Kinetics and Mechanism of Thermal Decomposition of Dinitramide

Kinetics of the thermal decomposition of dinitramide (HDN) in aqueous solutions and of NH₄N(NO₂)₂ (ADN) and KN(NO₂)₂ (KDN) in sulfuric acid, nitric acid and anhydrous acetic acid solutions was studied. The species N(NO₂)₋₂, HN(NO₂)₂ and H₂N(NO₂) were established to take part in the decomposition over a wide range of the medium acidity. Kinetic regularities of their thermal decomposition were determined. The role of the decomposition of dinitramide at the initial and self-acceleration stages of the decomposition of ADN was determined. The most likely mechanism of the decomposition of dinitramide, N(NO₂)₋₂ and H₂N(NO₂)₊₂ was proposed.     

Some Phenomenological Aspects of Heterogeneous Combustion of Condensed Systems

The combustion process of heterogeneous condensed systems (HCS) is a complex phenomenon characterized by some peculiarities: Phase transitions in the combustion wave, time and space inhomogeneity of the temperature and burning rate, agglomeration and dispersion of the condensed phase, concentration limits, etc. The order and completeness of chemical reactions in a HCS combustion wave depend not only on the energetic parameters but on the composite structure as well (porosity, component particle size and shape, etc.). Some phenomenological aspects of the HCS combustion process are analyzed. Peculiarities of metal particle agglomeration and its influence on the metal oxide size are discussed. The high‐temperature kinetics of Al+Al₂O₃ interaction are shown. The complexity of the analyzed phenomenon calls for a non‐traditional approach and technique.     

Multifunctional Magnetic-fluorescent Nanocomposites for Biomedical Applications

Nanotechnology is a fast-growing area, involving the fabrication and use of nano-sized materials and devices. Various nanocomposite materials play a number of important roles in modern science and technology. Magnetic and fluorescent inorganic nanoparticles are of particular importance due to their broad range of potential applications. It is expected that the combination of magnetic and fluorescent properties in one nanocomposite would enable the engineering of unique multifunctional nanoscale devices, which could be manipulated using external magnetic fields. The aim of this review is to present an overview of bimodal “two-in-one” magnetic-fluorescent nanocomposite materials which combine both magnetic and fluorescent properties in one entity, in particular those with potential applications in biotechnology and nanomedicine. There is a great necessity for the development of these multifunctional nanocomposites, but there are some difficulties and challenges to overcome in their fabrication such as quenching of the fluorescent entity by the magnetic core. Fluorescent-magnetic nanocomposites include a variety of materials including silica-based, dye-functionalised magnetic nanoparticles and quantum dots-magnetic nanoparticle composites. The classification and main synthesis strategies, along with approaches for the fabrication of fluorescent-magnetic nanocomposites, are considered. The current and potential biomedical uses, including biological imaging, cell tracking, magnetic bioseparation, nanomedicine and bio- and chemo-sensoring, of magnetic-fluorescent nanocomposites are also discussed.     

Wettability of Halides with Molten Metals. Physico-Chemical and Practical Aspects

A study is made on the wettability of sodium chloride and oxygen-free ionic compounds fluorides of alkaline-earth elements (CaF, MgF, BaF) by molten metals. The metals Cu, Sn, Ag, Au, In, and Ga do not wet these materials ( 120-140 deg). The wettability of fluorides by aluminum is somewhat greater ( 90-100 deg), in accordance with the greater chemical affinity of aluminum for fluorine. Chemically highly active and aggressive alloys of Ti, Zr, Hf, and V (with concentrations up to 70-80%) which completely wet and destroy known refractory materials (oxide, nitride, carbide, and carbon refractories, etc.) behave anomalously in regard to fluorides they do not wet their surface and are inert when in contact with them. This is attributable to the formation of an intermediate gaseous phase (a volatile fluoride) which separates the liquid metal from the solid surface. Effective use can be made of this phenomenon to develop refractories (crucibles, containers, jackets, etc.) for use in the isothermal melting, homogenization, and casting of alloys that contain Ti, Zr, Hf, and V.     

Structuring of Multiphase Compacts in the SiC′ ― Carbon System. Part 2. Structuring during Sintering

We have studied the effect of particle sizes in the starting powders in the silicon carbide carbon system, and also effects on the structure and phase composition of self-bonded silicon carbide (SBSC) that are associated with structural interactions between the starting components.     

Composite inorganic membranes containing nanoparticles of hydrated zirconium dioxide for electrodialytic separation

The aim of the work was to elucidate the nature of charge-selective properties of macroporous composite inorganic membranes modified with nanoparticles of hydrated zirconium dioxide. The membranes have been investigated using methods of standard contact porosimetry, potentiometry, electron microscopy and small-angle X-ray scattering. The ion exchanger has been found to deposit inside pores of ceramics. Differential curves of pore volume distribution have been resolved using Lorentz functions; each maximum has been related to structure elements of the matrix and ion exchanger by means of calculations according to homogeneous and heterogeneous geometrical models. It was found that the voids, the radius of which is 4 to 8 nm, are responsible for charge selectivity of the composite membranes. These pores are formed due to blocking of macropores of ceramics with aggregates of nanoparticles of the ion exchanger; the radius of these aggregates is 20 to 24 nm. The membranes were applied to desalination of the solution containing NaCl. The removal degree of the salt from the solution reached 95% and 9% for the composite and unmodified membranes, respectively.     

Effect of Mode Transformation in THz Clinotron

Extension of the theory of a clinotron is developed by use of the scattering matrix of an oversized T-junction on the ends of a slow wave system. The matrix contains elements corresponding to the transformation of slow grating modes into fast ones and vice versa. Those fast waves with low ohmic losses provide strong resonant properties of a clinotron even in the case of strong attenuation of the surface mode. Results of the theoretical simulation are compared with experimental ones and obtained dependencies explain strong resonances in sub-THz clinotrons.     

Liquidus Temperatures of Cryolite Melts With Low Cryolite Ratio

The effect of calcium fluoride on liquidus temperatures of the cryolite melts with a low cryolite ratio (CR) was studied. The systems KF-NaF-AlF₃ and KF-LiF-AlF₃ with CRs of 1.3, 1.5, and 1.7 have been investigated. The liquidus curves of systems containing CaF₂ are different and depend on the K/(K + Na) and K/(K + Li) ratios. In potassium cryolite with CRs of 1.3 and 1.5, the calcium fluoride solubility is low and increases with NaF (LiF) concentration.     

Surface plasmon enhanced energy transfer between donor and acceptor CdTe nanocrystal quantum dot monolayers

Surface plasmon enhanced Fo?rster resonant energy transfer (FRET) between CdTe nanocrystal quantum dots (QDs) has been observed in a multilayer acceptor QD-gold nanoparticle-donor QD sandwich structure. Compared to a donor-acceptor QD bilayer structure without gold nanoparticles, the FRET rate is enhanced by a factor of 80 and the Fo?rster radius increases by 103%. Furthermore, a strong impact of the donor QD properties on the surface plasmon mediated FRET is reported.