【作者】 郑环宇；

【导师】 安茂忠；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2007， 博士

【摘要】 本文将纳米级α-Al₂O₃颗粒与Zn、Ni共沉积,制备兼具纳米Al₂O₃颗粒与Zn-Ni合金优异性能的高耐蚀性纳米复合镀层,对进一步拓宽Zn-Ni合金基镀层的应用领域具有重要的现实意义。利用静态浸泡试验、电化学测试考察镀层的耐蚀性能,优化复合镀工艺。研究了超声对Zn-Ni合金电沉积的影响,并利用离子色谱分析纳米氧化铝颗粒在镀液中对Zn²⁺、Ni²⁺离子的吸附情况,进而研究超声波作用下复合电沉积的机理。利用XRD、SEM、XPS对镀层的结构、镀层的腐蚀过程和腐蚀产物进行分析,研究了纳米复合镀层及其钝化膜的耐蚀机理。对纳米氧化铝颗粒分散剂的研究表明,使用阿拉伯胶和阳离子表面活性剂CTAB（十六烷基三甲基溴化铵）协同作用可有效促进镀层中纳米氧化铝的均匀分散,并促进纳米氧化铝与Zn、Ni的共沉积,提高复合量。通过对电镀过程中纳米Al₂O₃分散方式的进一步研究,找到了一种有效的分散纳米氧化铝颗粒的方法,即内置式超声振荡。利用超声的空化作用可使镀液中的纳米Al₂O₃呈单分散状态,并且内置式超声波发生器发出的超声波在溶液中产生超声流,使纳米颗粒向阴极的运动速率加快,显著增大镀层中纳米氧化铝的复合量。因此在无分散剂作用下直接使用内置式超声即可制备单分散、纳米Al₂O₃含量高的复合镀层。该方法有效的解决了纳米复合镀液中纳米颗粒团聚这一制约纳米颗粒优异性能发挥的难题,并避免了使用分散剂可能给镀层耐蚀性能提高带来的负面影响。对内置式超声波作用下（Zn-Ni）-Al₂O₃纳米复合电沉积机理的研究表明,超声波通过增大液相传质影响基质金属Zn-Ni合金的电沉积,使镀层Ni含量下降。而纳米Al₂O₃对Ni²⁺离子的吸附强于对Zn²⁺离子的吸附,使复合镀层Ni含量增加。纳米Al₂O₃与基质金属的共沉积过程是在超声场和电场共同作用下完成的,吸附着Zn²⁺和Ni²⁺离子的纳米Al₂O₃颗粒运动到阴极表面,在纳米Al₂O₃颗粒上吸附的Zn²⁺和Ni²⁺离子直接还原,形成Zn-Ni合金,同时把Al₂O₃颗粒包裹入合金镀层中,因此基质金属镀层与纳米氧化铝颗粒结合紧密,这对镀层耐蚀性能的提高至关重要。通过对纳米（Zn-Ni）-Al₂O₃复合镀层腐蚀过程及腐蚀产物的研究表明,纳米（Zn-Ni）-Al₂O₃复合电镀层在腐蚀介质中表现出优异的耐蚀性能,主要是由于腐蚀过程中均匀分布于Zn-Ni基质金属中的纳米Al₂O₃微粒把腐蚀介质和晶粒隔开,有效地减少了基质金属在腐蚀溶液中的暴露面积,并且纳米Al₂O₃为不导电的纳米颗粒,基质金属镀层发生腐蚀时纳米颗粒可以分散腐蚀电流,从而有效抑制腐蚀介质对镀层的腐蚀。基质金属为γ相金属间化合物,腐蚀后生成ZnCl₂·4Zn（OH）₂,而不同于Zn镀层的腐蚀产物ZnO,该腐蚀产物不易溶解,它将纳米Al₂O₃和Ni包覆起来形成阻挡层,而腐蚀产物中富集的Ni和纳米Al₂O₃对腐蚀的抑制作用有效地提高了镀层的耐蚀性。对复合镀层钝化膜性能研究表明,Al₂O₃含量为3.7mass%的（Zn-Ni）-Al₂O₃复合镀层的钝化膜比Zn-Ni合金镀层的钝化膜更致密,并且纳米Al₂O₃被钝化膜完全包覆,该镀层在5mass%NaCl、pH3.5的醋酸溶液中出白锈和出红锈的时间分别为18.5h和230h,比Zn-Ni合金钝化膜的耐蚀性有大幅提高。研究表明,（Zn-Ni）-Al₂O₃复合镀层钝化膜具有较高耐蚀性的原因是在钝化膜和复合镀层之间存在镍和纳米Al₂O₃的富集层,它起到隔离腐蚀介质与复合镀层的作用,从而抑制复合镀层腐蚀反应的进行,提高纳米复合镀层的耐蚀性。更多还原

【Abstract】 The （Zn-Ni）-Al₂O₃ nano composite coatings with high anticorrosionperformance were fabricated using electrodeposition method with the aid ofultrasound, aiming to extend the application field of Zn-Ni alloy. Theelectrodeposition parameters were optimized by testing anticorrosion propertieswith immersion test and electrochemical technique. The effect of ultrasonicvibration on the Zn-Ni alloy deposition was investigated and the absorbance ofZn²⁺and Ni²⁺ on nano alumina particles was analyzed by ICP （inductivelycoupled plasma）. Furthermore, the mechanism of composite electrodepositionunder ultrasonic vibration was studied. The anticorrosion behaviors andmechanisms of the nano composite coating and its passivated film were exploredby analyzing the structure, corrosion process and corrosion products of thecoating byusing XRD, SEM and XPS.The studies on nano alumina dispersants demonstrate that the synergeticeffect of Arabic gum and CTAB （Hexadecyl trimethyl ammonium Bromide）promotes the codeposition and uniform dispersion of nano alumina particles inthe coating.By comparing the different dispersion methods a very effective way,inserted ultrasonic vibration, has been established to de-agglomerate nanoalumina particles in electrolyte, which can promote the incorporation of nanoalumina particles in the coating. The mono-dispersion and high content of nanoalumina particles in the coating should be attributed to the action of cavitationsand ultrasonic streaming generated by the ultrasonic vibration. The cavitationscaused by the collapse of cavitation bubbles de-agglomerate the nano particles,while the presence of ultrasonic streaming promotes the movement of the nanoparticles toward the cathode. Fabrication of nano composite coatings by usingultrasonic agitation during electrodeposition process resolves the agglomerationproblem of nano alumina particles which restricts super performance of nanoparticles, andavoids the adverse effects of dispersants on coating properties.The studies on electrodeposition mechanism of （Zn-Ni）-Al₂O₃ coating underultrasonic conditions indicate that the ultrasound decreases Ni content in thecoating by increasing the mass transport, and the codeposition of nano alumina increases the Ni content due to the more absorbance content of Ni²⁺ on nanoalumina particles than Zn²⁺. The incorporation of nano alumina particles intomatrix results from the synergetic effect of ultrasonic and electric field. Nanoparticles accompanying absorbed Ni²⁺ and Zn²⁺ moved to the cathode vicinity,and then the absorbed Ni²⁺ and Zn²⁺ are induced directly on the particle surface,which lead to the imbedding of the nano particles. This imbedding of nanoalumina particles into matrix is very tight, which would be beneficial to theanticorrosion property.The analysis of the corrosion process and corrosion products demonstratesthat the presence of compact and uniformly dispersed nano alumina particlesblocks off the corrosion medium and coating, decreases the contact area,disperses the corrosion current because of the existence of insulative nanoalumina particles, and therefore substantially inhibits the corrosion of Zn-Ni-Al₂O₃ composite coating. The matrix is composed ofγphase intermetalliccompound, and its corrosion products, different from the corrosion products ofZn coating can form a compact ZnCl₂·4Zn（OH）₂ layer. This product with nanoalumina particles and Ni formsan isolative layer. The corrosion inhibition effectsof the enrichedNi and nano alumina particles increase the anticorrosion propertysignificantly.The performance studies of thechromate conversion coating on the（Zn-Ni）-Al₂O₃ composite coating indicate that the passivated film on the compositecoating containing 3.7mass%weight content nano alumina is more compact thanthat on Zn-Ni alloy, and the nano alumina particles are completely covered. Theemergence time of white rust and red rust in 5mass%NaCl、pH3.5 acetic acidsolution are 18.5h and 230h respectively, and the anticorrosion properties areincreased significantly compared with the conversion coating on Zn-Ni alloy.The reason for super anticorrosion property of the composite coating afterchromate passivation is the presence of enriched Ni and nano alumina layerbetween the conversion film and composite coating, which isolates the corrosionmedium and composite coating, andinhibit the corrosion reaction.更多还原