Tribological Properties of Borate-Based Protic Ionic Liquids as Neat Lubricants and Biolubricant Additives for Steel-Steel Contact
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Synthesis of PILs
2.3. Thermal Analysis, Rheology, and Solubility
2.4. Friction and Wear Tests
- = wear volume
- = stroke length
- = contact ball radius
- = wear track width
- = wear track depth
3. Results
3.1. Thermal Analysis, Rheology, and Solubility
3.1.1. Thermogravimetric Analysis
3.1.2. Solubility
3.1.3. Rheology
3.2. Friction and Wear Tests
3.2.1. Ionic Liquids as Neat Lubricants
3.2.2. Ionic Liquids as Biolubricant Additives
4. Conclusions
- The thermal stability of the PILs increased with the molecular weight, following the series IL1 < IL2 < IL3 < IL4. Thermal stability of the mixtures was slightly reduced by the addition of the PILs.
- IL2 and IL4 showed higher viscosity than IL1 and IL3, which was attributed to a closely packed structure for that particular cationic configuration.
- BO + IL mixtures increased the viscosity of the base oil, except for BO + IL1, due to the poor solvation of the blend illustrated during the solubility study.
- IL1 and IL3 exhibited shear-thinning rheological behavior linked to the breakage of nanostructures when confined with stainless steel plates. This phenomenon was diminished in the case of IL2 and disappeared with the increment of the alkyl chain with IL4.
- When tested as neat lubricants, IL2 and IL3 prevented wear, as only superficial scratches were observed. Additionally, the PILs greatly reduced friction by 20–30% compared to BO. In the case of IL1, a solidification process led to the squeeze-out phenomena of the film.
- The 1 wt.% PILs mixtures reduced friction by 20–25% compared to BO. BO + IL1 reduced wear by 96% compared to BO and by 48% compared to BOA, performing the best among ionic liquids studied as biolubricant additives.
- The proficient performance of these PILs was mainly attributed to an adsorption phenomenon rather than a tribochemical reaction.
Supplementary Materials
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Code | R1 | R2 | Cation * | Anion * | Name |
IL1 | Ethanolamine 1,2-dodecanediol borate | ||||
IL2 | N-methylethanolamine 1,2-dodecanediol borate | ||||
IL3 | N’N-dimethylethanolamine 1,2-dodecanediol borate | ||||
IL4 | N-butylethanolamine 1,2-dodecanediol borate |
Parameter | Value |
---|---|
Normal load (N) | 3 |
Max. Hertz contact pressure (GPa) | 2.36 |
Stroke length (mm) | 3 |
Frequency (Hz) | 3 |
Duration (s) | 3600 |
Sliding speed (m/s) | 0.03 |
Sliding distance (m) | 64.8 |
Lubricant | Tonset (°C) |
---|---|
BO | 348.7 |
BOA | 348.5 |
IL1 | 268.0 |
IL2 | 273.6 |
IL3 | 293.7 |
IL4 | 263.1 |
BO + IL1 | 330.5 |
BO + IL2 | 324.5 |
BO + IL3 | 344.0 |
BO + IL4 | 349.2 |
Dynamic Viscosity (Pa s) | Arrhenius Parameters | |||||
---|---|---|---|---|---|---|
Lubricant | 25 °C | 40 °C | 100 °C | A (106) (Pa·s) | Ea (kJ/mol) | r2 |
BO | 0.0644 | 0.0392 | 0.0088 | 1.82 | 26.02 | 0.997 |
BOA | 0.0708 | 0.0427 | 0.0096 | 2.30 | 25.68 | 0.998 |
IL1 | 0.5294 | 0.2280 | 0.0260 | 2.27 × 10−2 | 42.02 | 0.998 |
IL2 | 97.48 | 24.42 | 0.1607 | 1.75 × 10−5 | 72.48 | 0.998 |
IL3 | 2.723 | 0.8661 | 0.0194 | 1.11 × 10−5 | 65.20 | 0.999 |
IL4 | 13.65 | 4.938 | 0.0556 | 2.86 × 10−4 | 61.34 | 0.992 |
BO + IL1 | 0.0461 | 0.0281 | 0.0060 | 1.32 | 25.95 | 0.995 |
BO + IL2 | 0.0862 | 0.0512 | 0.0113 | 2.00 | 26.44 | 0.997 |
BO + IL3 | 0.0735 | 0.0439 | 0.0096 | 1.70 | 26.47 | 0.997 |
BO + IL4 | 0.0811 | 0.0491 | 0.0109 | 2.42 | 25.84 | 0.998 |
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Sierra, A.; Coleman, M.G.; Iglesias, P. Tribological Properties of Borate-Based Protic Ionic Liquids as Neat Lubricants and Biolubricant Additives for Steel-Steel Contact. Lubricants 2022, 10, 269. https://doi.org/10.3390/lubricants10100269
Sierra A, Coleman MG, Iglesias P. Tribological Properties of Borate-Based Protic Ionic Liquids as Neat Lubricants and Biolubricant Additives for Steel-Steel Contact. Lubricants. 2022; 10(10):269. https://doi.org/10.3390/lubricants10100269
Chicago/Turabian StyleSierra, Alfonso, Michael G. Coleman, and Patricia Iglesias. 2022. "Tribological Properties of Borate-Based Protic Ionic Liquids as Neat Lubricants and Biolubricant Additives for Steel-Steel Contact" Lubricants 10, no. 10: 269. https://doi.org/10.3390/lubricants10100269