www.ireng.org
Technical Paper
Addition of B4C to slide gate plate refractory material showed an increase in hot strength as a function of the amount added (Figure 8) [18].
(A) Al B4C
0.0 0.0
0.5 0.5
0.75 0.25
1.0 0.0
Figure 8: Hot modulus of rupture with various amount of B4C addition; test temperature 1400o
C [18].
Al2O3-SiC-C monolith and MgO-C studies have shown that a combination of additives, in particular a metal together with B4C, are more effective in improving hot strength than a single additive (Figure 9) [16].
(B) Al B4C Strength
It is often stated that antioxidant additions improve hot strength. The explanation is that they form bridges between the different refractory components. Figure 7 shows the effect of Si or Al on the fired strength of the refractory. The changes are the result of the formation of additional phases when the Al or Si reacted with the prevailing atmosphere and the other constituents in the refractory.
Al B4C
0.0 0.0
C [16]
0.5 0.5
0.75 0.25
1.0 0.0
Figure 9: MgO-C brick: effect of the amount and type(s) of antioxidant on hot modulus of rupture at 1400o
Effect on Slag Resistance
According to some studies, steelmaking slags rich in iron oxides will result in the oxidation of the carbon and graphite fraction of the refractory. This leads to increased porosity which allows for the penetration of the slag into to refractory. If the slag is alumina and/or silica rich then it will react with the magnesia and or dolomite in the refractory resulting in low temperature melting phases [19].
It has also been shown that iron oxide in a ladle slag can lead to the formation of magnesia-wustite in the MgO-C slag line brick leading to a decrease in its refractoriness. This reaction takes place anytime iron oxide comes in contact with MgO [20].
Decreasing the porosity lowers the ability of the slag to penetrate/react with the refractory constituents while in service thereby improving its overall slag resistance.
Figure 7: Modulus of rupture of 80:20 alumina-graphite composites as a function of additive content, fired to 900o
C and 1600o C [17] May 2016 Issue ENGINEER THE REFRACTORIES 21
0.0 0.0
0.5 0.5
0.75 0.25
C, (B) after coking at 1000o C [16]
1.0 0.0
Figure 6: MgO-C brick: effect of amount of antioxidant on apparent porosity: (A) after tempering at 200o
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36
