Maximum Reaction Temperature Research Articles

Al-based binary reactive multilayer films: Large area freestanding film synthesis and self-propagating reaction analysis

This research mainly focuses on the development of Al-based binary Ti/Al and Zr/Al reactive multilayer films (RMFs). Magnetron sputtered deposited RMFs were investigated by considering two important aspects of large freestanding film synthesis and the analysis of the self-propagating reaction. Here, Ti/nAl (n = 1–3) RMFs with different Al molar ratios and 1Zr/1Al RMFs with various bilayer thicknesses of 20–55 nm were deposited on the copper substrate. To fabricate thick films, two types of processes of the continuous coating (process-1) and the coating with interval etching (process-2) were introduced in the Magnetron Sputter Ion Plating (MSIP) method. Microstructural characterization of as-deposited RMFs by scanning electron microscopy and transmission electron microscopy reveals the columnar microstructural morphology with coherent reactant layers. The coating process-2 exhibits the consistent and uniform film growth through the cross-section compared to the process-1. The use of a cost-effective copper substrate and the modification of the coating process in this work assure the fabrication of about 10 cm long and 45 µm thick freestanding Zr/Al RMFs with homogeneous film growth. Then, self-propagating reaction properties were analyzed after an electrical arc ignition in air. A high-speed microscope and a two-color pyrometer were used to record the reaction propagation and temperature profile simultaneously. Ti/Al and Zr/Al RMFs exhibit the maximum reaction velocity of 2.6 ± 0.6 m/s and 1.22 ± 0.4 m/s, respectively. The maximum reaction temperatures of 1581–1707 °C were found in Zr/Al RMFs, whereas Ti/nAl RMFs show the reaction temperature in the range of 1215–1298 °C. The reaction front velocity and temperature of the self-propagating reaction show the dependency on the reactants combinations, compositions, and bilayer thickness. Furthermore, this work describes the component and morphology dependent reaction properties of Zr/Al and Ti/Al RMFs and a simple approach to fabricate large sized freestanding reactive films.

Microwave-assisted catalytic pyrolysis of moso bamboo for high syngas production

Microwave-assisted pyrolysis of moso bamboo with the activated carbon-supported iron(III) ion catalyst was carried out with the aim of obtaining high quality and quantity syngas(H2 + CO). The effect of the catalyst on moso bomboo pyrolysis involving the temperature-rising characteristics, product distribution, tar conversion and gas compositions were investigated. The results indicated that the catalyst improved the microwave-absorption capability and increased the maximum reaction temperatures. The formation of gases was promoted by the catalyst mainly at the expense of the tar, indicating the catalyst had an excellent activity for the tar conversion .The catalyst had the positive influence on the formation of syngas with the maximum content reaching up to 81.14 vol% with H2/CO being 1.04 and inhibited the production of CH4 and CO2. The loading of iron(III) ion into activated carbon exerted a significant influence on bamboo pyrolysis. The addition of the catalyst increased the thermal efficiency of the reaction system.

Evaluation of Potential Safety Hazards Associated with the Suzuki–Miyaura Cross-Coupling of Aryl Bromides with Vinylboron Species

The potential safety hazards associated with the Suzuki–Miyaura cross-coupling of aryl bromides with vinylboron species were evaluated. In the Suzuki–Miyaura cross-coupling of 1-bromo-3-(trifluoromethyl)benzene with potassium vinyltrifluoroborate in the presence of potassium carbonate (K2CO3) in 9:1 dimethyl sulfoxide (DMSO)/water at 80 °C, the thermal profile revealed a significant exotherm upon the addition of catalytic 1,1′-bis(diphenylphosphino)ferrocene palladium(II) dichloride [Pd(dppf)Cl2]. Further investigations indicated that the exotherm was consistently higher and the reactions were faster in the studied aqueous systems compared to anhydrous conditions. Although under anhydrous conditions the exotherms were comparable among the studied cases, the rate of the exotherm was highly dependent on the choice of aryl electrophile, solvent, base, catalyst, as well as vinylboron species. In many of the studied cases the maximum temperature of a synthesis reaction (MTSR) was considerably higher than the b...

Synthesis and structural, magnetic characterization of nanocrystalline Zn1-xCoxO diluted magnetic semiconductors (DMS) synthesized by combustion reaction

Nanocrystalline Co+2 doped Zn1−xCoxO, where x = 0.02, 0.03, 0.07 and 0.1mol of Co+2 diluted magnetic semiconductors (DMS), were synthesized by combustion reaction for spintronic applications. The effects of Co+2 ion doping on the structural, morphological and magnetic properties of ZnO ware investigated. The products of the reactions were characterized by X-ray diffraction (XRD), nitrogen adsorption (BET), transmission electron microscopy (TEM), and magnetic measurements (VSM). XRD spectra data revealed the formation of a ZnO phase (removed text), indicating that the synthesis was efficient in diluting the Co+2 ions in the ZnO lattice. Increasing the Co2+ ion concentrations reduced the maximum reaction and ignition temperature and contributed to reduce crystallite and particle sizes. The samples showed the typical behavior of soft magnetic materials at all the Co2+ concentrations evaluated here. The Curie temperature (Tc) was higher than room temperature at all the Co2+ concentrations.

Two-component additive manufacturing of nanothermite structures via reactive inkjet printing

With an eye towards improving the safety of the deposition of energetic materials while broadening the scope of materials compatible with inkjet printing, this work demonstrates the use of combinatorial inkjet printing for the deposition of energetic materials. Two largely inert colloidal suspensions of nanoaluminum and nanocopper (II) oxide in dimethylformamide with polyvinylpyrrolidone were sequentially deposited on a substrate using piezoelectric inkjet printing. The materials were deposited in such a way that the aluminum and copper (II) oxide droplets were adjacent, and overlapping, to allow for in situ mixing of the components. The alternating deposition was repeated to create a sample with multiple layers of energetic materials. Energetic performance was subsequently tested on samples printed with 3, 5, and 7 layers of materials using a spark igniter. This ignition event was observed with a high speed camera and compared to representative samples printed with pre-mixed nanothermite. High speed thermal imaging supported a conclusion that the maximum reaction temperature of comparable samples printed with the dual nozzle technique was nominally 200 K less than the samples printed with a single nozzle. Scanning transmission electron microscopy images confirmed a claim that the material constituents were comparably mixed with the single and dual nozzle techniques. This work proves the feasibility of reactive inkjet printing as a means for depositing energetic materials from two largely inert suspensions. In doing so, it opens the doors for safer material handling and the development of a wide array of energetic materials that were previously deemed incompatible with inkjet printing.

Controlling diffusion in Ni/Al reactive multilayers by Nb-alloying

Metallic reactive multilayers are known as high energy-density storage systems. Conventionally, these multilayers are tailored for high reaction rates with the purpose to achieve high maximum reaction temperatures and explosive-like behavior upon mixing. However, in some instances such as neutralization of biological hazards or chemical energy-storage systems, a low heat flow rate is desired. In the present work, we show that Nb-alloying presents an efficient approach to stabilize the as-deposited state and to form a diffusion barrier in situ, effectively reducing the heat flow rate by more than 50%. The validation of the concept is carried out by a comparative study of thermally induced phase reactions in Ni/Al and (Nb-Ni)/Al reactive multilayers. Kinetics of the phase reactions in these systems were followed by differential scanning calorimetry, analytical scanning transmission electron microscopy, and in situ electron diffraction analysis. The results confirm alloying as a design strategy for tailoring reaction kinetics of reactive multilayers.

Effects of multilayer arrangement in ternary reactive film on self-propagating reaction properties

The effects of multilayer designs in ternary films on self-propagating exothermic reaction properties were reported. The magnetron sputtered deposited ternary reactive films with two different multilayer arrangements of Ti/Si/Ti/Al and Si/Ti/Al/Si with the identical bilayer of 29±5nm and total thickness of 6μm were investigated. The reaction properties in terms of reaction heat, temperature and reaction velocity were characterized for these two types of multilayer constructions. The reaction heat was calculated by using the thermodynamic simulation. As-deposited and reacted foils were characterized by using electron microscopes. After an electric ignition, the exothermic reaction front propagates in the films. The propagation velocity and temperature were measured by using a high speed camera and a two-color pyrometer. Reaction products were analyzed by means of X-ray diffraction (XRD) analysis. The steady state reaction fronts propagate through Ti/Si/Ti/Al films with the reaction velocity of 9.1±2m/s and the maximum reaction temperature of 1768±41°C. Moreover, both steady state and unsteady propagation modes were observed in Si/Ti/Al/Si reactive foil. This film shows a maximum reaction velocity of 2.7±0.8m/s. Compared to this film, Ti/Si/Ti/Al films exhibit higher reaction temperature and propagation velocity. Here, experimental results suggest the dependency of the reaction properties on the multilayer arrangement. Although both ternary films have similar reactant types and morphology, different reactant interfaces introduce the distinct interfacial reactions and local atomic mixing rates, which influence on the reaction characteristics. This research also shows a new opportunity to design nanoscale reactive films with different multilayer arrangements to control reaction propagation besides existing technology.

Droplet size distribution effects in an edge flame with a fuel spray

The impact of the initial droplet size distribution on the behavior of an edge flame formed in the mixing layer of laminar co-flowing streams of oxidant and a spray of liquid fuel initially separated by a splitter plate is investigated for the first time. The spray is modeled using the sectional approach, and three quite different size distributions are considered having a common Sauter Mean Diameter (SMD). The nonlinear governing equations are formulated within the thermal-diffusional framework, and solved using finite differences. A parametric study discloses that despite having the same SMD the actual initial droplet size distribution influences flame location, maximum reaction rate and temperature. But more critically it can be destabilizing and lead to flame oscillations, depending on the actual initial size distribution used.

Thermochemical analysis for the reduction behavior of FeO in EAF slag via Aluminothermic Smelting Reduction (ASR) process: Part II. Effect of aluminum dross and lime fluxing on Fe and Mn recovery

We investigated Fe recovery from EAF slag by means of aluminothermic smelting reduction (ASR) at 1773K with Al dross as the reductant, especially the effect of the added amount of the fluxing agent CaO on the Fe recovery. The maximum reaction temperature calculated using FactSage™ 7.0 decreased with increasing CaO addition, but the experimentally measured maximum temperatures increased with increasing CaO addition. We calculated the amounts of various phases before and after Al dross addition under different conditions of added CaO. FeO and Al2O3 contents in molten slag sharply varied within the first 5min of the reaction, stabilizing soon thereafter. The aluminothermic reduction of FeO appeared to proceed rapidly and in good stoichiometric balance, based upon the mass balance between the consumption of FeO and MnO (ΔFeO and ΔMnO) and the production of Al2O3 (∆Al2O3). Iron recovery from EAF slag was maximized at about 90% when 40g of CaO was added to 100g slag. Furthermore, Mn could also be reduced from the EAF slags by the metallic Al in the Al dross reductant. The solid compounds of spinel (MgO∙Al2O3) and MgO were precipitated from the slag during the FeO reduction reaction, as confirmed by means of XRD analysis and thermochemical computations. To maximize Fe recovery from EAF slag, it is crucial to control the slag composition, namely to ensure high fluidity by suppressing the formation of solid compounds.

Kinetic-Free Safe Optimization of a Semibatch Runaway Reaction: Nitration of 4-Chloro Benzotrifluoride

In this work the general Ψ number criterion for the safe operation of semibatch runaway reactions has been applied to the optimization of a nitration process of primary importance in the agrochemical industry, that is the nitration through mixed acids of 4-chloro benzotrifluoride to produce a widely employed class of fluorinated herbicides. Such a reaction, as is the case for almost all the organic nitrations, belongs to the most critical class of exothermic reaction processes, for which the maximum temperature of the synthesis reaction under adiabatic conditions overcomes the decomposition temperature of the system, without any tempering effect due to a solvent evaporation. It has been verified that higher productivity operating conditions can be easily implemented through the general Ψ number criterion, even without a kinetic characterization of the system, but just elaborating information already available at the laboratory scale, where the chemical recipe is developed. The results obtained have been f...

Passive isothermalisation of an exothermic reaction in flow using a novel “Heat Pipe Oscillatory Baffled Reactor (HPOBR)”

In this study, a heat pipe was integrated with a mesoscale oscillatory baffled reactor for the passive temperature control of an exothermic reaction. The thermal/chemical performance of this new Heat Pipe Oscillatory Baffled Reactor (HPOBR) was compared to a conventional jacketed OBR (JOBR) using central composite experiment designs for an imination reaction between benzaldehyde and n-butylamine, in the absence of solvent. The variables in the experimental designs were reactant net flow rate (Ren=4–20), fluid oscillation intensity (Reo=123–491) and heat pipe fill ratio (FR=11.5–26.5; methanol working fluid). In the JOBR, the fill ratio factor was replaced with jacket temperature (4–20°C). Both reactors were able to reduce the maximum reaction temperature below the butylamine boiling point in all experiments. Overall, a 20-fold reduction in reactant volume and 13-fold improvement in reaction rate were obtained in the HPOBR for this imination reaction, compared with the same reaction using a solvent. Advantages of the HPOBR demonstrated here are isothermal operation and passive thermal control. Both reactors offer accelerated reaction rates and the potential for screening exothermic reactions. The HPOBR is a novel reactor design that provides a new approach for achieving green chemistry through solventless operation.

A new criterion to identify safe operating conditions for isoperibolic homogeneous semi-batch reactions

The maximum temperature of a synthesis reaction (MTSR) is an important criterion for process risk assessment and reactor design. In this paper, the variation of the dimensionless MTSR0 and θMTSR (the instant corresponding to MTSR0) for isoperibolic processes is studied in detail. A new runaway criterion, denoted as MTSRC, is proposed. Based on the proposed operating diagrams, a robust procedure to identify generalized inherently safe operating conditions (GIS) characterized by both a sufficiently low accumulation and MTSR lower than MAT, is developed and used with limited kinetic information. These kinetic parameters are conveniently measured by performing only one adiabatic and two isothermal experiments at laboratory scale. Comparison between MTSRC and other safety criteria is performed. In conclusion, it is demonstrated that MTSRC is an efficient and robust criterion to identify inherently safe operating conditions.

Semi-batch reactors: Thermal runaway risk

The paper deals with the thermal safety and the runaway risk evaluation for semi-batch reactors (SBR). The main contributions consist in:-Construction of a new boundary diagram which describes the reaction temperature vs. target temperature and maximum allowable temperature in order to define the critical conditions for the thermal runaway;-Identification of the most important governing parameters;-Evaluation of the risk of accident by a probabilistic description of the prior cooling problem, the appropriate combination of the critical conditions and the assessment of occurrence probability of the thermal runaway accident.A heterogeneous liquid-liquid reacting system is considered as a case study. A sensitivity analysis is then performed in order to investigate the influence of cooling temperature on the maximum reaction temperature. Monte Carlo simulations are also used in order to calculate the probability of accidents.

Exploring the reaction mechanism in self-propagating Al/Ni multilayers by adding inert material

We present a new class of reactive materials termed “inert-mediated reactive multilayers” (IMRMs) that use inert material to decouple the effects of chemistry and maximum temperature in a reactive multilayer. Important considerations in the selection of composition and thickness for reactive and inert material in an IMRM are detailed. We then present the results from a specific set of IMRM samples that we fabricated using 23-nm-bilayer 1:1 Al:Ni reactive sections and 2:3 Cu:Ni inert sections. In these samples we observe a systematic reduction of heats of reaction, maximum reaction temperatures, and reaction propagation velocities as the volume fraction of reactive material is reduced. At the same time, metrics sensitive to the reaction mechanism and products indicate that there is little if any cross-contamination between inert and reactive material in any of the samples. This indicates that the IMRM samples all undergo the same net reaction (Al/Ni→AlNi) but at a range of different flame temperatures (roughly 1950K to 1300K). Using existing theoretical models for the relationship between flame temperature and propagation velocity, we analyze the experimental data to obtain the activation energy for the mixing process and find that this value varies significantly as the maximum reaction temperature changes. At high reaction temperatures we observe a very low activation energy (26kJ/mol) which suggests diffusion of Ni in molten Al is the rate controlling mixing mechanism in agreement with the conclusions of other studies focused on un-mediated Al/Ni reactive multilayers. However, as the reaction temperature decreases the activation energy appears to shift to much larger values implying a change in the reaction mechanism. We postulate that this shift indicates that solid products are able to form earlier in the reaction at these temperatures, impeding atomic diffusion and intermixing.

Real-Time Nonlinear Model Predictive Control of a Transport–Reaction System

Two real-time nonlinear model predictive control (NMPC) algorithms for a transport–reaction system are designed. The system is modeled by a hyperbolic partial differential equation and discretized by means of a two-time-level semi-implicit semi-Lagrangian scheme. For the resulting lumped-parameter system, a constrained optimal control problem is formulated and state constraints are implemented in the form of barrier functions. The NMPC algorithms perform a single step or several steps of an iterative solution routine of the optimal control problem at every sampling point. With this suboptimal solution strategy, a fixed maximum evaluation time and execution in real time are guaranteed. An analysis of the nominal stability is provided for one NMPC scheme. The robustness of the controllers is evaluated for an example problem, where a nonisothermal plug-flow reactor with irreversible exothermic reactions is considered. The control objectives are to limit the maximum reactor temperature (avoid hot spots) and to maximize the process output.

RE 13Pd25+x Zn28–x (RE = Y, Ho–Lu) – A 4 × 4 × 4 tungsten superstructure with short Pd/Zn dumbbells as structural motif

Abstract The rare earth-based zinc compounds RE 13Pd25+x Zn28–x (RE = Y, Ho–Lu) were synthesized from the elements in sealed niobium ampoules with a maximum reaction temperature of 1470 K followed by different annealing sequences. The structures of all compounds were refined from single crystal X-ray diffraction data, indicating substantial Zn/Pd mixing on one 8c and one 24g zinc site. Exemplarily, the homogeneity range of the solid solution Yb13Pd25+x Zn28–x was manifested from samples of different starting compositions and five single crystal data sets. The RE 13Pd25+x Zn28–x structures are cubic, space group I4̅3m with lattice parameters ranging from 1295 to 1307 pm, as a function of the rare earth element and the Zn/Pd mixing. Hierarchically, one can derive the RE 13Pd25+x Zn28–x structures from the simple bcc packing. A group–subgroup scheme was developed for this new 4 × 4 × 4 tungsten superstructure which shows vacancy ordering and dumbbell formation. Temperature dependent magnetic susceptibility measurements show diamagnetism for a Lu13Pd29Zn24 sample and Curie–Weiss paramagnetism for Tm13Pd29Zn24 down to 3 K.

Effect of dilution on reaction properties and bonds formed using mechanically processed dilute thermite foils

Thermites have been used for over a century for joining applications and in this paper we present fully dense diluted thermite foils that react in a self-propagating manner and produce sufficient heat and molten braze to join aluminum-, magnesium-, and iron-based alloys. Al:NiO, Al:CuO, and Al:Cu2O thermite systems were systematically diluted with Ni or Cu to decrease the maximum reaction temperature and hence the amount of gas generated during the self-propagating reactions. Velocities and mass ejection were measured for reactions within free-standing foils as a function of dilution. The dilution that leads to quenching during propagation within a bond is identified, and finally, Al:NiO:10wt%Ni and Al:CuO:40wt%Cu foils were used to demonstrate the ability to join aluminum-, magnesium-, and iron-based alloys.

Thermal hazard evaluation of cyclohexanone peroxide synthesis

Cyclohexanone peroxide, a crucial organic peroxide used as a curing agent or an initiator in free radical polymerization, is produced through a reaction of cyclohexanone with hydrogen peroxide in the presence of nitric acid as the catalyst. For this study, we used reaction calorimeter, differential scanning calorimetry, and accelerating rate calorimeter to evaluate the thermal hazard characteristics of cyclohexanone peroxide synthesis and the thermal stability of cyclohexanone peroxide. The overall kinetic parameters of the peroxide reaction, which were calculated based on the Levenberg–Marquardt algorithm, were validated using experimental data. By combining the maximum temperature of the synthesis reaction that was corrected by the yield and temperature, at which time to the maximum rate under adiabatic decomposition conditions was equal to 24 h, criticality classes were depicted to assess the cooling failure scenario of the peroxide reaction. This study enhances our understanding of the peroxide reaction and presents safer operating conditions and design protection measures for a safer and greener chemical industry.

Chemical and Isotopic Thresholds in Charring: Implications for the Interpretation of Charcoal Mass and Isotopic Data.

Charcoal plays a significant role in the long-term carbon cycle, and its use as a soil amendment is promoted as a C sequestration strategy (biochar). One challenge in this research area is understanding the heterogeneity of charcoal properties. Although the maximum reaction temperature is often used as a gauge of pyrolysis conditions, pyrolysis duration also changes charcoal physicochemical qualities. Here, we introduce a formal definition of charring intensity (CI) to more accurately characterize pyrolysis, and we document variation in charcoal chemical properties with variation in CI. We find two types of responses to CI: either linear or threshold relationships. Mass yield decreases linearly with CI, while a threshold exists across which % C, % N, and δ(15)N exhibit large changes. This CI threshold co-occurs with an increase in charcoal aromaticity. C isotopes do not change from original biomass values, supporting the use of charcoal δ(13)C signatures to infer paleoecological conditions. Fractionation of N isotopes indicates that fire may be enriching soils in (15)N through pyrolytic N isotope fractionation. This influx of "black N" could have a significant impact on soil N isotopes, which we show theoretically using a simple mass-balance model.

Alternative method to prevent thermal runaway in case of error on operating conditions continuous reactor

Thermal runaway was studied in a continuous tubular pilot reactor under steady-state regime. Different accident scenarii were conducted by making some errors on reactant concentrations and/or temperature feed. To prevent thermal runaway, control by direct contact by solvent injection was used at different reactor locations. This injection allowed controlling the maximum reaction temperature. A simplified analytical method to estimate the maximum reaction temperature along the reactor was used.Benefit of this control method was the diminution of computational time. Furthermore, by injecting solvent to control maximum reaction temperature, there is no need to shut down the unit. The control method was validated experimentally.