Emily M. Hunt

Ignition dynamics and activation energies of metallic thermites: From nano- to micron-scale particulate composites

Ignition behaviors associated with nano- and micron-scale particulate composite thermites were studied experimentally and modeled theoretically. The experimental analysis utilized a CO2 laser ignition apparatus to ignite the front surface of compacted nickel (Ni) and aluminum (Al) pellets at varying heating rates. Ignition delay time and ignition temperature as a function of both Ni and Al particle size were measured using high-speed imaging and microthermocouples. The apparent activation energy was determined from this data using a Kissinger isoconversion method. This study shows that the activation energy is significantly lower for nano- compared with micron-scale particulate media (i.e., as low as 17.4 compared with 162.5kJ∕mol, respectively). Two separate Arrhenius-type mathematical models were developed that describe ignition in the nano- and the micron-composite thermites. The micron-composite model is based on a heat balance while the nanocomposite model incorporates the energy of phase transformat...

Impact ignition of aluminum-teflon based energetic materials impregnated with nano-structured carbon additives

The inclusion of graphene into composite energetic materials to enhance their performance is a new area of interest. Studies have shown that the addition of graphene significantly enhances the thermal transport properties of an energetic composite, but how graphene influences the composite’s ignition sensitivity has not been studied. The objective of this study is to examine the influence of carbon additives in composite energetic material composed of aluminum and polytetrafluoroethylene (Teflon™) on ignition sensitivity due to low velocity, drop weight impact. Specifically, three forms of carbon additives were investigated and selected based on different physical and structural properties: spherically shaped amorphous nano particles of carbon, cylindrically shaped multi walled carbon nanotubes, and sheet like graphene flakes. Results show an interesting trend: composites consisting of carbon nanotubes are significantly more sensitive to impact ignition and require the lowest ignition energy. In contrast,...

Neutralizing bacterial spores using halogenated energetic reactions

The fight against biological warfare has prompted investigation of the chemistry and exothermic energy from energetic material reactions as a means for the neutralization of bacterial spores. The interaction between energetic reactions containing biocides and spore forming bacteria is not well understood. The goal of this work is to fundamentally examine the mechanisms of neutralization for Bacillus thuringiensis utilizing a halogenated energetic material reaction. Spore neutralization is attributed to a thermal effect from the reaction heat and the associated chemical influence of the halogen gas (i.e., produced from combustion). Results show heat transfer in the spore enhances the effectiveness of the halogen gas in the neutralization process and that elevated temperatures increase spore permeability, facilitating gas penetration and accelerating spore neutralization. Based on experimental results, a mathematical model was developed to predict spore behavior during reaction exposure over varying time scales. In the millisecond range, the model showed that the coupled thermal-biocidal gas mechanism will require elevated temperatures of 360°C to produce 80% neutralization in tens of milliseconds while thermal conditions alone would require nearly 1,000°C for the same neutralization. These results provide molecular-level insights into the components underpinning biological processes leading to spore neutralization.

Nanochargers: Energetic materials for energy storage

Nanochargers are energetic materials consisting of fuel metal particles and metallic oxide particles that absorb and store energy up to an ignition threshold. Once ignited a controlled exothermic reaction ensues producing energy. Nanotechnology has spurred the understanding of unique nanoparticle combustion behaviors that enable creation of nanochargers with optimized heat capacity for storing energy. Although in the initial stages, these experiments demonstrate evidence of the nanocharger’s potential for energy storage and transfer.

High-Speed Study of Drop-Weight Impact Ignition of PBX 9501 Using Infrared Thermography

Reaction in explosive materials does not occur as a result of homogenous heating of the sample, but rather from a localized region of high temperature called a hot spot. Observation of hot spot development is critical in understanding the heat transfer mechanisms occurring during reaction. Due to the strong temperature dependence of explosives, the overall reaction rate is dominated physically by these hot spots. Once formed, these hot spots either fail to react chemically due to thermal diffusion or react exothermically thus creating an ignition site in the solid explosive. The slightest difference of physical properties can change the positioning of hot spot development, creating an argument that the differences in material properties influence the formation of hot spots, which produce an exothermic reaction.

From Community College to Four-Year Institution: A Model for Recruitment and Retention

Increasing Numbers, Connections, and Retention in Science and Engineering (INCRSE) was funded with the goal of increasing the quantity, quality, and diversity of undergraduate students pursuing and obtaining degrees in Science, Technology, Engineering, and Mathematics (STEM) programs at West Texas A&M University (WTAMU). A major objective of INCRSE was to recruit STEM transfer students from regional community colleges (CC) and to provide academic and social support necessary for retention of these students. The INCRSE CC recruitment and retention model involved (a) strengthening relationships between faculty at WTAMU and regional CCs; (b) inviting CC faculty and staff to developmental workshops at WTAMU; (c) improving advising for transfer students at CCs and WTAMU; and (d) developing articulation agreements between WTAMU and regional CCs. Because INCRSE was funded in fall 2006, the number of CC STEM transfers enrolled at WTAMU increased from 214 to 253, an increase of 18%, while overall enrollment of CC transfers to WTAMU declined 3.5%. The number of new CC STEM transfers increased 22% from 92 in the 2006–2007 to 112 in 2008–2009 academic years. WTAMUs first-year retention of STEM transfers increased from 57% in 2006–2007 to 68% in 2007–2008, far surpassing the WTAMU first-year retention of traditional freshmen in the STEM fields by almost 30%. While all components of the model were important, much of the success can be attributed to improved relationships between WTAMU and CC faculty.

Thermal Influences on the Neutralization of Spore Forming Bacteria

Bacillus anthracis spores have shown extreme resistance to heat treatment methods. Various novel ideas have emerged including the use of thermite reactions for the de-activation of bacterial spores, focusing on the anthrax forming spore Bacillus anthracis. The basis of de-activation is dependent on the heat transfer to the spore and chemical interaction with the halogen gas. The objective of this work was to observe the mechanisms of de-activation as related to the thermal and halogen gas effect on the spore. Research focused on the specific roles of the heat transfer and the combination of heat and halogen gas. Results showed heat transfer in the spore greatly enhanced the effectiveness of the halogen gasses in the deactivation process. The observed results strengthen the hypothesis that the heat transfer affects the permeability of the bacterial spores, enabling the halogen gas to deactivate the spores. This novel observation leads to further studies in the combustion properties of thermites. Results from this study suggest that thermite formulations with increased heat of reaction will increase the thermal wave promoting spore neutralization.Copyright

Mechanical Engineering Education: Preschool to Graduate School

Google decided to re-invent television by creating Google TV: which is basically software that can access everything available on regular television channels and the vast sea of content on the Internet, all on the biggest screen in the house. One motivation was to transform their current 1 billion market share associated with computer and hand held browsers to 4 billion TV watchers. When this feat is accomplished, the current statistics that cite 70% of 4 to 6 year olds have used computers and been exposed to the Internet prior to kindergarten will likely increase to 100%. In these exciting times there is a need to integrate this multi-modal influence into engineering education on a massive scale. According to studies, this new generation of Millenials (born early 1980-2000) places significant emphasis on meaningful careers. By introducing impactful, engineering education to this generation by integrating literature, technology, and successful teaching and learning methods into their culture, there are no limits to the meaningful contributions that future engineers will make toward improving our way of life. This chapter will highlight mechanical engineering education from kindergarten to functioning society member. We will discuss what works and how it works with the new student and citizen of today.

Coating and Characterization of Mock and Explosive Materials

This project develops a method of manufacturing plastic-bonded explosives by using use precision control of agglomeration and coating of energetic powders. The energetic material coating process entails suspending either wet or dry energetic powders in a stream of inert gas and contacting the energetic powder with atomized droplets of a lacquer composed of binder and organic solvent. By using a high-velocity air stream to pneumatically convey the energetic powders and droplets of lacquer, the energetic powders are efficiently wetted while agglomerate drying begins almost immediately. The result is an energetic powder uniformly coated with binder, that is, a PBX, with a high bulk density suitable for pressing. Experiments have been conducted using mock explosive materials to examine coating effectiveness and density. Energetic materials are now being coated and will be tested both mechanically and thermally. This allows for a comprehensive comparison of the morphology and reactivity of the newly coated materials to previously manufactured materials.

Experimental Investigation of Mist Sprays Impinging on a Heated Cylinder

Experimental studies are conducted to investigate the effect of mist on the spray heat transfer in the cooling of a low-carbon steel cylindrical surface heated to the nucleate boiling temperature range. Multiple tests are performed to investigate the effect of the liquid mass flux, liquid-to-air loading, spray speed, and droplet size on the spray heat transfer along the circumference of the annulus cylinder. Infrared imaging is used to visualize the spray flow around the heated cylinder. Operating conditions for the air-mist spray cover variations in spray speed from 18 to 44 m/s, liquid mass flux from 0 to 1.54 kg/m 2 · s, and critical surface heat flux temperature from 123 to 130°C. The spray local heat transfer coefficients were obtained at various angular positions along the cylinder surface. The tests reveal that, with the introduction of a small amount of water in the spray, the heat transfer is dramatically increased. The spray heat transfer effectiveness decreases with the increase in the water mass flux. As a result, dilute sprays are more desirable than dense sprays in achieving higher heat transfer effectiveness and better efficiency for water utilization. The tests also reveal that, for the same spray speed and mean droplet flux, spray heat transfer effectiveness decreases with the increase in droplet size. The results of this study shall lead to a better understanding of the usage of dilute airmist sprays in optimizing the cooling on a cylindrical surface.