Reactions characteristics of different powders in heated steam

Three metal powders of Mg, an Al-Mg alloy (AM) and Al are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) techniques. This study focuses on the reactions of the metal powders with flowing steam heated at 600°C, 700°C, 800°C, and 900°C in a transparent pipe furnace. The phases of the solid reaction products are analyzed using XRD, and the residual metal content and ignition delay times are measured. The experimental results revealed that the Mg and AM powders ignite and burn in the 600°C heated steam; however, the Al powders do not ignite even at 900°C. The ignition delay time of AM powders was shorter than that of the Mg powders. The Al in the AM and Al powders does not react completely even when the temperature reached 900°C; however, the content of unreacted Al in the AM powders (13.9%) was much less than that in the Al powders (82.2%) at 900°C. The combustion process of the AM powders at 600°C is divided into three stages: the Mg in the alloy (Al₁₂Mg₁₇) first reacts with water to form magnesium hydroxide, and the remainder of the Al and Mg in the alloy formed the new alloy phase; then, the magnesium in the new alloy phase continues to react, forming magnesium oxide, and remaining elemental Al exists; finally, ignition occurs, and the aluminium in the AM powders reacts with the heated steam, forming Al₂MgO₄.