【作者】 陶玉强；

【导师】 周科朝； 李志友；

【作者基本信息】 中南大学 ， 材料科学与工程， 2012， 博士

【摘要】 NiFe2O4基金属陶瓷是目前最具工业化应用前景的铝电解惰性阳极材料之一,国内外相继开展了4kA和6kA级铝电解试验,试验发现其导电性能和抗热震性能仍需进一步改善。为改善金属陶瓷惰性阳极的导电性能及抗热震性能,同时又不降低阳极的耐腐蚀性能,本论文系统研究了烧结气氛氧分压和添加金属Ni对Cu与NiFe2O4间润湿性的影响,以及烧结过程中铜合金-铁酸镍金属陶瓷的相反应和烧结行为,在此研究基础上通过优化制备工艺,采用混合粉末烧结与熔渗工艺制备了致密的、具有互穿网络结构的铜合金-铁酸镍金属陶瓷,并研究了材料孔隙度、金属相含量、金属相组成、氧化温度对铜合金-铁酸镍金属陶瓷在空气气氛下氧化行为的影响,以及预氧化处理、电流密度、电解温度对阳极电解腐蚀行为的影响。论文的主要研究成果如下：(1)确定了一种可大幅度改善Cu与NiFe2O4间润湿性的方法。通过提高烧结气氛氧分压或向Cu中添加Cu2O可显著改善Cu与NiFe2O4间的润湿性,当Cu中Cu20加入量达7wt%时,1200℃下Cu与NiFe2O4间的润湿角可降至0°,并首次采用无压熔渗工艺制备了致密度达99%、具有互穿网络结构的Cu/NiFe2O4-10NiO金属陶瓷。(2)明确了NiO与金属相对铜合金-铁酸镍金属陶瓷烧结致密化的作用机制。NiO相在铜合金熔体中存在溶解再析出,从而在液相烧结过程中有利于金属陶瓷的烧结致密化。Cu-Ni金属相中Ni元素的氧化,可促进NiFe2O4相的分解和烧结致密化。(3)澄清了金属相中Ni含量升高的原因。NiFe2O4在氮气气氛下脱脂时存在还原现象,生成金属Ni,提高了Fe2+离子浓度。陶瓷相还原生成的金属Ni在烧结过程中被混合加入金属颗粒吞并是引起金属相中Ni含量升高的主要原因。脱脂过程中NiFe2O4相的还原可促进其烧结致密化。(4)获得了具有良好导电性和力学性能的铜合金-铁酸镍金属陶瓷。混合粉末烧结工艺制备的40(Cu-50Ni)/NiFe2O4-1ONiO金属陶瓷的抗弯强度达206MPa,断裂韧性达16.1MPa·m1/2,经200℃温差热冲击处理后材料的抗弯强度基本不发生变化,960℃下的电导率达513S/cm。熔渗工艺制备的26Cu/NiFe2O4-10NiO金属陶瓷的力学性能与混合粉末烧结工艺制备的金属含量40wt%的金属陶瓷的相当,具有金属导电特征,其在960℃的电导率达1369S/cm。(5)确定了抑制互穿网络结构铜合金-铁酸镍金属陶瓷中金属相快速电化学腐蚀的技术工艺。通过预氧化处理和调控电解温度,可实现金属相的先氧化后溶解腐蚀,避免金属相的快速电化学腐蚀。研究表明对40(Cu-50Ni)/NiFe2O4-10NiO金属陶瓷进行880℃、48h空气预氧化后再进行960℃电解,阳极底部可形成致密的陶瓷层,有利于阻碍电解质的渗透和金属相的电化学腐蚀,从而可获得良好的耐蚀性能。本论文的研究成果对金属陶瓷惰性阳极的烧结制备、金属陶瓷与合金导杆的连接,甚至对推动金属陶瓷阳极的工业化应用均具有重要意义。更多还原

【Abstract】 NiFe2O4based cermets are one of the most promising industrial inert anode materials, which have been carried out4kA and6kA pilot electrolysis. The electrolysis test shown that the electrical conductivity and thermal shock resistance of the cermet anodes need further improving. In order to increase the electrical conductivity and improve the thermal shock resistance of the cermet anodes, while not reducing the corrosion resistance, the effects of oxygen partial pressure and the addition of Ni on the wettability of Cu and NiFe2O4, and the phase reactions and sintering behavior of copper alloy-nickel ferrite cermets during sintering process were firstly studied. Then a dense copper alloy-nickel ferrite cermet with interpenetrating structure was preparated respectively by conventional ceramic process and infiltration through optimizing the sintering condition. The effects of the material porosity, metal phase content, metal phase composition, oxidation temperature on the oxidation behavior of the prepared cermets were studied. Also the influences of pre-oxidation thermal treatment, current density, electrolytic temperature on the corrosion behavior of the cermet anodes with interpenetrating structure were studied. The main results were shown as follow:(1) A new method to drastically improve the wettability of Cu and NiFe2O4was developed. It was found that increasing the oxygen partial pressure or adding Cu2O into Cu could improve the wettability of Cu and NiFe2O4. The contact angle decreased to0°at1200℃when Cu2O content was upto7wt%. A Cu/NiFe2O4-10NiO cermet with a relative density of99%and interpenetrating structure was firstly prepared by pressureless infiltration.(2) The mechanisms of NiO and the metal phase on the densification of copper alloy-nickel ferrite cermets were clarified. The dissolution precipitation mechanism of NiO was found in copper alloy melt, which was conducive to the sintering densification during liquid sintering process. The oxidation of Ni of Cu-Ni alloy could promote the decomposition and sintering densification of NiFe2O4phase.(3) The cause of the increase of Ni content in the metal phase was clarified. The reduction of NiFe2O4was found when binder burnout process was performed in N2, which produced metal Ni and increased the Fe2+content of NiFe2O4. The merging of new formed Ni with the additive Cu-Ni was the main reason that caused the increase of Ni content in the metal phase. The reduction of NiFe2O4during binder burnout process could promate the sintering densification of NiFe2O4.(4) A copper alloy-nickel ferrite cermet with good mechanical property and electrical conductivity was prepared. The bending strength and fracture toughness of40(Cu-50Ni)/NiFe2O4-10NiO cermets prepared by conventional ceramic process were206MPa and16.1MPa·m1/2, respectively. The bending strength hardly decreased after Δ200℃thermal treatment. The electrical conductivity of the cermets was about513S/cm at960℃. The mechanical property and electrical conductivity of26Cu/NiFe2O4-10NiO cermet prepared by infiltration were comparable with that of the cermets with40wt%metal phase content prepared by conventional ceramic process.26Cu/NiFe2O4-10NiO cermet has the characteristic of metal conductivity, whose electrical conductivity was about1369S/cm at960℃.(5) A technique that could inhibit the fast electrochemical corrosion of metal phase of copper alloy-nickel ferrite cermets with interpenetrating structure was developed. Oxidation of the metal phase before dissolution could be realized by pre-oxidation thermal treatment and controlling the electrolysis temperature, to avoid the fast electrochemical corrosion of the metal phase. The study showed that a dense ceramic layer could be formed on the bottom of40(Cu-50Ni)/NiFe2O4-10NiO cermet anode when electrolysis was carried out at960℃and pre-oxidized at880℃for48h in air, was conducive to impede the penetration of the electrolyte and metal phase electrochemical corrosion, and well corrosion resistance.This research is of great significance on the preparation of cermet inert anode, connection of cermet anode and alloy guide bar, even on the promotion of the industrial application of cermet anode.更多还原