Adiabatic thermokinetics and process safety of pyrotechnic mixtures

Pyrotechnic mixtures are susceptible to explosive decompositions. The aim of this paper is to generate thermal decomposition data under adiabatic conditions for fireworks mixtures containing potassium nitrate, barium nitrate, sulfur, and aluminum which are manufactured on a commercial scale. Differential scanning calorimeter is used for screening tests and accelerating rate calorimeter is used for other studies. The self heat rate data obtained showed onset temperature in the range of 275?C295?°C for the fireworks atom bomb, Chinese cracker and palm leaf cracker. Of the three mixtures studied, atom bomb mixture had an early onset at 275?°C. The mixtures in general showed vigor exothermic decompositions. Palm leaf mixture exhibits multiple exotherm and reached a final temperature of 414?°C. The thermal decomposition contributes to substantial rise in system pressure. The heats of exothermic decomposition and Arrhenius kinetics were computed. The kinetic data are validated by comparing the predicted self heat rates with the experimental data.     

Use of thermomagnetometry in the study of iron-containing pyrotechnic systems

Thermal analysis is routinely used to characterize pyrotechnic fuels, oxidants and fuel/oxidant mixtures [1]. Thermomagnetometry (TM) can provide additional information if the magnetic properties of the materials change during reaction. TG, TM and DTA results for the iron/potassium permanganate, iron/barium peroxide, and iron/strontium peroxide systems as loose powders or pressed pellets indicate predominantly solid-gas mechanisms for reactions in these systems.     

高效液相色谱法测定烟火药剂中的没食子酸

建立了烟火药剂中没食子酸的高效液相色谱检测方法。采用ZorbaxEclipse XDB-C18色谱柱(4.6×150 mm)分离,以甲醇-0.1%冰乙酸水溶液为流动相,梯度洗脱,流速1.0 mL/min;测定温度为25℃;采用紫外检测器检测,检测波长为274 nm。没食子酸的质量浓度在0.5~20μg/mL时与色谱峰面积之间线性关系良好(相关系数r=0.9999);对烟火药剂样品进行3个不同浓度水平的添加回收,回收率为90.8%~100.2%,相对标准偏差(RSD)为1.2%~6.4%。     

Thermoanalytical investigation of relative reactivity of some nitrate oxidants in tin-fueled pyrotechnic systems

In order to investigate relative reactivity of different oxidants in solid-state reactions of pyrotechnic mixtures, thermal properties of Sn + Sr(NO₃)₂, Sn + Ba(NO₃)₂, and Sn + KNO₃ pyrotechnic systems have been studied by means of TG, DTA, and DSC methods and the results compared with those of pure oxidants. The apparent activation energy (E), ΔG ^#, ΔH ^#, and ΔS ^# of the combustion processes were obtained from the DSC experiments. The results showed that the nature of oxidant has a significant effect on ignition temperature, and the kinetic of the pyrotechnic mixtures’ reactions, and the relative reactivity of these mixtures was found to obey in the following order: Sn + Sr(NO₃)₂ > Sn + Ba(NO₃)₂ > Sn + KNO₃.     

Primary photoprocesses in molecules of carbocyanine dyes in binary solvent mixtures

The effect of the composition of the dimethyl sulfoxide (DMSO)-toluene mixture on the photophysical processes of thia-, indo-, and imidacarbocyanine dyes was studied. In the mixtures with the DMSO content of more than 20 vol %, the dyes representing solvated cations are characterized by high efficiency of trans → cis photoisomerization and fluorescence, in contrast to the extremely low efficiency of intersystem crossing to the triplet state. With growing the toluene content in the mixture, ion pairs between the dye cation and Cl⁻, Br⁻, I⁻, or BF⁴⁻ anion are formed. In the cases when the dye counterions are Br⁻ or I⁻, a sharp increase in the yield of the triplet molecules and a decrease in their lifetime take place. The results are discussed in terms of “the external heavy atom effect” in ion pairs.     

Cyanine dyes from seven-membered heterocyclic systems

The condensation of o-aminothiophenol with tetrahydroacetophenone, 2-ethylidenecyclohexanone, and 2-benzylidenecyclohexanone and also the condensation of N-methyl-o-aminothiophenol with 2-benzylidenecyclohexanone has given the bases of derivatives of benzo[b]cyclohexano[f]- and -[e]-1,4-thiazepines. From the hydrochlorides, perchlorates, and quaternary salts of these bases, cyanine dyes have been synthesized. The dyes—norcyanines—exhibit solvatochromism, which is explained by the existence of a hydrogen bond between the molecules of the dye and an alcohol.For part IV, see [3].     

Hierarchical MoS2/polyaniline binary hybrids with high performance for improving fire safety of epoxy resin

Here we report a facile strategy to fabricate phosphoric acid doped polyaniline/molybdenum disulfide (PANI/MoS₂) hybrids as high-performance nanofillers in epoxy (EP) resin for the first time. In situ growth of PANI on the surface of two-dimensional MoS₂ template resulted in the uniform dispersion and strong interfacial adhesion of PANI/MoS₂ hybrids within EP matrix, which can be confirmed by the obvious increase (13.5°C) in glass transition temperature (T_g) of EP composites. The MoS₂ nanosheets also acted as a critical component to generate synergistic effect with PANI on reducing the fire hazards of EP resin. It resulted in a remarkable removal of flammable decomposed products and a considerable reduction of toxic CO yield. The dramatical decreases in real-time smoke density and total smoke production, and high-graphitized char layer in condensed phase were obtained for EP composite with 5 wt% PANI/MoS₂ hybrids. The multiple synergistic effects (synergistic dispersion and synergistic char formation) are believed to be the primary source for these obvious enhancements of properties of EP composites. This facile strategy may achieve the potential application of functionalized MoS₂ in polymeric nanocomposites.     

Interaction in binary fluoride systems

A series of factors affecting the interaction between fluorides is considered. Fluorides are distributed by valence and are arranged in accordance with an increase in the polarizing effect of cations. For eutectic-type melting diagrams, deviations of the experimental liquidus from the ideal one calculated by the Schröder equation are analyzed. In many systems of this type, complex formation is noted in the melts. The most informative factors determining the type of melting diagrams of fluoride systems are refined. Interrelation of various types of melting diagrams is considered.     

Reactions in binary iodide systems

Several factors that influence the interactions between iodides are considered based on the results of thermoanalytical experiments. The iodides are grouped according to the cation valence and are arranged in the increasing order of the cation polarizing powers (CPPs). The deviations of the liquidus in real eutectic iodide systems from an ideal liquidus are analyzed. Compound formation in melts, incomplete solid solubility, or immiscibility are observed in many systems. The structure of the melting-point diagram is found to correlate with the type of interaction in the system.     

Thermogravimetric examination of polyalcohol-formate binary systems

Mixtures of trimethylolpropane (TMP) or pentaerythritol (PER) with sodium or calcium formate (SF or CF) were investigated all over their composition range. Complete additivity was found to occur in the case of the TMP-SF and TMP-CF systems which renders it possible to determine the contents of both TMP and the given formate from in-dependent signals of weight loss over the entire range of quantitative composition of the mixtures under investigation. Additivity was found not to occur in the PER-SF system in the entire range of quantitative composition; SF content could only be determined from the ash weight. In the PER-CF system, additivity was absent at some signals; CF content could be determined in the full range from three independent signals, PER could be determined independently only at its content up to 50% by weight.     

Fluorometric study of solvation characteristics of ketocyanine dyes in mixed binary solvents

The fluorescence characteristics of two ketocyanine dyes have been studied in six mixed binary solvents. Several parameters such as the maximum energy E₁₂(F) of fluorescence, the quantum yield Φ₁₂ of fluorescence and the normalized intensity of the fluorescence have been investigated as functions of solvent composition. In protic+aprotic binary mixtures a dramatic change at the aprotic end has been observed. The results point to a preferential solvation of the solute by the protic component.     

Co-precipitation in some binary sulphate systems

Studies have been made of the distribution behaviour of tracers with alkaline earth sulphates, using the technique of precipitation from homogeneous solution. The co-precipitation of strontium with barium sulphate and of lead, lanthanum, and yttrium, separately, with barium sulphate, and with strontium sulphate, were investigated. Although there was qualitative correlation between the observed values of the distribution coefficient and the theoretical solubility product ratios for each of the binary systems studied, the divergence between theory and observation was so great that it seems unlikely that there is any quantitative correlation.     

Solid-state microcalorimetry on drug-cyclodextrin binary systems

Differential scanning calorimetry DSC has been applied to the analysis of drugcyclodextrin binary systems in order to gain experimental evidence of the interaction and determine the stoichiometry of the inclusion compound. Two model systems, paracetamolbetacyclodextrin and vinburnineg-ammacyclodextrin were tested through the comparison of thermal behaviors of interacted and non-interacted mixtures containing excess drug. DSC allowed a confirmation of both interaction and stoichiometry of the inclusion compounds.The authors wish to thank Prof. Amedeo Marini for helpful discussion and criticism.     

Thermoanalytical behavior of boric acid-polyoxaalkanol binary systems

Binary mixtures of orthoboric acid with selected ethoxylated derivatives of methanol, ethanol or butanol (polyoxaalkanols) were investigated thermoanalytically. Both TG and DSC measurements indicated a three-step reaction course in general, which was explained by the evaporation in turn of esterification water, polyoxaalkanol and ester. A relationship was established between the TG-determined and the assumed ester content.     

Study of the preferential solvation of some betaine dyes in binary solvent mixtures

The preferential solvation (PS) in mixed binary solvents, e.g. dichloromethane/acetonitrile, dichloromethane/methanol, acetonitrile/water has been studied by monitoring the charge transfer band of some betaine dyes. Since PS accounts for dielectric as well as specific interactions while dielectric enrichment only for the former, it was shown that in the case of dichloromethane/methanol, hydrogen bonding precedes dielectric enrichment whereas in the case of acetonitrile/water the inverse is true.     

Enhanced intra-aggregate charge separation from binary excitons in mixed J-aggregates of cyanine dyes

Well-ordered, two-dimensional, amalgamation-type J-aggregates consisting of two different kinds of structurally analogous anionic cyanine dyes were self-assembled on an amino-functionalized Au(111) electrode surface. Similar binary J-aggregates, though considerably less ordered in either one- or three-dimensional structure, could also be grown easily in a concentrated ( approximately 1.5 M) aqueous solution of NaCl. These binary J-aggregates are characterized by a singly peaked J-band associated with a unique molecular exciton shared by the two different dye components coherently. This cooperative binary excitonic state can live with substantial (more than 0.1 eV) energy gaps between the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) levels of the two dyes mixed together. These energy gaps allow the binary exciton to relax very rapidly to an intra-aggregate charge-separated state in good competition with the metal-induced quenching of the excited-state energy. The enhanced charge separation leads to a high-efficiency photocurrent generation with a simple binary J-aggregate-coated Au(111) electrode in a reversible redox solution and results in strong quenching of the fluorescence from the corresponding aggregate grown in solution free from substrate-induced quenching.