discription of ceramics

1. Ceramic Materials

2. Definition
• Ceramics are inorganic, non metallic materials
which consist of metallic and non metallic
elements bonded together primarily by ionic or
covalent bonds.

3. Ceramic Properties
In general most ceramics are:
• hard,
• wear-resistant,
• brittle,
• refractory,
• thermal insulators,
• electrical insulators,
• nonmagnetic,
• prone to thermal shock, and
• chemically stable.

4. Ceramic Products
• The best-known ceramics are pottery, glass, brick, porcelain, and
cement
• Clay construction products - bricks, clay pipe, and building tile
• Refractory ceramics - ceramics capable of high temperature
applications such as furnace walls.
• Cement used in concrete - used for construction and roads
• Glass - bottles, lenses, window pane, and light bulbs
• Glass fibers - thermal insulating wool, and fiber optics
communications lines
• Abrasives - aluminum oxide and silicon carbide
• Cutting tool materials - tungsten carbide, aluminum oxide, and
cubic boron nitride

5. Ceramic Products
• Ceramic insulators - applications include
electrical transmission components, spark
plugs, and microelectronic chip
• Nuclear fuels based on uranium oxide (UO2)
• Bio ceramics - artificial teeth and bones

6. Three Basic Categories
• Traditional ceramics - clay products such as pottery and bricks,
common abrasives, and cement
• New ceramics - more recently developed ceramics based on oxides,
carbides, etc., and generally possessing mechanical or physical
properties superior or unique compared to traditional ceramics
• Glasses - based primarily on silica and distinguished by their non-
crystalline structure

7. Mechanical Properties of ceramics
• Mechanical properties are important in
structural and building materials. They include
many properties used to describe
the strength of materials such
as: elasticity / plasticity, tensile
strength, compressive strength, shear
strength, fracture toughness & ductility (low
in brittle materials), and indentation hardness.

12. Refractories
• Mineral products , stable at high temp
• Used in construction of furnaces and allied
equipment.
• Acid, basic and neutral

13. Processing of Ceramics
• The majority of ceramic components are produced by sintering (firing) compacted powder
pre-forms. These pre-forms are usually referred to as 'green-state' and numerous powder-
forming processes have been developed including pressing and extrusion. However, the
powder consists of solid, hard, brittle particulates. A binder is usually added to enhance the
flow properties of the powder, leading to higher density in the final component. The binders
used vary according to the process to be used and the desired properties of the final product.
• Once the ceramic powders have been compacted to produce the green-state component,
they are approximately 50-70% dense. They are also relatively weak, but with care can be
machined to quite complex geometries. To impart strength, the green state components are
usually sintered.
• Initial heating (up to 250°C) volatilizes any organic processing additives (binders) and
decomposable constituents. As the temperature increases to the firing temperature,
sintering of the ceramic powders begins and is usually accompanied by shrinkage. This
shrinkage must be accounted for when machining in the green-state.
• Sintering can be assisted (decreasing temperature or time requirements) by the deliberate
addition of additives which will react to produce lower melting point secondary phases
(liquid phase sintering). These secondary phases can be envisaged as 'glueing' the ceramic
particles together. This is the case for ceramics such as alumina. Sometimes, sintering aids are
added to enhance diffusion (which aids sintering), this is the case when additions of boron or
aluminium are added to hot pressed silicon carbide.

15. • Slipcasting is a technique for the mass-production
of pottery and ceramics, especially for shapes not easily made on
a wheel. A liquid clay body slip (usually mixed in a blunger) is
poured into plaster moulds and allowed to form a layer, the cast, on
the inside cavity of the mould. In a solid cast mould, ceramic
objects such as handles and platters are surrounded by plaster on
all sides with a reservoir for slip, and are removed when the solid
piece is held within. For a hollow cast mould, once the plaster has
absorbed most of the liquid from the outside layer of clay the
remaining slip is poured off for later use. The cast piece is removed
from the mould, (trimmed neatly) and allowed to dry. This produces
a greenware piece which is then dried before firing, with or without
decoration.

17. • Sintering is the process of compacting and
forming a solid mass of material by heat
and/or pressure without melting it to the
point of liquefaction. Sintering happens
naturally in mineral deposits or as a
manufacturing process used with metals,
ceramics, plastics, and other materials.