Testing Guidelines For CALCE Personnel

Recommended Test Procedures, Sample Preparations, and Guidelines

Sample size 0.1-3 mm thick

Samples near the minimum and maximum limits may not produce acceptable results, depending on type of material and thermal properties.  The analysis assumes that the surface reactions are instantaneous compared to the travel time of the heat wave thru the material.  Therefore for very thin samples (~ .1m) this assumption might be violated, if on the diffusivity of the material is high enough.   

0.5 diameter, graphite coating

As a matter of course, all samples should be coated with a graphite layer.  When specific heat is to be measured, all samples which are to be tested with and compared to the references sample should be coated as a group along with the reference sample to insure relatively uniform and consistent that the coating is between all samples.

Suggested procedure

1.      Place all samples together on a piece of paper

2.      Holding graphite spray can approximately 6” from samples, make several passes over the samples.  (Try to avoid “pooling of graphite on samples)  Repeat this process 3 to 4 times, waiting several minutes between coatings to allow graphite to completely fry. 

3.      Turn samples over and coat opposite side of samples in a like manner.

Gold Coatings

For most non-metallic materials, a metallic coating is needed.  Unless you specifically know that the material is opaque at the infrared wavelength,  it is a good idea to coat your nonmetallic samples. Any metal can be used, however gold or gold alloys are typical used due to their high thermal diffusivity. Vapor deposition will generally be less expensive but can cause damage to the samples if not done properly.

Liquid Nitrogen

Liquid nitrogen is required to cool the IR detector during testing.  Nitrogen can be obtained thru Keith Rogers or can be purchased thru the chemistry department (across the hall from the chemistry store).  Use small dewer that is maintained with the Holometric system. A half filled dewer will provide enough nitrogen for a full days test.  The system should be filled with nitrogen at least half an hour before testing.  One system is topped off with nitrogen; it should be good for 6 to 8 hours.