氯化钽在离子液体1-丁基-3-甲基咪唑六氟磷酸盐中电化学行为

采用循环伏安法,研究了0.25 mol/L TaCl₅在离子液体1-丁基-3-甲基咪唑六氟磷酸盐([Bmim]PF₆)中的电化学行为。 实验结果表明,电沉积钽是受扩散控制、两步骤的不可逆电极反应过程,首先是Ta(Ⅴ)还原为Ta(Ⅲ),其次是Ta(Ⅲ)还原为金属钽和形成其它低价钽氯化物。 Ta(Ⅴ)/Ta(Ⅲ)和Ta(Ⅲ)/Ta在离子液体[Bmim]PF₆中的阴极传递系数分别为0.155和0.406。 Ta(Ⅴ)在离子液体[Bmim]PF₆中的扩散系数为1.629×10^-9 cm²/s。 在100 ℃和-1.25 V条件下,采用恒电势法在铂片上电沉积钽,扫描电子显微镜照片和EDS分析表明,沉积物为钽和钽的低价氯化物。     

The solubility products of some slightly soluble lead salts and the potentiometric titration of molybdate, tungstate, perrhenate and fluoride with use of a lead ion-selective electrode

The conditional solubility products of lead molybdate, lead tungstate and lead perrhenate were found to be 1.2 +/- 0.3 x 10(-13), 8.4 +/- 0.1 x 10(-11) and 6.9 +/- 0.8 x 10(-9), respectively. In the case of lead perrhenate, the conditional stepwise formation constants for PbReO(+)(4) and Pb(ReO(4))(2) were found to be 1.2 +/- 0.1 x 10(5) and 1.2 +/- 0.2 x 10(3), respectively. Conditions for the potentiometric titration of molybdate, tungstate, perrhenate and fluoride with lead were established. The precipitates obtained during the titration of molybdate, perrhenate and fluoride mixtures have been proved to be physical mixtures of lead molybdate, perrhenate, fluoride and hydroxide, by infrared spectrometry. The pK(sp)-values of the lead salts of chromate, molybdate and tungstate are shown to increase linearly with increasing atomic number or electronegativity of the Group VI metal ion.     

Green Colorants Based on Energetic Azole Borates

The investigation of green‐burning boron‐based compounds as colorants in pyrotechnic formulations as alternative for barium nitrate, which is a hazard to health and to the environment, is reported. Metal‐free and nitrogen‐rich dihydrobis(5‐aminotetrazolyl)borate salts and dihydrobis(1,3,4‐triazolyl)borate salts have been synthesized and characterized by NMR spectroscopy, elemental analysis, mass spectrometry, and vibrational spectroscopy. Their thermal and energetic properties have been determined as well. Several pyrotechnic compositions using selected azolyl borate salts as green colorants were investigated. Formulations with ammonium dinitramide and ammonium nitrate as oxidizers and boron and magnesium as fuels were tested. The burn time, dominant wavelength, spectral purity, luminous intensity, and luminous efficiency as well as the thermal and energetic properties of these compositions were measured.     

Prediction of shock response of pyrotechnic mixtures from thermal analysis

The thermal behavior of metal, oxide, and oxidizer mixtures, some with fluorine compound additions, has been studied in order to examine the influence of thermal properties on the initiation conditions for chemical reaction of pyrotechnic powders under dynamic loading conditions. The autoignition energies of the mixtures obtained from thermal analyses were compared with shock initiation energies, determined from planar shock measurements. Although some mixtures showed an approximate equivalency between the energies obtained from the two different experiments, the experimental results indicated that any comparison should be made with great care.We thank A. J. Lindfors and S. Pockrandt for the planar shock measurements.     

Differential thermal analysis and temperature profile analysis of pyrotechnic delay systems: Slow burning mixtures of boron and potassium dichromate

The slow burning pyrotechnic reaction between boron and potassium dichromate has been studied by differential thermal analysis and temperature profile analysis. The latter technique in which the combustion process is studied directly, shows the presence of two reaction stages and validates the results from differential thermal analysis obtained under non-ignition conditions. In the first stage potassium dichromate is reduced by boron to form potassium chromate. Differential thermal analysis shows that the reaction takes place below the melting temperature of potassium dichromate and becomes much more rapid above this temperature. The second stage which occurs in the region of 1000 K involves the reaction of potassium chromate with more boron. The first stage acts as a trigger for the second and it is this latter stage which propagates the combustion.     

Feuerwerk

Pyrotechnic is an old empiric science on the borderline between chemistry, technics, chemical and process engineering and art and it maintains its position as an integral part of events in culture and tradition. This contribution presents the steps a firework has to pass to develop from mere chemistry to the final show. Some chemical background, information about pyrotechnic mixtures like black powder, firework star mixtures, oscillating mixtures like blinking stars and whistles are explained as well as the manufacture of selected pyrotechnic items. Aspects of production and handling safety of exhibition fireworks and the recent developments in legislation like the pyrotechnics directive, the CE‐ standardisation and REACH are touched. Although the commercial environment is getting tougher the fascination for the pyrotechnic phenomena are still alive and may initiate the motivation for the reader to get involved in the exciting topic of pyrotechnics and the associated fields of science.     

高稳定性的氮掺杂氧化钽光催化甲醇C−H活化和直接C−C偶联制乙二醇

乙二醇是非常重要的基础化学品,不仅可以作为合成聚合物(如聚对苯二甲酸乙二醇酯)的重要单体,也可以用作防冻剂和燃料添加剂等,具有广泛的用途.乙二醇的年产量超过2500万吨,目前主要的工业合成路线是由石油衍生的乙烯通过环氧化制环氧乙烷,环氧乙烷再水解制乙二醇.甲醇是一种清洁的平台化合物,不仅可以由天然气和煤炭通过传统的合成...     

Complex citrates of metals in inorganic analysis

Summary A new method has been described for the quantitative separation of silver and lead in a solution. The method consists of adding an excess of sodium citrate solution to the solution of the mixture, when the insoluble citrates of silver and lead which at first precipitate out, redis-solve due to the formation of complex citrates. By the addition of hydro-chlorid acid to the solution, only silver chloride precipitates out and may be estimated gravimetrically. In the filtrate lead may be estimated gravimetrically as lead chromate. The method described here is quite reliable, as the results obtained by the analysis of a number of mixtures of different compositions have been found to be very satisfactory, the errors lying within permissible limits.     

Thermal and Spectral Characterization of 5-Cholro-2-methoxybenzoates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II)

The thermal stabilities of 5-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) were studied in air and nitrogen atmospheres. The complexes were obtained as mono-, di-, tetra-and pentahydrates with a metal to ligand ratio of 1:2 and with colours typical for M²⁺ ions (Mn-slightly pink, Co-pink, Ni-green, Cu-blue and Zn-white) and as polycrystalline compounds. When heated they dehydrate to form anhydrous salts which nextare decomposed to the oxides of the respective metals in air while in nitrogen to the mixtures of metal oxides and oxychlorides and carbon. The most thermally stable in air, nitrogen and argon atmospheres is 5-chloro-2-methoxybenzoate of Cu(II) while the least thermally stable is that of Co(II). This revised version was published online in July 2006 with corrections to the Cover Date.     

Chromate nanorods/nanobelts: general synthesis, characterization, and properties

A general synthesis route to a family of single-crystal chromate nanorods/nanobelts has been established. The effects of pH and surfactant on phase and morphology of these microcrystalline materials have been investigated. The physical properties of the as-synthesized chromate nanocrystals such as dielectric, electrochemical, UV-vis absorbance, and photoluminescent properties have also been studied. The present general synthesis of various low-dimensional chromate nanomaterials provides useful information on the possible synthesis of other microcrystalline transition metal oxysalts.     

Advanced kinetic tools for the evaluation of decomposition reactions

Summary An advanced kinetic study on the thermal behaviour of pyrotechnic ignition mixtures has been carried out by differential scanning calorimetry using different B/KNO3 mixtures (50:50, 30:70, 20:80) as a model reaction. The experimental conditions applied (isochoric conditions/closed crucibles and isobaric conditions/open crucibles) as well as the composition of the mixtures noticeably influences the relative thermal stabilities of the energetic materials. The kinetic study focused on the prediction of the thermal stability of the different mixtures both in extended temperature ranges and under temperature conditions at which ordinary investigation would be very difficult. Using advanced numerical tools [1], thermal ageing and influence of the complex thermal environment on the heat accumulation conditions were computed. This can be done for any surrounding temperature profile such as isothermal, non-isothermal, stepwise, modulated, shock, adiabatic conditions and additionally for temperature profiles reflecting real atmospheric temperature changes (yearly temperature profiles of different climates with daily minimal and maximal fluctuations). Applications of accurate decomposition kinetics enabled the determination of the time to maximum rate under adiabatic conditions (TMR_ad) with a precision given by the confidence interval of the predictions. This analysis can then be applied for the examination of the effects of the surrounding temperature for safe storage or transportation conditions (e.g. determination of the safe transport or storage temperatures).     

Electrochemical Oxidation of Tantalum in LiNO3-NaNO3-KNO3 Melt

Growth kinetics of anodic oxide films on tantalum in a molten eutectic mixture of lithium, sodium, and potassium nitrates was studied and the influence exerted by introduction of hydroxide and chromate ions into the nitrate mixture was considered. The basic kinetic parameters of anodic oxidation of tantalum under galvanostatic conditions were determined.     

Polyurethane–poly(vinylidene fluoride) (PU–PVDF) thin film composite membranes for gas separation

Aqueous polyurethane dispersions (PUDs) with poly(dimethylsiloxane) (PDMS), or mixed poly(dimethylsiloxane)/poly(ethylene glycol) (PDMS/PEG) as the soft segment were synthesized, and made into thin films for characterization with differential scanning calorimetry (DSC), thermogarvimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), size exclusion chromatography (SEC) and transmission electron microscopy (TEM). Seven thin film composite (TFC) membranes prepared on PUDs and PVDF substrates were evaluated by the separation of air as well as hydrocarbon–nitrogen mixtures. A promising membrane was then selected for further investigation of the morphological structure and permselectivities, using pure gases and binary mixtures of ethylene, ethane, propylene and propane with nitrogen at ambient temperature. It was found that PDMS/PEG-based PU membrane was typically solubility-selective for condensable hydrocarbons, and nitrogen permeance was marginally enhanced in hydrocarbon–nitrogen mixtures. It appears that the copolymer membrane with both urethane and PEG segments can effectively tolerate the swelling caused by the condensable gases. As a result, the selectivities of propylene and propane to nitrogen were substantially improved, e.g., in a mixture containing 28% propylene and 72% nitrogen, the selectivity of propylene to nitrogen reached 29.2 with a propylene permeance of 34.4 gas permeation unit (GPU).     

Applying the Taguchi Robust Design to Optimization of the Experimental Conditions for Synthesis of Lead Chromate Nanorods

Orthogonal array design was employed as statistical method for controllable, simple, and fast synthesis of highly uniform PbCrO₄ nanorods by precipitation method. Lead chromate nanorods were synthesized by addition of lead solution to chromate reagent. Effect of reaction conditions on the width of lead chromate rods were quantitavely evaluated by analysis of variance. Finally, optimum conditions for synthesis of lead chromate nanorods by this simple and fast method were proposed. The results of analysis of variance showed that 0.001 mol/L lead and chromate ion concentrations are optimum conditions for producing lead chromate nanorods with 87 ± 15 nm width.     

Condition of lead iodide in the medium of lyophilic sols

The condition of lead chromate in gelatin and agar agar medium has been studied. In presence of agar agar medium the colloid formed is stabilised by lead ions and coagulated by the excess of chromate ions. Lead chromate forms a very stable colloid in the presence of gelatin sol which could not be precipitated by excess of lead ions or chromate ions. Due to the formation of a very stable colloid in gelatin medium, well defined rings of lead chromate are not obtained in gelatin gel.     

Improving safety performance of lactose-fueled binary pyrotechnic systems of smoke dyes

The lactose/KClO₃ is a widely used pyrotechnic mixture to vaporize organic materials, such as smoke dyes. However, because of low ignition temperature of this mixture, serious precaution should be taken into account to prevent its accidental self-ignition. In order to find a safe and efficient alternative of this conventional mixture, KClO₃ has been replaced by common oxidizing agents including KMnO₄, KNO₃, KClO₄, Ba(NO₃)₂, PbO₂ and NH₄ClO₄. TG and DTA analysis have been used to obtain thermal characteristic of the mixtures. Based on ignition temperature of the pyrotechnic mixtures we can divide them into four categories as follows: (1) the mixture igniting at low temperature, i.e., at about 200 °C. (2) Moderate temperature igniting mixture, in which ignition occurs at 300–400 °C. (3) High temperature igniting mixture with ignition temperature higher than 400 °C .(4) Not igniting mixtures. Also, the apparent activation energy (E), ΔG ^#, ΔH ^#, ΔS ^# and critical ignition temperature (T _b ) of the ignition processes of low and moderate temperature igniting mixtures were obtained from the DSC experiments. Finally, among the investigated mixtures, lactose/KNO₃ can be considered as a safe and efficient pyrotechnic composition for vaporization of organic materials, such as smoke dyes, due to its moderate safe ignition temperature.     

Characterization of the aluminum/potassium chlorate mixtures by simultaneous TG-DTA

Thermogravimetry (TG) and differential thermal analysis (DTA) in the non-isothermal mode have been used to examine the thermal behaviour of the micron sized aluminum (Al) powder/potassium chlorate pyrotechnic systems in air, in relation to the behaviour of the individual constituents. The effects of different parameters of Al powder, such as particle size and its content in the mixtures, on their thermal property were investigated. The results showed that, the reactivity of Al powder in air increases as the particle size decreases. Also, it was found that neat Al with 5 μm particle sizes (Al₅) has a fusion temperature of about 647°C, that for 18 μm powder (Al₁₈) is 660°C. Pure potassium chlorate has a fusion temperature around 356°C and decomposes at 472°C. DTA curves for Al₅/KClO₃ (30:70) mixture showed a maximum peak temperature for the ignition of mixture at 485°C. Also, by increasing the particle size of Al powder, the ignition temperature of the mixture increased. On the other hand, the oxidation temperature increased by enhancing the Al content of the mixtures. In this particular study, we observed that the width of reaction peak for the mixtures corresponds to their Al contents of samples.     

Gamma irradiation effects of51Cr/III/ Isotope exchange in doped magnesium chromate — zinc chromate mixtures

Gamma irradiation effects of chromium isotope exchange in magnesium chromate — zinc chromate mixtures doped with⁵¹Cr/III/ were investigated. It was found that irradiation has an oxidation effect and the percentage of⁵¹Cr/VI/ exchanged increases with increasing -ray dose. The data were explained in terms of mechanistic model involving metal and ligand vacancies exchange and substitution reactions.     

Detection and imaging of chrome yellow (lead chromate) in latent prints,solid residues,and minerals by laser‐desorption/ionization mass spectrometry (LDI‐MS)

In the past, chrome yellow (lead chromate, PbCrO₄), a bright orange‐red substance, has been widely used as an inorganic pigment in the production of paints, coatings, and plastics. Herein, we demonstrate that laser desorption/ionization mass spectrometry (LDI‐MS) is a powerful tool for the detection of lead chromate in solid residues. In fact, lead chromate in trace amounts is easily detectable by LDI‐MS even from residues left as latent prints. For example, a latent print obtained by stamping the exposed laterally cut surface of a pencil over 50 years old on an acetonitrile‐moistened paper, was successfully imaged for both lead and chromate using a Synapt G2 HDMS mass spectrometer. After rastering the print with a 355 nm laser beam and recording positive‐ and negative‐ion mass spectra over the range m/z 50–1200, we generated false‐color ‘heat maps’ (single‐ion images) for ²⁰⁸Pb^+• (m/z 207.98) and Cr₂O₆^−• (m/z 199.85). The heat maps matched closely with the faint visual image of the pencil imprint. Moreover, our results confirmed that lead chromate was used in the pigment coatings of old pencils. Evidently, LDI‐MS imaging is an efficient procedure to survey for the presence of lead and chromate in minerals and other materials. Copyright © 2017 John Wiley & Sons, Ltd.     

The influences of combinative effect of temperature and humidity on the thermal stability of pyrotechnic mixtures containing strontium nitrate as oxidizer

The influences of combinative effect of temperature and humidity on the thermal stabilities of three pyrotechnic compositions are investigated in the study. The thermal behavior for each pyrotechnic is analyzed by SETARAM thermal analyzer. Activation energy is determined by Kissinger method and critical temperature of thermal explosion (T _b) of pyrotechnic compositions is also calculated. The results of thermal analysis revealed that relative humidity could decrease the thermal stability of pyrotechnic mixtures. The critical temperature of thermal explosion (T _b) of each pyrotechnics decreased as the relative humidity increasing. Based on the value of T _b, the thermal stabilities of the pyrotechnic mixtures are in the order of S_r(NO₃)₂/Mg₄Al₃/PVC/PF > S_r(NO₃)₂/S_rCO₃/KClO₄/Mg₄Al₃/PVC/PF > S_r(NO₃)₂/KClO₄/Mg₄Al₃/PVC/PF. The thermal stability of S_r(NO₃)₂/Mg₄Al₃/PVC/PF show the best thermal stability than other two mixtures whether it is in the condition of humidity or not.