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Spinel

Spinel refers to a class of minerals with the same structure. The chemical formula can be expressed as AO · R2O3, where A represents a divalent element ion, which can be Mg2 +, Fe2 +, etc .; R is a trivalent element, which can be Al3 +, Fe3 +, Cr3 + and so on.

Most of them exist in the form of isomorphous solid solution. All spinel forms a solid solution by expanding the crystal lattice. Spinel refractory can be divided into chrome brick, chrome magnesium brick, and magnesium chrome brick according to the raw materials and composition used. 3. Magnesium-aluminum spinel refractories.

It is an important class of neutral or plume-resistant refractories.

Application

Spinel is widely used in high-temperature industrial furnaces, open hearth furnaces, electric furnaces, ladles, outside furnace refining, cement rotary kiln, glass kiln heat storage chamber, copper smelting furnace, etc.

Classification

Spinel refers to minerals that are basically the same in structure. These same minerals all exist in the form of the same crystal type solid solution.

Natural spinel is rare, and all spinels used in industrial production are synthetic products. This type of refractory is a medium-to-high-grade refractory.

The commonly used steel-making materials are mainly magnesia-aluminum spinel refractories and magnesia-chrome bricks. Chrome-magnesia bricks are one of the ideal refractory materials in the steel-making process. According to Bartha’s classification method, spinel refractories can be divided into the following three categories:

  1. Al2O3 with a mass fraction of less than 30% is called periclase-spinel refractory.
  2. Al2O3 whose mass fraction is between 30% and 68% is called spinel-periclase refractory.
  3. Al2O3 whose mass fraction is between 68% and 73% is called spinel refractory.

Preparation

  1. Two-step calcination preparation. In the first step, the raw materials are calcined at 1100~1140°C to synthesize active spinel powder; in the second step, a dense sintered body is obtained through re-pulverization, grinding, molding and sintering.
  2. Wet chemical method. The use of wet chemical methods, such as hydroxide co-precipitation method, alkaline earth metal inorganic salt or organic salt sol-gel spray drying method and freeze drying method, etc., can successfully prepare high-purity spinel powder.
  3. High energy ball milling method. The high-energy ball milling method was originally used to prepare nanomaterials. With the continuous deepening of research, it is now used to synthesize spinel materials. The use of mechanical energy to directly participate in or initiate chemical reactions is a new idea. After high-energy ball milling, the specific surface area of the material increases, the crystal lattice is distorted, and many broken bonds are generated on the surface, which makes the powder store a large amount of deformation energy and surface energy. In this way, on the one hand, the sintering temperature can be reduced, on the other hand, due to long-term grinding, it will promote the formation of amorphous substances.

 

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