How to Improve Hydration Resistance

Hydration resistance is the ability of alkaline refractories to resist hydration in the atmosphere. cao, mgo, especially cao in alkaline refractories, are easily hygroscopic and hydrated in the atmosphere to produce hydroxides, which makes the products loose and destroyed. The chemical reaction formula is as follows:
CaO + H2O + Ca (OH)2
MgO H2O ≤ Mg (OH) 2
the hydration resistance of the basic refractory material is improved, and the following four methods are generally adopted:
High temperature firing method: increase the firing temperature to make it burn dead;
Adding a small amount of additives: as sintering aid, increase sintering density, or additives react with CaO or MgO to form a low melting phase to wrap CaO or MgO particles in isolation from the environment, or to form stable compounds that are not easy to hydrate, etc., usually adding rare earth oxides, Fe2O3,Al2O3,TiO2, etc.
Surface modification treatment: carbonation surface treatment is to use CO2 gas to treat magnesia-calcium sand under certain conditions to form carbonate film on its surface to achieve the purpose of hydration resistance. In addition, the surface treatment of CaO material can also be carried out with phosphate or polyphosphate solution to form phosphate coating on the surface of magnesia-calcium sand particles, so as to improve the hydration resistance of clinker particles.
Surface covering method: add protective layer (sealed packaging) to reduce contact with the atmosphere.
For the detection of hydration resistance of refractories, clinker particles and products are tested by different methods. The ASTM C492 (2003) in the United States can be used to determine the hydration resistance of clinker particles. The main points are as follows: 100g particles larger than 425 μ m are taken as samples, dried at 105 μ m ℃, placed in constant temperature and constant humidity box, kept for 24 h at 71 ℃ / 83% relative humidity, cooled, 425 μ m screen, weighing 425 μ m screen, so as to take the quality of the screen as the percentage of hydration of the sample. American A 
Hd=[(G-H)/G]*1
The ASTM C456 of the United States stipulates the method for determining the hydration resistance of products. The main points are as follows: 5 cubes with edge length 25mm without the skin of the original products are cut from 5 pieces of products, dried, put into porcelain crucible, placed in autoclave, kept continuously for 5 hours at 162 ℃ and 552kPa, and the deterioration of the sample is observed if there is no modification, and then autoclaved for 5 hours. Repeated accumulation up to 30 hours at most. The condition of the test block after hydration is divided into 4 grades I: unaffected; grade II: surface hydration; grade III: cracking or crushing; grade IV Collapse. The total number of hours of steaming and the situation of each sample after each steaming are also written.