Resistance to Oxidation

Oxidation resistance refers to the ability of carbon and other non-oxide refractories (mainly carbon compounds, borides, nitride, SiAlON,AlON, etc.) to resist oxidation in high temperature oxidation atmosphere.

To improve the oxidation resistance of carbon-containing refractories, the following measures can be taken:

Carbon materials with strong antioxidant capacity were selected.

Improve the structural characteristics of the products, enhance the density of the products, reduce the porosity;

Antioxidants are mainly added to metals (Si,Al,Mg,Zr,Ca, etc.), alloys (Al-Si,Al-Mg,Si-Ca) and non-oxide compounds (SiC,Si3N4,B4C,BN).

Graphite surface coating method, graphite surface coating method is to use physical or chemical methods to cover the graphite surface with a good wettability of oxides, metals, carbides, nitride and so on. The main methods of surface coating are as follows:

Hydrolysis deposition coating method. Graphite is used as the nucleating matrix of metal organic or inorganic salt hydrolysate, so that the graphite surface absorbs a layer of hydrolysate layer, and then heat treatment at a temperature lower than the oxidation temperature of graphite, so that the hydrolysate can be decomposed into corresponding oxides. At present, the hydrolysis deposition coating method is mainly TiO2 coating method and Al2O3 coating method.

Non-uniform nucleation method. ZrO2 coating was coated on graphite surface with ZrOCl2*8H2O as precursor.

The national standard GB/T13244-1991 specifies the test methods for the oxidation resistance of carbon-containing refractories:

For the carbon refractory containing oxidation inhibitor, the sample is placed in the furnace, heated to the test temperature at the prescribed heating rate in the oxidation atmosphere, and kept at this temperature for a certain period of time, cooled to room temperature and cut into two halves, and the thickness of the decarburized layer is measured. The sample is a cube with side length 50mm or a z cylinder with a diameter and height of 50mm. The heating rate is 8 ℃ 10 ℃ / min, from room temperature to 1000 ℃, 4 ℃ / min. from 1000 ℃ 1400 ℃. Air is passed through the furnace with the flow rate of 4L/min. The holding time is 2 h.

For carbon-containing refractory materials containing no oxidation inhibitors, the cubes with a side length of 50 mm were first carbonized, the residual carbon content was measured, and the mass after carbonization was weighed. Then put into the furnace, heat up to 1000℃ at the rate of 8~10℃/min in the oxidation atmosphere, and keep at this temperature for 5h. After cooling to room temperature, weigh the mass after oxidation. Using the measured data, the carbon loss rate is calculated.

There is no unified test standard for the determination of oxidation resistance of other non-carbon refractories, such as SiAlON,AlON and nitride refractories. Some researchers use variable temperature oxidation weight gain test or constant temperature oxidation weight gain test to weigh the quality of the sample before and after oxidation, calculate the mass change of unit area after oxidation to measure its oxidation resistance, and some researchers use the change of shape size and compressive strength before and after oxidation to determine the oxidation resistance of the material.