What are the light burned magnesia

The scientific name of light burned magnesia is magnesia, commonly known as magnesia, light burned powder and magnesia powder. Density 2.94, light yellow or white powder. Melting point 2852 ℃, boiling point 3600 ℃. Soluble in acids and ammonium salts, insoluble in water and ethanol. The specific surface area is 180m2 / g at 400 ℃. The specific surface area is only 3M2 / g at 1300 ℃. Deliquesce easily in the air. It belongs to the cementitious material of gas hardness.


Light burned magnesia is also called caustic bitter earth and active magnesia. It is a kind of light burned magnesia obtained from natural magnesite, brucite and magnesium hydroxide Mg (OH) 2 extracted from seawater or brine and calcined at 700 ~ 1000 ℃.


2 source


（1） Magnesite is one of the main sources of magnesia, and the content of MgO accounts for about 47%. MgCO3 is a solid powder (MgO) which is ground after calcined at 400-600 ℃. Mineral resources are widely distributed in Liaoning, Xinjiang, Sichuan, Shandong, Tibet and other provinces and autonomous regions, with reserves of 2.8 billion tons, accounting for 30% of the world's mineral resources.


（2） Dolomite [CaMg (CO3) 2] is also the main source of MgO, and its reserves are larger and more widely distributed, with MgO content accounting for about 22%. The content of Cao is about 30%, the rest is 48%. MgCO3 and Cao theoretical structure are one to one. The demarcation line of dolomite is based on the content of MgCO3 above 25%, otherwise, it can not be used as the ore for producing e69da5e887aae7999bee5baa6e997aee7ad9431333335313161 magnesium oxide, nor can it be called dolomite.


（3） Serpentine [MG6 (si4o10) (OH) 2] is also the raw material for the production of magnesium oxide, mainly magnesium silicate (3mgo · 2SiO2 · 2H2O)


（4） The slag of smelting light magnesium alloy is also the raw material of producing magnesium oxide.


3 admixtures


After the reaction of pure aqueous solution and MgO, Mg (OH) 2 is in a loose state, so there is no practical value. In 1867, Swedish scholar Sorrell invented magnesia cement. The compressive strength and flexural strength of the cement in dry environment are almost the same as those of the ordinary cement. The compressive strength is 110MPa / 28d, and the flexural strength is 20MPa / 28d.


（1） Magnesium chloride hexahydrate (MgCl2 · 6H2O) has the same compressive and flexural strength as ordinary silica cement, but it can only be used in dry environment. Magnesium chloride hexahydrate, also known as chlorite, is soluble in cold water at 0 ℃, with a relative density of 1.56 and a melting point of 712 ℃ at a water-soluble ratio of 281g / 100g. When heated to 118 ℃, hydrolysis begins and decomposes into MgO and HCl at high temperature.


MgCl2·6H2O→Mg(OH)Cl+HCl+5H2O


Mg(OH)Cl→MgO+HCl


To the fourth water, the second water, the first water and anhydrous magnesium chloride [2], please refer to the brief introduction of magnesium chloride of Anmei Industrial Development Co., Ltd. Its content accounts for 15-20% of MgO


（2） Magnesium sulfate heptahydrate (MgSO4 · 7H2O) is a curing agent as well as a waterproof agent. Its molecular weight is 246.48 colorless crystal or powder. No bromine or bitterness. When it is dissolved in water at 250 ℃, it becomes anhydrous magnesium sulfate (MgSO4), and above 400 ℃, it is reduced to MgO. It is a reaction product of MgO and H2SO4. The content of MgO is 15-20%. The cost is higher than MgCl2 · 6H2O.


（3） Ferrous sulfate heptahydrate (FeSO4 · 7H2O) is a waterproof agent, light blue monocrystal, also known as alum with relative density of 1.898 (at 18 ℃), which is easy to melt in water and has natural production of alum. The dosage accounts for 3% of the total.


（4） Styrene butadiene rubber latex (SBR solid content ≥ 45%) is waterproof rubber latex, with the content accounting for 6-12% of the total volume.


（5） Chloroprene rubber latex, also known as chloroprene rubber latex, accounts for 6-12% of the most stable amount of waterproof rubber latex in magnesium oxide materials, and 1% of (ohch2ch2) 3N is added at the same time.


（6） Silica sol, styrene acrylic latex and butyronitrile latex can be used as waterproof latex, accounting for 6-12% of the total volume.


（7） SiO2 type additives account for 10-15% of the total volume.


（8） The content of urea formaldehyde resin and melamine is 2-3% of the total.


（9） Phosphoric acid (H3PO4), also known as orthophosphoric acid, is a better curing waterproof agent, accounting for 4% of the total content.


（10） The content of modified sodium silicate is 1-3% of the total content


Four stages of hydration exothermic period of 4-mgo-cement


In the early stage of hydration induction, the first exothermic peak was formed within 10 minutes after the mixture was formed.


The induction period of hydration is the slow period of hydration reaction within 60 minutes.


The second exothermic peak appeared in the hydration accelerating period within 240 min.


The stable period of hydration deceleration is from the second exothermic peak to the end of hydration reaction at 14 h. It can be seen from the four stages that the initial setting time is 1.5h, the final setting time is 4-5h, and the exothermic curing time is 14 days after the end of 14h. After passing the test, it can be removed from the warehouse for installation (wall panel or various prefabricated parts) after 20d, and the cast-in-place magnesia concrete can be removed for 6h.


Calcination temperature and time are the key factors to determine the activity and dispersion of MgO.


Whether it is magnesite, dolomite and other raw materials in the calcination of decomposition reaction is endothermic reaction. Due to the decomposition of CO2 and H2O, the product with dense porous crystal structure formed by MgO has good activity and large dispersion (180m2 / g). In this case, when the temperature is 400 ℃ ~ 600 ℃, the product will be hydrated in a few minutes at room temperature after being ground. Therefore, a good calcination process should be controlled at 400 ℃ ~ 600 ℃, which means that the quality of energy saving products is good. When the temperature is higher than 900 ℃, the density and dispersion of the crystal is less than 1300 ℃, only 3 m2 / g, and it takes 75 days to hydrate 95% of MgO at room temperature. It can be seen from the lattice constant of Gleason that at 400 ℃, MgO reaches 0.425nm, and Mg (OH) reaches 0.424nm, at which time, the product has the best activity. That is to say, 400 ℃ ~ 600 ℃ light burning temperature is the best temperature, which is the source of light burning powder. The longer the calcination time is, the denser the crystal structure is, and it is difficult to hydrate.


Several elements of the optimum mix ratio:


（1） The specific gravity (relative density) of the water solution of the admixture