【作者】 景茂祥；

【导师】 沈湘黔；

【作者基本信息】 江苏大学 ， 材料学， 2007， 博士

【摘要】 氧化铝陶瓷因其价格低,硬度大,电绝缘性高,化学稳定性好等优点,在结构陶瓷、电子陶瓷、生物陶瓷等领域占有重要的位置。但断裂韧性较低是限制其更广泛应用的主要原因。陶瓷材料的脆性主要是由物质的化学键合性质和它的显微结构所决定,因此,优化材料整体显微结构均匀性及物相间晶界的化学键合状态是解决氧化铝陶瓷脆性的根本。同时,功能化已成为材料技术发展的新趋势,结合材料的功能性和结构性,开发新型功能化氧化铝陶瓷基复合材料已成为新材料领域的热点之一。本论文基于微球结构设计,首先采用非均相沉淀包裹—热还原工艺制备了纳米铁磁性金属（Fe、Co、Ni及其合金）包裹氧化铝复合微球粉体,然后以氧化铝/镍复合微球为原料,采用热压烧结法制备了氧化铝/镍复合金属陶瓷;通过采用不同原料及热压工艺对氧化铝/镍复合材料微观结构及界面结合状态进行了设计,并在此基础上,通过包裹掺杂钇稳定氧化锆制备了氧化锆/镍/氧化铝多相复合陶瓷。利用扫描电子显微镜（SEM）、能量发散谱仪（EDS）、X-射线衍射仪（XRD）对复合微球前驱体、热还原产物、热压烧结产物的形貌、宏观结构、成分进行了表征;采用透射电子显微镜（TEM）及电子能量损失谱仪（EELS）对氧化铝/镍复合金属陶瓷的微观结构及界面化学进行了表征和分析;利用阿基米德法测量了金属陶瓷的密度,并分别用三点弯曲法和单边切口横梁法对材料的抗弯强度和断裂韧性进行了评估;借助LCR自动测量仪和振动样品磁强计对复合金属陶瓷的电磁性能进行了检测。本论文取得的主要成果及创新点有:（1）开发了非均相沉淀包裹—热还原制备壳/核结构纳米金属/氧化铝微球新工艺,并利用这一工艺制备了一系列纳米金属（Fe、Co、Ni及其合金）包裹氧化铝复合微球。系统研究了非均相沉淀包裹过程中包裹颗粒浓度、加料速度、反应时间及表面活性剂等因素的影响。在优化条件（包裹颗粒浓度10～15g/L,加料速度4～SmL/min,反应时间1～2hr,表面活性剂5mL/L,搅拌速度1000r/min）下,获得了理想的纳米金属包裹氧化铝复合微球粉体前驱体,前驱体在氢气还原下容易转变成纳米金属/氧化铝复合微球。这一工艺可实现金属含量及组成、包裹层厚度、分布状态、金属颗粒大小可控,磁性能良好。（2）基于氧化铝/镍复合材料微观结构设计,系统研究了分别采用金属镍包裹氧化铝微球、氧化铝包裹金属镍微球及氧化铝/镍共沉淀微球来制备复合金属陶瓷,较好地调控了金属镍的分布方式,分别形成晶界型、晶内型以及晶内/晶界混合型结构。采用球形包裹结构复合粉体原料,大大改善了复合材料的结构均匀性。（3）在所制备的氧化铝/镍复合材料中,氧化铝与镍粒子界面通过非反应性成键形成-Ni-Ni-Al-O-Al强的界面键合,改善了材料界面结合状态;同时,金属镍粒子的引入大大细化了氧化铝晶粒,使氧化铝主晶界得到强化,断裂模式发生改变,达到了氧化铝陶瓷的韧化目的,抗弯强度可提高到600MPa左右,断裂韧性则可提高到6～8MPa·m^1/2。同时氧化铝/镍复合材料保持了较高的饱和磁化强度、矫顽力和介电常数;（4）系统地研究了氧化锆与镍共掺杂行为,发现氧化铝复合陶瓷与单相Al₂O₃相比,抗弯强度可提高28%,断裂韧性可提高141%,但复合材料的韧性增强并未高于Al₂O₃/Ni和Al₂O₃/ZrO₂两种复合材料韧性增强之和,即未出现韧性叠加效应,主要是ZrO₂的部分相变增韧效应被邻近大金属Ni粒子吸收掉。Ni和ZrO₂的引入增强了空间电荷的极化,使复合材料具有较高的介电常数。本论文开发的非均相沉淀包裹—热还原制备纳米金属包裹氧化铝复合微球粉体工艺,工艺过程简单,原料来源广泛,容易实现规模化生产;复合微球粒子流动性好,填充密度高,集合了纳米磁性金属与陶瓷各自的特点,比表面积大、表面活性高,分散性好,并具有核/壳结构协同特性,可成为良好的电磁波吸收剂及催化剂;采用这种复合微球粉体烧结制备结构陶瓷可以从根本上解决金属与陶瓷的弱结合、化学成分分布不均等问题,在刀具材料、铝电解惰性阳极、陶瓷—金属封接等领域具有广阔的潜在应用。更多还原

【Abstract】 Alumina has been and will continue to be widely used in structural,electronic, optical and biomedical applications due to its outstanding properties of low cost,high rigidity,high electrical resistance and chemical stability.However,the brittleness is a major limitation of alumina in many applications.It is well known that the brittleness of alumina is resulted from the chemical bonding characteristics among components and the microstructure,so that optimizing the microstructure and state of chemical bonds among components are keys to reduce the brittleness of alumina.Moreover,with the functionality has been a general tendency for materials technology,combining the functional and structural characteristics of ceramics and developing novel alumina-based composites have been a hotspot.Based on the structural design of microspheres,nano-ferromagnetic metals （Fe,Co,Ni and alloys）-coated alumina microspheres were prepared by heterogeneous precipitation,followed thermal-reduction process.Then,alumina-based Ni composite cermets were prepared by hot-press sintering alumina/Ni composite microspheres.The microstructure and interfacial bonding states for alumina/Ni composite cermets were tailored via adopting different sintering raw materials and hot-press sintering processes. Furthermore,alumina-based Ni and zirconia composites were prepared by coating Ni and yttrium-stablized zirconia successively on alumina microspheres.The morphologies, microstructure and composition or crystalline phases of the composite microspherical precursors,thermal-reduction products and resultant hot-press sintering cermets were characterized by scanning electron microscope（SEM）,energy dispersive spectroscope （EDS） and X-ray diffraction（XRD）,respectively.The microstructure and interfacial chemistry of alumina/Ni cermets were analyzed by transmission electron microscope（TEM） and electron energy loss spectroscopy（EELS）.The Archimedes’ method was used to measure the density of alumina/Ni cermets.The flexural strength and fracture toughness were estimated via the three-point bending and single-edge-notched beam methods respectively.And by means of the LCR automative meter and vibration sample magnetmeter（VSM） the electro-and magnetic properties of alumina/metal composites were investigated.The main results and innovations obtained in this study include:（1） A novel preparative route for core-shell structural nanometal-coated alumina microspheres has been developed and a series of nano-metals（Fe、Co、Ni and alloys）-coated alumina powders were successfully prepared by this novel heterogeneous precipitation coating-thermalreduction process.These spherical powders were characterized with controllable properties,such as metal content and constitutes,coating thickness,metal distributing state and size of metal particles,and excellent magnetic performance.The aqueous heterogeneous precipitation process were mainly influenced by the concentration of coated particles,adding raw materials rate,reaction time and surface active reagent,et al.At the optimized precipitation parameters,i.e.,10～15g/L of the concentration of alumina micropowders,4～5mL/min of the rate of adding reactants, 5mL/L of the surface active reagent,and 1～2 hr of the reaction time,the mechanical stirring speed of 1000r/min,the designed precursors of Ni-coated alumina microspheres were fabricated.Then Ni-coated alumina powders were prepared after the hydrogen reduction of the precursors.（2）Based on the microstructural design concept,three kinds of composite cermets with intergranular structure,intragranular structure or mixture of these two named according to the Ni particle location in the alumina matrix were prepared by hot-press sintering Ni-coated alumina microspheres,alumina-coated Ni microspheres and alumina/Ni coprecipitates respectively.These processes could adjust the distribution manners of Ni particles,and made the microstructural design for the alumina/Ni composites come true.（3）By adopting metal-coated powders,the structural uniformity of composite cermets were improved,and the interfacial bonding state between Ni and alumina was also amended by the formed strong bonds of -Ni-Ni-Al-O-Al at some hot-press sintering conditions.The introduction of Ni particles was also favorable to fine grain sizes of alumina.The toughening alumina was enhanced by strengthening matrix grain boundaries and changing fracture mode of alumina and a maximum mean values of about 600MPa for fracture strength and 6～8MPa·m^1/2 for fracture toughness were obtained.And these cermets exhibited high saturation magnetism,coercive force and relative high dielectric constants.（4）Comparing with monolithic alumina,the inclusions of Ni and ZrO₂ could increase the fracture strength of alumina by 28%and fracture toughness by 141%. However,the toughness enhancement of Al₂O₃/（ZrO₂+Ni） composites was not higher than the sum of the toughness enhancement of Al₂O₃/ZrO₂ and of Al₂O₃/Ni composites, because the toughness by phase transformation of ZrO₂ was absorbed by large Ni particles neighboring to ZrO₂ phase.And higher dielectric constants of composites were due to the intensification of space charge polarization by means of the inclusion of Ni and ZrO₂.This heterogeneous precipitation coating—thermal-reduction process for preparation of nanometal-coated alumina microspheres is featured with simple processing,rich raw materials resource,and easy scale-up production.These composite microspheres with excellent fluidity,high filling density,high specific surface areas and surface activeness,combined the properties of nanometals with alumina matrix and possessed the cooperative features of metal shell and alumina core,are promising excellent electromagnetic wave absorbers and advanced catalysts in hydrogen-production industry.Furthermore,by adopting these kinds of microspheres as sintering raw materials,many technical issues such as weak interfacial combinations between metal and alumina matrix,poor uniformity in chemical components etc.,will be resolved,and these materials have great potential uses in the fields of ceramic tool materials,large inert anode materials for aluminium electrolysis,and ceramic-metal seals,etc.更多还原