Reactivity of Al-2.5 Pct Li alloy with water as studied by the exploding wire technique
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I.
INTRODUCTION
THE mixing
of hot and cold fluids, particularly molten metal and water, is a complex hydrodynamic process because of thermal and sometimes, chemical interactions between the liquids at the interface. If the mixing results in fragmentation of molten metal into fine metal drops and rapid heat transfer between the liquids, a disastrous vapor explosion could take place.It-5] In addition to the heat transfer, the contact between the fluids can also result in an exothermic chemical reaction producing gas, depending upon chemical composition and temperature of the melt. Normally, physical mixing or even vapor explosion does not trigger any significant chemical reaction unless the melt temperature is extremely high (near the melting point of its oxide). If circumstances are provided such that a fast chemical reaction takes place, the fragmentation could be coupled with the reaction and lead to a chemical explosion. However, little is understood as to the exact initiating mechanism of the explosions and the time sequence of the events. In any event, the existence of a triggering pressure pulse impacting on the molten metal in water, whether internally induced or externally provided, is known to be crucial for its fine fragmentation. During the mixing process, the surface energy and structure of the molten metal interacting with water plays an important role in speeding the mixing rate. The role is well demonstrated in the mixing of molten AI-Li alloy in contact with water. The alloy is well known for the surface activity of the Li additive, t6] It is also reported that small concentrations of surface active elements like Li and Na yield large effects on the strength of the oxide skin of AI. [71 Highly explosive reaction occurring in the mixing of the molten alloy with water is largely attributed to the change in the surface oxide strength which helps produce a fast and fine fragmentation of the fresh melt within water. Such a fast dispersion helps increase not only the heat transfer rate but W. M. LEE is Research Physicist, Materials Division (Code R32), Naval Surface Weapons Center, Silver Spring, MD 20903-5000. R. D. FORD is Research Electrical Engineer, Plasma Physics Division, Naval Research Laboratories, Washington, DC 20375-5000. Manuscript submitted April 29, 1987. METALLURGICALTRANSACTIONS B
also the possibility of the chemical interaction between the liquids. However, the chemical aspect of the interaction has never been addressed. A major difficulty in studying molten-water system arises from the lack of proper experimental tools. Although a study of the system by laser heating was reported, [sj an instantaneous heating of a sizable metal sample without the accompanying heat loss to the water is not easily achievable. The heating of a wire conductor by a capacity electrical discharge t9] has a limit for some metals, e . g . , A1, because the electrical current through the wire is limited by the sudden increase of the wire resistance. Such difficulties can be resolved by the exploding wire techn
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