The sp3-bonded “transparent phase” of carbon, formed by compression of single-crystal graphite to 18 GPa, has been found to be quenchable to atmospheric pressure at low temperatures (<100 K). The quenched transparent phase reverts to graphite upon warming to room temperature, indicating that there is a surprisingly small activation barrier for a transformation that must involve carbon−carbon bond breakage. Visual observations and Raman spectroscopy are used to document the novel ambient pressure transformation.

We present studies of the rheological properties and dispersion stability of MR fluids as a function of particle shape by comparing fluids made with uniform nickel spheres to those employing nickel microwires suspended in silicone oil. The wires were fabricated using template-based electrodeposition having diameters in the range 300 ± 30 nm and lengths in the range of 5 – 25 μm . The properties of these wires were compared to commercial nickel carbonyl spheres (1–10 μm dia.). Qualitatively, the off-state (field off) viscosity of fluids containing only wires was found to be substantially greater than those fluids that contain only spherical particles. Rheological measurements of the on-state viscosities were conducted using a custom rheometer equipped with an electromagnet capable of magnetic fields up to 0.6 T. Placed in this field, we observed yield stresses of 1.88 ± 0.23 and 1.86 ± 0.26 kPa for 7.6 volume percent of pure nickel spheres and microwires, respectively. The fluids containing spherical nickel particles tended to settle rather quickly (< 20 minutes), while those containing only wires remained suspended even after several months.

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