Fluorine containing oxidizers, primarily polymers, are extensively used in pyrotechnic compositions.Fluorinated oxidizers are less explored for metalized propellants and explosives despite a potential advantage of sub...Fluorine containing oxidizers, primarily polymers, are extensively used in pyrotechnic compositions.Fluorinated oxidizers are less explored for metalized propellants and explosives despite a potential advantage of substantial heat release combined with gaseous combustion products. This review summarizes different types of fluorinated oxidizers used in energetic formulations or of potential interest for such systems, including gases, polymers, and inorganic compounds. Types of energetic formulations employing metals and fluoropolymers are discussed in more detail, including methods used to prepare composites and resulting salient features of the obtained materials. Laboratory experiments characterizing such materials, in particular, electron microscopy and thermal analysis, are discussed, showing characteristic morphologies and reaction sequences observed in different metal-fluorinated oxidizer composites. Striking similarities are noted in reaction sequences for diverse compositions hinting at possible similarities in the respective reaction mechanisms. Experiments probing ignition and combustion of metal-fluorinated oxidizer composites in laboratory conditions are also reviewed, including impact, flash heating and shock ignition. Finally, some practical performance tests for energetic formulations are described following by a brief discussion of the reaction mechanisms expected to govern ignition and combustion in various metal-fluorinated oxidizer composites. The conclusions are combined with recommendation for future research in the area of reactive metal-fluorinated oxidizer composites.展开更多
Rapid destruction of stockpiles of sarin and other chemical weapon agents(CWA)requires understanding and quantitative description of the relevant chemical reactions.Rapid reactions at elevated temperatures are of part...Rapid destruction of stockpiles of sarin and other chemical weapon agents(CWA)requires understanding and quantitative description of the relevant chemical reactions.Rapid reactions at elevated temperatures are of particular interest for prompt agent defeat scenarios.Diisopropyl methylphosphonate(DIMP)is a sarin surrogate particularly well suited to model sarin thermal decomposition and is often used in experiments.This article is a review of different experimental methods addressing decomposition of gasified DIMP,respective results and their interpretations.Major early decomposition products are propene,methylphosphonic acid,methyl(oxo)phosphoniumolate,and isopropanol.Early computational work using available kinetic data for fluorine and the phosphorus-fluorine bond predicted the decomposition under incineration conditions.Experiments using an isothermal flow reactor operated at 700-800 K were used to model DIMP decomposition as unimolecular reaction with results that were consistent with the earlier theoretical work.Decomposition in dynamic environments was studied using DIMP supported on rapidly heated substrates.The results showed different decomposition products and product sequences forming at different heating rates,suggesting the need for revised reaction kinetics.However,species quantification in such experiments is difficult because of inherent large temperature gradients.Plasma produced in a corona discharge was also reported to lead to rapid DIMP decomposition at low temperatures.Decomposition products were distinct from those observed at high temperatures.Shock tube experiments may be well suited to study decomposition of organophosphorus compounds like DIMP following their rapid heating in diverse environments.However,presently,only sarin surrogates other than DIMP have been investigated,and no intermediate reaction products,important for developing a validated mechanism,could be detected.展开更多
We describe a novel mechanism for the synthesis of a stable high-entropy alloy powder from an otherwise immiscible Mg-Ti rich metallic mixture by employing high-energy mechanical milling.The presented methodology expe...We describe a novel mechanism for the synthesis of a stable high-entropy alloy powder from an otherwise immiscible Mg-Ti rich metallic mixture by employing high-energy mechanical milling.The presented methodology expedites the synthesis of amorphous alloy powder by strategically injecting entropic disorder through the inclusion of multi-principal elements in the alloy composition.Predictions from first principles and materials theory corroborate the results from microscopic characterizations that reveal a transition of the amorphous phase from a precursor intermetallic structure.This transformation,characterized by the emergence of antisite disorder,lattice expansion,and the presence of nanograin boundaries,signifies a departure from the precursor intermetallic structure.Additionally,this phase transformation is accelerated by the presence of multiple principal elements that induce severe lattice distortion and a higher configurational entropy.The atomic size mismatch of the dissimilar elements present in the alloy produces a stable amorphous phase that resists reverting to an ordered lattice even on annealing.展开更多
Chemical warfare agents(CWA)are stockpiled in large quantities across the globe.Agents stored in inaccessible facilities need to be destroyed rapidly without dispersing the compounds to surrounding areas.Metal-based e...Chemical warfare agents(CWA)are stockpiled in large quantities across the globe.Agents stored in inaccessible facilities need to be destroyed rapidly without dispersing the compounds to surrounding areas.Metal-based energetic formulations are used in such prompt defeat applications to rapidly decompose the CWA by generating a high temperature environment.An alternate,and possibly a more effective decomposition pathway could be provided by chemicidal action of aerosolized condensed combustion products,which typically consist of metal oxides.Toxic fumes that escape the high temperature blast zone can be neutralized by smoke generated during combustion,depending on the particle size,surface characteristics,chemical properties,and concentration of this smoke.This review considers relevant experimental and modeling studies quantifying decomposition of CWA comprising organophosphorus compounds and their surrogates on the surface of various metal oxides.Dimethyl methylphosphonate(DMMP),a sarine surrogate,was used most commonly for such experiments.Many reported efforts focused on the mechanisms of adsorption of DMMP to various metal oxides and initial reaction steps cleaving various bonds from the chemisorbed molecules.For selected oxides,these experiments were supported by quantum-mechanical calculations.In other studies,the capacity of oxide surfaces to adsorb and decompose DMMP was quantified.In most cases,porous catalysts were used although limited experimental data are available for aerosolized nonporous oxide particles.The reported experimental data applicable to scenarios involving prompt decomposition of CWA are summarized.It is noted that information is lacking describing respective heterogeneous reaction kinetics.Preliminary estimates of aerosolized smoke particle concentrations required to destroy CWA are made considering gas phase diffusion rates and reported values of the oxide capacity to decompose CWA or their surrogates.展开更多
基金supported in parts by Defense Threat Reduction Agency(HDTRAl-15-1-00240)Air Force Office of Scientific Research(FA9550-16-1-0266)
文摘Fluorine containing oxidizers, primarily polymers, are extensively used in pyrotechnic compositions.Fluorinated oxidizers are less explored for metalized propellants and explosives despite a potential advantage of substantial heat release combined with gaseous combustion products. This review summarizes different types of fluorinated oxidizers used in energetic formulations or of potential interest for such systems, including gases, polymers, and inorganic compounds. Types of energetic formulations employing metals and fluoropolymers are discussed in more detail, including methods used to prepare composites and resulting salient features of the obtained materials. Laboratory experiments characterizing such materials, in particular, electron microscopy and thermal analysis, are discussed, showing characteristic morphologies and reaction sequences observed in different metal-fluorinated oxidizer composites. Striking similarities are noted in reaction sequences for diverse compositions hinting at possible similarities in the respective reaction mechanisms. Experiments probing ignition and combustion of metal-fluorinated oxidizer composites in laboratory conditions are also reviewed, including impact, flash heating and shock ignition. Finally, some practical performance tests for energetic formulations are described following by a brief discussion of the reaction mechanisms expected to govern ignition and combustion in various metal-fluorinated oxidizer composites. The conclusions are combined with recommendation for future research in the area of reactive metal-fluorinated oxidizer composites.
基金supported by the US Defense Threat Reduction Agency,Award HDTRA1-19-1-0023。
文摘Rapid destruction of stockpiles of sarin and other chemical weapon agents(CWA)requires understanding and quantitative description of the relevant chemical reactions.Rapid reactions at elevated temperatures are of particular interest for prompt agent defeat scenarios.Diisopropyl methylphosphonate(DIMP)is a sarin surrogate particularly well suited to model sarin thermal decomposition and is often used in experiments.This article is a review of different experimental methods addressing decomposition of gasified DIMP,respective results and their interpretations.Major early decomposition products are propene,methylphosphonic acid,methyl(oxo)phosphoniumolate,and isopropanol.Early computational work using available kinetic data for fluorine and the phosphorus-fluorine bond predicted the decomposition under incineration conditions.Experiments using an isothermal flow reactor operated at 700-800 K were used to model DIMP decomposition as unimolecular reaction with results that were consistent with the earlier theoretical work.Decomposition in dynamic environments was studied using DIMP supported on rapidly heated substrates.The results showed different decomposition products and product sequences forming at different heating rates,suggesting the need for revised reaction kinetics.However,species quantification in such experiments is difficult because of inherent large temperature gradients.Plasma produced in a corona discharge was also reported to lead to rapid DIMP decomposition at low temperatures.Decomposition products were distinct from those observed at high temperatures.Shock tube experiments may be well suited to study decomposition of organophosphorus compounds like DIMP following their rapid heating in diverse environments.However,presently,only sarin surrogates other than DIMP have been investigated,and no intermediate reaction products,important for developing a validated mechanism,could be detected.
基金supported in part by the National Science Foundation(NSF)award#CMMI-1944040。
文摘We describe a novel mechanism for the synthesis of a stable high-entropy alloy powder from an otherwise immiscible Mg-Ti rich metallic mixture by employing high-energy mechanical milling.The presented methodology expedites the synthesis of amorphous alloy powder by strategically injecting entropic disorder through the inclusion of multi-principal elements in the alloy composition.Predictions from first principles and materials theory corroborate the results from microscopic characterizations that reveal a transition of the amorphous phase from a precursor intermetallic structure.This transformation,characterized by the emergence of antisite disorder,lattice expansion,and the presence of nanograin boundaries,signifies a departure from the precursor intermetallic structure.Additionally,this phase transformation is accelerated by the presence of multiple principal elements that induce severe lattice distortion and a higher configurational entropy.The atomic size mismatch of the dissimilar elements present in the alloy produces a stable amorphous phase that resists reverting to an ordered lattice even on annealing.
基金This work was supported by the US Defense Threat Reduction Agency,DTRAGrant HDTRA1-19-1-0023.
文摘Chemical warfare agents(CWA)are stockpiled in large quantities across the globe.Agents stored in inaccessible facilities need to be destroyed rapidly without dispersing the compounds to surrounding areas.Metal-based energetic formulations are used in such prompt defeat applications to rapidly decompose the CWA by generating a high temperature environment.An alternate,and possibly a more effective decomposition pathway could be provided by chemicidal action of aerosolized condensed combustion products,which typically consist of metal oxides.Toxic fumes that escape the high temperature blast zone can be neutralized by smoke generated during combustion,depending on the particle size,surface characteristics,chemical properties,and concentration of this smoke.This review considers relevant experimental and modeling studies quantifying decomposition of CWA comprising organophosphorus compounds and their surrogates on the surface of various metal oxides.Dimethyl methylphosphonate(DMMP),a sarine surrogate,was used most commonly for such experiments.Many reported efforts focused on the mechanisms of adsorption of DMMP to various metal oxides and initial reaction steps cleaving various bonds from the chemisorbed molecules.For selected oxides,these experiments were supported by quantum-mechanical calculations.In other studies,the capacity of oxide surfaces to adsorb and decompose DMMP was quantified.In most cases,porous catalysts were used although limited experimental data are available for aerosolized nonporous oxide particles.The reported experimental data applicable to scenarios involving prompt decomposition of CWA are summarized.It is noted that information is lacking describing respective heterogeneous reaction kinetics.Preliminary estimates of aerosolized smoke particle concentrations required to destroy CWA are made considering gas phase diffusion rates and reported values of the oxide capacity to decompose CWA or their surrogates.
