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J Am Chem Soc. 2016 Feb 3;138(4):1252-7. doi: 10.1021/jacs.5b10936. Epub 2016 Jan 19.

Tilted Magnetic Levitation Enables Measurement of the Complete Range of Densities of Materials with Low Magnetic Permeability.

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Department of Chemistry and Chemical Biology, Harvard University , 12 Oxford Street, Cambridge, Massachusetts 02138, United States.
Wyss Institute for Biologically Inspired Engineering, Harvard University , 60 Oxford Street, Cambridge, Massachusetts 02138, United States.
Kavli Institute for Bionano Science and Technology, Harvard University , 29 Oxford Street, Cambridge, Massachusetts 02138, United States.


Magnetic levitation (MagLev) of diamagnetic or weakly paramagnetic materials suspended in a paramagnetic solution in a magnetic field gradient provides a simple method to measure the density of small samples of solids or liquids. One major limitation of this method, thus far, has been an inability to measure or manipulate materials outside of a narrow range of densities (0.8 g/cm(3) < ρ < 2.3 g/cm(3)) that are close in density to the suspending, aqueous medium. This paper explores a simple method-"tilted MagLev"-to increase the range of densities that can be levitated magnetically. Tilting the MagLev device relative to the gravitational vector enables the magnetic force to be decreased (relative to the magnetic force) along the axis of measurement. This approach enables many practical measurements over the entire range of densities observed in matter at ambient conditions-from air bubbles (ρ ≈ 0) to osmium and iridium (ρ ≈ 23 g/cm(3)). The ability to levitate, simultaneously, objects with a broad range of different densities provides an operationally simple method that may find application to forensic science (e.g., for identifying the composition of miscellaneous objects or powders), industrial manufacturing (e.g., for quality control of parts), or resource-limited settings (e.g., for identifying and separating small particles of metals and alloys).


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