【作者】 蒙延双；

【导师】 王达健；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2004， 硕士

【摘要】 在陶瓷涂层制备工艺中，溶胶-凝胶法可在低温下制备纯度高、成分控制精确的涂层而得到广泛研究。与其他方法相比，溶胶-凝胶法还具有易操作、成本低、可制备复杂形状涂层等优点。但溶胶-凝胶法的应用受到两大限制：1) 制备胶体多用醇盐或无机盐水解。以醇盐作为前驱体致使工艺成本太高；而用无机盐作为前驱体时，所得胶体含较多的杂质离子，要得到纯度很高的胶体涂层须先去除杂质离子，使工艺变得复杂，胶体成本高，且不宜实现大规模生产。2) 溶胶-凝胶法制备涂层时，因干燥过程中的龟裂问题，只能制备薄膜(<1μm)。因此，如何防止厚膜龟裂和改善其附着力是该领域的关键科学技术问题。本文针对上述溶胶-凝胶法涂层制备工艺的缺点，用工业薄水铝石制备稳定活性胶体，通过外加微米级陶瓷颗粒，借助纳米级胶团的分散作用，实现复合溶胶-凝胶(CSG，composite sol-gel)厚膜陶瓷涂层(≥10μm)。用喷雾方法在不锈钢和碳电极上制备涂层；为解决涂膜与基底的附着力问题，用磷酸对涂层进行处理，研究涂层与基底间的化学键合(CB，Chemically Bonded)的机理问题；初步分析了涂层与碳电极间浸润、扩散和渗透机理。研究了工业薄水铝石制备胶体的工艺。采用工业薄水铝石粉体，用硝酸和磷酸作为胶溶酸，制备了薄水铝石胶体。研究了胶体的流变性、稳定性、溶胶时间等与胶体固含量、pH值、温度等工艺条件的关系。结果表明，用硝酸调pH所得的胶体中，pH<4时可得到稳定的胶体，pH＞4则得到悬浮体；用磷酸调pH值时得到的全部是悬浮体。用硝酸作为胶溶酸所得薄水铝石稳定胶体的流变性、稳定性随胶体固含量、温度的增加及pH值的降低而增大；溶胶时间随胶体固含量、温度的增加及pH值的降低而降低。对薄水铝石的胶溶机理进行了分析。用硝酸作为薄水铝石胶溶剂时，胶粒表面因吸附H+而呈正电性，由于NO3-中O原子的电负性高于N原子的电负性，电子在NO3-中的分布不均匀，更有利于NO3-在呈正电性的薄水铝石胶粒表面吸附，吸附后形成的双电层之间的排斥作用使颗粒相互分开，打破Al-O-Al化学键。随着酸的不断加入，酸的“渗透”作用使胶粒彼此完全分开，从而得到分散良好的薄水铝石胶体。相比之下，H3PO4不能使薄水铝石颗粒问的Al-O-Al键断裂。用电镜和红外光谱分析表征了薄水铝石胶粒的结构特点。TEM图像显示薄水铝石胶粒的粒度约10nm，各胶粒间相互紧密结合形成念珠状的长链，这些长链形昆明理工人学硕士学位论文摘要成空间三维网状结构。傅立叶红外光谱(FTIR)分析结果表明胶体体系中的一N氏-除了与AI形成A卜NO3键外，还有部分一NO3一以游离态NO3一存在与胶体体系中。 采用复合溶胶一凝胶技术是解决涂层龟裂问题的重要技术途径。即在纳米颗粒的薄水铝石胶体中引入微米级TIB:陶瓷颗粒，均匀分散，组成纳米/微米(O一3)复合体系，热处理过程中陶瓷颗粒与胶体层间水的置换作用，在一定程度上抑制了厚膜开裂。对薄水铝石胶体/TIB:颗粒组成的陶瓷涂料的流变性、稳定性进行了实验测定。认为TIBZ颗粒与薄水铝石胶体间的相互作用包括化学吸附、化学反应和渗透作用。 采用喷雾方法在不锈钢基底上进行涂膜，然后用磷酸对涂层进行表面处理，最后进行热处理。涂层附着力检测结果表明，磷酸能明显提高涂层与基底间的结合力。涂层SEM结果表明，磷酸具有对涂层表面进行封孔和实现涂层与基底间化学键合两种作用。涂层电性能结果表明涂层的导电性能明显优于基底，但当磷酸浓度太高后，反而使涂层电阻率增加。作为特别的应用实例，采用同样的喷雾方法，对铝电解碳阳极试样进行了TIBZ涂层处理，涂层与基底间的结合机理与化学键合不同。 本文系统研究了薄水铝石胶体和TIBZ浆料的稳定性及其稳定机理，对涂层与基底间的键合机理进行了初步研究。研究结果对发展陶瓷清洁湿法成型技术的基础问题具有学术价值，对包括铝工业电极材料在内的高温陶瓷涂层和块体材料的制备技术具有应用价值。更多还原

【Abstract】 Among the fabrication techniques of ceramic coatings, sol-gel (SG) method has been the subject of extensive research studies over many decades worldwide as it provides a high-purity, low temperature synthesis and, especially a precise composition control. Meanwhile, the sol-gel method can overcome lots of the disadvantages of conventional techniques because it is simple, cost-effective and allows coating of complex geometry. The sol-gel method, however, is limited by two main disadvantages: 1) The precursors used in sol making are always aluminium alkoxides or aluminium salts. The aluminium alkoxides are expensive. The aluminium salts-derived sols contain a large quantity of impurity ions. Removing these impurity ions also increases the cost of the whole sol-gel processing. 2) SG technology often fails if the film is thicker than around 1um owing to the damaging shrinkage strains during drying process. Therefore, it is critical to prevent the cracking in the coatings and to improve the adhesivity between the coating and substrate.In our work, the problems as mentioned above are approached by usingcommercial boehmite powder as precursor and applying composite sol-gel (CSG) technology. The well-dispersed slurry used for coating (>10um) is made by adding micro-TiB2 particles into stabilized, active boehmite sols. The adhesivity between coating and metallic substrate is enhanced through sealing treatment with phosphoric acid, and the mechanism of chemical bonding involved is studied. Besides, the mechanisms of sol-drived TiB2 coating on porous carbon anode are preliminarily examined.The boehmite sol is made of commercial boehmite powder, using HNO3 and H3P04 as peptizing acids. The influences of solid concentration, pH value, temperature and other parameters on the viscosity, stability and soling time of the boehmite sols, are investigated. The experimental results show that a stable boehmite sol can be successfully made only by adding HNO3 until pH<4. On the contrary, only suspensions could be obtained under every pH values when H3P04 is used as peptizing agent. The viscosity and stability of the HN03-peptized boehmite sol increase with the decrease of the pH value and the increase of solid concentration and temperature.The peptization mechanisms of the boehmite powders are experimentally studied. In the case of HN03, since the electronegativity of 0 is higher than that of N, the electron density is not uniformly distributed over the nitrate ions. As a result, the - N(V ions are firstly adsorbed on the colloidal particles surface with positive charges, and form the adsorption layer and the diffusion layer. The repulsive force make the colloidal particles separated from one another. In comparison, H3PO4 is unlikely to break the A1-O-A1 bonds among the boehmite particles.TEM and FTIR technology are used to characterize the structures of the boehmite colloidal particles. TEM images show that the boehmite colloidal particles are of around lOnm and form a moniliform structure. Fourier transform infrared (FTIR) analysis reveals that some of N03- ions has reacted with A100H, forming A1-N03 bond, while the rest exists in the forms of dissociated ions.One important way to prevent the cracking in coating is through CSG technology. Namely, a nano-micro (0-3) slurry is obtained by dispersingmicro TiB2 particles into nano-scaled boehmite particulate sol. The displacement of intercalated water in sols by the added ceramic particles prevents the cracks in the coating. The viscosity and stability of the slurry were experimentally measured. The interactions between TiB2 particles and the surrounding colloid are supposed to be chemical adsorption, chemical reaction and penetration.The stainless steel substrates were coated by spraying using conventional pressurized air spray gun, then sealed with phosphoric acid solution, and finally heat treated. The adhesive strength between coating and substrate is obviously improved by in-situ chemical reactions. SEM results of sealed coatings show that the phosphoric acid play更多还原