wight@chem.utah.edu

Activities & Awards 
Alfred P. Sloan Fellow 1990-94
Fellow of AAAS

Research Interests 
Our research group conducts fundamental investigations of condensed phase reaction kinetics, with an emphasis on rocket propellants and high explosives. Over the past few years, we have developed new methods for extracting reliable estimates of reaction rate parameters (activation energies and numerically evaluated reaction models) from traditional thermal analysis techniques, including robust estimates of the uncertainties of the parameters. These kinetic methods help to reveal the underlying chemical mechanisms of decomposition and combustion reactions in complex systems.

Energetic Materials

Most solid rocket motors use ammonium perchlorate (AP) as the oxidizer and powdered aluminum metal as the fuel. These granular components are bound together as a tough rubbery material with the use of a polymeric binder such as hydroxy-terminated polybutadiene (HTPB, typically ~15% by weight). With the addition of cross-linkers, plasticizers and other additives, propellants become chemically complex mixtures. We have adopted a global kinetic approach to describing the rates of propellant decomposition (overall rate of formation of gas and heat from solid). In the lab, we make careful measurements of mass loss (thermogravimetric analysis) or heat evolution (differential scanning calorimetry) as a function of time and temperature when tiny (~1 mg) samples of propellant are heated under controlled conditions.Most of the scientific effort is to devise robust methods of analyzing these types of laboratory data to predict the rates of reaction at elevated temperatures associated with combustion in a rocket motor. Using this approach, we have studied many energetic materials, including AP, ammonium dinitramide, ammonium nitrate and FOX-7, a new energetic material proposed for use as a propellant additive.
A new area of research for us is in the field of ionic liquids. Taking 3-ethyl-1-methylimidazolium nitrate (EMIN) as a prototypical example, we are now starting to analyze the kinetics of thermal decomposition, the mechanistic pathways followed, and the thermodynamics of the material itself. Materials of this type are of increasing interest in propellant applications because they are relatively easy to handle and store, have low toxicity, and potentially are less sensitive to accidental ignition than their solid propellant counterparts. One of the interesting behaviors we discovered is an oscillating thermal decomposition reaction, in which the reaction rate exhibits periodic increases and decreases

as a result of complex chemical and physical interactions that occur at the surface of the decomposing liquid.

High explosives differ from most propellants in that the fuel and oxidizer components are contained in a single molecule. Our research group studies the kinetics of decomposition of HMX and associated plastic-bonded explosives. The objective is to be able to describe combustion behavior and to ultimately predict the explosive response of these materials to exposure to fire. The Department of Energy funds this research through the University of Utah Center for Simulation of Accidental Fires and Explosions.

Cryochemical Kinetics
Our group is also investigating fundamental aspects of simple atom-molecule reactions that take place in solids at cryogenic temperatures, Our main interest has been reactions of fluorine atoms (created by laser photolysis of F₂) with small molecules (e.g., NH₃, CH₄, O₂, NO, CO, C₂H₂, and HCN) in a solid argon crystal at 4-25 K. Using new experimental methods, we have synthesized and observed several new molecules (FO₃, F₂NO, HOON, FC=NH) using a combination of infrared, optical and EPR spectroscopies. More recently, we have reacted O atoms with acetylene molecules in solid argon to make the first-ever spectroscopic observation of triplet formylmethylene (CHOCH), a long-sought chemical intermediate in the Wolf rearrangement reaction.

Selected Publications 

• J. Wang and C. A. Wight, "Use of Kinetic Models for Solid State Reactions in Combustion Simulations", in Energetic Materials Part 2. Detonation, Combustion, P. Politzer and J. S. Murray, Eds. (Elsevier: Amsterdam, 2004 ) pp. 351-369.
• D. Zhou, E. A. Schmitt, G. G. Zhang, D. Law, S. Vyazovkin, C. A. Wight, and D. J. W. Grant, David J. W. "Crystallization kinetics of amorphous nifedipine studied by model-fitting and model-free approaches", J. Pharm. Sci. 2003 , 92(9), 1779-1792.
• D. Zhou, E. A. Schmitt, G. G. Z. Zhang, D. Law, C. A. Wight, S. Vyazovkin, and D. J. W. Grant "Model-free treatment of the dehydration kinetics of nedocromil sodium trihydrate", J. Pharm. Sci. 2003 , 92(9) , 1367-1376.