Dorothy W. Skaf

Electrochemical graphite intercalation with nitric acid solutions

Abstract Aqueous nitric acid solutions were used to intercalate graphite in an electrolysis cell under constant current conditions. The graphite potential required for intercalation increased with decreasing acid concentration from 70 to 65 wt.% nitric acid. Intercalation did not occur in 50 and 30 wt.% acid solutions. Limited studies showed no correlation of graphite intercalation potential with graphite thickness or surface area. The intercalation compounds were unstable in acid solutions. The voltage decay during spontaneous deintercalation in 70 wt.% HNO3 mirrored many of the features observed during intercalation.

Microstructure and properties of CVD tungsten carbide from tungsten hexafluoride and dimethyl ether

Tungsten carbide was deposited from tungsten hexafluoride, dimethyl ether, and hydrogen using a horizontal, cold-wall reactor. The effects of substrate temperature, reactor pressure, and reagent ratio on the coating growth rate, morphology, composition, and microhardness were studied. Under most conditions, the solid deposit was primarily W[sub 3]C with minor amounts of W. The tungsten carbide growth rate data fit an Arrhenius rate expression for temperatures from 425 to 550 C and had an activation energy of 24 kcal/mol at 70 mmHg total pressure and a WF[sub 6]/DME ratio of 6.3. A variety of surface morphologies and microstructures were observed. The microhardness of the coated substrates increased with coating thickness to a maximum value of 2,400 kg/mm[sup 2].

Electrochemical behavior of bis(β-diketonate)copper complexes

The use of copper to produce interconnects for microchip manufacture has prompted a renewed interest in its corrosion, deposition, and passivation processes. The aqueous electrochemistry of four bis(β-diketonate)copper complexes (where β-diketone = acacH, tfacH, hfacH, and tmhdH) in aqueous media has been investigated. Equilibrium constants were used to calculate potential-pH diagrams, varying the β-diketone ligand, ligand and/or copper concentrations, and the ionic strength of the buffer solution. The theoretical potential-pH diagrams showed good correlation to the experimental data obtained in aqueous solutions.

Sustained oscillations in simple models for chemical vapor deposition

Simple models for the chemical vapor deposition of carbide films are developed and their dynamic behavior is analyzed. By performing a parameter search, certain sets of model parameters were identified that yield stable limit cycles for the gas phase reagent concentrations at the substrate surface. The concentration oscillations are seen to arise from a balance between reagent supply to the substrate and concentration-dependent consumption terms. The changes in the surface concentration could alter the observed deposit from one form to another, and could lead to the laminar structure observed in certain carbide coatings.

The Effects of Photocatalyst and Solution Co-Contaminants onPhotocatalytic Oxidation of 1,3- Dinitrobenzene in Aqueous SemiconductorOxide Suspensions

Heterogeneous photocatalysis of 1,3-dinitrobenzene (DNB) using simulated solar irradiation in the presence of semiconductor oxides was studied. Comparison of TiO2 and ZnO showed that the former was a more efficient photocatalyst for the degradation of DNB. The addition of potential environmental co-contaminants such as acetic acid, fulvic acid and seawater salts to the DNB solutions all inhibited the DNB degradation rate. The addition of hydroxyl radical-generating compounds, including H2O2 and NaNO3, to the DNB solutions both slightly reduced the DNB degradation rate, indicating that hydroxyl radical generation is not a rate limiting step in the overall reaction process. The use of 5 volume % acetone cosolvent slowed the degradation rate, however for 15 volume % acetone despite the slower relative rate of destruction, the higher concentrations of DNB provided higher mass destruction rates.

Photocatalytic Oxidation of Dimethyl Methylphosphonate in AqueousSuspensions of TiO2

Heterogeneous photocatalysis using simulated solar irradiation in the presence of titanium dioxide was studied using dimethyl methylphosphonate (DMMP) as a surrogate for organophosphorus compounds including pesticides and chemical warfare agents. A reduction in solution pH accompanied DMMP degradation with the pH approaching the pKa of DMMP. Addition of peroxide before reaction increased the amount of DMMP degraded. Nearly complete destruction of DMMP was only achieved with the largest addition of peroxide. Photoreaction of DMMP in a pH 10 solution and a pH 10 carbonate buffer degraded a similar percent of the solute, with a more gradual reaction observed for the buffered solution. Variations in reaction conditions were studied to evaluate the effect of potential spill conditions. The presence of fulvic acid in the solution slightly enhanced the oxidation of DMMP and the absence of dissolved oxygen inhibited DMMP oxidation. DMMP solutions prepared in simulated sea water reached similar degradation percentages as pure solutions, however, reacted more slowly.