Exothermic Reaction Kinetics Research Articles

Correlation between Microstructure and Exothermic Reaction Kinetics of Al-CuO Thermite Nanocomposite Powders Fabricated by Cryomilling

Correlation between Microstructure and Exothermic Reaction Kinetics of Al-CuO Thermite Nanocomposite Powders Fabricated by Cryomilling

Thermal decomposition of ammonium perchlorate/exfoliated-graphene and the relationship between activation energy and band gap

ABSTRACTThe thermal decomposition of ammonium perchlorate AP with electrochemically exfoliated graphene flakes (EGF) was studied at different heating rates in nitrogen and the combustion behavior of AP/EGF propellant was evaluated. The exothermic reaction kinetics were studied by simultaneous thermal analysis (STA) in non-isothermal conditions and compare with the thermal decomposition of pure AP applying the same experimental conditions. Using the Kissinger method, the calculated activation energies Ea for the low- and high-temperature exothermic reactions were 87 and 198 kJ/mol for pure AP, contrasting with 91 and 55 kJ/mol obtained from AP with 5 wt% EGF. From our experimental activation energy values together with reported and calculated band gaps Eg, it was found the empirical relationship:where Ea0 corresponds to the activation energy associated with the high-temperature thermal decomposition of pure AP, Eac is the activation energy associated to the high-temperature thermal decomposition of AP-EGF, E0 = 2.7 eV is the catalyst band gap threshold required to activate the electron transfer mechanism and n = 6 is the exponential factor associated to pure AP.

Boron-Metal Fluoride Reactive Composites: Preparation and Reactions Leading to Their Ignition

Composite powders combining boron with and were prepared using mechanical milling. As-received amorphous boron and boron initially washed with acetonitrile to remove the hydrated surface oxide were used as starting materials. In the prepared composite powders, each particle was a dense agglomerate of primary, nano-sized boron particles coated with metal fluorides. Reactions occurring upon heating in both aerobic and anaerobic environments were characterized using thermoanalytical measurements and mass spectroscopy. Powders were ignited on an electrically heated wire. Ignition sensitivity of the powders to electrostatic discharge was found to be low. For composite powders prepared using commercial boron, low-temperature reactions catalyzed by hydrated boron oxide occurred upon heating, leading to formation of gaseous boron fluorides. At high heating rates, such reactions led to ignition at very low temperatures. The exothermic reaction kinetics and ignition temperatures for such powders were not affected by the fluoride oxidizer. For composites using boron washed in acetonitrile, exothermic reactions began at higher temperatures. Respectively, such powders ignited at higher temperatures. For powders using washed boron, both kinetics of the exothermic reactions and ignition temperatures were affected by the type of fluoride: materials using reacted and ignited at temperatures lower than those using .

Thermal decomposition and shelf-life of PETN and PBX based on PETN using thermal methods

The kinetics of exothermic reactions are important in assessing the potential of materials and systems for thermal explosion. In this paper, the thermal behavior and decomposition kinetics of pentaerythritol tetranitrate (PETN) and polymer-bonded explosives (PBXs) based on PETN were investigated using Thermogravimetric analysis (TGA) and Vacuum Stability Test (VST) methods. The Arrhenius activation energies and pre-exponential factors were determined by the Ozawa and Kissinger methods. Based on the overall kinetic parameters of decomposition reactions, the shelf-life of PETN and PBXs based on PETN could be calculated and predicted.

Exothermic Reaction Kinetics in High Energy Density Al-Ni with Nanoscale Multilayers Synthesized by Cryomilling

The Al-Ni system is known as a high energy density materials (HEDM) because of its highly exothermic nature during intermetallic compound (IMC) formation. In this study, elemental Al and Ni powder were milled to explore the effect of cryomilling atmosphere on the microstructure and exothermic behavior. Scanning electron microscope (SEM) observations show continuous structural refinement up to 8 h of cryomilling. No IMC phase was detected in the X-ray diffraction (XRD) spectrum. Differential thermal analyzer (DTA) results show two exothermic peaks for 8 h cryomilled powder as compared to that of powder milled for 1 h. The ignition temperature of prepared powder mixture also decreased due to gradual structural refinement. The activation energy was also calculated and correlated with the DTA and SEM results. The cryomilled Al-Ni powder is composed of fine Al-Ni metastable junctions which improve the reactivity at a lower exothermic reaction temperature.

The Thermal Decomposition of Ammonium Perchlorate-Aluminum Propellants in Presence of Metallic Zinc Particles

The thermal decomposition of ammonium perchlorate (AP) with Al and Zn metallic particles was studied at different heating rates in dry air atmosphere and the combustion behavior of AP/Al/Zn propellant was evaluated. The exothermic reaction kinetics was studied by differential thermal analysis (DTA) in non-isothermal conditions and compare with the thermal decomposition of pure AP and AP/aluminum particles analyzed in the same experimental conditions. The Arrhenius parameters were estimated according to the Ozawa and Kissinger methods. The calculated activation energies for the low and high temperature exothermic reactions were 91 and 229 kJ/mol for pure AP, 90 and 112 kJ/mol for 80 wt% AP/20 wt% Al particles. When zinc was incorporated, activation energy of 56 kJ/mol was determined for the only exothermic peak observed for 90 wt% AP/10 wt% Zn and 44 kJ/mol for 78.4 wt% AP/19.6 wt% Al/2 wt% Zn propellant composition.

Properties of Cement Pastes with Zeolite During Early Stage of Hydration

Properties of cement pastes with various replacement levels of natural zeolite were tested by isothermal calorimetry and rotational rheology. Zeolite from the Eastern Slovakia region was used for tests. Kinetics of exothermic reaction during early-stage of hydration were monitored by calorimetry. The role of different replacement level of zeolite on main rheological parameters is discussed in the paper. The onset point of formation of C-S-H products and the main calorimetric peak move to earlier times with increased zeolite content. Zeolite causes acceleration of hydration before the heat flow peak time and the following deceleration proportionally to its content. Zeolite in cement promotes the AFt formation, which increases the elastic response of fresh paste at the beginning of hydration. Trends of G’ and phase angle show that zeolite accelerates the hydration of C3S and early C-S-H formation.

Front waves and complex spatiotemporal patterns in a reaction-diffusion-convection system with thermokinetic autocatalysis

We analyze dynamics of stationary nonuniform patterns, traveling waves, and spatiotemporal chaos in a simple model of a tubular cross-flow reactor. The reactant is supplied continuously via convective flow and/or by diffusion through permeable walls of the reactor. First order exothermic reaction kinetics is assumed and the system is described by mass and energy balances forming coupled reaction-diffusion-convection equations. Dynamical regimes of the reaction-diffusion subsystem range from pulses and fronts to periodic waves and complex chaotic behavior. Two distinct types of chaotic patterns are identified and characterized by Lyapunov dimension. Next we examine the effects of convection on various types of the reaction-diffusion regimes. Remarkable zigzag fronts and steady state patterns are found despite the absence of differential flow. We employ continuation techniques to elucidate the existence and form of these patterns.

Thermal degradation of a composite solid propellant examined by DSC

The thermal decomposition of ammonium perchlorate (AP)/hydroxyl-terminated-polybutadiene (HTPB), the AP/HTPB solid propellant, was studied at different heating rates in dynamic nitrogen atmosphere. The exothermic reaction kinetics was studied by differential scanning calorimetry (DSC) in non-isothermal conditions. The Arrhenius parameters were estimated according to the Ozawa method. The calculated activation energy was 134.5 kJ mol-1, the pre-exponential factor, A, was 2.04×1010 min-1 and the reaction order for the global composite decomposition was estimated in 0.7 by the kinetic Shimadzu software based on the Ozawa method. The Kissinger method for obtaining the activation energy value was also used for comparison. These results are discussed here.

Safe and Unsafe Boundaries of Regions of Critical Phenomena in the Kinetics of Exothermic Reactions

Safe and Unsafe Boundaries of Regions of Critical Phenomena in the Kinetics of Exothermic Reactions

Characterization and kinetic analysis of the thermal decomposition of 2-oxy-4,6-dinitramine-s-triazine in non-isothermal conditions

The compound 2-oxy-4,6-dinitramine- s -triazine (DNAM) is a nitrated derivative of 2,4,6-triamine- s -triazine that, due to its energetic properties, is a candidate substance for energetic formulations. The thermal decomposition of DNAM and preliminary information on the exothermic reaction kinetics were studied by simultaneous thermal analysis in non-isothermal conditions. The Arrhenius parameters were estimated according to well-established methods but emphasis is given on statistical analysis of the correspondent regression procedures. DNAM presents good thermal stability in a wide temperature range below its exothermic decomposition that starts, according to the heating rates employed, above 473 K. The results of the kinetic analysis are critically discussed taking into account the complexity of the exothermic reaction, its relation with the heating rate, and some problems that are typical in the reaction kinetics of solids.