INEXPENSIVE, OFF THE SHELF HYBRID MICROWAVE SYSTEM Page: 4 of 5
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another 30 minutes. Power was turned off and the
system cooled for about 4 hours. Notice the
pyrometer does not begin to read until 6000C,
necessitating the use of an internal thermocouple to
measure the full range of temperatures of the sample.
While the sample is at temperature, there is a
good bit of radiant "shine" emanating in all
directions. The alumina foam filter (Fig.2) attached
to the internal thermocouple effectively blocks the
shine and helps maintain the temperature of the ultra-
Torr Seal o-ring connection to the quartz tube at or
near ambient. Fig. 5 shows the IR2 pyrometer
reading during a process run again at 1100 -11500C,
along with the measured temperatures of the upper
and lower parts of the o-ring connection. The heat-
sink and instrument fan help remove the heat,
maintaining 29 to 330C at the o-ring.
The temperature rise is rapid for these process
runs. The observed increase based on the pyrometer
is about 800C per minute from about 500 to 1100 C.
The temperature control using the ON/OFF power
control of the magnetron is within +50C at 1100 C.
~I- Time vs Upper
A - - - Timev11 Lower
- Time vs IR2 Temp
- r 1Temp of TorrSeal area
\ of Heat Sink
moles of gas, the system will be described
mathematically as having two distinct temperature
zones that are the hot volume Vh, and the cold volume,
Vc, which is the measured manifold temperature.
Using the Ideal Gas Law,
Eq. (1) can be divided into hot and cold volumes
m - P
Vc + 'H
VC + Hx
where Vc is the cold volume, VH is the hot volume, To
is the cold temperature, TH is the hot temperature, PI is
the pressure when the charge tube is at the hot
temperature, and P2 is the pressure when the charge
tube is at the cold temperature. Cold temperature is
usually the room, or starting temperature. Solving for
the hot volume,
13:00:00 15:00:00 17:00:00 19:00:00 21:00:00
Fig.5 Temperature range of o-ring
IV. MEASUREMENT OF A GAS
The quantitative measurement of a gas requires
the knowledge of the total system volume, the charge
volume, the hot volume, the initial cold temperature,
the initial pressure, the final pressure, the final cold
temperature, and the hot temperature. The total
system volume and the hot volume are calibrated
once and are constants throughout successive runs.
IV.A. Hot Volume Determination
During operation, part of the system is heated to
about 12000C with a temperature gradient to the
temperature of the rest of the system, which is near
ambient temperature. For purposes of determining
where m is the ratio of the system pressure at the hot
temperature to the pressure at the cold temperature
(Eq.2), and VT is the total volume, Vc + VH. To
determine the hot volume, a known ZrO2 charge and an
initial pressure of N2 at room temperature was heated to
12000C and obtained steady state pressure. This was
repeated for several starting pressures. The data are in
TABLE I. Hot Volume
IV.B. Gas Production Determination
The decomposition of CaCO3 to CO2 was used to
demonstrate that a gas can be produced in the system
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Walters, T; Paul Burket, P & John Scogin, J. INEXPENSIVE, OFF THE SHELF HYBRID MICROWAVE SYSTEM, article, June 21, 2007; [Aiken, South Carolina]. (digital.library.unt.edu/ark:/67531/metadc881416/m1/4/: accessed October 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.