How to clean platinum rhodium S-type thermocouple correctly？

How to clean platinum rhodium S-type thermocouple correctly？

The high temperature precious metal S-type platinum rhodium thermocouple is a commonly used temperature measuring instrument, which has certain applications in many fields. The purpose of cleaning high-temperature precious metal platinum-rhodium thermocouples is to remove surface dirt, improve their thermocouple characteristics, and extend the life of thermocouples. So do we understand the maintenance and cleaning methods of high-temperature precious metal platinum-rhodium thermocouples?

1. Annealing: Annealing is to remove the internal stress in the electrode, improve the crystal phase of the high-temperature precious metal platinum-rhodium thermocouple, and improve the stability of the high-temperature precious metal platinum-rhodium thermocouple. Through proper annealing temperature and annealing time, the desired goal can be achieved. Generally, there are two annealing methods: energized annealing and furnace annealing.

2. Pickling: Use the oxidizing power of acid to remove organic matter on the surface of the high-temperature precious metal platinum rhodium thermocouple and other impurities that can be dissolved by acid. Put the high-temperature precious metal platinum rhodium thermocouple disc into a circle with a diameter of about 80mm and place it in a beaker, introduce 30%-50% (according to the volume ratio) chemically pure dilute hydrochloric acid (or dilute nitric acid) for one hour, take it out and put it in the beaker. Boil in distilled water several times to completely remove the acid. The purpose of pickling is to clean some organic matter and oxides on the electrode surface.

3. Sodium borate cleaning: the used high temperature precious metal platinum rhodium thermocouple should be cleaned with sodium borate after pickling. First, hang the high-temperature precious metal platinum rhodium thermocouple electrode on the platinum wire on the annealing cabinet, and then adjust the current to make the thermocouple pole burn to 1100°C. Touch the hot spot with block-shaped sodium borate to make the boric acid solution flow down the electrode. After cleaning, slowly reduce the current, and then cut off the power supply. Remove the plate into a circle with a diameter of 80 mm and place it in a beaker, and boil it several times with distilled water. , The borate is completely precipitated.

The purpose of sodium borate removal is mainly to affect metals and oxides that are insoluble in hydrochloric acid. Because the sodium borate melts at high temperature and the metal impurities and metal oxides attached to the high-temperature precious metal S-type platinum rhodium thermocouple hot electrode form a boron glass solution, which flows away along the hot electrode to achieve the purpose of removing dirt on the outer layer of the electrode.