Kinetic Regularities of the Heat Release for the Interaction of Some Organic Compounds with Ammonium Nitrate

Ammonium nitrate (AN) is used as an oxidant in a series of systems with a wide spectrum of applications, from explosive compositions up to smokeless stoichiometric self‐burning compositions with low combustion temperature. The knowledge of the thermal stability of such compositions is of great importance in using them in practice. In this work the research of kinetics of heat release in the interaction of AN with different organic compounds has been performed using the automatic differential calorimeter.     

Ways to Create Fuels for Stoichiometric Gas‐Generating CHNO‐Compositions with Low Ammonium Nitrate Fraction

The investigation is aimed to study the possibility of the creation of new CHNO‐fuels for smokeless stoichiometric gas‐generating compositions for airbag inflators. New fuels must have a rather high content of oxygen (to decrease the ammonium nitrate content) as well as a moderate enthalpy of formation in order to prevent an increase of the combustion temperature and of the amount of toxic gases (CO and nitrogen oxides) in the combustion products. Ways to create such new fuels are examined, mainly by introducing low‐enthalpy oxygen containing groups together with oxidizing groups (such as NO₂, ONO₂, NNO₂) into molecules. For several hypothetic substances, the enthalpy of formation has been calculated, thermal stability has been qualitatively estimated, combustion temperatures of stoichiometric compositions have been calculated, and possible ways of their synthesis have been considered.     

Influence of combustion aids on suspension combustion synthesis of mullite powders

Mullite powders were obtained by suspension combustion synthesis. The reaction was performed in a combustion reactor designed in the laboratory, which presents some advantages over other classical procedures (heating with a hot-plate, a furnace or a microwave oven). Aluminium nitrate, as a source of Al, and either TEOS or a colloidal silica suspension, as a source of Si, were used as reagents. Urea, at either 100 or 200% excess over the stoichiometric ratio, was used as fuel. NH₄NO₃, HNO₃, NH₄Cl and H₂O₂ were compared as combustion aids. Mullite phase with a high crystallinity and a high specific surface area was directly obtained by using aluminium nitrate, colloidal silica suspension, a 100% excess of urea and either NH₄NO₃ or H₂O₂. The selection of a combustion aid determines the characteristics of the as-synthesized powders. In addition to enthalpy predictions the reduction potential is a key parameter for the combustion to occur.     

Facile,scalable synthesis of nanocrystalline calcium zirconate by the solution combustion method

Single phasic nanocrystalline CaZrO₃ powder has been synthesized by glycine nitrate solution combustion method around 300 °C using nitrate as oxidant and glycine as fuel. The as prepared product obtained as a result of combustion itself is crystalline and nearly single phasic CaZrO₃ confirmed by X-ray diffraction (XRD). The product calcined at 600 °C reveals carbonate free single phasic orthorhombic structured CaZrO₃. To study the impact of oxidant to fuel ratio (O/F) and ignition temperature, a systematic variation of O/F and ignition temperature of combustion reaction has been investigated by analyzing the products through XRD in each case. These products have been characterized by XRD, Fourier Transform Raman spectroscopy, Thermal Analysis (TGA/DTA), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Raman Spectrum reveals single phasic nanocrystalline perovskite CaZrO₃. Spherical shaped particles were observed through SEM. TEM results also confirm the particles to be in nano regime (30–90 nm).     

Solution combustion synthesis of FeCr2O4 powders for pigment applications: Effect of fuel type

Solution combustion synthesis of iron chromite was reported using iron(III) nitrate nonahydrate and chromium(III) nitrate nonahydrate as starting materials, as well as glycine, urea, citric acid, and ethylene glycol as fuels. The influence of fuel type on the structure, molecular, microstructure as well as chromatic properties of samples was investigated. The X-ray diffraction (XRD) patterns showed that unlike themodynamical prediction, glycine fuel led to strongest combustion and consequent highest XRD peak intensities and lower lattice parameters. Moreover, the change of fuel type and mixing of fuels affected XRD data. Fourier transform infrared analysis showed that the band position of Cr–O and Fe–O bonds were shifted to higher frequencies by using of fuels with weaker combustion reactions. In addition, scanning electron micrographs showed that different morphologies of FeCr₂O₄ particles were obtained depending on the fuel type and ratios. Energy-dispersive X-ray spectroscopy analysis of the samples showed that oxygen concentration of samples was less than that of stoichiometric ratio of FeCr₂O₄ due to local reducing atmosphere. Furthermore, chromatic properties of the powders showed that the pigment synthesized with glycine fuel has a better and lighter grayish brown color than the other ones and can be used as a suitable industrial candidate to create a brown color in the ceramic glaze.     

A comparative study of hydroxyapatites synthesized using various fuels through aqueous and alcohol mediated combustion routes

Nano-sized calcium hydroxyapatite, [Ca₁₀(PO₄)₆(OH)₂] has been synthesized by the sol–gel combustion method using calcium nitrate and di-ammonium hydrogen phosphate as precursors in the aqueous medium. Triethyl phosphite was used as a phosphate precursor for alcohol mediated combustion. The aqueous and alcohol media were employed for the investigation of combustion synthesis in the presence of various fuels such as urea, glycine, alanine, hydrazine and hexamine. The metal-to-fuel ratio in the synthesis was maintained at 1 to facilitate complete combustion and the Ca/P ratio was maintained at 1.67 to aid the stoichiometric formation of hydroxyapatite. The combustion products were calcined at 800 °C for 10 h and were characterized by powder XRD, FT-IR, HR-SEM and HR-TEM techniques. All the five fuels used under the alcohol mediated combustion, resulted in forming phase pure hydroxyapatite; whereas the aqueous mediated combustion method yielded biphasic calcium phosphate containing Ca₁₀(PO₄)₆(OH)₂ and β-TCP depending on the nature of the fuel.     

Microwave sintering of mullite–cordierite precursors prepared from solution combustion synthesis

Mullite–cordierite composite was synthesized using the solution combustion synthesis method and glycine as a fuel and aluminum nitrate, magnesium nitrate and colloidal silica as the reagents. The effect of fuel to oxidizer ratio on the combustion behavior, as well as chemical composition and morphology of the formed powders was investigated. All synthesized powders were amorphous with submicron particle size. It was found that the change of fuel to oxidizer ratio had no effect on synthesis of this composite without heat treatment. The smallest particle size of composite powder was obtained as 302 nm for ratio less than 1 (rich of fuel). Mullite, cordierite and spinel were detected after microwave heating at 1200 and 1400 °C. Mullite and cordierite were detected as the only crystalline phases when the stoichiometric ratio of fuel to oxidizer was chosen and this composite obtained the highest density of 2.61 g/cm³.     

Combustion synthesis and characterization of Sr3Al2O6

In this paper, the synthesis by solution combustion (SCS) of tri-strontium aluminates (Sr₃Al₂O₆), using different fuel amounts, has been studied. The main objective was to understand the effect of the amount of fuel on phase formation, yield and purity of the product using urea as fuel. The combustion temperatures of each reaction were followed by digital pyrometry. Phase compositions were determined by X-ray diffraction (XRD). The microstructural characteristics during the SCS process were studied by field emission scanning electron microscopy (FESEM). The specific surface area was calculated with the BET model from adsorption data. The results showed that the Sr₃Al₂O₆ was the main phase obtained in all syntheses. This aluminate with high content of Sr is considered attractive for use in applications requiring radiopacity as biomaterials for dental and bone repair. The maximum measured temperature during synthesis, with excess fuel, was approximately 987°C. It was higher than that obtained in the case of using stoichiometric amounts of fuel which was 762°C. The product obtained in this second case had a submicrometer structure, with highly crystalline particles and a specific surface of 0.21 m²/g. It was higher than that obtained with excess of fuel (0.07 m²/g).     

The Strontium Complex Nitrates of Carbohydrazide as a Non‐Azide Gas Generator for Safer Driving–the Thermal Behavior of the Sr Complex with Various Oxidizing Agents

As a new azide‐free gas generant, the thermal behavior of the Sr complex nitrate of carbohydrazide was investigated in the mixed system with various oxidizing agents (KClO₄, KBrO₃, Sr(NO₃)₂, KNO₃). For the differential thermal analysis, the initial temperature of the reaction of mixtures with KBrO₃ was lower than that of the pure complex, and the reaction was very vigorous. The reactions with oxidizing agents except for KBrO₃ were thought to proceed moderately. The heat of combustion at the stoichiometric composition increased according to the tendency of the calculated theoretical value based on the chemical stoichiometric equation. The burning rate of the KBrO₃ system was very high compared with the other mixed systems, and was controlled by the rate of reaction. The pressure dependence was high in the case of using the nitrate as an oxidizing agent. In all the systems, N₂ and CO₂ gases account for 99% of all the evolved gases during the combustion. In the case of using an oxidizing agent containing a halogen, the halogen ion was only slightly detected during the combustion.     

Effects of initial temperature on the structure of laminar CH4-air premixed flames

The growing popularity of natural gas as a eco-friendly fuel, is of paramount motivation of present investigation. In the present paper, the effect of initial temperature on the flame structure have been investigated in which laminar one-dimensional planar propagating flames of CH₄/air mixtures is simulated numerically using detailed chemical kinetic scheme and realistic transport models. The burning velocities are fundamentally important in developing models to predict progress of combustion. Hence, the burning velocities as a function of initial temperature of unburnt gas have been computed for stoichiometric mixture. The present predictions of burning velocities are compared with reported experimental data of Stone et al. [Combust. Flame. 114 (1998) 546], Hill and Huang [Combust. Sci. Technol. 60 (1980) 7] and Rallis and Garforth [Combust. Flame 31 (1978) 53]. The present prediction lies within the scatter of experimental data. A correlation in the form of S_u/S_u,0=(T_u/T_u,0)^1.575 has been developed to describe the dependence of initial temperature on the burning velocity for stoichiometric mixture. The structures of flame are investigated in details for initial temperature of 300 and 600 K which clearly indicate that detailed chemical kinetics are essential for prediction of the effects of initial temperature on the burning velocities. The present study will help in designing and developing the regenerative combustion systems.     

Method for predicting the performance of an internal combustion engine fuelled by producer gas and other low heating value gases

Gasification can be seen as a process in which solid biomass is converted into a mixture of combustible gases, which complete their combustion in a second device, usually a reciprocating internal combustion engine (RICE). Downdraft moving-bed gasifiers coupled with RICE are a good choice for moderate quantities of available biomass, the equivalent of up to 500 kW of electric power. The producer gas must be mixed with additional air in order to have a stoichiometric mixture to fuel the RICE. To predict the engine performance working with such a fuel, a so-called Engine Fuel Quality (EFQ) parameter has been developed by the authors. This parameter considers the combined effect of stoichiometric air–fuel ratio and stoichiometric mixture heating value, both depending on the producer gas composition. The estimation of engine power made by using the EFQ parameter indicates that power at full load is reduced at about two-thirds of the maximum obtained with a conventional liquid fuel. A more detailed prediction of engine performance requires the use of computer simulation of several types. The authors have used successfully a two-zone thermodynamic model to predict engine performance. Model results include the fraction of mass burned, the pressure and temperature evolution, and pollutant emissions. The detailed results for power confirm the first order prediction based on the EFQ parameter.     

Effect of nitrogen pressure and aluminum content in a Fe2O3/Al mixture on combustion and chemical composition of combustion products

The possibility of obtaining cast aluminum oxynitrides in the combustion of iron-aluminum termite in a nitrogen atmosphere is shown. The combustion was carried out in a sealed reactor at an initial nitrogen pressure up to 10 MPa. The effect of the initial nitrogen pressure and aluminum content (in excess of stoichiometric) in the initial mixture on the bound nitrogen content in the oxide product of the synthesis is studied. Based on thermodynamic calculations and experimental results, a model was proposed for the chemical transformation of the initial mixture in the combustion wave with formation of a two-phase high melt.     

Combustion synthesis of lithium cobaltate

A feasibility of combustion synthesis of lithium cobaltate powders using oxide sources was investigated. Cobalt oxide Co₃O₄ and lithium carbonate Li₂CO₃ were used as starting reactants. Two different oxidizers were explored: (i) ammonia nitrate NH₄NO₃ and (ii) lithium nitrate LiNO₃. Some organic reducers (ORs)—such as CH-polymers, melamine, urotropine, etc.—were used as a fuel. Investigated was the effect of green composition/density and inert gas pressure on combustion parameters (burning velocity and combustion temperature) and product micro structure/composition. Best results were obtained for LiNO₃-Co₃O₄-OR blends. Relative green density ρ was found to have a crucial effect: good results might be obtained only for ρ > 65%. XRD data testified that the combustion products obtained in optimized conditions contained pure lithium cobaltate LiCoO₂. According to SEM data, the obtained powders had a mean particle size of 20 μm.     

Preparation and Characterization of Nano-Crystalline LiNi0.5Mn1.5O4 Cathode Material by the Soft Combustion Reaction Method

Nano-crystalline LiNi_0.5Mn_1.5O₄ with a unique powder characterization has been successfully synthesized by a soft combustion reaction method, using lithium nitrate, manganese nitrate, and nickel nitrate as the starting materials, and no organic materials being introduced in the whole process. The LiNi_0.5Mn_1.5O₄ powders synthesized by the soft combustion reaction method were investigated by differential thermal analysis and thermogravimetry, X-ray diffractometer, and transmission electron microscopy. The resultant product was a pure phase of LiNi_0.5Mn_1.5O₄ without any other impurities. Electrochemical measurements were also performed.     

燃烧法制备纳米ZnO及光催化降解甲基橙的研究

分别以甘氨酸和柠檬酸为燃料,Zn（NO3）2为氧化剂,采用燃烧法制备纳米ZnO粉体并采用模拟太阳光进行甲基橙光催化降解研究。XRD和SEM表征样品表明,燃烧法能简单、快速制备纳米ZnO粉体。研究表明,燃烧剂和氧化剂的配比以及反应温度对制备的纳米ZnO降解甲基橙效果有较大影响。Zn（NO3）2与甘氨酸之比为0．2～0．5（物质的量比）,反应温度为5000C;Zn（NO3）2与柠檬酸之比为1．5,反应温度为600℃进行反应制备得到的纳米ZnO降解甲基橙效果较好。降解实验的结果表明,纳米ZnO能有效地光催化降解甲基橙染料。以柠檬酸为燃料制备的ZnO样品,在1h内对10mg·L^-1甲基橙溶液的降解率为90％。     

贫氧条件下正癸烷在Pt/ZSM-5上的催化燃烧特性

航空煤油实际燃烧过程中往往存在高化学当量比（Φ）的贫氧条件,导致航空煤油着火困难、燃烧效率较低。本文以航空煤油一元替代燃料正癸烷为燃料,实验研究了贫氧条件下（Φ=2~4）微圆管内Pt/ZSM-5催化剂和石英砂填充床中正癸烷的贫氧催化/无催化燃烧特性,分析了当量比（Φ=2~4）、温度（300~450℃）和催化剂对正癸烷转化率、燃烧效率以及气相产物分布特性的影响。结果表明：Pt/ZSM-5催化剂对正癸烷燃烧反应的促进作用明显,存在温度激增现象,当量比Φ从2增大到3.5时,动态着火点从196℃上升到271℃,而无催化则没有明显的着火点。贫氧催化条件下正癸烷的转化率始终低于无催化条件,但燃烧效率明显高于无催化。正癸烷催化燃烧的主要气相产物为CO₂,无催化的主要气相产物则为CO和烯烃。     

Brown pigment of the nanopowder spinel ferrite prepared by combustion reaction

The purpose of the present work was to prepare nanometric brown pigments spinel (Zn_1−xNi_x)Fe₂O₄ (with x = 0, 0.5 and 1 mol of the Ni²⁺) structures by combustion reaction and characterize the resulting powders. The compositions were prepared by a single-step solution combustion reaction using nitrates and urea as fuel. Stoichiometric compositions of metal nitrate and urea were calculated using the total oxidizing and reducing valences of the components, which serve as the numerical coefficients for the stoichiometric balance, so that the equivalence ratio Φ_c is equal to unity and the energy released was maximum. The resulting powders were characterized by X-ray diffraction (XRD), nitrogen adsorption by BET, scanning electron microscopy (SEM), helium pycnometry, sedimentation, transmission electron microscopy (TEM), and CIE-L*a*b* color-measurements. The results demonstrated that the synthesis by combustion reaction was very fast and safe resulting in crystalline spinel containing nanoparticles (18–26 nm) for all of the compositions studied. The results demonstrate the viability of using these powders as brown ceramic pigments.     

A new route for the direct synthesis of Al2O3/SiC nanopowder mixtures by the carbothermal reduction of parent oxides

The direct synthesis of Al₂O₃/SiC nanopowders from the parent oxides Al₂O₃ and SiO₂ through mullite carbothermal reduction as intermediate phase has been investigated. The effect of the amount of excess stoichiometric carbon (active charcoal, AC) as sole carbon source on the microstructure evolution has been studied. The effect of type of carbon source (AC, graphite (G), 50 wt % AC 50 wt % G mixture, 57 wt % AC 43 wt % G mixture) on the microstructure evolution was investigated using 30 wt % excess stoichiometric carbon. The effect of reaction temperature, reaction duration, initial green compact thickness, and carbon source on the mullite conversion, morphology, and surface area of the final powders has been thoroughly investigated. The calculated activation energy is in the range of 203–230 kJ mol^?1, depending on the carbon source used. The synergetic effect observed for the AC/G mixtures has been accordingly explained. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Morphology of Oxide Particles Made by the Emulsion Combustion Method

Various oxide powders were prepared by the emulsion combustion method (ECM) using metal precursors, kerosene, and a surfactant. The product particles were characterized by transmission electron microscopy (TEM), nitrogen adsorption, and X-ray diffraction. Hollow γ-Al₂O₃ particles were produced from aluminum nitrate or chloride precursors dispersed in air, whereas dispersion of the precursor emulsion in oxygen resulted in solid α-Al₂O₃ particles. Hollow spheres were obtained also for TiO₂, ZrO₂, and Y₂O₃ by ECM of TiCl₄, zirconium oxynitrate, and yttrium nitrate in aqueous solution. A simple method was developed to predict the thickness and diameter of hollow particles using the nitrogen adsorption data and initial droplet concentration of the ECM spray. The TEM diameter and shell thickness of hollow particles were consistent with those predicted. In contrast, solid particles were formed by ECM for ZnO, Fe₂O₃, CeO₂, and MgO from aqueous solutions of their corresponding nitrates.     

Combustion Synthesis of Metal Chromite Powders

Fine-particle metal chromites (MCr₂O₄, where M = Mg, Ca, Mn, Fe, Co, Ni, Cu, and Zn) have been prepared by the combustion of aqueous solutions containing the respective metal nitrate, chromium(III) nitrate, and urea in stoichiometric amounts. The mixtures, when rapidly heated to 350°C, ignite and yield voluminous chromites with surface areas ranging from 5 to 25 m²/g. MgCr₂O₄, sintered in air at 1500°C for 5 h, has a density of 4.0 g/cm³.