Effect Of Modified Graphite And Additives On Structure And Performance Of Low Carbon Magnesium Carbon Material

Carbon compound refractory material which is a kind of important refractory materialscould not only make the pollution of carbon addition to the molten steel reduced, but also makegraphite resource saved and energy consumption reduced when its carbon content is lower. Inthis paper, the development and the main problems of low carbon magnesium carbon refractorymaterials were summarized. The graphite was modified with the method of liquid precipitation.The CA2material with low expansion was synthesized with industrial residue and manufacturedalumina. The effects of modified graphite and materials with different CA2contents on theconventional physical properties, thermal shock resistance, oxidation resistance and slagresistance of low carbon magnesium carbon refractory were studied. The relationship betweenmicrostructure properties of the materials was analyzed through the X-ray diffraction and fieldemission scanning electron microscopy. The conclusions are as follows:(1)The carbon with one-dimensional nanostructure was generated on the surface of graphiteafter the heat treatment of the mixture of graphite which was modified with Ni(NO3)2solution bythe method of liquid coating and phenolic resin at1100℃in reducing atmosphere. The modifiedgraphite which was not treated in the reducing atmosphere was used as carbon source forpreparation of low carbon magnesium carbon. And there were a lot of nanometer fibers in thematerials after the heat treatment under the same conditions. The nanometer fiber which wasanalyzed with energy spectrum was not the carbon with one-dimensional nanostructure, butcould be Al4C3、AlN、AlON and MgAlON. The slag resistance of the materials had changed little,but the oxidation resistance was improved a little. The thermal shock resistance had beenimproved obviously due to the reinforcing and toughening of nanometer fibers.(2)Two kinds of additives with different CA2contents which were labeled as1~#and2~#wereprepared after heat treatment at1600℃for3hours by industrial residue and manufacturedalumina. The apparent porosity of additives after heat treatment was25.32%,16.02and thedensity was2.74g/cm~3,2.60g/cm~3. The main phases of them were magnesium aluminate spineland calcium dialuminate. And the phase compositions which were estimated according to theternary phase diagram of Al2O3-MgO-CaO were56wt%,28wt%;62wt%,38wt%, respectively. Inaddition, there was calcium hexaluminate with the approximate content of16wt%in additive1~#.(3)The prepared additives labeled as1~#,2~#and industrial residue which were used forreplacing part of magnesia with fine powder were added to the low carbon magnesium carbonbricks. The thermal expansion coefficients of the bricks were reduced due to the three additives.The high-temperature bending strength was decreased, but the index of R_e/E which stands for theratio of high-temperature bending strength to elasticity modulus was increased. Therefore, the thermal shock resistance of the materials was improved effectively. In contrast, the thermalshock resistance of materials was the best when the additive2~#was added.(4)With the quantity of additive2~#added to the low carbon magnesium carbon materialswas increased, the oxidation resistance of sample was decreased, but better than the one withoutthe additive. And the thermal shock resistance of sample was improved significantly because theextent of reduction of thermal expansion coefficient was large and the index of R_e/E wasincreased. But the thermal shock resistance of sample improved little and the slag resistance ofmaterials was influenced when the addition amount of additive2~#was excessive. In thisexperiment, the appropriate amount of additive2~#was6wt%.