Variable pathlength colorimetric spectroscopy of greases 0314021
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The document outlines an enhancement to the existing ASTM D7918 methodology for evaluating grease color using colorimetric spectroscopy. It introduces a new spectrometer that allows for variable pathlength assessment, addressing limitations from excessive absorbance in standard testing. Proposed next steps include integrating a new colorimeter, revising the ASTM standard, and continuing research on grease-specific color relationships.
Variable pathlength colorimetric spectroscopy of greases 0314021
- 1. Variable Pathlength Colorimetric Spectroscopy of Greases; an enhancement to D7918 Rich Wurzbach, MRG Labs York, PA, USA 12/12/18
- 2. Introduction Grease comes in a wide array of colors New and In-Service Grease can be evaluated Methodology introduced in ASTM D7918-15 iLab, Spectroscopy Box, Thin Film Substrate of grease
- 3. 3 CIE Color Space Chromaticity Diagram
- 4. 4 L* 40 50 60 70 80 90 a* 40 50 60 70 80 90 b* 40 50 60 70 80 90 CIE color space chromaticity diagram ASTM E308 Defines CIE Color a* is the change in color in the red spectrum. a* is positive in the red direction and negative in the green direction. b* is the change in color of the yellow spectrum. b* is positive in the yellow direction and negative in the blue direction. L* is the change in shade from white to black.
- 6. Grease Color Examples Three different greases Follows the patterns identified by the chromaticity diagram Colors Sample 1 2 3 Light…dark L* 48.6 63.5 61.3 Red…green a* 42.5 13.6 25.8 Yellow…Blue b* -14.0 -52.1 3.8
- 7. New Grease to End of Life 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 400 450 500 550 600 650 700 Wavelength (nm) Transmission New Fluid In-Service Fluid End of Life Fluid
- 8. Limitations of Method in D7918 iLab Spectrometer is called out in method iLab Spectrometer is no longer manufactured or supported A review of 5+ years of testing shows that the majority of in-service submitted grease samples are “flatlined” in the visible spectrum due to excessive absorbance at the 1mm nominal thickness of die extrusion
- 9. iLab following D7918: limited response, “black grease” #384
- 10. Grease under varying conditions New grease (Vigo) Significantly dark (3418) Moderately dark (384) Slightly dark (389) Significantly dark (391)
- 11. Improvements to D7918 Introduction of a new spectrometer Recognition of the limitations of method due to excessive absorbance Development of new method to allow variable pathlength of the grease sample Allows for a screening process for greases without requiring die extrusion High transmittance samples (light, new) and low transmittance samples (used)
- 12. Sample 3418; current D7918 result
- 13. Sample 3418: 0.035” path vs. 0.010” path
- 14. Sample 384; current D7918 result
- 15. Sample 384: 0.035” path vs. 0.010” path dE iLab 0.035 0.010 3418 139.1 50.0 38.3 384 209.9 45.6 13.8
- 16. Sample 2885; current D7918 result
- 17. Sample 2885: 0.035” baseline vs. inservice – “Red” grease
- 18. Next Steps Inclusion of new Grease Thief Colorimeter in current ASTM Inter-Laboratory Study (ILS) Submit research report and ballot revision to D7918, removing spectrometer-specific references, and retaining spectrum option Continue to find grease-specific data relationships to color-influencing parameter changes Continue to evaluate and create new color-based and grease specific criteria