Alan M. Lane

Promotion of Pt/γ-Al2O3 by Ce for preferential oxidation of CO in H2

Hydrogen for fuel cells can be produced by reforming hydrocarbons. The H2-rich reformate typically contains about 1 mol% CO which will poison the anode of polymer electrolyte fuel cells. The CO concentration can be reduced by preferential oxidation (PROX) using near-stoichiometric amounts of O2. The conversion of CO should be over 99% while minimizing oxidation of H2. Supported Pt catalysts with and without promotion by Ce were compared for the catalytic oxidation of CO by O2 in a H2 stream. With unsupported Pt catalysts, selectivity (to CO2 as opposed to H2O) was highest at low temperatures and low O2/CO ratios, however conversion was low. Addition of Ce significantly improved CO conversion under these conditions.

Ethyl lactate: a green solvent for magnetic tapecoating

The hazardous air pollutants (MEK, MIBK and toluene) used in magnetic tape coatings are replaced with ethyl lactate, which is not a hazardous air pollutant and made from renewable resources. A magnetic dispersion, containing 50/50 ethyl lactate and tetrahydrofuran, has rheological properties similar to a conventional dispersion and gave tape samples with magnetic properties comparable to VHS tape. The materials cost of the formulation containing ethyl lactate was higher than the costs of the conventional formulations.

Exchange coupled SrFe12O19/Fe-Co core/shell particles with different shell thickness

SrFe12O19/Fe-Co core/shell particles with different shell thickness were synthesized by polyol reduction of Fe and Co ions at 180°C with SrFe12O19 particles dispersed in solvent. The core/shell structure is formed by magnetic self-assembly due to the remanent magnetization of SrFe12O19 particles. Within a limited concentration range, the shell thickness could be controlled by regulating the concentration of Fe and Co ions. Core/shell structured SrFe12O19/Fe-Co particles showed more effective exchange coupling effects between hard and soft phases than physically mixed SrFe12O19 and Fe-Co particles.

Rheological and magnetic properties of a metal particle dispersion exposed to magnetic fields

We present a series of experiments in which a DC magnetic field is applied to a magnetic dispersion of acicular ferromagnetic iron particles. For DC fields above the lower limit of the switching field distribution, the magnetic susceptibility and the storage modulus of the sample increase linearly. We believe that this increase is caused by the break-up of doublets and other aggregates that are normally present in a magnetic dispersion. The break-up increases the number of free particles in the dispersion, which in turn increases the magnetic interactions and elasticity of the dispersion.

Magnetization and Intrinsic Coercivity for τ-phase Mn 54 Al 46 /α-phase Fe 65 Co 35 Composite

We have synthesized ferromagnetic τ-phase Mn 54 Al 46 /α-phase Fe 65 Co 35 composite by annealing a mixture of paramagnetic e-phase Mn 54 Al 46 and ferromagnetic α-phase Fe 65 Co 35 particles at 650℃. The volume fraction ( f h ) of hard τ-phase Mn 54 Al 46 of the composite was varied from 0 to 1. During the annealing, magnetic phase transformation occurred from paramagnetic e-phase to ferromagnetic τ-phase Mn 54 Al 46 . The magnetization and coercivity of the composite monotonically decreased and increased, respectively, as the f h increased. These results are in good agreement with our proposed composition dependent coercivity and modified magnetization equations.

Probing magnetic paints through magnetorheological and susceptibility measurements

Linear viscoelastic measurements with and without a superimposed magnetic field are used to characterize the structure of model magnetic paints comprised of metal particles, cyclohexanone and polyvinylchloride wetting resin. Simple network modeling is used to derive a formula for the field-induced increase of G′ with the single parameter, critical field Hcrit, which characterizes dispersion quality by how easily particles align under the magnetic field. Milling weakens the structure of the paint, provided sufficient resin concentration is maintained, as revealed by a decrease of G′ and Hcrit with milling time. At low resin concentration G′ increases with milling time indicating that milling induces structural reorganization which, being unsupported by resin adsorption, results in forming a stronger network. Magnetorheological measurements are correlated with susceptibility measurements in a small alternating magnetic field which probes particle interactions without breaking the structure. As the resin concentration increases, rheological spectra shift to shorter relaxation times due to structure transformation from a network to small aggregates. Susceptibility spectra shift to longer times due to weakening of particle interactions.Linear viscoelastic measurements with and without a superimposed magnetic field are used to characterize the structure of model magnetic paints comprised of metal particles, cyclohexanone and polyvinylchloride wetting resin. Simple network modeling is used to derive a formula for the field-induced increase of G′ with the single parameter, critical field Hcrit, which characterizes dispersion quality by how easily particles align under the magnetic field. Milling weakens the structure of the paint, provided sufficient resin concentration is maintained, as revealed by a decrease of G′ and Hcrit with milling time. At low resin concentration G′ increases with milling time indicating that milling induces structural reorganization which, being unsupported by resin adsorption, results in forming a stronger network. Magnetorheological measurements are correlated with susceptibility measurements in a small alternating magnetic field which probes particle interactions without breaking the structure. As the resin con...

Transverse susceptibility of magnetic inks

The transverse susceptibility, χt, of a suspension of single-domain ferromagnetic particles in a viscous fluid is calculated. The yield stress is introduced to describe the structure formation. Magnetic interactions are taken into account through the mean-field model. Calculations are compared to experiments in which a dc field, H, is slowly increased. The experiments were performed on a model iron oxide dispersion. The function χt(H) goes through a maximum which decreases and shifts to a higher field when the pigment concentration is increased. This is attributed to an increase of the yield stress and the mean-field interaction parameter in our model.

Polymer adsorption on magnetic particles

Abstract Adsorption of PVC-SO 4 on the magnetic particles used to make magnetic tape was correlated with the dispersion quality of magnetic paint. Total adsorption and type of bonding was determined using thermogravimetric analysis (TGA). The dispersion quality was indicated by AC susceptibility. Two TGA peaks were observed at about 450 and 770°C corresponding quantitatively to weak hydrogen bonding and strong chemical bonding, respectively. Acidic particles displayed mainly the lower temperature weight loss because the acidic sites could only hydrogen-bond to the acidic polymer. The other particles, being more neutral and basic, chemically bonded to the polymer and displayed high temperature weight loss behavior. The dispersion quality was directly proportional to the total amount of adsorbed polymer, whether by chemical or hydrogen bonding demonstrating that good dispersions do not necessarily yield good physical properties in the final tape product.

Testing the structure of magnetic paints with and without superimposed shear

The structure development in dispersions of magnetic barium ferrite particles in cyclohexanone with polyvinylchloride wetting resin was tested by oscillatory rheological measurements and orthogonal superposition of steady and oscillatory shear. The optimum dispersion is achieved at the resin concentration c=c0, which corresponds to a minimum in the viscoelastic modulii. At c c0 the system becomes less elastic, more flexible, less thixotropic and H(τ) is dominated by short τ, which indicates that the structure formation in this case is dominated by small aggregates rather than a network. By superimposing steady and oscillatory shear we show that the steady shear dramatically break the structure and shifts H(τ) to very short τ.

Microhydrodynamical modeling of transverse susceptibility of magnetic inks (Theory of ‘DIMAG’)

Abstract The time and field dependence of the transverse susceptibility, χ t , of a suspension of single domain ferromagnetic Brownian particles in a viscous fluid is calculated. Magnetic interactions are taken into account through the mean field model. The model is used to interpret (so far qualitatively) the so-called DIMAG experiment, in which a DC field is applied to the ink sample for a short period of time and a small perpendicular AC field probes χ t before, during and after the DC field impact. The relative increase in χ t , after the DC field is switched on was used earlier to characterize the dispersion quality of inks. We show that in the systems with negative interactions (acicular particles) this increase has a maximum when plotted as a function of the DC field. The maximum shifts to higher fields as the interaction increases, which corresponds to what happens in the DIMAG testing of less dispersed inks.