先进陶瓷材料概论(英文)第二章.ppt

A quick review of the last class,Definition,Classification,Branch,Vocabulary,1. Try to get a Reference book (hardcopy or e-book) by every possible means. (For everyone),2. Watch movies or read books to find a application of Advanced Ceramics, and give a 5-mins talk in the next class using PPT. (For each group),Homework,Please share your method with all of us,Part II: Advanced Structural Ceramics,Oxide Ceramic,Non-Oxide Ceramic,Advanced Structural Ceramic,Alumina (Al2O3),Alumina is the most cost - effective and widely used structural engineering material in the family of advanced ceramics. The raw materials from which this high -performance, technical grade ceramic is produced are readily available and reasonably priced, resulting in good value for the cost in fabricated alumina shapes.,掌握词汇：raw material 原料， corundum krndm 刚玉， inertness in:tnis惰性， ceramic armor 陶瓷装甲， biomedical 生物医学的， dielectric permittivity ,pmtvti 介电常数， dielectric loss 介电损耗， integrated ntretd circuit s:kts 集成电路， spark plug 火花塞,Hence, alumina (corundum, - Al2O3) is considered the “ workhorse material ” of the structural ceramics industry. Its high hardness, abrasion resistance, and chemical inertness makes it an ideal material to perform well in a variety of aggressive environments, ranging from mining industry to chemical industry to metal manufacturing and processing, to ceramic armor and biomedical applications. Its electrically insulating nature, coupled with its moderate thermal conductivity, reasonably low dielectric permittivity, and low dielectric loss, offer a plethora of applications that include electronic substrates for integrated circuits ( IC s) and automotive spark plugs.,An overview of the important properties of alumina ceramics is provided in Table 7.1 . The wide range of values attests to the fact that alumina ceramics depend on processing parameters, including the sintering temperature, sintering atmosphere, impurity content, grain size, and other extrinsic and intrinsic factors. For example, the extremely pure and fine - grained alumina specifications used in femoral heads for hip endoprostheses demonstrate noticeably higher strengths, toughness, and hardness characteristics.,掌握词汇：processing parameter 工艺参数， sintering temperature 烧结温度， sintering atmosphere 烧结气氛， impurity content 杂质含量， grain size 晶粒尺寸，femoral head 股骨头， hip endoprostheses 髋关节假肢 ， characteristics 特性,掌握词汇： 相对密度 热膨胀系数 抗压强度 抗拉强度 抗弯强度 抗磨损强度 断裂韧性 热导率 比热 弹性模量 剪切模量 体积弹性模量 显微硬度 介电强度 介电常数 体积电阻,High - purity alumina parts and devices can be utilized in both oxidizing and reducing atmospheres to 1925 C. The mass loss in vacuum between 1700 C and 2000 C ranges from 10 5 to 10 7 g cm 2 s 1 . Alumina resists attack by all gases except for wet fluorine, and is resistant to all common reagents except for hydrofluoric and hot orthophosphoric acids. An elevated temperature corrosion occurs in the presence of alkali metal vapors, particularly at lower purity levels ( 90% Al2O3 content). The additions of either chromium oxide or manganese oxide is known to improve the material s hardness and toughness. Other additions can be made to improve the ease and consistency of metal films fired to alumina ceramics for subsequently brazed and soldered assemblies.,掌握词汇： mass loss 质量损失， fluorineflrin 氟， hydrofluoric acid 氢氟酸，orthophosphoric acid 磷酸， elevated temperature 高温， alkali metal vapors 碱金属蒸汽 ， chromium oxide 氧化铬， manganese oxide 氧化锰,Processing of Alumina The process of producing pure alumina from bauxite ore (Bayer process) has changed very little since its inception in 1893, and can be divided into three stages of extraction, precipitation, and calcination.,掌握词汇： bauxite ore 铝土矿， Bayer process 拜耳法， extraction kstrkn 萃取， precipitation prspten 沉淀， calcination ,klsnen 煅烧,The ore is washed, crushed and milled (step A) to reduce the particle size and make the minerals more available for extraction. It is then combined with the process caustic liquor and sent as slurry to a heated pressure digester for extraction (step B). Although the application of higher temperatures would, in theory, be advantageous, there are several disadvantages that include corrosion problems and the possibility of oxides other than the alumina dissolving into the caustic liquor.,Following the extraction stage, the insoluble oxide residue must be separated from the aluminum - containing liquor by a process known as settling (step C). Here, the liquor is purified by filtering before being transferred to the precipitators. The insoluble, so - called “ red mud ” from the first settling stage is thickened and washed to recover the caustic soda, which is then recycled back into the main process.,Extraction The aluminum hydroxide (gibbsite, - Al(OH) 3 ) and oxyhydroxide (boehmite, - AlOOH; diaspore - AlOOH) minerals in bauxite ore are selectively extracted from the insoluble components (mostly quartz, clay minerals, and iron and titanium oxides) by dissolving the ore in a solution of sodium hydroxide (caustic soda) according to: Al (OH)3 + OHAl (OH)4 ,掌握词汇： aluminum hydroxide 氢氧化铝 , gibbsite 三水铝矿 , oxyhydroxide 氢氧化物 , boehmite 勃姆石, diaspore 水铝石, insoluble 不溶的 , quartz 石英, sodium hydroxide 氢氧化钠 , caustic soda 苛性钠, crushed 压碎 , milled磨 , caustic liquor 腐蚀性液体, slurry 浆料 , digester 蒸炼器, purified 精炼，纯化, filtering 过滤, precipitator 沉淀器,Precipitation Crystalline pure aluminum hydroxide (gibbsite) is then precipitated from the so - called “ pregnant ” digestion liquor after cooling and diluting, and adding seed crystals (step D) according to: Al(OH)4 Al (OH)3 + OH ,This is essentially the reverse of the extraction process, except that the product s nature is carefully controlled by the plant conditions, including seeding or selective nucleation, precipitation temperature, and the cooling rate. The gibbsite crystals are then classified into size fractions and fed into a rotary or fluidized - bed calcination kiln (step E). Undersized particles are fed back into the precipitation stage.,掌握词汇： diluting 稀释的， seed crystal 晶种，size fraction 粒级， kiln 窑炉,The calcination process must be carefully controlled since it dictates（影响） the properties of the final product. A secondary process stream containing dried gibbsite can be separated to produce aluminates, zeolites, filler materials for toothpaste, fire retardants, and others (steps F H).,Calcination The gibbsite（三水铝矿） crystals are calcined (step E) to form high - purity alumina ( - Al2O3) as the precursor material for a variety of alumina ceramics according to: 2 Al (OH)3Al2O3 + 3H2O,掌握词汇： precursor priks前驱体， aluminate ljm,net 铝酸盐类 ， zeolites zi,lat 沸石， filler material 填充材料， fire retardants 阻燃材料,Structure of Alumina Polymorphs (Fundamentals of Inorganic non-metallic materials for details) - Al2O3 (corundum), The thermodynamically stable polymorph between room temperature and the melting point at 2050 C is - Al2O3 (corundum), which forms a lattice of hexagonally close -packed oxygen atoms with stacking order AB - AB , in which two - thirds of the octahedral sites are occupied by Al cations (Figure 7.2 ). Corundum crystallizes in the symmetry group 3m space group ( S.G. ) R c 3 with ditrigonal scalenohedra as the general forms and a lattice constant a = 513 pm, = 55 16 . The oxygen octahedra share edges to form six - membered rings that are linked into gibbsite - like sheets parallel (0001). The sheets are stacked into a framework structure by sharing the faces and corners of octahedra. In the hexagonal cell (a = 475 pm, c = 1298 pm), six gibbsite - like sheets are stacked in such a way that positions ABCDEF indicated in Figure 7.2 lie on one common line parallel 0001.,掌握词汇： Polymorphs 多晶型， thermodynamically 热力学的 hexagonally close packed 六方紧密堆积 octahedral sites 八面体位 Cation 阳离子 ditrigonal scalenohedra复三方偏三角面体（中级晶族单形）,Selected Applications of Alumina Ceramics Of the approximately 6 million tons of non - metallurgical alumina produced worldwide in 2006, about 50% was used to produce refractory and wear ceramics, 20% abrasives, 15% whiteware and spark plugs, and 15% other technical ceramics. Owing to its favorable mechanical, electrical and chemical properties, the typical uses of polycrystalline - alumina ceramics include: Wear pads Sealing rings and washers (e.g., for hot water mixing batteries and automotive water pumps) High - temperature electrical insulators High - voltage insulators, as in spark plugs Abrasion - and erosion - resistant pipe and elbow liners Cutting tool bits Grinding media Ballistic armor Electronic substrates Nose cones and radomes for missiles, infrared detector windows for short -range attack missiles,敢不敢讲点儿我们感兴趣的啊，老师？,Part II: Advanced Structural Ceramics,Sapphire(Al2O3+Ti, Fe),Ruby (Al2O3+Cr),Star Sapphire(Al2O3+Rutile),Spinel(MgAl2O4),掌握词汇： Sapphire sfa 蓝宝石 Ruby rubi红宝石 Rutile rtil金红石(TiO2),General Properties and Applications The important physical and mechanical properties of sintered titania are summarized in Table 7.10 . The structural applications of sintered titania are limited by its relatively poor mechanical properties, in particular its low modulus of rupture, compressive strength, and fracture toughness (Table 7.10 ). Today, the predominant application of titania is still in pigments, owing to its optical properties and stability against ultraviolet ( UV ) radiation. However, other applications have emerged including oxygen sensors, antimicrobial coatings, photocatalysts to clean waste gases and liquids, and potential photovoltaic cells with a high degree of energy conversion.,Titania (TiO2),掌握词汇： modulus of rupture 断裂模量，pigment pgmnt颜料， ultraviolet ,ltrvalt紫外线， antimicrobial ,ntmakrbl抗菌的，photocatalyst ,futuktlist光催化剂， photovoltaic,ftvltek cells 光伏电池， energy conversion 能量转换,损耗角正切,Processing of Titania Pure primary titanium dioxide does not occur naturally, but is derived by weathering from ilmenite (FeTiO3 ), perovskite (CaTiO3 ), and titanite (sphene) (CaTiSiO5 ). The most prevalent occurrence of titania is in rutile or ilmenite mineral sands mined in Canada, Australia, the USA, and South Africa. These ores are the principal raw materials used in the manufacture of titanium dioxide pigment. The first step to purify the ore is basically a refinement, using either sulfuric acid (sulfate process; Gesenhues et al ., 2003 ) or chlorine (chloride process) as an extraction agent. (Classic and Advanced Ceramics Ch7 P236 for details),掌握词汇： ilmenite lmnat钛铁矿， perovskite prvzkait钙钛矿， titanite tatn,nat榍石， sulfuric slfjrk acid 硫酸， chlorine klrin氯,Structure of Titania Titanium dioxide occurs as a mineral in three polymorphic modifications: tetragonal(四角形的) rutile ( P42 /mnm (136); tetragonal anatase（锐钛矿） ( I41 /amd (141); and orthorhombic（斜方） brookite （板钛矿）( Pbca (61). The crystal structure of the thermodynamically stable rutile consists of edge - sharing TiO6 octahedra that form straight chains parallel 001. The chains are linked by sharing corners of the octahedra. As evident from Figure 7.46 a, this configuration resembles an f.c.c. lattice. However, the close packed oxygen sheets are slightly kinked (by about 20 ) to permit only a tetragonal symmetry with a 4 2 screw axis. This causes also a distortion of the individual TiO6 octahedra. In anatase, the TiO6 octahedra share four edges to form a pseudo tetragonal framework structure, and in brookite the octahedra share three edges. Each distorted （扭曲的）octahedron is linked with three others to form zigzag chains, with each octahedron sharing one edge with an octahedron of the neighboring chain thus forming nets parallel (100) (Figure 7.46 a,b).,敢不敢再讲点儿我们感兴趣的啊，老师？,Part II: Advanced Structural Ceramics,Zirconia (ZrO2),Over the past forty years, zirconia has been developed into a highly sophisticated advanced ceramic material that is utilized in many important applications via the exploitation of its superior mechanical and unique functional properties.,The exceptional mechanical properties of zirconia are mainly based on the phenomenon of transformation toughening (this is described in detail below). The delayed martensitic transformation of the tetragonal high - temperature modification into the monoclinic low - temperature modification by adding stabilizing oxides leads to increased stress intensity factors K Ic and also R - curve behavior. Hence, appropriately stabilized zirconia has been dubbed “ ceramic steel ” (Garvie et al ., 1975 ).,掌握词汇： transformation toughening 相变增韧， martensitic transformation 马氏体相变,Transformation Toughening of Zirconia Ceramics The tetragonal monoclinic phase transformation in zirconia shows a marten