Corrosion resistance is the ability of refractories to resist corrosion and erosion of various media at high temperature. It is a very important indicator of erosion chemical resistance and mechanical wear resistance of refractories. 

Factors that affect the corrosion resistance of refractories include intrinsic factors and extrinsic factors. Intrinsic factors include the chemical and mineral composition, micro-structure and other properties of refractories. Extrinsic factors the properties of corrosive media, operating conditions (temperature, pressure, etc.) and the interactions between media and refractories.

 

The chemical and mineral composition of refractories

Refractories with different chemical compositions have different corrosion resistance. Acid refractories have good corrosion resistance to acid media, while basic refractories have bad corrosion resistance to acid media.

 

Refractories is made of several crystal phases, including the main crystal phases and the matrix. The main crystal phases have higher refractoriness, bigger crystal grains, less crystal grain boundaries and better corrosion resistance. If the impurity content in the matrix is high, it is easy to form a liquid phase. If the viscosity of the liquid phase is low, the refractories will have bad corrosion resistance.

 

The micro-structure of refractories mainly refers to the distribution of each crystal phase and the amount, size, shape and distribution of pores.

 

The bulk density, apparent porosity, thermal shock resistance, oxidation resistance and volume stability at high temperature of the refractories have big influence on the corrosion resistance. Dense refractories with high volume density and low porosity have better corrosion resistance than porous refractories. Refractories with bad thermal shock resistance, when suffering from thermal shock, may crack or spall, which aggravates the in-diffusion of corrosive media and reduces the corrosion resistance. Carbon-containing refractories have bad oxidation resistance and will form a decarburized layer after the surface is oxidized, which has a loose structure and easy to fall off and reduce the corrosion resistance. Refractories with bad volume stability at high temperature also have bad corrosion resistance. 

 

The corrosive media include slags(blast furnace, converter, refining furnace, non-ferrous furnaces, calcining furnaces, reactors), fuel, ash, iron, lime, cement clinker, garbage, liquid molten metal, molten glass, acid and base, electrolyte solution, various gaseous substances (gas, CO, sulfur, zinc and alkali vapor) and the like. The chemical composition, PH, viscosity, temperature, flowing rate and atmosphere of the corrosive media also have influence on the corrosion resistance of refractories. 

 

The refractories can react with the corrosive media and form new phases with high melting point or high viscosity, which will improve the corrosion resistance of refractories. 

 

The operating conditions include temperature, pressure, atmosphere, contact time and area, etc..

 

Based on the above analysis, the following approaches can be adopted to improve the corrosion resistance of refractories:

1)Improve the purity of raw materials, ameliorate the mineral composition and reduce the amount of impurities.

2)Select the suitable refractories and reduce or avoid the inter-facial reaction between the materials at high temperature. 

3)Choose the right manufacturing method to get refractories with dense and uniform structure. 

 

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