Degradation Analysis of Lubricants Based on ASTM E2412 by Fourier Transform Infrared Spectrophotometer FTIR

Significance of the Topic

Engine lubricants are vital for maintaining machinery performance by reducing friction, dissipating heat, and preventing wear and deposits. Over time, lubricants degrade through oxidation, additive depletion, and contamination, leading to reduced engine efficiency and potential mechanical damage. Monitoring lubricant condition enables timely maintenance, extends equipment life, and reduces operational costs.

Objectives and Study Overview

This application note examines the degradation of automotive engine lubricants before and after use by applying Fourier Transform Infrared (FTIR) spectroscopy in accordance with ASTM E2412. Two commercial engine oils, designated A and B, were selected to identify chemical changes linked to oxidation, nitration, moisture absorption, and antioxidant consumption.

Methodology and Used Instrumentation

Transmission FTIR measurements were conducted using an IRSpirit™-T spectrophotometer equipped with a Pearl™ horizontal type liquid transmission accessory. This setup allows easy sample placement by dripping the oil between KBr windows, minimizes air bubble intrusion, and simplifies cleaning.

• Instrument: IRSpirit™-T FTIR spectrophotometer
• Accessory: Pearl™ horizontal liquid transmission (100 µm path length)
• Resolution: 4 cm⁻¹; Accumulation: 40 scans
• Apodization function: Happ–Genzel; Detector: DLATGS

Main Results and Discussion

Comparison of infrared spectra revealed that lubricant A, after 3,000 km and three months of high-rpm use, displayed increased bands characteristic of moisture uptake, carbonyl groups (oxidation), and nitro functionalities (nitration). Lubricant B, after 5,000 km and one year of general urban driving, showed diminished antioxidant additive peaks and signs of nitration, while oxidation bands around 1,800–1,670 cm⁻¹ remained relatively unchanged, indicating additive protection against oxidation.

Benefits and Practical Applications

This FTIR approach requires no sample pretreatment and provides rapid, multi-parameter assessment of lubricant health. The Pearl™ accessory ensures consistent optical path length and ease of handling, improving laboratory throughput and reproducibility. Compliance with ASTM E2412 facilitates standardized lubricant monitoring in quality control and research environments.

Future Trends and Potential Applications

Emerging developments may focus on inline FTIR sensors for continuous lubricant monitoring, advanced chemometric models for automated degradation diagnostics, and integration with complementary techniques such as gas chromatography and ICP-AES to deliver comprehensive multiparameter analyses in real time.

Conclusion

FTIR spectroscopy using a horizontal transmission accessory offers a fast, reliable method for detecting key chemical changes in engine lubricants. By adhering to ASTM E2412, this technique supports proactive maintenance practices, enhances engine reliability, and contributes to more efficient asset management.

Reference

Shimadzu Corporation. Application Note No. A603: Degradation Analysis of Lubricants Based on ASTM E2412 by FTIR. First Edition, November 2019.