Synthesis Method of Magnesium Aluminum Spinel
December 14, 2018
Synthesis method of magnesium aluminum spinel
There are many synthetic methods and techniques for magnesium aluminum spinel. The simplest and most straightforward method is the direct reaction between oxide compounds, which uses pure magnesium oxide and alumina materials, and then is pressed into a ball and sintered or fused to form a homogeneous synthetic spinel. The block is finally broken into granules and powdered material.
(1) Sintered spinel.
When the synthetic spinel is produced by the sintering method, it is preferable to use an oxide having a higher activity, such as light burntite and industrial alumina, which is easier to sinter than sinter and fused corundum. It can also be directly ground with carbonate or oxalate instead of pure oxide.
Whether the MgO or Al2O3 is excessive in the ingredients, the mixture is sintered to form a spinel solid solution, and the magnesium-rich spinel and the aluminum-rich spinel are respectively formed.
Sintered dense synthetic spinel, the average grain size is 20~30μm, and the density is more than 90%. Generally, the bulk density can reach 3.25 g/cm3, and the aluminum-rich spinel is slightly larger. The main crystal phase in the mineral composition is magnesium aluminum spinel, which is in direct contact. In addition, there may be a small amount of a subcrystalline phase such as periclase or corundum, depending on the content of MgO and Al2O3. In addition, a small amount of silicates M2S, CMS, C3MS2, C2S and cordierite are present in the interstices between the grains. The type of silicate mineral depends on the CaO/SiO2 ratio in the impurity. When the CaO/SiO2 ratio is large, the wettability of the melt to the crystal is low.
(2) Casting a spinel.
Synthetic magnesium aluminum spinel can also be produced by fusion. If the production of magnesium-rich spinel frit, the MgO in the batch should be controlled at 35~50%, not too high or too low, otherwise the melt viscosity is high and difficult to pour. If the melt containing excess MgO is condensed, the composition is segregated, making the frit a heterogeneous structure. The magnesium-rich spinel precipitates pure spinel above the eutectic temperature and is distributed in the lower part of the frit; the spinel crystal precipitated below the eutectic temperature is a solid solution in which the periclase is dissolved and distributed in the upper part of the frit. The compactness of each part of the frit is also inconsistent. The upper and side honeycombs have many pores, generally accounting for 20~30% of the frit. A chemically calculated spinel frit with the largest number of pores.