FEI Quanta FEG 250, Руководство пользователя

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System Options: Heating Stage 1000 °C / Heating Stage 1500 °C
9-45
FIGURE 9-37 TEMPERATURE PROFILE
When the last cycle is finished, the controller holds at 600 °C (the last
setpoint) indefinitely until further action is taken.
Temperature Conductivity
The sample crucible temperature matches the thermocouple reading.
The actual sample temperature however varies, depending on the
sample thermal conductivity and its thickness.
The temperature at the conductive sample surface is closer to that at
the crucible, as heat is more likely to spread throughout. The
temperature at the non-conductive sample top surface is lower than
that at the bottom. This difference increases with a sample thickness.
With large samples, the exposed surface area provides a great deal of
heat loss through radiation; therefore the exposed surface is cooler
than the bottom, which is in contact with the crucible. Also, higher
chamber pressures causes more heat loss through convection.
HS 1500 contains MgO crucibles with Pt wire in its centre and Pt paint
on top and bottom. The Pt wire leeds heat from the crucible bottom to
its top (sample), thus the wire and its surrounding has slightly higher
temperature compare with the rest of the crucible.
Both Heating stages have the same heater design which is intended
to minimize a sample temperature discrepancies. The heater is
essentially a micro-furnace which provides heating from the bottom
and from the sides.
To obtain accurate heat conduction through the sample, it should be
cemented or otherwise firmly mounted onto the crucible with a good
thermal contact. Use conductive carbon paint for temperatures below
900 °C; and a high temperature adhesive for temperatures above
900 °C.
FIGURE 9-38 TEMPERATURE AND CONDUCTIVITY