produced for TGA analysis and SEM characterisation. The specimen size was 40x40 mm cylindrical and the heating rate was 20ºC/hr for the TGA measurement.
Figure 11 illustrates the dry-out behaviour of microsilica gel bonded NCCs. The drying rate of both specimens was the same up to ~125 ºC after which the drying rate of the NCC specimen with EMSIL-DRY is much higher than the reference specimen. At 185ºC, the specimen with EMSIL-DRY reached its maximum drying rate of 0.19% water per minute, whereas the reference specimen exploded. The drying rate before the explosion was merely 0.08% per minute.
When the temperature exceeds the melting point of EMSIL-DRY numerous channels are produced, facilitating water removal during the ebullition stage, as exemplified in Figure 12. The NCC EMSIL-DRY sample contains needle-like channels, while the reference specimen does not, indicating that the vapour pressure inside the NCC specimen with EMSIL-DRY should be much lower than the reference. Therefore, at a heating rate of 20 ºC/ min during the TGA, the NCC with EMSIL-DRY remains intact, while the reference exploded at 185ºC.
with and without drying/anti-explosion agents, the following conclusions can be drawn.
• The type of drying agent has a strong influence both on flowability and drying behaviour.
• The heat-up schedule and the physical dimensions of the cast refractory bodies play essential roles during the dry-out process of the NCCs.
• The microsilica-gel bond system contains only small amounts of bound water. Once the free water is removed, the castables can be fired at very high heating rates.
• With introduction of EMSIL-DRY, the drying rate has been significantly improved.
• The microsilica-gel bonded NCC with EMSIL-DRY has excellent explosion resistance. A 400kg block was heated, with no holding times, from 20 to 850°C at a heating rate of 50°C/hr – it came out perfect!
R.G Reid, J. M.Pr
ausnitz, B.E Poling, “The properties of gases and liquids”, McGraw-Hill International, pp 208-209, (1989).
2. R. Saloao, L.R.M Bittencourt, V.C Pandolfelli, “Drying behaviour for refractory castables: aluminium powder and polymeric fibers”, Ceramica, 54, pp 259-267 (2008).
C. Parr, Ch. Wöhrmeyer, “The advantage of calcium aluminate cement as a castable bonding system”, St. Louis Section meeting, USA, 2006.
4. C.W. Connors, M.W. Anderson. Colloidal silica refractory system for an electric arc furnace. US Patent 6528011. March 04, (2003).
5. M. R. Ismael, R. D.Anjos, R .Salomão, V. C. Pandolfelli, “Colloidal silica as a nano-structured binder for refractory castables”, Refract. Appl. News 11 (4) (2006), pp 16–20.
6. B 7.
H. Peng, B. Myhre, “Comparison of Setting Behaviour and Mechanical Properties of Various Silica-Bonded No-cement Castables”, China’s Refractories, vol 26. No.1 (2017), pp 8-12.
B. Myhre and K. Sunde, "Alumina based castables with very low contents of hydraulic compound. Part II." Strength and High- Temperature Reactions of No-cement Castables
Alumina and Microsilica”, Proc. UNITECR'95, Kyoto, Japan, Nov. 19-22 (1995), p. II/317-24.
8. B. Myhre and H. Peng, “Microsilica-gel bonded castables – a bond with potential”, Proc. 53th Symp. On Ref. Am. Ceram. Soc (2015), pp 43-56.
Figure 12: SEM of fractured surface of samples heated at 200ºC for 12hrs. a) NCC-REF, and b) NCC-EMSIL-DRY
All this demonstrates that the explosion resistance/drying behaviour of microsilica-gel bonded NCCs was significantly improved by the introduction of EMSIL-DRY that contributes to fast dewatering during firing. It indicates that true rapid heating is possible.
Based on our studies of flowability, drying behaviour and explosion resistance, TGA and SEM characterisation of microsilica-gel bonded NCCs
September 2018 Issue
H. Peng, B. Myhre, “Comparison of Setting Behaviour and Mechanical Properties of Various Silica- Bonded No-cement Castables”, China’s Refractories, vol 26. No.1 (2017), 8-12.
10. B. Myhre and H. Peng, “Why do industrial-sized no-cement castables sometimes explode during heat-up? A remedy to ensure safe and fast heat-up of microsilica-gel bond castables”, Proc. 53th Symp. On Ref. Am. Ceram. Soc (2017), pp 43-56.
11. B. Myhre and Hong Peng, “Microsilica-gel bond castables with potentials”, Proc. 49th Symp. On Ref. Am. Ceram. Soc 2015, pp.112-121.
12. H. Peng and B. Myhre, “Microsilica-gel bonded refractory castable with improved setting behaviour and mechanical properties”, Refractories World Forum, vol. 3, (2015), pp. 69-75.
ENGINEER THE REFRACTORIES
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