A Thermodynamic Proposal for the Exposition of Critically and other Subtle Features in Self-Deflagrating Ammonium Perchlorate Systems

A first comprehensive investigation on the deflagration of ammonium perchlorate (AP) in the subcritical regime, below the low pressure deflagration limit (LPL, 2.03 MPa) christened as regime I$^{\prime}$, is discussed by using an elegant thermodynamic approach. In this regime, deflagration was effected by augmenting the initial temperature (T$_{0}$) of the AP strand and by adding fuels like aliphatic dicarboxylic acids or polymers like carboxy terminated polybutadiene (CTPB). From this thermodynamic model, considering the dependence of burning rate ($\dot{r}$) on pressure (P) and T$_{0}$, the true condensed (E$_{\text{s,c}}$) and gas phase (E$_{\text{s,g}}$) activation energies, just below and above the surface respectively, have been obtained and the data clearly distinguishes the deflagration mechanisms in regime I$^{\prime}$ and I (2.03-6.08 MPa). Substantial reduction in the E$_{\text{s,c}}$ of regime I$^{\prime}$, compared to that of regime I, is attributed to HClO$_{4}$ catalysed decomposition of AP. HClO$_{4}$ formation, which occurs only in regime I$^{\prime}$, promotes dent formation on the surface as revealed by the reflectance photomicrographs, in contrast to the smooth surface in regime I. The HClO$_{4}$ vapours, in regime I$^{\prime}$, also catalyse the gas phase reactions and thus bring down the E$_{\text{s,g}}$ too. The excess heat transferred on to the surface from the gas phase is used to melt AP and hence E$_{\text{s,c}}$, in regime I, corresponds to the melt AP decomposition. It is consistent with the similar variation observed for both the melt layer thickness and $\dot{r}$ as a function of P. Thermochemical calculations of the surface heat release support the thermodynamic model and reveal that the AP sublimation reduces the required critical exothermicity of 1108.8 kJ kg$^{-1}$ at the surface. It accounts for the AP not sustaining combustion in the subcritical regime I$^{\prime}$. Further support for the model comes from the temperature-time profiles of the combustion train of AP. The gas and condensed phase enthalpies, derived from the profile, give excellent agreement with those computed thermochemically. The $\sigma _{\text{p}}$ expressions derived from this model establish the mechanistic distinction of regime I$^{\prime}$ and I and thus lend support to the thermodynamic model. On comparing the deflagration of strand against powder AP, the proposed thermodynamic model correctly predicts that the total enthalpy of the condensed and gas phases remains unaltered. However, 16% of AP particles undergo buoyant lifting into the gas phase in the `free board region' (FBR) and this renders the demarcation of the true surface difficult. It is found that T$_{\text{s}}$ lies in the FBR and due to this, in regime I$^{\prime}$, the E$_{\text{s,c}}$ of powder AP matches with the E$_{\text{s,g}}$ of the pellet. The model was extended to AP/dicarboxylic acids and AP/CTPB mixture. The condensed ($\Delta $H$_{1}$) and gas phase ($\Delta $H$_{2}$) enthalpies were obtained from the temperature profile analyses which fit well with those computed thermochemically. The $\Delta $H$_{1}$ of the AP/succinic acid mixture was found just at the threshold of sustaining combustion. Indeed the lower homologue malonic acid, as predicted, does not sustain combustion. In vaporizable fuels like sebacic acid the E$_{\text{s,c}}$ in regime I$^{\prime}$, understandably, conforms to the AP decomposition. However, the E$_{\text{s,c}}$ in AP/CTPB system corresponds to the softening of the polymer which covers AP particles to promote extensive condensed phase reactions. The proposed thermodynamic model also satisfactorily explains certain unique features like intermittent, plateau and flameless combustion in AP/ polymeric fuel systems.

Phase relations and thermodynamic properties of condensed phases in the system calcium-copper-oxygen

The isothermal sections of the phase diagram for the system Ca-Cu-0 at 1073 and 1223 K have been determined. Several compositions in the ternary system were quenched after equilibration, and the phases present were identified by optical microscopy, X-ray diffraction, and electron probe microanalysis. Two ternary compounds Ca2CuO3 and Cao.8&uO1.9s were identified at 1073 K. However, only Ca2CuO3 was found to be stable at 1223 K. The thermodynamic properties of the two ternary compounds were determined using solid-state cells incorporating either an oxide or a fluoride solid electrolyte. The results for both types of cells were internally consistent. The compound C ~ O . ~ & U Ow~h.i~ch~ c, a n also be represented as Ca15Cu18035h, as been identified in an earlier investigation as Cao.828CuOz. Using a novel variation of the galvanic cell technique, in which the emf of a cell incorporating a fluoride electrolyte is measured as a function of the oxygen potential of the gas phase in equilibrium with the condensed phase electrodes, it has been confirmed that the compound Cao.828CuO1.93 (Ca15Cu18035d) oes not have significant oxygen nonstoichiometry. Phase relations have been deduced from the thermodynamic data as a function of the partial pressure of oxygen for the system Ca-Cu-0 at 873, 1073, and 1223 K.

From Molecular to Supramolecular: An Exploration into the Modes of Self-assembly in Conformationally Locked Polycyclitols

This brief account highlights the notable findings of our investigation into the supramolecular chemistry of conformationally locked polycyclitols in the solid state. The study was aimed at analyzing the crystal packing and unraveling the modalities of non-covalent interactions (particularly, intramolecular vis-a-vis intermolecular OH center dot center dot center dot O hydrogen bonds) in polyols. The know-how obtained thereof, was successfully utilized to engineer self-assemblies of designer polycyclitols, having hydrogen bond donors and acceptors fettered onto a trans-decalin scaffold. The results seek to draw particular attention to the intrinsic attribute of this rigid carbocyclic framework to lock functional groups into spatially invariant positions and bring potential intramolecular hydrogen bonding partners into favorable interaction geometry to engender predictability in the self-assembly patterns.

Influence of clofibrate administration on the rate of synthesis of macromolecules in regenerating rat liver

Administration of the antihypercholesterolaemic drug clofibrate stimulates the rates of synthesis of nucleic acids and proteins in rat liver. The biosynthesis of mitochondrial proteins also is enhanced by the drug. In drug-fed animals, the rates of incorporation in vivo of radioactive precursors into DNA, RNA and proteins are stimulated even when the liver undergoes regeneration following partial hepatectomy. The rate of synthesis of mitochondrial proteins in the regenerative phase is higher in clofibrate-fed animals. These effects are consistent with the hepatomegalic and mitochondria-proliferating property of the drug.

Evolution of crystallographic texture and microstructure in the orthorhombic phase of a two-phase alloy Ti-22Al-25Nb

Evolution of crystallographic texture in the orthorhombic phase of a two-phase alloy Ti–22Al–25Nb (at%), consisting of orthorhombic (O) and bcc (β/B2) phases, was studied. The material was subjected to deformation in two-phase field as well as in the single β phase field. The resulting evolution of microstructure and crystallographic texture were recorded using scanning electron microscopy and X-ray diffraction. The orthorhombic phase underwent change in morphology (from platelets to equiaxed) on rolling in the two-phase field with the texture getting sharper with the amount of deformation. Rolling above β transus temperature led to hot deformation of single β phase microstructure and its subsequent cooling produced transformed coarse platelets of orthorhombic phase with texture in orientation relation with the high temperature deformed β phase.

Origin of the activation barrier in the process of hydrogen abstraction: the perturbation treatment

The perturbation treatment previously given is extended to explain the process of hydrogen abstraction from the various hydrogen donor molecules by the triplet nπ* state of ketones or the ground state of the alkyl or alkoxy radical. The results suggest that, as the ionization energy of the donor bonds is decreased, the reaction is accelerated and it is not influenced by the bond strength of the donor bonds. The activation barrier in such reactions arises from a weakening of the charge resonance term as the ionization energy of the donor bond increases.

Origin of the activation barrier in the process of hydrogen abstraction: the perturbation treatment

The perturbation treatment previously given is extended to explain the process of hydrogen abstraction from the various hydrogen donor molecules by the triplet nπ* state of ketones or the ground state of the alkyl or alkoxy radical. The results suggest that, as the ionization energy of the donor bonds is decreased, the reaction is accelerated and it is not influenced by the bond strength of the donor bonds. The activation barrier in such reactions arises from a weakening of the charge resonance term as the ionization energy of the donor bond increases.

Studies On Hydrogen Bonds: Part IV. Proposed Working Criteria for Assessing Qualitative Strength of Hydrogen Bonds

The data obtained in the earlier parts of this series for the donor and acceptor end parameters of N-H. O and O-H. O hydrogen bonds have been utilised to obtain a qualitative working criterion to classify the hydrogen bonds into three categories: "very good" (VG), "moderately good" (MG) and weak (W). The general distribution curves for all the four parameters are found to be nearly of the Gaussian type. Assuming that the VG hydrogen bonds lie between 0 and ± la, MG hydrogen bonds between ± 1 and ± 2, W hydrogen bonds beyond ± 2 (where is the standard deviation), suitable cut-off limits for classifying the hydrogen bonds in the three categories have been derived. These limits are used to get VG and MG ranges for the four parameters 1 and θ (at the donor end) and ± and ± (at the acceptor end). The qualitative strength of a hydrogen bond is decided by the cumulative application of the criteria to all the four parameters. The criterion has been further applied to some practical examples in conformational studies such as α-helix and can be used for obtaining suitable location of hydrogen atoms to form good hydrogen bonds. An empirical approach to the energy of hydrogen bonds in the three categories has also been presented.

Kinetics of oxidation of pseudocumene in the vapor phase

The kinetics of pseudocumene oxidation in the vapor phase with tin vanadate as catalyst have been studied over the following ranges of the variables: Oxygen concentration, 0.909 to 2.857 mole/m3; pseudocumene concentration, 0.071 to 0.125 mole/m3; temperature, 260 to 320°C; space time, 22.5 to 90 × 104 g. catalyst/mole sec. Oxidation-reduction models have been found to describe the kinetics adequately. The mechanism is found to remain the same throughout the temperature range covered.

Studies on hydrogen-bonds .4. proposed working criteria for assessing qualitative strength of hydrogen-bonds

The data obtained in the earlier parts of this series for the donor and acceptor end parameters of N-H. O and O-H. O hydrogen bonds have been utilised to obtain a qualitative working criterion to classify the hydrogen bonds into three categories: “very good” (VG), “moderately good” (MG) and weak (W). The general distribution curves for all the four parameters are found to be nearly of the Gaussian type. Assuming that the VG hydrogen bonds lie between 0 and ± la, MG hydrogen bonds between ± 1s̀ and ± 2s̀, W hydrogen bonds beyond ± 2s̀ (where s̀ is the standard deviation), suitable cut-off limits for classifying the hydrogen bonds in the three categories have been derived. These limits are used to get VG and MG ranges for the four parameters 1 and θ (at the donor end) and ± and ± (at the acceptor end). The qualitative strength of a hydrogen bond is decided by the cumulative application of the criteria to all the four parameters. The criterion has been further applied to some practical examples in conformational studies such as α-helix and can be used for obtaining suitable location of hydrogen atoms to form good hydrogen bonds. An empirical approach to the energy of hydrogen bonds in the three categories has also been presented.

ENDOR studies of hydrogen bonding of the AsO44- centre in x-ray irradiated KH2AsO4

We here report what we believe to be an important method for studying hydrogen bonding in systems containing a paramagnetic centre. The technique of electron-nuclear double resonance ( ENDOR) has been applied to study the hydrogen-bond network around the AsO44-. centre in X-ray irradiated KH2AsO4. ENDOR transitions from several sets of hydrogen nuclei surrounding the centre were observed at 4.2 degrees K and the spectra for two sets of neighbouring nuclei are identified. The angular dependences for these spectra are fitted with a spin-Hamiltonian to obtain the isotropic and anisotropic magnetic hyperfine constants. The results are discussed in terms of the available spectroscopic and crystallographic data on KH2AsO4 and the order-disorder model of ferroelectrictricity in this class of crystals.

Quantum chemical study on influence of intermolecular hydrogen bonding on the geometry, the atomic charges and the vibrational dynamics of 2,6-dichlorobenzonitrile

FT-IR (4000-400 cm(-1)) and FT-Raman (4000-200 cm(-1)) spectral measurements on solid 2,6-dichlorobenzonitrile (2,6-DCBN) have been done. The molecular geometry, harmonic vibrational frequencies and bonding features in the ground state have been calculated by density functional theory at the B3LYP/6-311++G (d,p) level. A comparison between the calculated and the experimental results covering the molecular structure has been made. The assignments of the fundamental vibrational modes have been done on the basis of the potential energy distribution (PED). To investigate the influence of intermolecular hydrogen bonding on the geometry, the charge distribution and the vibrational spectrum of 2,6-DCBN; calculations have been done for the monomer as well as the tetramer. The intermolecular interaction energies corrected for basis set superposition error (BSSE) have been calculated using counterpoise method. Based on these results, the correlations between the vibrational modes and the structure of the tetramer have been discussed. Molecular electrostatic potential (MEP) contour map has been plotted in order to predict how different geometries could interact. The Natural Bond Orbital (NBO) analysis has been done for the chemical interpretation of hyperconjugative interactions and electron density transfer between occupied (bonding or lone pair) orbitals to unoccupied (antibonding or Rydberg) orbitals. UV spectrum was measured in methanol solution. The energies and oscillator strengths were calculated by Time Dependent Density Functional Theory (TD-DFT) and matched to the experimental findings. TD-DFT method has also been used for theoretically studying the hydrogen bonding dynamics by monitoring the spectral shifts of some characteristic vibrational modes involved in the formation of hydrogen bonds in the ground and the first excited state. The C-13 nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the Gauge independent atomic orbital (GIAO) method and compared with experimental results. Standard thermodynamic functions have been obtained and changes in thermodynamic properties on going from monomer to tetramer have been presented. (C) 2013 Elsevier B.V. All rights reserved.

Role of water contamination within the GC column of a GasBench II peripheral on the reproducibility of O-18/O-16 ratios in water samples

The GasBench II peripheral along with MAT 253 combination provides a more sensitive platform for the determination of water isotope ratios. Here, we examined the role of adsorbed moisture within the gas chromatography (GC) column of the GasBench II on measurement uncertainties. The uncertainty in O-18/O-16 ratio measurements is determined by several factors, including the presence of water in the GC. The contamination of GC with water originating from samples as water vapour over a longer timeframe is a critical factor in determining the reproducibility of O-18/O-16 ratios in water samples. The shift in isotope ratios observed in the experiment under dry and wet conditions correlates strongly with the retention time of analyte CO2, indicating the effect of accumulated moisture. Two possible methods to circumvent or minimise the effect of adsorbed water on isotope ratios are presented here. The proposed methodology includes either the regular baking of the GC column at a higher temperature (120 degrees C) after analysis of a batch of 32 sample entries or conducting the experiment at a low GC column temperature (22.5 degrees C). The effects of water contamination on long-term reproducibility of reference water, with and without baking protocol, have been described.

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

A galvanic sensor for SO3/SO2 based on CaF2/CaSO4 couple

Measurements on the solid state cell, View the MathML source using single crystal CaF2 as the solid electrolyte and CaSO4 as an auxiliary electrode, indicate that the EMF is in agreement with that predicted by the Nernst equation when equilibrium is assumed in the gas phase near the electrodes. The cell can be used to measure the View the MathML source content of gases at temperatures near 1200 K, where approximately 2 h ate required to obtain a steady EMF, without the use of catalysts to improve the kinetics of exchange reaction in the auxiliary electrode. For most applications, the cell EMF will be affected by the presence of water vapour in the gas phase. The cell is well suited for thermodynamic measurements on sulfates, pyrosulfates and their solid and liquid solutions.