Rodney L. Williamson

Optical properties of gold colloids formed in inverse micelles

We discuss the formation of gold metal colloids in a variety of surfactant/solvent systems. Static and dynamic light scattering, small angle x‐ray and neutron scattering, TEM analysis, and UV‐visible absorbance are used to characterize the kinetics of formation and final colloid stability. These gold colloids exhibit a dramatic blueshift and broadening of the plasmon resonance with decreasing colloid size. Several types of reduction method are discussed and differences between micelle (water‐free) or microemulsions as reaction media are compared. Use of inverse micelles allows smaller clusters to be formed with greater long‐term stability.

Generating strange magnetic and dielectric interactions: Classical molecules and particle foams

When a soft magnetic particle suspension is subjected to a vertical uniaxial magnetic field the particles polarize, the positive dipolar interactions causing particle chain formation. If instead an audio-frequency rotating magnetic field is applied in a horizontal plane, the particles experience an average interaction that to first order is a negative dipolar interaction, causing particle sheet formation in the biaxial field plane. When a vertical uniaxial field and a horizontal biaxial field are simultaneously applied with the field amplitudes balanced, the positive and negative dipolar interactions cancel to first order, and one might expect no dipolar interactions at all. But in this balanced triaxial field an isotropic second-order dipolar interaction of surprising magnitude remains. This triaxial interaction can be attractive or repulsive, and exhibits strong many-body interactions that lead to a variety of unexpected effects, including stable clusters with molecular geometries, the emergence of a particle foam, and the production of vortices in the fluid. By manipulating the triaxial field, a variety of particle structures can be made that cannot be produced by any other known means.

Generating strange interactions in particle suspensions

When a soft magnetic particle suspension is subjected to a vertical uniaxial magnetic field the particles polarize, the positive dipolar interactions causing particle chain formation. If instead an audio-frequency rotating magnetic field is applied in a horizontal plane, the particles experience an average interaction that to first order is a negative dipolar interaction, causing particle sheet formation in the biaxial field plane. When a vertical unaixial field and a horizontal biaxial field are simultaneously applied with the field amplitudes balanced, the positive and negative dipolar interactions cancel to first order, and one might expect no dipolar interactions at all. But in this balanced triaxial field an isotropic second-order dipolar interaction of surprising magnitude remains. This classical triaxial interaction can be attractive or repulsive, and exhibits strong many-body interactions that lead to a variety of unexpected effects, including stable clusters with molecular geometries, the emergence of a particle foam, and the production of vortices in the fluid. By manipulating the triaxial field, a variety of particle structures can be made that cannot be produced by any other known means.

A Nonlinear Reduced Order Model for Estimation and Control of Vacuum Arc Remelting of Metal Alloys

Vacuum arc remelting (VAR) is an industrial metallurgical process widely used throughout the specialty metals industry to cast large alloy ingots. The VAR process is carried out in a vacuum with the aim of melting a large consumable electrode (.4 m in diameter and 3000 kg in mass and larger) in such a way that that the resulting ingot has improved homogeneity. The VAR control problem consists of adjusting arc current to control electrode melt rate, which also depends on the electrode temperature distribution and adjusting electrode ram speed to control the arc gap between the electrode and the ingot. The process is governed by a 1 dimensional heat conduction partial differential equation with a moving boundary, which leads to an infinite dimensional, nonlinear system. In addition to the process nonlinearity, the inputs and all of the available measurements are corrupted with noise. In order to design a controller and a Kalman based estimator for this process, integral methods are used to derive a set of two coupled nonlinear ordinary differential equations in time, which capture the steady state and transient characteristics of melting in a VAR furnace. The model with the experimentally measured noise is then used to construct an estimator and a controller. The system can be described by two state variables that change in time: thermal boundary layer and melted length or alternatively electrode gap. The reduced order model compares favorably to an accurate finite difference model as well as melting data acquired for Ti-6Al-4V. It will be shown how this model can be used to obtain dynamic closed loop melt rate control while simultaneously controlling electrode gap. This controller and estimator were tested on a laboratory furnace at Timet.© 2005 ASME

Simple compact monochromatic imaging system for plasma diagnostics

A simple compact monochromatic imaging system for plasma diagnostics is described. The system consists of a small monochromator, single lens, and video camera.

Field-structured composite studies.

Field-structured composites (FSCs) were produced by hosting micron-sized gold-coated nickel particles in a pre-polymer and allowing the mixture to cure in a magnetic field environment. The feasibility of controlling a composites electrical conductivity using feedback control applied to the field coils was investigated. It was discovered that conductivity in FSCs is primarily determined by stresses in the polymer host matrix due to cure shrinkage. Thus, in cases where the structuring field was uniform and unidirectional so as to produce chainlike structures in the composite, no electrical conductivity was measured until well after the structuring field was turned off at the gel point. In situations where complex, rotating fields were used to generate complex, three-dimensional structures in a composite, very small, but measurable, conductivity was observed prior to the gel point. Responsive, sensitive prototype chemical sensors were developed based on this technology with initial tests showing very promising results.

Optical diagnostics for metallurgical processes

Many industrially important metallurgical processes are accompanied by the emission of light, the analysis of which often supplies useful information concerning the current state of the process while also providing insight into the details of specific process mechanisms. Optical diagnostic techniques are finding an increasingly wide range of application throughout the metallurgical community. This paper discusses the application of emission spectroscopy and imaging techniques to the analysis of such diverse processes as vacuum arc remelting, laser welding, and arc welding. A discussion of these techniques is presented, addressing such subjects as instrumentation, data analysis, the kind of information available and its potential impact on the selection of process parameters. Special attention is given to discussing the difficulties encountered in applying these diagnostic technologies to /open quotes/real life/close quotes/ processes in non-laboratory environments. 44 refs., 6 figs.