Determination of Sulfur in Carbon Black

Significance of the Topic

Determining total sulfur in carbon black is critical for the rubber manufacturing industry. Sulfur content influences vulcanization, affecting rubber strength and brittleness. Accurate sulfur analysis in carbon black fillers enables formulators to optimize filler-to-sulfur ratios, improving product durability and performance.

Objectives and Study Overview

This application note evaluates the LECO S832 and S832DR macro combustion sulfur determinators for measuring sulfur in carbon black. Key aims include:

• Demonstrating precision and repeatability of sulfur measurements.
• Comparing single-cell (S832) and dual-range (S832DR) infrared detection performance.
• Validating compliance with ASTM D1619 Method A.

Instrumentation Used

The analysis employed:

• LECO S832 and S832DR macro combustion sulfur determinators.
• High-temperature horizontal ceramic combustion furnace (1350 °C) under pure oxygen.
• Non-dispersive infrared cells for SO₂ detection (single-path for S832; dual-path long/short cells for S832DR).
• Pre-baked ceramic combustion boats, crucible tongs, and spatula.
• LECO Certified Reference Materials (LCRM®) and NIST standards for calibration.

Methodology

Sample Preparation and Conditioning:

1. Dry carbon black at 125 ±5 °C for ≥1 hour; store in a desiccator.
2. Bake combustion boats at 1000 °C for ≥40 minutes; cool in a desiccator.
3. Weigh ~0.25–0.50 g sample into a boat; record mass and ID.

Instrument Setup and Calibration:

• Set furnace to 1350 °C; configure NDIR parameters (baseline delay 2 s, integration 120–360 s).
• Perform blank determinations (≥3 replicates) ensuring blank standard deviation ≤0.001 %S.
• Calibrate with five replicates of certified reference coal (1.08 %S) using a zero-forced linear fit.

Sample Analysis:

1. Load sample boats manually or via autoloader.
2. Run five replicates per sample.
3. Apply moisture correction if required (oven dry coal at 107 ±3 °C).

Key Results and Discussion

Typical replicate data showed high precision for both models:

• S832DR: average sulfur content ~1.43 %S in sample A (s=0.004 %); sample B ~1.19 %S (s=0.002 %); low-level sample C ~0.0114 %S (s=0.0002 %).
• S832: average ~1.44 %S in sample A (s=0.002 %); sample B ~1.20 %S (s=0.003 %); sample C ~0.0121 %S (s=0.0004 %).

The S832DR dual-range detector extended dynamic range without sacrificing sensitivity, ensuring reliable results across high and low sulfur levels. Both instruments met ASTM D1619 precision requirements.

Benefits and Practical Applications

The described method provides:

• Rapid, accurate sulfur quantification for process control in rubber compounding.
• Enhanced throughput with autoloading capability.
• Robust performance across diverse carbon black grades and sulfur concentrations.

Manufacturers can leverage reliable sulfur data to fine-tune formulations, reducing material waste and improving product consistency.

Future Trends and Opportunities

Advancements may include:

• Integration of automated sample handling for increased laboratory efficiency.
• Enhanced IR detection cell materials to further expand dynamic range.
• Software developments enabling real-time data analytics and cloud-based reporting.

Emerging regulatory demands for trace sulfur analysis will drive adoption of more sensitive detectors and streamlined workflows.

Conclusion

The LECO S832 and S832DR determinators offer precise, reproducible sulfur measurements in carbon black, fulfilling industry standards and supporting optimized rubber production. The dual-range S832DR model provides extended analytical range for varying sulfur levels, while both systems ensure consistent results and operational flexibility.

Reference

ASTM D1619 Method A: Standard Test Method for Sulfur in Petroleum Products (Lamp Method).
LECO Certified Reference Materials (LCRM®) for sulfur analysis.
LECO S832 Operator’s Instruction Manual.