Castable formula of high purity calcium aluminate cement
At present, low cement castables containing activated alumina or silica fume (silica fume) need strong dispersion system. The appearance of dispersion system in low cement castables causes another interaction. Alcoa has developed dispersed alumina to optimize the flow and settlement behavior of castables at different ambient temperatures, as shown in Figure 8.
At present, low cement castables containing activated alumina or silica fume (silica fume) need strong dispersion system. The appearance of dispersion system in low cement castables causes another interaction. Alcoa has developed dispersed alumina to optimize the flow and settlement behavior of castables at different ambient temperatures, as shown in Figure 8. It is well known that the physical properties of refractory castable can be improved by reducing the amount of water added, because the stacking between components of the material becomes more compact, and the porosity is also reduced. However, under normal circumstances, there is a limit to water demand below which castables will not flow. Compared with the traditional dispersant, the dispersant of Alcoa reduces the water demand, and has better control over the flow and settlement behavior of the castable at different temperatures.
By measuring the exothermic reaction, controlling the sedimentation and hardening of the plate like corundum self flow castable, the castable has different ratios of delayed dispersion and accelerated dispersion of alumina. The delay effect of ADS3 is stronger than that of ADS1, and ADW1 accelerates dispersion. Pure ADS3 can make castable never settle.
For many years, the traditional additives for low cement castables have not changed much. They are all chemical substances. Phosphate is used as a deflocculating agent, typical sodium hexametaphosphate or sodium tripolyphosphate, water reducer such as citric acid or sodium citrate, and occasionally accelerator such as lithium salt is used to overcome the delay effect of other additives. Banerjee summarized the effects of various additives on the properties of castables . The advantages of additives have been proved. However, the disadvantage is that the demand for these materials is very small. Only a few thousandths can significantly change the settlement and flow of the castable. The first concern is how to make additives physically dispersed in the whole dry castable during the batching process. Because the dispersed alumina is very fine active alumina, it is mixed with organic components, and it acts as a carrier to make the dispersant more evenly mixed in the castable. The dispersed alumina system requires that the overall addition amount of additives be increased, so that the mixing is more sufficient and the consistency of castables is greatly improved.
When dispersed alumina is combined with 70% calcium aluminate cement, its effect is different. Compared with the traditional phosphate/citrate system with the same amount, the dispersed alumina can greatly reduce the amount of water added. Figure 10 shows that when the two systems are switched, water demand decreases. Therefore, the physical properties have been significantly improved. How about the thermal shock resistance of such dense castables? However, the thermal shock resistance test shows that the castable with this formula has no deformation after 20 times of thermal shock.
The effect of the original dispersed alumina ADS1, ADS3, and ADW1 in the system containing silicon powder is not good. Because these systems are important formulations of low cement and ultra-low cement castables, a new system matching dispersed alumina with silica containing micro powder has been developed. The dispersants M-ADS1 and M-ADW1 were tested by the tabular corundum based gravity flow castable containing 3% silicon micro powder, as shown in Figure 11. Pouring with different ratios of accelerated dispersion and delayed dispersion alumina.
The exothermic curve of the material shows that the control of sedimentation and hardening of products containing silica compatible dispersed alumina is similar to that of products containing other dispersed alumina.
Key words: calcium aluminate powder