Method and device for microwave sintering large ceramic articles

Patent · Mon Jan 01 00:00:00 EST 1990

OSTI ID:867563

Kimrey, Jr., Harold D. ^[1]

---

1. (Knoxville, TN)

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 (United States)
• 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

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