Ch 1 Introduction
•What is Ceramic?
Five categories of materials : Metals, polymers, ceramics,
semiconductors, and composites
Metals:
−Delocalized electrons overcome the mutual repulsion between the metal ion cores.
−Both pure and alloy
−Mainly transitional elements
−Some metals(alloys) contain nonmetallic elements (C in Fe).
−Some metals contain ceramics (carbides such as Fe3C and W6C).
−Good electrical and thermal conductivity
Polymers:
−Macromolecules formed by covalent bonding of many mers
−Organic compounds based on carbon, hydrogen, sulfur, chlorine, etc.
−Plastics
Ceramics:
−Mixed bonding of covalent, ionic, and sometimes metallic
−Arrays of interconnected atoms, not discrete molecules -I2 (discrete molecules),
paraffin wax (long chain alkane molecules), ice (discrete H2O)
−Mainly oxides, nitrides, carbides
−“ Most solid materials that aren’t metal, plastic, or derived from plants or
animals are ceramics”
Semiconductors:
−Electrically between conductor and insulator
−Wide band gap (3 eV )
−SiC, GaN, etc.
Composites:
−Combinations of more than one materials or phase
−Ceramics can be reinforcement or matrix.
•General Properties of Ceramics? misunderstanding?
1) Brittleness
Because of mixed ionic-covalent bonding
But, at higher temperatures (above Tg), glass no longer brittle
Brittle only at room T, not at elevated temperature
2) Poor electrical and thermal conduction
Valence electrons are not free.
But, diamond has the highest thermal conductivity (by phonons)
ReO3 has and electrical conductivity, similar to Cu.
YBa2Cu3O7 is superconductor, zero resistivity below 92 K.
3) Compressive strength
Stronger in compression than in tension (in metal, both are similar).
if compressive condition, load-bearing application is possible.
4) Chemical insensitivity
Generally chemically and thermally durable
Pyrex glass in lab or in bakeware
5) Transparent
Sapphire watch covers, precious stones, optical fibers.
Metal can be thin only with very thin (< 0.1 µm)
•Types of Ceramic and their applications
Traditional ceramics: Based on clay and silica, low technology, low cost
Advanced ceramics: special, technical, engineering, recently developed
•Market
General distribution of industry sales Overall glass market distribution in US
Market distribution of advanced Ceramics
•Critical issues for the future
1. Structural ceramics
Si3N4, SiC, ZrO2, B4C, and Al2O3 are used in applications such as cutting
tools, wear components, heat exchangers, and engine parts.
Key issues
• Reducing cost of the final product
• Improving reliability
• Improving reproducibility
2. Electronic ceramics
BaTiO3, ZnO, Pb(Zr,Ti)O3, AlN, superconductors are used in applications as
capacitor dielectrics, varistors, MEMS, substrate, and IC packages.
Key issues
• Integrating with existing semiconductor technology
• Improving processing
• Enhancing compatibility with other materials
3. Bioceramics
Inert(Al2O3, ZrO2, bioactive(hydroxyapatite, glass-ceramic), and resorbable
(tricalcium phosphate).
Key issues
• Matching mechanical properties to human tissues
• Increasing reliability
• Improving processing methods
4. Coating and Films
To modify the surface properties bioactive coating on bioinert implant
Economic reason diamond coating on a cheap cutting tool
Better performance HTSCs coating and better electrical transport
Key issues
• Understanding film deposition and growth
• Improving film/substrate adhesion
• Increasing reproducibility
5. Composites
Main purpose of CMCs is to increase fracture toughness through reinforcement.
The roles of ceramics in MMCs is to increase strength, enhance creep resistance,
and greater wear resistance.
Key issues
• Reducing processing costs
• Developing compatible combination of materials
• Understanding interfaces
6. Nanoceramics
Mainly in cosmetic products, catalysis, fuel cells, coatings, and other devices
Key issues
• Making them
• Integrating them into devices
• Ensuring that they do not have a negative impact on society
•Relation between microstructure, processing, and applications
1. The strength of polycrystalline ceramics depends on the grain size (Hall-
Petch effects)
2. Transparent or translucent ceramics depends on the pores or second-
phases.
3. Thermal conductivity of commercially available polycrystalline AlN is
usually lower than that predicted by theory because of the presence of
impurities, mainly oxygen, which scatter phonons.
4. The permeability of soft ferrites is a function of grain size and large
defect-free grains are preferred because we need to have very mobile
domain walls.
5. For the electrical insulators(high electrical resistivity) pure alumina is not
used. Silicates are added to reduce the sintering temperature. But
silicates make glassy phase and it increases conductivity.
•You should be careful !!
• Toxicity : the manufacturer supplied information on the hazards. Please
read this information and keep it.
• Small particle : not be inhaled (< 1µm)
• High temperature : even 400 °C of ceramic will not show a change in
color.
• Organics : used as solvents or binders in ceramic processing. Materials
Safety Data Sheets (MSDS) should be readily accessible for all the materials
you are using.
