Electric and electromagnetic tests, speaking about material characterization, are in many cases specific for the final application Polymers and plastics in general, are usually classified as 'electrical insulator'. Tests are for this designed for low resistivity materials. On a material, we can generally distinguish between volume tests (bulk) or surface tests for continous or alternate currents. On ther other side there are technological tests on products, as example for electrical cables. Generally speaking, we can divide the analysis in 'low voltages tests' (from 0 to 380 Volts) and 'high voltages tests'.
VOLUME CONDUCTIVITY MEASUREMENTS
Sample preparation and conditioning
Preparation and conditioning are fundamental factors for all electrical characterization measurements. Tests need to be carried out on many specimens, in order to measure reproducibility of results. It is useful to remember that measures have to be done in a controlled atmosphere, with standard humidity and temperatures. If you compare data obtained in a not controlled room, you are loosing time.
We stress on the importance of preparation and conditioning of specimens. Is important to consider a climatic chamber in order to test with different conditions of temperature and humidities. This chamber has to be sufficient in dimension for our equipments and specimens. The measure needs tension/current alimentation and a sensible tester, a pc controlled multimeter is the best. Electrodes are fundamental and specific for specimens. For set-up of experiment an oscilloscope is surely useful.
If specimens are careful prepared, adequately conditioned and connected to electrodes, the most is done: attention must be then put on control of tension and currents, for transient and stable states. The us of pc controlled instrumentation allows a knowledge of what effectively happens to the material.
SURFACE CONDUCTIVITY MEASUREMENTS
Preparation and testing of specimens
Same consideration for volume measurements are valid: preparation and conditioning of specimens are of fundamental importance for the tests. Meausures have to be carried out on different specimens, to test reproducibility of measure.
A climatic chamber could be useful, if you need to do tests in a controlled environment, and the chamber must be great in order to contain the instrumentation and specimens. Measure instrumentation is similar to that for volume measurements. Electrodes are obviously different and specific.
HIGH VOLTAGES TESTS
Preparation and conditioning
With high voltages, you need to measure the tension on which samples are broken by current. For preparation you need conditioning and control care as for other tests, but you have to take care of the high tensions: for this reason the measurements take more time than bulk/surface measurements and mistakes costs more.
Alimentation of current must give up to 100000 Volts. Dimensions and costs are important. Safety characteristics must be adequate; we can consider to buy these facilities only if we need intense measurement's sessions; if not, it would be better to give outside measurements.
The results are number of electrical variables (for example the tension when the specimen breaks). It could be important to analyze the specimens during the tests, and after the ruptures. Currents and tensions can be dangerous: keep attention!
Some measurements are specific. Without entering in details, standard recomandations are:
- perfect preparation and conditioning of specimens.
- if we can chose, we have to prefer low tension and currents tests
- Safety first ! For electrical tests is fundamental.
Dr. Maurizio Veronelli - Specialist in Polymer Science
RDLab137 srl - Milano
Last revision: 01/25/2017