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

Journal Article · Mon Aug 01 04:00:00 EDT 2005 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.1990265· OSTI ID:20714036

Hunt, Emily M; Pantoya, Michelle L ^[1]

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1. Department of Mechanical Engineering, West Texas A and M University, Canyon, Texas 79015 (United States)

Ignition behaviors associated with nano- and micron-scale particulate composite thermites were studied experimentally and modeled theoretically. The experimental analysis utilized a CO{sub 2} 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 162.5 kJ/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 transformation in the alumina shell theorized to be an initiating step in the solid-solid diffusion reaction and uniquely appreciable in nanoparticle media. These models were found to describe the ignition of the Ni/Al alloy for a wide range of heating rates.

• OSTI ID: 20714036
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 3 Vol. 98; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ACTIVATION ENERGY
ALUMINIUM
ALUMINIUM ALLOYS
ALUMINIUM OXIDES
CARBON DIOXIDE LASERS
COMBUSTION
COMPOSITE MATERIALS
DIFFUSION
HEATING RATE
IGNITION
NANOSTRUCTURES
NICKEL
NICKEL ALLOYS
PARTICLE SIZE
PELLETS
PHASE TRANSFORMATIONS
REINFORCED MATERIALS
THERMOCOUPLES