Ceramic Materials Structures and Properties Ceramic Materials Inorganic

Ceramic Materials — Structures and Properties

Ceramic Materials 陶瓷材料 • Inorganic materials 無機材料 • Nonmetallic materials 非金屬材料 • Most ceramics are compounds between metallic and nonmetallic elements • Composed of at least two elements, and often more • Atomic bonding in ceramics ranges from purely ionic to totally covalent

Material Ca. F 2 Mg. O Na. Cl Al 2 O 3 Si. O 2 Si 3 N 4 Zn. S Si. C Ionic Character 89% 73% 67% 63% 51% 30% 18% 12%

Electronegativity 電負度、陰電性

Stable and unstable cation-anion coordination configuration - + - stable - + - - stable + - unstable Cations are ordinarily smaller than anions cation 陽離子 anion 陰離子

Coordination Number 配位數 2 3 4 6 8 Cation-Anion Radius Ration r. C/r. A <0. 155 -0. 225 -0. 414 -0. 732 -1

Crystal Structures • AX Type – Rock Salt Structure 岩鹽結構 – Cesium Chloride Structure 氯化銫結構 – Zinc Blende (Sphalerite) Structure 閃鋅礦結 構 • AX 2 Type – Fluorite Structure 螢石結構、氟石結構 • ABX 3 Type – Perovskite Structure 鈣鈦礦結構 • AB 2 X 4 Type – Spinel Structure 尖晶石結構

Rock Salt Structure 岩鹽結構 • Na. Cl, Mg. O, Mn. S, Li. F, Fe. O r. Na+ = 0. 102 nm r. Cl = 0. 181 nm r. Na+/r. Cl = 0. 564

Cesium Chloride Structure 氯化銫結構 • Cs. Cl r. Cs+ = 0. 170 nm r. Cl = 0. 181 nm r. Cs+/r. Cl = 0. 939

Zinc Blende Structure 閃鋅礦結構 • Zn. S, Zn. Te, Si. C, Zn. O r. Zn 2+ = 0. 074 nm r. O 2 = 0. 140 nm r. Zn+2/r. O 2 = 0. 529

Fluorite Structure 螢石結構 • Ca. F 2, Zr. O 2, UO 2, Pu. O 2, Th. O 2 r. Ca 2+ = 0. 100 nm r. F = 0. 133 nm r. Ca+2/r. F = 0. 8

Perovskite Structure 鈣鈦礦結構 • Ba. Ti. O 3, Sr. Zr. O 3, Sr. Sn. O 3

Interstitial position 填隙位置、間隙位置 • Tetrahedral position 四面體位置 • Octahedral position 八面體位置 close-packed structure 最密堆積結構、緊密堆積結構

Crystal structure • Hexagonal Close-Packed (HCP) 六方最密堆積 A sites – ABAB. . . Stacking Sequence c B sites A sites a • Face-Centered Cubic (FCC) 面心立方 – ABCABC. . . Stacking Sequence A B C

Determine Crystal Structures 1. Stoichiometry 化學計量 l Charge Neutrality 2. Cation-anion radii ratios (coordination number) 3. Covalent character

Ceramic Density Computation Number of formula units/unit cell AC: atomic weight of cation AA: atomic weight of anion VC: Volume of unit cell NA: Avogadro’s number

Silicate Ceramics 矽酸鹽陶瓷

Silica 矽石、二氧化矽 • Crystalline structure of Silica – Quartz 石英 – Cristobalite (Crystobalite) 白矽石、方矽石 – Tridymite 鱗石英、鱗矽石 • The strong Si-O bond leads to a strong, high melting temperature (1710 C)

Cristobalite (Crystobalite) 白矽石、方矽石

Silica Glass 矽石玻璃 • fused silica or vitreous silica 熔凝矽石或 玻化矽石 • B 2 O 3 and Ge. O 2 – Network former • Ca. O and Na 2 O – Network modifier • Ti. O 2 and Al 2 O 3 – Intermediate • Modifiers and Intermediates lowers the melting point and viscosity of a glass

Crystalline silicon dioxide Noncrystalline silicon dioxide

Silicate 矽酸鹽

Two-dimensional silicate sheet structure (Si 2 O 5)2

Layered Silicates • Can change the counterions (相對離子) – this changes layer spacing – the layers also allow absorption of water • Mica 雲母 KAl 3 Si 3 O 10(OH)2 • Bentonite 膨土、火山黏土 – – used to seal wells packaged dry swells 2 -3 fold in H 2 O pump in to seal up well so no polluted ground water seeps in to contaminate the water supply

Structure of kaolinite clay 高嶺黏土

Carbon 碳 • Diamond 鑽石 – metastable state 介穩態、準穩態 • Graphite 石墨 • Fullerene 芙、芙樂、富勒、芙樂烯、富勒烯 • C 60 – Buckminsterfullerenes 巴克明斯特芙樂烯 – Buckyball 巴克球

Diamond cubic crystal structure

Structure of Graphite

Structure of a C 60 Molecule

Structure of a Carbon Nanotube

Imperfections in Ceramic • Imperfection 缺陷 • Electroneutrality 電中性 • Atomic Point Defect – Vacancy 空位 – Interstitial 填隙、間隙 • Defect Structure – Frenkel defect 夫倫克耳缺陷 – Schottky defect 肖特基缺陷 • Stoichiometry or Nonstoichiometry

Defect Structure Schottky defect Frenkel defect

Impurities in Ceramics • Electroneutrality 電中性 • Solid solution 固溶體 – substitutional type – interstitial type

Diffusion in Ionic Materials • Diffusion in ionic materials usually occurs by a vacancy mechanism • Electroneutrality 電中性

Ceramic Phase Diagrams Mg. O-Al 2 O 3

Brittle Fracture of Ceramics • • • brittle fracture 脆性斷裂 plastic deformation 塑性形變 fractography 斷口形像學 crack 裂痕、裂紋、裂縫 branch or bifurcate 分叉

Stress-Strain Behavior • Stress 應力 • Strain 應變 • flexural strength 抗彎強度、抗撓強度、 撓曲強度 • modulus of rupture 破壞模數 • fracture strength 破裂強度 • bend strength 彎曲強度

Plastic Deformation • Crystalline ceramics • Noncrystalline ceramics – Viscosity 黏度、黏性