Instrumental Gas Analysis (IGA)
Instrumental Gas Analysis (IGA) refers to a set of analytical techniques for accurately measuring Carbon (C), Sulfur (S), Oxygen (O), Nitrogen (N), and Hydrogen (H) content in a range of solids including metals and alloys, ceramics, metal oxides, metal sulfides, slag, and cement. The samples can be in the form of small blocks, chips, powders, pins, or granules. IGA methods, also termed Elemental Analyzers, convert these elements to gaseous form and detect them by infra-red absorption or thermal conductivity detectors. The techniques used in IGA include combustion analysis for C and S, and Inert Gas Fusion analysis for O, N, and H.
Combustion analysis for C and S determination, using IGA, involves combustion of the solid sample and infrared detection of the combusted products. The solid sample is placed in a ceramic crucible or boat within a furnace, in the presence of an Oxygen gas stream. The high-temperature furnace (~1500 0C) can be a resistance type with precise temperature control or an induction furnace with precise current control to achieve optimum results. Due to the Oxygen-rich environment in the furnace, C and S in the sample are oxidized to form carbon dioxide (CO2) and sulfur dioxide (SO2), respectively. A small amount of carbon monoxide (CO) can also be produced, depending on the concentration of C in the sample. The extracted gases from the furnace are passed through a gas purification system, to a Non-Dispersive Infrared Detector (NDIR) system for quantification.
The Inert Gas Fusion for O, N, and H measurement is performed in an impulse furnace. This involves placing the pre-weighed sample in a graphite crucible that is located between two electrodes. An inert gas (He or Ar) atmosphere is maintained and a high current is passed through the crucible, creating a high temperature that melts the sample and generates gases. The output current of the furnace is monitored and can be automatically optimized to separate surface contamination from bulk content. Elemental Oxygen combines with the Carbon from the Graphite Crucible, to form CO And CO2, which are detected by NDIR cells. The CO, CO2, N2, and H2 then flow through a heated reagent, where CO and H2 are oxidized to CO2 and H2O respectively. The CO2 and H2O are measured by another set of NDIR cells after which they are scrubbed out of the gas stream. The component finally left is Nitrogen which is detected by a Thermal Conductivity Detector (TCD). The O, N, and H concentrations of unknown samples can be determined based on prior calibration with known standard samples.
Video 01: Carbon/Sulfur gas analyzer