Testing during polishing

FIGURE 4.15 Pad condition during polishing tests with and without conditioning (from Ref. 24). 

After 32 days at 88°C in 33% Prestone II (a commercial engine coolant solution that contains silicate inhibitors), ZA-8 and Alloy 3, either as-cast or polished, showed no corrosion. Dynamic tests confirmed the suitability of ZA-8 at 118°C. ZA-27 displayed intergranular attack when tested as-cast but not when its surface was polished before testing. Possibly, the soft, zinc-rich phase had been smeared over the whole surface during polishing. 

A polished steel spindle is immersed into 300 mL of fuel maintained at 100°F (37.8°C). The fuel is continually stirred during the entire test period. Upon immersion for 30 minutes, 30 mL of distilled water are added to the fuel. After remaining in the fuel for an additional 3lh hours, the spindle is removed and the surface is rated for percent corrosion. 

Where possible the stray-light was estimated, the instrument readings were corrected for the turbidity of the water, and sample cells and caps were carefully matched, orientated and cleaned (the outside of the sample cell was polished with silicon), air bubbles were removed, etc. Note that during these tests turbidity-free water (as low as 0.02 FNU by filtering distilled water through a 0.45- xm-mcmbra n c filter) was used. Even under these conditions the instrumental error at low turbidity values was within +3% and +8% at a nominal value of 0.5 FNU and -1.3% to +10% at a nominal value of 1 FNU. 

---