Question

Electronic materials corrode in the presence of condensed water vapor and atmospheric pollutants. The corrosion rate of gold was measured to be 435 mg/m2 -day in an environment consistening of 95% relative humidity and SO2 and NO2 pollutants. The atomic weight of gold is 197.0 g/mol and its density is 19.3 g/cm3 . a) What is the corresponding corrosion current density in amperes per square meter for the following anodic reaction: 3 Au Au e3 → ++ − b) What is the penetration rate in millimeter per year? c) Based on the penetration rate calculated above, how long will it take to corrode through a gold film which is 0.5 mm in thickness? d) Based on the “Severity of Corrosion Rates” chart (Lecture 15 ppt), is this an acceptable rate of corrosion?

Electronic materials corrode in the presence of condensed water vapor and atmospheric pollutants. The corrosion rate of gold was measured to be 435 mg/m²-day in an environment consistening of 95% relative humidity and SO2 and NO2 pollutants. The atomic weight of gold is 197.0 g/mol and its density is 19.3 g/cm. a) What is the corresponding corrosion current density in amperes per square meter for the following anodic reaction: Au Au +3e b) What is the penetration rate in millimeter per year? c) Based on the penetration rate calculated above, how long will it take to corrode through a gold film which is 0.5 mm in thickness? d) Based on the "Severity of Corrosion Rates" chart (Lecture 15 ppt), is this an acceptable rate of corrosion?

Answer 1

Answer:

The anodic reaction for gold is

Au$\rightarrow$Au3+ +3e-

Given that,

Corrosion rate of gold = 435 mg/m2-day

Atomic weight of gold = a= 197 g/mol

Gold density =d= 19.3 g/cm3

Answer attached in the sheet
Answer: - The anodic rean for gold is a Au Außt +3é Given that, Corrosion rate (CR) of Au = 435 mg m2 day Atomic weight Au= a A4 = 1979 1mol Deustę Au = sau = 1913 gla3 We know that corrosion rate in mpy (myls per year) e 3 ആങ്ങ 534W CR (miles) = ☺ 8 At AY Where, w= Weight lossining A = Area in sq. inch t= time in hr 8 = density in gleuß we need to first convert given CR in persa inch hour 1550 inch 24hr of 4 – 495 any 49150 = 0.01169 Mohan -

Substitute Value of egr in egno Ramis ) = 534 W) SAU At Weight loss ng her Inche inch - 534x 0.01169 mg in 1913 glam CR = 0.3234 milslyn zupy or CR = 0.3 234 X 10 3 x Preh/yr = 0.323 4x10 3 x 25.4 milyr CR = 0.008214 mm/yr as finding Corrosion current density (coor) So mpy = So 0.129 x ax laor u nas Here, a= atonic Weight (glna) = corrosion curmat deaply MA n = no. of e 23 » 0.3234 rupy = 0.129 X 1979 x icon 3x 19.3 g/cm3 or Cuz 0.3234 20.43 89 (coor icons z 0.7368 MA Lost = 0.7368 X 166 A to 6 m2 = 0.7368A 22
corrosion rate rate in mm per year already solved in the problem above

C. Thickness of gold film given = 5mm

Time required to corrode = 5/0.008214

= 608.7 years

D. In the above calculation we have founded that the corrosion rate for gold is 0.3234 mpy or 0.008214 mm/year. Well if these two values are below the allowable limits then the rate is ok.