Determining Compositional Variation in Silicon-Metal Alloys by Parsing SEM/EDS Hyperspectral Images.

High-temperature differential scanning calorimetry was used to understand the thermal properties of Si-rich metal­silicon alloys. Insoluble metals (A and B) were found to produce an alloy with discrete ASi2 and BSi2 dispersed phases. In contrast, metals that form a solid solution result in a dispersed phase that has a composition of AxB1−xSi2, where x varies continuously across each inclusion. This complex composition distribution is putatively caused by differences in the solidification temperatures of ASi2 versus BSi2. Though this behavior was observed for several different combinations of metals, we focus here specifically on the Cr/V/Si system. To better understand the range and most probable element concentrations in the dispersed silicide domains, a method was devised to generate histograms of their Cr and V concentrations from energy-dispersive X-ray spectroscopy hyperspectral images. Varying the Cr/V/Si ratio was found to change the shape of the element histograms, indicating that the distribution of silicide compositions that form is controlled by the input composition. Adding aluminum was found to result in dispersed phases that had a single composition rather than a range of Cr and V concentrations. This demonstrates that aluminum can be an effective additive for altering solidification kinetics in silicon alloys.

Electronic Structure and Potential Reactivity of Silaaromatic Molecules.

Silicon-based materials are crucial for conventional electronics. The fascinating properties of the new two-dimensional material silicene, the silicon analogue of graphene (one atom-thick silicon sheets), offer a potential bridge between conventional and molecular electronics. The ground-state configuration of silicene is buckled, which compromises optimal constructive overlap of p orbitals. Because silicene is not planar like graphene, it has a lower intrinsic electron/hole mobility than graphene. This motivates a search for improved, alternative, planar materials. Miniaturization of silicene/graphene hybrid monolayers affords diverse silicon-organic and -inorganic molecules, whose potential as building blocks for molecular electronics is unexplored. Additionally, hybridization of pure silicon rings (or sheets) is a versatile way to control the geometrical and electronic characteristics of the aromatic ring. In this work we systematically investigate, computationally, architectures and electronic structures of a series of hybrid silaaromatic monomers and fused-ring oligomers. This includes the thermochemistry of representative reactions: hydrogenation and oxidation. The effect of various skeletal substituents of interest is elucidated as well. We show that the specific location of carbon and silicon atoms, and their relative populations in the rings are crucial factors controlling the molecular geometry and the quasi-particle gap. Furthermore, we suggest that electron-withdrawing substituents such as CN, F, and CF3 are promising candidates to promote the air-stability of silaaromatics. Finally, on the basis of the analysis of benzene-like silaaromatic molecules, we discuss a set of alternative, prototype ring molecules that feature planarity and delocalized π bonds. These motifs may be useful for designing new extended materials.

Development of a tubular high-density plasma reactor for water treatment.

Experiments have yielded a number of important insights into the energy distribution, sparging and oxidation of methyl tert-butyl ether (MTBE), benzene, ethylbenzene, toluene, m- and p-xylene, and o-xylene (BTEX) in a dense medium plasma reactor (DMPR). It has been found that the DMPR transferred a relatively small amount of electrical energy, approximately 4% in the form of sensible heat, to the surrounding bulk liquid. Rate constants associated with plasma initiated oxidation, interphase mass transfer and photolysis were determined using a combination of non-linear least squares analysis and Matlab optimization for each species. The rate constants developed for the DMPR, in conjunction with a species mass balance on a prototype tubular high-density plasma reactor, have been applied to determine the removal rates of MTBE and the BTEXs when operating in batch and continuous flow configurations. The dependence of contaminant concentration on parameters such as treatment time, the number of pin electrodes, electrode gap, and volumetric flow rate has been determined. It was found that, under various design specifications and operating conditions, the tubular high-density plasma reactor may be an effective tool for the removal of volatile organic compounds from aqueous solutions.

Treatment of methyl tert-butyl ether contaminated water using a dense medium plasma reactor: a mechanistic and kinetic investigation.

Plasma treatment of contaminated water appears to be a promising alternative for the oxidation of aqueous organic pollutants. This study examines the kinetic and oxidation mechanisms of methyl tert-butyl ether (MTBE) in a dense medium plasma (DMP) reactor utilizing gas chromatography-mass spectrometry and gas chromatography-thermal conductivity techniques. A rate law is developed for the removal of MTBE from an aqueous solution in the DMP reactor. Rate constants are also derived for three reactor configurations and two pin array spin rates. The oxidation products from the treatment of MTBE-contaminated water in the DMP reactor were found to be predominately carbon dioxide, with smaller amounts of acetone, tert-butyl formate, and formaldehyde. The lack of stable intermediate products suggests that the MTBE is, to some extent, oxidized directly to carbon dioxide, making the DMP reactor a promising tool in the future remediation of water. Chemical and physical mechanisms together with carbon balances are used to describe the formation of the oxidation products and the important aspects of the plasma discharge.