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markx
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Quote: Originally posted by Hennig Brand  | | You have built some very neat things. I really like the drop hammer/impact sensitivity tester. For the melting point apparatus I would suggest a
block, or cylinder would even be better, of aluminum with no fins and maybe even some added insulation would be a good idea. What works best is a
large thermal mass. A large thermal mass resists sudden changes in temperature (the thermal flywheel effect), which is what works best when trying to
get an accurate value for melting point. Fins are designed to allow the heat sink to transfer heat/energy to the surroundings as quickly as possible.
I see that you did already say that it wasn't the best choice of heat sink, but I thought I would comment anyway. |
You are absolutely right....hence I did reconstruct the contraption to a more suitable form for the task at hand:
http://www.sciencemadness.org/talk/viewthread.php?tid=250&am...
I cut off the fins and added an insulating layer of wood (again perhaps not the best of choices for temperatures upwards of 280C) around the block of
remaining aluminium. Works like a charm now 
Exact science is a figment of imagination.......
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Hennig Brand
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Nice looking setup you got there. I have been using a three or four hundred gram block of aluminum heated with a low flame on a propane torch and a
thermocouple probe to measure temperature. Not very high tech, but with a good size piece of aluminum (fairly large thermal flywheel) and the
thermocouple probe calibrated against a decent mercury thermometer the setup gets me reasonably close. Your setup looks quite accurate and
sophisticated, nice work.
"A risk-free world is a very dull world, one from which we are apt to learn little of consequence." -Geerat Vermeij
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markx
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| Quote: Originally posted by Hennig Brand | | Nice looking setup you got there. I have been using a three or four hundred gram block of aluminum heated with a low flame on a propane torch and a
thermocouple probe to measure temperature. Not very high tech, but with a good size piece of aluminum (fairly large thermal flywheel) and the
thermocouple probe calibrated against a decent mercury thermometer the setup gets me reasonably close. Your setup looks quite accurate and
sophisticated, nice work. |
The PID controller+SSR combo that I constructed (I really can not remember for what purpose exactly) has so far proven to be the most versatile piece
of equipment ever. I can use it to control basically any equipment that works off the 220V line and can be PWM-d. Starting from soldering iron and
ending up with the HMX reactor or a melting point apparatus
But the key is to properly calibrate the sensor against a reliable standard if one wishes to get precise results. The k type thermocouples can be off
several degrees, especially in the low end spectrum (say below 100C ). Always calibrate against the desired setpoint...the fact that the sensor is
true at 350C does not mean that it will be true at 70C.
Exact science is a figment of imagination.......
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Hennig Brand
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I recently calibrated one of my k type thermocouple probes and meters against a good quality fisher scientific mercury thermometer at about 80C in hot
water. I was aiming for about the melting point of TNT. It was off (low) somewhere between 2 and 2.5C. I have tested the mercury thermometer in
boiling water too just to make sure it showed 100C. I have some cheap alcohol filled thermometers that read high by as much as 5C in boiling water. I
don't mean to imply that only mercury thermometers are accurate however. I was going to go with an electrical resistance heater too, because of the
great control which can be obtained, but I never got around to it yet.
"A risk-free world is a very dull world, one from which we are apt to learn little of consequence." -Geerat Vermeij
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PHILOU Zrealone
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This temperature problem is why in lab we usually do mp testing in parallel inside glass capilarity tube.
Pure sample (or other compound with identical or close mp) vs the unknown/to test sample.
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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nzyzaw
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please, why crude HMX and RDX mixture dissolved in hot water and don't crystallization
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nzyzaw
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[Edited on 25-10-2018 by nzyzaw]
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