Pykrete
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Pykrete (also known as picolite) is a composite material made of approximately 14% sawdust (or, less frequently, wood pulp) and 86% water by weight then frozen, invented by Max Perutz and proposed during World War II by Geoffrey Pyke to the Royal Navy of the United Kingdom as a candidate material for making a huge, unsinkable aircraft carrier, Project Habakkuk, actually more of a floating island than a ship in the traditional sense. Pykrete has some interesting properties, notably its relatively slow melting rate (due to low thermal conductivity), and its vastly improved strength and toughness over pure ice, actually closer to concrete, while still being able to float on water. Pykrete is slightly harder to form than concrete, as it expands while freezing, but can be repaired and maintained from the sea's most abundant raw material.
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[edit] History
Pyke managed to convince Lord Mountbatten of the worth of his project some time around 1942, and trials were made in two locations in Alberta. Blocks of Pykrete were attacked with various explosives and it was found that a charge corresponding to a torpedo warhead would have made only a minor dent in the planned Habbakuk carrier.
At the Quebec Conference of 1943 Mountbatten brought a block of Pykrete along to demonstrate its potential to the bevy of admirals and generals who had come along with Winston Churchill and Franklin D. Roosevelt. Mountbatten entered the project meeting with two blocks and placed them on the ground. One was a normal ice block and the other was Pykrete. He then drew his service pistol and shot at the first block. It shattered and splintered. Next, he fired at the Pykrete to give an idea of the resistance of that kind of ice to projectiles. The bullet ricochetted off the block, grazing the trouser leg of Admiral Ernest King and ending up in the wall. The Admiral was impressed by Mountbatten's unorthodox demonstration.[citation needed] Thus, the small pilot project was given the go-ahead. Early experiments on the viability of pykrete were carried out by Max Perutz following Pyke's inspiration, in a secret location underneath Smithfield Meat Market in the City of London.[1][2] The experiments were carried by Perutz and his collaborators in a refrigerated meat locker in a Smithfield Market butcher's basement, behind a protective screen of frozen animal carcasses.[3] The tests confirmed that pykrete was as strong as concrete and, unlike pure ice, did not shatter, but also that it sags under its own weight at temperatures higher than -15 C.[4] Despite these tests, the main Project Habbakuk was never put into action. The funds simply were not available due to other WWII projects, as well as the belief that the tides of the war were beginning to turn in favour of the Allies using more conventional methods.[5]
According to the memoirs of British General Ismay:
- "A good deal of consideration, much of it highly technical, was also given to the feasibility of building floating platforms which could either be used by fighters to support opposed landings until such time as airfields ashore were available, or act as staging points for ferrying aircraft over long distances. The idea as originally conceived by a member of Combined Operations staff, and vehemently supported by Mountbatten, was that these floating platforms should be constructed out of icebergs. They would be provided with engines which would enable them to steam at slow speed, and with refrigeration plants to prevent them melting. They would be unsinkable. The whole thing seemed completely fantastic, but the idea was not abandoned without a great deal of investigation. Various alternative methods of construction were then considered by the United States naval authorities, but in the end there was general agreement that carriers and auxiliary carriers would serve the same purpose more effectively."[6]
In September 1943, a proposal for making smaller pykrete vessels included the following table of characteristics. Strengths are in units of pounds per square inch:[7]
| Mechanical properties | Ice | Concrete | Pykerete |
|---|---|---|---|
| Crushing strength | 500 | 2,500 | 1,100 |
| Tensile | 160 | 250 | 700 |
| Density | 0.91 | 2.5 | 0.98 |
Since WWII pykrete has remained a scientific curiosity, unexploited by research or construction of any significance. New concepts for pykrete however crop up occasionally among architects, engineers and futurists, usually regarding its potential for mammoth offshore construction or its improvement by applying super-strong materials such as synthetic composites or Kevlar.
[edit] Durability
Pykrete has a crush resistance of greater than 21 megapascals (3,000 psi) so a very short 25 by 25 mm (1 inch by 1 inch) column could support the weight of a typical car. The wood pulp also makes the pykrete stable at higher temperatures. If a .303 caliber bullet is fired at the pykrete, it will penetrate only 16 cm (6.5 in).
For example:
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| A one inch thick 50% mixture (by volume using shredded wood mulch) hit by a single 7.62 × 39 mm rifle round fired from 30 feet which bounced off the surface. It took an additional 15 rounds of .223 fired from 15 feet to crack the block. | A two inch thick 50% mixture (by volume using shredded wood mulch) hit by a single 7.62 × 39 mm rifle round fired from 30 feet which bounced off the surface. It took an additional 7 rounds of 7.62 × 39 mm fired from 15 feet to penetrate the block. |
[edit] Construction
Pykrete can be easily formed using water and any porous and fibrous material, such as shredded paper or sawdust. Anything that can be molded with this wet pulp can be frozen into a strong and non-brittle solid.
The resistance comes from the dust which acts as a nucleation particle for ice crystal formation.[citation needed]
[edit] References
[edit] Notes
- ^ Gratzer, Walter (2002-03-05). "Max Perutz (1914–2002)". Current Biology 12 (5): R152-R154. doi:.
- ^ Ramaseshan, S (2002-03-10). "Max Perutz (1914–2002)". Current Science 82: 586-590. Indian Academy of Sciences. ISSN 0011-3891.
- ^ Collins, Paul (2002). "The Floating Island". Cabinet Magazine (7).
- ^ "Max Perutz OM" (2002-02-07). The Daily Telegraph.
- ^ Perutz, 1948.
- ^ Ismay 1960, p319.
- ^ The National Archives, ADM 1/15677 - Proposals and inventions of Mr Geoffrey Pyke; gravity propelled ball bomb, pykrete and power driven rivers.
[edit] General references
- Collins, Paul (2002).The Floating Island. Cabinet Magazine, Issue 7, Summer 2002. Retrieved 23 July 2004.
- Ismay, General Lord (1960). The Memoirs of Lord Ismay. Heinemann.
- Lampe, David (1959). Pyke, the Unknown Genius. London: Evans Brothers.
- Perutz, Max. "A Description of The Iceberg Aircraft Carrier [1948]", in Gerald Seligman: The Journal of Glaciology, Volume I (January 1947 - October 1951). The British Glaciological Society.
- Perutz, Max (2002 - paperback). I Wish I Made You Angry Earlier. Oxford University Press. ISBN 0-19-859027-X.
