Thermocouples are usually made of precious or precious metal alloys and are expensive. It is easy to lead to the loss of function and the reduction of service life if you do not pay attention to maintenance of thermocouples, so people hope that platinum-rhodium thermocouple can prolong its working life to save the production cost. If you operate as required and maintain it regularly, you can make the best use of the thermocouple to reduce the loss. The routine maintenance techniques of the platinum-rhodium thermocouple are as follows.
The oxidation capacity of acid can be used to remove the organic matter on the surface of the platinum-rhodium thermocouple and other impurities that can be dissolved by acid. Place the platinum-rhodium thermocouple disk into a circle about 80mm in diameter in a beaker and then immerse it in 30 to 50 percent (by volume ratio) of chemically pure dilute hydrochloric acid (or dilute nitric acid) for an hour, then put it in a beaker and boil it in distilled water several times to remove the acid completely. The purpose of pickling is to clean some of the organic compounds and oxides on the electrode surface.
Sodium borate removal
The used platinum-rhodium thermocouple should be washed with sodium borate after pickling. First, hung the platinum-rhodium thermocouple electrode on the platinum wire annealing on ark, then adjust the current to make the hot thermocouple to 1100 ° C; touch the hot spot with a lump of sodium borate to make the boric acid whose solution flows down the electrode, and then slowly reduce the current after cleaning; finally, cut off the power and place the 80mm circle into the beaker, and boil it in distilled water several times to precipitate the borates completely. The main purpose of sodium borate removal is to remove metals and oxides that are insoluble in hydrochloric acid.
The purpose of annealing is to remove the internal stress in the electrode and to improve the crystal phase and the stability of the platinum-rhodium thermocouple, which can be achieved by proper annealing temperature and annealing time. Usually, there are two methods of electric annealing and furnace annealing.