A revised phase diagram for the bornite-digenite join from in situ neutrondiffraction and DSC experiments

Phase relations along the join bornite (Cu5FeS4)-digenite (Cu8.52Fe0.12S4.8 8) have been redefined using a combination of in situ high-resolution neutr on diffraction and differential scanning calorimetry (DSC). Time-of-night n eutron diffraction patterns were collected on a synthetic sample of bn90 at 16 temperatures between 35 and 350 degrees C. This data is compared with d ata from a natural end-member bornite sample obtained in an earlier study u nder identical conditions. Phase relations along the bornite-digenite join are inferred from the temperature evolution of the lattice parameters and t he intensity of subcell and supercell reflections of coexisting phases. The DSC scans over the temperature range 50-300 degrees C were performed on a natural digenite sample and samples synthesized at 5 mol.% intervals along the join Cu5FeS4-Cu9S5. The thermal anomalies are correlated with structura l phase transitions in component phases and the solvus temperature for each bulk composition, A phase diagram topology is: defined, which was consiste nt with both diffraction and calorimetric data, but in marked contrast to p revious diagrams, shows a consolute point at X = Cu5FeS4 and T = 265 degree s C, This temperature corresponds to that of the tricritical intermediate-h igh transition in bornite, Isothermal annealing experiments carried out on synthetic starting materials for up to 7 months showed coarsening behaviour consistent with the revised phase diagram topology.