www.ireng.org when the temperature in the center reached close to 300ºC.


Discussion The calcium aluminate hydrate gel formation in the presence of MP20 seems to be responsible for a microstructure that favours water release from the castable at low dry-out temperatures. The gel phase formation and its de-watering at temperatures below 150ºC seem to be the reason for the significantly higher gas permeability. Since very few crystalline calcium aluminate hydrates or aluminium hydroxide are formed, less hydrate water needs to be removed at temperatures above 150ºC. And with the higher permeability already at 110ºC more water can be transported to the surface at lower temperatures. This is a significant advantage for the dry-out process as pressure decreases with the temperature at which the water can be removed from the castable. The formation of the calcium aluminate hydrate gel is most likely also the reason for the somewhat lower strength that is observed compared to the MP20-free castables. Nevertheless high early green strength has been observed with MP20-containing formulations which is quite different from silica sol/gel bonded castables that typically show low green strength. Other investigations [7, 8] have shown, that despite a higher permeability with MP20, the slag penetration resistance remains largely unaffected. Pore size distribution measurements of AS10 and AM6 showed that despite a larger population of macro-pores after drying in the presence of MP20, the pore size evolution with temperature is somewhat different from the MP20-free systems and results after firing at high temperatures in a quite similar pore structure.


Summary The permeability enhancing active compound REFPAC®


Technical Paper


[4] Salomão R, Zambon AM, Pandolfelli VC. Polymeric fiber geometry affects refractory castable permeability. Am. Ceram. Soc. Bull., Apr 2006, Vol. 85, No. 4, 9201-5


[5] Hiroshi A. The effect of permeability on the explosion of castables during drying. J. Tech. Asso. Refract., Ja pan, 2004, 24 [2], 115-9


[6] Cobane IC. Explosive spalling of low cement castable refractories – A dryout service company’s experiences,


observations, and


recommendations. http://www.hotwork.com/wp-content/uploads/ 2015/12/Technical_Paper_IRE.pdf


[7] Zetterström C, Auvray JM, Wöhrmeyer C, Parr C. Enhanced permeability for a rapid dry-out of refractory castables, Proc. Unitecr15, Vienna, 2015


[8] Auvray JM, Zetterström C, Wöhrmeyer C, Parr C, Kebli F. The impact of permeability for a rapid dry-out of refractory castables, Proc. Unitecr15, Vienna, 2015


[9] Nouri-Khezrabat M, Braulio MAL, Pandolfelli VC, Golestani-Fard F, Rezaie, HR. Nano-bonded refractory castables. Ceram. Int., May 2013, 39 (4), 3479-97


MIPORE 20


creates at lower temperature higher gas permeability than PP-fibers. Furthermore the formation of gel-like calcium aluminate hydrates favours a lower de-hydration temperature. The removal of a large amount of water becomes possible at temperatures below 150ºC which helps to avoid high steam pressure build-up inside the castable. MP20 has shown a robust performance at low and high ambient temperatures and after different curing conditions. De-watering happened with different dry-out speeds and sample sizes in a quite similar way and generally at lower temperatures than MP20-free castables. This represents a significant increase of safety and minimization of risk of explosive steam spalling.


Acknowledgement


The authors would like to thank all teams of the Kerneos Research and Technology Center in France for the contribution to this study.


References [1] Semler CE. The ongoing evolution of refractories technology. Ref. Manual 2000, Vol. 7, No. 2, 44-7


[2] Innocentini MDM, Ribeiro C, Salomão R, Pandolfelli VC. Assessment of mass loss and permeability changes during the cewatering process of refractory castables containing polypropylene fibers. J. Am. Ceram. Soc., 2002, 85 [8] 2110–12


[3] Salomão R, Pandolfelli VC. Polypropylene fibers and their effect on processing refractory castables. Int J. App. Ceram. Tech. 4 (6), Dec 2007, 496-502


November 2017 Issue


ENGINEER THE REFRACTORIES


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