Browsing by Subject "Thermite"
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Item Characterizing energy transfer using an infrared camera from a reacting nano-composite thermite embedded in a steel target(2009-05) Crane, Charles A.; Pantoya, Michelle; James, Darryl; Rivero, Iris V.A method to study energy transfer from a reacted thermite placed on a steel target substrate was presented as a function of thermite composition. A high speed infrared camera captured a temporally evolving thermal distribution through the substrate, while the thermite, which was placed in a v-notch, self propagated. Two thermite compositions were studied: Boron with Iron (III) Oxide (B-Fe2O3) and Aluminum with Iron (III) Oxide (Al-Fe2O3). A numerical model was developed to predict temperatures near the v-notch in order to estimate the amount of energy transferred into the steel by using a control volume energy balance. Results quantified the percent of the overall energy available from the chemical reaction that was conducted through the substrate and was compared to energy lost. The B-Fe2O3 reaction was more efficient in transferring energy into the steel, 46% of its heat of reaction, than Al-Fe2O3, 10% of its heat of reaction, based largely on the lower contribution of losses by radiation and convection. The Al-Fe2O3 reaction produced more gas by chemistry, 10% by mass, which transported more energy away from the v-notch region as compared to the non gas producing B-Fe2O3. The reaction times for Al-Fe2O3 propagation rate were roughly two to three times faster than the B-Fe2O3 which lowered the heating rate of the substrate. Much work had been performed that examine the combustion behaviors from a reacting thermite, but there are very few studies that attempt to quantify the energy transfer from a reacting thermite to a target. This diagnostic approach and numerical analysis was the first step towards quantifying energy transferred from a thermite into a target, and lost to the environment.Item Characterizing the energy transfer from a thermite reaction to a target(2007-12) Burkhard, Jonathan N.; Pantoya, Michelle; James, Darryl; Berg, Jordan M.Nano-sized materials often have novel properties that drastically improve performance. Very few studies on the nano-aluminum and water combustion reaction have been done without the addition of a gelling agent. The depth at which gas fueled underwater cutting torches can be used is limited by their fuel gas storage pressure restrictions. Using a nano-aluminum and water thermite reaction as the fuel for an underwater cutting torch eliminates depth limitations and creates a unique opportunity to use ambient water from the surrounding environment as the oxidizer for the reaction. Reaction characteristics were studied with high speed video analysis in inert and oxidizing environments. The heat transfer characteristics of the nano-aluminum and water reaction were compared to baseline methylacetylene-propadiene and propane fueled torches by collecting temperature data on metal test plates with thermocouples and a high speed infrared camera. Additives, such as Teflon powder, were mixed with the original thermite reactants to improve heat transfer to the test plates from the reaction. High speed video data showed that flame propagation rates were not significantly affected by the environment surrounding the reaction. Differential scanning calorimeter data confirmed that the aluminum was reacting efficiently. Temperature data from the test plates was compared after 0.9 s of heating. Thermocouple data confirms infrared camera temperature measurements. The MAPP gas torch, propane torch, Al/water reaction, and Al/water/Teflon reaction heated the plates at an average rate of 29.3 ± 0.2, 23.1 ± 0.2, 54 ± 3, and 38 ± 1 K/s respectively. The temperature change per mass of fuel burned was calculated for each torch and reaction as 400 ± 200, 500 ± 200, 180 ± 60, and 130 ± 30 K/g respectively. The time required to reach the oxidation temperature of steel for each torch and reaction was 40 ± 20, 50 ± 30, 21 ± 9, and 30 ± 10 seconds respectively. This study concludes that the Al/water reaction could significantly improve an underwater cutting device because surrounding water could be used as the primary oxidizer, the reaction has a higher heating rate than gas fuels, and the usable depth is not limited by fuel storage pressures.Item Combustion behavior of sol-gel synthesized aluminum and tungsten trioxide(Texas Tech University, 2006-05) Prentice, DanielCalcined (to remove impurities) and non-calcined tungsten trioxide (WO3) aerogels as well as micron-scale and nano-scale commercial WO3 powders were mixed with nano-scale aluminum (Al) and their combustion performance in the form of combustion wave speeds was compared in loose powder and pressed pellet configurations. Results show that both the calcined and non-calcined, aerogel based mixtures outperformed the commercial based mixtures in both configurations. Combustion wave speed was also found as a function of mixture bulk density. Results show that conduction is the dominant energy transfer mechanism in pressed pellets while convection is the dominant mechanism in loose powder form. This causes material purity to be the most important factor for pressed pellets and oxidizer particle size to be the most important factor for loose powders. A preliminary aging study was conducted which showed a 7% performance reduction after 4 days of laboratory air exposure and 91-98% performance reduction after 22 months of exposure.Item Combustion behaviors of bimodal aluminum size distributions in thermites(2005-05) Moore, Kevin M.; Pantoya, Michelle; Hope-Weeks, Louisa J.; Weeks, Brandon L.In recent years many studies that incorporated nano-scale or ultrafine aluminum (Al) as part of an energetic formulation demonstrated significant performance enhancement. Decreasing the fuel particle size from the micron to nanometer range alters the material¡¦s chemical and thermal-physical properties. The result is increased particle reactivity that translates to an increase in the combustion velocity and ignition sensitivity. Little is known, however, about the critical level of nano-sized fuel particles needed to enhance the performance of the energetic composite. Ignition sensitivity and combustion velocity experiments were performed using a thermite composite of Al and molybdenum trioxide (MoO3) at the theoretical maximum density (TMD) of a loose power (5% TMD) and a compressed pellet (50% TMD). A bimodal Al particle size distribution was prepared using 4 or 20 ƒÝm Al fuel particles that were replaced in 10% increments by 80 nm Al particles until the fuel was 100% 80 nm Al. These bimodal distributions allow the unique characteristics of nano-scale materials and their interactions with micron scale Al particles to be better understood.Item Combustion behaviors of bimodal aluminum sizedistributions in thermites(Texas Tech University, 2005-05) Moore, Kevin M.In recent years many studies that incorporated nano-scale or ultrafine aluminum (Al) as part of an energetic formulation demonstrated significant performance enhancement. Decreasing the fuel particle size from the micron to nanometer range alters the material¡¦s chemical and thermal-physical properties. The result is increased particle reactivity that translates to an increase in the combustion velocity and ignition sensitivity. Little is known, however, about the critical level of nano-sized fuel particles needed to enhance the performance of the energetic composite. Ignition sensitivity and combustion velocity experiments were performed using a thermite composite of Al and molybdenum trioxide (MoO3) at the theoretical maximum density (TMD) of a loose power (5% TMD) and a compressed pellet (50% TMD). A bimodal Al particle size distribution was prepared using 4 or 20 ƒÝm Al fuel particles that were replaced in 10% increments by 80 nm Al particles until the fuel was 100% 80 nm Al. These bimodal distributions allow the unique characteristics of nano-scale materials and their interactions with micron scale Al particles to be better understood.Item Combustion characteristics of A1 nanoparticles and nanocomposite A1+MoO3 thermites(2005-05) Granier, John J.; Pantoya, Michelle; Seshaiyer, Padmanabhan; Oler, James W.; Levitas, Valery; Berg, Jordan M.Scientific advances in material synthesis such as exploding wire technology, plasma nucleation and wet precipitation have enabled industrial manufacturers to produce metal and metal oxide powders with nanometer-sized particles. These processes have enabled better overall quality control (i.e. more definitive particle size, smaller particle size distributions, oxide coating control and decreased contaminate concentration) and faster production rates. Much interest has been formed in the science and application of nano-sized aluminum (nm-Al) combustion. A thermite (or aluminothermic) reaction is an oxidation reaction between aluminum and a metal oxide with highly exothermic energy release. Thermite reactions of traditional Al powder (typically micron-sized particles) and Iron-oxide have been used for decades in welding and other intense heat applications. Nano-thermite reactions, have shown unique properties in ignition sensitivity and deflagration (flame propagation) speeds which have propelled thermites to new realms of applications. The decrease in required ignition stimuli of nano-thermites is an improvement for many payload critical applications, but the ignition sensitivity also creates various hazards during material handling and seems to be a factor in decreased reactivity of aged nano-thermites. Nano-thermites have displayed reaction rates near detonation speeds presenting applications as more efficient incendiary devices. The precise particle size control of nano-thermites is leading researchers to develop highly-tunable energy release mechanisms that can be applied as heat signature flare decoys. Studies have shown that the thermite reaction of nm-Al+MoO3 has a large theoretical energy density [19], increased ignition sensitivity [23][8], and near detonation flame propagation speeds [5][6] in comparison to traditional micron-particle thermites. This work will present macroscopic combustion behaviors (such as flame speed) along with experimental results focusing on the molecular reactions and thermal properties of nanocomposite Al+MoO3 thermite materials This work will outline the successes and precautions of several nm-Al+MoO3 powder mixing methods and several cold-pressing techniques used to form compressed solid samples. A general relationship of sample density as a function of pressing force and with a systematic methodology is presented to allow other researchers to produce similar samples for future comparison. Second, results from laser experiments performed to determine flame speeds of nano and micron-sized Al+MoO3 composites through a range of sample densities. Flame propagation speeds were measured using high-speed digital video. Samples were also tested to determine thermal conductivity, specific heat and thermal diffusivity as a function of compressed sample density. Theories are presented for the unique trends of the nano and micron-composite results. Third, experimental work is presented analyzing the effects of pre-heated compressed nm-Al+MoO3 samples. Sample pre-heating is achieved by volumetric heating using an isothermal oven and by varying the applied laser power to allow conductive heating. Both methods of preheating show unique behaviors and elevated flame propagation speeds compared to previous results. Results and discussion of this work also discuss the difficulties and critical time response of using bare-wire thermocouples to accurately measure nano-thermite reaction temperatures. Fourth, a series of DSC/TGA experiments were performed on the reaction of Al and gaseous oxygen to analyze the purest and ¡¥simplest¡¦ form of the Al oxidation (void of any reaction mechanisms dependent on the metal-oxide decomposition). Results are presented showing unique reaction onset temperatures, oxidation rates and activation energies for nano and micron-Al reacting in a gaseous oxygen environment. Fifth, a series of DSC/TGA experiments were performed on the reaction of Al and nano-MoO3. Results are presented for reaction onset temperatures, peak temperatures, heat of reaction values, and activation energies for Al+MoO3 composites with Al particles ranging from 50 nm to 20 ƒÝm. A final set of experiments was designed using the DSC/TGA to determine reaction duration and reaction self-propagation criteria for Al particle sizes ranging from 50 nm to 20 ƒÝm. Heating programs were manipulated for micron and nano-Al+MoO3 samples to determine the relationship between sample heating rate and reaction mechanisms. DSC tests were done using isothermal time intervals displaying that the nm-Al+MoO3 reactions are temperature dependent and not self-sustaining. Isothermal time intervals applied to ƒÝm-Al+MoO3 reactions displayed a delayed peak temperature. Finally, all of the results and experiments are combined as evidence in support of a single theory of the oxidation reaction of spherical Al particles. The presented results portray unique evidence in support of the nano and micron-sized Al reaction characteristics.Item Combustion characteristics of aluminum nanoparticles and nanocomposite aluminum+moly-trioxide thermites(Texas Tech University, 2005-05) Granier, John J.; Pantoya, Michelle; Seshaiyer, Padmanabhan; Oler, James W.; Levitas, Valery; Berg, Jordan M.Scientific advances in material synthesis such as exploding wire technology, plasma nucleation and wet precipitation have enabled industrial manufacturers to produce metal and metal oxide powders with nanometer-sized particles. These processes have enabled better overall quality control (i.e. more definitive particle size, smaller particle size distributions, oxide coating control and decreased contaminate concentration) and faster production rates. Much interest has been formed in the science and application of nano-sized aluminum (nm-Al) combustion. A thermite (or aluminothermic) reaction is an oxidation reaction between aluminum and a metal oxide with highly exothermic energy release. Thermite reactions of traditional Al powder (typically micron-sized particles) and Iron-oxide have been used for decades in welding and other intense heat applications. Nano-thermite reactions, have shown unique properties in ignition sensitivity and deflagration (flame propagation) speeds which have propelled thermites to new realms of applications. The decrease in required ignition stimuli of nano-thermites is an improvement for many payload critical applications, but the ignition sensitivity also creates various hazards during material handling and seems to be a factor in decreased reactivity of aged nano-thermites. Nano-thermites have displayed reaction rates near detonation speeds presenting applications as more efficient incendiary devices. The precise particle size control of nano-thermites is leading researchers to develop highly-tunable energy release mechanisms that can be applied as heat signature flare decoys. Studies have shown that the thermite reaction of nm-Al+MoO3 has a large theoretical energy density [19], increased ignition sensitivity [23][8], and near detonation flame propagation speeds [5][6] in comparison to traditional micron-particle thermites. This work will present macroscopic combustion behaviors (such as flame speed) along with experimental results focusing on the molecular reactions and thermal properties of nanocomposite Al+MoO3 thermite materials This work will outline the successes and precautions of several nm-Al+MoO3 powder mixing methods and several cold-pressing techniques used to form compressed solid samples. A general relationship of sample density as a function of pressing force and with a systematic methodology is presented to allow other researchers to produce similar samples for future comparison. Second, results from laser experiments performed to determine flame speeds of nano and micron-sized Al+MoO3 composites through a range of sample densities. Flame propagation speeds were measured using high-speed digital video. Samples were also tested to determine thermal conductivity, specific heat and thermal diffusivity as a function of compressed sample density. Theories are presented for the unique trends of the nano and micron-composite results. Third, experimental work is presented analyzing the effects of pre-heated compressed nm-Al+MoO3 samples. Sample pre-heating is achieved by volumetric heating using an isothermal oven and by varying the applied laser power to allow conductive heating. Both methods of preheating show unique behaviors and elevated flame propagation speeds compared to previous results. Results and discussion of this work also discuss the difficulties and critical time response of using bare-wire thermocouples to accurately measure nano-thermite reaction temperatures. Fourth, a series of DSC/TGA experiments were performed on the reaction of Al and gaseous oxygen to analyze the purest and ¡¥simplest¡¦ form of the Al oxidation (void of any reaction mechanisms dependent on the metal-oxide decomposition). Results are presented showing unique reaction onset temperatures, oxidation rates and activation energies for nano and micron-Al reacting in a gaseous oxygen environment. Fifth, a series of DSC/TGA experiments were performed on the reaction of Al and nano-MoO3. Results are presented for reaction onset temperatures, peak temperatures, heat of reaction values, and activation energies for Al+MoO3 composites with Al particles ranging from 50 nm to 20 ƒÝm. A final set of experiments was designed using the DSC/TGA to determine reaction duration and reaction self-propagation criteria for Al particle sizes ranging from 50 nm to 20 ƒÝm. Heating programs were manipulated for micron and nano-Al+MoO3 samples to determine the relationship between sample heating rate and reaction mechanisms. DSC tests were done using isothermal time intervals displaying that the nm-Al+MoO3 reactions are temperature dependent and not self-sustaining. Isothermal time intervals applied to ƒÝm-Al+MoO3 reactions displayed a delayed peak temperature. Finally, all of the results and experiments are combined as evidence in support of a single theory of the oxidation reaction of spherical Al particles. The presented results portray unique evidence in support of the nano and micron-sized Al reaction characteristics.Item Hydrodynamical analysis of nanometric aluminum/teflon deflagrations(2008-05) Stacy, Shawn Christopher; Pantoya, Michelle; Levitas, Valery; Weeks, Brandon L.The hydrodynamics of deflagrations from reactive materials (RM) submerged underwater can be studied using a modified aquarium test. Normally loose powder RM will disperse after being submerged in water. Introducing hydrophobic materials such as Teflon into the reactant matrix, enables a barrier against permeation of water into the reactants. Also, ignition via resistance heating can be difficult underwater because significant energy is lost by convection off the wire into the water. Nano-Al particles require significantly less energy for ignition than their micron scale counterparts such that underwater ignition via resistance heating can be achieved. The objective of this study is to examine the reaction hydrodynamics from a submerged nano Al-Teflon mixture as a function of mixture composition and bulk density. Submerged Aluminum/Teflon mixtures were ignited and the ensuing reaction was recorded with a high speed camera and a pressure transducer. The resulting bubble shape, size, and pressure histories along with the burn time and rate allow the analysis and comparison of different fuel/oxidizer compositions and powder packing densities. Results show that as the density of the powder decreases the reaction transitions from a slow jet of multiple bubbles to quick single bubble. One observation is that as the percentage of aluminum increases the bubble radius also increases even though there is less of the gas producing Teflon in the mixture. This could imply that the excess aluminum is reacting with water.Item Modeling the melt dispersion mechanism for nanoparticle combustion(2007-12) Francis, Andrew; Pantoya, Michelle; Levitas, Valery; Oler, James W.Thermite particles have long been known to increase in reactivity as they decrease in size. However, during fast heating (106 - 108 K/s) of Al nanothermites, the diffusion mechanism that explains micron size thermite reactions cannot explain the extremely fast ignition times and much higher flame propagation velocities. A new mechanism known as the melt dispersion mechanism has recently been introduced to explain the fast oxidation of these Al nanothermites. A model has been created dependant upon key parameters to predict the reactivity of Al nanothermites. In this study, flame propagation velocities are statistically evaluated in terms of an integral that employs a probability density function (pdf) for key parameters and a flame velocity equation dependent on relative particle size (Al core radius divided by oxide shell thickness), oxide shell formation temperature, and oxide shell strength. It is shown that flame propagation velocity depends sensitively on relative particle size, relative particle size distribution, oxide shell formation temperature, and shell strength. It is also dependant upon particle size, and oxide shell thickness but not as sensitively. Both single and bimodal particle sizes were studied. Combining smaller nanoparticles with larger nanoparticles in a bimodal mixture significantly increases the flame propagation velocity as compared to a composite consisting of only the larger particles. The results presented here suggest that better reproducibility of the flame velocity may be achieved experimentally by selecting a material with a narrow relative particle size distribution. A combination of increased oxide shell formation temperature and increased oxide shell strength could be used to maximize the flame velocity in particles with increased relative particle size.Item Quantification of heat flux from a reacting thermite spray(2009-08) Nixon, Eric; Pantoya, Michelle; Berg, Jordan M.; Oler, James W.Characterizing the combustion behaviors of energetic materials requires diagnostic tools that are often not readily or commercially available. For example, a jet of thermite spray provides a high temperature and pressure reaction that can also be highly corrosive and promote undesirable conditions for the survivability of any sensor. Developing a diagnostic to quantify heat flux from a thermite spray is the objective of this study. Quick response sensors such as thin film heat flux sensors can not survive the harsh conditions of the spray, but more rugged sensors lack the response time for the resolution desired. A sensor that will allow for adequate response time while surviving the entire test duration was constructed. The sensor outputs interior temperatures of the probes at known locations and utilizes an inverse heat conduction code to calculate heat flux values. The details of this device are discussed and illustrated. Temperature and heat flux measurements of various thermite spray conditions are reported. Results indicate that this newly developed energetic material heat flux sensor provides quantitative data with good repeatability.Item The effects of fuel particle size on the reaction of Al/Teflon mixtures(Texas Tech University, 2006-05) Osborne, Dustin Travis; Pantoya, Michelle; Weeks, Brandon L.; Levitas, ValeryReactive mixtures of aluminum (Al) and Teflon have applications in propellants, explosives, and pyrotechnics. This study examines the thermal degradation behavior of Teflon and nanometer scale Al particles compared with micron-scale Al particles. Differential scanning calorimetry and thermo-gravimetric analyses were performed in an argon environment on both nanometer and micron scale mixtures revealing lower onset temperatures and larger exothermic activity for the nanometer scale Al mixture. A pre-ignition reaction (PIR) unique to the nano-Al mixture is found. Experiments show the mechanism of the PIR to be the adsorption of fluoride ions from the Teflon polymer onto the aluminum oxide shell of the Al particles. The decreased alumina surface area inherent in larger Al particles lowers the exothermic effect of the PIR. The PIR may be the mechanism of ignition for nano-composite samples heated in air. Experimental results are discussed along with reviewed literature to explain the thermal degradation process of the mixtures. These results are helpful in the fundamental understanding of Al/Teflon degradation and particle size effects on the reactivity of Al/Teflon composites. The effects of Teflon particles on the sensitivity of thermite composites are also studied experimentally using a drop-weight apparatus. It was found that the addition of Teflon to an Al/MoO3 thermite composite increases its sensitivity to impact.Item The influence of gas generation on flame propagation for nano-Al based energetic materials(2008-12) Dean, Steven W.; Pantoya, Michelle; Weeks, Brandon L.; Levitas, ValeryThis study examines the reactions of two nanocomposite thermites, aluminum (Al) with copper oxide (CuO) and aluminum with nickel oxide (NiO). These oxidizers were selected based on their predicted properties: similar adiabatic flame temperatures but significantly opposing gas generation properties. Thermal equilibrium calculations predicted that the Al+CuO would have a high gas output and the Al+NiO would produce little to no gas. Flame propagation rates and peak pressure measurements were taken for both composites at various equivalence ratios using an instrumented flame tube apparatus. Results show that over the range of equivalence ratios studied, Al+CuO had an average propagation rate of 582.9 ± 87.6 m/s, while Al+NiO had an average velocity of 193.7 ± 72.2 m/s. The average peak pressures observed for the reactions were 3.75 ± 0.85 MPa for Al+CuO and 1.68 ± 0.88 MPa for Al+NiO. A DSC/TGA was also used to determine the properties of the composites and reactants under low heating rates. These low heating rate tests indicate that the gas production properties of the composites are highly dependent on heating rate, with both composites experiencing almost no mass loss under slow heating. The results suggest that the melt-dispersion mechanism, which is only engaged at high heating rates, leads to a dispersion of high velocity molten Al clusters that promotes a pressure build-up by inducing a bulk movement of fluid. This mechanism may promote convection without the need for additional gas generation.