The mechanism and function of antioxidants in carbon containing composite refractories are briefly described.
Mechanism analysis of silicon actionWhen silica fume is added to the carbon composite refractory, the phase changes and chemical changes are as follows:<1> Si (s) +C (s) =SiC (s) Delta G ~ =-522+1.50T (kJ)<2> Si (s) +MgO (s) =Si (g) +Mg (g) Delta G ~ =203.9-0.13T (kJ)<3> 2Si (s) +CO (g) =SiC (s) +SiO (g) Delta G ~ =-963.2+0.31T (kJ)<4> SiC (s) +CO (g) =SiO (g) +2C (s) Delta G ~ =81.47-0.15T (kJ)<5> SiO (g) +CO (g) =SiO2 (s) +C (s) Delta G ~ =-668.8+0.33T (kJ)From the above diagram and the reactions seen at high temperatures has joined the Si SiO and Mg volatiles, but <4> and <5> reaction have played a role in inhibiting carbon oxidation, and the condensation of SiO2 to a certain extent the role of protective film.The total reaction process is CO reduction to C, and there is a certain volume expansion, so that the pores are blocked and the density of bricks is increased. Therefore, the oxidation resistance of brick is improved.
With the advantages of carbon refractories especially excellent slag resistance and high heat stability, but graphite under high temperature oxidation, in order to improve the oxidation resistance of carbon composite refractory materials, often adding a small amount of antioxidants, to improve the oxidation resistance of carbon composite refractories. Antioxidant additives commonly used in metal powder, silicon powder, magnesium powder, silicon carbide powder and so on.
3, the selection principle of antioxidant and its thermodynamic and kinetic mechanism31 selection principles of antioxidants:(1) according to the thermodynamic data and the conditions of use, the possible condensed phase and the vapor pressure of each gas phase are determined;(2) compare the size of each coacervation and oxygen affinity, and the possibility of reaction with CO.(3) the influence of various reactions on the microstructure of brick was analyzed.The thermodynamic and kinetic mechanism of 3.2 antioxidantsFrom a thermodynamic point of view, at the operating temperature, the additives or additives that react with carbon react with oxygen more closely than carbon and oxygen, giving priority to carbon oxidation, thus protecting carbon;From the analysis of dynamics point of view: the compound additive with oxygen and carbon monoxide reaction changed the microstructure of carbon composite refractory materials, such as increasing the density, blocked pores, hinder the diffusion of oxygen and reaction products.
