Steam Explosions of Single Drops of Molten Silicon-Rich Alloys
Commercial quantities of ferrosilicon alloys and silicon metal in the form of granules are available. They are produced in water granulation, a process involving the risk of large-scale steam explosions. To learn about these steam explosions, we have investigated single drops of molten alloys when released into water. When single drops of molten ferrosilicon alloy with 75 wt.% Si (FeSi75) or silicon metal at its liquidus or melting temperature were released into cold, room temperature or hot water, spontaneous explosions never occurred. We could, however, initiate steam explosions by exposing the drops to upwarddirected pressure transients generated in the water with an encapsulated impactor. For water at room temperature, we determined (a) the strength of the pressure transients needed to initiate the steam explosion of a single drop, and (b) the range of fall depths over which the drop can be triggered to explode with this transient. When varying the water temperature we learned that the triggered explosions became less vigorous as the temperature increased. The explosions became more vigorous also when the Al and/or Ca content in the molten drop decreased. Photographic images of the bubbles generated during the steam explosions indicate that the maximum energies released correspond to about 1 % to 2% (dependent on drop size) of the total enthalpy of the molten ferrosilicon at its liquidus temperature. During the explosions, tiny bubbles of a permanent gas, presumably hydrogen, were generated. Video images show that ferrosilicon drops with diameters between 3 mm and 11 mm fall through water at about 0.5 m/s. Shutter wheel photographs confirm these fall rates and also indicate the onset of solidification of the drops and show that steam explosions can occur in partially solidified drops.
The Release of Drops of Molten Ferrosilicon and Silicon into Water : Pressure Transients Generated During Triggered Steam Explosions
The experiments described here were directed toward interpreting and understanding pressure-time records generated during triggered steam explosions of single drops of molten silicon and ferrosilicon. These experiments extend the observations of pressurizations produced last year during a triggered explosion of a single drop of molten silicon. After discussing experimental improvements and the characterization of Impactor 3, we describe new experiments performed with single drops of the molten ferrosilicon alloy (75 wt. % Si, 25 wt. % Fe) and drops of silicon, both nonalloyed and containing small amounts of Al and/or Ca additives. We obtained new information about the triggered steam explosions of drops of these molten metals primarily from new instrumentation used this year: the transducer-oscilloscope pressure measuring system, a high-speed video system, and a hydrogen collection and measuring system. Of greatest importance has been the ability to correlate individual video images exactly in time with various characteristics of the pressure-time traces. INTRODUCTION During the year 2000, our experiments were devoted primarily to obtaining and interpreting the pressuretime records generated during triggered steam explosions of single drops of molten silicon and ferrosilicon. These experiments extend the observations made during 1999 of the pressure transients produced in one preliminary experiment (D-150-1) in which a single drop of molten silicon was triggered and exploded (Nelson et al., 2000). Early in 2000 we concentrated mostly on recording pressure transients generated during triggered explosions of single drops of the molten ferrosilicon alloy that contains nominally 75 wt. % silicon and 25 wt. % iron (FeSi75). Later in the year, we turned to recording the transients generated similarly during the triggered explosions of single drops of molten silicon and compared them with the transients produced by the drops of molten ferrosilicon and the triggering pulses used to initiate the explosions. We also examined the effects on these interactions of (a) triggering drops of molten silicon at various depths and (b) of alloying small amounts of Al and Ca with the silicon. At midyear, we borrowed a high-speed video system that provided very valuable information in three important experiments.
The solubility of hydrogen in liquid binary Al-Li alloys
The solubility of hydrogen in liquid binary aluminum alloys with 1, 2, and 3 wt pct lithium has been determined for the temperature range of 913 to 1073 K and pressure 5.3 × 104 to 10.7 × 104 Pa, using an appropriate version of Sieverts’ method. The results fit the Van’t Hoff isobar and Sieverts’ isotherm and the solubility,S, is given by: Al-1 pct Li: log(S/S°) − 1/2 log(P/P°) = −2113/T/k + 2.568 Al-1 pct Li: log(S/S°) − 1/2 log(P/P°) = −2797/T/k + 3.329 Al-1 pct Li: log(S/S°) − 1/2 log(P/P°) = −2889/T/k + 3.508 whereS° is a standard value of solubility equal to 1 cm3 of diatomic hydrogen measured at 273 K and 101,325 Pa per 100 g of metal, andP° is a standard pressure equal to 101,325 Pa. Added lithium progressively increases the solubility of hydrogen in liquid aluminum, due more to its effect on the entropy of solution of hydrogen, through its influence on the liquid metal structure than to an increase in the solute hydrogen atom binding enthalpy.