Results from 100 h electrolysis testing of NiFe2O4 based cermet as inert anode in aluminum reduction

1 Introduction Since the Hall-Héroult process was applied in aluminum production, an inert anode was always the target that the aluminum industry was seeking for in the new technology field[1]. Some selection criteria have been defined in order to ident…     

Preliminary testing of NiFe_2O_4-NiO as ceramic matrix of cermet inert anode in aluminum electrolysis

1　INTRODUCTIONTheideaofusinginertanodes(alsocallednon consumableoroxygen evolvinganodes)inaluminumproductionisasoldastheHall H啨ｒｏｕｌｔｐｒｏｃｅｓｓ ,dat ingbacktothediscoveryofoneoftheinventors ,Hall[1] .Inertanodesareintendedtoreplacethecon sumablecarbonanodethatiscurrentlyused .Withacarbonanode ,thecellreactionisAl2 O3+ 3/ 2C =2Al+ 3/ 2CO2 (1)where　acryolite basedmelt(Na3AlF6 AlF3 CaF2 )atnear 96 0℃servesassolventforthealumina .Withaninertanode ,thecellreactionwillbeAl2 …     

铝电解用NiFe2O4-10NiO基金属陶瓷惰性阳极的耐腐蚀性能

制备铝电解用NiFe2O4-10NiO基金属陶瓷惰性阳极,并在实验室电解槽中考察其电解腐蚀性能。结果表明,电解过程中虽然惰性阳极在960°C熔盐电解质中表现出优异的耐腐蚀性能,但采用XRD、SEM/EDX和金相分析其物相组成和微观结构后发现,电解后阳极中的金属相发生了优先腐蚀,在阳极表面产生大量孔洞。NiFe2O4相中的 Fe 元素的优先溶解可能导致 NiFe2O4晶粒的不均匀腐蚀。溶解在电解液中的 Al2O3与阳极中的 NiO 或FeO 发生反应生成的 NiFe2O4-NiAl2O4-FeAl2O4相对 NiO 相的吞并以及体积膨胀,阳极表面形成致密的NiFe2O4-NiAl2O4-FeAl2O4保护层。因此,致密的NiFe2O4-NiAl2O4-FeAl2O4保护层可以阻挡阳极表面金属相的损失和陶瓷相的腐蚀。     

Effect of NiO content on corrosion behaviour of Ni-xNiO-NiFe2O4 cermets in Na3AlF6-Al2O3 melts

5Ni-xNiO-NiFe2O4 cermets with different NiO contents were prepared and the corrosion behaviour in Na3AlF6-Al2O3 melts was investigated in laboratory electrolysis tests. The results indicate that adding NiO is unfavorable to the densifieation of NiFe2O4-xNiO ceramics, while small Ni doping can greatly improve the sintering property. The electrolysis tests show that excess NiO is beneficial to the reduction of Fe while has little effects on that of Ni in the bath; the steady-state concentrations of Ni, Fe are below the corresponding solubilities of NiFe2O4-xNiO, implying that corrosion mechanism changes while electrifying. Post-electrolysis examination of anodes shows that Ni metal leaches at the anode surface, yet the substrate ceramic prevents the penetration of bath and the further loss of metal phase.     

Effect of Ni content on corrosion behavior of Ni/（10NiO-90NiFe2O4） cermet inert anode

Ni/（10NiO-90NiFe2O4） cermet inert anodes with metal Ni content of 0, 5, 10, 15 and 20 （mass fraction, %） were prepared and their corrosion behavior in Na3AlF6-Al2O3 melts was investigated in laboratory electrolysis tests. The results indicate that the content of metal Ni in anodes has little effect on the steady-state concentration of impurities Ni and Fe in electrolyte and the values range in （114-173）×10^-6 and （287-385）×10^-6, but the content of impurities in the metal aluminum manifolds. There is preferential corrosion for metal Ni in NiO-NiFe2O4 based cermet anodes. Considering the corrosion resistance and electrical conductivity, the cermet containing 5%Ni （mass fraction） behaves best among NiO-NiFe2O4 based cermet anodes studied, and should be further studied.     

Electrical resistivity of NiFe_2O_4 ceramic and NiFe_2O_4 based cermets

NiFe2O4 ceramic and NiFe2O4 based cermets, expected to be used as the inert anodes in aluminum electrolysis, were prepared and their electrical resistivities were measured at different temperatures. The effects of temperature and composition on their electrical resistivities were investigated. The results indicate that the electrical resistivities of NiFe2O4 based cermets mainly depend on temperature, resistivity of ceramic matrix, composition and dispersion of the metal phase among ceramic matrix. The electrical resistivity of NiFe2O4 ceramic decreases from 10. 094 Ω · cm to 0. 475 Ω · em with increasing temperature from 573 K to 1 233 K. The electrical resistivities of NiFe2O4 based cermets are greatly lowered, but decrease with increasing the temperature with similar trend compared to that of NiFe2O4 ceramic. The resistivities of NiFe2O4 based cermets containing 5 % Ni, 5 % Cu and 5 % CuNi alloy are 0. 046 8, 0.066 8 and 0. 0532 Ω · cm at 1 233 K, respectively, which are all acceptable as inert anode materials compared to that of the current carbon anode used for aluminum electrolysis.     

铝电解用NiFe2O4-Cu金属陶瓷惰性阳极的制备

以高温固相合成法合成的NiFe2O4陶瓷粉体和金属Cu粉为原料, 采用冷压-烧结法制备了Cu含量在5%～20%之间的NiFe2O4-Cu金属陶瓷惰性阳极, 研究了烧结气氛和烧结温度对其物相组成、微观形貌和基本物理性能的影响. 结果表明 通过控制烧结气氛中氧分压在NiO和Cu2O的离解反应平衡氧分压之间, 可以制备出具有目标物相组成的NiFe2O4-Cu金属陶瓷; 烧结温度和保温时间对所得NiFe2O4-Cu金属陶瓷的相对密度有较大影响; NiFe2O4和Cu之间的不润湿性限制了NiFe2O4-Cu金属陶瓷烧结温度的提高和保温时间的延长, 在保证金属相分布均匀且不溢出的前提下, 所制备的NiFe2O4-Cu金属陶瓷的相对密度较小; 金属相Cu含量越高, NiFe2O4-Cu金属陶瓷最高烧结温度越低、最长保温时间越短, 从而相对密度越低、孔隙率越高; 除了尽量降低金属相含量外, 还可向NiFe2O4-Cu金属陶瓷中添加其他金属如Ni和Co等, 以改善陶瓷相与金属相之间的润湿性, 以提高烧结温度, 进而提高其相对密度和耐腐蚀性能.     

NiFe2O4基金属陶瓷惰性阳极的腐蚀研究进展

综述了近年来国内外铝电解用NiFe2O4基金属陶瓷惰性阳极在阳极组元的溶解与分布、腐蚀率的预测与测定以及氧化物和金属相对阳极腐蚀的影响三个方面所做的研究工作。     

EFFECT OF Cu-Ni CONTENT ON THE CORROSION RESISTANCE OF （Cu-Ni）/（10NiO-90NiFe204） CERMET INERT ANODE FOR ALUMINUM ELECTROLYSIS

（Cu-Ni）/（10NiO-90NiFe204） cermet inert anodes containing metal Cu-Ni0, 5, 10, 15 and 20 wt pct were prepared and their corrosion resistance to Na3AlF6-Al2O3 melts was investigated. The results indicate that the content of metal Cu-Ni has little effect on the steady-state concentration of Ni in the electrolyte and the values could not be used to effectively differentiate their corrosion resistance. The steady-state concentration of Fe decreases from 304×10^-6 to 168×10^-6 and that of Cu increases from 21×10^-6 to 71×10^-6 with the content of metal Cu-Ni increasing from 0 to 20 wt pct. Post-examination shows that metallic phase Cu-Ni is corroded preferentially during electrolysis and many pores are left at the anode surface. Considering the corrosion resistance and electrical conductivity, the cermet containing metal Cu-Ni 5 wt pct should be selected and studied further.     

Effect of metallic phase content on mechanical properties of （85Cu- 15Ni）/（10NiO-NiFe2O4） cermet inert anode for aluminum electrolysis

（85Cu-15Ni）/（10NiO-NiFe2O4） cermets were prepared with Cu-Ni mixed powders as toughening metallic phase and 10NiO-NiFe2O4 as ceramic matrix. The phase composition, microstructure of composite and the effect of metallic phase content on bending strength, hardness, fracture toughness and thermal shock resistance were studied. X-ray diffraction analysis indicates the coexistence of （Cu-Ni）, NiO and NiFe2O4 phases in the cermets. Within the content range of metallic phase from 0% to 20% （mass fraction）, the maximal bending strength （176.4 MPa） and the minimal porosity （3.9%） of composite appear at the metallic phase content of 5%. The fracture toughness increases and Vickers＇ hardness decreases with increasing metal content. When the thermal shock temperature difference （At） is below 200 ℃, the loss rate of residual strength for 10NiO-NiFe2O4 ceramic is only 8%, but about 40% for （85Cu-15Ni）/（10NiO-NiFe2O4）cermets. As At is above 200 ℃, the residual strength sharply decreases for sample CN0 and falls slowly for samples CN5-CN20.     

Preparation and preliminary testing of cermet inert anode for aluminum electrolysis

1　INTRODUCTIONAluminumhasthelargest productivityamongthenonferrousmetals ,2 4Mtperyearintheworld .Whilegreatprogresshavebeenmadeintheprimaryaluminum production ,theindustrycontinuestopur sueresearchtosolvesomeformidablechallenges ,suchas quitealargeenergyintensity(14 0 0 0 15 0 0 0kW·hpertonaluminum) ,highcon sumptionofcarbonanode(5 0 0 6 0 0kgpertonalu minum) ,significantemissionsofgreenhousegas(1.71tpertonaluminum )andotherdetrimentalgases ,highcapitalinvestmentandcost[1] .Inertelectr…     

大尺寸NiFe2O4-10NiO/17Ni型金属陶瓷惰性阳极的制备

研究以PVA为主要成分的粘结剂体系的热分解特性对大尺寸粉末压坯脱脂行为的影响,发现PVA的不均匀热分解是造成大尺寸粉末压坯脱脂失效的原因之一,开发一种具有稳定热分解反应特性的新型粘结剂体系,实现大尺寸粉末压坯的无缺陷热脱脂;研究烧结气氛、金属相的添加对NiFe2O4-10NiO致密化行为的影响。结果表明：N2气氛烧结及加入Ni可有效提高NiFe2O4-10NiO陶瓷基体的烧结致密度,1350℃时于N2气氛中烧结的NiFe204．10NiO／5Ni型金属陶瓷材料的相对密度达到97．28％。采用优化工艺实现d120mmX140mm深杯状NiFe2O4-10NiO／17Ni金属陶瓷惰性阳极脱脂预烧坯的烧结,所得烧结坯平均相对密度为95．21％。     

Yb2O3或Y2O3掺杂Cu-(NiFe2O4-10NiO)惰性阳极的导电性和耐蚀性

在氧分压约为100 Pa的氮气氛下烧结制备了掺杂Y2O3、Yb2O3的10Cu-(NiFe2O4-10NiO)金属陶瓷,并对其进行导电性能测试和10h(Na3A1F6-Al2O3体系中)铝电解实验.采用XRD、SEM和EDS分析稀土氧化物以及其与陶瓷基体反应产物的分布,考查电解实验后材料表层显微结构变化尤其是金属相的流失情况,评价稀土氧化物的添加对金属陶瓷电解初期腐蚀行为的影响.结果表明:掺杂稀土氧化物均使NiO相呈连通迹象,掺杂Yb2O3金属陶瓷晶粒较未掺杂的粗大,其与陶瓷相反应生成物成点线状分布于NiFe2O4相晶界,Y2O3与陶瓷相反应生成物则分布于NiO与NiFe2O4相间;所制备材料具有半导体特征,随着稀土氧化物的掺杂,材料导电性呈下降趋势;掺杂稀土氧化物尤其是Yb2O3有利于提高材料的耐蚀性能.     

EFFECT OF Cu-Ni CONTENT ON THE CORROSION RESISTANCE OF (Cu-Ni)/(10NiO-90NiFe2O4) CERMET INERT ANODE FOR ALUMINUM ELECTROLYSIS

(Cu-Ni)/(10NiO-9ONiFe2O4 ) cermet inert anodes containing metal Cu-Ni 0,5, 10, 15 and 20 wt pet were prepared and their corrosion resistance to Na3AlF6-Al2O3 melts was investigated. The results indicate that the content of metal Cu-Ni has little effect on the steady-state concentration of Ni in the electrolyte and the values could not be used to effectively differentiate their corrosion resistance. The steady-state concentration of Fe decreases from 304×10-8 to 168×10-6 and that of Cu increases from 21×10-6 to 71×10-6 with the content of metal Cu-Ni increasing from 0 to 20 wt pct. Post-examination shows that metallic phase Cu-Ni is corroded preferentially during electrolysis and many pores are left at the anode surface. Considering the corrosion resistance and electrical conductivity, the cermet containing metal Cu-Ni 5 wt pct should be selected and studied further.     

Effect of additive on corrosion resistance of NiFe2O4 ceramics as inert anodes

In order to improve the corrosion resistance of NiFe2O4 ceramics as inert anode, additive V2O5 was added to raw materials NiO and Fe2O3. The inert anodes of nickel-ferrite ceramics were prepared by powder metaUurgic method and the static corrosion rate in Na3AlF6-Al2O3 was determined by mass loss measurement. The effect of V2O5 on sintering property and corrosion resistance was studied. The results show that V2O5 can promote the grain to develop completely and improve sintering property. EDS results show the reaction product Ni2FeVO6 distributes along the grain boundary. The corrosion tests show that V2O5 is beneficial to improving corrosion resistance remarkably. The reasons that V2O5 can improve the corrosion resistance must be V2O5 promoting the gains to develop completely and Ni2FeVO6 distributes along the grain boundary. The stable structure can control the chemical dissolution of ceramics anode and the reinforced grain boundary can control the grain-boundary corrosion rate.     

基于GA-BP的NiFe2O4基金属陶瓷阳极优化设计

采用BP神经网络对铝电解NiFe2O4基金属陶瓷惰性阳极的电解腐蚀过程进行了系统辨识。建立了以Al2O3质量浓度、电解温度、分子比、面积比和电流密度为输入,腐蚀率为输出的网络模型。在材料的设计中,采用了GA-BP优化方法,BP网络参与GA迭代计算时对个体的评价。应用结果表明,NiFe2O4基金属陶瓷惰性阳极的电解腐蚀率预测结果与实测值吻合;优化设计的结果与实验值很接近。     

惰性阳极基体材料NiFe2O4尖晶石的研制

本文用Ni2O3和Fe2O3为原料制备了铝电解用惰性阳极基体材料NiFe2O4尖晶石,详细介绍了整个制备过程。通过对NiFe2O4尖晶石的含量、真密度以及开口孔隙率等重要指标进行研究比较,最终得出了制备NiFe2O4尖晶石最佳工艺条件,并用最佳工艺条件重新制取试样进行热腐蚀实验。     

高能球磨法制备NiFe2O4基惰性阳极

本文以NiO和Fe2O4为主要原料,采用机械化合两步烧结法制备NiFe2O4基金属陶瓷试样。研究了球磨时间、助磨剂含量、球磨转速对制备前驱体粒度的影响,并利用X射线衍射和扫描电子显微镜等进行表征。结果表明,球磨参数越好,粉体颗粒越细,提高冷等静压压坯的致密度、降低试样烧结温度,最终提高惰性阳极试样密度,改善试样的导电性和抗腐蚀性等性能并达到保护环境、节约能源的效果。本实验制备惰性阳极球磨阶段最佳球磨条件为：助磨剂含量150ml、球磨时间6h、球磨转速300r／min,此条件下制得了体积密度为5．68g／ml的阳极试样。     

铝电解金属陶瓷惰性阳极的机械加工及大型化研究

本文用普通钻头和设计的专用走具,采用传统机械加工方法对金属陶瓷铝电解惰性阳极钻孔,同时也研究了金属陶瓷惰性阳极的磨削、抛光等加工方法。用这些方法成功地解决了金属陶瓷铝电解惰性阳极的机械加工和大型化问题。     

磷酸盐连接NiFe2O4基金属陶瓷的界面形貌和连接机理

针对铝电解用金属陶瓷惰性阳极材料与金属导杆的电连接困难问题,以Al(H2PO4)3为胶粘剂,CuO为固化剂,NiFe2O4陶瓷粉和Cu-Ag合金粉为填充料,连接NiFe2O4基金属陶瓷.通过分析Al(H2PO4)3与CuO的反应过程,观察磷酸盐连接NiFe2O4基金属陶瓷的界面形貌,探索其高温连接机理.结果表明:Al(H2PO4)3与CuO反应后生成的Cu-P-O化合物是主要连接物相;Cu-P-O化合物随温度的变化逐步发生一系列物相变化,并在960~1 000℃下逐步分解为CuO和P2O5;在不同热处理温度下,磷酸盐与NiFe2O4基金属陶瓷连接界面始终保持紧密结合状态:低温下连接层与金属陶瓷润湿性良好并依靠吸附作用相互连接,高温下连接层与金属陶瓷依靠互扩散作用相互连接.