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.
Steam explosions of single drops of pure and alloyed molten aluminum
Abstract Studies of steam explosion phenomena have been performed related to the hypothetical meltdown of the core and other components of aluminum alloy-fueled production reactors. Our objectives were to characterise the triggers, if any, required to initiate these explosions and to determine the energetics and chemical processes associated with these events. Three basic studies have been carried out with 1–10 g single drops of molten aluminum or aluminum-based alloys: untriggered experiments in which drops of melt were released into water; triggered experiments in which thermal-type steam explosions occurred; and one triggered experiment in which an ignition-type steam explosion occurred. In untriggered experiments, spontaneous steam explosions never occurred during the free fall through water of single drops of pure A1 or of the alloys studied here. Moreover, spontaneous explosions never occurred upon or during contact of the globules with several underwater surfaces. When Li was present in the alloy, H 2 was generated as a stream of bubbles as the globules fell through the water, and also as they froze on the bottom surface of the chamber. The triggered experiments were performed with pure A1 and the 6061 alloy. Bare bridgewire discharges and those focused with cylindrical reflectors produced a small first bubble that collapsed and was followed by a larger second bubble. When the bridgewire was discharged at one focus of an ellipsoidal reflector, a melt drop at the other focus triggered only very mildly in spite of a 30-fold increase in peak pressure above that of the bridgewire discharge without the reflector. Experiments were also performed with globules of high purity A1 in which the melt release temperature was progressively increased. Moderate thermal-type explosions were produced over the temperature range 1273–1673 K. At about 1773 K, however, one experiment produced a brilliant flash of light and bubble growth about an order of magnitude faster than normal; it destroyed the chamber. The exceptional vigor of this latter interaction was attributed to ignition of the metallic A1. In both the triggered steam explosions with drops of high purity A1 and untriggered experiments with drops of A1Li, only a few tens of cm 3 of hydrogen per gram of metal were generated; the extent of metal-water reaction was only a few percent at most. The information obtained from these studies with triggered and untriggered drops of molten aluminum-based alloys can be used directly in certain safety studies where hypothetical core or component meltdown occurs in a production reactor. Moreover, this information is consistent with recent advances in the understanding of single-drop steam explosion triggering and concepts of the development of larger scale steam explosions.
What is an archival education?1
This article introduces the approach to Master's level archival education adopted at the University of Manitoba. It is intended as a contribution to the recently renewed discussion of graduate archival education in the UK and Ireland. The author maintains that recent major developments in the accessibility, uses, and very conception of archives powerfully underscore the distinctiveness of archival work. These developments foster continued collaboration between archivists and those in related professions such as records management, but, more importantly, reinforce their longstanding distinctiveness. The article discusses why and how the University of Manitoba has responded to the increasingly complex challenges facing archivists and archival educators in this evolving setting with an archival, conceptual, historical, and research-oriented curriculum.