Summary for red oxide under acidic conditions Discussion
red oxide under acidic conditions is the core question here: Richard Greenwald reported that one oil sample tested extreme for red oxide (9/9) with no dark metallo-oxide and an acid number of 1.8 by ASTM D974, but a second sample from the same batch tested four weeks later showed black oxide at 5/10, red oxide at 0, and a much lower acid number of 0.374. He asked whether the small amount of acid could have turned the red oxide into black oxide and nearly neutralized the oil. The excerpt provided contains only the question and no posted answer, so no conclusion is given in the source. Based on the wording alone, the thread is about whether the change reflects a real chemical conversion, a sampling/lab difference, or another test-related effect.
Q. I tested an oil sample that had shown red oxide as extreme, 9 on a scale of 0 – 9. It also had dark metallo-oxide as 0. In addition, this oil had an acid number of 1.8 per ASTM D974.
I took an additional sample of the same batch and sent it to a different lab for testing 4 weeks after the initial sample had been sent in. The new results were 5 out of 10 for black oxide, and red oxide 0. The AN went down to .374.
Is it possible that the small amount of acid in the oil turned the red oxide to black oxide, and became almost neutralized?
Richard Greenwald
Lubricant Sales – Beachwood, Ohio USA
March 22, 2018