4 | CONCLUSIONS
CaCl2 · 6H2O is a promising PCM for low temperature heat storage, which can be utilized in improving the efficiency of air-cooled power plants. For this hydrated salt to be used, any container (encapsulation material) used to contain it must resist corrosion by the salt throughout the system’s life. Long-term corrosion tests of CaCl2 · 6H2O in contact with four common metals (copper, low carbon steel, Al 5086, and Al 6061) were performed. The corrosion tests were carried out for four test periods (2, 4, 8, and 16 weeks), and three temperature conditions (30, 50, and 80 °C). The important findings of these tests are as follows:
(1) Effect of time on corrosion rate. For all temperature conditions, the corrosion rates of carbon steel, Al 5086, and Al 6061, were found to decrease as test time increased. This was expected as it is well known that corrosion rates begin to slow down as a protective oxide layer forms on the surface of the metal. Interestingly, copper did not follow this trend, with the corrosion rate of copper increasing with time for the 80 °C temperature condition.
(2) Effect of temperature on corrosion rate. While temperature is known to accelerate corrosion in many situations, its impact on the corrosion rate of metals immersed in CaCl2 · 6H2O has not been reported in the literature. Testing of the four metals at 30, 50, and 80 °C confirmed the hypothesis that an increase in temperature results in an increase in the corrosion rate for each of the metals. Plotting the natural log of the corrosion rate versus 1/T, these test results were shown to follow an Arrhenius relationship, with apparent activation energies for the corrosion reactions being found.
