A study on kinetics of ignition reaction of B4C/KNO3 and B4C/KClO4 pyrotechnic smoke compositions

Journal of Thermal Analysis and Calorimetry - Presented herein is a study on the ignition reaction kinetics and mechanism of B4C/KNO3 and B4C/KClO4 pyrotechnic smoke compositions using the...     

Heterogeneous catalytic ignition of n-butane/air mixtures on platinum

The heterogeneous catalytic ignition of lean to stoichiometric n-butane/air mixtures were studied at various total pressures between 10 and 100 kPa and at temperatures equal to or larger than the critical ignition temperatures. The induction periods, ignition and extinction temperatures were measured under strict isothermal conditions. The discussion presented in this paper is based on several literature models. The data analysis allowed for the determination of the overall kinetic parameters. The rigorous isothermal conditions indicated that the extinction temperatures are lower than the ignition, a behavior different from the results obtained in stagnation-point flow reactors.      

Chain ignition of propane-air and pentane-air mixtures in a heated vessel

The spatial propagation of the chain ignition of propane-air and pentane-air mixtures with oxygen at a pressure of 1 atm and T = 600–800 K is studied. It is established that the features of the spatial propagation of chain ignition process are determined by the conditions of the reactor’s surface. It is shown that the site (or sites) of ignition are located on the surface of the reaction vessel; the flame front propagates from the site into the volume at a normal speed corresponding to the reactor temperature and the composition of the combustible mixture.     

Thermal behaviour and firing characteristics of Zr/KClO4 primer mixture containing CuO

The effect of CuO on the thermal behaviour of Zr/KClO₄ primer mixtures was studied by thermoanalytical techniques, and the Bruceton method and its related calculation. It was found that the CuO catalytically promoted the decomposition of Zr/KClO₄ primer mixtures and shifted the exothermic peak of DSC curves to lower temperatures. In addition, the Zr/KClO₄ primer mixture containing CuO had a significant effect on the firing characteristics of electro-explosive devices.     

Thermosonimetry and thermomicroscopy of the decomposition of NaClO4 and KClO4

Thermal decompositions of NaClO₄ and KClO₄ were followed by simultaneous TS-DTA and thermomicroscopy. For NaClO₄ TS curves corresponding to melting/decomposition and solidification of molten NaCl were found to consist of six peaks. During decomposition of KClO₄, three TS peaks appeared. The origin of these TS peaks is discussed on the basis of thermomicroscopic observations during which melting of the particles, evolution of bubbles of different sizes, formation of solid products of varied morphologies, vigorous vibration of these solids, and precipitation of NaCl or KCl were observed.     

Low temperature absorption spectra of TcO 4 − and ReO 4 − in KClO4

The low temperature spectra of TcO ₄ ^– and ReO ₄ ^– both show two band systems with pronounced vibrational structures. The bands are identified as¹ A ₁¹ T ₂ transitions. No other bands are observed with certainty. It seems likely that the KClO₄ crystals contain KReO₄ crystallites. They are therefore not pure mixed crystals. It is concluded that the virtual orbital (2e) used in the construction of the low lying states resembles an atomic nd orbital more and more when going from n=3, Mn to n=5, Re.

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Zusammenfassung Die Tieftemperaturspektren von TcO ₄ ^– und ReO ₄ ^– zeigen beide zwei Bandensysteme mit ausgeprägten Schwingungsstrukturen. Die Banden werden als ¹ A ₁¹ T ₂-Übergänge identifiziert. Keine anderen Banden werden mit Sicherheit beobachtet. Es scheint wahrscheinlich, daß die KClO₄-Kristalle KReO₄-Kristallite enthalten und deswegen keine reinen Mischkristalle sind. Es wird geschlossen, daß das virtuelle Orbital (2e), welches zur Konstruktion der tiefliegenden Zustände gebraucht wird, in der Reihe n=3, Mn bis n=5, Re immer weitgehender einem nd-Atomorbital ähnelt.

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Nachwuchsstipendiat, Schweizerischer Nationalfonds.     

Solvent effects on complexation of crown ethers with LiClO4, NaClO4 and KClO4 in methanol and acetonitrile

The thermodynamic formation constants K_f for complexation of Li⁺, Na⁺ and K⁺ with the crown ethers 12C4 and 15C5 have been determined in methanol and acetonitrile at 25°C using precision conductivity data. The method permits evaluation of very small K_f values (e.g., K_f=6.98 mol^–1-dm³ for LiClO₄+12C4 in methanol) as well as fairly large values (e.g., K_f=2.73×10⁴ mol^–1-dm³ for NaClO₄+15C5 in acetonitrile). The determination of K_f values from conductivity data takes into consideration the often neglected ion pair formation of both the uncomplexed and the complexed cations. Our results for K_f are generally consistent with previously reported values based on potentiometry, calorimetry and polarography, but there are significant differences in several cases which we attribute to neglect of ion association both for the uncomplexed or free cation K_a and the macrocyclic complexed cation K_a2. Our results are also consistent with the well known concepts relating the magnitude of K_f to both the cavity diameter and ion-solvent interactions. Limiting molar conductivities ₂ ⁰ for the complex salt (M-crown ether) (ClO₄) in both solvents were generally found to be smaller or very close to the corresponding quantity ₁ ⁰ for the binary MClO₄-solvent system. However, in methanol, single ion limiting molar conductivities for the cationic complexes ₂ ⁰ exhibit anomalous behavior which is attributed to solvation differences between free cations and complexed cations.     

Annealing of radiomanganese in KMnO4 and in mixed crystals of KMnO4 with KClO4, KReO4 and KBF4

The influence of recoil energy, ionizing radiation and crystal composition, on the retention and on the thermal annealing of radiomanganese in KMnO₄ is studied. It is reported, that the recoil energy is of no great influence. In pure KMnO₄ two annealing processes can be distinguished, one with a relatively low energy of activation leading to MnO₄⁻ as a result of oxygen transfer, and one with a higher energy of activation comprizing the reaction of recoil manganese with its former oxygen ligands. The second process can be suppressed by ionizing radiation and by fast neutron irradiation. The increase of the retention in mixed crystals with KClO₄ and KReO₄ is tentatively ascribed to the tendency to form species which have structures which are as similar as possible to that of the host matrix.     

A Convenient,Rapid and New Catalyst Oxidation Method with KClO3/H2SO4/FeSO4 for Preparing Aryl Azo Compounds

Using potassium chlorate, sulfuric acid and ferrous sulfate as a catalytic oxidation system to oxidize the aryl substituted semicarbazide to prepare azo compounds in one phase have been described first time in this paper. Fourteen azo compounds have been synthesized in excellent yields(>90%). This method only needs cheap reagents, simple instrument and short reaction time. A possible mechanism has been suggested.     

Modeling processes of thermal decomposition of hydrocarbon fuels in heated channels

We introduce a mathematical model of the nonequilibrium process of thermal decomposition of hydrocarbon fuel in heated channels of a ramjet combustion chamber cooling system. This mathematical model is based on describing the process using intermediate asymptotics formed when taking into account the equilibrium gas composition, which is determined using open source software for calculating the equilibrium state of the chemical reaction products. A procedure was introduced allowing at different stages of the process of thermal decomposition of fuel to separate kinetically irreversible and reversible chemical reactions and to exclude from consideration chemical reactions which remained incomplete in a limited size engine. We present the features of the process of thermal decomposition of liquid and solid fuels which can be used in high-speed aircraft engines.     

镁在DMF中电沉积机理的研究

自本世纪初始,人们一直试图在非水体系中电沉积镁,迄今尚未见到令人满意的报道。此外,有关镁在非水体系中,在固态电极上电沉积机理的研究工作也未见系统报道。本工作首先确证了在高氯酸镁的DMF溶液中、在光亮铂电极上能电沉积出金属镁。在此基础上初步研究了这一电沉积过程的动力学特征,提出了在该体系中镁电沉积的机理。     

The catalytic effect of Ag/CNTs nanocomposite on the ignition reaction of Mg/KNO3 pyrotechnic by determination of the kinetic triplet

Journal of Thermal Analysis and Calorimetry - The ignition reaction of Mg/KNO3 was improved with addition of Ag/CNTs nanocomposite as catalyst. The nanoparticles of Ag(0) was deposited on the...     

Catalytic Effect of Some Chromites on the Thermal Decomposition of KClO4. Mechanistic and non-isothermal kinetic studies

The catalytic effect of two different groups of chromites on the non-isothermal decomposition of KClO₄was studied. TG and DSC curves of the thermal behaviour obtained for KClO₄-alkaline earth chromites (Series 1) mixtures indicate the formation of K₂Cr₂O₇, through a solid-solid interaction, before accelerating the decomposition stage of KClO₄. Such an accelerating effect becomes more pronounced in the case of admixing KClO₄ with some transition metal chromites (Series 2). The results were discussed taking into consideration the electronic configuration of cations and the electrical properties of the chromite catalysts. The presence of coordinatively active cations, able to form surface complex with the oxygen of the perchlorate anion, was proved to be necessary for obtaining an active catalyst. The kinetic parameters and models describing the catalyzed thermal decomposition process of KClO₄ were evaluated by using a computer program that allows the analysis using five different methods. It was found that the adopted kinetic model for pure KClO₄ and that mixed with catalysts from Series 1 is one-dimensional movement of phase boundary. On the other hand, random nucleation mechanism was achieved in the presence of catalysts from Series 2. Finally, a tentative reaction mechanism consistent with the obtained results was suggested. This revised version was published online in July 2006 with corrections to the Cover Date.     

稀土偶联剂对Mg(OH)2的改性作用及其在PP/Mg(OH)2体系中的应用

研究了稀土偶联剂(ReC)对Mg(OH)2的表面改性作用及PP/Mg(OH)2体系的燃烧性能、流动性能、力学性能及老化性能.稀土偶联剂可显著改善Mg(OH)2在非极性介质中的分散性;PP/Mg(OH)2体系当Mg(OH)2填充量超过50%时,氧指数(OI)≥28.5,但这时冲击强度不足纯PP的30%,熔体流动速率(MFR)低于0.6g/10min;而填科用2.59%(质量)ReC处理后,填充量为50%的体系冲击强度接近纯PP,MFR达2.8g/10min;Mg(OH)2对体系光氧老化过程有加速作用,而对热氧老化过程有阻滞作用;稀土偶联剂对体系光氧老化过程有轻微的促进作用,而对热氧老化过程无明显影响.     

稀土偶联剂对Mg(OH)_2的改性作用及其在PP/Mg(OH)_2体系中的应用

研究了稀土偶联剂 (ReC)对Mg(OH) 2 的表面改性作用及PP/Mg(OH) 2 体系的燃烧性能、流动性能、力学性能及老化性能。稀土偶联剂可显著改善Mg(OH) 2 在非极性介质中的分散性 ;PP/Mg(OH) 2 体系当Mg(OH) 2 填充量超过 5 0 %时 ,氧指数 (OI)≥ 2 8.5 ,但这时冲击强度不足纯PP的 30 % ,熔体流动速率 (MFR)低于 0 .6g/1 0min ;而填料用 2 .5 % (质量 )ReC处理后 ,填充量为 5 0 %的体系冲击强度接近纯PP ,MFR达 2 .8g/1 0min ;Mg(OH) 2对体系光氧老化过程有加速作用 ,而对热氧老化过程有阻滞作用 ;稀土偶联剂对体系光氧老化过程有轻微的促进作用 ,而对热氧老化过程无明显影响     

镁离子掺杂对LiFePO4/C材料电池性能的影响

通过PVA(聚乙烯醇)包覆工艺利用固相法合成了镁离子掺杂的LiFePO₄/C.材料的高温电导率特征曲线和电阻率与掺杂含量变化的曲线表明，材料中由于Mg离子的掺杂，使得其导电机制由n型半导体向p型半导体转换.在镁离子掺杂原子百分含量为0.3％(x)下，研究了材料的结晶性能随烧成温度的变化.973 K下合成材料具有良好的微观结构，材料的亚微米颗粒和PVA裂解产生的碳黑形成了粒径在10 μm左右的团簇体.在循环伏安特性曲线中，存在两个小的肩峰,表明在循环过程中，锂离子可以通过由掺杂产生的锂空位进行插入和脱出.材料在0.1 C的充放电速率下，首次充放电曲线具有平稳的电压平台和较大的充放电容量.当充放电速率为0.5 C时，材料仍然具有大于120 mA•h•g^－1的充放电容量；经过100次循环后，基本上没有发现材料的循环容量衰减的情况.     

Thermodynamic behavior and relaxation processes of mixed DPPC/cholesterol monolayers at the air/water interface

This study investigated the thermodynamic behavior and relaxation processes of mixed DPPC/cholesterol monolayers at the air/water interface at 37°C. Surface pressure–area isotherms and relaxation curves for the mixed monolayers were obtained by using a computer-controlled film balance. In the thermodynamic analysis of the mixed monolayers, the areas of monolayers exhibited negative deviations from the ideal values at all compositions for lower surface pressures. However, at higher surface pressures, distinctively positive deviations from ideality were observed at lower DPPC contents. Excess free energies of mixing had been calculated and the most stable state of the mixed monolayer with x_DPPC=0.5 or 0.6 was found. Moreover, the relaxation kinetics of the mixed monolayers was investigated by measuring the surface area as a function of time at a constant surface pressure of 40 mN m⁻¹. It was shown that the relaxation processes could be described by the models considering nucleation and growth mechanisms.     

Studies on InFeMO4 (M=Mg, Co, Ni, Cu and Zn) compounds: Crystal structure and cation distribution

The crystal structure and the cation distribution in a series of InFeMO₄ compounds (M=Mg, Co, Ni, Cu and Zn) have been studied by means of X-ray powder diffraction and ⁵⁷Fe Mössbauer spectroscopy. The M=Mg, Co and Ni samples were confirmed to crystallize with the cubic spinel structure (space group Fd-3m), whereas the M=Cu and Zn samples adopted a hexagonal structure. For all the phases, the cation stoichiometry was found to deviate from the ideal molecular formula, InFeMO₄. The paramagnetic Mössbauer spectra of the samples were analyzed using a four-component fitting model suggested by a statistical simulation with point-charge calculation. The Mössbauer data confirmed the trivalent state for iron at both cation sites in all samples. The results from the fitting of the Mössbauer spectra were also employed in Rietveld refinement of the X-ray diffraction data for the determination of exact cation distribution. It was seen that the distribution of Fe at the A and B sites follows very closely the 1:2 ratio of the ideal formula AB₂O₄ for all samples, whereas trivalent indium was clearly seen to favor the A site and divalent M cation the B site.     

Isothermal pyrolysis of a fire retardant coating heated by free convection in air

Pyrolysis studies of a fire retardant coating were conducted under isothermal conditions by taking into account the kinetic data of the overall reaction and the heat transfer process. The coating was made of Polyurethane and chlorinated paraffin. A 160Μm thick film was heated by free convection from heated air, and conduction through the coating. Profiles of temperature developed through the coating were obtained by calculation, as well as those of loss in weight due to the thermal decomposition. The thermal conduction did not vary because of the formation of a porous char resulting from the coating decomposition.