Boron Carbide
Hot-pressed boron carbide is one of the hardest materials available
in commercial shapes, and gives outstanding resistance to abrasive
wear.
It can be polished to a mirror finish and has good resistance
to acids. It is refractory and chemically inert, but less resistant
to oxidation than silicon carbide.
Boron Carbide tends to contain second-phase graphite and it
is this property which has a major influence on the strength
of the material.
The composition ranges from B4C at 78.25 wt% boron to at least
B6.5C at 85.4 wt% boron.
Production of Boron Carbide
Commercial boron carbide is produced by reacting and fusing
boric oxide and carbon, in an electric arc furnace.
Boron carbide does not melt congruently, therefore the liquid
in contact with the boron carbide, does not have the same composition
as the solid. This means that the liquid must be solidified
at a rate so that the liquid and solid don"t reach an
equilibrium.
The material which is in a molten state becomes increasingly
rich in carbon, therefore when the liquid solidifies its composition
is one of boron carbide and graphite.
Hot pressing (including hot isostatic pressing) is a way of
producing covalent ceramic materials such as boron carbide,
which are fully dense and in pure single-phase form.
Hot pressing limits the size and complexity of shapes which
can be produced, to shape these diamond grinding is used.
Properties:
- Low thermal conductivity
- Susceptible to thermal shock failure
- Outstanding hardness
- Extremely brittle
- Semiconductor
- Good thermal-neutron capture
Typical Uses:
- Thermal-neutron absorber
- Loose abrasive
- Nozzles for abrasive slurries
- Wear applications (Load compressing or sliding)
|
