Simulation of the Corrosion Caused by Water Soluble Salt in Dust

Dust may cause corrosion in humid environment. Investigation of water solution of dust collected from Beijing and Shanghai showed that SO₄^-2 and Cl^-1 were the major negative ions and Na⁺¹, K⁺¹, Ca⁺² dominated the positive ions. Obvious corrosion was formed on the coupon surface when such solution was dropped on. Artificial particles including NaCl, Na₂SO₄ and CaSO₄ are selected to simulate dust corrosion in laboratory. Solution of NaCl particles can cause serious corrosion on copper and gold plated coupon. However, the corrosion formed by Na₂SO₄ and CaSO₄ solution is too slight to be observed. The result is mainly affected by characteristics of negative ions in salt solution, as well as relative humidity and temperature. The characteristic factors include penetration, adsorption, solubility, and acidity of ions. An effective method to reproduce corrosion found on failed contacts in laboratory setup would be spraying NaCl solution with limited concentration on SiO₂ particles spread on coupon surface, thus producing SiO₂ particles surrounded with NaCl. It is shown that NaCl with 2.5% concentration would be the effective method from repeated experiments. It takes tenths or even hundreds of fretting cycles to push SiO₂ particles surrounded with corrosion product away. The number decreases to only several cycles for the particles without surrounded by corrosion products. It can be deduced that trapping effect of corrosion product on SiO₂ particles is not neglected, and particle corrosion should be included in laboratory simulation of dust particles.