺ are observed to be optimized.     

In-situ TiB2 and Al2O3 formation by DC plasma spraying

In-situ plasma spraying (IPS) is a promising process to fabricate composite coatings with in-situ formed thermodynamically stable phases. In the present study, mechanically alloyed Al-12Si, B₂O₃ and TiO₂ powder was deposited onto an aluminum substrate using atmospheric plasma spraying (APS). It has been observed that, during the coating process, TiB₂ and Al₂O₃ are in-situ formed through the reaction between starting powders and finely dispersed in hypereutectic Al-Si matrix alloy. Also, obtained results demonstrate that in-situ reaction intensity strongly depends on spray conditions.     

Study of Al2O3 coatings on AISI 316 stainless steel obtained by controlled atmosphere plasma spraying (CAPS)

The tribological behaviour of Al₂O₃ coatings on AISI 316 stainless steel, obtained by the process of controlled atmosphere plasma spraying (CAPS), is studied in this work. Atmospheric plasma spraying (APS) and high pressure plasma spraying (HPPS) were applied in order to produce these coatings. The APS coatings exhibited lower microhardness values compared to the values of HPPS coatings. Regarding the HPPS coatings it was found that plasma composition, through its heat capacity, does influence the heat transfer to particles, and, consequently, their flattening and densification process, which govern coating properties. It was revealed that tribological behaviour of coatings was influenced by the applied spraying method too. Coatings from HPPS under high-enthalpy conditions led to worst wear behaviour. In general, properties, such as microstructure, microhardness, coefficient of friction and wear resistance depended on the processing conditions such as pressure and composition of the spraying chamber atmosphere.     

Synthesis, structure and optical properties of CoAl2O4 spinel nanocrystals

CoAl₂O₄ nanocrystals were synthesized by sol-gel method using citric acid as a chelating agent at low temperature. The as-synthesized samples were characterized by thermal analysis, X-ray powder diffraction, infrared spectroscopy and transmission electron microscopy. The results show that CoAl₂O₄ spinel is the only crystalline phase with a size of 10-30 nm in the temperature range 500-1000 °C. The temperature dependence of the distribution of Al³⁺ and Co²⁺ ions in the octahedral and tetrahedral sites in nanocrystals was investigated by X-ray photoelectron spectroscopy (XPS). It is observed that the inversion parameter decreases with increasing annealing temperature. Analysis of the absorption properties indicates that Co²⁺ ions are located in the tetrahedral sites as well as in the octahedral sites in the CoAl₂O₄ nanocrystals. The origin of the green color (300-500 nm absorption band) should be due to the octahedrally coordinated Co²⁺ ions.     

利用FCVA法和CO2、N2制备Ti(C,O,N)纳米复合薄膜的研究

使用CO2和N2利用磁过滤阴极弧法（FCVA）在Si（100）和304不锈钢上沉积Ti(C,N,O)薄膜。采用XPS, XRD, Raman, SEM, 摩擦磨损试验机,电化学实验站检测得出气体流速对薄膜成分、相结构和薄膜性能的作用。当混合气体流量从10sccm升高的50sccm时,薄膜中的C和N含量有明显增加,而O和Ti含量有小幅下降;当混合气体流量从50sccm升高到80sccm时,薄膜中的C和N含量下降,而Ti含量有小幅上升,O含量急剧上升。薄膜由nc-Ti(C,N,O)纳米晶结构,转变为nc-Ti(C,N,O)/a-CNx,a-TiO2/a-CNx,N-doped a-TiO2/a-C纳米复合结构。N-doped a-TiO2/a-C纳米复合结构薄膜具有最低的摩擦系数（0.34）,nc-Ti(C,N,O)/a-CNx,N-doped a-TiO2/a-C纳米复合结构薄膜在Hanks溶液中均表现出良好的抗腐蚀能力。     

The corrosion behavior of plasma sprayed Fe2Al5 coating in molten Zn

Aluminum coating was plasma sprayed on Fe-0.14-0.22 wt.% C steel substrate, and heat diffusion treatment at 923 °C for 4 h was preformed to the aluminum coating to form Fe₂Al₅ inter-metallic compound coating. The corrosion mechanism of the Fe₂Al₅ coating in molten zinc was investigated. SEM and EDS analysis results show that the corrosion process of the Fe₂Al₅ layer in molten zinc is as follows: Fe₂Al₅ → Fe₂Al₅Zn_x (η) → η + L(liquid phase) → L + η + δ(FeZn₇) → L + δ → L. The η phase and the eutectic structure (η + δ) prevent the diffusion of zinc atoms efficiently. Therefore the Fe₂Al₅ coating delays the reaction between the substrate and molten zinc, promoting the corrosion resistance of the substrate.     

Microstructure and properties of Cr3C2-modified nickel-based alloy coating deposited by plasma transferred arc process

The nickel-based alloy with 30 wt.% chromic carbide (Cr₃C₂) particles has been deposited on Q235-carbon steel (including 0.12 wt.% C) using plasma transferred arc (PTA) welding machine. The microstructure and properties of the deposited coatings were investigated using optical microscope, scanning electron microscope (SEM) equiped with X-ray energy spectrometer (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), microhardness testes, and sliding wear test. It was found that the γ(Ni, Fe), M₇(C,B)₃, Ni₄B₃, and (Cr,Fe)₂B phases existed in the Cr₃C₂-free nickel-based alloy coating obtained by PTA process. The typical hypoeutectic structure and composition segregation in the solid solution could be found clearly. The addition of 30 wt.% Cr₃C₂ particles led to the existing of Cr₃C₂ phase and the microstructure changing from hypoeutectic structure into hypereutectic structure. The composition segregation in the solid solution could not be found clearly. The average microhardness of the Cr₃C₂-free nickel-based alloy coating increased by 450-500 HV after the addition of 30 wt.% Cr₃C₂ particles. The partial dissolution of Cr₃C₂ particles led to the enrichment of carbon and chromium in the melten pool, and hence caused the formation of more chromium-rich carbides after the solidification process. The undissolved Cr₃C₂ particles and the increasing of chromium-rich carbides was beneficial to enhance the hardness and wear resistance of the Cr₃C₂-modified nickel-based alloy coating deposited by PTA process.     

Q125级套管钢高频电阻焊接头耐CO2/H2S腐蚀行为

采用SEM,EBSD和电化学等手段研究了Q125级石油套管钢高频电阻焊接头的耐CO₂/H2S腐蚀行为.结果表明,Q125级套管钢高频电阻焊接头处母材的耐腐蚀性能最好,热影响区次之,而焊缝的耐腐蚀性能最差,导致高频电阻焊接头在CO₂/H₂S腐蚀环境中产生了沟槽腐蚀.试验钢焊缝处的大角晶界比例高于母材和热影响区,从而使焊缝区反应速度常数高于母材和热影响区,这是焊缝区腐蚀速率最高的一个重要原因.通过电化学分析表明,焊缝处的电极反应的极化阻力最小,腐蚀反应易于发生;而母材的电极反应的极化电阻最大,腐蚀反应不易进行,这与腐蚀试验所得结果及极化曲线分析结果一致.     

Surface composition and electrochemical behavior of LiNi1/3Co1/3Mn1/3O2 cathode material with copper additive

LiNi_1/3Co_1/3Mn_1/3O₂（NCM） cathode material containing copper was prepared by co-precipitation method.The material was characterized by X-ray photoelectron spectroscopy（XPS） and galvanostatic cycling.XPS data indicate that surface compositions of the samples containing copper are different from the bare NCM.Copper on surface of particles was enriched,while nickel and lithium content was reduced.The electrochemical performance of NCM was affected by the change of surface compositions.Cycling performance charged to the cutoff voltage of 4.6 V was improved by introducing copper into the material.The effects of copper content on electrochemical behaviors of NCM at 4.5 V were discussed.     

Effect of (NaPO3)6 concentrations on corrosion resistance of plasma electrolytic oxidation coatings formed on AZ91D magnesium alloy

Different plasma electrolytic oxidation (PEO) coatings were prepared on AZ91D magnesium alloy in electrolytes containing various concentrations of (NaPO₃)₆. The morphologies, chemical compositions and corrosion resistance of the PEO coatings were characterized by environmental scanning electron microscopy (ESEM), X-ray diffractometer (XRD), energy dispersive analysis of X-rays (EDAX), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) test. The results showed that the PEO coatings were mainly composed of MgO, Mg₂SiO₄, MgAl₂O₄ and amorphous compounds. As the (NaPO₃)₆ concentrations increased from 0 to 10 g/l, the thickness and surface roughness of the coatings approximately linearly increased; the MgO and Mg₂SiO₄ phase increased within the concentration range of 0–3 and 0–5 g/l, and then decreased within the range of 3–10 and 5–10 g/l, respectively, while the MgAl₂O₄ phase gradually decreased. Moreover, the corrosion resistance of the coatings increased within the range of 0–5 g/l and then decreased within the range of 5–10 g/l. The best corrosion resistance coating was obtained in electrolyte containing 5 g/l (NaPO₃)₆, it had the most compact microstructure. Besides, a reasonable equivalent circuit was established, and the fitting results were consistent with the results of the EIS test.     

Structural evolution of mechanically alloyed Al-12Si/TiB2/h-BN composite powder coating by atmospheric plasma spraying

In the present study, mechanically alloyed Al-12Si/TiB₂/h-BN composite powder was deposited onto an aluminum substrate by atmospheric plasma spraying. The effect of mechanical alloying (MA) and plasma spray parameters on composite powder and coating structure were investigated. It has been observed that the MA process has a significant effect on the composite powder morphology and reactivity between the selective powders. Results also demonstrate that, at relatively high milling time h-BN decomposes into B and N and forms a solid solution. Also, it has been found that, the relative amount of the in-situ formed AlN through the reaction between h-BN and Al and/or the decomposition of Al-B-N solid solution is independent from the plasma parameters (arc current and secondary gas flow rate). However, spray parameters remarkably affects the coating hardness due to coarsening of Si during the solidification of the coating.     

Mechanical and tribological performance of Al2O3-TiO2 coatings elaborated by flame and plasma spraying

Mechanical properties and wear rates of Al₂O₃-13 wt.% TiO₂ (AT-13) and Al₂O₃-43 wt.% TiO₂ (AT-43) coatings obtained by flame and atmospheric plasma spraying were studied. The feed stock was either ceramic cords or powders. Results show that the wear resistance of AT-13 coatings is higher than that of AT-43 and it seems that the effect of hardness on wear resistance is more important than that of toughness. Additionally, it was established that, according to conditions used to elaborate coatings and the sliding tribological test chosen, spray processes do not seem to have an important effect on the wear resistance of these coatings.     

复合热源喷涂NiCr-Cr3C2涂层及其性能分析

采用激光与等离子复合热源喷涂技术,在38CrMoA1基体上制备NiCr-Cr3C2涂层,对涂层的结合强度、显微硬度、微观组织结构以及抗高温滑动摩擦磨损性能等进行了测试分析.结果表明,与传统的等离子喷涂层相比,复合热源喷涂时,NiCr-Cr2C2粉末受热熔融更充分,流动性好,铺展均匀.涂层实现了冶金结合,具有更高的结合强...     

纳米LiInO2光催化剂的溶胶-凝胶法制备与表征

本文利用溶胶-凝胶法制备了LiInO₂纳米材料,采用X-射线衍射(XRD)、扫描电镜(SEM)和紫外-可见吸收光谱等测试手段,研究了制备条件对LiInO₂微观结构的影响因素,并以亚甲基蓝为目标降解物研究了LiInO₂的光催化性能。研究结果表明：制备的LiInO₂纳米粒子具有LiFeO₂的晶型,颗粒尺寸约50-100纳米,制备样品的焙烧温度对其结构和性能产生了明显地影响,在氙灯(300W)照射90 min条件下,纳米LiInO₂对亚甲基蓝的光催化降解率达92%,活性位点捕获实验表明光生空穴在降解亚甲基蓝的机制中占主导作用。