Oxidation mechanism of MgO–C in air at various temperatures

Abstract

During charging, tapping, hot repairing, and idling, the refractory lining also comes into direct contact with the air. Oxidation of MgO-C refractories containing 20 wt-% At the face opposite the hot face of the refractories, the graphite was conducted by measuring the weight loss temperature is low and the face may also come into contact at regular intervals at various temperatures from 800 with air which comes through cracks, crevices, etc. Besides to 1600°C in air. T he rate of decarburisation increased direct air oxidation, FeO present in slag plays a significant with rise in temperature from 800 to 1400°C and then role in the oxidation of carbon in MgO-C bricks. remained more or less constant from 1400 to 1600°C.Oxidation of carbon and its prevention is a subject of T he oxidation kinetics were analysed in detail and great interest in the field of BOF refractories. Different reaction rate models derived for the temperature range techniques1-6 have been used for studying air oxidation of 800-1400°C. T he reaction rate was found to be con-MgO-C samples. In the present work, it was studied under trolled by diVusion of oxygen through the decarburised isothermal conditions by measuring the weight loss at layer. At higher temperatures (>1400°C), oxidation regular intervals. One of the most important parameters is of graphite also takes place indirectly by the reacobviously the temperature. When heated in air, carbon is tion MgO(s)+C(s) Mg(g)+CO(g). T he magoxidised at temperatures from around 600-700°C to form nesium vapour thus produced is reoxidised at the outer CO or CO 2 . Oxidation studies were, therefore, conducted surface and redeposited as MgO. T his leads to a at various temperatures ranging from 800 to 1600°C. reduction in porosity in the decarburised outer shellAlthough MgO-C bricks can contain from 5 to 35 wt-% and, consequently, a reduction in the rate of oxidation. carbon, the amount of carbon usually ranges from 5 to BCT /364 20 wt-%. It was, therefore, thought appropriate to study the effect of temperature on MgO-C specimens containing At the time the research was carried out the authors 20 wt-% graphite.

Studies of the decarburisation phenomena during preheating of submerged entry nozzles (SEN) in continuous casting processes

“…Hence, it is of great importance to obtain knowledge about the SEN's behaviour during the preheating process. Previous studies have shown that all RBMs that contain graphite have a high probability to be decarburised during the preheating operation, which is due to an increased oxygen activity near the inner wall of the refractory [8][9][10][11]. Here, it should be noted that RBMs normally contains about 5 to 35 wt-% graphite.…”

“…This was done, according to reactions (1)- (3) and with the assumption that the activity of carbon equal to unity. Since the major constituents of Al 2 O 3 -C SEN are Al 2 O 3 and C the direct oxidation of graphite reactions that could take place during the preheating process are as follows [8][9][10][11]16]: …”

“…Moreover, laboratory experiments with MgO-C RBMs which were heated isothermally showed that the decarburisation rate increased with an increased temperature in the temperature range of 800 to 1400°C. Thereafter, the decarburisation rate was approximately constant in the temperature range of 1400 to 1600°C [10]. Therefore, the time between the end of the preheating operation and the start of the casting should be kept to a minimum to increase the chances of a successful start of the casting operation.…”

The Effect of Zirconium Disilicide (ZrSi2) Additions on the Carbon Oxidation Behavior of Alumina/Graphite Refractory Materials

“…This, in turn, may lead to volume expansion and cracking of the refractory bulk. 3) .................... (2) .... (3) Sunayama et al 4) have investigated the influence of aluminum additions on the oxidation rate of Magnesia/ graphite refractory, which showed a slight improvement of the oxidation resistance at temperatures below 1 823 K. Wang et al 5) have investigated the influence of Al 8 B 4 C 7 additions on the decarburization resistance of magnesia/ graphite refractory. In addition, Gokce et al 3) have evaluated the effects of various antioxidants such as Si, Al, B 4 C and SiC on the decarburization resistance of magnesia/ graphite refractory.…”

“…More specifically, graphite oxidation starts at 873-973 K in air to form carbon monoxide or carbon dioxide. 2) .............. (1) A method to inhibit the decarburization of Al 2 O 3 -C refractories is the addition of so-called antioxidants. An antioxidant is an element or a compound with a high oxidation affinity.…”