ZACH WINGERTER AE4718 QUESTION 1: Type 1 can occur between 900º to 950º C in gaseous mixtures of air or pure oxygen. Type 2 can be observed from 650 to 750 C when the sulfite gas is present in the gaseous mixture. For type 1, it is initiated from a liquid sodium sulfate on the alloy. Oxygen and sulfur are then removed from this deposit and this causes formation of sodium oxide. Sodium oxide destroys the alloy’s protective oxide layering. This oxide can accelerate formation of nickel oxide and/or aluminum oxide. These products cause the alloy’s original oxide to travel from the inside of the alloy to the sodium sulfate, where they solidify as discontinuous particles. This whole process is unaffected by the gaseous composition. Type 2 also goes through acidic corrosion when in the 900 to 1000 C range. In type 2 the microstructure will have pits that go deep into the alloy. When the sulfite pressures are high, sulfide formation is prominent. Also cobalt ions can diffuse into the liquidus sulfate solution on the alloys surface. They then will harden and cause a discontinuity. This type depends on the S03 pressures.