Initial Observations

Once the samples were removed from the furnace following contact times listed in Table 5.1.4, they were inspected with the naked eye to distinguish whether any changes to the refractory were evident. These initial observations of the samples are detailed in this section.

1)

8 H

OURS

C

ONTACT

T

IME

For the slag samples which had been held in the magnesia-chrome refractory crucibles for 8 hours, the remaining FCS slag was approximately 4mm thick. The pool of calcium ferrite slag remaining in the crucible after experiments was approximately 2mm thick. The original dark brown colour of the magnesia-chrome refractory crucible had changed to black in the case of calcium ferrite slag, suggesting that the slag had penetrated right through the refractory material via the pore network. Calcium ferrite slag was also evident on the

magnesia crucible supporting the magnesia-chrome crucible. On the contrary, FCS slag/brick samples indicated no sign of FCS slag penetration through the refractory, as no colour differentiation was observed on the outer surface of the brick crucible and the magnesia crucible was free of any slag residue.

Comparison of the initial observations from the two experiments regarding the extent of slag penetration suggests that under similar conditions, calcium ferrite slag viscosity and slag/brick interfacial tension is much lower than that between FCS slag and the same refractory brick.

2)

32 H

OURS

C

ONTACT

T

IME

Following 32 hours of experimental time, calcium ferrite slag had not only penetrated the magnesia-chrome refractory crucible but also penetrated through the magnesia crucible safeguarding the sample and onto the supporting platform. FCS slag had penetrated further into the magnesia-chrome crucible with little slag remaining in the refractory crucible however no colour differential was evident on the outer surface of the crucible to signify complete penetration. FCS slag did not penetrate the magnesia crucible. Whilst there was no slag/brick interface present in the calcium ferrite slag sample because the slag had penetrated the brick, this was not the case for ferrous calcium silicate slag sample, where a distinct interface was observed. The attack of FCS slags and calcium ferrite on the refractory material is illustrated in Figures 5.1.5 and 5.1.6, respectively. It is evident that the level of penetration of FCS slag is far less severe than that of calcium ferrite slag even at extended experimental times. As observed in Figure 5.1.6, although calcium ferrite slag penetrated through the magnesia crucible, no degradation of the crucible is evident; suggesting that limited attack of the periclase phase in the refractory by the ferrite slag has occurred.

FCS Slag

Magnesia-Crhome Brick

Figure 5.1.5: Magnesia-chrome brick in contact with FCS slag at 1300oC, an oxygen partial pressure of 10-6 atm. for 32 hours.

magnesia crucible Slag w hich penetrated

through the magnesia

crucible Penetrated slag on the platform Magnesia - Chrome crucible

Figure 5.1.6: Attack by calcium ferrite slag at 1300oC, an oxygen partial pressure of 10-6 atm. for 32 hours.

3)

1400

O

C

AND

FCS

SLAG At 1400oC FCS slag had penetrated almost completely into the refractory, with only a small amount of slag remaining in the magnesia-chrome crucible. Similar to the case of calcium ferrite slag in the 8 hour test, the colour of the magnesia-chrome refractory had changed from dark brown to black on outer surface of the refractory crucible, suggesting increased slag penetration. Nonetheless, the magnesia crucible housing the sample was free of any slag residue and FCS slag did not penetrate or attack the magnesia crucible.

The only explanation for the increased penetration of slag into the refractory is that with an increase in temperature either or both slag viscosity and slag/brick interfacial tension have decreased. As per Equation 5.1.2, the relationship between the viscosity of liquids and temperature, an increase in temperature results in a decrease in viscosity. However the effects of temperature on the viscosity of FCS slag are unknown, with no data found in literature on the physical properties of the slag. Nonetheless, the decrease in viscosity with increase temperature in the range of 1200-1500oC was observed by Vartiainen and Sumita et al. for iron silicate and calcium ferrite slags respectively, at a fixed oxygen partial pressure. Vartiainen found that at a Fe/SiO2 ratio of 1.44 and an oxygen partial pressure of 10-7 atm, the

viscosity of iron silicate slag decreased from 0.25 Pa.s at 1300oC to 0.09 Pa.s at 1400oC. Sumita et al. found that for calcium ferrite slag, the viscosity decreased from 0.03 Pa.s at 1300oC to 0.02 Pa.s at 1400oC. The viscosity of iron silicate slag is affected by temperature far more than calcium ferrite slag due to its structure of large complex silicate anions. With silica and lime both present in FCS slag, it is likely that the viscosity of FCS slag will be between iron silicate and calcium ferrite slags and be fairly sensitive to temperature.

Studies on the effects of temperature on the interfacial tension between FCS slag and magnesia-chrome refractory were not found in literature and neither were studies found for the silicate and ferrite slags. However, according to theory on the effects of temperature on the interfacial tension between solids and liquids, it decreases linearly with increasing temperatures (Verein Deutscher Eisenhuttenleute, 1995)

In document FCS slag for continuous copper converting (Page 181-184)