The current anti-burst techniques used in castables include
(1) Optimize the design of particle gradation or use high-efficiency water reducer (dispersant) to reduce the amount of water added as much as possible under the condition of ensuring construction performance.
(2) According to the bursting temperature range of the poured sample, a reasonable drying system should be formulated. Near the burst point temperature, the heating rate should not be too fast.
(3) Add metal aluminum powder, under the catalysis of alkaline ions in the castable, react with water to release hydrogen. When the hydrogen gas accumulates and reaches a certain pressure, it escapes from the inside of the material to form a through-type pore channel, so that subsequent water vapor can be quickly discharged along this channel, reducing the resistance generated. However, if the particle size of the aluminum powder is too fine or the amount added is too much, the material will swell or even crack due to the generation of a large amount of hydrogen gas.
(4) Add explosion-proof fiber, which generally melts in the range below 200°C to form holes in the material, increasing the pore size and number of holes, which is conducive to the discharge of water vapor. But the length and diameter of the fiber will affect the fluidity.
(5) Use an organic foaming agent, such as azodicarbonamide, calcium aluminate cement and water to generate calcium salts, and then the calcium salts decompose with changes in temperature and time to generate N2, CO2, and NH3 gases, forming open pores. Compared with Al powder, the decomposition reaction of azodicarbonamide is less affected by temperature, and the amount of gas generated is less and not violent, which reduces the problem of material swelling.
Study on Bursting Resistance of Magnesium Castable
The burst resistance of magnesia castables is also closely related to the thermal decomposition behavior (water loss temperature range) of the hydration bonded phase in the material. When the free water and adsorbed water are quickly removed, the hydration product magnesium hydroxide phase contains structural water, which undergoes thermal decomposition in the range of 350-420 °C; when the internal temperature of the sample reaches this temperature range, water is produced sharply inside Vapor, when the rate of production of water vapor is higher than the rate of discharge, will accumulate and cause high stress on the material, prone to bursting. In addition to the common anti-burst technology mentioned above, the anti-burst performance of magnesium castables can be improved by reducing the formation of magnesium hydroxide hydration phase or increasing the early bonding strength of materials. In addition, if the moisture in the hydration phase is decomposed in multiple stages, the risk of large stress caused by the concentrated discharge of water vapor is reduced, that is, the burst resistance of the material is improved.