Question 1

Which antioxidants work best with PAG base oils?

Accepted Answer

PAGs respond exceptionally well to both phenolic and aminic antioxidants. Phenolic antioxidants provide excellent radical-scavenging below 120°C. For high-temperature applications exceeding 120°C, aminic antioxidants or synergistic phenolic-aminic blends are required to maintain thermo-oxidative stability and prevent varnish.

Question 2

What is the typical treat rate for lubricant antioxidants?

Accepted Answer

Standard treat rates range from 0.25% to 2.0% by weight. Light-duty applications like turbine oils use 0.25% to 0.5%, while demanding high-temperature gear oils or compressor fluids may require up to 1.5% or 2.0% of a synergistic blend.

Question 3

Why are aminic and phenolic antioxidants used together?

Accepted Answer

Combining them creates a powerful synergistic effect. The phenolic antioxidant acts as a sacrificial hydrogen donor that continuously regenerates the aminic radical during the radical-scavenging process, extending the active lifespan of both additives.

Question 4

How does temperature affect antioxidant selection in industrial lubricants?

Accepted Answer

Operating temperature is the primary driver. Phenolic antioxidants are effective up to 120°C but degrade at higher temperatures. Aminic antioxidants possess higher thermal stability and become more effective above 120°C, making them essential for extreme-temperature applications.

Antioxidant Selection Guide for PAG Lubricants