Method and device for microwave sintering large ceramic articles

Patent · 01 January 1990

OSTI ID:867563

A microwave sintering system and method are provided for extremely uniform sintering of large and/or irregular shaped ceramic articles at microwave frequencies of at least 28 GHz in the hundreds of kilowatts power range in an untuned cavity. A 28 GHz, 200 kw gyrotron with variable power output is used as the microwave source connected to an untuned microwave cavity formed of an electrically conductive housing through an overmoded waveguide arrangement which acts in conjunction with a mode promoter within the cavity to achieve unexpected field uniformity. The part to be sintered is placed in the cavity and supported on a removable high temperature table in a central location within the cavity. The part is surrounded by a microwave transparent bulk insulating material to reduce thermal heat loss at the part surfaces and maintain more uniform temperature. The cavity may be operated at a high vacuum to aid in preventing arcing. The system allows controlled increased heating rates of greater than 200.degree. C./min to provide rapid heating of a ceramic part to a selected sintering temperature where it is maintained by regulating the microwave power applied to the part. As a result of rapid heating, the extent of non-isothermal processes such as segregation of impurities to the grain boundaries are minimized and exaggerated grain growth is reduced, thereby strengthening the mechanical properties of the ceramic part being sintered.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN
• Assignee: United States of America as represented by Department of Energy (Washington, DC)
• Patent Number(s): US 4963709
• OSTI ID: 867563
• Country of Publication: United States
• Language: English

Related Subjects

/219/264/425/
200
28
achieve
allows
allows control
allows controlled
applied
arcing
arrangement
articles
boundaries
bulk
cavity
cavity formed
central
central location
ceramic
ceramic article
ceramic articles
conductive
conductive housing
conjunction
connected
controlled
degree
device
electrically
electrically conductive
exaggerated
extent
extremely
extremely uniform
field
formed
frequencies
ghz
grain
grain boundaries
grain growth
growth
gyrotron
heat
heat loss
heating
heating rate
housing
hundreds
impurities
increased
increased heat
insulating
insulating material
irregular
irregular shape
kilowatts
kw
location
loss
maintain
maintained
material
mechanical
mechanical properties
method
microwave
microwave cavity
microwave frequencies
microwave power
microwave sintering
microwave source
microwave transparent
minimized
mode
non-isothermal
operated
output
overmoded
placed
power
power applied
power output
preventing
processes
promoter
properties
provide
provided
range
rapid
rates
reduce
reduce thermal
reduced
regulating
removable
result
segregation
selected
shaped
shaped ceramic
sintered
sintering
sintering temperature
source
source connected
strengthening
supported
surfaces
surrounded
table
temperature
thermal
thermal heat
transparent
unexpected
uniform
uniform temperature
uniformity
untuned
vacuum
variable
variable power
wave cavity
wave frequencies
waveguide