Effect of La on arc erosion behaviors and oxidation resistance of Cu alloys

Cu with and without La addition was prepared and the effect of a trace amount of La on the arc erosion behaviors and oxidation resistance of Cu alloys was investigated. The results indicate that CuLa alloy exhibits superior oxidation resistance and arc erosion resistance. The contact resistance and temperature rise were obviously improved. The oxidation resistance of CuLa alloy mainly is due to the interface wrapping of La₂O₃ particles and CuLa alloy phase on Cu atoms. Thermodynamic calculation indicated that La₂O₃ could form preferentially in the CuLa alloy, which was beneficial for the protection of the Cu substrate. According to kinetics analysis, the activation energy of CuLa alloy was higher than that of pure Cu, indicating the better oxidation resistance of CuLa alloys.     

La2O3包埋渗硼TB2钛合金的腐蚀与磨损性能

为了改善TB2合金的表面性能,采用4％La2O3(质量分数)包埋渗硼法对TB2合金进行1100℃,20 h渗硼处理,研究TB2钛合金的渗硼层组成与厚度以及腐蚀与磨损性能.结果表明,La2O3在渗硼过程中促进硼化物层的生长,提高其连续性和致密性,TiB晶须长度从16.80增至21.84μm.这是因为La2O3能与B反应生...     

In situ synthesis and electrical properties of CuW–La2O3 composites

CuW–La₂O₃ composites were fabricated using an in-situ synthesis. The breakdown voltage in vacuum, moving trajectory of cathode spots, electrical conductivity, and hardness of CuW–La₂O₃ composites were carefully examined. The microstructures were characterized by a scanning electron microscope (SEM). The results show that CuW–La₂O₃ composites have the maximum hardness of 220HB and the electrical conductivity of 45% IACS when the content of La₂O₃ is 0.75 wt.%. In comparison with CuW alloy, the dielectric strength, arc life and the arc mobility of the CuW–La₂O₃ composites increased by 36.9%, 9.7% and 46.6%, respectively. As a result, the addition of La₂O₃ is useful to improve the properties of CuW alloys and the in situ synthesized CuW–La₂O₃ composites should have excellent arc erosion resistance.     

A Study on Effect of Reactive and Rare Earth Element Additions on the Oxidation Behavior of Mo–Si–B System

Mo–9Si–8B–1Ti, Mo–9Si–8B–1.8Ti, Mo–9Si–8B–0.2La and Mo–9Si–8B–0.4La₂O₃ (at.%) alloys were prepared using mechanical alloying followed by hot isostatic pressing and field assisted sintering. XRD, SEM and EBSD analysis confirmed the formation of Mo solid solution, A15 and T2 phases in the alloys. Isothermal oxidation behavior of the specimens was studied in the temperature range from 750 to 1,300 °C for up to 100 h. Both the Ti and La containing alloys showed superior oxidation behavior compared to unalloyed Mo–Si–B at 900 °C at the initial periods of oxidation. Ti-added alloys suffered higher rate of weight loss at higher temperatures (1,000–1,300 °C) due to the formation of non-protective low viscosity SiO₂-TiO₂-B₂O₃ scale. La-alloyed Mo–Si–B showed superior oxidation resistance at intermediate temperatures (900 °C) as well as at higher temperatures. Enrichment of La at the oxide/alloy interface was found to be the reason for improved oxidation behavior of La-alloyed Mo–Si–B. Amongst the four materials studied, the La₂O₃ containing alloy showed the best oxidation resistance at 900 °C.     

TEM studies of cross sections of oxidized Fe-25Cr-6Al-La alloy

The oxidation behavior of the alloy Fe–25%Cr–6%Al-RE (rich in lanthanum) was investigated by means of TEM analysis. The results show that after 2 hr oxidation of the alloy, in pure oxygen at 1200° C, La precipitated in the oxide scale at the top of -Al₂O₃ grains and at the grain-boundary regions in the form of tiny particles of hexagonal La₂O₃. These tiny particles prevented aluminum from diffusing toward the surface and suppressed lateral growth of the oxide scale. The rare-earth constituents accelerated the internal oxidation of the alloy during thermal cycling between 1200° C and room temperature. They appeared as particles of aluminum oxide and lanthanum oxide. Particles of cubic La₂O₃ precipitated in the alloy matrix near the oxide scale-metal interface in a direction parallel to grain boundaries.     

High-Temperature Oxidation of Ni Coated with La2O3 by Atomic-Layer Chemical-Vapor Deposition (ALCVD)

The effects of superficial (30–100 nm) La₂O₃ surface coatings on the oxidation kinetics of Ni from 700 to 1100°C in air and the oxide morphology of the NiO scales have been investigated. The parabolic rate constant is lower than for uncoated Ni by a factor of 5 to 10. The oxide morphology changes with the La₂O₃ coatings: The oxide scale consists of an outer fine-grain layer with an inner region of coarser, but still equiaxed, grains. SIMS shows that the majority of the La remains at the surface where a highly oxygen-defective spinel, La₂Ni₄O₇, was found by TEM. Two-stage oxidation followed by SIMS profiling reveals that the oxide growth occurs inside the scales.     

Improvement in Oxidation Resistance of Stainless Steel by Molten-Salt Electrodeposition of La

Improvement in the oxidation resistance of SUS304 stainless steel was accomplished by electrodeposition of La in a molten salt. The electrolysis of La was conducted using a potentiostatic-polarization method in an equimolar NaCl–KCl melt containing 3.5 mol. LaF ₃ at 1023 K. Observation of the specimen surface after polarization at –1.8 V (vs. Ag/Ag⁺ (0.1)) for 0.18 ks showed that La particles were uniformly dispersed on the surface. The oxidation resistance of the electrodeposited stainless steel was significantly improved as compared with the untreated stainless steel. The scale formed on the untreated stainless steel after oxidation was thick and consisted of Fe₂O₃ and Fe₃O₄, whereas the scale formed on the elecrodeposited stainless steel was extremely thin, and mainly consisted of Cr₂O₃.     

La2O3/CeO2颗粒尺寸对Ni-La2O3/CeO2复合电镀层高温氧化性能的影响（英文）

通过向普通硫酸镍电镀液中添加一定含量的微米或纳米La2O3/CeO2颗粒,采用复合电镀制备微米或纳米La2O3/CeO2颗粒分布的Ni基复合镀层,并研究La2O3/Ce O2颗粒尺寸对Ni-La2O3/CeO2复合镀层在1000°C抗氧化性能的影响。结果表明:与普通Ni镀层相比,Ni-La2O3/CeO2复合镀层中的La2O3/Ce O2颗粒通过溶解扩散进入氧化膜中,阻碍Ni的外扩散,从而降低氧化速度;此外,与La2O3/CeO2纳米颗粒相比,La2O3/Ce O2微米颗粒在氧化初期还起到扩散障碍层的作用,对阻碍Ni的外扩散具有更强的作用。     

Effect of La and Hf Additions on the High-Temperature Oxidation Resistance of High-Purity Fe–20Cr–5Al Alloy Foils

The oxidation behavior of 30- or 50-m thick high-purityFe–20 w/o-Cr–5 w/o Al alloy foil and similar alloy foilscontaining La and La–Hf was examined in cyclic-oxidation tests at1373 and 1473 K in air. The oxidation process proceeded in three stages. Inthe first stage, an Al₂O₃ scale grew until all the Alin the foil had been removed. In the second stage, a Cr₂O₃layer grew between the Al₂O₃ layer and the substrateon the alloys containing La or La–Hf, while a (Cr, Al)₂O₃layer formed on the alloy without La and La–Hf. In the third stage,breakaway oxidation occurred. The addition of La decreased the oxidationrate in both the first and the second stages. The addition of La–Hfdecreased the rate further. The growth rate of alloys containing La orLa–Hf in the second stage was found to be proportional to thediffusion rate of oxygen in the Al₂O₃ scale. Therefore,it is inferred that the inward oxygen diffusion rate in the Al₂O₃scale on the alloy containing La–Hf was reduced compared with that onthe alloy containing La, resulting in a decrease in the oxidation rate inthe first stage.     

Improving the protective properties of La‐conversion coating on α‐brass surface by the combined use of La2O3 nanoparticles incorporation and electrodeposition

The La₂O₃ nanoparticles incorporation and electrodeposition were used together to prepare the La‐conversion coatings on α‐brass surface in a basal solution containing rare earth salt. The results showed that both techniques can improve the protective properties of coatings. A ‘critical nano‐La₂O₃ content’ and a ‘critical deposition potential’ were observed, under which the conversion coatings had the highest protective properties. Increased electrodeposition time improve the quality of conversion coatings. The La‐conversion coatings could provide important protection against α‐brass corrosion for considerable immersion periods in 3.5 wt% sodium chloride solution because it ennobled the corrosion potential and decreased the anodic current.     

X100管线钢双丝埋弧焊接头微观组织与力学性能

利用光学显微镜、扫描电子显微镜、拉伸及冲击材料试验机等对X100钢级管线钢组织与力学性能进行了研究.结果表明,X100钢级管线钢焊缝区组织主要为针状铁素体和粒状贝氏体,热影响区组织有多边形铁素体存在,且晶粒粗大,发生了软化和脆化.焊接接头最高抗拉强度和断后伸长率分别达805 MPa,10.7%.接头的冲击吸收功(-10℃)大于110 J;剪切面积百分比(-10℃)平均值达到85%,呈现为韧性断裂.硬度测试结果显示,热影响区硬度外焊高于内焊.     

La2O3对MGH956合金TIG焊焊缝组织和性能的影响

为了研究La₂O₃对焊缝组织和性能的影响,分别以未填加、填加2%和4%La₂O₃的填充材料对MGH956合金进行TIG焊接,应用光学显微镜、扫描电镜和透射电镜对焊缝的微观组织和拉伸断口进行观察,同时测试焊缝的抗拉强度.结果表明,适当提高La₂O₃含量,可以使焊缝晶粒得到细化,填加2%La₂O₃的焊缝晶粒最细小均匀,焊缝中的颗粒相增多且分布均匀,强化机制是由细晶强化和Orowan强化共同作用,但当La₂O₃加入量达到4%时,发现颗粒相有团聚现象,强化主要由位错塞积引起.填加2%La₂O₃的焊缝抗拉强度最大,为628 MPa,拉伸断口为韧-脆混合断裂.     

Metallic interconnects for solid oxide fuel cell: Performance of reactive element oxide coating during long time exposure

One of challenges in improving the performance and cost‐effectiveness of SOFCs (solid oxide fuel cells) is the development of suitable interconnects materials. Chromia‐forming alloys and especially ferritic stainless steels, like Crofer22APU, are considered to be among the most promising candidate materials as interconnects in SOFC stacks. However, the performance of chromia‐forming materials can be limited by the low electronic conductivity of the oxide scale (high ASR – area specific resistance – value). Such degradation are unacceptable regarding the long‐term operation (>40 000 h). A previous study 1 demonstrated that in air, the addition of a nanometric reactive element oxide (La₂O₃) layer applied by metal organic chemical vapor deposition (MOCVD) drastically improved both corrosion rate and electrical properties of Crofer22APU and Haynes230 alloys for 100 h at 800 °C. In this present study coating performances were checked after 10 months (7500 h) and 20 months (15 000 h) at 800 °C in air. The corrosion products were carefully analyzed by SEM, EDX, and XRD. ASR measurements are realized after long time exposure. This study demonstrates that the Crofer22APU alloy has a good oxidation resistance after 15 000 h in air but this alloy has an ASR value equal to 0.370 Ω cm². The coatings composed of a thin reactive element oxide such as La₂O₃ resulted in an important improvement in the high temperature oxidation resistance; the ASR values are equal to 0.154 Ω cm². Haynes230 alloy has a better oxidation resistance but the formation of an insulating Al₂O₃/SiO₂ layer could be detrimental.     

New La326 type compounds substituted with sodium and potassium

New members of La326 type compounds La₂Ca_1−xNa_xCu₂O_6−δ, La_2−xSr_xCa_0.7Na_0.3Cu₂O_6−δ, La_2−xK_xCaCu₂O_6−δ, and La_1.6K_0.4Ca_1−xSr_xCu₂O_6−δ were prepared with solid state reaction. Experiments show that calcination and sinter temperatures as well as the heating rate used to prepare single phase La326 type compounds substituted with sodium and potassium are lower than those used to prepare Ln_2−xA_1+xCu₂O_6−δ (A=Ca, Sr). Their structures were verified with Rietveld refinement to belong to the structure type of typical La326 type compounds La_2−xA_1+xCu₂O_6−δ (A=Ca, Sr). The D.C. magnetic susceptibility dependence of the temperature of the La_1.7Sr_0.3Ca_0.7Na_0.3Cu₂O_5.86 sample shows that the sample displays a diamagnetic signal at 63 K.     

Effect of La2O3 Particles on the Oxidation of Electrodeposited Nickel Films

Electrodeposited Ni-La₂O₃composite films with nanometer-sizeLa₂O₃ oxide inclusions werefabricated by the codeposition of nickel withLa₂O₃ particles. The comparativeoxidation behavior in air at 900 and 1000°C of nickel coated with theNi-La₂O₃ composite and films withand without nickel-plating was studied by TGA, AE,SEM/EDX, EPMA, and TEM/EDX. In general, theNi-La₂O₃ composite-coated nickelhad the slowest rate and the best resistance tothermal cycling. AE tests revealed that cracking eventsin NiO scales on Ni-La₂O₃composite-coated nickel was significantly reduced incomparison to that of the scale on nickel-coated nickel during thermalcycling at 900°C. SEM investigation showed that theLa₂O₃-free NiO scale was composedof outer coarse columnar grains and inner equiaxed ones.By contrast, the scale on the Ni-La₂O₃composite-coated nickel consisted of only fine equiaxedNiO grains. The scale on theLa₂O₃-free samples wascharacterized by cracks that originated at thescale-substrate interface and spanned the scale thickness. By contrast,no scale cracks formed at theLa₂O₃-doped NiO scale-substrateinterface, but small voids were created at the triplepoints of the grain boundaries of NiO. In the La₂O₃-doped NiOscale, segregation of La ions to the NiO grainboundaries near the scale-surface was observed by EDXmicroanalyses in the TEM. It is believed that the Laions segregated at the grain boundaries of NiO led to an increase in thecohesion between nickel oxides and in a reduction of thescaling rate and the formation of scale with fineequiaxed crystal structure by blocking the outward and lateral growth of scale. The latter was dueto the predominant outward diffusion of nickel along NiOgrain boundaries being inhibited effectively by thesegregated La ions. The mechanism of the effect of the added La₂O₃particles on the nickel electrodeposits is discussed indetail.     

La0.6Sr0.4Co0.2Fe0.8O3 protective coatings for solid oxide fuel cell interconnect deposited by screen printing

La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) is applied on a Crofer22 APU interconnect for solid oxide fuel cells (SOFCs) by screen-printing method. The above coated alloy was first checked for their compositions, morphology and interface conditions. It was then tested in a simulated oxidizing environment, 800 °C for 200 h. The results showed that the LSCF film can change the oxidation behavior of Crofer22 APU. After sintering the screen printed alloy was under 1050 °C in N₂ atmosphere, the adhesion between the LSCF layer and alloy substrate is excellent. Long-term electrical resistance measurement indicated that area-specific resistance (ASR) of the alloy with coated film is significantly lower than that of the uncoated. The use of LSCF coating for metallic interconnect could reduce working temperature for solid oxide fuel cell.     

低氧压预氧化对FeCrAlSiY合金耐LBE熔液腐蚀性能的影响

为进一步提高核反应堆系统的结构材料 Fe-Cr 基合金抗 LBE 腐蚀的性能,对其进行成分优化和表面处理十分重要。 对 Fe-12Cr-xAl-2Si-0.6Y 合金进行低氧压预氧化试验,分析并讨论氧分压和 Al 含量对合金预氧化产物的影响,并研究预氧化前后的合金在 LBE 合金熔液中的耐腐蚀性能。结果表明,Fe-12Cr-2Al-2Si-0.6Y 合金在不同氧分压下进行预氧化后生成的表面氧化物均以 Al2O3 为主,氧分压越大,合金表面发生选择性氧化速度越快。不同 Al 含量的 Fe-12Cr-xAl-2Si-0.6Y 合金在 10^?15 atm(1 atm=0.101 3 MPa)氧分压下进行预氧化,随着 Al 含量的增加,合金表面氧化物由以 Cr₂O₃为主逐渐变为以 Al₂O₃ 为主,还混合有少量复合氧化物。进行低氧压预氧化处理能有效提高合金在 450 o C 的 LBE 合金熔液中的耐腐蚀性能。研究成果可为设计和开发耐 LBE 熔液腐蚀的 FeCrAlSiY 合金提供参考,促进该体系合金在核电工业领域的运用。     

Effect of La2O3 on corrosion resistance of laser clad ferrite-based alloy coatings

The ferrite-based alloy powders with different contents of La₂O₃ were laser clad on a steel substrate. The microstructural features and phase structure of these coatings were studied by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The results showed that the microstructure of the coatings with La₂O₃ was refined and purified. The main phase of the coatings was γ (Fe, Ni). Moreover, the electrochemical properties of the coatings were investigated by anodic polarization curves and electrochemical impedance spectroscopy (EIS). Anodic polarization results indicated that both polarizing voltage and polarization current density were reduced with the addition of La₂O₃. EIS results showed that, with the increment of La₂O₃, the inductive arcs shrunk and capacitive arcs expanded. The inductive arc at low frequency was disappeared and changed to capacitive arc thoroughly when the content of La₂O₃ reached 1.2 wt.%. The corrosion weight loss experiment results showed that the corrosion rate was lower and the corrosion attack was lighter in the coatings with La₂O₃ than that without La₂O₃, resulting in a substantial improvement of the corrosion resistance.     

Synthesis, characterization, shape-preserved transformation, and optical properties of La(OH)3, La2O2CO3, and La2O3 nanorods

A simple method to directly synthesize stable and crystalline pure phase La(OH)₃ nanorods, with a diameter of around 15 nm and lengths in the range of 120-200 nm, was developed using cationic surfactant (cetyltrimethylammonium bromide, CTAB). The obtained La(OH)₃ nanorods can be successfully converted to La₂O₂CO₃ and La₂O₃ nanorods via calcination under appropriate conditions. Analytical methods such as X-ray diffraction (XRD) spectra, Fourier transformed infrared (FTIR) spectrum, differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) were employed to characterize the morphology and microstructure of the final products. The results reveal that La(OH)₃ nanorods were shape-preserved and transformed to La₂O₂CO₃ nanorods at 400 °C for 2 h and to La₂O₃ nanorods at 800 °C for 2 h, respectively. TEM images indicate that the as-obtained La₂O₂CO₃ and La₂O₃ entirely consist of uniform nanorods in high yield with diameters of about 15 nm and 23 nm, lengths of 200-300 nm and 300-500 nm, respectively. The formation mechanism of the La(OH)₃, La₂O₂CO₃ and La₂O₃ nanorods was investigated. Room-temperature photoluminescence (RTPL) properties were investigated under the excitation of 275 nm. The ⁵D₃ → ⁷F_j (j = 2-6) emission peaks at the wavelength below 500 nm were found in the RTPL spectra.     

Thermal conductivity and phase stability of plasma sprayed ZrO2–Y2O3–La2O3 coatings

Thermal conductivity and phase stability of La₂O₃,Y₂O₃ stabilized ZrO₂ plasma sprayed coatings were investigated. La₂O₃ was selected as a stabilizer because it had a significant effect on reducing densification of Y₂O₃ stabilized ZrO₂ (YSZ). The developed coating showed low thermal conductivity even after high temperature exposure due to its high resistance to sintering. However, phase stability and thermal cycle life of the coating decreased as the amount of La₂O₃ was increased. It was concluded that optimum amount of La₂O₃ addition was about 1 mol% to suppress sintering with little degradation of other properties.