The role of ultrafine powder in refractory castables
The main function of ultrafine powder in refractory castables is to enhance filling properties and improve construction properties. Moreover, as the flow performance of the castable increases, the bulk density will also increase.
After adding ultrafine powder to refractory castables, the apparent porosity decreases while the strength increases significantly. Other high temperature properties will also be improved accordingly. The role of ultrafine powder is inseparable from admixtures. Only by choosing the right type of ultrafine powder and admixtures and using the right amount can they play their maximum role.
The mechanism of action of ultrafine powder is complex, because different varieties of ultrafine powder have different mechanisms of action. However, the amount of ultrafine powder cannot exceed 7%. If it exceeds 7%, there will be more than enough to fill the gaps. The remaining ultrafine powder will require a large amount of water and will not be dense, but there will be no change in the pores. If the dosage is controlled to less than 5%, the gaps in the castable will be filled, the water consumption will be large, the volume density will be small, and the apparent pores will be high. Therefore, the best usage range is between 5-7%.
In fact, the function of ultrafine powder is to fill. The bulk density of traditional refractory castables is relatively large, and many pores will be filled by the excess water. After the water is removed, pores will be left. When ultrafine powder is added, the pores will be filled with ultrafine powder. Filling, a very small amount of micropores are filled with water. In this way, when the refractory castable is mixed, the amount of water is reduced. After molding and demoulding, the water will be discharged, and the remaining pores will be much less. In other words, adding ultrafine powder will reduce the amount of water added, increase the bulk density of the castable and reduce the porosity.
In short, the filling effect of ultrafine powder is better than that of silica powder in refractory castables, and the dosage is also less. The particle size distribution activity of a-Al2O3 ultrafine powder is better than that of Sio2, because the proportion of ultrafine powder less than 1 μm accounts for 96.5%, while the active Sio2 is only 69%. The fineness, shape, and activity of ultrafine powder are stronger than Sio2 silica fume. .