The Study of Corrosion Resistance of R-SiC and Si3N4-SiC in Aluminum Silicon Molten

The wettability of silicon carbide and silicon nitride in molten metal is poor. In addition to the infiltration of magnesium, nickel, chromium alloy and stainless steel, they can not be infiltrated by other metals, so their corrosion resistance is outstanding, and they are widely used in the aluminum electrolysis industry.

In this paper, the corrosion resistance of recrystallized silicon carbide ( R-SiC ) and silicon nitride bonded silicon carbide ( Si₃N₄-SiC ) in thermally circulated Al-Si alloy melt is investigated from several latitudes.

Based on the experimental data of 9 thermal cycles of two samples in molten Al-Si alloy at 495 ~620℃ in 1080 hours, the following results are obtained.

With the increase of corrosion time, the corrosion rate of R-SiC and Si₃N₄-SiC samples decreased, and the corrosion rate accorded with the attenuation logarithmic relationship. ( Fig. 1)

Both R-SiC and Si₃N₄-SiC samples have no Al or Si element by EDS analysis, and a certain amount of Al-Si peak value in XRD spectrum is the residual Al-Si alloy on the surface. ( Fig. 2 - Fig. 5)

SEM analysis shows that the overall structure of R-SiC and Si₃N₄-SiC samples is slightly loose with the increasecorrosion time, but there is no obvious damage. ( Fig. 6 - Fig. 7)

The surface tension of the interface between aluminum liquid and ceramic is σ_s/l>σ_s/g, the wetting angle between the interface is θ>90° , and the interface between aluminum liquid and sheet ceramic material is not moist.

Therefore, the two materials ( R-SiC and Si₃N₄-SiC ) have excellent corrosion resistance to aluminosilicate melts, but the cost of Si₃N₄-SiC is relatively low, so Si₃N₄-SiC has been applied for many years.