Thermal Diffusivity and the Laser Flash Method
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- Turn on the machine and wait for the warm-up process to end (approximately 2 hours).
- Fill up the detector compartment with liquid nitrogen using a small funnel until the nitrogen vapor can be seen coming from the detector. Let the liquid settle until there is no more vapor coming out and close the detector.
- Measure the thickness of your sample with a micrometer over several spots and calculate the average thickness and the standard deviation. The edges of the sample should be between 6mm and 25.4mm, with a flat geometry either round or rectangular. Additionally, the thickness of the sample should be uniform and between 1mm and 4mm. High thermal diffusivity samples work best with thicker samples. Here, we are using a standard iron disc sample.
- In order to maximize the absorbance of the sample and ensure uniform emissivity, spray a thin coating of graphite on the sample using colloidal graphite. Repeat three times allowing sample to dry between passes. Once done with the first side, carefully flip the sample and spray the other side.
- Once dry, place the sample in the bottom half of the small sample support and cover it with the top half of the sample support.
- Open the furnace by simultaneously pressing the safety button on the right side of the machine and the button on the front side of the machine labeled furnace with a down arrow. Rotate the detector around clockwise looking down in order to have more mobility around the furnace.
- The sample stage in the furnace has three locations designed to hold the samples. Put the sample support containing the sample in one of the three locations (take note of which one) then realign the detector and the furnace before closing the furnace. To do so, press the safety button and the labeled furnace with an up arrow.
- Before turning on the vacuum pump, make sure that the vent valve located to the right behind the detector is closed. Once closed, turn on the vacuum pump. Slowly open the vacuum valve and pump a vacuum until the pressure indicator light on the front side of the machine is stabilized to its lowest level. A vacuum is pulled to remove all air from the chamber before purging with inert gas.
- Open the regulator on the Argon cylinder and make sure the pressure is set between 5 psi and 10 psi. Close the vacuum valve, open the backfill valve then press the purge button to purge the sample space so there is no trapped gas from the sample.
- Repeat steps 8 and 9 three times to make sure that there is no air left in the chamber. This is to eliminate the chance of oxygen, nitrogen or other air constituents reacting with compounds present at the surface of the sample, particularly at elevated temperatures.
- The furnace should be left with a very slight positive pressure from the purge gas in order to ensure that air does not flow back into the furnace.
- Launch the machine's software from the desktop icon labeled "LFA 457". Select Service → Hardware Info → Switches then click the box to turn on the purge. This should turn on the Purge light on the front of the LFA-457.
- Open the vent valve while the purge light is on.
- Open a database or create a new one and enter all the necessary information, including all the necessary fields in the tabs General, Autosampler Position, Initial Conditions, Temperature Steps & Final Conditions.
- If the experiment takes longer than 8 hours, the detector will need to be filled up again. This might happen, especially if multiple samples are being run.
- Samples are then removed in a similar fashion to how they were inserted. The software automatically displays the results, here shown from an iron standard material.
Source: Elise S.D. Buki, Danielle N. Beatty, and Taylor D. Sparks, Department of Materials Science and Engineering, The University of Utah, Salt Lake…
本视频中的章节
0:07
Overview
1:35
Principles of the Laser Flash Method
3:35
Laser Flash Measurement
7:31
Analysis of the Data
8:41
Applications
10:01
Summary