Microsilica containing refractory castables - Elkem

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$ageing of refractory castables; which interactions exist and ... - Elkem$

FS20 then becomes relatively stable, the sampleswith Calgon continues the trend towards longer andlonger set time. The set time of the samples in theclimate controlled room seems the most affected,extending the set time up to 4 days in the worstcase.phosphates could be an option. The humidity wouldassist these processes if not take active part. Suchassumptions must be thoroughly investigated inseparate tests though.10080FS20Calgon96:00:0076:48:00FS20CalgonSelf-flow (%)6040TTS (h:min)57:36:0038:24:002019:12:000Start point 30 90 180Storage time (days)0:00:00Start point 30 90 180Storage time (days)(a) Stored in warehouseSelf-flow (%)100806040200(a) Stored in warehouseFS20CalgonStart point 30 90 180Storage time (days)(b) >50% RH at 20 o CTTS (h:min)96:00:0076:48:0057:36:0038:24:0019:12:000:00:00FS20CalgonStart point 30 90 180Storage time (days)(b) >50% RH at 20 o CFigure 15: Set-time of bauxite LCC after storage ina) warehouse in Kristiansand and b) >50% RH at20 o C, respectivey.Figure 14: Self-flow of bauxite LCC after storage:a) warehouse in Kristiansand and b) the climatecontrolled room at >50% RH and 20 o C,respectively.According to Fryda et al. 7 , humidity is a key factorin ageing, and this is also shown here as the highhumidity in the climate controlled room acceleratesdecay as compared to the warehouse condition.Very interesting is the difference in behaviourbetween Calgon and FS20. To explain this wouldimply some speculations, but immunisation orsealing of the cement surface by calciumConclusion.Because of interactions between cement andmicrosilica, additives has to be used in order toensure good flow of a castable. The flow of thecastable is then dependent on the proper amount ofadditive, and the set is dependent on it as well. Theoptimum addition level is not always easy topredict as sometimes there are opposite effects, likethe example with Calgon that has long set time atoptimum flow. It may therefore be concluded thatconcerning flow and set, one will often face atradeoff between the desired properties. Alsoregarding shelf life of castables, it is not
insignificant what choice is made. Choosing oneadditive over another may in some cases be on theexpense of the longevity of the castable.References:1 R.K. Iler, “The chemistry of silica”, John Wiley& Sons, New York 1979.2 H. Hommer and K. Wutz:” Recent Developmentsin Deflocculants for Castables” in procUNITECR’05, Am. Ceram Soc. p.186-1903 C.H. Fentiman et. al in " Advances in Ceramicsvol. 13, New Developments in MonolithicRefractories" ed. by Robert E. Fisher, The Am.Ceram. Soc. Inc. Columbus, Ohio 1985 p. 131-1354 L. S. Wells and E. T. Carlson; J. Res. Natl. Bur.Stand., RP2723, 57, 335 (1956)5 Steffen Möhmel: in “ Die Reaktionen vonCalciumaluminaten bei Hydratation undthermischer Belastung – Beiträge zur Chemie derHochtonerdezemente” dr. ing thesis Tech. Univ.Freiberg Germany 2003.6 B.Myhre, ” Microsilica in Refractory Castables-How does Microsilica Quality influenceperformance?” in proc. UNITECR 2005 OrlandoUSA Nov. 9, 20057 Fryda et al., “A New Insight into theCharacterisation of Ageing and Mechanisms ThatDetermine the Shelf Life of Low CementCastables“ in Proc UNITECR 2009, SalvadorBrasil Oct 13-16 2009.
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