Electrophoretic deposition of thermites onto micro-engineered electrodes prepared by direct-ink writing.

This work combines electrophoretic deposition (EPD) with direct-ink writing (DIW) to prepare thin films of Al/CuO thermites onto patterned two- and three-dimensional silver electrodes. DIW was used to write the electrodes using a silver nanoparticle ink, and EPD was performed in a subsequent step to deposit the thermite onto the conductive electrodes. Unlike conventional lithographic techniques, DIW is a low-cost and versatile alternative to print fine-featured electrodes, and adds the benefit of printing self-supported three-dimensional structures. EPD provides a method for depositing the composite thermite only onto the conductive electrodes, and with controlled thicknesses, which provides fine spatial and mass control, respectively. EPD has previously been shown to produce well-mixed thermite composites which can pack to reasonably high densities without the need for any postprocessing. Homogeneous mixing is particularly important in reactive composities, where good mixing can enhance the reaction kinetics by decreasing the transport distance between the components. Several two- and three-dimensional designs were investigated to highlight the versatility of using DIW and EPD together. In addition to energetic applications, we anticipate that this combination of techniques will have a variety of other applications, which would benefit from the controlled placement of a thin film of one material onto a conductive architecture of a second material.

Solvent screening for a hard-to-dissolve molecular crystal.

Materials with a high-degree of inter- and intra-molecular hydrogen bonding generally have limited solubility in conventional organic solvents. This presents a problem for the dissolution, manipulation and purification of these materials. Using a state-of-the-art density-functional-theory based quantum chemical solvation model we systematically evaluated solvents for a known hydrogen-bonded molecular crystal. This, coupled with direct solubility measurements, uncovered a class of ionic liquids involving fluoride anions that possess more than two orders of magnitude higher solvation power as compared with the best conventional solvents. The crystal structure of one such ionic liquid, determined by X-ray diffraction spectroscopy, indicates that F- ions are stabilized through H-bonded chains with water. The presence of coordinating water in such ionic liquids seems to facilitate the dissolution process by keeping the chemical activity of the F- ions in check.

Zirconium and hafnium hydrogen monothiophosphates, H2Zr(PO3S)2 and H2Hf(PO3S)2. Syntheses and selective ion-exchange properties of sulfur-containing analogues of H2M(PO4)2 (M = Zr, Hf).

The reactions between aqueous solutions of M4+ (M = Zr, Hf) and PO3S3- each result in the precipitation of a white gel that can be dried to a powder. Elemental analysis results for the white polycrystalline product yield a stoichiometry of H2M(PO3S)2. These new compounds are characterized by thermal analysis (DSC, TG-MS), vibrational spectroscopy (FT-IR, FT-Raman), 31P MAS NMR spectroscopy, energy-dispersive spectroscopy (EDS), and powder X-ray diffraction (XRD). On the basis of the characterizations and the results of trialkylamine intercalation experiments, we conclude that the H2M(PO3S)2 compounds have a layered structure that is likely similar to that of alpha-H2Zr(PO4)2.H2O. The interlayer spacing for both H2M(PO3S)2 compounds, determined by XRD, is approximately 9.4 A. Our characterization results suggest that the sulfur atom of each PO3S3- group is preferentially pointed into the interlayer region of the compound and is protonated. Two of the many potentially interesting properties of H2Zr(PO3S)2, its ion-exchange capacity and selectivity, are investigated. H2Zr(PO3S)2 is demonstrated to be an effective and recyclable ion-exchange material for both Zn2+(aq) and Cd2+(aq). Mass balance experiments indicate that the removal of Cd2+(aq) and Zn2+(aq) ions by solid H2Zr(PO3S)2 occurs by an ion-exchange process. Ion exchange results in the formation of the new compounds H0.2Cd0.9Zr(PO3S)2 and H0.50Zn0.75Zr(PO3S)2. The extraction of metal ions is monitored by XRD, vibrational spectroscopy, and elemental analysis. H2Zr(PO3S)2 reversibly intercalates Zn2+(aq) ions through three complete cycles of intercalation and deintercalation without any loss of ion-exchange capacity.