A series of crystalline homometallic and heterometallic cobalt and nickel hydroxides and oxides were prepared using a continuous hydrothermal flow synthesis system. In all syntheses, the relevant metal salt solutions were pumped under high pressure to meet pH or other chemical modifiers (H 2 O 2 or PVP) before the mixture was brought into contact with a feed of superheated (or supercritical) water, whereupon precipitation and particle growth occurred. The resulting nanoparticle (typically less than 100 nm in diameter) suspensions were collected from the outlet of the back-pressure regulator of the hydrothermal system. The collected suspensions were centrifuged, and the washed solids were freeze-dried prior to analyses. The nanopowders were characterized by a number of analytical methods including X-ray powder diffraction, Brunauer-Emmett-Teller (BET) surface area measurements, and simultaneous thermogravimetric analysis/differential scanning calorimetry.

The synthesis of permanently porous, highly cross-linked, poly(methacrylate) resins using supercritical CO 2 is described. The pressure-adjustable solvent properties associated with supercritical fluid solvents are exploited to fine-tune the average pore size and surface area of the materials. It was found that the materials' properties varied in a discontinuous manner with respect to the CO 2 pressure. A minimum in the BET surface area (and a maximum in the pore diameter) was observed at a reaction pressure of approximately 2600 psi. These trends were rationalized by the fact that the mechanisms of nucleation, aggregation, and pore formation are highly sensitive to the nature of the porogenic solvent environment.

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