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

2

2ionic character 1A BX X

e

Material Ionic Character

CaF2 89%

MgO 73%

NaCl 67%

Al2O3 63%

SiO2 51%

Si3N4 30%

ZnS 18%

SiC 12%

Electronegativity 電負度、陰電性

Stable and unstable cation-anion coordination configuration

- -

- -+

unstable

- -

- -+

stable

- -

- -+

stable

Cations are ordinarily smaller than anionscation 陽離子 anion 陰離子

Coordination Number 配位數

2 3 4 6 8

Coordination Number 配位數

Cation-Anion Radius Ration rC/rA

<0.155 0.155-0.225 0.225-0.414 0.414-0.732 0.732-1

rC/rA > 1 配位數 12

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

• AX2 Type– Fluorite Structure 螢石結構、氟石結構

• ABX3 Type– Perovskite Structure 鈣鈦礦結構

• AB2X4 Type– Spinel Structure 尖晶石結構

Rock Salt Structure 岩鹽結構• NaCl, MgO, MnS, LiF, FeO

rNa+ = 0.102 nm

rCl = 0.181 nm

rNa+/rCl = 0.564

Cesium Chloride Structure 氯化銫結構

• CsCl rCs+ = 0.170 nm

rCl = 0.181 nm

rCs+/rCl = 0.939

Zinc Blende Structure 閃鋅礦結構• ZnS, ZnTe, SiC, ZnO

rZn2+ = 0.074 nm

rO2 = 0.140 nm

rZn+2/rO2 = 0.529

Fluorite Structure 螢石結構• CaF2, ZrO2, UO2, PuO2, ThO2

rCa2+ = 0.100 nm

rF = 0.133 nm

rCa+2/rF = 0.8

Perovskite Structure 鈣鈦礦結構

• BaTiO3, SrZrO3, SrSnO3

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– ABAB... Stacking Sequence

• Face-Centered Cubic (FCC)

面心立方– ABCABC... Stacking Sequence

c

a

A sites

B sites

A sites

ABC

Determine Crystal Structures

1. Stoichiometry 化學計量 Charge Neutrality

2. Cation-anion radii ratios (coordination number)

3. Covalent character

Ceramic Density Computation

A

AC

NV

)AA(n

C

Number of formula units/unit cell

AC: atomic weight of cation AA: atomic weight of anion VC: Volume of unit cellNA: 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 (1710C)

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

• B2O3 and GeO2

– Network former

• CaO and Na2O– Network modifier

• TiO2 and Al2O3

– 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 (Si2O5)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 KAl3Si3O10(OH)2

• Bentonite 膨土、火山黏土– used to seal wells– packaged dry

– swells 2-3 fold in H2O

– 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

• C60

– Buckminsterfullerenes 巴克明斯特芙樂烯 – Buckyball 巴克球

Diamond cubic crystal structure

Structure of Graphite

Structure of a C60 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

Frenkel defect

Schottky 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 DiagramsMgO-Al2O3

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