Effect of sodium oxide(Na2O) on properties of refractory castables

In the traditional production of refractory castable, many people pay little attention to the content of sodium oxide in alumina powder, but the content of sodium oxide in alumina has a great influence on the performance of refractory castable.

The final performance of the product is for the site construction effect and use effect. Because the high content of sodium oxide will increase the amount of low melt, it will have a great influence on the dispersion of mud, and on the construction performance and setting time of refractory castable.

Because the dissolution of sodium oxide into the solution will shorten the hydration time of pure aluminum calcium cement and alumina slurry, the higher the content of sodium oxide in alumina, the greater the influence of powder surface area. At the same time, the formation of hydrate, the setting time and the properties and microstructure of castable body after solidification are affected to a certain extent. The activity, integrity and surface characteristics of alumina powder will have a certain influence on the construction performance of castable, cause the construction of condensation too fast or not.

The particle size distribution of alumina powder also has great influence on the performance of refractory pouring material. The smaller the particle size, the larger the surface area. The more sodium oxide and other ions get into the solution. As a result, the service time or erosion resistance of refractory castable is reduced.

The particle size distribution of alumina powder has great influence on the filling and packing degree of refractory castable. The particle size distribution of alumina powder can be divided into single-peak and multi-peak. The single bee distribution has only one peak value and only one mode particle size on the particle size distribution curve. Multimodal distribution means that there are two or more peaks on the circular line of the number diameter distribution, that is, there are two or more modal particle sizes. The larger the peak size distribution, the greater the bulk density of alumina powder, because smaller particles are more likely to fill the void formed by larger particles. Denser refractory castable and more resistant to erosion.

The bulk density of alumina powder with single peak distribution is small. It is easier to obtain higher volume density of refractory powder by using alumina powder with multi-peak particle size distribution than by using single peak particle size distribution. The alumina powder with wider distribution has better filling ability and higher packing density.

Therefore, the sodium content of alumina powder can not be high, otherwise it will affect the density of refractory castable.