www.ireng.org % Al2 O3


CaO MgO LoI


Typical dosage Application area Main function Area of improvement REFPAC® 100 (RP100)


58.0 - 65.0 25.0 - 30.0 -


7.0 - 13.0 1


Castables with high silica fume content Deflocculant


Increased robustness to raw material impurities


Table 1: Typical composition of REFPAC® active compounds


deflocculant sodium tri-polyphosphate (TPP) and with a polycarboxylate ether based additive designed for silica fume deflocculation (PCE-SF). RP100 is a multi-component active compound [1] consisting of organic molecules combined with mineral additives and hydratable calcium aluminate phases. With RP100, 1% of the cement and the TPP respectively the PCE-SF have been replaced.


When exchanging the fine part of the bauxite (BX1) with a lower alumina- containing bauxite powder (BX2) and/or the silica fume (FS1) by a fume with lower silica content (FS2) soluble impurities get introduced into the castable as shown with ICP measurements (Table 3). That results in a lower flow when PCE-SF and TPP are used as shown in Figure 1. Contrary to that the flow of the castable using RP100 remains unaffected by the change of bauxite and silica fume. A clear difference in the structuration process is observed with RP100. Figure 2 shows the ultrasound velocity and heat flow profiles for the castables containing the more pure raw materials BX1 and FS1. When using RP100 a solid structure develops within one single step. As soon as the structuration starts with the initial stiffening a continuous solidification process is launched towards the maximum velocity that corresponds to


Raw material Bauxite aggregates


Bauxite fines BX1 / BX2 Silica Fume FS1 / FS2 Calcined Alumina


Calcium Aluminate Cement


Deflocculating Active Compound Deflocculant Deflocculant Water


Specification 0-6mm


0-0.09 mm


AC44B4 Secar®


Refpac® Na-TPP PCE-SF


the massive calcium aluminate hydrate precipitation and significant green strength formation. In comparison, the structuration in the presence of TPP and PCE-SF involves two distinct steps. A first velocity increase corresponds to the early stiffening but is followed by an intermediate phase in which the velocity increase is reduced for a certain period of time before the velocity further increases again to its maximum. This is confirmed by the heat flow evolutions for the mixes with TPP and RP100 (PCE-SF has not been measured). The heat flow has been measured only on the fine part of the castables.


Predictability of setting of steel ladle castables at variable ambient temperatures


To evaluate the ambient temperature robustness of high purity ladle castables a model alumina spinel formulation as presented in table 4 has been used. The reference formulation uses the calcium magnesium aluminate


binder (CMA) in combination with AL200, a PCE-based


deflocculant designed for alumina-magnesia and alumina-spinel mixes. The new deflocculating active compound RP500 contains both, mineral


REFPAC® 500 (RP500)


57.3 - 60.3 15.9 - 20.7 12.5 - 15.0 7.8 - 8.7 1


Castables with low/no silica fume content


Deflocculant


Increased robustness to ambient temperature


Technical Paper REFPAC® MIPORE 20 (MP20)


39.0 - 43.0 12.5 - 14.0 16.0 - 20.0 21.0 - 28.0 2.5


All castable types Deflocculant & Permeability Enhancer


Easier castable dry-out


%


66 19 5 5


71 100 (RP100)


4 1


5 +0.08 +0.1 +5.5 Table 2: Model silica fume containing LCC with different deflocculants 5


Table 3: Chemical composition of different silica fumes and bauxite powders and content of soluble elements September 2017 Issue ENGINEER THE REFRACTORIES 15


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