Amorphous refractory castable and castable prefabricated parts have been widely used by more and more high temperature industrial kilns because of their advantages of convenient construction, fast and low labor intensity.
However, many business users find that refractory fire castable or prefabricated parts are found in the storage or maintenance process of some abnormal phenomena, such as powder, long white hair and other phenomena.
In fact, these are the high alumina cement hydration products in refractory castable and atmospheric acid gas contact caused by. After the prefabricated castable is formed, with the evaporation of water in the castable, salt substances continue to migrate and precipitate to the surface, and then slowly aggravate the damage process of refractory fire castable. We will analyze these phenomena today.
The phenomenon of pulverization occurs in the storage process of refractory castables made of cement. Some of them grow "white hair" on the surface, commonly known as white alkali, causing pulverization of the surface layer of castables, and in severe cases, the strength of castables decreases.
Carbonation of castable
Carbonation of high alumina refractory cement castables is often considered to be one of the main reasons leading to structural degradation and spalling of castables. The high alumina cement bonded refractory castable is exposed to air and the hydration product reacts with CO2 gas in the air to carbonation. In addition, carbonic acid is more likely to occur in refractory fire castables under high humidity conditions, and compared with dense castables, light castables with high water content are more likely to pulverize, which indicates that in the presence of water, hydration products interact with CO2 acid gas, and the PH value of liquid in the single pore of phase decreases sharply, which makes all hydration neoorganisms in refractory castables become unstable.
Compared with the carbonation of hydration products of high aluminum cement, the phenomenon of sulphation has not caused enough attention of the construction and user manufacturers. In the atmosphere, in addition to CO2 acid gas, there are also SO2, H2S and other gases, which also have a strong erosion effect on the hydration products of the matrix part of high aluminum cement castable, eventually leading to the pulverization and spallation of castable.
In addition to the acidification process caused by SO2 and H2S in the air, high-alumina cement hydrates may also interact with SO42- or H+ in the water source. With the increase of the activity and acidity of these two compounds, the stability of the hydration products of the three high-alumina cements also decreases sharply.
Salting-out phenomenon of castable
The salting-out phenomenon on the surface of refractory castable is another important factor which aggravates the structural failure of castable. During the curing or natural drying process of refractory fire castables, with the evaporation of water, some soluble carbonate, sulfate, chloride, phosphate and other salt compounds focus on the surface of castables and crystallize out. This phenomenon is often called salt-out phenomenon.
As water evaporates from the surface of refractory castable, these ions migrate and aggregate with water molecules from the inside to the surface of castable, or react with acid gas in the air on the surface of castable, and the salts generated after the reaction of hydrate focus on the surface. Finally, these salt compounds crystallize out because they exceed the solubility in water.
In fact, all soluble salts containing crystalline water, including chlorides, sulfates, carbonates, etc., all have the process of crystalline water removal, accompanied by the change of crystal shape and volume, which is one of the reasons for the aggravation of surface structure pulverization, spalling and falling off during the curing of castables in air.
Solution method
1, castable after construction as soon as possible to dry, eliminate moisture, eliminate the carrier of sodium salt in the pouring body, so that alkali retention in the construction body, no longer to the surface migration
2, or the construction conditions can not reach the timely drying, it is necessary to do a good job of castable environment closed, the surface covered with plastic film, prevent water carrying alkali to the surface migration
3, refractory castable with low alkali content of refractory raw materials, improve the viscosity of refractory fire castable and fast hardening, can reduce the speed of sodium salt migration, strengthen quality management, strict control of construction water
