New oxidized at 1200 ° C and chemically decomposed

New Ceramics

In general, new ceramics are based on compounds other than
the various variations of aluminum silicate. New ceramics such as oxides,
carbides, nitrides, and borides are chemically simpler than traditional
ceramics.

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The new ceramics are arranged as oxides, carbides and
nitrides according to chemical compound categories.

Oxide Ceramics

The most important oxide is ceramic aluminum oxide. Aluminum
oxide can be synthetically produced by using electric furnace, strength and
toughness are developed in comparison with natural precedent. Aluminum oxide
has high corrosion resistance, low thermal conductivity and good hot hardness.
bioceramics, alloy contents in glass, refractory bricks, cutting tool tips can
be applied.

Carbides

The carbides include silicon carbide (SiC), tungsten carbide
(WC), tantalum carbide (TaC), titanium carbide (TiC) and chromium carbide
(Cr3C2).

·      
 WC, TiC,
TaC are valuable both for cutting tools and for other applications where these
properties are required in terms of hardness and abrasion resistance.

·      
 First
developed, the most important and most common carbide is tungsten carbide.

·      
WC is produced by carburizing tungsten powders.

·      
Tantalum carbide is formed by pure tantalum
powder and tantalum pentoxide tantalum carbide.

·      
Titanium carbide is formed by the carburation of
rutile or ilmenite minerals.

Chromium carbide is made by carburizing
chromium oxide.

Last but not least Except for SiC, each of
the carbides mentioned herein must be associated with a metal binder such as
cobalt and nickel to produce a useful solid product.

Nitrides

Important nitrile ceramics are silicon nitride (Si3N4),
boron nitride (BN), and titanium nitride (TiN).

·      
• Silicon nitride is promising in high
temperature structural applications. Si3N4 is oxidized at 1200 ° C and
chemically decomposed at 1900 ° C.

·      
Boron nitride is found in various structures,
just like carbon.

Important forms;

Hggagonal like graphite

Cubic like diamond

       • Titanium
nitride has high hardness, good wear resistance and low coefficient of friction
with ferrous metals.           

 

A new ceramic material related to nitrides
and oxide groups at the same time is an oxinitride ceramic called sialon.

 

 

 

 

 

Processing
of New Ceramics

1) Preparation of starting materials

2) Forming

3) Sintering

4) Finishing

 

1) PREPARATION OF STARTING MATERIALS

Powder preparation can be mechanical and
chemical.

The mechanical methods are the same as the
ball milling process used for traditional ceramics.

Chemical methods are freeze drying and
sedimentation.

• In freeze-drying, salts with the
appropriate starting culm are precipitated in water and the precipitate is
sprayed to form small droplets that rapidly freeze. The water is then removed
from the droplets in a vacuum chamber and the salt formed is separated by
heating. Freeze drying is not suitable for all ceramics. it may not be a
suitable water-soluble salt as starting material.

• When the solution is precipitated, the
desired compound is dissolved from the starting ceramic mineral so that foreign
substances can be filtered out.

 

2) FORMING

There are four types of shaping: hot
pressing, isostatic pressing, stripping knife processing and powder injection
molding.

A) Hot pressing produces high density and
finer grain size, but the die’s service life is shortened due to hot and
abrasive particles coming to the surface.

B) Isostatic pressing uses hydrostatic
pressure to squeeze ceramic powders from all sides. Thus, the problem of
inhomogeneous density in the final product, which is often observed in the conventional
uniaxial pressing method, is eliminated.

C) Stripping blade operation, which is used
to produce thin ceramic slabs.

D) Powder injection molding is carried out
by mixing a thermoplastic polymer which serves as a ceramic particle carrier
and which has suitable flow properties at molding temperatures. The mixture is
then heated and injected into the mold cavity. After cooling, the mold is
opened and the mold is removed. the piece is raw.

 

3) SINTERING

The function of the sintering is as before.

1) Connecting individual particles to form
a single solid mass

2) Increase in density

3) Reduction or removal of porosity

 

4) ENDING

1) Increasing dimensional error

2) Improve the surface appearance

3) Make small changes in the geometry of the
fragment.

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