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Abstract To date, research on the low temperature (< 240 °C) decomposition of ammonium perchlorate (AP) has typically presented decomposition data either as mass loss curves or Avrami equation fits. Neither approach measures true decomposition reaction rates, which should be a fundamental and early consideration in understanding the chemistry underlying AP decomposition. In addition, concern for low temperature AP decomposition usually occurs in confined environments where unvented product gases may react in a heterogeneous manner with the pristine AP material. In this work, we show evidence that decomposition gas products play a role in promoting the decomposition of solid AP, which suggests that heterogeneous reactions are a major driving force behind these decomposition reactions. A simple heterogeneous chemistry model is proposed to describe the growth and evolution of pores as AP decomposes. The model qualitatively predicts a size dependence on maximum decomposition rates with respect to particle size using kinetic information derived from literature. The experimental data and model provide some insight into decades-old questions surrounding the unique decomposition behavior of AP. An understanding of the role that heterogeneous reactions play in AP decomposition may be used to develop gas scavenging strategies that can protect AP-based propellants from thermal threats. [ABSTRACT FROM AUTHOR]

In this work, a boundary layer fluid dynamics model is used to numerically investigate the heterogeneous/homogeneous combustion of n -dodecane in a platinum coated channel. An elementary lumped surface chemistry model is used to describe the oxidation of n -dodecane and its intermediates on Pt. A parallel plate microcombustor with Pt-coated walls was designed based on findings from the model. Experimental analysis of the n -dodecane/air fueled parallel plate microcombustor with Pt-coated walls shows that the combustor is capable of complete oxidation while operating at high temperatures (>1100 K) relevant to next generation thermal-to-electric power conversion. Chemiluminescence imaging in the combustor suggests that a weak flame exists, which is capable of driving oxidation to completion while avoiding extreme temperatures. This reactor shows promise as a heat source for high temperature compact thermal-to-electric power conversion. [ABSTRACT FROM AUTHOR]

Highlights: [•] A Pt-coated parallel plate channel serves as a hetero-/homogeneous (HH) reactor. [•] Dodecane is used to examine reactor operation with low diffusivity (tactical) fuel. [•] The level of confinement (gap between reactor walls) is critical to HH operation. [•] Tuning confinement allows for high, uniform reactor temperatures. [•] HH reactors show promise for tactical fuel-to-electric power conversion. [ABSTRACT FROM AUTHOR]

Abstract: The properties of TiO2 nanoparticles synthesized using the flame stabilized on a rotating surface method (FSRS) are investigated. The method uses a laminar, premixed, stagnation flame, combining particle synthesis and film deposition in a single step. The current study examines the effects of flame properties on particle characteristics. Synthesized particles were characterized using X-ray diffractometry, Transmission Electron Microscopy and UV–vis spectrometry in order to quantify the effects of equivalence ratio and precursor loading on particle size, crystallinity and optical band-gap. Results show that flame stoichiometry significantly affects crystal phase, but it has little to no effect on particle size and light absorption band edge. In addition, precursor loading impacts both the particle size and the crystal phase. The study demonstrates the potential of the FSRS method for producing tailored nanoscale TiO2 particles for a variety of applications. [ABSTRACT FROM AUTHOR]

Abstract: A new method is proposed to fabricate nanocrystalline titania (TiO2) films of controlled crystalline size and film thickness. The method uses the laminar, premixed, stagnation flame approach, combining particle synthesis and film deposition in a single step. A rotating disc serves as a combination of substrate-holder and stagnation-surface that stabilizes the flame. Disc rotation repetitively passes the substrates over a thin-sheet, fuel-lean ethylene–oxygen–argon flame doped with titanium tetraisopropoxide. Convective cooling of the back side of the disc keeps the substrate well below the flame temperature, allowing thermophoretic forces to deposit a uniform film of particles that are nucleated and grown via the flame stabilized just below the surface. The particle film grows typically at ∼1μm/s. The film is made of narrowly distributed, crystalline TiO2 several nanometers in diameter and forms with a 90% porosity. Analysis shows that the rotation of the stagnation-surface does not reduce the stability of a stagnation flame, nor does it affect the fundamental chemistry of particle nucleation and growth that occurs between the flame and the stagnation surface. [Copyright &y& Elsevier]

Abstract: The evolution of the soot particle size distribution function (PSDF) and particle morphology are studied for premixed ethylene–oxygen–argon flat flames at equivalence ratio over the maximum flame temperature range of 1600–1900 K. Experiments were carried out using an in-situ probe sampling method in tandem with a scanning mobility particle sizer (SMPS), yielding the PSDF for various distances from the burner surface. The morphology of the particles was examined by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Within the particle size range that can be detected, the PSDF transitions from an apparent unimodal PSDF for high temperature flames () to a bimodal PSDF at lower temperatures (). The bimodal PSDF has a noticeable trough that separates the nucleation tail and log-normal mode. This mode-transition trough had been previously thought to occur at a fixed particle size, but these results show a continuous shift of the trough location towards smaller sizes with increasing flame temperature. TEM images show that the particles are spherical, even when the PSDF is bimodal, suggesting that the bimodality occurs as the primary particles undergoes mass and size growth, and is not a result of particle aggregation. Atomic force microscopy of substrate deposited particles shows that particles spread and form hill like structures upon impact with the substrate surface, indicating that the particles are liquid-like at the time of impact. [Copyright &y& Elsevier]