THE
REFRACTORIES ENGINEER
Technical Paper
Fig. 7: XRD patterns of microsilica-gel bonded NCCs, ULCC and LCC, pre-fired at 1400 and 1500°C. a) MSZ-7, b) MSZ-5, c) MSZ-3, d) ULCC-7 and e) LCC-7
Fig. 8: SEM micrographs of etched polished surfaces of specimens fired at 1400°C. a) MSZ-3, b) MSZ-7 and c) ULCC-7
content of mullite in microsilica-gel bonded NCCs. MSZ-7 contains more mullite than MSZ-5 at both temperatures, while no trace of mullite can be detected in sample MSZ- 3. This confirms that a relatively high level of microsilica is most important to develop mullite, and consequently to improve thermo- mechanical properties of alumina-silicate castables. It also implies that it may not be such a good idea to substitute microsilica by reactive alumina. In the LCC-7, some mineral phases besides corundum can be detected after prefiring at 1400°C. These are anorthite (CaAl2
) and mullite. However, they disappear at 1500°C and corundum becomes the only mineral phase.
Si2 O8
The microstructure of MSZ-3, MSZ-7 and ULCC-7 after HMOR testing at 1400°C are shown in Fig. 8. Needle-like mullite is clearly visible in MSZ-7 and ULCC-7, while no mullite can be detected in MSZ-3.
With an increase in temperature to 1500°C, more mullite is observed in MSZ-7 and ULCC- 7, but the mullite changes its morphology from needle-like to columnar, as shown in Fig. 9. Furthermore, more glassy phase is observed in ULCC-7 and LCC-7 than at 1400ºC, and no
Fig. 9: SEM micrographs of etched polished surfaces of specimens fired at 1500°C. a) MSZ-3, b) MSZ-7, c) ULCC-7 and d) LCC-7
September 2019 Issue 25
www.irengineers.co.uk www.ireng.org
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
