On the principles and mechanism of the combustion of ammonium perchlorate

Conclusions The dependence of the rate of combustion of ammonium perchlorate on the pressure, temperature, particle size, density, and addition of ammonium chloride was studied, and a mechanism of the combustion of ammonium perchlorate was formulated on the basis of the principles obtained.     

Theoretical calculation of the reduced viscosity of aqueous suspensions of charged spherical particles

The origin of the variety of characteristics of the reduced viscosity of aqueous suspensions of charged spherical particles has been an unsolved problem. To solve the problem, the reduced viscosity due to interparticle electrostatic interactions between charged spherical particles are calculated as a function of particle concentration with scanning various parameters, such as diameter of particle, number of charges per particle, and added‐salt concentration. The result successfully reproduced the variety of characteristics. Of all the scanned parameters, the diameter of the particle has a significant role to display the variety of characteristics when other parameters are fixed. When the diameter is very small (～0 Å), the calculated reduced viscosity of aqueous suspensions of charged spherical particles increases with decreasing particle concentration and it shows a maximum. This behavior is very similar to the reduced viscosity of linear chain polyelectrolyte solutions. Whereas, when the diameter is large (>2000 Å), the calculated reduced viscosity decreases with decreasing particle concentration and it does not show a maximum. When the diameter is <1000 Å, the calculated reduced viscosity shows both the maximum and minimum. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1068–1074, 2004     

Effect of associating polymer on the viscosity behavior of suspensions consisting of particles with different surface properties

Associating polymers which consist of water-soluble long-chain molecules containing a small fraction of hydrophobic groups (hydrophobes) behave as flocculants in aqueous suspensions. The effects of associating polymers on the rheological behavior are studied for single suspensions of particles with hydrophilic and hydrophobic surfaces, and their mixtures. For particles with hydrophilic surfaces, the suspensions are highly flocculated by a bridging mechanism, because the water-soluble chains adsorb onto hydrophilic surfaces. On the other hand, the particles with hydrophobic surfaces cannot be dispersed in water without polymer and the additions of a small amount of polymer are required for preparation of homogeneous suspensions. The associating polymer acts as a dispersant at low concentrations. However, further additions of polymer lead to a drastic increase in viscosity. Since the hydrophobes on one end of molecules adsorb onto hydrophobic surfaces and other hydrophobes tending from the particles can form micelles, the particles are connected by linkage of interchain associations. By mixing two suspensions of particles with hydrophilic and hydrophobic surfaces, the viscosity is substantially reduced and the flow becomes nearly Newtonian. The associating polymer in complex suspensions acts as a binder between the hydrophilic and hydrophobic surfaces. The hetero-flocculation which leads to the formation of composite particles may be responsible for the viscosity reduction of complex suspensions.     

Influence of dispersed CaCO<Subscript>3</Subscript> on the viscosity of montmorillonite suspensions containing NaCl

The plastic flow of concentrated polydisperse montmorillonite suspensions that contain sodium chloride and dispersed calcium carbonate and that are subjected to the action of atmospheric CO₂ is studied. It is shown that small amounts of calcium carbonate (0.05–0.5 wt%), as an impurity, and added sodium chloride can lead to significant variations in the structural organization of suspensions. Anomalous behavior of suspensions is observed at NaCl concentrations of 2–3 g/dm³. Mechanisms of structural transformation of concentrated clay suspensions are discussed. It is shown that the CaCO₃ transformation can proceed by the mechanisms of the Ostwald ripening or chemical recondensation depending on the interaction of a disperse silicate system with the ambient medium and on the presence of NaCl.     

The effect of the concentration of dispersed particles on the mechanisms of low-frequency dielectric dispersion (LFDD) in colloidal suspensions

There are two mechanisms which are currently used to explain the low-frequency (kHz range) dispersion of the dielectric permittivity of suspensions in electrolyte solutions (LFDD). The first, the surface diffusion mechanism (SDM), associates the LFDD with the diffusion of bound ions along the particle surface caused by the applied electric field. The second, the volume diffusion mechanism (VDM), follows from the generalization for alternating fields of the classical theory of the relaxation effect in electrophoresis and associates the LFDD with the diffusion of free ions in the diffuse double layer. It has been found that VDM is much more strongly dependent on particle concentration than SDM, opening new possibilities for the investigation of each of these two mechanisms separately. The reason is that when the concentration of particles in suspension increases, the characteristic length for the propagation of volume diffusion processes decreases together with the decrease of the free electrolyte volume, whereas the characteristic length for the surface diffusion remains constant. Correspondingly, when particle concentration is raised, the relaxation time of the VDM effect must decrease, whereas it must remain constant for the SDM mechanism. Thus, by varying the concentration of particles in suspension, one can separate the dispersion curves of SDM and VDM. A simple model is elaborated which can be useful to predict the volume fraction dependence of the parameters of LFDD; in particular, its amplitude and critical frequency. The results are compared with experimental data obtained with polymer latex dispersions of volume fractions ranging from 3 to 16%. It is found that the dielectric behaviour (the volume fraction dependence of both the amplitude and critical frequency of LFDD) of the dispersions is reasonably well explained with our model, thus demonstrating that VDM prevails in the systems studied. Experimental data previously found by other authors are also discussed in the light of the model presented.     

Electrocatalytic oxidation of formic acid on platinum particles dispersed in SWNT/PANI composite film

Single-walled carbon nanotube (SWNT)/Polyaniline (PANI) composite film with good dispersion was prepared by electropolymerization of aniline containing well-dissolved SWNTs. Platinum (Pt) particles were electrodeposited on the SWNT/PANI composite film subsequently. The presence of SWNTs and platinum in the composite film was confirmed by XRD analysis. Four-point probe investigation exhibits that the electrical conductivity of SWNT/PANI composite film is significantly higher than that of pure PANI film. Cyclic voltammogram and Chronoamperogram show that Pt-modified SWNT/PANI electrode performs higher electrocatalytic activity than Pt-modified pure PANI electrode toward formic acid oxidation.     

Thermal decomposition of ammonium perchlorate in the presence of bimetallic additives

The catalytic activity of the thermolysis products of double complex compounds in the decomposition reaction of ammonium perchlorate was studied. The products used are C_1.4N_1.6H₃CoFe (I), C₆N₈Co₄Fe₃ (II), O₁₁Co₄Fe₃ (III), O_8.5(CN)_0.3Cu₃Fe₂ (IV), and reactive CuO. All active phases decrease the temperature of complete decomposition of NH₄ClO₄, and the order of temperature decreasing is the following: I ≈ II (120 °C) > IV > III (80 °C) ? CuO.     

A facile synthesis of boron nanostructures and investigation of their catalytic activity for thermal decomposition of ammonium perchlorate particles

In this research, ultrasound irradiation as a simple method was used to produce boron nanostructures. Reaction conditions such as boron concentration and sonication time show important roles in the size, morphology and growth process of the final products. The boron nanostructures (nanoparticles and nanorods) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, small-angle X-ray scattering and inductively coupled plasma atomic emission spectroscopy techniques. Primary evaluation of results showed that nanoparticles and nanorods of boron successfully have been prepared with 25–40 and 50–100 nm average particle size, respectively. These nanostructures (nanoparticles and nanorods) were studied as an additive for promoting the thermal decomposition of ammonium perchlorate (AP) particles. Thermochemical decomposition behaviors of treated samples were characterized by thermal gravimetric analysis and differential scanning calorimetry techniques. Also, the kinetic parameters of thermal decomposition processes of pure and treated samples were obtained by nonisothermal methods proposed by Kissinger and Ozawa. However, boron nanoparticles with the smallest average particle size (25–40 nm) have the most significant catalytic effect including the decrease in decomposition temperature of AP + B nanocomposite by 100 °C, increase in the heat of decomposition from 580 to 1354 J g^?1 and decrease in activation energy from 207 to 110 kJ mol^?1.     

Aggregation in colloidal suspensions and its influence on the suspension viscosity

Influence of aggregate formation on rheological properties of concentrated suspensions is discussed and reviewed. Methods of Stokesian and Brownian dynamic simulations of aggregation are discussed and the results of simulations for both Brownian and non-Brownian particles are presented.     

Effect of catocene on the thermal decomposition of ammonium perchlorate and octogen

Simultaneous TG/DSC-FT-IR was employed to study the effect of catocene with a high concentration (5, 15, and 25 %) on the thermal decomposition of ammonium perchlorate (AP) and octogen (HMX) with different particle sizes. The experimental results show that catocene has effect on the thermal decomposition of AP and HMX, but the role that catocene playing changes with the concentration of catocene and the particle size of AP and HMX. High concentration of catocene (more than 15 %) benefits the decomposition of fine AP and HMX at low temperature, but has little effect on the decomposition of median and coarse AP. The thermal decomposition of HMX is affected by catocene mainly through increasing the heat release of the first decomposition step, while through both increasing the heat release and decreasing the decomposition temperature of the first decomposition step for the thermal decomposition of AP.     

Nonlinear viscoelasticity, percolation and particles dispersibility of PVA/aluminum hydroxide composite gels

We investigated the rheological properties of a composite gel consisting of poly(vinyl alcohol) and aluminum hydroxide particles, and discussed the relation among nonlinear viscoelasticity, percolation and particles dispersibility. The dynamic viscoelastic measurements revealed that the storage modulus at volume fractions ? < 0.04 satisfied with the Krieger-Dougherty equation representing random dispersion of particles. The storage modulus did not show any nonlinear viscoelastic response at ? < 0.04. However, the storage modulus at ? > 0.06 took a value which is far larger than that expected by the equation, indicating heterogeneous distribution of particles. Additionally, the nonlinear viscoelastic response was recognized clearly at ? > 0.06, suggesting a partial contact between particles. The storage modulus at ? > 0.18 showed a further increase satisfied with the percolation theory, therefore, the volume fraction is considered to be the percolation threshold of 3-dimension. Microscopic observations of the gel showed a clear network with a mesh size of few μm that is considered to be a partial network of particles.     

Self-assembled CuO nanoarchitectures and their catalytic activity in the thermal decomposition of ammonium perchlorate

CuO shuttle-like and flower-like nanocrystals were synthesized through a one-step, low-temperature solution-phase method in the presence of a cation surfactant, hexadecyl trimethyl ammonium bromide. These nanocrystals were studied as an additive for promoting the thermal decomposition of ammonium perchlorate (AP). With the addition of CuO shuttle-like and flower-like nanocrystals, the thermal decomposition temperature of AP decreased. The structure, particle size, and morphology of resulting CuO powders were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Thermogravimetric analysis technique was applied to investigate the thermal decomposition of mixtures of AP and as-prepared CuO nanocrystals.     

Effect of ammonia on the thermal decomposition of orthorhombic and cubic ammonium perchlorate

The inhibiting effect of ammonia vapours on the kinetics of the thermal decomposition of ammonium perchlorate(AP) in the temperature range 215–270°C has been investigated. An initial ammonia pressure of about 200 Torr is necessary for the practically full suppression of the decomposition of the orthorhombic crystals at temperatures close to the point of AP polymorphic transformation (240°C). With the cubic crystals, 0.5 Torr is the corresponding pressure required. In the case of complete inhibition of the decomposition in the presence of ammonia, AP crystals become yellowish. The activation energy of decomposition of the orthorhombic modification is 29 ± 0.6 kcal mole^?1 in the absence of ammonia, and 38 ± 1.1 kcal mole^?1 under ammonia vapour pressure of 6.5 Torr. A kinetic analysis of the traditional proton model of AP decomposition has been made showing that the increase of the activation energy in the presence of ammonia may be derived from this model.     

Preparations of polystyrene/aluminum hydroxide and polystyrene/alumina composite particles in an ionic liquid

Polystyrene (PS)/aluminum hydroxide (Al(OH)(3)) composite particles were successfully prepared by the sol-gel process of aluminum isopropoxide (Al(OPr(i))(3)) in a hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]) using ammonium hydroxide (NH(4)OH) as a catalyst in the presence of PS seed. Transmission electron microscopy observation of ultrathin cross-sections of the composite particles revealed that the composite particles had a core-shell morphology consisting of a PS core and a Al(OH)(3) shell having high crystallinity. The amount of secondary nucleated Al(OH)(3) could be reduced by dropwise addition of NH(4)OH. Moreover, PS/η-Al(2)O(3) composite particles were successfully prepared by heat treatment of PS/Al(OH)(3) at 300 °C in N(2) atmosphere, which is below the decomposition temperature of PS.     

On the fracture of composites based on ultrahigh-molecular-weight polyethylene and fine aluminum particles

Mechanical characteristics of polymerization filled composite materials based on ultrahigh-molecular-weight polyethylene and fine aluminum particles are studied. The prepared composites preserve their ability for high plastic deformations even when the volume filler content is φ = 0.57. For the tensile drawing of the composite material with randomly distributed particles, an equation describing the dependence of breaking stress on the volume filler content is derived. For the model of the composite with regularly ordered particles, the Nielsen equation is the approximation of the equation proposed in this work for a material with randomly distributed particles.     

The role of copper-chromium oxide catalysts in the thermal decomposition of ammonium perchlorate

The catalytic effects of doped or mixed CuO-Cr₂O₃ oxides on the thermal decomposition of ammonium perchlorate (AP) were investigated by using DTA, electrical conductivity and X-ray diffraction techniques. The results obtained revealed that the decrease in the defect electron of CuO catalyst doped with 1 at.% Cr³⁺ inhibited its activity, while the opposite effect was observed when Cr₂O₃ was doped with 1 at.% Cu²⁺. On increase of the concentrations of both oxides, the catalyst containing 70 at.% Cr³⁺ was found to be the most active during the decomposition of AP. The existence of CuCr₂O₄ at this ratio was demonstrated by X-ray diffraction. The activity of this spinel was explained on the basis of a hopping mechanism between Cr³⁺/Cr⁴⁺ active sites. Finally, the activation energies of different decomposition stages of AP alone and mixed with catalysts were calculated.

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Zusammenfassung Mittels DTA, Röntgendiffraktion und elektrischer LeitfÄhigkeit wurden die katalytischen Wirkungen von versetzten oder gemischten CuO-Cr₂O₃ Oxiden auf die thermische Zersetzung von Ammoniumperchlorat (AP) untersucht. Die erhaltenen Ergebnisse zeigen, da\ die Abnahme an Defektelektronen von CuO-Katalysator, versetzt mit 1 mol% Cr³⁺, seine AktivitÄt vermindern, wÄhrend ein entgegengesetzter Effekt bei Cr₂O₃ beobachtet wird, das mit 1 mol% Cu²⁺ versetzt ist.Durch Erhöhung der Konzentrationen beider Oxide zeigt der Katalysator bei der Zersetzung von AP die grö\te AktivitÄt bei einem Cr³⁺-Gehalt von 70 mol%. Mittels Röntgendiffraktion konnte bei dieser Zusammensetzung die Existenz von CuCr₂O₄ gezeigt werden. Die AktivitÄt dieser Spinellstruktur wurde durch einen Hüpfmechanismus zwischen Cr³⁺/Cr⁴⁺-aktiven Stellen erklÄrt. Weiterhin wurden die Aktivierungsenergien von verschiedenen Zersetzungsstufen von AP mit und ohne Katalysatoren berechnet.