α-SiC在Na_2SO_4蒸氣與其熔鹽中腐蝕之熱化學探討

Thermochemical Studies of the Corrosion of α-SiC by Na_2SO_4 Vapors and its Melt

劉祥鈞(S. C. Liu) ； 薛文景(W. C. Say)

《鑛冶：中國鑛冶工程學會會刊》 37卷2期 (1993/06) Pp. 129-134

摘要

可由Na-O-S系之Kellogg熱化學相圖及其三元系相圖瞭解到α-SiC在Na_2SO_4之蒸氣及其熔鹽中熱腐蝕機構。當Na_2SO_4在高溫下分解出S_2-SO_2-SO_3-O_2等氣體，與Na_2SO_4／Na_2O達到平衡之氧壓足使α-SiC氧化，在其表面形成SiO_2膜，並可保護SiC繼續氧化。若Na_2SO_4耗盡時，Na_2O隨即分解氣化Na-O_2氣體，熔蝕SiO_2層，形成Na_2O-SiO_2熔鹽。如SiO_2在此熔鹽達到飽和，隨即沉澱形成麟石英，裹止α-SiC繼續氧化。

並列摘要

Kellogg thermochemical and ternary diagrams of Na-O-S system are constructed to deduce the hot corrosion mechanism of α-SiC. The diagrams indicate that high temperature behaviour of various species, S_2-SO_2-SO_3-O_2 dissociated from Na_2SO_4, melt will be present in the state of Na_2SO_4/Na_2O equilibrium. The oxygen potential to the equilibrium leads to the formation of SiO_2 film which protects the surface of the solid SiC. At the expense of Na_2SO_4 the liquid phase of Na_2O will evaporate into gaseous Na and O_2 to react with SiO_2 layer to form a Na_2O-SiO_2 molten salt. In addition, the excess SiO_2 precipitated from the salt in the form of tridymite, is essential in preventing α-SiC from further oxidation.