Magnesia cementing materials board includes
Magnesium oxychloride cement board
Magnesium oxychloride cement is a special kind of cement. It is also called Sorel cement for the reason that it was invented by Sorel in 1867. At the same time, its main ingredient is magnesium oxide, and people often call it magnesium cement. In many enterprises, due to the characteristics of magnesium oxide and magnesium chloride as the main raw materials, it is also referred to as double magnesium cement. Usually, people are also accustomed to call it magnesite cementing material and magnesite cement, because its main raw material is light burned magnesite powder which is calcined from magnesite ore. Later, people used glass fibers to enhance magnesium oxychloride cement get inorganic composite materials, which was called FRIM. So magnesium oxychloride cement was called FRIM.
Magnesium oxychloride cement is a kind of cement hardening body formed by light burned powder obtained from calcined magnesite ore or ash powder from calcined dolomite at low temperature as cement (the main component is MgO) and water-soluble magnesium salts such as magnesium chloride hexahydrate (MgCl2 6H2O) as blending agent and water.
The main components of hardened magnesium oxychloride cement is crystalline phase complex salt of magnesium oxide-magnesium chloride-water composed of 5Mg（OH）2 · MgCl2 ·8H2O and 3Mg（OH）2 · MgCl2 · 8H2O crystalline phase. In addition, there is a part of Mg (OH)2 cementite.
Magnesium oxysulphate cement board
The biggest difference between magnesium oxysulfide cement board and magnesium oxychloride cement board is that the acid radicals of the mixing solution are different, so the properties of the two magnesium-based cementing materials, such as fire resistance, thermal insulation, durability and environmental protection, are basically the same. Magnesium oxysulfide cement retains the above properties of magnesium oxychloride cement and avoids the hidden danger that manufacturers pay for moisture absorption and brine return of magnesium oxychloride cement.
Modified by basic magnesium carbonate, the strength phase is a layered structure with magnesium oxide octahedron as the framework and sulfate as the filling ion. The mechanical properties and durability of magnesium oxysulfate cement can be significantly improved.
Magnesium chloride hexahydrate
Magnesium chloride hexahydrate (molecular formula MgCl2·6H2O), with molecular weight of 203.3, colorless crystals, columnar or needle like, bitter, soluble in water and ethanol, easy to deliquescence when humidity is large and subject to decomposition at 116～118℃.
Epsom salt (molecular formula MgSO4·7H2O) is a white or colorless acicular or oblique columnar crystal, odorless, cool and bitter, molecular weight: 246.47, specific weight 1.68, soluble in water, slightly soluble in ethanol and glycerol, soluble in its own crystalline water at 67.5℃, decomposed by heat, losing crystallized water of four molecules at 70 to 80℃, losing all crystallized water at about 200℃ to anhydrous substances, and easy to dehydrate and weather into powder in air (drying). When it is heated, it will gradually remove crystalline water and transform into anhydrous magnesium sulfate.
The corrosion process of glass fiber and magnesium cement board (magnesium oxychloride board) on carbon steel
The corrosion of metals is mainly electrochemical corrosion, because metals inevitably contact the atmosphere in the environment, and the surface of metal materials must absorb a layer of water film, which contains oxygen and other substances, including carbon dioxide, so that metal materials are under complex chemical reaction conditions. When metal contacts magnesium oxychloride plate with 8 to 12% water content and 1.5 to 10% chloride ion dissolution, MgCl2·6H2O adhering to metal surface is easy to dehydrate and absorb moisture, and constitutes positive electrodes in electrochemistry with impurities such as carbon in metal surface structure. Metals themselves constitute negative electrodes of batteries. In the process of reaction, the negative electrode itself loses electrons and is oxidized. It separates from metal crystals in the form of ions and enters the water film. The positive electrode is the reduction electrode for electrons.
Under weak acidity or neutral and alkaline conditions, oxygen in the water film is
directly reduced to form hydrogen and oxygen radicals and diffuse into the water film. They are concentrated around the positive electrode. The alkalinity of the water film near the cathode is increased. If metal ions diffuse here, they combine with hydroxide to form hydroxide to aggregate and precipitate. For carbon steel, ferrous hydroxide will deposit first, which can quickly oxidize with oxygen in the water film to form iron hydroxide, and then dehydrate to form rust. The main component of rust is iron oxide (Fe2O3). The porous rust cannot prevent the steel products from contacting air and water, and it retains air and water on the surface of carbon steel products, which further aggravates the corrosion on carbon steel.
Rust is a brown-red substance, it is not as hard as iron, easy to fall off. After a piece of iron is completely rusted, the volume can expand by eight times. If the rust is not removed, the spongy rust finds it particularly easy to absorb moisture and the carbon steel will be rusted faster.
MagMatrix Group's MgO Chloride Free Magnesia Cement, modified by basic magnesium carbonate and macromolecule inorganic phosphate, with microporous glass as filler, density 1.8, moisture content 3.7%, chloride ion dissolution 0.021%, water content 3.7%. Its essence is the crystalline water with complex salts composed of epsom salt and ternary compound, which is removed and not reacted when it is heated up to more than 100℃. The dissolution of chloride ion of 0.021% is the impurity brought in by magnesium sulfate and stirring water.
When the metal contacts magnesium oxysulfate plate, magnesium sulfate trihydrate MgSO4·3H2O attached to the metal surface does not react with carbon steel. The corrosion of chloride ion dissolution 0.021% on carbon steel is too small and can be negligible.
Corrosion on carbon steel by Cl- and SO42-
Formula for calculating corrosion rate on carbon steel in fresh water (without considering the effect of water temperature and flow rate):
Magnesium chloride hexahydrate desorbs moisture in air (wet) and becomes liquid, ionizes Cl-- ions, which are easy to connect in air (dry). The corrosion rate of Cl-- ions on carbon steel can be calculated by the above formula.
Epsom salt does not desorb moisture in air (wet), and is easily dehydrated and weathered into powder in air (dry).
As the MagMatrix magnesium sulfate magnesia cement board ionize SO42--ions in the air (wet), it does not corrode carbon steel.