The Structure of the Allotropic Forms of He3 and He4
In 1908 Kamerlingh Onnes first liquefied helium. He observed that it remained liquid, even when cooled as low as 0.83°K, which was his lowest obtainable temperature. He correctly supposed that, if cooled under its own vapor pressure, helium would remain liquid down to absolute zero. The question remained however, whether or not helium could be solidified. Keesom in 1926 found that freezing required a pressure of at least 25 atm. Osborne, Abraham, and Weinstock , who in 1951 first solidified the lighter isotope, He3, observed that a similar pressure was needed.
KeywordsMolar Volume Hexagonal Close Packing Close Packed Structure Melting Line Allotropic Form
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