Michael J. Kulis

Synthesis Methods, Microscopy Characterization and Device Integration of Nanoscale Metal Oxide Semiconductors for Gas Sensing

A comparison is made between SnO2, ZnO, and TiO2 single-crystal nanowires and SnO2 polycrystalline nanofibers for gas sensing. Both nanostructures possess a one-dimensional morphology. Different synthesis methods are used to produce these materials: thermal evaporation-condensation (TEC), controlled oxidation, and electrospinning. Advantages and limitations of each technique are listed. Practical issues associated with harvesting, purification, and integration of these materials into sensing devices are detailed. For comparison to the nascent form, these sensing materials are surface coated with Pd and Pt nanoparticles. Gas sensing tests, with respect to H2, are conducted at ambient and elevated temperatures. Comparative normalized responses and time constants for the catalyst and noncatalyst systems provide a basis for identification of the superior metal-oxide nanostructure and catalyst combination. With temperature-dependent data, Arrhenius analyses are made to determine activation energies for the catalyst-assisted systems.

An investigation of micro-hollow cathode glow discharge generated optical emission spectroscopy for hydrocarbon detection and differentiation.

The analytical utility of a micro-hollow cathode glow discharge plasma for detection of varied hydrocarbons was tested using acetone, ethanol, heptane, nitrobenzene, and toluene. Differences in fragmentation pathways, reflecting parent compound molecular structure, led to differences in optical emission patterns that can then potentially serve as signatures for the species of interest. Spectral simulations were performed emphasizing the CH (A2Δ–X2Π), CH (C2∑–X2Π), and OH (A2∑+–X2Π) electronic systems. The analytical utility of selected emission lines is demonstrated by a linear relationship between optical emission spectroscopy and parent compound concentration over a wide range, with detection limits extending down to parts per billion (ppb) levels.

An elementary model for autoignition of laminar jets.

In this paper, we formulate and analyse an elementary model for autoignition of cylindrical laminar jets of fuel injected into an oxidizing ambient at rest. This study is motivated by renewed interest in analysis of hydrothermal flames for which such configuration is common. As a result of our analysis, we obtain a sharp characterization of the autoignition position in terms of the principal physical and geometrical parameters of the problem.

Spectroscopic characterization and comparison between biologics, organics and mineral compounds using pulsed micro-hollow glow discharge

A new mode of operation – pulsed – is demonstrated for compound identification of solid materials in the form of dry powders. Both plasma and analytical utility are characterized spectroscopically. The acquired emission spectra provided molecular and elemental information. The microgram sample analysis capability and atmospheric pressure operation are demonstrated for benign and biological organics, a commercial fertilizer and other inorganic materials. The plasma temperature is estimated by spectral simulation of the NO (A2Σ+ → X2Π) bands, and the inferred temperature is 1300 °C. Atomic transitions from C (1P0 → 1S) and molecular bands from CH (B2Σ → X2Π) and CH (A2Δ → X2Π) were manifestly observed in the optical emission spectra of organic materials. Relative intensities of common spectral signatures could distinguish biological agents from common benign organic materials. High-resolution spectra were particularly useful in resolving and identifying atomic transitions such as Mg, Ca, Fe and Si for the inorganic materials. Such a detector system has the capability to rapidly sense hazards with the added advantage of portability.

On Autoignition of Co-Flow Laminar Jets

This paper is concerned with the derivation and mathematical analysis of a model for autoignition of laminar co-flow jets. Such jets consist of two parts: an inner part with oxidizer that is surrounded by an outer part with fuel, or the reverse. To derive a model we use a combination of Burke--Schumann theory of diffusion flames and Semenov--Frank-Kamenerskii theory of thermal explosion. The main advantage of our model is that it gives a well-defined condition for autoignition of a jet. We provide detailed analysis of the model that reveals dependency of the autoignition position on principal physical and geometric parameters involved. Moreover, we give explicit expressions for autoignition position in asymptotic regimes relevant to applications.