Summary:
Magnesium oxide MgO-C is a basic high-melting (melting point 2800 deg.] C) and high melting point of the slag carbon material difficult to invasion as a raw material of non-oxide to add various additives. Bonded with the binding agent does not burn carbonaceous carbon refractory composites. The main site for the MgO-C converter, AC electric arc furnace, a DC arc furnace lining, ladle slag line and the like.
As a MgO-C refractory composites to effectively utilize the high thermal conductivity and strong resistance to slag erosion and magnesia carbon and low expansibility, the biggest drawback to compensate poor chipping magnesia.
Its main features are: a good high temperature performance, strong anti-sludge ability, good thermal shock resistance, low temperature creep.
Product Introduction
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effect:
Magnesium oxide MgO-C is a basic high-melting (melting point 2800 deg.] C) and high melting point of the slag carbon material difficult to invasion as a raw material of non-oxide to add various additives. Bonded with the binding agent does not burn carbonaceous carbon refractory composites. The main site for the MgO-C converter, AC electric arc furnace, a DC arc furnace lining, ladle slag line and the like.
As a MgO-C refractory composites to effectively utilize the high thermal conductivity and strong resistance to slag erosion and magnesia carbon and low expansibility, the biggest drawback to compensate poor chipping magnesia.
Its main features are: a good high temperature performance, strong anti-sludge ability, good thermal shock resistance, low temperature creep.
production process:
raw material
The main raw material of MgO-C brick comprises sintered magnesia or fused magnesia, flake graphite, and organic binding agent is an antioxidant.
Magnesia
The main raw material is magnesia MgO-C brick has fused magnesia and sintered magnesia points. Compared with the advantage of fused magnesia sintered magnesia having a periclase crystal grain coarsening, bulk density and other large particles, MgO-C production is the main material selected. Common magnesia refractory production, raw material requirements of magnesia having a main high-temperature strength and corrosion resistance properties, and thus focus on the purity of the chemical component in the magnesia C / S ratio and the content of B2O3. With the development of metallurgical industry, metallurgical condition increasingly demanding, in magnesia Application metallurgical equipment (converter, electric furnace, ladle, etc.) MgO-C bricks used, in addition to the chemical composition, the organizational structure, also requires high density and large crystals.
Carbon source
Whether in traditional or MgO-C brick low-carbon MgO-C brick in the current heavy use, the main use of flake graphite as a carbon source. Graphite as the main raw material of MgO-C brick, mainly due to its excellent physical properties: ① no wettability of the slag. ② high thermal conductivity. ③ low thermal expansion. In addition, the refractory graphite eutectic occurs at a high temperature, high refractoriness. Purity graphite greater impact on the performance of the MgO-C bricks, graphite is generally used a carbon content of greater than 95%, preferably greater than 98%.
In addition to graphite, carbon black are generally used in the production of magnesia-carbon brick. Carbon black is a thermal decomposition of hydrocarbons or incomplete combustion of hydrocarbons obtained black powder carbonaceous material has a highly dispersed carbon black fine particles (less than 1 m), a large specific surface area, the carbon content is 90 to 99%, high-purity, large powder resistivity, high thermal stability, low thermal conductivity, is a hard carbon. Addition of carbon black can effectively improve the spalling resistance of the MgO-C bricks, the amount of carbon residue increases, and increase the density of brick.
Binding agent
Production MgO-C bricks commonly used binding agents are coal tar, coal tar pitch and petroleum pitch, and carbonaceous special resin, a polyol, a phenol resin modified bitumen, synthetic resin or the like. Currently binding agent used in the following types:
1) bituminous material. Tar pitch is a thermoplastic material having a graphite, magnesia affinity large, high residual carbon after carbonization, low cost, has been widely used in the past; however, tar pitch contains carcinogenic aromatic hydrocarbons, particularly benzo content Zhuo high; due to enhanced environmental awareness, now in reducing the amount of tar pitch.
2) a resin-based material. Synthetic resins from the reaction of phenol and formaldehyde was prepared, and the refractory particles will be able to mix well at room temperature, the residual carbon after carbonization is high, the current production of MgO-C bricks primary binding agent; charring but it is formed glassy network structure, not ideal for refractory thermal shock resistance and oxidation resistance.
3) On the basis of the pitch and resin, the resulting material after modified. If the binding agent is capable of forming a damascene structure charring and in situ formation of a carbon fiber material, then this binding agent will improve the high temperature properties of the refractory material.
Antioxidants
In order to improve the oxidation resistance of the MgO-C bricks, often by adding small amounts of additives, additives are commonly Si, Al, Mg, Al-Si, Al-Mg, Al-Mg-Ca, Si-Mg-Ca, SiC, B4C , BN and recently reported Al-BC, and Al-SiC-C-based additive such as [5-7]. The principle role of the additive can be divided into two aspects: one is from the thermodynamic point of view, i.e. at the operating temperature, and carbon additive or additive reaction of other substances, their affinity for oxygen greater than the affinity for oxygen and carbon , the carbon is oxidized preferentially thus protecting carbons; on the other hand, the additive that is considered from the perspective of the dynamics of O2, CO generated by reaction of a compound or a carbon-carbon composite microstructure changes refractories, such as induced increase density, clogging the pores and hinder the diffusion of oxygen and reaction products, and the like.
