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Physical & Chemical properties

Melting point / freezing point

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Description of key information

The melting behaviour of iron pellets was inferred from reference data for pure di-iron trioxide, thermodynamic modelling studies on iron sinter andiron oxides and laboratory-scale experiments performed under the auspices of the ECSC research programme. These studies all indicate that incipient melting of iron pellets begins at >1000°C with complete melting taking place at temperatures >1300°C.

Key value for chemical safety assessment

Melting / freezing point at 101 325 Pa:
1 000 °C

Additional information

Iron pellets are composed essentially of di-iron trioxide with small amounts of gangue constituents comprised of the oxides of calcium, silicon, magnesium and aluminium. The product may thus be regarded as di-iron trioxide with impurities and, consequently, the melting point of pellets will differ from that of the pure oxide phase. The melting point of pure di-iron trioxide is 1565°C and the other species present, typically silicates and aluminosilicates, all have melting points >1000°C. The methods for melting point determination listed in the ECHA guidance are not applicable for substances with melting points > 1000°C and therefore direct measurements of the melting point or, to be more correct, the melting point range cannot be performed using the recommended methods. Moreover, the melting point range of pellets is not available from reference data sources.

Owing to the different phases present, melting takes place over a significant temperature range and the degree to which melting has occurred is very difficult to determine with any degree of accuracy. The melting behaviour of pellets can be estimated by use of thermodynamic modelling approaches using FACTSAGE and MTDATA software. Read-across of data from thermodynamic modelling calculations on iron sinter (Thompson, 2010; Small et al, 2010) indicate the melting point of iron pellets will be >1000°C. The only relevant experimental studies studies are those carried out by Clixby (1987) under the auspices of the ECSC research programme. This work was peer reviewed by an expert committee of ironmaking experts, which confirms its validity. In this work a robust laboratory scale apparatus was developed to study the softening and melting properties of iron sinter and iron pellets under reducing atmospheres that simulated the blast furnace process. These studies showed that incipient melting of iron pellets begins to occur at temperatures >1000°C and complete melting occurs at temperatures >1300°C.