Ceramic composition for absorbing electromagnetic waves and method for manufacturing the same

DETAILED DESCRIPTION OF THE INVENTION Preferably, the mixture around the raw powder has by weight between about 0.
0005 and about 0.
004% Bi.
sub.
2 O.
sub.
3 as the plasticizer and hexamethanol as the dispersing agent.
The step ii) is a wet grinding method using a ball mill for 2 hours to 4 hours so as to make the mixed powder having a particle distribution of between about 1 .
mu.
m and about 3 .
mu.
m.
The step iii) is a spray drying method maintaining a temperature of an entrance of a spray-drier between 550.
degree.
C.
and 600.
degree.
C.
and maintaining a temperature of an exit of the spray-drier between 100.
degree.
C.
and 150.
degree.
C.
so as to make the granulates which have by weight between about 0.
1% and about 0.
4% moisture.
Also, the step iv) is forming the granulates by using a metal pressing means at a pressure of between 800 kg/cm.
sup.
2 and 1200 kg/cm.
sup.
2.
Preferably, the step v) has the steps of: i) heating the shaped body loaded in a furnace up to a first temperature of about 400.
degree.
C.
for about 3 hours after loading the shaped body in the furnace, ii) maintaining the first temperature of the furnace at about 400.
degree.
C.
for about 1 hour, iii) heating the shaped body loaded in the furnace up to a second temperature of about 900.
degree.
C.
for about 4 hours, iv) maintaining the second temperature of the furnace at about 900.
degree.
C.
for about 2 hours, v) heating the shaped body loaded in the furnace up to a third temperature of about 1200.
degree.
C.
for about 3 hours, and vi) maintaining the third temperature of the furnace at about 1200.
degree.
C.
for about 2 hours.
Also, preferably, the step vi) further has the steps of: i) making the furnace airtight and cooling gradually the sintered body loaded in the furnace between about 40 hours and about 60 hours, and ii) unloading the sintered body from the furnace at a temperature below about 200.
degree.
C.
and cooling gradually the sintered body in an atmosphere.
In the case that the raw powder comprises by weight between about 65% and about 75% Fe