Slags conductivities

The interelectrode insulators, an integral part of the electrode wall stmcture, are required to stand off interelectrode voltages and resist attack by slag. Well cooled, by contact with neighboring copper electrodes, thin insulators have proven to be very effective, particularly those made of alumina or boron nitride. Alumina is cheaper and also provides good anchoring points for the slag layer. Boron nitride has superior thermal conductivity and thermal shock resistance. 

Fig. 16. Insulator wall designs (a) peg wall (b) conducting bar wall and (c) segmented bar wall. The gas-side materials are tungsten and tungsten—copper composite, the base material, copper, and the insulators, boron nitride. Slagging grooves are shown.

The principles pertaining to carbon blast furnace hearths apply as well to submerged-arc furnace hearths. In some processes, such as in d-c arc furnaces, the electrical conductance of carbon is a most important factor. The long life of carbon linings in these appHcations is attributable to carbon s exceptional resistance to corrosive slags and metals at very high temperatures. 

Bricks of silicon carbide, either recrystaUized or clay-bonded, have a high thermal conductivity and find use in muffle walls and as a slag-resisting material. 

Thermal property is another critical property for furnace slag. Because of their more porous structure, blast furnace slag aggregates have lower thermal conductivities than conventional aggregates. Their insulating value is of particular advantage in applications such as frost tapers (transition treatments in pavement subgrades between frost-susceptible and nonfrost-susceptible soils) or pavement base courses over frost-susceptible soils. 

An investigation was carried out on concrete containing up to 30% of PE foam waste in order to optimise the thermal conductivity of the concrete. An amorphous aggregate of ash-slag waste was utilised to decrease the thermal conductivity of the concrete. 5 refs. 

The element is still best known, however, in the form of its oxide. Zirconia linings for metallurgical furnaces are very permanent, and, because of their low heat conductivity, may be made very thin. Zirconia refractories, such as crucibles, are very resistant to the action of heat, slags, and most acids, and may safely be plunged into water while red-hot (42). 

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