Inorganic Carbon & Sulfur Determination by High-Frequency Combustion

1. The Metallurgy of Carbon & Sulfur Control

In iron and steel production, carbon content dictates tensile strength, hardness, and ductility, while sulfur induces hot shortness, micro-porosity, and sulfide inclusions. In ultra-low carbon (ULC) steels and electrical steels, carbon and sulfur must be maintained below 10 ppm (0.0010%), requiring extreme analytical sensitivity.

2. The Induction Combustion Process

The metallic sample (0.5 g to 1.0 g) is weighed into a pre-ignited ceramic crucible along with pure tungsten and iron accelerators. The crucible is raised into a high-frequency (HF) induction coil operating at 20 MHz. The electromagnetic field couples with the metal charge, causing instantaneous Joule heating above 2000°C in a pure oxygen stream.

• Carbon Oxidation: All carbon oxidizes instantly into CO and CO2 gas.
• Sulfur Oxidation: All sulfur oxidizes into SO2 gas.
• Dust Filtration: Heated metal filters remove particulate iron oxide spatter.
• Catalytic Conversion: Rare-earth catalysts convert trace CO to CO2.

3. Non-Dispersive Infrared (NDIR) Detection

The combustion gases flow through temperature-stabilized solid-state NDIR cells. Gold-plated absorption cells with narrowband optical filters measure specific absorption wavelengths for SO2 and CO2, calculating total mass against NIST calibration curves.