Dual-environment effects on the oxidation of metallic interconnects

Metallic interconnects in solid oxide fuel cells are exposed to a dual environment: fuel on one side (i.e., H₂ gas) and oxidizer on the other side (i.e., air). It has been observed that the oxidation behavior of thin stainless steel sheet in air is changed by the presence of H₂ on the other side of the sheet. The resulting dual-environment scales are flaky and more friable than the single-environment scales. The H₂ disrupts the scale on the air side. A model to explain some of the effects of a dual environment is presented where hydrogen diffusing through the stainless steel sheet reacts with oxygen diffusing through the scale to form water vapor, which has sufficient vapor pressure to mechanically disrupt the scale. Experiments on preoxidized 316L stainless steel tubing exposed to air-air, H₂-air, and H₂-Ar environments are reported in support of the model. This paper was presented at the ASM Materials Solutions Conference & Show held October 18–21, 2004 in Columbus, OH.     

氧化银对惰性阳极耐熔盐腐蚀性能的影响

以Fe2O3、NiO和Ag2O为主要原料,采用固相烧结工艺制备了NiFe2O4/Ag惰性阳极,用X射线衍射和扫描电子显微镜对材料的组成和微观结构进行了研究,采用水冷法测量了样品的抗热震性,并测量了其在冰晶石熔盐中的电解腐蚀速率。结果表明:Ag2O的加入提高了样品的抗热震性,降低了惰性阳极试样在冰晶石熔盐中的电解腐蚀速率,当Ag2O含量为6%时,试样的电解腐蚀速率最低。     

银氧化锡合金废料电解综合回收工艺研究

采用直流电解法和化学法回收银氧化锡(AgSnO2)合金废料中的银和锡。优化得到的电解银工艺参数为:槽电压1.5~3.0 V,电解周期为24 h,电解液中Ag⁺浓度为150~260 g/L,HNO3浓度为15~20 g/L,同极距120~140 mm,极板排布为六阴极五阳极间隔交替排列。一个周期银氧化锡废料电解银直收率接近95%,主体纯银粉在阴极析出。富含氧化锡的阳极泥和残极用硝酸浸出少量残余银,不溶渣还原熔炼回收锡,硝酸浸出的含银溶液中加入氢氧化钠调节pH值到10,沉淀得氧化银,500℃焙烧得到单质银。废料中的银和锡均得到有效回收。全流程银的回收率不低于99%。     

Zr4+和Y3+掺杂MCeO3(M=Ca、Sr、Ba)质子导体的制备与表征

采用尿素燃烧法制备了Zr掺杂MCeO3(M=Ca、Sr、Ba)型钙钛矿质子固体电解质前驱体粉末,经X射线衍射(XRD)和热重差热(TG-DTA)分析可知,在600℃下煅烧前驱体粉末得到纳米级细小钙钛矿结构晶体,且该晶体在H2S气氛、700℃下保持化学稳定。粉末于200 MPa下等静压成型,高温烧结6 h后,固体电解质样品密度为理论密度的92%以上。利用恒电位仪测定3种电解质片CaCe0.9-xZrxY0.1O3(CCZY))、SrCe0.9-xZrxY0.1O3(SCZY)和BaCe0.9-xZrxY0.1O3(BCZY)(x=0.1~0.3)组成的水蒸气浓差电池,电动势可验证固体电解质的质子导电性的强弱,电池电动势的大小顺序为BCZY>SCZY>CCZY;且随着温度的升高,电动势逐渐增大,但达到700℃后,EMF值逐渐趋于平缓;在中温范围(500~750℃)内,BCZY的电导率最高可达到10-2S/cm以上,SCZY的也接近10-2S/cm,这有利于减小固体氧化物燃料电池的欧姆损失。     

Sm2O3和Nd2O3共同掺杂CeO2基电解质材料的研究

采用柠檬酸-硝酸盐法合成出单一相、均匀的Ce0.8SmxNd0．2-xO19粉体，XRD结果表明该粉体为单相萤石结构，粒径约在11．7nm～20．1nm之间。将粉体干压成型，在1400℃下无压烧结5h可得到高致密度陶瓷。SEM照片显示陶瓷微观结构均匀，晶粒尺寸在2μm～4μm。经直流四端电极法测试得到该样品在500℃时电导率约在0．012 S／cm。该结果说明与单项掺杂相比，两相共掺杂会进一步提高材料的电导率。     

固体氧化物燃料电池的研究进展

回顾了固体氧化物燃料电池的发展历史以及目前发展状况。介绍了固体氧化物燃料电池的工作原理以及作为燃料电池的阳极、阴极、电解质和连接材料的选择依据。评述了分别应用于阳极、阴极、电解质以及连接材料的材料目前的研究状况和面临的一些问题。最后提出了固体氧化物燃料电池能够得以应用必须解决的一些瓶颈因素。     

水和乙醇悬浮液等离子喷涂SOFC (Ce0.80Gd0.20)O1.9电解质层的比较

选用水和乙醇两种溶剂配置悬浮液,研究了分散剂含量对(Ce_0.80Gd_0.20)O_1.9 (GDC)悬浮液粘度的影响和pH值对GDC颗粒Zeta电位的影响。结果表明：水悬浮液优化参数是：PAA含量为2.5 wt.%,pH=10;乙醇悬浮液优化参数为：PAA含量2.0 wt.%,pH=10。采用GDC悬浮液等离子喷涂制备固体氧化物燃料电池电解质层。利用XRD、SEM和电子探针分别分析了喷涂前后GDC的相结构、电解质层微观组织及化学成分。研究表明：GDC喷涂前后没有相结构的变化,乙醇悬浮液得到的电解质层结构更精细,水和乙醇悬浮液得到电解质的孔隙率分别为5.64 ％和1.25 %,但是氧化铈有烧损,水和乙醇悬浮液电解质层氧化铈分别烧损了15.8 %和 16.8 %。     

Selection and surface treatment of alloys in solid oxide fuel cell systems

Cost and performance considerations determine the selection of various component materials in a solid oxide fuel cell power system. While the use of commercial alloys provides an opportunity for cost reduction, the requirements of different components vary widely. The interconnect materials must provide low electrical resistance while isolating the oxidizing and reducing gases. The air preheat and heat-exchanger components face high-temperature oxidizing conditions, while the fuel feed and reformer sections encounter highly reducing atmospheres that may contain varying levels of sulfur and CO, and thus are prone to sulfidation and metal dusting. Thus, each of the components requires both a judicious selection of the alloy composition and appropriate surface treatments. Coating processes were developed for two classes of alloy materials for potential use as interconnects and fuel feed hardware or process piping. This paper was presented at the ASM Materials Solutions Conference & Show held October 18–21, 2004 in Columbus, OH.     

阳极组分对热喷涂制备SOFC输出特性的影响

针对传统管状与板块结构SOFC的特点,提出了集两种结构设计的优点为一体的金属陶瓷支撑管状结构SOFC,并采用低成本的火焰喷涂与等离子喷涂制备电池各结构层.采用3种不同成分与结构的阳极探讨了阳极结构对电池输出特性的影响,结果表明,阳极结构对电池运行时的极化产生显著影响,采用小颗粒的NiO与YSZ的复合粉末制备的阳极,可以有效增加阳极的三相界面,从而降低阳极极化,显著提高电池的输出功率密度,1000℃时可达到最大值0.57 W/cm2.这些结果为优化电池阳极结构层的设计与制备提供了依据.     

Observations on the microstructure of 20Cr-25Ni-Nb stainless steel after exposure to iodine vapor during creep at 750°C

The microstructure of 20Cr-25Ni-Nb stainless steel creep specimens has been examined in detail using optical and electron microscopy, after exposure to iodine vapor, air, or vacuum for periods up to 1600 hr at 750°C. The overall corrosion-oxidation rate in iodine vapor was linear and the duplex product which formed was typical of enhanced oxidation of this steel in other environments. Three significant subsurface microstructural changes observed during long-term exposure to iodine vapor were the formation of subsurface intergranular voids, enhanced chromium depletion, and increased intragranular precipitation of chromium-rich particles; each of these effects is discussed in detail and interpreted in terms of the breakdown of the initial protective oxide by iodine vapor.     

Microstructural and compositional evolution of nanoporous silver during dealloying of rapidly solidified Mg65Ag35 alloy

Microstructural and compositional evolution of nanoporous silver (NPS) during dealloying of rapidly solidified Mg₆₅Ag₃₅ alloy in the 1 wt% HCl solution has been investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis. The amount of MgAg phase decreases and that of f.c.c. Ag increases with increasing dealloying time, and no intermediate phase occurs during dealloying. The residual Mg content in NPS decreases with increasing dealloying time, following an exponential decay formula. The coarsening of ligaments in NPS with dealloying time follows a nonlinear relationship, and the coarsening exponent (n) is ∼4.8 for the dealloying of Mg₆₅Ag₃₅. In addition, the activation energy is 55.7 ± 2.9 kJ mol⁻¹ for the chemical dealloying of the rapidly solidified Mg₆₅Ag₃₅ alloy in the HCl solution.     

Volatilization kinetics of chromium oxide,manganese oxide,and manganese chromium spinel at high temperatures in environments containing water vapor

Performance degradation of solid oxide fuel cells due to chromium volatilization is a well‐investigated issue in the literature. Therefore, retention coatings were developed to distinctly reduce the chromium volatilization. One approach was by alloying with manganese to ferritic steels to form manganese chromium spinel which is reported to decrease chromium volatilization by 61–75%. In the present paper, the volatilization rates of pure manganese chromium spinel ceramics were examined as well as those of the two oxides forming this spinel—pure chromium oxide and pure manganese oxide—in synthetic air containing 10% water vapor (high p(O₂)) and argon/hydrogen containing 10% water vapor (low p(O₂)) at 850°C, 950°C, and 1,050°C. Chromium oxide showed higher volatilization rates in high p(O₂), whereas manganese oxide demonstrated higher volatilization rates in low p(O₂). Contradictory to the literature, manganese chromium spinel displayed the highest volatilization rates in both atmospheres and nonlinear kinetics behavior. This deviation from linear behavior can be attributed to diffusion‐controlled volatilization in high p(O₂).     

连接体合金在SOFC还原气氛下氧化膜的形成及热应力分析

针对新型金属连接体材料Fe-Cr-Co合金,通过750℃的循环氧化实验研究其在SOFC阳极气氛(N2+2％H2+60％H2O)下的高温氧化行为,随后基于真实氧化膜和合金的界面微观形貌进行热应力分析.利用X射线衍射仪(XRD)和配备能谱仪(EDS)的场发射扫描电子显微镜(SEM)对合金氧化膜的相结构和截面形貌以及成分进行...     

La0．9Sr0．1Ga0．8Mg0．2O2．85固体电解质合成及其性能

在NH4OH-(NH4)2CO3沉淀体系中用相转移分离法制备了La0.9Sr0.1Ga0.8Mg0.2O2.85(LSGM1020)固体电解质前驱体,并在较低的烧结温度得到了纯度较高,杂质含量低的电解质陶瓷.用XRD,Raman光谱,直流四电极,交流阻抗谱和扫描电镜分析了电解质的晶体结构,电化学性能和显微结构.XRD和Raman分析表明LSGM1020电解质具有菱方钙钛矿结构,800oC时测量得到的氧离子电导率达到0.12S?cm-1.SEM和交流阻抗分析表明,烧结体具有良好的微观结构.采用相转移分离法合成LSGM1020有利于降低烧结温度,改善电解质的性能.     

流延-共烧法制备掺杂氧化铈基阳极／电解质双层结构

采用甘氨酸／硝酸盐（GNP）法合成了具有较高烧结活性的Ce0.8Gd0.05Y0.15O1.9（GYDC）粉体，通过流延-共烧法制备了NiO—GYDC阳极／GYDC电解质双层结构。结果表明：GYDC电解质薄膜经过1400℃保温4h后可烧结致密，说明GNP法制备的GYDC粉体的烧结活性较高；通过流延．共烧法可以成功制备外观完好、平整的NiO-GYDC／GYDC双层结构，满足SOFC的组装要求。     

Influence of Atmospheric Plasma-Sprayed Composite Cathode on the Performance of Solid Oxide Fuel Cells

Ni-Al2O3 cermet supported tubular solid oxide fuel cells(SOFCs)with different cathodes were fabricated by thermal spraying.The anode,electrolyte and cathode were deposited by atmospheric plasma spraying(APS)aimed at reducing the manufacturing cost of SOFCs.Three porous composite cathodes of lanthanum strontium manganite(LSM)and yttria-stabilized zirconia(YSZ),lanthanum strontium cobalt oxide(LSC)and YSZ,LSC and scandia-stabilized zirconia(ScSZ)were prepared to investigate influence of cathode constitutions on the cell’s performance.The electrode polarization can be improved through using a composite cathode.The maximum power density of the cell with APS YSZ electrolyte and LSC/ScSZ composite cathode is increased about 12%than pure LSM cathode.The maximum output power density of the cell with APS ScSZ electrolyte and LSC/ScSZ composite cathode reaches 1.0 W/cm 2 at 1000 o C.The further optimization of the performance of plasma-sprayed composite cathode can be made through improving the interface contact between YSZ electrolyte and composite cathode.     

Effect of manganese addition on reactive evaporation of chromium in Ni-Cr alloys

Chromium is used as an alloy addition in stainless steels and nickel-chromium alloys to form protective chromium oxide scales. Chromium oxide undergoes reactive evaporation in high-temperature exposures in the presence of oxygen and/or water vapor. Deposition of gaseous chromium species onto solid oxide fuel-cell electrodes can reduce the efficiency of the fuel cell. Manganese additions to the alloy can reduce the activity of chromium in the oxide, either from solid solution replacement of chromium with manganese (at low levels of manganese) or from the formation of manganese-chromium spinels (at high levels of manganese). This reduction in chromium activity leads to a predicted reduction in chromium evaporation factors as much as 35 at 800 °C and 55 at 700 °C. Quantifying the effects of manganese additions on chromium evaporation should aid alloy development of metallic interconnects and balance-of-plant alloys. This paper was presented at the ASM Materials Solutions Conference & Show held October 18–21, 2004 in Columbus, OH.     

热处理对铝箔氧化膜和比电容的影响

对铝箔分别在300℃、400℃和500℃进行0.5h、1h和2h真空退火.测定了铝箔的氧化膜厚度和比电容,并用扫描电子显微镜观察了退火铝箔的腐蚀形貌.结果表明,在400℃退火的铝箔氧化膜最薄,300℃退火的居中,500℃退火的最厚.在300℃退火时,随着保温时间的延长,铝箔的氧化膜厚度减小;而在400℃和500℃退火时...     

银粉和触变剂对低温银浆挥发速率影响的研究

采用不同密度的银粉,改变触变剂类型及含量,以线路复烤前后的电阻值变化率表征银浆的溶剂挥发速率,研究不同条件对银浆溶剂挥发速率的影响。结果表明,低振实密度粉体、有机膨润土、改性聚脲化合物和气相二氧化硅均能快速提高银浆溶剂挥发速率。由振实密度1.6～1.8 g/cm~3的片状银粉、0.25%有机膨润土、0.5%改性聚脲化合物搭配热塑性聚氨酯制备银浆,在150℃×1 min条件下,银浆快速干燥固化,附着力为5B,复烤后电阻变化率3%。     

High-velocity DC-VPS for diffusion and protecting barrier layers in solid oxide fuel cells (SOFCs)

High-temperature fuel cells of the solid oxide fuel cell (SOFC) type as direct converter of chemical into electrical energy show a high potential for reducing considerably the specific energy consumption in different application fields. Of particular interest are advanced lightweight planar cells for electricity supply units in cars and other mobile systems. Such cells, in one new design, consist mainly of metallic parts, for example, of ferrite steels. These cells shall operate in the temperature range of 700 to 800 °C where oxidation and diffusion processes can be of detrimental effect on cell performance for long-term operation. Problems arise in particular by diffusion of chromium species from the interconnect or the cell containment into the electrolyte/cathode interface forming insulating phases and by the mutual diffusion of substrate and anode material, for example, iron and chromium from the ferrite into the anode and nickel from the anode into the ferrite, which in both cases reduces performance and system lifetime. Additional intermediate layers of perovskite-type material, (e.g., doped LaCrO₃) applied with high-velocity direct-current vacuum plasma spraying (DC-VPS) can reduce such effects considerably if they are stable and of high electronic conductivity. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.