|
|
Microwave
Sintering accelerates densification by irradiating
Microwave to powders. The principle of Microwave
Sintering is as follows:
Dielectric coefficient
of a ceramics dielectric can be described
as ε = ε’ + ε” , where ε’ represents real quantity
and ε” represents imaginary
quantity, respectively. If electric field
E(with frequency f) is applied, owing
to dielectric loss, a dielectric releases
heat P per second.
P = 2πfε‘‘tanδ (tanδ = ε‘’/ε‘)
As
you can see, an object can be effectively
heated if dielectric coefficient ε‘‘ of
an object and frequency f of microwave is
high. However, penetration depth of microwave
is Dp = (πfμσ)-1/2,
so that frequency of microwave should be
conrolled appropriately to prevent surface
heating. Usually, microwave with frequency
2.45 GHZ is applied.
There are a
couple of advantage of Microwave Sintering;
first, driving force for sintering is strong
because growth of grain is prohibited by
rapid heating, secondly, sintering is promoted
because particle surface is activated by
plasma, thirdly, different from other indirect
heating methods, this method expedites lattice
vibration. For this reason, diffusion velocity
is fast. From these advantages, we can acquire
ceramics having high densification and fine
microstructure in a short time. Accordingly,
Microwave Sintering is fitting to Ceramics
Nano Materials which are in the spotlight
nowadays.
|
|
