The push-rod dilatometer is used to measure the expansion of a sample as compared to with a known expansion. Normal operation of the experiment would be to select a temperature range for the sample to be tested under. This could include heating the sample to a specified temperature, then holding that temperature for a given length of time, and the cooling the sample back down close to room temperature. These options can be specified for the sample to tested.
The temperature range of the push-rod dilatometer is designed to heat a sample from room temperature to 1500 degres celcius. This is done through the use of an electrical furnace surrounding the sample and NIST standard. One of the modifications made to the dilatometer by TPRL was to include routines for cryogenic studies. With this modifications a lower temperature of -190 degrees celcius can be obtained. This is done through the use of liquid nitrogen pumped into the testing enviroment.
The environment of the push-rod dilatometer can be from a total vaccum to a mixture of different gasses depending on the customers requirements.
The procedure to testing the sample consists of selecting an appropriate standard to measure against. The sample is measured to find its length. This is preffered to be 2.00 inches long. Please note that the precision length of the sample must be known to properly calculate the expansion. In the following picture, the copper rod is the standard that is used as a known linear expansion. The sample is next to the copper rod. The thin wire is a thermocouple to measure the temperature of the sample.
After the sample and standard are set in place, and the enclosing tube is placed over experiment, a vaccuum pump is turned on. After the pressure inside the tube is below 1 torr, the pump may be turned off and a inert gas of helium is feed in. The gas is to help prevent any possible reactions with the sample at the higher temperatures.
After the samples are set in the dilatometer, the computer is programmed to run the experiment. The computer controls the major functions of the experiment and records the temperature and the difference between the standards expansion and the sample. From this data the computer can calcuate the actual expansion of the sample. The measurements are taken through the use of an HP voltmeter. This information is then translated into the temperature and expansion difference.
Currently TPRL, Inc. is working on development of a molten metal thermal expansion of a sample. This process is currently being tested with a few samples actually tested for customers. This process is done through the use of a high temperature furnace with a window for optical measuremnts of the expansion. This expansion process is done strictly with optical measurements. The temperature measurements are done through the use of an optical pyrometer.
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