Advanced Ceramics Introduction

1. ADVANCED CERAMICS
GENERAL (II)
1

2. POINTS FOR DISCUSSION
# Definition of Ceramic Materials
# What are Advanced Ceramics
# Why/How Advanced Ceramics developed
# Properties of Ceramics applied for Advanced
# Mech. performance of Ceramics – New view
# Classifications of Advanced Ceramics
# Applications of Advanced Ceramics
# Production of Advanced Ceramics
2

3. 3
What are Ceramic Materials
The word Ceramic is derived from Keramos, the Greek word for
Potter’s clay or ware made from clay and fired for drying & strength.
 Ceramics are normally strong and brittle in nature and generally
non-conductor of heat and electricity.

4. What are Advanced Ceramics
# Ceramics for today’s engineering applications can be considered
to be non-traditional / non-conventional. The new and emerging
family of ceramic materials referred to as a new group of ceramics
called “Advanced Ceramics.
# Utilise highly refined materials and new forming techniques. High
purity materials and precise production methods are employed.
# Used as engineering material, posses several properties superior
to metal-based systems such as high resistance to abrasion, high
thermal stability, excellent hot strength, chemical inertness, high
machining speeds (as tools) and dimensional stability.
# Placed in a most attractive position, for above said properties,
not only in the area of performance but also cost effectiveness.
4

5. 5

6. Why and how Advanced Ceramics developed
- Metals have unique properties: ductility, tensile strength, abundance, simple
chemistry, relatively low cost of production, ease of forming, joining, etc.
- But due to limits of metal-based systems new materials capable of operating
under higher temp. higher speeds, longer life factors and lower maintenance costs
are required, to maintain pace with technological advancements.
- On the other hand, Ceramics are brittle by nature, have more complex chemistry
than metal. However, there have been continuing evolution of ceramic materials
with rapid acceleration of associated technologies (Methods of handling, forming
and finishing revised to maintain pace with rapid progress of new technologies.)
- With advanced processing technology and equipment, Advanced Ceramic
materials got developed and well established in many areas satisfying requirement.
- The improvements in performance, service life, savings in operational and
maintenance costs are clear evidence of the benefits of advanced ceramics.
6

7. Brittleness / High Hardness
Electrical and Thermal Resistance and Conductivity
8

8. Mechanical Strength
Chemical Insensitivity
Transparency
9

9. Changed view on mech. performance of Ceramics
With the advances of understanding in ceramic chemistry, crystallography and the
more extensive knowledge gained in regard to the production of advanced and
engineered ceramics, the potential of these materials has been realised.
One of the major developments this century was the work by Ron Garvie et al on
PSZ (partially stabilised zirconia) and development of its phase transformation
toughening. This advancement changed the way ceramic systems were viewed.
Techniques previously applied to metals were now considered applicable to
ceramic systems. Phase transformations, alloying, quenching and tempering
techniques were applied to a range of ceramic systems. Significant improvements
to the fracture toughness, ductility and impact resistance of ceramics were
realised and thus the gap in physical properties between ceramics and metals
began to close.
More recent developments in non-oxide and tougher ceramics (e.g. nitride
ceramics) have closed the gap even further.
10

10. 11

11. 12
1. Oxide Ceramics 2. Non-Oxide Ceramics 3. Ceramic Matrix Composites
<..............................Non Oxide Ceramics.....................>

12. CMC - CERAMIC MATRIX COMPOSITES
- The matrix is relatively hard and brittle and the reinforcement must have high
tensile strength to arrest crack growth
- The reinforcement must be free to pull out as a crack extends, so the bond
between reinforcement-matrix must be relatively weak
- CMCs are used in applications where resistance to high temp. and corrosive
environment is desired. CMCs are strong and stiff but lack toughness (ductility)
- Matrix materials are usually silicon carbide, silicon nitride and aluminum oxide,
and mullite (compound of Al, Si & O). They retain their strength up to 3000 o
F.
- Fiber materials used commonly carbon and aluminum oxide.
- Applications are in jet and automobile engines, deep-see mining, cutting tools,
dies and pressure vessels.
13

13. Fields of Applications of Advanced Ceramics
14

14. 15

15. 16

16. 17

17. 18
Production of Advanced Ceramics
Design
The properties of advanced materials need to be considered when designing
structures, components and devices.
The final design and material selection must ultimately be cost effective, must
function reliably and, ideally, should be an improvement upon existing
technology.
Where for any new application prior knowledge may not be available,careful
observation and recording of performance characteristics of the experimental
model, or in plant trial, is needed. Materials Engineer should work in close
contact with the research team to cooperatively develop the new concept.
New techniques such as Finite Element Analysis have proven beneficial
regarding above. The use of computer modelling allows the structures to be
created on screen without the need for costly prototypes.

18. 19
Production of Oxide Ceramics
Mineral processing > Concentrate > *Removal of unwanted impurities and
addition of other compounds (through typically wet chemistry process to
create the desired starting composition for sintering) > Heat treatment to
create controlled crystal structures > High purity starting materials (powders)
> Powders generally ground to an extremely fine or ultimate crystal size to
assist ceramic reactivity
> Plasticisers & binders blended with the powders to suit the preferred method
of forming (pressing, extrusion, slip casting, etc.) to produce the raw material.
> Raw material is formed (high and low-pressure forming techniques) into the
required “green” shape or precursor (machined or turned to shape if required)
> Firing to high temperatures in air or a slightly reducing atmosphere to
produce a dense product.
(* Most imp. stage in high performance oxide ceramics, generally high purity
systems; minor impurities can have a dynamic effect, e.g. small amounts of
MgO can have a marked effect upon the sintering behaviour of alumina.)

19. 20
Plant Production
Some general important requirements
Raw materials selection to be made on a case-by-case basis, based on
performance requirements while optimizing production costs.
Cost savings are all the more significant as the production process is repetitive,
even for a large number of parts to be produced.
Shaping better to be done by pressing the ceramic powder to obtain parts as
close to final dimensions as possible without machining.
Densification to take place inside a high-temperature furnance during sintering.
Extreme dimensional or geometric tolerances (micron range) to be obtainable
through an additional machining process, e.g. material removal by abrasion
using diamond-based techniques.

20. 21
Production of Non-Oxide Ceramics
Usually the three stage process.
Preparation of precursors or starting powders > Mixing of precursors to
create the desired compounds (Ti + 2B, Si + C, etc.) > Forming and sintering of
the final component.
The formation of starting materials and firing for this group, require carefully
controlled furnace or kiln conditions to ensure the absence of oxygen during
heating as these materials will readily trend to oxidise during firing.
This group of materials generally require quite high temp. to effect sintering.
Similar to oxide ceramics, carefully controlled purities and crystalline
characteristics are needed to achieve the desired final ceramic properties.
Fabrication of Ceramic Matrix Composite (CMC)
General Processes :
Simple sintering, Liquid impregnation, Lamination, Chemical Vapour Deposition
(CVD), Chemical Solution Deposition (CSD) etc.