Thermal decomposition of ethylene diamine diperchlorate

Thermal decomposition of ethylene diamine diperchlorate (EDDP) has been studied by differential-thermal analysis (DTA), thermogravimetric analysis (TGA), isothermal weight-loss measurements and mass-spectrometric analysis of the decomposition products. It has been observed that EDDP decomposes in two temperature regions. The low-temperature decomposition stops at about 35 to 40 percent weight loss below 250°C. The reason for the low-temperature cessation may be the adsorption of excess ethylene diamine on the crystal surface of EDDP. An overall activation energy of 54 kcal per mole has been calculated for the thermal decomposition of EDDP. Mass-spectrometric analysis shows that the decomposition products are mainly CO2, H2O, HCl and N2. The following stoichiometry has been proposed for the thermal decomposition of EDDP: (−CH2NH3CIO4)2→2CO2O+2HCl+N2

Large Eddy Simulation

Large eddy simulation (LES) is an emerging technique for obtaining an approximation to turbulent flow fields It is an improvement over the widely prevalent practice of obtaining means of turbulent flows when the flow has large scale, low frequency, unsteadiness An introduction to the method, its general formulation, and the more common modelling for flows without reaction, is discussed Some attempts at extension to flows with combustion have been made Examples from present work for flows with and without combustion are given The final example of the LES of the combustor of a helicopter engine illustrates the state-of-the-art in application of the technique

Synthesis, infrared spectra and thermoanalytical properties of transition metal sulfite hydrazine hydrates

Transition metal sulfite hydrazine hydrates, MSO3·xN2H4·yH2O whereM=Mn, Fe, Co, Ni and Zn have been prepared and characterized by chemical analysis, infrared spectra, thermoanalytical and combustion studies. The colours,x andy parameters of the complexes varied depending upon the preparation conditions. Thermal decomposition characteristics differ from metal to metal yielding metal oxides at relatively low temperatures.Mittels chemischer Analyse, IR-Spektren, thermoanalytischen und Verbrennungsstudien wurden die Hydrazinhydrate der hergestellten Übergangsmetallsulfite MSO3·xN2H4·yH2O mitM=Mn, Fe, Co, Ni und Zn beschrieben. Farbe sowie die Parameterx undy der Komplexe hängen von den Herstellungsbedingungen ab. Die thermische Zersetzung, bei der bei relativ niedrigen Temperaturen Metalloxide entstehen, ist von Metall zu Metall verschieden.

Solid State Electrochemical Sensors in Process Control

The basic principles of operation of gas sensors based on solid-state galvanic cells are described. The polarisation of the electrodes can be minimised by the use of point electrodes made of the solid electrolyte, the use of a reference system with chemical potential close to that of the sample system and the use of graded condensed phase reference electrodes. Factors affecting the speed of response of galvanic sensors in equilibrium and non-equilibrium gas mixtures are considered with reference to products of combustion of fossil fuels. An expression for the emf of non-isothermal galvanic sensors and the criterion for the design of temperature compensated reference electrodes for non-isothermal galvanic sensors are briefly outlined. Non-isothermal sensors are useful for the continuous monitoring of concentrations or chemical potentials in reactive systems at high temperatures. Sensors for oxygen, carbon, and alloying elements (Zn and Si) in liquid metals and alloys are discussed. The use of auxiliary electrodes permits the detection of chemical species in the gas phase which are not mobile in the solid electrolyte. Finally, the cause of common errors in galvanic measurements, and tests for correct functioning of galvanic sensors are given. 60 ref.--AA

Novel kinetic scheme for the ammonium perchlorate gas phase

A novel gas-phase kinetic scheme for ammonium perchlorate (AP) deflagration involving 22 reactions among 18 species is developed. The kinetic scheme is based on a study of the effect of initial conditions on the solution of the differential equations of adiabatic constant-pressure combustion kinetics. The existence of condensed-phase reaction products providesalternate pathways for the consumption of NH3 and HCIOl produced by gas-phase dissociation of AP. Theoretically obtained temperature-time profiles of the novel scheme do not change when the conventional reaction pathways are included, indicatingthat the novel scheme is a substantially faster rate process. The new scheme does not involve the species CIO, which has long been considered a critical component of the AP gas phase and which is included in the conventional reaction pathways.The new scheme develops faster overall reaction rates, steeper temperature-time profiles, and in a deflagration model will result in higher heat-transfer rates from gas phase to the condensed phase.

Synthesis and characterization of spherical and rod like nanocrystalline Nd2O3 phosphors

Spherical and rod like nanocrystalline Nd2O3 phosphors have been prepared by solution combustion and hydrothermal methods respectively The Powder X-ray diffraction (PXRD) results confirm that hexagonal A-type Nd2O3 has been obtained with calcination at 900 C for 3 h and the lattice parameters have been evaluated by Rietveld refinement Surface morphology of Nd2O3 phosphors show the formation of nanorods in hydrothermal synthesis whereas spherical particles in combustion method TEM results also confirm the same Raman studies show major peaks which are assigned to F-g and combination of A(g) + E-g modes The PL spectrum shows a series of emission bands at similar to 326-373 nm (UV) 421-485 nm (blue) 529-542 nm (green) and 622 nm (red) The UV blue green and red emission in the PL spectrum indicates that Nd2O3 nanocrystals are promising for high performance materials and white light emitting diodes (LEDs) (C) 2010 Elsevier B V All rights reserved

A thermodynamic protocol for explaining subcriticality and other subtle features in self-deflagrating solids

A novel universal approach to understand the self-deflagration in solids has been attempted by using basic thermodynamic equation of partial differentiation, where burning mte depends on the initial temperature and pressure of the system. Self-deflagrating solids are rare and are reported only in few compounds like ammonium perchlorate (AP), polystyrene peroxide and tetrazole. This approach has led us to understand the unique characteristics of AP, viz. the existence of low pressure deflagration limit (LPL 20 atm), hitherto not understood sufficiently. This analysis infers that the overall surface activation energy comprises of two components governed by the condensed phase and gas phase processes. The most attractive feature of the model is the identification of a new subcritical regime I' below LPL where AP does not burn. The model is aptly supported by the thermochemical computations and temperature-profile analyses of the combustion train. The thermodynamic model is further corroborated from the kinetic analysis of the high pressure (1-30 atm) DTA thermograms which affords distinct empirical decomposition rate laws in regimes I' and 1 (20-60 atm). Using Fourier-Kirchoff one dimensional heat transfer differential equation, the phase transition thickness and the melt-layer thickness have been computed which conform to the experimental data.

Low-temperature preparation and characterization of phase-pure lanthanide chromates (V) by the citrate gel process

Phase-pure, crystalline lanthanide chromates LnCrO4 (V), where Ln = La, Pr, Nd, Sm, Gd, Dy, Ho, Yb, Lu and Y, have been prepared by the controlled combustion of the corresponding lanthanide biscitrato chromium (III) complexes at comparatively low temperatures. Formation of chromates (V) was confirmed by X-ray diffraction, infrared and electronic spectroscopy. Phase purity of the materials has also been confirmed by X-ray photoelectron spectroscopy.

Synthesis, characterization and photoluminescence properties of CaSiO3: Eu3+ red phosphor

CaSiO3:Eu3+ (1-5 mol%) red emitting phosphors have been synthesized by a low-temperature solution combustion method. The phosphors have been well characterized by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and optical spectroscopy. PXRD patterns reveal monoclinic CaSiO3 phase can be obtained at 900 degrees C. The SEM micrographs show the crystallites with irregular shape, mostly angular. Upon 254 nm excitation, the phosphor show characteristic fluorescence D-5(0) -> F-7(J) (J = 0, 1, 2, 3, 4) of the Eu3+ ions. The electronic transition located at 614 nm corresponding to D-5(0) -> F-7(2) of Eu3+ ions, which is stronger than the magnetic dipole transition located at 593 nm corresponding to D-5(0) -> F-7(1) of Eu3+ ions. Different pathways involved in emission process have been studied. Concentration quenching has been observed for Eu3+ concentration >4 mol%. UV-visible absorption shows an intense band at 240 nm in undoped and 270 nm in Eu3+ doped CaSiO3 which is attributed to oxygen to silicon (O-Si) ligand-to-metal charge-transfer (LMCT) band in the SiO32- group. The optical energy band gap is widened with increase of Eu3+ ion dopant. (C) 2010 Elsevier B.V. All rights reserved.

Dye sensitized visible light degradation of phenolic compounds

The present research work reports the eosin Y (EY) and fluorescein (FL) sensitized visible light degradation of phenol, 4-chlorophenol (CP), 2,4-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP) using combustion synthesized nano-TiO2 (CS TiO2). The rate of degradation of the phenolic compounds was higher in the presence of EY/CS TiO2 compared to FL/CS TiO2 system. A detailed mechanism of sensitized degradation was proposed and a mechanistic model for the rate of degradation of the phenolic compound was derived using the pyramidal network reduction technique. It was found that at low initial dye concentrations, the rate of degradation of the phenolic compound is first order in the concentration of the dye, while at high initial dye concentrations, the rate is first order in the concentration of the phenolic compound. The order of degradation of the different phenolic compounds follows: CP > TCP > DCP > phenol. The different phenolic and dye intermediates that were formed during the degradation were identified by liquid chromatography-mass spectrometry (LC-MS) and the most probable pathway of degradation is proposed. (C) 2010 Elsevier B.V. All rights reserved.

Ce0.98Pd0.02O2-delta: Recyclable, ligand free palladium(II) catalyst for Heck reaction

Palladium substituted in cerium dioxide in the form of a solid solution, Ce-0.98 Pd-0.02 O-1.98 is a new heterogeneous catalyst which exhibits high activity and 100% trans-selectivity for the Heck reactions of aryl bromides including heteroaryls with olefins. The catalytic reactions work without any ligand. Nano-crystalline Ce-0.98 Pd-0.02 O-1.98 is prepared by solution combustion method and Pd is in +2 state. The catalyst can be separated, recovered and reused without significant loss in activity.

Photocatalytic Inactivation of Escherichia coli with LbL Fabricated Immobilized TiO2 Thin Films

Photocatalysis using semiconductor catalyst such as TiO2, in presence of UV light, is a promising technique for the inactivation of various microorganisms present in water. In the current study, the photocatalytic inactivation of Escherichia coli bacteria was studied with commercial Degussa Aeroxide TiO2 P25 (Aeroxide) and combustion synthesized TiO2 (CS TiO2) catalysts immobilized on glass slides in presence of UV irradiation. Thin films of the catalyst and polyelectrolytes, poly(allyl amine hydrochloride) and poly(styrene sulfonate sodium salt), were deposited on glass slides by layer by layer (LbL) deposition method and characterized by SEM and AFM imaging. The effect of various parameters, namely, catalyst concentration, surface area and number of bilayers, on inactivation was studied. Maximum inactivation of 8-log reduction in the viable count was observed with 1.227 mg/cm(2) of catalyst loaded slides. With this loading, complete inactivation was observed within 90 min and 75 min of irradiation, for Aeroxide and CS TiO2, respectively. Further increase in the catalyst concentration or increasing number of bilayers had no significant effect on inactivation. The effect of surface area on the inactivation was studied by increasing the number of slides and the inactivation was observed to increase with increasing surface area. It was also observed that the immobilized catalyst slides can be used for several cycles leading to an economic process. The study shows potential application of TiO2, for the inactivation of bacteria, in its fixed form by a simple immobilization technique.

Stretch effects extracted from inwardly and outwardly propagating spherical premixed flames

Unsteady propagation of spherical flames, both inward and outward, are studied numerically extensively for single-step reaction and for different Lewis numbers of fuel/oxidizer. The dependence of flame speed ratio (s) and flame temperature ratio are obtained for a range of Lewis numbers and stretch (kappa) values. These results of s versus kappa show that the asymptotic theory by Frankel and Sivashinsky is reasonable for outward propagation. Other theories are unsatisfactory both quantitatively and qualitatively. The stretch effects are much higher for negative stretch than for positive stretch, as also seen in the theory of Frankel and Sivashinsky. The linearity of the flame speed ratio vs stretch relationship is restricted to nondimensional stretch of +/-0.1. It is shown further that the results from cylindrical flames are identical to the spherical flame on flame speed ratio versus nondimensional stretch plot thus confirming the generality of the concept of stretch. The comparison of the variation of (ds/dkappa)kappa=0 with beta(Lc - 1) show an offset between the computed and the asymptotic results of Matalon and Matkowsky. The departure of negative stretch results from this variation is significant. Several earlier experimental results are analysed and set out in the form of s versus kappa plot. Comparison of the results with experiments seem reasonable for negative stretch. The results for positive stretch are satisfactory qualitatively for a few cases. For rich propane-air, there are qualitative differences pointing to the need for full chemistry calculations in the extraction of stretch effects.

Stretch effects extracted from propagating spherical premixed flames with detailed chemistry

This paper is concerned with extracting stretch effects from outward propagating spherical flames with full chemistry. It is a continuation of a recently published study from this laboratory where it is shown that single-step chemistry is insufficient to explain the experimental results on methane, propane and hydrogen-air systems. Comparisons of the present full chemistry calculations with the experimental results for several fuel/air systems are good/excellent, with the exception of rich propane-air for which it is argued that soot chemistry with attendant radiation loss need to be invoked. The reversal in trends of stretch effects due to change in pressure, initial temperature and N-2 dilution (observed in experiments) can be predicted well by full chemistry but not with simple single-step chemistry. Analysis of the results shows the important role played by many intermediate species and explains why full chemistry is needed to predict stretch effects.