Doloma brick

V. DOLOMA-BASED REFRACTORY PRODUCTS A. Direct-Bonded Doloma Bricks (Fired)... 

It is the lime phase of the doloma grain that provides the direct bond and is responsible for the chemical behavior of the brick. The microstructure of a fired doloma brick shows a high degree of direct bond, as Figure 3 shows. 

Further improvements to the slag resistance of both direct-bonded and carbon-bonded doloma bricks have been made through the addition of high-purity magnesia. Doloma bricks that have been enriched with MgO are typically used in areas of ladles and AOD vessels where higher slag resistance is required. The chemical and physical properties of the direct-bonded bricks used in steel making are shown in Table 6. 

Table 6 Chemical and Physical Properties for Various Direct-Bonded Doloma Brick...

Like aU basic refractories, doloma bricks thermal conductivity is higher than high-alumina brick. The consequence of this feature is that doloma linings are prone to develop open joints and to metal penetration. 

The chemistry of Dolomite 2 corresponds to the upper limit of impurities that would be suitable for the production of doloma for refractory brick purposes. This dolomite would have to be dead-birmed in such a way that there would be no significant pickup of impruities during the process (i.e., requires high-purity fuels). 

In the past there has been some reluctance to using direct-bonded bricks for steel-making applications because of their susceptibility to thermal shock. Significant improvement in the thermal shock resistance of the brick was accomplished through the addition of small amounts of zirconia. The enhancement is attributed to microcracking caused by the expansile formation of calcium zirco-nate as a result of reaction between the lime in the doloma and the zirconia. The microcracking is clearly illustrated in the microstructure shown in Figure 4. 

A variety of doloma-based monolithic materials are designed to be used in conjunction with brick, and also monolithic lining materials or for maintaining and patching vessel linings. 

---