Grease Additives:
A Selection Guide.

A finished grease is one of the more elegant formulation challenges in lubricant chemistry. You're combining a thickener (which decides NLGI grade and drop point), a base oil (which decides viscosity and temperature range), and an additive system (which decides everything else: EP capability, water tolerance, oxidation life, corrosion protection). Get one variable wrong and the finished product fails in service.

This guide walks through additive selection for the five most common grease problems.

Problem 1: Shock Loads — EP Selection

Shock-loaded service (CV joints, hammer mills, mining drives) needs EP chemistry. The choice depends on the thickener:

• Lithium 12-OH — Standard sulfur-phosphorus EP works well. Treat 1.5–2.5% by weight.
• Lithium complex — Same chemistry, slightly higher treat (2.0–3.5%) because the complex thickener consumes some additive.
• Calcium sulfonate — The thickener itself contributes significant EP performance (the over-based calcium structure has anti-wear character), so additive EP can be reduced.
• Polyurea — More compatible with MoDTC (organic Mo) than with sulfurised EP, because the urea structure can react with aggressive sulfur. Mo-loaded polyurea greases for EV motor bearings are common.

Problem 2: Vibration & Wash-Out — Tackifier Selection

Open-air service (open gears, wire ropes, conveyor chains) loses grease to centrifugal flinging, vibration, and water spray. Tackifiers — high-MW polymers, usually PIB or polyacrylate — keep the grease in place.

PIB is more cost-effective and works in most thickener systems. Polyacrylate is more compatible with food-grade aluminium complex greases. Both should be added at 1–3% treat. Watch the bleed: too much tackifier reduces oil release and the grease will starve at the contact.

Problem 3: Slow Speed / Boundary Contact — Solid Additives

Greases for slow-speed boundary contact (heavily loaded slow-rotation joints, anti-seize compounds, open gears) benefit from solid additives that physically bridge the surfaces.

• MoS2 — Workhorse solid. Black colour. Treat 1–5%. Excellent for boundary lubrication; can corrode in wet service.
• Graphite — Higher temperature than MoS2; better for hot dry service. Black-grey colour.
• h-BN (hexagonal boron nitride) — White solid. Used in food-grade applications, optical equipment, or where MoS2 / graphite is undesirable for visual reasons.
• PTFE micropowder — Treat 2–5%. Excellent friction reduction; thermal limit ~250 °C.

Problem 4: High Temperature — Antioxidant Selection

For greases that see 150 °C + bulk temperatures (industrial bearings near hot processes, oven chains, wheel bearings under disc-brake heat), oxidation will eventually destroy the grease — soften the consistency, increase oil bleed, increase wear.

Combination AO works best: phenolic (low-MW, high activity at moderate temp) plus aminic (high-MW, persistent at high temp). Typical treat 0.5–1.5% combined. Watch compatibility with the thickener — aminic AO can react with carboxylic-acid thickener intermediates.

Problem 5: Corrosion — CI Selection

Greases that see water (marine, mining, automotive wash-down) need corrosion inhibitors targeted to the metals in contact.

• Ferrous protection — Alkenyl succinic acid (ASA) at 0.5–1.5%.
• Yellow metal (Cu, brass) protection — Tolyl-triazole derivatives at 0.05–0.2%.
• Marine salt spray — Use calcium sulfonate thickener (which itself is corrosion-protective) plus supplemental ASA.

The Disciplined Approach

The right way to formulate a grease additive package is bottom-up: define the service environment, identify the failure modes (wear, oxidation, corrosion, washout, slow-speed boundary), pick a single additive for each failure mode at minimum effective treat rate, then check interactions. Resist the temptation to over-treat. A grease with too many additives at too-high treat rates is more expensive, less consistent, and often performs worse than a leaner package.