【作者】 王菊平；

【导师】 李青；

【作者基本信息】 西南大学 ， 无机化学， 2008， 硕士

【摘要】 第三代稀土钕铁硼（NdFeB）永磁材料由于具有高的饱和磁通量、矫顽力和磁能积（BH）_max、良好的机械加工特性和相对低廉的价格,在许多领域得到广泛的应用。但NdFeB永磁材料的化学稳定性差,在使用环境中容易发生氧化,而且在湿热条件下会发生严重的电化学腐蚀,大大影响了其应用范围。NdFeB永磁材料的耐蚀性是国内外关注的焦点,因为它直接关系到磁体的使用问题,因此对NdFeB永磁材料的表面防护技术研究具有十分重要的意义。本文在综述了近年来烧结型NdFeB永磁材料腐蚀机理和防护处理研究的基础上,通过溶胶-凝胶涂层、磷化膜层、纳米复合电镀n-TiO₂/Ni层,以及复合膜层对烧结型NdFeB永磁材料进行表面防护研究。以无机镁盐为前驱物,无水乙醇为溶剂,添加适量的表面活性剂,采用溶胶-凝胶法在烧结型NdFeB永磁材料表面首次成功制备了MgO膜层。讨论了不同工艺条件对溶胶-凝胶稳定性的影响,采用XRD、DSC-TGA及静态腐蚀测试表征了膜层的结构和性能,结果表明:（1）前驱物镁离子浓度在0.03～0.15mol·L^-1范围内,无水乙醇与表面活性剂（火棉胶）体积比=6:4～8:2时,均能制备出透明、稳定的溶胶;（2）通过最佳热处理工艺在烧结型NdFeB永磁材料表面形成了致密、耐蚀的MgO膜层,且MgO的晶粒取向在（200）和（220）晶面上,在450℃热处理后的MgO平均晶粒尺寸为23.43nm。研究在烧结型NdFeB永磁材料表面形成无毒、无污染的磷化膜之方法来解决其表面腐蚀问题。讨论了前处理工艺、磷化液组成、磷化成膜温度、磷化成膜时间等因素对磷化膜制备的影响。采用金相显微镜（OM）、SEM、动电位极化曲线测试和静态腐蚀测试表征了磷化膜的成膜性及耐蚀性能,确定了最佳成膜工艺参数。结果表明:采用新研制的磷化配方及工艺在烧结型NdFeB永磁材料表面能形成致密的磷化膜层,该磷化膜层可有效地对烧结型NdFeB永磁材料进行腐蚀保护。以普通电镀Ni液为基液,添加不同晶形纳米TiO₂微粒,在烧结型NdFeB永磁材料表面实施纳米复合电镀n-TiO₂/Ni。采用XRD表征纳米复合电镀n-TiO₂/Ni层的结构,采用动电位极化曲线测试、静态腐蚀测试、孔隙率测试和结合力检测表征了纳米复合电镀n-TiO₂/Ni层的性能。XRD分析表明,纳米TiO₂微粒的掺杂,并未改变基质金属Ni镀层的结构,且复合镀层中TiO₂和Ni在特定的角度分别出现其衍射特征峰;通过耐蚀性检测、结合力测试和孔隙率测试,表明复合电镀n-TiO₂/Ni层具有优良的耐蚀性保护性能。且该镀层与烧结型NdFeB永磁材料结合力强,孔隙率低。为了得到更好的腐蚀保护层,在烧结型NdFeB永磁材料表面实施复合膜层,先应用磷化工艺在烧结NdFeB表面制备磷化膜,将其作中间过渡膜层,再应用电沉积法,在磷化膜层表面制备n-TiO₂/Ni复合镀层。采用XRD测试、XPS测试、动电位极化曲线测试、静态腐蚀测试、孔隙率测试和结合力测试表征了复合膜层的性能。研究结果表明,该复合膜层能大幅提高烧结型NdFeB永磁材料表面的耐蚀性能。更多还原

【Abstract】 NdFeB permanent magnetic material as the third-era permanent magnet is widely used in many industries because of its outstanding properties, such as high saturation magnetization, coercive force, magnetic energy product （BH）_max, machinability, and comparatively low price. Unfortunately, it is prone to oxidation in common environments, especially in damp heat atmosphere, severe electrochemical corrosion will occur. So poor corrosion resistance of NdFeB permanent magnetic material is the main obstacle to its widely applications. As relation to the life-span of the magnetic material, the corrosion resistance of NdFeB permanent magnetic material was the focus of the world. Thus it is of great significance to investigate the surface modification technology of NdFeB permanent magnetic material.In this thesis, different surface modification technologies of sintered NdFeB permanent magnetic material were investigated, including sol-gel coating, phosphating coating, n-TiO₂/Ni nano-composite electroplating coating, based on the corrosion mechanism and anticorrosion treatment research of the papers in the recent years.The MgO thin films were first successfully prepared by sol-gel method taken Mg（NO₃）₂·6H₂O as precursor, anhydrous enthanol as solvent and proper surfactant. The different technique conditions on the sol stability were investigated and the surface properties were analyzed by DSC-TGA, XRD, immersion test. The results indicated that （1） transparent steady sol was achieved by keeping the concentration of Mg～（2+） at a range of 0.03～0.15mol·L^-1 and the volume ratio of solvent and surfactant at 6:4～8:2; （2） density, anti-corrosion MgO thin films were obtained on sintered NdFeB permanent magnetic material surface after optimal heat treatment technique, and the crystal face structure of the thin film will be transformed to main （200） and （220）, the average grain size of crystalline MgO is 23.43nm after 450℃heat treatment.The nonpoisonous and friendly phosphating conversion coatings have been successfully prepared on sintered NdFeB permanent magnet material to improve its corrosion resistance. The effect factors on the preparation such as the pretreatment technique, the components and concentration of the solution, temperature and duration of the coatings formation were investigated. The preparation and anticorrosion properties of the conversion coatings on NdFeB surface were analysed by OM, SEM, potentiodynamic polarisation curve test, immersion test. And the optimum technological parameters were settled. The results show that the phosphating conversion coatings prepared under optimum technological parameters, were much more compact and anti-corrosive.n-TiO₂/Ni composite coatings were prepared on sintered NdFeB permanent magnet by composite electroplating method to improve anticorrosion property of the substrate. n-TiO₂/Ni composite coatings were electrodeposited from a traditional plating Ni bath containing nano-TiO₂ particles of different phase. The properties of n-TiO₂/Ni composite coatings were analysed by XRD, potentiodynamic polarization curve test, immersing test, porosity test and adhesion strength test. The results show that the structure of the matrix nickel was not changed with adding of nano-TiO₂ particles. XRD patterns of the gradient deposit showed that the Ni and TiO₂ particle diffraction peaks at their own given angles respectively, independent of each other. n-TiO₂/Ni composite coatings were no porosity, with a good adhesion to the NdFeB permanent magnet. The anticorrosionproperties of the n-TiO₂/Ni composite coatings were improved greatly.The composite films were prepared on sintered NdFeB permanent magnet, in order to obtain most effective protective coatings. Substrates were immersed in phosphating solution to form phosphating coatings before n-TiO₂/Ni composite electroplating. The properties of coatings were analysed by XRD, XPS, potentiodynamic polarization curve test, immersion test, porosity test and adhesion strength test. The anticorrosion properties of the composite films were improved greatly.更多还原