Carbon Black At-line Characterization Using a Portable Raman Spectrometer

Significance of the Topic

Carbon black is a widely used reinforcing filler in tires and rubber goods, as well as a pigment in coatings and paper. Its molecular structure and degree of crystallinity directly influence its performance in end products. Rapid, at-line characterization of carbon black is critical for real-time process control, ensuring consistent quality and optimizing manufacturing efficiency.

Objectives and Study Overview

This work demonstrates the feasibility of portable Raman spectroscopy for fast at-line characterization of carbon black materials. The specific goal is to exploit the intensity ratio of the disorder-induced D-band and the graphitic G-band to assess structural order, estimate microcrystallite size, and monitor batch uniformity in an industrial setting.

Used Instrumentation

• i-Raman Plus portable Raman spectrometer with 532 nm excitation and 4.5 cm⁻¹ spectral resolution
• Video microscope sampling accessory for precise laser focus
• Back-thinned TE-cooled CCD detector (–2 °C) offering low dark noise and high quantum efficiency
• BWSpec software featuring adaptive iteratively reweighted Penalized Least Squares (airPLS) baseline correction and peak analysis

Methodology

• Three commercial carbon black samples analyzed at room temperature
• Spectral acquisition: 40 mW laser power, 120 s integration time
• airPLS baseline correction applied to remove fluorescence background
• Peak fitting to extract D-band (~1337 cm⁻¹) and G-band (~1580 cm⁻¹) intensities

Main Results and Discussion

• All samples exhibited clear D-bands (disorder) and G-bands (graphitic order)
• Measured ID/IG ratios: 0.81 (C1), 0.98 (C2), 1.23 (C3)
• ID/IG < 1 indicates more ordered microcrystalline structure; > 1 reflects higher disorder
• ID/IG inversely correlates with crystallite size above ~2 nm, enabling size estimation
• Consistent ratios across multiple spots demonstrate capability for batch uniformity assessment

Benefits and Practical Applications

• Rapid, non-destructive at-line or on-line measurement without sample preparation
• Real-time monitoring and control of carbon black production processes
• Quantitative assessment of crystallinity, structural disorder, and grain size

Future Trends and Possibilities

• Direct integration of portable Raman sensors into production lines for continuous monitoring
• Development of chemometric and machine-learning models for automated spectral interpretation
• Extension to other carbonaceous materials and composites in quality assurance
• Advances in spectral resolution and faster acquisition for high-throughput screening

Conclusion

Portable Raman spectroscopy reliably differentiates the disorder-related D-band and the graphitic G-band in carbon black, using the ID/IG ratio as a metric for structural disorder and microcrystallite size. Its high sensitivity, minimal sample preparation, and rapid at-line capability make it an invaluable tool for process control and product consistency in carbon black manufacturing.

References

1. D.T. Norman What Is Carbon Black Continental Carbon
2. S. Reich, C. Thomsen Phil Trans R Soc Lond A 2004 362 2271-2288
3. Y. Wang, D.C. Alsmeyer, R.L. McCreery Chem Mater 1990 2 557-563
4. F. Tuinstra, J.L. Koenig J Chem Phys 1970 53 1126
5. Z.-M. Zhang, S. Chen, Y.-Z. Liang Analyst 2010 135 1138-1146
6. R.P. Vidano, D.B. Fischbach, L.J. Willis, T.M. Loehr Solid State Commun 1981 39 341