Why T321 Sulfurized Isobutylene Dominates Sulfur-Based EP Additives

Sulfur-based EP additives and anti-wear additives are among the oldest and most widely used categories, particularly suited for high-temperature and high-load operating conditions. They act as the core additives in automotive gear oils, industrial gear oils, and metalworking fluids. Among them, T321 sulfurized isobutylene accounts for 50%–70% of applications in gear oils.

 

What are Extreme Pressure and Anti-Wear Additives?

Extreme pressure and anti-wear additives (EP/AW additives) are functional additives commonly used in lubricating oils and greases. They are designed to prevent scuffing, galling, wear, and seizure/welding on metal friction pairs, making them particularly suitable for harsh operating conditions involving high speeds, raised temperatures, and heavy loads. Their primary function is to reduce friction resistance, lower wear and scuffing, and improve the load-carrying capacity of lubricants.

 

Chorus provides a wide variety of extreme pressure additives for applications spanning engine oils, gear oils, hydraulic fluids, compressor oils, metalworking fluids, lubricating greases, and other industrial lubricants-all at competitive prices. Feel free to contact us for the latest quotes.
 

 

Why are sulfur-containing extreme pressure and anti-wear additives used in gear oils?

 

Gear meshing operates under "direct metal-to-metal contact, flash temperature, and shock" conditions, which are essentially boundary lubrication under high temperature and high pressure. Mineral oils lack chemical reactivity on their own, whereas sulfur-containing extreme pressure and anti-wear additives react with ferrous metal surfaces to form an iron sulfide intermediate layer that prevents direct contact, thereby improving surface smoothness and reducing wear.

Moreover, the higher the active sulfur content in the molecule, the more readily it reacts with the metal surface, exhibiting extreme pressure (anti-seizure) performance that surpasses standard anti-wear properties. With a sulfur content as high as 40%–48%, sulfurized isobutylene (SIB) functions primarily as an exceptional anti-scuffing agent in gear oils.

What are the advantages of sulfurized isobutylene T321 in gear oils?

Anti-Scuffing Under High-Speed Impact Loads

Sulfurized isobutylene T321 features a high sulfur content and excellent extreme pressure (EP) activity, delivering outstanding anti-scuffing performance, particularly under high-speed impact loads.

 

Gear meshing is a contact process characterized by high speeds and impact loads under boundary lubrication conditions.

Under the instantaneous high temperature (flash temperature) generated at the gear tooth contact surfaces, the C–S bonds in T321 break down to release active sulfur, which then reacts with the iron surface to form an iron sulfide (FeS) film. This film melts at approximately 1200 °C, maintains its lubricating function at 800 °C, and is capable of self-healing after being sheared off.

Balance Between Extreme Pressure Performance and Corrosiveness

Typically, high sulfur content implies high corrosiveness. However, sulfurized isobutylene maintains moderate reactivity even at sulfur contents exceeding 40%, achieving a copper corrosion rating of only Grade 1 (100 °C, 3 hours). Through process design, T321 ensures sulfur remains primarily bound in C–S bonds (moderate bond energy, ~250 kJ/mol). These moderate C–S bonds are stable at 100–200 °C and exhibit low corrosiveness to copper and non-ferrous metals, breaking down to provide extreme pressure protection only under flash temperatures above 300 °C-striking an excellent balance between EP performance and corrosion resistance.

High Oil Solubility and Blending Stability

It demonstrates superior oil solubility in mineral oils, dissolving in base oils at high concentrations to form transparent, homogeneous, and stable true solutions. It remains non-stratified, non-precipitating, and non-cloudy during long-term storage and under low-temperature conditions.

Highly Adjustable Reactivity

Product sulfur content can be adjusted by controlling sulfur activation temperatures, sulfur-to-olefin ratios, and reaction temperatures. The activation temperature influences the cleavage sites of sulfur chains, resulting in different numbers of linked sulfur atoms in the final product. This yields extreme pressure responses ranging from "mild" to "aggressive," catering to diverse application fields.

Process & Compliance Advantages: Clean, Ashless, and Low Dosage

Ashless Type: Free of metals, leaving no residue accumulation.

 

Light Color & Low Odor: High-pressure process products surpass traditional two-step methods, making them ideal for formulations with aesthetic requirements.

 

Cost-Efficient Dosage: Treatment rates of 1.5%–5.0% cover the full spectrum of requirements from industrial gear oils to API GL-5 specifications, offering better overall cost efficiency than other EP additives.

 

Chorus Sulfurized Isobutylene T321 is a high-sulfur, ashless extreme pressure and anti-wear additive for gearboxes subjected to shock loads and is widely used in automotive gear oils, industrial gear oils, and other industrial lubricants. Manufactured through a high-pressure process, this chlorine-free product delivers superior formulation compatibility. Contact us today to request detailed product specifications.