Kinetic compensation effect and thermolysis mechanisms of organic polynitroso and polynitro compounds

The present study starts from the published values of the Arrhenius parameters E_a and log A of thermolysis in the condensed state of seven nitrosamines and one hundred organic polynitro compounds. On the basis of the linear relationship between E_aand log A, the set studied has been divided into several reaction series, each of which is characterized by a mechanism of primary thermolysis. For compounds with intense intermolecular interactions in a crystal, the classification mentioned is codetermined by the stabilizing effect of the crystal lattice. In the context of this effect, the absence of an effect of solid-liquid transition on thermal reactivity of octogen (HMX) has been confirmed. The idea also presented is that, in the primary homolysis in thermolyses of polynitro compounds, there takes place a mutual interaction of molecules of the given compound, which is analogous to termination interactions of nitroarenes in radical polymerizations.     

The relationship between the kinetic data of the low-temperature thermolysis and the heats of explosion of inorganic azides

The primary chemical processes of the thermal decomposition and detonation change of inorganic azides possessing explosive character is considered by means of the linear relationship between the activation energies, E, of the initial stage of low-temperature thermolysis, and the heats of explosion of these substances. Also, the possibility of applying E values in the estimation of the initiation capability of azides is considered.     

Note on the use of the vacuum stability test in the study of initiation reactivity of attractive cyclic nitramines in Formex P1 matrix

The zero-order reaction rates (specific rate constants) of isothermal decomposition at 120 °C of plastic bonded explosives (PBXs) were measured by means of the Czech vacuum stability test, STABIL. The PBXs are based on 1,3,5-trinitro-1,3,5-triazinane (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole (BCHMX), and ε 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-HNIW, ε-CL-20) with 13 wt% of the Formex P1 type matrix, i.e., a matrix of the explosive with pentaerythritol tetranitrate (PETN) bound by 13 wt% of a mixture of 25 wt% of styrene–butadiene rubber and 75 wt% of an oily material. Dependencies were found between the specific rate constants mentioned and the detonation velocities of PBXs, and consequently between these constants and the impact and electric spark sensitivities of pure explosive fillers, i.e., RDX, HMX, HNIW, BCHMX, and PETN. It is stated that the higher impact or electric spark sensitivity of their pure explosive fillers corresponds to the higher thermal reactivity of the given PBXs.     

Bentonite stability,speciation and migration behaviour of some critical radionuclides

The contribution is focused on chemical, geochemical and mineralogical research of bentonite stability with the aim to determine the effect of saturation medium composition and loading by heat on bentonite stability. The main part of the research is directed to the experimental results of bentonite and bentonite leachate samples obtained for the bentonite interaction under laboratory experiments. Computer-modeling methods were used to calculate equilibrium thermodynamic principles, the distributions of predominant aqueous species, and potential solubility controls for the environmentally important oxidation states of each investigated radioactive contaminants. The Eh–pH diagrams of individual chemical species of the tested radionuclides were calculated by the geochemical software tool Geochemist’s Workbench that included the actual chemical compositions of the solid–liquid systems under the given experimental conditions. It was confirmed that smectites are transformed to more stable silicate phases, such as illite/smectite mixed layers, illite. The data obtained from the model calculations conform with experimental results. The effect of the variable aqueous phase composition on bentonite stability using Ca–Mg and Na–Ca bentonites for the experiments was studied. The synthetic granitic waters with the higher concentration of the K⁺ and Mg²⁺ cations were applied for the study of bentonite stability.     

Effect of selenium in organic and inorganic form on liver,kidney, brain and muscle of <Emphasis Type="Italic">Wistar</Emphasis> rats

Selenium is a micronutrient, localized in the active sites of enzymes such as glutathione peroxidase and thioredoxin reductase, and participating together with these enzymes in an antioxidant defence system of organisms against free radicals. Administration of selenium is necessary for maintaining oxidative homeostasis. The present experiment is aimed at investigation of selenium impact on basal metabolic processes and selected antioxidants in a Wistar rat model, fed selenium in organic and inorganic forms. Liver, kidney, brain and muscle were sampled during a month-long feeding with four different doses of selenium (0.075 mg or 1.5 mg of inorganic and/or organic selenium per kg of feed). We found a significant reduction in glutathione level in liver tissue regardless of the form of the administered selenium. On the other hand, selenium caused a decreased glutathione reductase level in the liver and metallothionein level in the liver, kidney and muscle.      

Facile One-step Synthesis of Zn1–xMnxSiN2 Nitride Semiconductor Solid Solutions via Solid-state Metathesis Reaction

We report on the synthesis of the II-IV-N₂ semiconductors ZnSiN₂, MnSiN₂, and the Zn_1–xMn_xSiN₂ solid solutions by a one-step solid-state metathesis reaction. The successful syntheses were carried out by reacting the corresponding metal halides with stoichiometric amounts of silicon nitride and lithium azide in sealed tantalum ampoules. After washing out the reaction byproduct LiCl, powder X-ray diffraction patterns were indexed with orthorhombic space group Pna2₁. Single phase products were obtained without applying external pressure and at a moderate reaction temperature of 700 °C. The resulting ZnSiN₂ was found to consist of nano-sized grains and needle-shaped nano-crystals. With increasing manganese content in the Zn_1–xMn_xSiN₂ solid solution, we found the reaction product to be increasingly crystalline. Both the cell parameters and the bandgap values across the different compositions of the solid solutions change linearly. The sample Zn_0.95Mn_0.05SiN₂ synthesized by means of solid-state metathesis reaction is an intense red emitter with a broad emission maximum at λ_max ≈ 619 nm when excited with ultraviolet light after annealing the sample at a pressure of 6 GPa and a temperature of 1200 °C.     

More fine structural global square sequences

We extend the construction of a global square sequence in extender models from Zeman [8] to a construction of coherent non-threadable sequences and give a characterization of stationary reflection at inaccessibles similar to Jensen’s characterization in L.     

Substoichiometeric determination of traces of molybdenum by neutron activation analysis

A rapid, simple activation method for the selective determination of traces of molybdenum is proposed. With substoichiometric reagent addition, the required element need not be isolated in a weighable form and the chemical yield need not be determined. Molybdenum is simultaneously separated not only from metal impurities but also from the bulk of matrices such as germanium