Abstract
A new method to estimate the degree of a corrosion attack on silver taking into account seasonal variations of temperature and relative humidity was developed in order to evaluate the corrosivity of an atmospheric environment. In addition to measuring the thickness of corrosion product on silver using a resistance-type corrosion sensor, temperature and relative humidity were measured in a machine room for a certain period. Based on these measured data, we investigated a method to estimate the thickness of corrosion product on silver that forms in one year. First, the temperature in the machine room was estimated for a one-year period by adding the seasonal component of temperature at the nearest monitoring site of the Japan Meteorological Agency (JMA), the difference in temperature between the machine room and the JMA site, and the irregular component of temperature in the machine room. The relative humidity was estimated by substituting the estimated temperature in the machine room and the absolute humidity at the JMA site into the Sonntag formula. Second, a corrosion gas coefficient was determined by using the thickness of corrosion product on silver and the temperature and relative humidity in the machine room for the measurement period. Third, the thickness of corrosion product on silver for a unit period was calculated by substituting the corrosion gas coefficient and the estimated temperature and estimated relative humidity for a unit period into the already proposed estimation equation of silver corrosion under a constant environment. The thickness of corrosion product on silver for a yearly period can be estimated by accumulating the thickness of corrosion product on silver for the unit period. With a preferable measurement period of three months, except for the winter season, the yearly thickness of corrosion product on silver can be estimated within a 10 percent margin of error.
