Various magnesia bricks of refractory bricks
But in hot water or boiling water it's the chemical equation that reacts: MgO + H2O= heating =Mg(OH)2 The reaction takes place in hot water. So this reaction depends on the conditions under which it happens. It reacts with water for the following reasons:
1. Magnesium hydroxide generated by the reaction of magnesium oxide with water is a water-soluble substance, which is wrapped in the surface of magnesium oxide and inhibits the further reaction of magnesium oxide and water. Although Mg(OH)2 is insoluble in water, it is a medium strong base, so there is always a little bit of water, and the amount of just generated is very, very small. If the solution is saturated, a small amount is attached to the magnesium brick, but it is not visible. Mg(OH)2 decomposes above 200 degrees.
2, the rate of chemical reaction and temperature are closely related, usually in chemical reactions, the higher the temperature, the higher the reaction rate. Another theory is that according to A. R. Mihailenko's "Nonferrous Metallurgy Furnace" data, the production process of magnesium bricks is to mix dead burned magnesia (particles below 5 mm to fine powder) with an appropriate amount of sulfite pulp waste liquid or caustic magnesia as A binder under the press molding. The composition of magnesia brick is: metallurgical magnesia, sulfite pulp waste liquid, caustic magnesia. Metallurgical magnesia is the MgO decomposed from magnesite above 1600℃, which is divided into: MgO: 92-93.5%, Fe2O3:1.5-3%, AL2O3:0.5-3%, CaO: 1-2.5%, SiO2:2-2.5%. From the above composition, it can be seen that Fe2O3, AL2O3 and SiO2 do not hydrolysis in humid air, and MgO is a magnesite crystal with a high melting point (about 2500℃), so hydrolysis does not occur. Only CaO and H2O occur CaO+H2O=Ca (OH) 2, so metallurgical magnesia itself has a certain water absorption. Sulfite paper slurry is a polymer viscous colloidal substance with hydrophilic properties, which makes magnesium bricks absorb water in humid air. Caustic magnesia is the decomposition of magnesite at 800-900 ℃ according to MgCO3=MgO+ CO2-28900 kcal. This magnesia is exactly the opposite of the above high-temperature 1600℃ dead burned metallurgical magnesia, hydrolysis occurs in the humid air: MgO+H2OM→Mg (OH) 2 The reaction just shows the reason why magnesium brick occurs in the encounter of moisture and water vapor
Magnesium calcium is the same family, but the same family does not mean that the nature is exactly the same, the nature of magnesium calcium is similar, but calcium is much stronger than the gold properties of magnesium, for example, calcium can react violently with cold water, but magnesium can only react with hot water
