chapter 15: 15 - 1 · pdf filechapter 15: ceramic materials vitrification : melting, or...

© 2011 Cengage Learning Engineering. All Rights Reserved.15 - 1

Chapter 15:

Ceramic Materials

Chapter 15: Ceramic Materials

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Learning Objectives

1. Applications of ceramics

2. Properties of ceramics

3. Synthesis and processing of ceramic powders

4. Characteristics of sintered ceramics

5. Inorganic glasses

6. Glass-ceramics

7. Processing and applications of clay products

8. Refractories

9. Other ceramic materials


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© 2011 Cengage Learning Engineering. All Rights Reserved.

15 - 3

Introduction

Ceramic

An inorganic material with high melting temperature. Usually hard and brittle.

Most ceramics exhibit good strength under compression; however, they exhibit virtually no ductility under tension.


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© 2011 Cengage Learning Engineering. All Rights Reserved. 15 - 4

Table 15.1 - Functional Classification of Ceramics


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Table 15.2 - Properties of Commonly Encountered Polycrystalline Ceramics


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Table 15.3 - Mechanical Properties of Selected Advanced Ceramics


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Synthesis and Processing of Ceramic Powders


Powder A collection of fine particles

Synthesis Steps conducted to make a ceramic powder

Spray drying A slurry of a ceramic powder is sprayed into a large chamber in the presence of hot air

Tape casting A process for making thin sheets of ceramics using a ceramic slurry consisting of binders, plasticizers, etc.

Slip casting Forming a hollow ceramic part by introducing a pourable slurry into a mold

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Green ceramic A ceramic that has been shaped into a desired form but has not yet been sintered

Powder processing Unit operations conducted to convert powders into useful shapes

Sintering A process in which a material is heated to a high temperature so as to densify it

Powder metallurgy Powder processing routes used for converting metal and alloy powders into useful shapes

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Figure 15.1


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Figure 15.2


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Compaction sintering

Cermet

A ceramic-metal composite providing a good combination of hardness with other properties such as toughness.

Cold isostatic pressing (CIP)

A powder-shaping technique in which hydrostatic pressure is applied during compaction.

Hot pressing

A processing technique in which sintering is conducted under uniaxial pressure.

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Hot isostatic pressing

A powder-processing technique in which large pieces of metals, alloys, and ceramics can be produced using sintering under a hydrostatic pressure generated by a gas

Reaction bonding

A ceramic processing technique by which a shape is made using one material that is later converted into a ceramic material by reaction with a gas

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Figure 15.3


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Tape casting

A process for making thin sheets of ceramics using a ceramic slurry consisting of binders, plasticizers, etc. The slurry is cast with the help of a blade onto a plastic substrate. The resultant green tape is then dried, cut, and machined and used to make electronic ceramic and other devices.

Extrusion and injection molding

A processing technique in which a thermoplastic mass (loaded with ceramic powder) is mixed in an extruder-like setup and then injected into a die to form complex parts.

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Figure 15.4


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Characteristics of Sintered Ceramics


Grains and grain boundaries

The average grain size is often closely related to the primary particle size. Ceramics with a small grain size are stronger than coarse-grained ceramics.

Porosity

Apparent porosity is determined by weighing the dry ceramic (Wd), then reweighing the ceramic both when it is suspended in water (Ws) and after it is removed from the water (Ww).

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Characteristics of Sintered Ceramics


True porosity

where

B is the bulk density and ρ is the true density

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Figure 15.5


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Figure 15.6


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Figure 15.7


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Figure 15.8


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Figure 15.9


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Figure 15.10


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Figure 15.11


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Figure 15.12


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Table 15.6 - Compositions of Typical Glasses (in Weight Percent)


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Processing and Applications of ClayProducts


Vitrification: Melting, or formation, of a glass.

Forming techniques for clay products

Hydroplastic forming processes, including extrusion, jiggering (forming of clay in a rotating mold using a profile tool to form the inner surface), and hand working, can be applied to these plastic mixes.

Applications of clay products

Many structural clay products and whitewares are produced using these processes.

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Figure 15.14


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Table 15.7 - Compositions of Typical Refractories (Weight Percents)


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Other Ceramic Materials


Cements

Ceramic raw materials are joined using a binder that does not require firing or sintering in a process called cementation.

xNa2O·ySiO2·H2O + CO2 → glass ( not balanced)

Al2O3 + 2H3PO4 → 2AlPO4 + 3H2O

CaSO4·(1/2) H2O + (3/2) H2O → CaSO4·2H2O

Coatings

Common commercial coatings include glazes and enamels.

Thin films and single crystals

Thin films are produced using different techniques such as sputtering, sol-gel, and chemical-vapor deposition (CVD).

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15 - 31

Other Ceramic Materials


Fibers

Fibers are produced from ceramic materials for several uses: as a reinforcement in composite materials, for weaving into fabrics, or for use in fiber-optic systems.

Joining and assembly of ceramic components

Ceramics are often made as monolithic components rather than assemblies of numerous components. When two ceramic parts are placed in contact under a load, stress concentrations at the brittle surface are created, leading to an increased probability of failure.

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Key Terms


Glazes

Enamels

Powder

Synthesis

Spray drying

Tape casting

Slip casting

Green ceramic

Powder processing

Sintering

Powder metallurgy

Cermet

Cold isostatic pressing (CIP)

Hot pressing

Hot isostatic pressing

Injection molding

Apparent porosity

True porosity

Bulk density

Glass-transition temperature

Glass formers

Intermediate oxide

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15 - 33

Key Terms


Parison

Tempered glass

Laminated glass

Glass-ceramics

Hydroplastic forming

Firing

Ceramic bond

Flux

Refractories

Cementation

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chapter 15: 15 - 1 · pdf filechapter 15: ceramic materials vitrification : melting, or...

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