BS in Materials Engineering
Materials Engineering Department
Six steel samples each were twin wire arc sprayed with Hastelloy C-276 or Nickel-Shield 200 coatings approximately 0.020″ thick. These samples were then cut into 3″ by 3″ squares. A 2″ diamond grit hole saw was used to abrade and polish to a smooth surface a ring in the middle in order to get an O-ring mechanical seal. The samples were then weighed and loaded into a jig that started from the bottom up with a stainless steel plate, then the sample, then a Viton O-ring, a ¾″ thick glass plate with a 1 3/4″ hole cut in it, another O-ring, and then another stainless steel plate. The plates were bolted together tightly in the corners. This setup was designed to expose only the top surface of the coated sample to sulphuric acid, which is an accurate representation of an application of the coating. The samples were tested with 98% concentrated sulphuric acid at room temperature, 100⁰F, and 200⁰F over a period of 2 weeks. The corrosion rates could not be calculated accurately due to leakage of the sulphuric acid onto the sample. However, there were macroscopic signs of corrosion product on the Ni-Shield 200 samples that were not present on the Hastelloy C-276 samples. The microstructures of both samples also showed signs of surface attack. While a precise corrosion mechanism could not be identified, the Ni-Shield 200 sample did react with the sulphuric acid enough to warrant further study into its mechanisms and methods.