Limestone is mainly composed of calcium carbonate (CaCO3). Lime and limestone are widely used as building materials and important raw materials for many industries. Limestone can be directly processed into stone and fired into quicklime. Lime includes quicklime and hydrated lime. The main component of quicklime is Cao, which is generally massive, pure white, and light gray or light yellow with impurities. Quicklime becomes hydrated lime by absorbing moisture or adding water. Hydrated lime is also called hydrated lime, and its main component is Ca (OH) 2. Hydrated lime is blended into lime slurry, lime paste, etc., which is used as coating material and tile adhesive, and is also commonly used in power plant desulfurization.
Calcium carbonate is a compound, the chemical formula is CaCO3. CAS 471-34-1. It is a common material on earth and can be found in rocks. The main components of animal shell and snail shell. It exists in nature as calcite and aragonite. Calcite belongs to cubic system, hexagonal crystal, pure calcite is colorless and transparent, generally white, contains 56% Cao, 44% CO2, density is 2.715g/cm3, Mohs hardness is 3, the property is brittle. Aragonite belongs to orthorhombic strain, rhombic crystal, gray or white, with density of 2.94g/cm3 and Mohs hardness of 3.5-4. The crystal size of calcite is very important for the physical properties of limestone. Dense limestone has a fine crystal structure with low porosity and high strength. The density of limestone is about 2.65 ~ 2.80g/cm3, dolomitic limestone is 2.70-2.90g/cm3, dolomite is 2.85-2.95g/cm3. Bulk density depends on porosity.
Thermal expansion of Limestone: some data show that the average thermal expansion coefficient of microcrystalline limestone is (4.5 ~ 5.0) * 10 ^ (- 6) / ℃ when the temperature of limestone is below 800 ℃, while that of coarse crystal increases to 10.1 * 10 ^ (- 6) / ℃. The heating experiment of limestone is very important in lime production. At 800 ℃ below the decomposition point of limestone, the limestone crystal will expand, and cracks will be formed in the highly crystallized limestone, while the larger crystals will be broken into powder by heating, which is more serious for the limestone with well-developed crystals and many dense calcites.
Calcium carbonate, the main component of limestone, is decomposed into calcium oxide and carbon dioxide at high temperature. In addition, it has the following chemical properties.
l) Chemical resistance
Except acid, many corrosive substances can not or can only slowly erode limestone.
2) Acid fast character
Limestone reacts with all strong acids to form calcium salts and emit carbon dioxide. The reaction rate depends on the impurities in limestone and their crystal size. The higher the impurity content and the larger the crystal, the lower the reaction rate. The reaction rate of dolomite is slower than that of limestone. Determination method of dolomite and Limestone: when 10% hydrochloric acid is dropped on dolomite, a small amount of bubbles will be produced, while when it is dropped on limestone, tasteless bubbles will be produced violently, and the produced gas can make the clarified lime water turbid.
3) Resistance to various gases
The reaction of chlorine and hydrogen chloride with CaCO3 in dry bath and at room temperature was very slow, and it began to accelerate after 600 ℃ to form CaCl2; Sulfur dioxide has no significant effect on CaCO3 at room temperature; Nitrogen dioxide (NO2) reacts with CaCO3 at 15 ℃ to form Ca (NO3) 2, no and CO2.