Thermodynamics / Interactive learning model

Baur–Glässner Diagram

Explore how temperature and the CO/CO₂ or H₂/H₂O gas ratio determine the equilibrium stability of iron and its oxides. Move the probe to see the gas fraction required for each reduction step.

Iron oxide equilibrium · CO / CO₂

Colored fields show the most stable condensed phase within this model. FeO is excluded below the model's wüstite stability limit.

Fe₂O₃Fe₃O₄FeOFe

Click the chart to set temperature and gas fraction. With chart keyboard focus, ← / → changes temperature and ↑ / ↓ changes the gas fraction. Use the input boxes for exact values. The hematite field can be very close to 0%; its small threshold is reported in the table.

Predicted stable phase at the probe—

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Gas requirement for metallic iron—

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Equilibrium and driving force

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Reduction steps at the temperature probe
Reduction step	Equilibrium reducing fraction	ΔG at probe gas kJ / reaction

Negative ΔG favors the reduction reaction as written. At exactly 0% or 100%, gas-ratio ΔG is a limiting infinite value; finite gas mixtures are required in practice.

Equations and the meaning of the fields

ΔG = ΔG° + RT ln Q

K = exp(−ΔG° / RT)

For a single-oxygen removal step: x_red,eq = 1 / (1 + K)

The gas fraction is p(CO)/[p(CO)+p(CO₂)] or p(H₂)/[p(H₂)+p(H₂O)]. It describes the reactive gas pair, not the fraction of CO or H₂ in a gas diluted by N₂ or other species.

System boundary and data limitations

A stability field expresses equilibrium at the selected temperature and gas composition. It does not predict the conversion reached inside a furnace, reduction time, or industrial fuel demand.

Sources and reproducibility

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CSV exports include boundary fractions, probe conditions, the model phase and reaction driving forces. The optional carbon line is reported separately.