Ceramics Science and Technology
Description
Built on the solid foundations laid down by the 20-volume series Materials Science and Technology, Ceramics Science and Technology picks out this exciting material class and illuminates it from all sides.
Materials scientists, engineers, chemists, biochemists, physicists and medical researchers alike will find this work a treasure trove for a wide range of ceramics knowledge from theory and fundamentals to practical approaches and problem solutions.
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I-Wei Chen is currently Skirkanich Professor of Materials Innovation at the University of Pennsylvania since 1997, where he also gained his master's degree in 1975. He received his bachelor's degree in physics from Tsinghua University, Taiwan, in 1972, and earned his doctorate in metallurgy from the Massachusetts Institute of Technology in 1980. He taught at the University of Michigan (Materials) during 1986-1997 and MIT (Nuclear Engineering; Materials) during 1980-1986. He began ceramic research studying martensitic transformations in zirconia nano crystals, which led to work on transformation plasticity, superplasticity, fatigue, grain growth and sintering in various oxides and nitrides. He is currently interested in nanotechnology of ferroelectrics, thin film memory devices, and nano particles for biomedical applications. A Fellow of American Ceramic Society (1991) and recipient of its Ross Coffin Purdy Award (1994), Edward C. Henry Award (1999) and Sosman Award (2006), he authored over 90 papers in the Journal of the American Ceramic Society (1986-2006). He also received Humboldt Research Award for Senior U.S. Scientists (1997).
Content
PART I: Ceramic Material Classes
CERAMIC OXIDES
Introduction
Aluminum Oxide
Magnesium Oxide
Zinc Oxide
Titanium Dioxide
Zirconium Oxide
Cerium Oxide
Yttrium Oxide
NITRIDES
Silicon Nitride
Boron Nitride
Aluminum Nitride
Titanium Nitride
Tantalum Nitride
Chromium Nitride
Ternary Nitrides
Light-Emitting Nitride and Oxynitride Phosphors
GALLIUM NITRIDE AND OXONITRIDES
Introduction
Gallium Nitrides
Gallium Oxides
Gallium Oxonitrides
Outlook
SILICON CARBIDE- AND BORON CARBIDE-BASED HARD MATERIALS
Introduction
Structure and Chemistry
Production of Particles and Fibers
Dense Ceramic Shapes
Properties of Silicon Carbide- and Boron Carbide-Based Materials
Applications of Carbides
COMPLEX OXYNITRIDES
Introduction
Principles of Silicon-Based Oxynitride Structures
Complex Si-Al-O-N Phases
M-Si-Al-O-N Oxynitrides
Oxynitride Glasses
Oxynitride Glass Ceramics
Conclusions
PEROVSKITES
Introduction
Crystal Structure
Physical Properties
Chemical and Catalytic Properties
THE Mn+1AXn PHASES AND THEIR PROPERTIES
Introduction
Bonding and Structure
Elastic Properties
Electronic Transport
Thermal Properties
Mechanical Properties
Tribological Properties and Machinability
Concluding Remarks
PART II: Structures and Properties
STRUCTURE-PROPERTY RELATIONS
Introduction
Self-Reinforced Silicon Nitrides
Fibrous Grain-Aligned Silicon Nitrides (Large Grains)
Fibrous Grain-Aligned Silicon Nitrides (Small Grains)
Grain Boundary Phase Control
Fibrous Grain-Aligned Porous Silicon Nitrides
DISLOCATIONS IN CERAMICS
Introduction
The Critical Resolved Shear Stress
Crystallography of Slip
Dislocations in Particular Oxides
Work Hardening
Solution Hardening
Closing Remarks
DEFECT STRUCTURE, NONSTOICHIOMETRY, AND NONSTOICHIOMETRY RELAXATION OF COMPLEX OXIDES
Introduction
Defect Structure
Oxygen Naonstoichiometry
Nonstoichiometry Re-Equilibration
INTERFACES AND MICROSTRUCTURES IN MATERIALS
Introduction
Interfaces in Materials
Practical Implications
Summary and Outlook
PART III: Mechanical Properties
FRACTURE OF CERAMICS
Introduction
Appearance of Failure and Typical Failure Modes
A Short Overview of Damage Mechanisms
Brittle Fracture
Probabilistic Aspects of Brittle Fracture
Delayed Fracture
Concluding Remarks
CREEP MECHANISMS IN COMMERICAL GRADES OF SILICON NITRIDE
Introduction
Material Characterization
Discussion of Experimental Data
Models of Creep in Silicon Nitride
Conclusions
FRACTURE RESISTANCE OF CERAMICS
Introduction
Theory of Fracture
Toughened Ceramics
Influence of Crack Growth Resistance Curve Upon Failure by Fracture
Determination of Fracture Resistance
Fatigue
Concluding Remarks
SUPERPLASTICITY IN CERAMICS: ACCOMMODATION-CONTROLLING MECHANISMS REVISITED
Introduction
Macroscopic and Microscopic Features of Superplasticity
Nature of the Grain Boundaries
Accommodation Processes Superplasticity
Applications of Superplasticity
Future Prospective in the Field
PART IV: Thermal, Electrical, and Magnetic Properties
THERMAL CONDUCTIVITY
Introduction
Thermal Conductivity of Dielectric Ceramics
High-Thermal Conductivity Nonoxide Ceramics
Mechanical Properties of High-Thermal Conductivity Si3N4 Ceramics
Concluding Remarks
ELECTRICAL CONDUCTION IN NANOSTRUCTURED CERAMICS
Introduction
Space Charge Layers in Semiconducting Ceramic Materials
Effect of Space Charge Profiles on the Observed Conductivity
Influence of Nanostructure on Charge Carrier Distributions
Case Studies
Conclusions and Observations
FERROELECTRIC PROPERTIES
Introduction
Intrinsic Properties: The Anisotrophy of Properties
Extrinsic Properties: Hard and Soft Ferroelectrics
Textured Ferroelectric Materials
Ferroelectricity and Magnetism
Fatigue in Ferroelectric Materials
MAGNETIC PROPERTIES OF TRANSITION-METAL OXIDES: FROM BULK TO NANO
Introduction
Properties of Transition Metal 3d Orbitals
Iron Oxides
Ferrites
Chromium Dioxide
Manganese Oxide Phases
Concluding Remarks
1
Ceramic Oxides
DuSan Galusek and KatarÍna Ghillányová
1.1 Introduction
Ceramic oxides represent the most extensive group of ceramic materials produced today. Traditionally, but rather artificially, the oxide ceramics are divided into "traditional" and "advanced" groups. The "traditional" ceramics include mostly silica-based products prepared from natural raw materials (clays), including building parts (bricks, tiles), pottery, sanitary ware, and porcelain, but also ceramics with other main components (e.g., alumina, magnesia), which are applied in the field of electroceramics (insulators), or industrial refractories.
"Advanced" ceramics require a much higher quality and purity of raw materials, as well as the careful control of processing conditions and of the material's microstructure. They usually comprise oxides, which donot quite fall within the traditional understanding of the term "silicate" materials and ceramics. Oxides found in these ceramics include mostly oxides of metals such as aluminum, zirconium, titanium, and rare earth elements. Originally investigated mainly as materials for structural applications (especially alumina and zirconia), ceramic materials (and not only oxides) partly failed to meet the expectations, mainly due to problems with reliability and high production costs. In recent years, therefore, a significant shift has been observed in pursuing and utilizing the functional properties of ceramic materials, especially chemical (high inertness), optical, electrical, and magnetic properties. Another area of research which has been pursued in recent years is the refinement of microstructure to the nanolevel. It is widely anticipated that such microstructure refinement will not only improve the known properties of ceramics, but will also bring new properties to already known materials. The attempts to prepare nano-structure materials bring new challenges: from the synthesis of suitable nanopowders, through their handling, the rheology of nanosuspensions, and health and safety issues, to the development of sintering techniques that allow densification without any significant coarsening of the microstructure.
In the following sections, an attempt is made to address the questions of recent developments in the field of ceramic oxides. As this topic cannot be covered fully within the space available, oxides have been selected which are considered to be the most important for the field (Al2O3, ZrO2), as well as those that have recently become a subject of interest for the ceramic community due to their interesting properties, such as TiO2, ZnO, CeO2, and Y2O3. Those materials which are only used as minor components of ceramic materials, or ternary compounds such as titanates or spinels, have been excluded at this stage.
1.2 Aluminum Oxide
From the point of view of the volume of production, polycrystalline alumina is the material most frequently used as ceramics for structural applications. However, in comparison with for example, silicon nitride, where the influence of various additives on microstructure and properties has been well characterized and understood, and despite several decades of lasting research effort, alumina remains a material with many unknown factors yet to be revealed. Alumina-based materials can be divided roughly into three groups:
- Solid-state sintered aluminas:Here, research is focused on a better understanding of sintering processes with the aim of preparing nanocrystalline materials with superior mechanical properties (e.g., hardness and wear resistance), and possibly also transparency to visible light. The prerequisite for the successful preparation of submicrometer aluminas with desired properties are sufficiently fine-grained and reactive nanopowders of high purity. Their synthesis and characterization has, therefore, been intensively pursued during the past years.
- Liquid-phase sintered (LPS) aluminas: Despite the fact that LPS aluminas represent a substantial part of industrially produced alumina-based materials, and despite a tremendous amount of research work, many unknowns remain. Although sintering additives have a profound influence on mechanical properties (especially on hardness, creep, and wear resistance, and to a certain extent also on bending strength and fracture toughness), there remains some confusion as to how individual additives or their combinations influence the microstructure and behavior of alumina-based materials. The sintering additives used include mostly silica, alkali oxides, the oxides of alkali earth metals, and combinations thereof. Doping with rare earth oxides is studied with the aim of understanding and enhancing the creep resistance of polycrystalline aluminas.
- Alumina-based composites: These comprise especially zirconia-toughened alumina (ZTA), and alumina-based nanocomposites with non-oxide second phases such as SiC or TiC. However, the latter two, in particular, are beyond the scope of this chapter.
1.2.1 Crystal Structure
The only thermodynamically stable crystallographic modification of alumina is a-Al2O3, or corundum. Corundum has a hexagonal crystal lattice with the cell parameters a = 4.754 Å, and c = 12.99 Å. The ions O2? are arranged in close hexagonal arrangement, with the cations Al3+ occupying two-thirds of the octahedral interstitial positions (Figure 1.1). Some selected materials properties of a-alumina single crystal are summarized in Table 1.1.
Figure 1.1 Crystal structure of a-Al2O3.
Except for the thermodynamically stable a modification, there exist also numerous metastable modifications, denoted ?, ?, ?, ?, e, d, ?, and ?. These modifications are often used as supports for catalysts. All metastable modifications have a partially deformed closely packed hexagonal oxygen sublattice with various configurations of interstitial aluminum atoms. On approaching the equilibrium, the crystal lattice becomes more ordered until the stable a modification is formed. The type of metastable polymorph influences the morphology of the formed a-Al2O3 particles.
1.2.2 Natural Sources and Preparation of Powders
Aluminum is one of the most abundant elements on Earth and, in its oxidized form, is a constituent of most common minerals. Pure aluminum oxide is relatively rare, but may be found in the form of single crystal, when it is used as a gemstone in its colorless (sapphire) or red (ruby, due to the admixing of chromium) modifications. The most important raw material for the production of aluminum oxide is bauxite, which is a mixture of the minerals boehmite (a-AlO(OH)), diaspor (ß-AlO(OH)), and gibbsite (Al(OH)3), with a high content of various impurities such as Na2O, SiO2, TiO2, and Fe2O3. Bauxite is refined using the Bayer process, which has been well described in many books dealing with the topic (e.g., Ref. [1]). Very pure commercial powders are prepared via the calcination of alum, NH4Al(SO4)2·12 H2O.
Table 1.1 Some selected properties of single crystal a-alumina.
Property Value Melting point 2053 °C Thermal conductivity 25 °C 40 WmK?1 1000°C 10WmK?1 Thermal expansion coefficient (25-1000 °C) Parallel with c 8.8.10?6 K?1 Density Perpendicular to c 7.9.10?6 K?1 3.98 g cm-3 Young's modulus Parallel with c 435 GPa Poisson ratio Perpendicular to c 386 GPa 0.27?0.30The preparation of submicrometer-grained aluminas requires well-defined pure nanopowders which, themselves, exhibit many exploitable characteristics, such as low-temperature sinterability, greater chemical reactivity, and enhanced plasticity. Thus, a range of methods has been developed for the preparation of nanopowders with desired properties. These can be roughly allocated to: (i) high-temperature/flame synthesis; (ii) chemical synthesis, including sol-gel; and (iii) mechanically assisted processes, such as high-energy milling.
1.2.2.1 High-Temperature/Flame/Laser Synthesis
The method usually comprises the injection of a suitable gaseous, or liquid aluminum-containing precursor into the source of intensive heat (e.g., laser [2], d.c. arc plasma [3-5], or acetylene, methane, or hydrogen flame [6, 7]), where the precursor decomposes and converts into the oxide. In most cases, transient aluminas are formed, and in order to obtain a-Al2O3 a further high-temperature treatment, usually accompanied by significant particle coarsening, is required. Possible precursors include metal-organic compounds such as trimethylaluminum or aluminum tri-sec-butoxide. Metastable alumina powders with particle sizes ranging from 5 to 70nm can be prepared in this way.
1.2.2.2 Chemical Methods
These normally utilize the low- and medium-temperature decomposition of inorganic aluminum salts and hydroxides, or metal-organic compounds of aluminum. Typical precursors include aluminum...
