Magnesia is one of the most critical raw materials for refractories, and it is used to manufacture various magnesia bricks, magnesia-alumina bricks, ramming mixes, furnace repair mixes and other products. It is mainly classified into three categories: dead burnt magnesia, light burnt magnesia and fused magnesia.
Basic Overview
It is divided into three major types: dead burnt magnesia, light burnt magnesia and fused magnesia. Magnesia ranks among the most vital raw materials for refractories, and it is adopted to produce various magnesia bricks, magnesia-alumina bricks, ramming mixes, furnace repair compounds and other products. Grades with high impurity content are applied for laying the bottom of steelmaking furnaces.
The main component of magnesia is magnesium oxide, with impurities including CaO, SiO₂, Fe₂O₃ and others. Magnesium oxide is a basic oxide with a melting point of 2800°C. After high-temperature calcination, it transforms into stable cubic crystals commonly known as periclase.
Material Sources
Magnesia can be produced by calcining or electrically fusing natural magnesite, extracting from seawater and salt lake brines, as well as separating from dolomite, serpentine and brucite. In China, magnesia is mainly obtained through calcination or electrofusion of magnesite ore, while Japan and Western European countries primarily extract magnesia from seawater.
Dead Burnt Magnesia
GB/T 2273-1998 integrated two national standards, namely Magnesia and High-Grade Magnesia, into a single standard entitled Dead Burnt Magnesia.
Dead burnt magnesia (DBM) is mainly produced by high-temperature calcination of magnesite, brucite, or magnesium hydroxide extracted from seawater, and it features strong hydration resistance.
When magnesite is calcined at 700–950 °C, carbon dioxide escapes. The resultant magnesia is soft, porous and loose, which cannot be used as refractory raw material. Magnesite calcined at 1550–1600 °C is fully sintered and defined as dead burnt magnesia. Dead burnt magnesia refers to fully sintered magnesia manufactured from natural magnesite via single-stage or two-stage calcination in high-temperature facilities such as vertical kilns and rotary kilns. Dead burnt magnesia is classified into 18 grades according to its physical and chemical indexes, as specified in the national standard GB/T 2273-1998.
Magnesia melted in an electric arc furnace with raw materials like magnesite and then cooled down to solidify is known as fused magnesia; magnesia derived from magnesium oxide extracted from seawater is named seawater magnesia.
High-purity magnesia is prepared by flotation purification of premium-grade natural magnesite ore, followed by light calcination, fine grinding, ball pressing, and ultra-high-temperature calcination in oil-fired vertical kilns. It serves as a premium raw material for manufacturing shaped bricks and unshaped refractories.
Medium-grade magnesia is produced using lightly calcined magnesia with 97% MgO content through ball pressing and high-temperature vertical kiln calcination. This product boasts a high sintering degree and dense crystals. It is a high-quality raw material for medium-grade magnesia refractory products, and can also be used to produce various magnesia bricks, magnesia-alumina bricks, ramming mixes, furnace repair compounds and other products. Grades with high impurity contents are applied for laying the bottom of steelmaking furnaces and similar applications.
Main Physical and Chemical Indexes
| MgO%≥ | SiO2%≤ | CaO%≤ | Fe2O3%≤ | lgL%≤ | B·D≥(g/cm) | |
| MS-98 | 97.7 | 0.5 | 1.2 | 0.5 | 0.3 | 3.3 |
| MS-97a | 97.5 | 0.6 | 1.2 | 0.7 | 0.3 | 3.3 |
| MS-97b | 97 | 0.7 | 1.4 | 0.8 | 0.3 | 3.25 |
| MS-96 | 96 | 1.0 | 1.4 | 0.8 | 0.3 | 3.25 |
Light Burnt Magnesia
Light burnt magnesia powder is an air-setting cementitious material featuring high flexural strength, compressive strength and mechanical strength. It is widely applied in national defense, medicine, chemical industry, papermaking, shipbuilding and other sectors.
In the building materials industry, it can be used to produce mold base boards, particle boards, thermal insulation columns, railings, artificial marble, asbestos tiles, ordinary tiles, wall panels and floor paving materials.
With advances in science and technology, light burnt magnesia powder has found an even broader range of applications. It can be fabricated into civil engineering products, light and heavy mechanical packaging boxes, packaging base beams and high-temperature refractory materials. It can also be processed into elegant furniture with high glossiness, and serves as casting molds in the machinery industry.