Aerodynamic

levitation Levitation (from Latin ''levitas'' "lightness") is the process by which an object is held aloft in a stable position, without mechanical support via any physical contact. Levitation is accomplished by providing an upward force that counteracts ...

is the use of gas pressure to levitate materials so that they are no longer in physical contact with any container. In scientific experiments this removes contamination and nucleation issues associated with physical contact with a container.

Overview

The term aerodynamic levitation could be applied to many objects that use gas pressure to counter the force of

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

, and allow stable

. Helicopters and air hockey pucks are two good examples of objects that are aerodynamically levitated. However, more recently this term has also been associated with a scientific technique which uses a cone-shaped nozzle allowing stable levitation of 1-3mm diameter spherical samples without the need for active control mechanisms.

Aerodynamic levitation as a scientific tool

These systems allow spherical samples to be levitated by passing gas up through a diverging conical nozzle. Combining this with >200W continuous CO₂ laser heating allows sample temperatures in excess of 3000 degrees Celsius to be achieved. When heating materials to these extremely high temperatures levitation in general provides two key advantages over traditional furnaces. First, contamination that would otherwise occur from a solid container is eliminated. Second, the sample can be undercooled, i.e. cooled below its normal freezing temperature without actually freezing.

Undercooling of liquid samples

Undercooling, or

supercooling Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its melting point without it becoming a solid. It achieves this in the absence of a seed crystal or nucleus around which a crystal ...

, is the cooling of a liquid below its equilibrium freezing temperature while it remains a liquid. This can occur wherever crystal nucleation is suppressed. In levitated samples, heterogeneous nucleation is suppressed due to lack of contact with a solid surface. Levitation techniques typically allow samples to be cooled several hundred degrees Celsius below their equilibrium freezing temperatures.

Glass produced by aerodynamic levitation

Since crystal nucleation is suppressed by levitation, and since it is not limited by sample conductivity (unlike electromagnetic levitation), aerodynamic levitation can be used to make glassy materials, from high temperature melts that cannot be made by standard methods. Several silica-free, aluminium oxide based glasses have been made.

Physical property measurements

In the last few years a range of

in situ ''In situ'' (; often not italicized in English) is a Latin phrase that translates literally to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in ...

measurement techniques have also been developed. The following measurements can be made with varying precision: electrical conductivity,

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...

, surface tension,

specific heat capacity In thermodynamics, the specific heat capacity (symbol ) of a substance is the heat capacity of a sample of the substance divided by the mass of the sample, also sometimes referred to as massic heat capacity. Informally, it is the amount of heat t ...

, In situ aerodynamic levitation has also been combined with: X-ray synchrotron radiation,

neutron scattering Neutron scattering, the irregular dispersal of free neutrons by matter, can refer to either the naturally occurring physical process itself or to the man-made experimental techniques that use the natural process for investigating materials. Th ...

NMR spectroscopy Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. The sample is placed in a magnetic fie ...

References

{{DEFAULTSORT:Aerodynamic Levitation Levitation Aerodynamics