Carbon based refractories



Carbon is an element that can exist in three forms in nature: diamond, graphite, and carbon. Carbon has excellent fire resistance properties, such as slag non-wetting properties and high thermal conductivity. It can be used as a refractory material in two ways: as an additive or binder (coal tar, petroleum pitch, or resin) in carbon-containing refractories, and as an additive in carbon-based refractories. Carbon-containing refractories are made by mixing graphite or carbon into oxide refractories. In carbon-containing refractories, aggregates are mainly composed of one or more of the six high melting point oxides or their related mineral phases. Carbon is usually present in the matrix as a binder phase or as an additive, or both.

The performance of carbon-based refractories is different from typical ceramic refractories, mainly because carbon-based refractories are conductive rather than insulating. All carbon-based refractory lining systems are used as "conduction cooling systems" rather than the classic definition of refractory linings, which are usually "insulation systems". Therefore, any carbon-based refractory lining system should always use proper cooling to help keep the refractory temperature below the critical etching temperature below the critical chemical attack temperature to prevent oxidation, alkali, CO degradation, or liquid metal dissolution of carbon.

The terms carbon, formed carbon, artificial carbon, amorphous carbon, or calcined carbon refer to the process of mixing particles of carbon-containing filler material (such as calcined anthracite, petroleum coke, or carbon black) with a binder (such as pitch) . Petroleum or coal tar, these mixtures are formed by molding or extrusion, and these molded parts are usually baked in an oven at a temperature of 800°C to 1400°C to carbonize the binder. By introducing an additional binder into the vacuum-baked charcoal, the conventionally baked charcoal can be densified to improve its permeability, and the resulting product can be re-baked to char the material.

Carbon-based monolithic refractories The most common carbon-based monolithic refractories are electrode paste and carbon ramming paste. The electrode paste is composed of coke or calcined anthracite as aggregate and coal tar pitch as a binder. It is mainly used to make electrodes but is also sometimes used as an unshaped refractory material. Coal slurry aggregate can be composed of calcined anthracite, anthracite, coke, tar, and coal tar. Asphalt, resin, or a combination thereof can be used as a binder. Al2O3 and other ingredients can be used as additives. Based on the insulation design concept, carbon paste can be used as a refractory furnace lining, just like the submerged arc furnace used to produce silicomanganese, and it can also be used to fill in the gaps. Between carbon-carbon joints.

Carbon-based shaped refractory materials There are four categories of pre-formed carbon-based refractory materials, namely amorphous carbon, semi- or partial graphite, semi-semi-graphite and graphite bricks. Binder and shape the mixture, then cook it to the desired temperature. For molded refractories, the priority is to achieve the maximum density of the molded shape. The aggregate, filler, and binder are ground, sieved, and classified to the desired particle size, then mixed and blended at a typical temperature of 160-170°C. The mixture is then cooled to about 125°C and shaped. Three molding techniques are used to shape the carbon block: extrusion, compression, and isostatic pressing. After molding, the molded product is scorched by heating to a temperature between 800°C and 1400°C in an inert atmosphere. This process is called carbonization. The product produced at this stage is called carbon brick. During the carbonization process, the product becomes porous due to the loss of volatile substances. In order to achieve the required porosity and quality, the product is impregnated with coal tar pitch or polymer in an autoclave. Repeat impregnation and carbonization until the required performance is met. During the carbonization process, the binder becomes coke.