Chromium magnesia, also known as magnesia or magnesia chrome spinel, is a magnesia raw material (sintered magnesite, natural magnesite or sea (halogen) water magnesium hydroxide calcined magnesium powder) and chromite Coordination, an alkaline refractory raw material with periclase and chrome spinel as the main constituent minerals obtained by artificial synthesis (sintering or electroporation).

Raw materials for the manufacture of magnesia chrome
       1. The raw material containing MgO is magnesite, flotation magnesium concentrate, sea (halo) water-extracted magnesium hydroxide, light burnt magnesium powder, and the like.The basic requirement for it is that the SiO2, Al2O3, and Fe2O3 contents are as low as possible. Generally, a relatively pure raw material such as light burned magnesium powder obtained by seawater or light burnt magnesium powder obtained by flotation of magnesium concentrate is used.
       2. chromite ore can choose better quality chromite or chrome concentrate. The SiO2 content in the chromite is required to be low: there is no particular limitation on the F2O3 content.

Content of Cr2O3 in magnesia-chrome sand
       The content of Cr2O3 in magnesia-chrome sand depends on the use of magnesia and its performance requirements. Generally, the more the chromite is added, the higher the total amount of spinel in the magnesia chrome, and the higher the strength and corrosion resistance of the chrome sand.
       According to China's experience in the production of sintered magnesia chrome sand by flotation of magnesium concentrate concentrate and chromium concentrate, the Cr2O3 content is 5%~10%.

Crafting process
       The various raw materials are weighed, mixed in proportion, and then fed into a ball press to be pressed into a billet (dry method into a ball). The spheroid is calcined in a fuel shaft kiln, and the firing temperature is 2000 ° C. The kiln atmosphere is controlled, and the quality of the synthetic sand calcined in an oxidizing atmosphere is good. The temperature of the sintered sand kiln is 100~150 °C. Magnesia-chrome sand can also be calcined at high temperatures in tunnel kiln and brick kiln.
       The electrofusion method is also a common method for producing synthetic magnesia chrome, especially for synthetic sand with a high Cr2O3 content. The difference between it and sintered sand is that the periclase and the spinel have a direct bonding structure, and the intercrystalline spinel has a high degree of self-formation; the structure is dense, the particle porosity is low; and the silicate phase content is relatively low. Therefore, fused magnesia chrome has better corrosion resistance. It can even achieve the performance of fused magnesia chrome bricks by making large particles and then combining magnesia chrome bricks, which is obviously superior to sintered sand. The sintered sand has good thermal shock resistance and low cost.

Due to the complexity of the raw material chromite ore used, the synthetic magnesia chrome sand often contains a variety of spinels composed of FeO, MgO and Fe2O3, Al2O3, Cr2O3.
       In the structure of sintered magnesia-chrome sand, the periclase has been significantly sputtered, that is, there is a star-shaped magnesia-chromium spinel inside the periclase crystal. The silicate phase is rare, the pores are less, and the size is basically the same and the distribution is uniform. In the sintered magnesia chrome sand with high Cr2O3 content, there are sometimes chromite particles, which are surrounded by magnesium chrome spinel, and the thermal stability of the sand brick is better.
       The mineral composition of synthetic magnesia chrome sand is very complicated. In addition to periclase and chrome spinel, there are also calcium forsterite (CMS), forsterite (M2S) and tetracalcium iron aluminate (C4AF).