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This site uses cookies to assist with navigation, analyse your use of our services, collect data for ads personalisation and provide content from third parties. By using our site, you acknowledge that you have read and understand our Privacy Policy and Terms of Use. Share Twit Share Email. Home Physics General Physics. Solid oxygen with the different spin green alignments as reported in PRL.
Image source: Stefan Klotz. Explore further. Oxygen is a chemical element — a substance that contains only one type of atom. Its official chemical symbol is O, and its atomic number is 8, which means that an oxygen atom has eight protons in its nucleus. Oxygen is a gas at room temperature and has no colour, smell or taste. Oxygen is found naturally as a molecule. Two oxygen atoms strongly bind together with a covalent double bond to form dioxygen or O 2.
Ozone is another form of pure oxygen. Ultraviolet light UV splits O 2 molecules into single oxygen atoms. The single oxygen atoms latch onto O 2 molecules to form O 3 the chemical formula for ozone. The stratosphere has higher concentrations of O 3 because there is more UV present. The ozone layer filters out UV, which reduces the opportunity to split O 2 molecules in the lower atmosphere troposphere , where we live.
Ozone can still form in the troposphere when O 2 is put under high heat and pressure. Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative. Advanced search. Skip to main content Thank you for visiting nature.
Just a pretty phase? Download PDF. Solid red oxygen: useless but delightful. The storage application was eventually rejected because no practical means could be found to transfer the solid. Relevant and important past cryogenic engineering work with solid oxygen includes work at Aerojet-General on cryogenic oxygen storage 4 , production of slush oxygen and hydrogen at NBS now NIST 5 , and studies of the magnetic properties of solid oxygen 6.
There is also currently ongoing research including that reported here 7 in solid oxygen and hydrogen cryogenics being done at the Air Force Phillips Lab and, through their funding, at various universities. This work is motivated by the desire to stabilize more energetic oxidizers in a solid oxygen matrix to obtain a higher energy density propellant. Although the solid mixture holds the promise of greater energy release, the use of the cryogenic solids themselves creates new engineering problems.
The need for fundamental data on the mechanical properties of solid oxygen arises from design questions about the feed and injection of the solid for a propulsion system.
The shear strength must be known to design an extrusion device, and since oxygen is known to be abrasive, some information is needed about how this abrasiveness will affect the design. Some simple experiments were thus attempted to get a preliminary estimate of the shear strength of solid oxygen. Estimates of shear strength based on the literature and experience implied a value as high as 7 MPa, but based on hydrogen pellet extrusion experiments that measure a 0. Common experience with a Van der Waals solid is primarily with the inconvenience these solids cause when they occur accidentally in a liquid cryogen system.
Examples are solid air in the bottom of a helium, dewar or solid nitrogen blocking a nitrogen gas line. Pressures of 1 to 2 MPa are not enough to clear a blocked line, suggesting the possibility that estimates of shear strength could be made by measuring the pressure required to clear a line of a solid blockage. This liquid would then be frozen by lowering the tube into a liquid helium dewar.
The helium pressure required to dislodge this solid from the smooth tube would give a measurement of the shear strength. Designing such a simple experiment was in fact very difficult. The primary problems were the possibility of an explosive discharge when solid oxygen breaks, and the temperature sensitivity of the measurements.
The heat transfer to the walls of the tube is sufficient to quickly melt the solid oxygen adhering to the wall and negate any test results. This implies the need for shielding the end with helium and liquid nitrogen, which in turn leads to complications for an explosive pellet discharge. The analysis of these problems suggested alternate experiments using nitrogen instead of oxygen.
Nitrogen does not have the fire hazards of oxygen and has similar freezing temperatures and molecular forces, so that its strength and behavior should be similar to that of oxygen. By crimping the end of a stainless steel tube and pushing a rubber stopper down to the end, a freezing cup was created. Liquid nitrogen LN 2 was then poured into the tube and allowed to solidify at the bottom on the order of an hour.
A solid nitrogen test consisted of 1 quickly withdrawing the tube from the dewar, 2 inverting it over a LN 2 cooled block, 3 Waiting a few seconds until the heat transfer to the tube melted the side of the solid nitrogen plug and it dropped out of the tube, 4 quickly manipulating the plug to a test position, and 5 performing a short mechanical or visual test on the plug.
The plug survived about 5 seconds before total evaporation. Clear, condensation-free, visual access was obtained by taking advantage of the density stability of the cold gas that prevented water vapor from interfering with inspection through the open top of the apparatus.
The most interesting insight gained by manipulating these plugs is that they are clearly plastic at higher temperatures. In the case of a cylinder placed between two supports over a LN 2 bath, it would initially maintain its position in response to a downward force at the center and then bend into a U shape.
A similar plastic behavior was seen in response to impact with a hammer. The cylinder would squash but never shatter or splatter. This was very surprising behavior that implied that the solid nitrogen is a plastic material of moderate strength.
These observations confirmed the behavior of the solid during the more sophisticated shear tests. The solid can be clear or white, depending on the condensation history - the white color arises from included voids. A cryogenic mechanical testing apparatus 8 was used to measure the shear forces needed to move a metal rod embedded in solid oxygen. A Sintech Model computer-integrated mechanical strength testing system was used in combination with a Janis 10CNDT cryostat capable of operation between room temperature and 1.
Figure 1 shows a schematic of the assembled apparatus. The cryostat is a standard model with vacuum insulation between a liquid nitrogen dewar surrounding a liquid helium dewar, in turn surrounding a gaseous helium test volume that contains the mechanical testing apparatus.
The primary design difficulties for this experiment were to: 1 develop an apparatus that could be easily assembled yet support significant mechanical shearing forces, 2 fit the apparatus within the small cryostat test volume 5 cm diameter, 12 cm long , 3 provide enough heat capacity and thermal conductivity to liquefy then solidify the oxygen in a reasonable time, 4 distribute the loading on the solid to give accurate shear measurements, 5 provide entry and exit for the oxygen gas through the cryostat's thermal barriers and make the flow rate high enough to fill the cup relatively quickly, 6 provide a precisely metered oxygen supply source, 7 contain the oxygen so it only condenses in the cup and not on the colder surfaces of the dewar, and 8 provide temperature monitoring and temperature control to be able to perform experiments at different temperatures.
Procedures also had to be developed to feed the oxygen gas, liquefy it, solidify it, and then achieve the test temperature. Some of the lessons learned were: 1 The gas feed tube is easily blocked if its temperature is below the oxygen solidification temperature, 2 The oxygen is density stable in a cold helium bath and the gas diffusion rates are very slow, so gaseous oxygen can easily be kept in an open cup without significant losses to condensation on farther away colder surfaces; a vacuum container is not needed, 3 To minimize solidification time it is necessary to have enough heat capacity in the supporting structure to solidify the oxygen than to rely on convective and conductive heat transfer from cold external helium gas, 4 Thermal equilibration times for the solid oxygen can be long if the solid dimensions approach 1 cm, making experiments long, 5 The assembly, thermal, structural, space, liquid containment, shearing geometry, and motion constraints on the shearing apparatus lead to a very complicated design, 6 Proper condensation of the oxygen is crucial.
Oxygen condensation on parts of the cryostat where it was not wanted prevents accurate filling of the shearing volume and can lead to an explosion in the vacuum pump during pumpdown. Condensation in the shearing apparatus might also cause additional solid contact that would confuse the shear measurement.
An important aspect of the solidification of oxygen is the supply of thermal energy needed to solidify the oxygen from the gas. Cooling through solid oxygen is very slow, so the volume of oxygen to be used was minimized by a metal insert in the solidification cup to keep the solidification time as short as possible.
The insert also absorbed much of the heat of condensation. On a volume basis the specific heat of available materials at 67 K does not vary with material, so the most convenient material - aluminum - was chosen. Care was taken to assure that shearing did not take place against the aluminum. The oxygen needed to fill the cup was estimated to result in a K warm up of the structure, such that if solidification is begun with the shearing apparatus at 60 K, the structure remains cold enough to keep the oxygen from boiling 90 K , after which the liquid could be solidified by thermal conduction.
The minimum temperature of the structure was 55 K to prevent blockage of the gas inlet tube by solid formation this happened quickly in practice at lower temperatures.
The overall shearing apparatus Fig. The configuration of the cryogenic shearing fixture is also shown in Fig. This fixture consists of an inner central tension fixture designed to assure strictly axial loading of the puller rod in the solid, and an outer stress-transmitting shell ending in the oxygen cup. Brass, copper, and aluminum are the materials of choice for use with oxygen.
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