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20 TECHNICAL PAPER


Material design for new insulating lining concepts


Andreas Buhr, Dagmar Schmidtmeier, Rainer Kockegey-Lorenz, Marion Schnabel, Jerry Dutton


Introduction Synthetic raw materials based on calcium hexaluminate (CA6


Properties Of Ca6 ) are


commercially available as dense aggregate “Bonite” and super lightweight aggregate “SLA-92”. Both are used successfully in various applications. The key properties of CA6


such as high chemical purity, high


refractoriness and high thermal shock resistance are well known in the industry. Particularly outstanding is the low thermal conductivity of SLA- 92 in the high temperature range above 1200°C. This is also the case with the dense Bonite when compared to other minerals with a similar density. In recent years energy saving concepts and environmental friendly solutions have increasingly become the focus of attention as the industry has to cope with increasing energy costs and ever changing environmental regulations, e.g. limitation of CO2


emissions. Therefore


innovative concepts and material solutions are required in order to optimise the performance of the processes. The combination of dense and lightweight CA6


enables the development of tailor-made solutions


which take into account density, strength and thermal insulation without changing the chemical-mineralogical composition of the refractory. New insulating castable concepts will be presented and discussed in this paper.


Materials


Both SLA-92 and Bonite are composed of about 90% CA6 minor content of corundum and traces of calcium dialuminate (CA2 CA6


, with only a ). The


aggregates show the typical hexagonal plate-like crystal structure


(Figure 1 and 2). Whereas SLA-92 is a super lightweight raw material with a porosity of typically 70 – 75%, Bonite is the dense sintered counterpart with a much lower porosity. The properties of SLA-92 and Bonite are summarised in table 1 and have been discussed in detail in previous papers. [1-7].


Experimental The properties of CA6


based castables are demonstrated in two pure SLA-


92 based vibration castables and two pure Bonite based ones (Bonite LD and Bonite) representing the low and the high density range respectively. In addition two castable formulations with intermediate densities were developed as examples to demonstrate the combined use of SLA-92 and Bonite (table 2). These castables are named according to their fired density, for example mix “VIB 1.1” has a fired density of 1.1 g/cm³. Two SLA-92 based patch mixes are also included in this investigation to show the multiple range of application for CA6


materials (table 3).


Test bars and bricks from all castables were prepared and tested according to the European standard EN 1402 “Unshaped refractory products”, parts


SLA-92


Mineralogical composition Main phase Minor phase


Chemical analysis [mass-%] Al2O3 CaO


Figure 1: Microstructure of lightweight CA6 SLA-92


Fe2O3 SiO2 Na2O


Femag


Physical properties Bulk density [g/cm³] Lose bulk density [kg/l] Apparent porosity [vol.-%]


Available sizes 3 - 6 mm 1 - 3 mm


0.5 - 1 mm 0 - 1 mm


0 - 0.5 mm - 45 MY - 20 MY


Figure 2: Microstructure of dense CA6 Bonite (different scale to be considered compared to figure 1)


Table 1: Properties of SLA-92 and Bonite


0.8 0.5


70 - 75


x x


x Bonite (LD) Bonite


CA6 (~ 90%) CA6 (~ 90%) CA6 (~ 90%) Corundum Corundum


Corundum 91 8.5


0.04 0.07 0.4


91 7.7


0.08 0.5


0.01 2.8 24


x x x x x x x


91 7.6


0.08 0.9


0.01 3 9.8


x x x x x x x


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