# Eco-Friendly Illite as a Sustainable Solid Lubricant in Calcium Grease: Evaluating Its Thermal Stability, Tribological Performance, and Energy Efficiency

## TL;DR

Adding illite to calcium grease improves its thermal stability, reduces friction and wear, and makes it a more energy-efficient and eco-friendly lubricant.

## Contribution

The study identifies illite as an optimal solid lubricant additive for calcium grease at 0.1 wt.%, enhancing tribological and energy performance.

## Key findings

- 0.1% illite reduces friction and wear by 53% and 57%, respectively, compared to base calcium grease.
- Illite increases thermal stability up to 400 °C in nitrogen but promotes oxidative degradation in oxygen.
- Grease with 0.1% illite shows 93% higher frictional energy density and 47% lower wear intensity.

## Abstract

What are the main findings?
Optimal illite concentration (0.1 wt.%) reduces friction and wear by 53% and 57%, respectively, when compared to calcium grease without the additive.Calcium grease with 0.1% illite exhibited a 93% higher apparent frictional energy density, a 47% lower wear intensity, a 21% higher load–wear index, and 6% lesser current consumption than CG.Illite increases the thermal stability of calcium grease (CG) up to 400 °C in a nitrogen atmosphere, but promotes oxidative degradation in an oxygen atmosphere.Illite’s layered structure provides helpful anti-wear and friction-reducing characteristics.

Optimal illite concentration (0.1 wt.%) reduces friction and wear by 53% and 57%, respectively, when compared to calcium grease without the additive.

Calcium grease with 0.1% illite exhibited a 93% higher apparent frictional energy density, a 47% lower wear intensity, a 21% higher load–wear index, and 6% lesser current consumption than CG.

Illite increases the thermal stability of calcium grease (CG) up to 400 °C in a nitrogen atmosphere, but promotes oxidative degradation in an oxygen atmosphere.

Illite’s layered structure provides helpful anti-wear and friction-reducing characteristics.

What are the implications of the main findings?
Calcium greases containing illite particles can be a suitable alternative as an environmentally friendly grease.The findings support the goals of sustainable tribology and green engineering and promote the development of high-performance, eco-friendly green lubricants.

Calcium greases containing illite particles can be a suitable alternative as an environmentally friendly grease.

The findings support the goals of sustainable tribology and green engineering and promote the development of high-performance, eco-friendly green lubricants.

This study investigates the influence of the additive illite on the thermal, tribological, and energy efficiency characteristics of calcium grease (CG) at different concentrations (0.05 wt.%, 0.1 wt.%, 0.2 wt.%, 0.4 wt.%, 0.6 wt.%, and 0.8 wt.%). Thermo-gravimetric analysis under inert and oxidative atmospheres revealed that illite enhances thermal stability by increasing inorganic residue under N2, but promotes oxidative degradation under O2, limiting practical thermal use to around 400 °C. Grease with 0.1 wt.% illite (CGI2) performed well in tribological tests by reducing the coefficient of friction and wear scar diameter by 53% and 57%, respectively, compared to the base grease. Fleischer’s energy-based wear model showed that all grease samples operated within the mixed friction regime, and CGI2 exhibited a 93% higher apparent frictional energy density and a substantially lower wear intensity that was 47% lower than the base grease, indicating improved energy dissipation and wear resistance. All samples had the same weld load (1568 N), but CGI2 had a 21% higher load–wear index than the base grease in the extreme-pressure test, indicating better load-carrying capacity. In the energy consumption test, a 6% reduction in current consumption was observed in CGI2 in comparison with the base grease. Overall, illite at an optimal concentration significantly enhances lubrication performance, wear protection, and energy efficiency.