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A V McCormick

Publications and source records attributed to A V McCormick.

8 recordsLinked to original sources
PubMed2005

Tuning the reactivity of energetic nanoparticles by creation of a core-shell nanostructure.

This article presents a novel method for tuning the reactivity of nanoenergetic materials by coating a strong oxidizer nanoparticle (potassium permanganate; approximately 150 nm) with a layer of a relatively mild oxidizer (iron oxide). The measured reactivity for a nano-Al/composite oxidizer could be varied by more than a factor of 10, as measured by the pressurization rate in a closed vessel (psl/micros), by changing the coating thickness of the iron oxide. The composite oxidizer nanoparticles were synthesized by a new aerosol approach in which the nonwetting interaction between iron oxide and molten potassium permanganate aids the phase segregation of a nanocomposite droplet into a core-shell structure.

Aluminum↗
PubMed1997

Factors influencing polybutadiene deposition within porous chromatographic zirconia.

We have studied the effect of the conditions for the deposition of polymers in the preparation of polybutadiene-coated porous zirconia particles for reversed-phase chromatography. Chromatographic performance improves when the particle surface is pre-coated with elemental carbon by a chemical vapor deposition (CVD) process. Conversely, performance is significantly degraded when the solvent is removed very slowly during the deposition process. No improvement results when the particles are coated using small sequential loads of polymer. We hypothesize that the polymer deposition process is controlled by the rate at which the solvent meniscus recedes during solvent evaporation, by the affinity of the polymer for the zirconia surface, and by polymer-solvent and polymer-polymer interactions.

Butadienes↗
PubMed1997

Fluidization characteristics of and protein adsorption on fluoride-modified porous zirconium oxide particles.

Porous zirconia particles of specific gravity approximately 3.2 g/ml, mean particle sizes of approximately 50 microns, and terminal settling velocity of approximately 2.8 mm/s in water, were synthesized using an oil emulsion method from 1000 A colloids and were evaluated for their potential use in expanded bed protein adsorption. Expanded beds of particles were stable even for small volume, shallow beds (settled bed: 10 ml, height to diameter ratio < 1.0) and even for fluidization velocities common to much larger particles (210 cm/h for a three-fold bed expansion). When the surface of these particles was modified by fluoride adsorption, the total bed capacity for bovine serum albumin (BSA) adsorption was 42 +/- 2 mg BSA/ml of settled bed volume at linear velocities of 109-210 cm/h. Residence time distribution studies of several solutes under non-binding conditions were performed to assess the degree of liquid mixing and channeling in the expanded bed as a function of fluidization velocity. Liquid mixing and channeling were also studied as a function of distributor design. With these very dense particles, the degree of channeling and mixing did not worsen with the degree of expansion. Elution of adsorbed BSA while the bed was expanded (by a step increase in ionic strength) was rapid resulting in a narrow peak at high fluidization velocities without resorting to settling of the bed. The dynamic binding capacity of BSA at 5% breakthrough (protein effluent concentration equal to 5% of the inlet concentration) was the same for a two-fold expanded bed as for a settled bed (22 +/- 2 mg BSA/ml of settled bed volume), though it decreased for higher bed expansions. BSA binding was reproducible following repeated cleaning of the adsorbent with 0.25 M sodium hydroxide.

Adsorption↗
PubMed1997

Models for polybutadiene pore wall coatings in porous zirconia.

We present three models of the changes in measured pore size distribution for cylindrical pores when a polymer is deposited in the pores by evaporation from a volatile solvent. The predicted results serve as an aid in interpreting experimental nitrogen adsorption data for polybutadiene (PBD) coatings on porous zirconia. At low loadings, PBD appears to deposit in thin layers on the surface with no preference for filling either large or small pores. At higher PBD loadings, the polymer deposits preferentially in smaller pores. This is in qualitative agreement with PBD coatings on porous silica.

Butadienes↗
PubMed1996

A compendium of potential energy maps of zeolites and molecular sieves.

We present potential maps of xenon in 20 different zeolites and molecular sieves. The potential maps reveal both the accessible pore volume and localized adsorption sites and so are important in understanding adsorption and diffusion processes in nanoporous materials. We examine zeolites and molecular sieves with one-dimensional channel-like nanopores (zeolite-Theta 1, AlPO4-5, zeolite-Omega, zeolite-L, ZSM-12, AlPO4-8, and VPI-5), with two-dimensional intersecting channel-like nanopores (ZSM-5 [silicalite], ZSM-11, ferrierite, mordenite, and zeolite-Beta), and with three-dimensionally connected cagelike nanopores (zeolite-A, zeolite-Rho, zeolite-Y, sodalite, chabazite, cloverite, cation-poor zeolite-A, and cation-rich zeolite-A). We report the fraction of pore volume accessible, the maximum energy well depth at the adsorption sites, and the activation energy to move between sites. We note several examples of surprising similarities and differences between various molecular sieves. In several instances, we show that these potential profiles are relevant for other small Lennard-Jones-like molecules. By comparison with published Monte Carlo and molecular dynamics simulations, we show that the density distributions of adsorbates at low density are well predicted by the potential maps.

Cations↗
PubMed1994

Study of the irreversible adsorption of proteins on polybutadiene-coated zirconia.

The cause of irreversible adsorption of proteins on polybutadiene-coated zirconia is investigated by comparing the chromatographic properties of polybutadiene-coated zirconia with that of other reversed-phase packing materials such as bonded phase silica, polybutadiene-coated alumina and polybutadiene-coated silica. We find that the polybutadiene-coated zirconia has a micropore size distribution similar to that of the polybutadiene-coated alumina, from which some proteins can be eluted. Thus, the irreversible adsorption of proteins on polybutadiene-coated zirconia is not caused by entrapment of proteins in the micropores of the packing. The high hydrophobicity of the polybutadiene coating and the strong Lewis acid sites on the zirconia surface cause strong interactions between proteins and the stationary phase, the combination of which lead to irreversible adsorption of proteins on polybutadiene-coated zirconia.

Adsorption↗
PubMed1993

Zeolite adsorption site location and shape shown by simulated isodensity surfaces.

The graphics software package Ribbons is used to display isodensity surfaces of Xe atoms adsorbed in the alpha cage of zeolite NaA. The location, size, and shape of the adsorption sites are highly dependent on the loading and the crystal cation content. When the zeolite has a high number of cations, ellipsoidal sites arrange in a cuboctahedron. When the zeolite has fewer cations, cone-shaped sites arrange in an octahedron at low loading, but at high loading the sites become ellipsoidal and new sites form at cuboctahedral positions. The effect of the nature of the adsorption site on the development of a universal adsorption model is discussed.

Adsorption↗