Sulfur and Carbon Determination in Soda-Lime Glass

Importance of the Topic

The control of sulfur and carbon levels in soda-lime glass directly affects glass quality characteristics such as bubble removal efficiency, redox state, color and mechanical properties. Reliable quantification of these elements is essential for production monitoring, quality assurance and process optimization in both industrial and research laboratories.

Objectives and Study Overview

This application note describes a validated analytical protocol for rapid and accurate determination of total sulfur and carbon in soda-lime glass using the LECO SC832HT series combustion analyzer. The aim is to equip production and QA/QC personnel with dependable metrics to assess batch consistency, remove gas inclusions and maintain desired optical properties.

Methodology and Instrumentation

An overview of the analytical workflow:

• Sample preparation: grind to uniform powder or beads; weigh ~0.25–0.50 g into pre-baked ceramic boats (528-203) previously heated at 1000 °C for ≥ 40 min and stored in a desiccator.
• System conditioning: analyze at least three matrix-matched samples prior to blanks and calibration to stabilize the combustion environment.
• Blank determination: perform three replicate blank analyses to establish instrument baseline.
• Calibration and drift correction: use certified reference materials (LECO CRM, NIST SRM 80a for medium S; NIST SRM 92 for low S) in triplicate; apply linear calibration through the origin.
• Sample analysis: run each glass sample in manual or autoloader mode with a minimum of three replicates, recording mass and detector response for sulfur and carbon.
• Instrument settings: furnace temperature 1550 °C; baseline stability delay 2 s; comparator values 0.30 V for S, 1.00 V for C; integration times 60–360 s (S) and 180–595 s (C).

Used Instrumentation

• LECO SC832HT series combustion analyzer
• Ceramic boats (528-203), crucible tongs (761-929), spatula (501-614)
• Muffle furnace for boat preheating at 1000 °C

Key Findings and Discussion

Results from soda-lime glass matrices:

• Standard beads (0.068–0.111 % S): mean S = 0.084 % (s = 0.0025); C = 0.006 % (s = 0.0006).
• Low-boron powder (0.0122–0.0222 % S): mean S = 0.014 % (s = 0.0004); C = 0.133 % (s = 0.004).

High precision and accuracy were achieved with linear calibration and stable baselines, demonstrating method robustness across different glass compositions.

Benefits and Practical Applications

• Direct assessment of bubble content and color-forming species for process control.
• Rapid screening of raw materials and finished products in production lines.
• Support for R&D in novel glass formulations and defect analysis.

Future Trends and Applications

• On-line integration of combustion analyzers for real-time process feedback.
• Advanced automation with robotic sample handling and scheduling.
• Extension to multi-element and speciation analysis in glass matrices.
• Enhanced detection limits using improved furnace designs or detector technologies.

Conclusion

The LECO SC832HT method provides a straightforward, precise and reproducible approach for total sulfur and carbon determination in soda-lime glass. Its ease of use and reliable performance make it a valuable tool for industrial quality control and research applications.

References

• NIST SRM® 80a and 92 certified reference materials.
• LECO SC832 Operator’s Instruction Manual.