| dc.description.abstract | The aim of this thesis was to determine data for the phosphorus(P) distribution
coefficients between ferrosilicon(FeSi) or silicon(Si) and calcia-silica(CaO SiO2)
slags. The work was carried out due to inconsistencies in literature on the phosphorus
distribution between Si and slag and because phosphorus distribution between
FeSi and CaO SiO2 slag has not been previously been determined for silicon rich
FeSi alloys. Calcia-silica slags of compositions 43:57,50:50 and 65:35 in weight% (wt%) doped
with approximately 300 parts per million(ppm) of P and Fe:Si alloys of compositions
20:80,50:50, and 80:20 (wt%) have been prepared in induction furnaces. Equilibrium
experiments were performed by holding metal and slag in a graphite crucible
inside a furnace with resistance heating for 3 hours at 1600 °C in argon atmosphere.
The samples were then quenched. After sample preparation, slag and metal were
analyzed by Inductive Coupled Plasma Mass Spectroscopy. One experiment was
also conducted with 20:80 wt% Fe:Si and CaO SiO2 containing 5.4 wt% P2O5.
After a holding time of 3 hours at 1600 °C, the sample was cooled at a rate of 1
°C per minute down to the solidification temperature of the metal (1360°C). This
sample was analyzed by Electron Probe Micro Analyzer.
Equilibrium experiments with quenching showed that the phosphorus distribution
coefficients between Fe50:Si50 (wt%) and SiO2 CaO slags were 0.08 ± 0.06,
0.14 ± 0.15 and 0.53 ± 0.42 for CaO contents of slag of 35, 50 and 57 wt% respectively.
Experiments with Fe20:Si80 and SiO2 CaO slags gave values for the
phosphorus distribution coefficient of 0.14 ± 0.15, 0.13 ± 0.3 and 0.52 ± 0.41 for
CaO concentration in slag of 35,50 and 57 wt% respectively. Between Si and
CaO SiO2 slags the phosphorus distribution coefficients were 0.12 ± 0.09 and 0.4
for CaO concentration in slag of 50 and 57% respectively.
The main findings were that the phosphorus distribution coefficient did not
change significantly with alloy composition. Slag composition on the other hand
had a large impact on the phosphorus distribution coefficient. The phosphorus
distribution coefficient increases with increasing basicity or CaO/SiO2 ratio of
the slag. Increasing the basicity also lead to increased calcium pick up in the
metal which was consistent with published data. Thermodynamic modeling of the
system should be conducted by including phosphorus in slag in the form of both
phosphate and phosphide. The average loss of phosphorus after the experiment was
100 ppm. The use of graphite crucible most likely leads to the loss of phosphorus as
P4 in gas phase. The experiment with controlled cooling gave equal concentration
of phosphorus in FeSi and Si. Phosphorus was not detected in the slag matrix.
Some minor areas in the slag which also contained alumina and magnesia had a
phosphorus concentration double of what was detected in the metals. | |
