Propellant Chemistry Research Articles

Nanocrystalline Manganese Iron Oxide as a Charge Storage Electrode

AbstractPhase pure nanocrystalline manganese iron oxide [(Mn0.37Fe0.63)2O3] was synthesized by combustion technique based on propellant chemistry principle employing citric acid as fuel. The synthesized powder was characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), BET, BJH analysis and electrochemical studies for possible application as a charge storage electrode. The average crystallite size was found to be 18.6 nm from XRD analysis. BET analysis yielded the surface area and specific pore volume of the powder to be 22.96 m2 g−1 and 0.0098 cm3 g−1 respectively. The specific capacitance from cyclic voltammetric studies at scan rate 5 mV s−1 was found to be about 30 F g−1 cm−2 while from charge discharge studies was found to be 27±1 F g−1 cm−2. In addition, the material showed appreciable stability during charge‐discharge cycling.

Observation of enhanced magnetic pinning in Sm3+ substituted nanocrystalline Mn[sbnd]Zn ferrites prepared by propellant chemistry route

We report the effect of Sm3+ substitution on the structural and magnetic properties of nanocrystalline Mn0.5Zn0.5SmyFe2-yO4 (y = 0.00, 0.01, 0.03 and 0.05) samples prepared by propellant chemistry route using a mixture of fuels. Rietveld refinement of XRD patterns confirmed the formation of cubic spinel phase with space group Fd3¯m. The lattice parameter values decreased with Sm3+ substitution up to y = 0.03, but with a noticeable increase for the sample with y = 0.05. In all the samples, entire amount of Zn2+ and Sm3+ were found to be present at the A and B sites, respectively. A distribution of Mn2+ ions at the tetrahedral (A) and the octahedral (B) sites of the spinel Mn0.5Zn0.5Fe2O4 was observed. The microstructures of the samples were observed using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). For all the samples, the average crystallite size decreased with increase in Sm3+ concentration, as determined using Williamson-Hall method. The FTIR spectra showed prominent absorption bands at ∼540 and ∼390 cm−1 corresponding to the stretching vibrations of the metal ion complexes at the tetrahedral (A) and the octahedral (B) sites, respectively. Magnetic properties such as saturation magnetization (Ms), remanence (Mr) and magneton number (ηB) were found to decrease, while the coercivity (Hc) and reduced remanence (Mr/Ms) of the samples were found to increase with increasing Sm3+ content. The increase in Hc with increase in Sm3+ concentration is interpreted as the enhanced pinning of the magnetic moments at the magnetic defects created by Sm3+ ions, which is further confirmed by Mössbauer spectroscopy through a nearly constant magnetic hyperfine field. This results in an increase in the magnetic particle size in spite of decreasing average crystallite size. Our work suggests that, Sm3+ substitution can be used to alter the magnetic hardness of MnZn ferrites and to enable them to be used as potential materials for various technological applications.

Síntese por reação por combustão de nanopós de hexaferrita de estrôncio dopada com cromo

Nanopós de hexaferrita de estrôncio dopadas com cromo foram sintetizadas por reação por combustão. A influência do Cr3+ nas proporções de x = 0, 0,2, 0,3 e 0,4 no sistema SrCr xFe12-xO19 foi investigada. Os pós foram preparados de acordo com o conceito da química dos propelentes, aquecidos em placa convencional. Os pós sintetizados foram caracterizados por difratometria de raios X, microscopia eletrônica de varredura e medidas magnéticas. Os resultados mostraram que foi possível obter nanopós de hexaferrita de estrôncio dopada com cromo, que a presença da fase secundária (SrFe2O5) diminui com o aumento da adição de cromo, e que a proporção de x = 0,4 de cromo favoreceu o aumento da magnetização de saturação.

Magnetic and dielectric interactions in nano zinc ferrite powder: Prepared by self-sustainable propellant chemistry technique

The structural, magnetic and dielectric properties of nano zinc ferrite prepared by the propellant chemistry technique are studied. The PXRD measurement at room temperature reveal that the compound is in cubic spinel phase, belong to the space group Fd−3m. The unit cell parameters have been estimated from Rietveld refinement. The calculated force constants from FTIR spectrum corresponding to octahedral and tetrahedral sites at 375 and 542cm−1 are 6.61×102 and 3.77×102Nm−1 respectively; these values are slightly higher compared to the other ferrite systems. Magnetic hysteresis and EPR spectra show superparamagnetic property nearly to room temperature due to comparison values between magnetic anisotropy energy and the thermal energy. The calculated values of saturation magnetization, remenant magnetization, coercive field and magnetic moment supports for the existence of multi domain particles in the sample. The temperature dependent magnetic field shows the spin freezing state at 30K and the blocking temperature at above room temperature. The frequency dependent dielectric interactions show the variation of dielectric constant, dielectric loss and impedance as similar to other ferrite systems. The AC conductivity in the prepared sample is due to the presence of electrons, holes and polarons. The synthesized material is suitable for nano-electronics and biomedical applications.

Effect of Surface Roughness and Radiation on Graphite Nozzle Erosion in Solid Rocket Motors

A numerical analysis is performed to study the effect of surface roughness and radiation on graphite nozzle erosion in solid rocket motors loaded with non-metalized ammonium perchlorate/hydroxyl-terminated polybutadiene composite propellants. An integrated theoretical/numerical formulation established previously to predict the chemical erosion of nozzle material has been extended to investigate the effects of surface roughness and radiation. The framework takes into account propellant chemistry, detailed thermofluid dynamics for a multi-component flow, energy transport in the solid phase, heterogeneous reactions at the nozzle surface, and nozzle material properties. Typical combustion species of non-metalized composite propellant at practical motor operating conditions are considered at the nozzle inlet. The two-layer turbulence model has been modified to account for surface roughness. The contribution from radiative heat transfer is included in the overall energy balance at the gas-solid interface. Results show that the heat- transfer rate to the nozzle material is enhanced for a rough surface, leading to a higher erosion rate than that for a smooth surface. For non-metalized propellant, the erosion rate has been found to decrease slightly due to radiation, and change in the rate strongly depends on the gas-phase emissivity.

Preparation of Nanocrystalline Magnesium Aluminate Spinel Powder by Thermal Explosion Mode of LCS

The nanocrystalline MgAl2O4powder was prepared by thermal explosion mode of low-temperature combustion synthesis (LCS) using urea as fuel and nitrates as oxidizers. The molar ratio of nitrates to urea and the adiabatic flame temperature was calculated according to the propellant chemistry and combustion thermodynamics theory respectively, and the effect of thermal explosion temperature on the properties of powder was investigated. The phase and morphology of the synthesized powder were investigated by X-ray diffraction and scanning electron microscopy. The results showed that the combustion process completed in very shortly time, and the cauliflower-like powder with porous structure was obtained. The crystalline size of MgAl2O4increased with the increasing of thermal explosion temperature, and the powder had good crystalline shape and purity. The average crystalline size of MgAl2O4prepared at 400 was approximately 40nm.

A novel microwave combustion approach for single step synthesis of α-Al 2O 3 nanopowders

A novel method for synthesis of nano-sized α-Al 2O 3 particles in a single step using microwave is being reported for the first time. The sol of aluminum nitrate with urea mixed in the stoichiometric ratios in accordance with jet propellant chemistry, when combusted in a microwave oven gave fine single phase α-Al 2O 3 nanoparticles. The resultant oxide powder was characterized by TGA (Thermo-Gravimetric Analysis), FTIR (Fourier Transform Infra-Red Spectroscopy), XRD (X-ray Diffraction) and TEM (Transmission Electron Microscopy). The XRD analysis of the microwave combusted powder showed complete formation single phase α-Al 2O 3 without contamination of other phases of alumina. In comparison to the well known furnace combustion method for the direct synthesis of α-Al 2O 3, microwave combustion gave finer particles with very small agglomerate size as revealed by TEM analysis.

Solution combustion synthesis of Cu nanoparticles: a role of oxidant-to-fuel ratio

Solution combustion synthesis technique is one of the novel techniques used to prepare nanoparticles, nanocomposite and ceramic oxides. The authors prove in this study the usefulness of the technique in producing copper nanoparticles. In solution combustion, the stoichiometric ratio, according to propellant chemistry, needs the oxidiser-to-fuel ratio to be unity. The combustion of cupric nitrate and citric acid at stoichiometric ratio results in copper nanoparticles. The copper nanoparticles were characterised by different techniques, such as X-ray diffraction, thermal gravimetry/differential thermal analyser, Fourier transform infrared, FT-Raman and scanning electron microscopy. The Cu nanoparticles get oxidised to Cu 2 O slowly at 250°C and to CuO at 530°C. The combustion of the reactants with lean and rich oxidant-to-fuel ratio (O/F) ratios results in mixed phases except in the 1:0.71 ratio. The phases in lean O/F ratios were Cu, CuO, Cu 2 O, whereas only CuO was present in rich O/F ratios.

Síntese, por reação de combustão em forno de microondas, de nanoferritas de níquel dopadas com cromo

Pós nanométricos de ferritas de níquel dopadas com cromo foram sintetizados por reação de combustão em forno de microondas. A influência da concentração de Cr3+ nas proporções de x = 0; 0,5 e 1 no sistema NiCr xFe2-xO4 foi investigada. Os pós foram preparados de acordo com o conceito da química dos propelentes e aquecidos em forno microondas com potência 980 W. Os pós sintetizados foram caracterizados por difratometria de raios X, adsorção de nitrogênio (método BET), microscopia eletrônica de varredura, picnometria de hélio e medidas magnéticas. Os resultados mostraram que foi possível obter nanopós de ferritas de níquel dopadas com cromo e que a elevação da concentração de cromo causou um aumento no tamanho de partículas (15 nm para 55 nm) e redução nos parâmetros magnéticos.

Evaluation of the Morphology and Magnetic Properties of Cr<sup>3+</sup>- Doped Ni-Zn Ferrites

This work involved a morphological, microstructural and magnetic characterization of nanosized powders and sintered samples of Ni-Zn ferrite doped with chromium. The effect of substituting Fe3+ for Cr3+ on the final characteristics of the powders and sintered samples was investigated. The Ni-Zn ferrite powders were prepared by combustion reaction using nitrates and urea as fuel, based on the concepts of propellant chemistry. The samples were uniaxially compacted by dry pressing (385 MPa) and sintered at 1200oC/2h, using a heating rate of 5°C/min. The Ni-Zn powders and compacted samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the measures of their magnetic properties. The results revealed the formation of the cubic crystalline phase of the inverse spinel of Ni-Zn-Cr ferrite. The average crystallite size was 21 nm and 57 nm while the saturation magnetization was 47.0 and 73.1 emu/g for the powder and the sintered sample, respectively.

One-Step Synthesis of Nanocrytalline Perovskite LaMnO 3 Powders via Microwave-Induced Solution Combustion Route

Perovskite LaMnO 3 powders with an average crystallite size of 12.5 nm were rapidly synthesized via a microwave-induced autocombustion reaction using glycine as a fuel and nitrate as an oxidant. After self-propagating combustion, the desired nanocrystalline perovskite LaMnO 3 was obtained and no further calcination was carried out. The possible processes of combustion reaction were discussed according to the principle of propellant chemistry. The autocombustion and thermal decomposition of the precursor were investigated using the TG-DTA and FT-IR techniques. The influences of glycine-nitrate molar ratio and heat-treatment temperature on the perovskite phase formation and crystallite size of as-burnt powder were studied by XRD. The morphology and size of the as-burnt powder before and after milling were characterized and compared by TEM.

Nanocrystalline GdFeO3 via the gel-combustion process

Nanocrystalline GdFeO3 powder was synthesized by a combustion technique, using glycine as the fuel and the corresponding metal nitrates as oxidants. Five different molar ratios of fuel-to-oxidant were chosen to study the effect of fuel content on the phase formation and the powder properties. The powders after calcination were characterized by x-ray diffraction (XRD) and crystallite sizes calculated by x-ray line broadening. The crystallite sizes for the phase pure products after calcination at 600 °C were in the range 40–65 nm. The transmission electron microscopy observations clearly highlight the pronounced crystallinity for the propellant chemistry samples. The nature of the agglomerates was investigated by light scattering studies. The lattice thermal expansion behavior was also studied by high-temperature XRD.

Preparation and characterization of Sr0.09Ce0.91O1.91, SrCeO3, and Sr2CeO4 by glycine–nitrate combustion: Crucial role of oxidant-to-fuel ratio

The title compositions were prepared by the gel-combustion process using glycine as the fuel and the corresponding metal nitrates as oxidants. The powders after calcination at 600 °C were characterized by x-ray diffraction for phase identification. The lattice parameters were refined by least squares method for each of the title compounds. Sr0.09Ce0.91O1.91 could be prepared in situ, that is, without any further external heating at higher temperatures, whereas phase pure SrCeO3 and Sr2CeO4 could be prepared only after calcination at 950 °C for 3 h. Sr0.09Ce0.91O1.91 was prepared using three different oxidant-to-fuel ratios: the fuel-deficient ratio, the propellant chemistry (stoichiometric) ratio, and the fuel-excess ratio. The crystallite size as calculated by x-ray line broadening was found to be 13 nm, 20 nm, and 42 nm for the products from fuel-deficient, propellant, and fuel-excess ratios, respectively. It was found that the extreme fuel-deficient ratio of 1:0.5 failed to give phase pure Sr0.09Ce0.91O1.91. The transmission electron microscopy studies showed that majority of the particles were in the range 80–100 nm and 200–250 nm for SrCeO3 and Sr2CeO4, respectively. The compositional characterization was done by energy dispersive x-ray. A careful control of the oxidant-to-fuel ratio was found to be necessary to get the desired products, due to their different thermodynamic stabilities. Thus, the versatility of combustion process in synthesizing the products with different thermodynamic stabilities has been shown, which was hitherto unexplored.

Low-temperature combustion synthesis and characterization of nanosized tetragonal barium titanate powders

Nanosized tetragonal barium titanate has been directly prepared by low-temperature combustion synthesis process (LCS). According to thermochemical calculations of propellant chemistry theory, the optimum molar ratio of reactants was obtained with the Ba(NO 3) 2–TiO(NO 3) 2–citric acid–NH 4NO 3 system. The influence of the ratio of reactants on the properties of the final products was investigated. The results showed that tetragonal BaTiO 3 with high purity was produced at low ignition temperature (∼300 °C). The crystalline size of the powder obtained is less than 50 nm. The crystal structure, crystalline size and morphology were analyzed by XRD, SEM and TEM.

Mathematical modeling of rheological properties of hydroxyl‐terminated polybutadiene binder and dioctyl adipate plasticizer

AbstractSolid composite propellants contain 80–90% of a crystalline oxidizer like ammonium perchlorate and powdery metallic fuel like aluminum with 10 to 15% organic binders like HTPB or CTPB, to bind the solids together and maintain the shape under severe stress and strain environment. Also, the propellant must not crack or become brittle at subzero temperatures. Formulating and processing of the highly filled composite propellants are difficult tasks and need a thorough understanding of rheology, even apart from a knowledge of propellant chemistry, particulate technology, manufacturing methods, and safe handling of explosives and hazardous materials. The flow behavior or rheology of the propellant slurry determines the ingredients and some of the abnormalities of the motor during firing. The propellant viscosity and mechanical properties are determined by the binder system, and the unloading viscosity of the propellant slurry is dependent on the initial viscosity of the binder system, solid loading, particle size, and its distribution, shape, temperature, and pressure. In the present report an attempt is made to study the dependency of viscosity of the HTPB binder system on temperature, plasticizer level (composition), and torque (angular velocity of spindle). The viscosity measurements were made using a Brookfield viscometer model DV III at different plasticizer levels (10–50%), temperatures (30–65°C), and torques (50–100%). The data indicate that the viscosity of HTPB, DOA, and their mixture decreases with increasing temperature and is constant with torque. The Arrhenius equation gives the energy for viscous flow to be ≅35 kcal/mol for HTPB. The variation of viscosity with temperature of HTPB/DOA and their mixture follows a mathematical model expressed as where T is the temperature and a1, a2, a3, a4, and a5 are the constants. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1002–1007, 2002

Investigation of obturator and ignitor effects on low velocity starting of the ram accelerator

An experimental investigation of the effects of obturator geometry, propellant chemistry, and onboard pyrotechnic ignitor systems on the starting characteristics of the ram accelerator at low launch velocity has been conducted at the University of Washington 38-mm-bore facility. The ram accelerator was successfully started at entrance velocities as low as 760 m/s using stoichiometric methane/oxygen propellants with various levels of carbon dioxide dilution and obturator configurations at a fill pressure of 2.5 MPa. Experiments using an onboard pyrotechnic ignitor demonstrated that ignition of the propellant and starting of the ram accelerator could occur without the presence of the obturator-driven normal shock.

Kinetics of the O(3P) + N2O Reaction. 2. Interpretation and Recommended Rate Coefficients

The reaction O(3P) + N2O is important to models of NOx pollutant and propellant chemistry and to the understanding of the thermal decomposition of N2O, which has historically played a key role in the development of unimolecular reaction theory. The reaction has two important product channels: O + N2O → NO + NO (ΔH0 = −36 kcal/mol) (R1); O + N2O → O2 + N2 (ΔH0 = −79 kcal/mol) (R2). Rate coefficients of these reactions have been the subject of several reviews. However, clear reasons why many of the evaluated, nonretained data differ from recommendations have not previously been known. There has been a great deal of controversy over the rate coefficients, particularly for reaction R2. Here, the relevant data are critically evaluated using detailed chemical modeling as an important tool. The results explain many of the discrepancies. Some of the data of central importance in earlier evaluations are shown to be incorrect. Additionally, some important features of the global behavior of the mixtures studied, which had previously not been understood, are explained, and the possible effects of hypothetical H2O contamination on N2O shock tube studies was quantitatively investigated. It is shown that the bulk of the rate coefficient results remaining after the evaluations can be combined with the intermediate temperature results for ktot = k1 + k2 from FGFAM (Fontijn, A.; Goumri, A.; Fernandez, A.; Anderson, W. R.; Meagher, N. E. J. Phys. Chem., preceding paper in this issue) to obtain fitted recommendations: k1 = 1.52 × 10-10 exp(−13 930/T) cm3 molecule-1 s-1 (1370−4080 K); k2 = 6.13 × 10-12 exp(−8,020/T) cm3 molecule-1 s-1 (1075−3340 K). Until recently, it was believed rate coefficients of the two product channels were approximately equal over a very wide temperature range. In contrast, the present study has led to the conclusion that reaction R2 dominates below, and reaction R1 above, 1840 K.

Preparation of La1-xSrxMnO3 powders by combustion of poly(ethylene glycol)-metal nitrate gel precursors

La1−xSrxMnO3 powders were prepared by auto-ignited combustion of poly(ethylene glycol) (PEG)–metal–nitrate gel precursors. The thermal behaviour of the precursors strongly depends on the ratio of PEG to metal nitrate, which is closely related to the ratio of fuel to oxidizer. The burning behaviour in a furnace was successfully explained by valence concepts normally encountered in propellant chemistry. The formation of a pure perovskite phase was significantly influenced by the homogeneity of the gel precursor. Perovskite structured oxides were formed through two different paths, one of which was direct formation from the burning of a gel precursor and the other was a subsequent structural evolution by heat treatment after burning. The formation procedure of the perovskite and the morphology of powders could be explained in terms of the burning behaviour of the precursor and the role of organic residue.

Some features of solid propellant chemistry

Some features of solid propellant chemistry

Energetics of Propellant Chemistry.

Energetics of Propellant Chemistry.