BaO掺杂对10NiO-NiFe2O4复合陶瓷烧结致密化的影响

利用冷压一烧结技术制备BaO掺杂的10NiO-NiFe2O4复合陶瓷,研究BaO掺杂量及烧结温度对10NiO-NiFe2O4复合陶瓷物相组成、显微结构及致密度的影响。结果表明：当BaO掺杂量（质量分数）为0,-4％时,烧结样品中主要含NiO和NiFe2O4,BaO与10NiO-NiFe2O4陶瓷组分反应并形成瞬时液相BaFe2O4和Ba2Fe2O5,且Ba2＋固溶到基体中,促进致密化烧结,降低了烧结致密化温度;1250℃烧结时,1％BaO掺杂样品的相对密度最大,达到98．90％,比未掺杂样品的相对密度提高6．27％;但当BaO掺杂量为2％和4％时,陶瓷样品相对密度基本不变。     

CaO掺杂10NiO-NiFe2O4复合陶瓷的导电性能

研究添加剂CaO含量和烧结温度对CaO掺杂10NiO-NiFe2O4复合陶瓷的物相组成和电导率的影响。结果表明:CaO含量在0~4%范围内,烧结试样的X射线衍射谱仅有NiO和NiFe2O4的衍射峰;10NiO-NiFe2O4复合陶瓷在空气中升温过程存在明显的吸氧和失氧行为;CaO含量对1 473 K烧结的10NiO-NiFe2O4复合陶瓷的电导率影响显著;当CaO含量为0~1%时,随测试温度的升高,材料电导率逐渐增大,随后在773~923 K出现1~2个数量级的突降,然后重新缓慢增大;当CaO含量为2%和4%(质量分数,下同)时,材料电导率在298~1 233 K范围内随着测试温度的升高而增大;2?O掺杂10NiO-NiFe2O4复合陶瓷在不同测试温度下均具备最高电导率,1 233 K下达到16.29 S/cm,远高于未掺杂试样的1.03 S/cm;烧结温度由1 473 K提高到1 573 K时,未掺杂试样在1 233 K时电导率提高近15倍,2?O掺杂试样1 233 K时电导率略有提高。     

气氛对NiFe2O4陶瓷烧结致密化的影响

采用不同的烧结工艺制备了NiFe2O4陶瓷材料,研究了真空、大气、N2 3种气氛对NiFe2O4陶瓷材料烧结致密度的影响,解决了烧结过程中NiFe2O4陶瓷的离解问题.结果表明:在制备NiFe2O4陶瓷过程中,烧结气氛严重影响着陶瓷的离解和致密化;真空烧结将导致NiFe2O4陶瓷的离解,N2气氛保护烧结所制备出的NiFe2O4陶瓷样品的密度较大气气氛烧结所制备出的样品的密度高出14.6%～32.6%.分析结果表明:因NiFe2O4陶瓷高温失氧所带来的表面能和晶体缺陷的差异是影响其致密化的关键;无论在何种气氛下烧结,提高烧结温度都有利于提高NiFe2O4样品的烧结密度.     

Yb_2O_3掺杂对15(20Ni-Cu)/(NiFe_2O_4-10NiO)金属陶瓷性能的影响

采用冷压-烧结技术制备NiFe2O4-10NiO基金属陶瓷材料;通过对烧结体的显微结构和物相组成、电导率、电解试样的表层形貌、电解质和阴极铝的杂质增量等的分析检测,研究Yb2O3掺杂对15(20Ni-Cu)/NiFe2O4-10NiO金属陶瓷致密度、导电率和耐腐蚀性能的影响。结果表明:1 300℃烧结的0.5%Yb2O3-15(20Ni-Cu)/(NiFe2O4-10NiO)金属陶瓷具有较好的性能,相对密度为98.53%,960℃时的电导率为53.06 S/cm,电解腐蚀后金属腐蚀层厚度为20~30μm,总杂质增量为0.079 g。     

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。     

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。     

纤维/NiFe2O4复合陶瓷惰性阳极的制备及性能

以高温固相合成法,采用两步烧结法制备镀铜碳纤维增强的纤维/NiFe2O4复合陶瓷惰性阳极,即先以NiO、Fe2O3、微量V2O5和MnO2为原料制备NiFe2O4尖晶石基体材料,然后以该NiFe2O4尖晶石基体材料和镀铜碳纤维为原料,采用冷压烧结法制备纤维/NiFe2O4复合陶瓷惰性阳极.研究镀铜碳纤维添加量对NiFe2O4复合陶瓷惰性阳极体积密度、气孔率和抗弯强度的影响.结果表明:添加镀铜碳纤维可以显著改善NiFe2O4复合陶瓷材料的性能,当镀铜碳纤维添加量为3%(质量分数)时,其体积密度比不添加镀铜碳纤维试样的体积密度提高约12%,其抗弯强度比不添加镀铜碳纤维的提高约22%.     

CrO3对陶瓷复合钢管致密化及力学性能的影响

利用离心自蔓延高温合成法 ,制备陶瓷复合钢管。用 X射线衍射仪测定了陶瓷层的相成分 ,研究了添加剂Cr O3对陶瓷复合钢管致密化及力学性能的影响。结果表明 :添加 Cr O3可以升高反应体系的反应温度 ,提高陶瓷复合钢管的致密化程度和力学性能。     

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.     

烧结温度对ZrB2-SiC超高温陶瓷致密化的影响

利用放电等离子烧结技术（SPS）在不同的烧结温度下对ZrB2-SiC超高温陶瓷进行烧结，研究了烧结温度对烧结体致密化的影响。结果表明，在烧结温度分别为1650℃、1750℃、1850℃和1950℃，升温速度为200℃／min，保温时间为1min，压力为50MPa时，随着烧结温度的提高，烧结体的致密度呈上升趋势。当烧结温度高于1850℃时，烧结体的致密化过程明显加剧；通过对不同烧结温度下制得的试样的XRD谱图分析发现，当温度高于1850℃时ZrB2-SiC陶瓷中的SiC相会发生3C相到4H相的转变，这可能就是当烧结温度高于1850℃时烧结体致密度会急剧上升的原因。     

Effect of BaO addition on electric conductivity of xCu/10NiO-NiFe2O4 cermets

The effects of BaO addition on the phase composition, relative density and electric conductivity of xCu/10NiO-NiFe2O4 （x=5, 10） eermets were studied, which were prepared with cold isostatic pressing-sintering process. The results show that the relative densities of 5Cu/10NiO-NiFe2O4 cermet doped with 1% BaO （mass fraction） and 10Cu/10NiO-NiFe2O4 cermet doped with 1% BaO sintered at 1 473 K in nitrogen atmosphere, are increased by about 9.86% and 9.75% compared with the undoped BaO cermets, respectively. And the electric conductivities 22.79 S/cm of 5Cu/10NiO-NiFe2O4 cermets adding 1% BaO and 23.10 S/cm of 10Cu/10NiO-NiFe2O4 cermets adding 1% BaO are obtained, which are 2.21 times and 1.47 times of those of undoped samples, respectively. Moreover, the 10Cu/10NiO-NiFe2O4 cermets doped with 1% BaO have a maximum σ0 of 58.91 S/cm and electric conductivity of 23.10 S/cm at 1 233 K. Maybe low melting-point phases of BaFe2O4 and Ba2Fe2O5 have an excellent electric conductivity in xCu/10NiO-NiFe2O4 （x=5, 10） cermets at 1 233 K.     

Influence of Yb2O3 addition on microstructure and corrosion resistance of 10Cu/（10NiO-NiFe2O4） cermets

10Cu/(10NiO-NiFe₂O₄) cermets doped with Yb₂O₃ were prepared by conventional powder metallurgy technique. The effects of Yb₂O₃ content and sintering temperature on the relative density, phase composition, microstructure of the sintered cermets and the corrosion resistance to Na₃AlF₆-Al₂O₃ melts were investigated by sintered density test, XRD analysis and SEM. YbFeO₃ phase, which distributes in the ceramics grain boundary as particles or film, is produced by the reaction between Yb₂O₃ and ceramics. The addition of Yb₂O₃ accelerates the sintering process of ceramics matrix, eliminates pores in the boundary and results in coarsened crystalline grain. The relative density of the cermets with about 1% (mass fraction) Yb₂O₃ sintered at 1275 °C increases to above 95%. Addition of about 1.0% Yb₂O₃ can inhibit obviously the corrosion of NiFe₂O₄ grain boundary and Cu phase in Na₃AlF₆-Al₂O₃ melts.     

Densification of Ni-NiFe_2O_4 cermets for aluminum electrolysis

1INTRODUCTION Aluminumelectrolysisconsumesenormous energyandresources,andtheconsumptionwillbeconsiderablydecreasedbyintroductionofinert anodeandwettablecathode.However,underthe toughworkingconditionofaluminumelectrolysis,i.e.highlycorrosiveNa3AlF6Al2O3moltensalts athightemperature(940960℃),theinert anodesnecessaryforthesuccessfulproductionofaluminummighthavethefollowingproperties:be insolubleinafluoridemelt,beresistanttowards anodeoxygen,havegoodelectricalconductivity,possessadequatestr…     

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.     

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.     

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.