含Ca阻燃镁合金的高温氧化行为

Ca的加人大大提高了镁合金的燃点,当Ca含量大于1.7%时,Mg-Ca合金能在1 173 K的高温下暴露于大气中30min而不燃烧.SEM和XRD分析表明:合金表面生成了主要由氧化钙和氧化镁组成的复杂氧化膜,氧化膜内侧组织主要是Mg2Ca,该氧化膜具有保护性,但薄厚不一,极不规则.高温氧化动力学研究显示:该合金在673 K和873 K氧化符合抛物线规律,而在773 K氧化遵循立方规律.热力学计算结果表明:在Mg-2.5Ca合金中从室温到1 143 K温度范围内Ca都比镁优先与氧结合生成CaO,当Ca含量降低到一定程度时,镁又与氧结合生成MgO,所以形成了MgO CaO的复合保护膜.

Oxidation behavior of ignition-proof magnesium-calcium alloys

Ignition point of ignition-proof magnesium alloy was improved by the addition of calcium. When the content of Ca is larger than 1.7%, the alloy Mg-2.5Ca can avoid from ignition at 1 173 K for 30 min. XRD and SEM analyses of oxide scale reveal that the protective oxide film formed on the surface of Mg-2.5Ca alloy is composed of MgO and CaO, and beneath the film is Mg_2Ca. The film has protective function, but is inhomogeneous in structure. High-temperature kinetics measurements indicate that the oxidation dynamics curves measured at 673 K and 873 K follow parabolic law and the curve investigated at 773 K follows the cubic law. Thermodynamic calculation reveals that from room temperature to 1 143 K, Ca can react with O to form CaO prior to Mg. When the content of Ca decreases to some degree, Mg can react with O to form MgO, resulting in the formation of MgO CaO composite film.