Magnesia Products

Magnesia products are alkaline refractories. The melting point of magnesium oxide is very high, so the use temperature is also very high, in the oxidation atmosphere can be used up to 2000℃, in the reduction atmosphere can be used up to 1700℃. It is suitable for smelting many kinds of metals, precious metals, heavy metals and rare metals because of its strong corrosion resistance to alkaline slag. Production methods of magnesia ceramic products: alcohol mud casting molding method, cement mud casting molding method, isostatic pressing molding method, mud extruder molding method and machine pressing molding method.

Alcohol mud casting molding method is suitable for producing magnesium oxide crucible, thermocouple tube, furnace tube, insulating tube, round rod, flake shape and other products.

High purity magnesium oxide was used as raw material. The chemical composition of domestic high purity magnesium oxide is shown in table 14-18.

The chemical composition of high purity electrofused magnesia in three-phase electric arc furnace is shown in table 14-19.

The high purity fused magnesia is crushed and crushed to make the particle size less than 0.5mm, and then iron is removed by a strong magnetic separator, usually not less than two times, and stored in a completely sealed plastic bag and container to prevent hydration of fused magnesia.

The preparation of alcohol slurry material is, first will be less than 0.5mm of granular material with dry grinding particle size less than 200 mesh, and then add alcohol wet grinding (with hard jade ball grinding). The particle size of mud material less than 2 microns is more than 70%. The density of the slurry made of alcohol is 1. 9 ~ 2. 0 g/cm3.

Cast in plaster. The drawing rate of gypsum mold is 13% ~ 14%. In general, small products can be used on injection molding. After the blank body is naturally dried, repair the blank, remove the rough edges and polish, and heat and dry it at 80 ~ 100℃ for 48h. The products were fired in the high-temperature kiln at 1780 ~ 1800℃ for 2 ~ 4h, and the total firing time was 35 ~ 45h.

Electrofused magnesia is also easy to produce hydration reaction, that is, electrofused magnesia can absorb water in the air to produce magnesium hydroxide. The hydration reaction product causes the volume expansion to make the product crack and gradually pulverize. So with the water method of mud casting molding increase a lot of difficulties, must take measures to prevent the generation of hydration.

To the magnesium oxide powder material to carry on the hydration treatment, namely in the magnesium oxide powder material added distilled water for full hydration, so that the water content in the raw material in 32%. The hydrated powder was fired at 1450 ~ 1600℃ for 6 ~ 8h, and the true density of raw materials was 3.50 ~ 3.55g/cm3.

After firing, the material blocks were dry-ground for 45 ~ 90h in the ball mill (with the same medium as the steel jade mill), and then wet-ground with distilled water for 75 ~ 90min. The mud density was 1.70 ~ 1.80g/cm3, pH value was 7 ~ 8, and the material was poured into the gypsum mold and the slurry suction speed was 0.15 ~ 1.5mm/min. It is important to shorten the process time as much as possible. After demoulding, under the condition of ventilation, slowly heating to 70℃, drying for 24h, and then roasting at 1250℃. After cooling and shaping, the billet is heated at 1750 ~ 1800℃ for 4h. The process flow of water mud casting products is shown in figure 14-4.

When producing magnesia ceramic products by water, the hydration of magnesite suspension can be controlled by adding cerium oxide (CeO2) or erbium oxide (ErO). Therefore, due to hydration, it is not yet possible to use water slurry to cast large magnesium oxide products.

With high purity fused magnesia, through crushing, fine grinding particle size less than 20 mu m, less than 20 microns in more than 30% of the powder materials, with special rubber mold (small scale rate of 10% ~ 20%, large scale rate 30%), 180 ~ 200 mpa pressure hitches in isostatic press forming, in the 1780 ~ 1800 ℃ high temperature stove insulation 4 h burning, total 35 ~ 45 h burning time. Magnesium oxide ceramic products formed by isostatic pressure have higher thermal stability and better effect than those formed by mud.

Magnesia high temperature insulation material is used for magnetic fluid generator insulation material. This kind of equipment big power, high conversion efficiency, but because of the air flow in the high temperature (2500 ℃), air velocity, large (800 ~ 100 m/s), potassium ion in the gas, the heat insulation lining erosion, and when the operating temperature, cooling time is very short (only a few seconds), so the high requirement of high temperature insulation lining.

The magnesium oxide insulation material developed and produced by luoyang refractory research institute is made of high purity electrofused magnesia as raw material and petroleum rubber solution as binder. The material is formed by machine press with the molding pressure of 100MPa and is fired at 1800℃.

Physical and chemical properties of magnesium oxide ceramics produced by luoyang refractory research institute are shown in table 14-20.

Physical and chemical properties of magnesium oxide products by alcohol and water slurry casting and their comparison are shown in table 14-23. The influence of a small amount of cerium oxide or erbium oxide on the properties of products by water slurry casting is shown in table 14-24.

Physical and chemical properties of isostatic pressed magnesium oxide crucible produced by luoyang refractory research institute are shown in table 14-25.

Table 14-26 and table 14-27 show the performance of magnesium oxide insulation materials for magnetofluid power generation produced by luoyang refractory research institute.

The stability of magnesium oxide crystal shape is cubic model, melting point 2800 ℃, true density of 3.8 g/cm3, mohs hardness 6, magnesium oxide ceramics and low compression strength of about 300 mpa, 20 ~ 1000 ℃ average linear expansion coefficient is larger 13.5 x 10-6 ℃, 20 ℃ - 1 to 1700 the average linear expansion coefficient of 15.6 x 10-6 ℃ - 1100 ~ 1000 ℃ the thermal conductivity of 4.2 ~ 33.5 w. (m. K) 1 x 107-1100-0 ℃ resistivity Ω cm, 1600 ℃ the resistivity of 5 x 103 Ω cm, Magnesium oxide products can be used up to 2000 ~ 2200℃ in oxidation atmosphere, 1700℃ in reduction atmosphere and 1600 ~ 1700℃ in vacuum. Magnesia products can be made into crucible for smelting iron, nickel, uranium, thorium, zinc, aluminum, sodium, molybdenum, magnesium, copper, platinum and other metals. Thermocouple protection tube and insulating tube with temperature greater than 1800℃ shall be measured. The high purity magnesium oxide crucible formed by isostatic pressure has high thermal stability, and the crucible made by isostatic pressure has long service life and good effect in smelting rare metals, platinum and other precious metals and alloys.

In the new type of oil-fired magnetofluid power generation equipment, the combustion gas contains more potassium ions, high temperature (2500℃), high flow rate, large temperature fluctuations and frequent, the use of high purity magnesia insulation material to achieve good results.