H. Richard Naslund

Electrocatalytic reduction of oxygen: Gold and gold-platinum nanoparticle catalysts prepared by two-phase protocol

This paper describes recent results of an investigation of gold (Au) and gold-platinum (AuPt) nanoparticle electrocatalysts for fuel cell reaction at the cathode, i.e., oxygen reduction reaction (ORR). The Au nanoparticles and AuPt nanoparticles with different bimetallic ratios were prepared by a two-phase protocol and supported on carbon black materials. The catalysts were thermally activated under controlled calcination temperatures. The electrocatalytic ORR activities were characterized using voltammetric and rotating disk electrode techniques. We have also attempted an initial comparison of the electrocatalytic activities of our Au/C and AuPt/C catalysts with commercially-available Pt/C and PtRu/C catalysts (E-tek) under the same voltammetric measurement conditions. The results revealed important insights into the electrocatalytic activity of our catalysts, and have important implications to the design of highly active fuel cell catalysts.

Chromium-assisted synthesis of platinum nanocube electrocatalysts

This report demonstrates a novel strategy of chromium-assisted synthesis of platinum nanocubes as electrocatalysts for oxygen reduction reaction with enhanced specific activity.

Oxygen isotope composition of magnetite in iron ores of the Kiruna type in Chile and Sweden

Abstract Magnetite-apatite iron ores of the Kiruna type, unaffected by deformation, have structures and textures similar to those of igneous rocks. The best examples are the El Laco deposits in northern Chile which resemble lava flows, pyroclastic deposits and dikes. El Laco magnetites have δ18O values between 2.3 and 4.2‰ (V-SMOW). Magnetite from ore with a magmatic texture has a mean of 3.7‰, and the mean for magnetite intergrown with pyroxene in veins is 2.4‰. Oxygen isotope data given here, fluid inclusion results and geological evidence indicate that ore formation took place in a cooling magmatic system. Major orebodies resembling lava flows and near-vent pyroclastic deposits crystallized from magma at ca. 1000°C. Fluids from cooling magma deposited magnetite and pyroxene (±apatite) at ca. 800°C in fissures and open spaces, now present as veins cutting major orebodies. There is little evidence for significant magnetite precipitation during hydrothermal conditions. A large province of magnetite-apatite iron ore in central Chile (the Cretaceous iron belt) and the Kiruna district in northern Sweden also contain primary ore of magmatic appearance. Major deposits in the Chilean iron belt and Kiruna contain magmatic-textured magnetites with the following δ18O means: Algarrobo = 2.2‰, Romeral = 1.2‰, Cerro Imán = 1.6‰, and Kiirunavaara = 1.5‰. We consider all oxygen isotope data for unoxidized, magmatic-textured magnetite as representative of the Fe-rich magmas. Magnetites affected by hydrothermal alteration, recrystallization and subaerial oxidation have modified isotope signatures.

Magnetite spherules in pyroclastic iron ore at El Laco, Chile

Abstract The El Laco iron deposits in northern Chile consist of magnetite (or martite) and minor hematite, pyroxene, and apatite. The orebodies are situated on a volcanic complex and resemble lavas and pyroclastic deposits, but a magmatic origin is rejected by some geologists who regard the ores as products of hydrothermal replacement of volcanic rocks. This study describes spherules of magnetite in the ore at Laco Sur and outlines a previously unrecognized crystallization process for the formation of spherical magnetite crystal aggregates during volcanic eruption. Mining at Laco Sur, the second largest deposit at El Laco, shows that most of the ore is friable and resembles pyroclastic material; hard ore with vesicle-like cavities occurs subordinately. The friable ore is a porous aggregate of 0.01–0.2 mm magnetite octahedra with only a local stratification defned by millimeter-thin strata of apatite. Films of iron phosphate are common on magnetite crystals, and vertical pipes called gas escape tubes are abundant in the ore. A SEM study reveals that magnetite spherules in the range 0.05–0.2 mm occur in most samples of friable ore from the central-lower part of the deposit. The proportion of spherules in a sample varies from high to nil, but overall the spherule content is low in the ore. The spherules are aggregates of octahedral crystals, or single octahedra, that have been rounded by stepwise, subparallel growth of magnetite with a systematic slight shift in orientation of successive steps. The shape of the spherules demonstrates that they formed unattached to any surface. Growth from hot magmatic gas saturated in iron in a volcanic plume and deposition as ash fall can account for the features of the spherule-bearing friable ore.

Determination of aluminum in high fat content biological materials using emulsions and direct current plasma

A new sample dissolution method employing an emulsion has been developed and evaluated for the determination of aluminum (Al) in high fat content biological samples. An emulsion is used to disperse the residual fat left over from nitric acid digestion to form a stable homogeneous moiety before aspiration into the direct current plasma (DCP) source. The method eliminates the need to filter the fat or extract fat soluble Al species from the undigested fat before analysis. Comparisons were made between the present method and two conventional sample dissolution methods for the determination of Al present in spiked and certified biological samples. The results indicated that the emulsification procedure offers simplicity, speed and improved accuracy/precision for the DCP determination of Al, especially for biological materials containing high amounts of fat and fat soluble Al complex(es).

Characterizations of Core-Shell Nanoparticle Catalysts for Methanol Electrooxidation

This paper describes the results of an investigation of the structure and composition of core-shell gold and alloy nanoparticles as catalytically active nanomaterials for potential fuel cell catalysis.