Methods of Enhancing Dolomite Brick Anti-Hydration Ability
Dolomite bricks is a kind of refractory brick made from calcined dolomite sand. Dolomite brick main components are CaO and MgO, accompanied with little silica, alumina and ferric oxide, etc. Because there are un-bonded CaO in dolomite bricks, they are easy to be hydrated in air and result to crack, not suitable for long term storage.
Lots of researches have suggested that the reason contributes to MgO-CaO series dolomite bricks hydration is water vapor below 490℃. How to control CaO hydration at low temperature or temperature below 490℃ is the key to make MgO-CaO series refractory material have good anti-hydration ability. Currently, the following measures are taken to prevent CaO hydration.
- Sintering: Including ① activated sintering（two steps sintering and hydration）② Sintering with Additive. The additives used can divided into two categories: The first additives can form liquid phase, such as Al2O3, Fe2O3, SiO2 and other oxide, nitride, baron carbide, baron, aluminum, etc. The second additives can form sosoloid, such as CeO2, ZrO2, Y2O3, Cr2O3 and other oxide.
- Surface treatment: Including ① organic solvent surface coating, such as tar, pitch, paraffin, lipidol and various kinds of resin, organic silicon compound, organic acid-organic acid salt compound, etc. ② Inorganic surface coating, usually used are gaseous coating thin film ( CaO+CO2→ CaCO3 ) and liquid phase coating solution(phosphate acid, sodium phosphate, aluminum di-hydrogen phosphate, oxalic acid, etc. These solution can react with free CaO on the surface of MgO-CaO series clinker and produce indissolvable or sparingly soluble compound, adhering to the clinker surface.
To prevent dolomite brick hydration, wax immersion and water free packing are usually used. Wax immersion is: immerse the 60~100℃ dolomite brick into liquid paraffin and cools in the air. The liquid paraffin permeates into brick pores and form a thin film about 10 μm after solidification. On one hand, it effectively seals brick surface, on the other hand, it blocks vapor invasion. In this way, the storage period of dolomite bricks can be prolonged 1~3 months and can also exert function in a short term after unpacking. Some factories use pitch as the coating, but pitch have severe environment pollution and are gradually abandoned.
Water free packing is putting dolomite bricks into aluminum foil and sealed packed after vacuum pumping. If this method is not available, water proof plastic can be adopted to make sealed package by thermal plasticity, then add appropriate quick lime in the inner of package box. The storage period is about 1 year.
