NiFe₂O₄基惰性阳极制备及金属/NiFe₂O₄润湿性研究

【作者】 姚云；

【导师】 谢刚；

【作者基本信息】 昆明理工大学 ， 冶金物理化学， 2013， 博士

【摘要】 惰性阳极材料应用于铝电解工业是当前研究的热门课题,更是铝生产工业实现节能环保、减少排放与提高效率的重要发展方向。经过多年的研究,惰性阳极制备与性能研究已取得较大进展,但因金属/陶瓷间不润湿、金属析出等问题而很难达到现行铝电解工艺下的高电导率、耐腐蚀、高机械强度等要求,严重阻碍了铝电解用惰性阳极实现工业化进程。本论文通过球磨—煅烧—二次球磨—冷等静压(CIP)成型—烧结工艺路线制备NiFe2O4-NiO-Cu-Ni隋性阳极,主要解决NiFe2O4基惰性阳极中金属铜/陶瓷之间的润湿问题和金属析出的问题,提高了惰性阳极的抗热震性、抗腐蚀性等性能。论文系统地研究了粉体的球磨工艺参数、CIP成型工艺参数、金属/NiFe2O4间的润湿性,烧结制度等工艺过程,实现了金属/NiFe2O4之间的完全润湿,为金属陶瓷惰性阳极的制备奠定了更加全面的基础。本论文的主要研究内容和结论如下：(1)系统地研究了球磨工艺参数,采用离散元(DEM)理论分析了球磨工艺参数与球磨效率、颗粒粒度之间的关系,得出最佳球磨工艺参数为：填水率64.1%～85.47%；小大球个数比18；转速300.9rpm；填粉率10.88%；填球率20.53%～23.88%；球磨时间6h。通过对粉体进行XRD、SEM、BET和混匀度表征得出,球磨法可制备出平均粒度为200nm左右,粒度分布较宽的不规则片状粉体。球磨混合6h可得到混匀度大于96.80%的粉体。以此同时,使用声波测量仪研究了球磨效率与球磨噪声能消耗的关系得出,球磨效率与球磨噪声能消耗关系的经验公式,并发现球磨机的工作效率随着噪声能消耗的增大而降低,粉体的粒度随着噪声能消耗的减小而减小。(2)对CIP成型中的升压速率、成型压力、保压时间、泄压速率、压坯的长径比等因素进行了系统的研究,得出最佳成型工艺参数为：成型压力240MPa左右；升压速率1.0MPa·s-1；保压时间对小直径压坯的影响不大；最佳泄压速率不大于0.5MPa·s-1;最佳长径比8.00。对影响CIP成型的压力和长径比的关系模拟分析得出,压坯体积密度与成型压力成正相关关系,并且得到了压缩特性曲线方和相关参数值；对压坯的平均体积密度与长径比的关系分析得到了相关方程和对应的参数值。(3)对新型PVP+无水乙醇复合助磨剂、分散剂、成膜剂和黏结剂进行了研究。通过SEM、EDS和XRD表征表明,随着PVP的增加和球磨时间的延长,Cu粉在陶瓷基体中的分散性提高,粉体的粒度变细,当PVP掺杂量为2%,球磨时间为24h时,混合粉体的分散性最好,平均粒度最细为43.7nm,极大地提高了球磨法制备NiFe2O4-NiO-Cu-Ni超细粉体的质量。(4)测量了不同制备工艺所得NiFe2O4-NiO-Cu-Ni惰性阳极的润湿角,对润湿的机理进行了探讨。通过研究得出：普通方法制备的NiFe2O4-NiO-Cu-Ni惰性阳极中金属/陶瓷的润湿角为116.7°,金属/陶瓷之间的二面角为124.6°；以无水乙醇+PVP为新型助磨剂、分散剂、成膜剂和黏结剂制备的NiFe2O4-NiO-Cu-Ni超细粉体为原料,制备的惰性阳极中金属/陶瓷的润湿角为44.3°,金属/陶瓷之间的二面角为32.7～72.9°；以无水乙醇+PVP为新型助磨剂、分散剂、成膜剂和黏结剂,Ti粉取代TiO2添加剂,制备的NiFe2O4-NiO-Cu-Ni超细粉体为原料,制备的惰性阳极中金属/陶瓷的润湿角为0°,金属/陶瓷变为全润湿,形成铺展,解决了NiFe2O4-NiO-Cu-Ni惰性阳极中金属/陶瓷之间的润湿问题。(5)研究表明在Ar气氛下烧结,可制备得惰性阳极目标产物,不造成金属氧化。研究了多种不同的惰性阳极制备工艺,通过比较得出,球磨—煅烧—添加水乙醇及PVP—二次球磨—CIP成型—烧结工艺是全润湿型NiFe2O4-NiO-Cu-Ni惰性阳极的最佳制备工艺。(6)通过研究得出：NiFe2O4-NiO-Cu-Ni超细粉的最佳烧结温度为900℃；掺杂Ti可在金属陶瓷中形成固溶体和合金,并产生反应性润湿,使金属/陶瓷间形成完全润湿,促进烧结,使金属形成均匀的半连续、连续的立体网状结构分布,阻止了晶粒长大,降低了材料的气孔率,使材料的致密度由95%左右提高到了99%以上；掺杂Ti的全润湿型惰性阳极的抗热震性提高了185.71%；静态腐蚀率比一般方法制备的惰性阳极降低了10倍以上,最小为1.235mm·y-1;随着Ti掺量的增加,惰性阳极的静态腐蚀率降低,通过研究得出惰性阳极中Ti的最佳掺杂量为1%左右。更多还原

【Abstract】 Inert anode is becoming a hot topic and has great applied value in electrolytic production of aluminium. Energy-saving, environmentally friendly, reducing emissions and increase of efficiency are the main developing trend in electrolytic production of aluminium. Inert anode preparation and performance investigation have made great progress after many years of research. Even so, the good performance of NiFe2O4based cermet still could not meet the requirement of the inert anode for aluminum electrolysis industry due to their non-wetting of metal/NiFe2O4, electrical conductivity, corrosion resistance and mechanical strength, etc. These problems have seriously hindered the development of industrialization of inert anode.In the thesis, the NiFe2O4-NiO-Cu-Ni inert anode was synthesized by manufacturing route of planetary mill grinding, calcination, secondary planetary mill grinding, cold isostatic compaction (CIP) and sintering technology. The research aimed at resistances to thermal shock, corrosion resistances and wettability of metal/NiFe2O4in NiFe2O4-NiO-Cu-Ni Inert anode systems. The experimental operating parameters of mill grinding, experimental operating parameters of CIP, the wettability of metal/NiFe2O4in NiFe2O4-NiO-Cu-Ni Inert anode systems and sintering technology were studied systematically. Main contents and conclusions of this thesis are as follows:(1) The relations of grinding efficiency and noisy-power dissipation in NiO/Fe2O3wet grinding process have been studied. The experimental results show that the best grinding parameters are as follows:water-tilling ratio64.1%～85.47%, balls number ratio18, rotation-to-revolution speed300.9rpm, powder-filling ratio about10.88%, ball-filling ratio20.53%～23.88%, grinding time about6h. By the XRD, SEM and BET characterization, the results show that the particle size is about200nm, the appearance of particle is plate-shaped. The degree of mixedness of powder is>95%by mathematical analysis. Furthermore, the discrete element method (DEM) is employed to investigate and analyze the relations of noisy-power dissipation and efficiency. The empirical equation between noisy-power dissipation and ball-filling ratio was obtaind by fitting. It is interesting to find that the mean particle size of powder increase, the efficiency of planetary ball mill grinding and utilization of specific impact energy decrease with the noisy-power dissipation increases. (2) The lifting pressure rate, briquetting pressure, dwell time, pressure release rate and length diameter ratio are investigated on the CIP. The experimental results show that the best CIP parameters are as follows:lifting pressure rate1.0MPa·s-1, briquetting pressure～240MPa, dwell time has less influence on small-diameter pressed green compact, pressure release rate≤0.5MPa·s-1, length diameter ratio8.00. Based on the model analysis on the briquetting pressure and length diameter ratio, the results show that the bulk density of pressed compact is positively correlated with briquetting pressure. The empirical Equation between bulk density of pressed compac and briquetting pressure is as follows:ph=bpα, a=0.127and6=1.70. The empirical Equation between mean bulk density of pressed compac and length diameter ratio is as follows: ph=q(1+x)n, the p=-0.052and q=3.722.(3) The CH3CH2OH+PVP as novel grinding aid, dispersant agent, filmogen and binders is investigated. The results show that the disperstiveness of Cu in the NiFe2O4powder is improved and powder particle size is much smaller with increasing PVP and grinding time based on XRD, SEM and EDS characterization. The the disperstiveness of Cu in the NiFe2O4powder is great and grinded powder particle size is the smallest when the PVP=2%and grinding time=24h, and the NiFe2O4-NiO-Cu-Ni powder particle size is43.7nm. The high disperstiveness NiFe2O4-NiO-Cu-Ni nano-powder are prepared by mill grinding at first time.(4) The wetting angles of Cu-Ni/NiFe2O4-NiO are measured about NiFe2O4-NiO-Cu-Ni inert anodes by different preparation methods at first time. The wetting mechanism is discussed. The results show that the wetting angles of Cu-Ni/NiFe2O4-NiO is116.7°about NiFe2O4-NiO-Cu-Ni inert anodes by common preparation methods, and the dihedral angle of Cu-Ni/NiFe2O4-NiO is124.6°. The wetting angles of Cu-Ni/NiFe2O4-NiO is44.3°about NiFe2O4-NiO-Cu-Ni inert anodes by the novel preparation methods which NiFe2O4-NiO-Cu-Ni nano-powder is raw material and CH3CH2OH+PVP as novel grinding aid, dispersant agent, filmogen and binders. And the dihedral angle of Cu-Ni/NiFe2O4-NiO is32.7～72.9°. The wetting angles of Cu-Ni/NiFe2O4-NiO is0°when the Ti-doped in NiFe2O4-NiO-Cu-Ni inert anodes by the annovel preparation methods which NiFe2O4-NiO-Cu-Ni nano-powder is raw material and CH3CH2OH+PVP as novel grinding aid, dispersant agent, filmogen and binders. And the dihedral angle of Cu-Ni/NiFe2O4-NiO is0°.The problem of Cu-Ni/NiFe2O4-NiO wetting is fixed at first time.(5) The research results show that NiFe2O4-NiO-Cu-Ni inert anode can be obtained by sintering with Ar atmospheres. Six preparation methods for NiFe2O4-NiO-Cu-Ni inert anode preparation are studied. By analysis and comparison, it is the best manufacturing route that CH3CH2OH+PVP is novel grinding aid, dispersant agent, filmogen and binders planetary mill grinding, Ti-doped, cold CIP and sintering technology.(6) The research results show that the best sintering temperature is900℃. The small amount of Cu(Ti) solid solution and Cu4Ti alloy is formed by Ti-doped in NiFe2O4-NiO-Cu-Ni inert anode. And the nterfacial reaction wetting may be formed on the grain boundary due to reactive metal Ti-doped. And this makes the sprawl of Cu-Ni/NiFe2O4-NiO, acceleration of sintering, refine the grain and second phase particles, improvement of cermet inert anode density. The resistances to thermal shock is improved to185.71%and static corrosion is smaller than2.046mm·y-1by Ti-doped in NiFe2O4-NiO-Cu-Ni inert anode. Research result shows that the static corrosion decreases with the Ti-doped increases in NiFe2O4-NiO-Cu-Ni inert anode. The best Ti-doped amount is about1%in NiFe2O4-NiO-Cu-Ni inert anode.更多还原