Scientists observe liquid dripping upwards
(21 February 2002)
Durham University academics have captured the attention of the scientific world with their chance observation of an unusual phenomenon during preparations for an undergraduate class.Dr David Wood, Reader in the School of Engineering, called in a colleague from Physics, Dr Damian Hampshire, after seeing liquid oxygen dripping upwards as he set up a demonstration on superconductivity - where certain materials at low temperatures have almost no resistance to electrical current.
Their findings are reported in the latest issue of the prominent science journal Nature and a University of Durham web page complete with photos and video.
Dr Wood, who says it was "a classic case of looking for one thing and finding something else," was setting up a well-known demonstration - which the University has shown many times to school pupils visiting its annual Festival of Science, as well as to undergraduates. A magnet is levitated in mid-air above a metal superconductor, cooled to about 200 degrees below zero using liquid nitrogen. Dr Wood noticed liquid oxygen drops forming on the superconductor, dripping upwards, hitting the magnet and then boiling.
He called in Dr Hampshire to help explain what was happening and they got Physics Lab Technician Vicky Greener to produce a short video of the demonstration. The idea for the Nature paper sprang from there because this was a desktop demonstration of something that otherwise had only been done on a large-scale.
Dr Wood adds: "The whole experiment was done in a few minutes, without expensive equipment, on the window ledge in my office. Many schools will have the facilities to recreate the experiment. It shows you don't always need megabucks and huge labs to make scientific advances."
The observation is particularly interesting because of the small-scale of the equipment and because the findings could help other scientists. For example stocks of liquid nitrogen need to be kept pure when preserving cooled biological specimens. If contaminated with liquid oxygen they will go off. This has implications for the long-term storage of cells, tissues and organisms.
The scientists explain that oxygen condensed out of the air into the liquid nitrogen being used to cool the superconductor. Liquid oxygen has a type of magnetic property and it can be pulled into the high-field region between the magnet and the superconductor to form a "bridge". Some of the supercurrents that help to keep the magnet floating are produced by the penetration of the magnetic field into the superconductor. Large drops of liquid oxygen gather together on the surface of the superconductor and build up to bridge the gap between itself and the magnet. Small drops can produce a continuous process in which a new drop starts to form on the superconductor after an old one has been pulled across the gap onto the magnet and boiled away.
Notes to Editors
1. The Nature paper is: "Oxygen drips upwards from superconductors" by D Wood, V Greener and D P Hampshire, University of Durham
2. News teams can see the Website information at: http://www.dur.ac.uk/d.p.hampshire/drop.html.
3. Superconductors have many applications in industry because they are very energy-efficient in carrying electricity and can carry very high electrical currents. They are used in electrical motors and generators, and for Magnetic Resonance Imaging (bodyscans) in medicine.
Dr David Wood, Reader, School of Engineering
Tel: +44 (0)191 374 2564
Fax: +44 (0)191 374 7492
Dr Damian Hampshire, Reader, Department of Physics
Tel:+44 (0)191 374 2167
Fax: +44 (0)191 374 3749