Thermodynamic analysis of pure and impurity doped pentaerythritol tetranitrate crystals grown at room temperature

Pentaerythritol tetranitrate (PETN) powders are used to initiate other explosives. During long-term storage, changes in powder properties can cause changes in the initiation performance. Changes in the morphology and surface area of aging powders are observed due to sublimation and growth of PETN crystals through coarsening mechanisms, (e.g. Ostwald ripening, sintering, etc.). In order to alleviate the sublimation of PETN crystals under service conditions, stabilization methods such as thermal cycling and doping with certain impurities during or after the crystallization of PETN have been proposed. In this report we present our work on the effect of impurities on the morphology and activation energy of the PETN crystals. The pure and impurity doped crystals of PETN were grown from supersaturated acetone solution by solvent evaporation technique at room temperature. The difference in the morphology of the impurity-doped PETN crystal compared to pure crystal was examined by optical microscopy. The changes in the activation energies and the evaporation rates are determined by thermogravimetry (TG). Our activation energies of evaporation agree with earlier reported enthalpies of vaporization. The morphology and activation energy of PETN crystals doped with Ca, Na, and Fe cations are similar to that for pure PETN crystal, whereas the Zn-ion-doped PETN crystals have different morphology and decreased activation energy.     

Thermal analysis of Na2CO3 · H2O crystals

Monohydrated sodium carbonate crystals have been grown by slow evaporation of its aqueous solution maintained at 40 ± 1°C. The thermal dehydration of this crystal has been studied by dynamic and isothermal TG measurements. It is observed from dynamic TG that the single molecule of water of crystallization is lost in two steps of 0.3 mole and 0.7 mole at temperatures 426 ± 5 and 454 ± 5 K, respectively. From isothermal and dynamic TG measurements, the kinetic parameters E and Z are calculated using different known forms of the function F(). It is observed that consistency of E and Z values in isothermal and dynamic TG measurements for the two dehydration steps gives the correct function F() = −[log(1-)]^0.5. The activation energies for this function for the two dehydration steps are ≈6 and ≈9 kcal mole⁻¹, respectively.     

Investigation of thermal decomposition reactions by means of thermal analysis and dielectric constant measurement

Dielectric constant measurements as a function of temperature and thermal analysis were performed in copper sulphate pentahydrate and sodium nitrite to study the nature of the decomposition reactions. The application of these combined techniques to the study of several possible mechanisms of thermal decomposition is advanced.     

Structure and morphology of heavily deformed single crystals of a polydiacetylene. I. Electron microscopy and x-ray diffraction

The structure and morphology of heavily deformed single crystals of a diacetylene polymer have been studied using a combination of x-ray diffraction and electron microscopy. Crystals have been deformed by both rolling and hammering. The crystals remain intact during deformation and can be reduced in thickness by a factor of over 5 in directions perpendicular to their chain axes. It is found that the chain orientation is maintained during both hammering and rolling. A greenish-colored surface skin develops during both types of deformation but the structure of the interior of the crystals depends upon the type of deformation employed. The interior of the hammered crystals consists of crystal blocks ca. 50 μm thick formed by cleavage perpendicular to the chain direction whereas the rolled crystals tend to be fibrous with no evidence of molecular fracture. The possible deformation mechanisms which have given rise to the different structures have been discussed.     

Effect of solid dilutin on the crystal spectra of cobalt ammonium sulphate hexahydrate

Spectra of single crystals of cobalt ammonium sulphate hexahydrate diluted with magnesium ammonium sulphate hexahydrate have been studied as a function of dilution. It has been suggested that the solid dilution lowers the vibrational perturbation and changes the crystal field parameters.     

Shish-kebab structures of nylon-6 obtained from quiescent solutions by application of self-seeding

A study has been made of the morphology and structure of nylon-6 crystals grown from diluted 1,4-butanediol solution. Isothermal crystallization from homogeneous solution resulted in smooth ribbons or lath-shaped crystals aggregated into sheaves. Shish-kebab structures of nylon-6 could be grown from the quiescent solution by self-seeding techniques. Electron microscopic investigations and small-angle x-ray measurements showed that the molecules in the lath-shaped backbones of the shish kebab are folded and oriented perpendicular to the long axis of the crystals. The polyamide laths have the α-monoclinic crystal structure with the hydrogen bonds parallel to the long axis. It is suggested that due to the anisotropic type of bonding in the crystal lattice the crystals fragment laterally during the heating stage in the self-seeding technique. Structural defects, e.g., twinning sites introduced during the dissolution and subsequent crystallization may cause the growth of shish-kebab structures from quiescent solution.     

Pseudo-phase changes in cupric sulfate pentahydrate during dehydration

A study of the dehydration kinetics of a model system, cupric sulfate pentahydrate, was made using the temperature programmed desorption technique. The three decomposition steps from the pentahydrate to the anhydrous salt were clearly resolved into distinct spectral peaks even at sample heating rates in excess of 10 K. min^?1. A linear relationship between spectral peak temperature and square root of heating rate was observed for each dehydration step. The kinetic data revealed different activation enthalpies and entropies for each dehydration sequence for heating rates above and below approximately 8 K min^?1. These latter findings are interpreted in terms of crystalline to amorphous pseudo-phase changes in the solid hydrate during decomposition which become apparent only at fast sample heating rates. Enthalpy and entropy changes associated with these structural alterations are evaluated. The results also help to clarify earlier work on the dehydration mechanism in calcium phosphates.     

Thermal decomposition of copper(II) glutarate trihydrate. Part I. The mechanism of dehydration of copper(II) glutarate trihydrate

The mechanism of thermal dehydration of copper(II) glutarate trihydrate has been determined from the analysis of the kinetic data for isothermal and non-isothermal dehydration experiments. Microscopic investigations for the dehydration process of a single crystal of copper(II) glutarate trihydrate have been carried out to support the mechanism. The simultaneous DTG—DTA—TG curves of the salt are also described.     

SOLUTION CRYSTALLIZATION OF METALLOCENE SHORT CHAIN BRANCHED POLYETHYLENE:MORPHOLOGY AND MECHANISM*

Solution crystallization of metallocene short chain branched polyethylene (SCBPE) was carried out and very nicesingle crystals were obtained. Compared with single crystals grown from linear polyethylene, SCBPE single crystals are dirtydue to intermolecular heterogeneity The crystal morphology changes with crystallization temperatures. Lozenge, truncatedlozenge, hexagonal, rounded and elongated crystal morphologies have been found at much lower crystallization temperaturethan in linear polyethylene. The electron diffraction shows there is a possibility that the single crystals may have hexagonalpacking in a crystallization temperature range. The lateral habits of single crystal are discussed based on roughening theories.     

The effect of nitric acid (HNO3) on growth,spectral, thermal and dielectric properties of triglycine sulphate (TGS) crystal

The effect of nitric acid (HNO₃) addition on the growth of triglycine sulphate (TGS) crystal has been studied from the aqueous solution for various concentrations of nitric acid. Significant changes in the crystal size and morphology have been observed in all the grown samples. Single crystal and powder X-ray diffraction analyses confirm the structure and cell parameter values of pure and HNO₃ doped TGS crystals. FT-Raman and FTIR spectra confirm the characteristics absorption bands of pure and HNO₃ doped TGS crystals. The composition of TGS crystals have been confirmed by CHNS analysis. Physical properties such as thermal, dielectric and mechanical studies have been performed for the pure and HNO₃ doped TGS crystals. The dielectric constants of the crystals have been studied as a function of frequency. The results suggest that the HNO₃ is doped into TGS crystal and that the doping increases its dielectric constant.     

Tunable Mechanical Response from a Crystal Undergoing Topochemical Dimerization: Instant Explosion at a Faster Rate and Chemical Storage of a Harvestable Explosion at a Slower Rate

Strain developed in crystals in response to stimuli causes mechanical response. Methods to tune such mechanical response is important for practical applications. Crystals of a monomer having azide and alkyne units pre‐organized in a ready‐to‐react orientation, undergo thermal topochemical dimerization and show rate‐dependent mechanical response. When the reaction rate is fast, the crystals explode violently. When the reaction rate is slow, the crystals absorb water from the surroundings contemporaneously with the reaction to form the dimer‐hydrate in a single‐crystal‐to‐single‐crystal (SCSC) manner. Crystals of the dimer‐hydrate upon dehydration also undergo explosion. Thus, at slow reaction rate, the strain gets stored in crystals by hydration and the explosion can be harvested, at will, by dehydration. Use of this rate‐dependent explosion in the automatic activation of a remedial electrical circuit in case of a sudden rise in temperature has been demonstrated.     

Investigations of morphological changes during annealing of polyethylene single crystals

The morphological evolution of isolated individual single crystals deposited on solid substrates was investigated during annealing experiments using in situ and ex situ atomic force microscopy techniques. The crystal morphology changed during annealing at temperatures slightly above the original crystallization temperature of the crystals, far below their melting temperature. Evenly distributed cavities penetrated the crystals, and the number of cavities increased with a rising annealing temperature until the adjacent cavities coalesced. The thickness of the crystals increased during annealing at temperatures slightly above the crystallization temperature. Annealing experiments at fixed temperatures showed that the reorganization process (cavity formation and single‐crystal thickening) was fast. Depending on the annealing temperature, the final morphology was formed in seconds. This behavior suggests high chain mobility as well as a homogeneous solid‐state reorganization of the entire single crystal at low annealing temperatures. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 763–770, 2001     

How much is the accuracy of activation energy affected by ignoring thermal inertia?

This work estimates the magnitude of the effect of thermal inertia on the value of the activation energy determined from heat-flux differential scanning calorimetry (DSC) data. The estimates are obtained via analysis of the literature data on crystallization of copper and thermal degradation of isotactic polystyrene (iPS). The copper crystallization data have been obtained for very large masses (200 mg) and fast heating rates up to 80 K min⁻¹. The iPS degradation data have been collected on small masses (3 mg) and at the heating rates up to 20 K min⁻¹. For crystallization of copper, the Kissinger activation energy obtained from the DSC data corrected for thermal inertia is 34% larger than the value estimated from uncorrected data. This difference drops to 8% and becomes statistically insignificant when the fastest heating rate used is decreased to 10 K min⁻¹. For iPS degradation, the difference in the isoconversional activation energies estimated, respectively, from corrected and uncorrected DSC data is less than 3% and is not statistically significant. Overall, the effect of thermal inertia on the activation energy appears negligible provided that DSC measurements are conducted on smaller samples and at slower heating rates, that is, as advised by the International Confederation for Thermal Analysis and Calorimetry (ICTAC) recommendations. It is suggested that the difference in the activation energies should generally be within the typical 5-10% uncertainty as long as the product of the time constant and the maximum heating rate does not exceed 2-3 K.     

主链含间位联结的聚芳醚酮的形态结构

选取分子主链中含有间位结构的聚芳醚酮低聚物为研究对象,利用TEM技术,发现这类低聚物晶体中存在一种新的四角叶片状单晶,此单晶的四角对角线夹角为101.9°,与从晶胞参数计算所得的102.6°一致,从而直观地证明这类含间位结构聚芳醚酮的晶胞按(110)面生长,球晶按b轴方向生长.     

Influence of Operating Conditions on BaSO4 Crystal Size and Morphology in a Continuous Couette Precipitator

Precipitation of a sparingly soluble salt in the annular gap of a continuous Couette reactor with two unpremixed feeds has been experimentally investigated. Barium chloride and sodium sulphate in stoichiometric ratio are fed at different flow rate in the lower part of the reactor; different feeding modes have been considered. The dependence of precipitation yield, mean crystal size and particle size distribution on rotation speed, axial flow rate and initial supersaturation ratio has been studied. Depending on the operating conditions crystals with different morphologies have been obtained, varying from dentritic tabular crystals to complex pyramidal ones and from single crystals to aggregates. This revised version was published online in August 2006 with corrections to the Cover Date.     

Non-isothermal dehydration and decomposition of <Emphasis Type="Italic">dl</Emphasis>-lactates of transition metals and alkaline earth metals

A comparative study of the non-isothermal decomposition of the dl-lactate hydrates of magnesium, calcium and strontium has been made with that of the dl-lactate hydrates chromium(III), manganese(II), iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) keeping dry air as the purge gas and the heating rate maintained at 10 K min^-1. While the dl-lactates of manganese(II), cobalt(II) and copper(II) followed single step decomposition scheme suggesting that dehydration and decomposition steps overlapped, the dehydration steps of the other compounds were distinct. &agr;-T plots of none of the dehydration steps showed any induction period, indicating no physical desorption, nucleation or branching. Neither the &agr; _max-values nor the onset temperatures of the dehydration steps did show any pattern. The TG data of the dehydration steps have also been analyzed using the Freeman-Carroll, Horowitz-Metzger, Coats-Redfern, Zsak&oacute;, Fuoss-Salyer-Wilson and Karkhanavala-Dharwadkar methods. Values of order of reaction, activation energy and Arrhenius factor have been approximated and compared. There are similarities in the activation energy values for the dehydration steps (&lt; 60 kJ mol^-1 in general). It is higher with group 2 metals and lower in transition metals (maximum in magnesium and lowest in chromium and iron lactates). In cases of overlapping of dehydration and decomposition steps, the activation energy values are on the lower side with the same trend (lower in cobalt and copper cases).     

Improvement of ion chromatography with ultraviolet photometric detection and comparison with conductivity detection for the determination of serum cations

Studies were made of the analytical conditions required for indirect photometric ion chromatography using ultraviolet photometric detection (UV method) for the determination of serum cations following a previously developed serum pre-treatment. The sensitivities of the conductivity detection (CD) and UV methods and the amounts of serum cations determined by both methods were compared. Attempts to improve the sensitivity of the conventional UV method are reported. It was found that the mobile phase previously reported by Small and Miller showed no quantitative response when more than 4 mM copper(II) sulphate pentahydrate was used. As a result, there was no significant difference in the amounts of serum cations shown by the CD and UV methods. However, by adding 0.5-5 mM cobalt(II) sulphate heptahydrate, nickel(II) sulphate hexahydrate, zinc(II) sulphate heptahydrate or cobalt(II) diammonium sulphate hexahydrate to 0.5-1.5 mM copper(II) sulphate pentahydrate, higher sensitivity and a quantitative response were attained.     

二维网状结构超分子化合物[Cu(dafo)2(H2O)2](Cl04)2的两种同分异构体的合成与表征

用4，5—二氮芴-9-酮（dafo）、邻苯二甲酸、高氯酸铜和4，5—二氯芴—9— 酮(dafo)、苯甲酸、高氯酸铜进行混和反应时分别得到亮蓝色和蓝绿色晶体，它们 的结构通过单晶X射线衍射法测定。其单晶结构表明，这两种化合物是同分异构体 ，组成都是C22H16Cl2CuN4O12。这两种化合物是通过氢键形成的具有二维网状结构 的超分子化合物，并通过元素分析、红外光谱、热分析对两种化合物进行了表征。     

Effect of pulverization and dehydration on the pharmaceutical properties of calcium lactate pentahydrate tablets

The effects of heat conduction and pulverization on dehydration kinetics and tablet hardness were studied by a variety of kinetic equations and physical models. The dehydration behavior of unpulverized calcium lactate pentahydrate (UCLP) and pulverized calcium lactate pentahydrate (PCLP) tablets was investigated by using differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD). The hardness of both UCLP and PCLP tablets was significantly decreased after dehydration. The relationship between the extent of dehydration and the tablet hardness of both UCLP and PCLP tablets was linear. The results suggest that the reduction in tablet hardness is dependent on the dehydration of crystal water, and the values of the slopes indicate that the bonding energy of the UCLP was stronger than that of the PCLP. The dehydration of both UCLP and PCLP tablets at 55 °C followed a one-dimensional diffusion mechanism, whereas dehydration at storage temperatures of 60–80 °C followed a three-dimensional diffusion mechanism. UCLP and PCLP tablets contracted in thickness and diameter during dehydration, but final contraction ratios showed that PCLP tablets were more affected than UCLP tablets. In contrast, the micropore radius of both UCLP and PCLP tablets increased after dehydration. Thus, the pharmaceutical properties of calcium lactate pentahydrate (CLP) tablets are affected both by pulverization and by the extent of dehydration of the bulk powder in the tablet formulation.