Mechanism and rates of zinc corrosion in tropical countries

A five-nation study has investigated the rate and mechanism of atmospheric corrosion of zinc in Australia, Indonesia, Thailand, The Philippines and Indonesia. During this study, 18 sites were established in these countries including severe marine, severe industrial, industrial, marine/industrial, urban and highland sites. At each location, zinc plates were exposed for three-month periods and for one year. Further, a wide range of climatic and surface response parameters was measured at each location including gaseous SOx and NOx, airborne salinity, RH and temperature, rainwater composition, surface temperature and time of wetness (TOW). Exposed plates were used to determine mass loss, the nature of corrosion products (using FTIR and SEM-EDS) and the morphology of the corrosion layers (via SEM-EDS). Laboratory experiments were also carried out to elucidate the factors controlling oxide formation and stability. Regression analysis indicated that the prime factors controlling zinc corrosion were climatic (temperature and rainfall) and surface response (TOW), and surprisingly not pollutant levels. This was despite a high levels of variation in SOx levels across the sites. The possible reasons for this observation are discussed