Russian Journal of Physical Chemistry B最新文献

The mechanism of the initiation of isoolefins in the presence of ethylaluminum dichloride–proton donor (water, phenol, hydrochloric acid) complex catalysts is studied by ab initio HF.3.21G. The energetics of these reactions is estimated, and the values of its activation energy and thermal effects are obtained. It is found that among the studied catalysts, an increase in the activation energy of the reaction of the initiation of oligomerization of isoolefins contributes to an increase in the selectivity of the process.

Intermetallic alloys are synthesized in the 5Ti + 3Si + xNi system by the method of self-propagating high-temperature synthesis (SHS) and mechanosynthesis. The influence of the nickel content on the morphology, size, and yield of composite particles after the mechanical activation (MA) of the mixtures is studied. The dependencies of the maximum temperatures and combustion rates, phase composition, morphology, and elongation of synthesis products on the nickel content for the initial and MA mixtures are studied. Under the conditions of the experiments conducted in this study, the combustion process is realized and at the same time the samples burn completely at a nickel content of 10 to 60 wt % in the 5Ti + 3Si + xNi system. After the MA, the samples from the 5Ti + 3Si mixture burn completely, and during the activation of the 5Ti + 3Si + 40% Ni mixture, mechanochemical synthesis takes place. With the increasing nickel content, the combustion temperature decreases, and the combustion rate behaves nonmonotonically, the size of composite particles increases and the yield of the mixture after MA decreases. MA practically does not affect the maximum combustion temperatures of mixtures of 5Ti + 3Si + xNi. A multiple (from 0.7 to 2.9 cm/s) increase in the burning rate of samples from MA mixtures with an increase in the Ni content from 20 to 30 wt % is recorded. An increase in the nickel content leads to an increase in the content of triple phases and the amount of melt in the synthesis products of mixtures of 5Ti + 3Si + xNi.

Impurity paramagnetic ions Mn²⁺ and high spin Fe³⁺ (S = 5/2) are shown to be very informative paired spin labels to investigate structural transformations in natural aluminosilicate clay minerals by ESR spectroscopy. Second derivative ESR (SD ESR) enables to detect minor narrow lines of the ions against the background of intense broad lines of other paramagnetic impurities. Complex SD ESR spectra of the ions are explained by the Jahn-Teller effect and hyperfine interactions with OH-groups. SD ESR spectra before and after heating (620 and 900°C) proved transformations of octahedral crystal cells accompanied by the loss of the OH-groups, displacement of the ions to equivalent positions.

Gallium nitride (Ga–N) nanocage can effectively remove alkali and alkaline earth metal ions from water. Therefore, it has been found a selective competition for metal cations in the Ga–N. The electronic, magnetic and thermodynamic properties of alkali-alkaline earth metal ion-adsorbed Ga–N have been investigated using density functional theory. The results denote that alkali/alkaline earth-metal ion-adsorbed Ga–N systems are stable compounds, with the most stable adsorption site being the center of the cage ring. In addition, because of charge transfer from Ga–N to the alkali/alkaline earth-metal cations show clear n-type adsorbing behavior. The absorption of alkali metal atoms on alkali/alkaline earth-metal cations occur via chemisorption. In this article, the behavior of trapping of main group cations of Li⁺, Na⁺, K⁺, Be²⁺, Mg⁺ and Ca²⁺ by gallium nitride nanocone was observed for sensing the water metal cations. The essence of covalent traits for these clusters has displayed the similar energy value and image of the PDOS for the p states of N, the d states of Ga and s orbitals of metal cations including Li⁺, Na⁺, K⁺/Be²⁺, Mg²⁺ and Ca²⁺ through water treatment. The partial density of states (PDOS) can also estimate a certain charge assembly between Li⁺, Na⁺, K⁺/Be²⁺, Mg²⁺ and Ca²⁺ and Ga–N which indicate the complex dominant of metallic features and an exact degree of covalent traits between alkali/alkaline earth-metal cations and gallium nitride nanocage. Furthermore, the NMR spectroscopy has indicated the remarkable peaks around metal elements of Li⁺, Na⁺, K⁺, Be²⁺, Mg⁺ and Ca²⁺ through the trapping in the Ga–N during ion detection and removal from water; however, there are some fluctuations in the chemical shielding behaviors of isotropic and anisotropy attributes. In addition, all accounted (Delta G_{R}^{o}) amounts are very close, which demonstrate the agreement of the measured specifications by all methodologies and the reliability of the computing values.

In this article, the characterization of intermetallic MgAl and the possibility for hydrogen storage in the fuel cells through doping with transition metals including Ni, Pd, Pt, Cu, Ag and Au have been investigated. The importance of the electrical double layer at the interface between a metal and Mg/Al atoms together with its interaction with hydrogen molecule to produce initially electrostatic adsorption are highlighted. The important step in which molecules enable energy storage is production of a physical barrier where a physical adsorbed barrier of molecules prevent movement near the metal surface or decrease in metal reactivity where chemisorbed hydrogen molecule stick to active area on the metal surface. The projected density of state can also estimate a certain charge assembly between (Ni, Pd, Pt, Cu, Ag, Au) and MgAl surface which indicate the complex dominant of metallic features and an exact degree of covalent traits between transitions metals and MgAl surface during H₂ adsorption. In the nuclear magnetic resonance spectroscopy, it has been observed the remarkable peaks around metal elements of Ni, Pd, Pt, Cu, Ag, Au through the doping on the MgAl nanoalloy, however there are some fluctuations in the chemical shielding behaviors of isotropic and anisotropy attributes. Furthermore, all accounted (Delta G_{{{text{dop}}}}^{o}) amounts are very close, which demonstrate the agreement of the measured specifications by all methodologies and the reliability of the computing values.

The effect of mechanical activation (MA) and the cobalt content on the combustion velocity, maximum combustion temperature, elongation of samples during synthesis, the size of composite particles of the mixture after MA, phase composition, and morphology of combustion products in the Ni + Al + Co system is studied. Activation of the Ni + Al + xCo mixture allowed the samples to burn at room temperature, with a cobalt content of up to 50 wt %. An increase in the cobalt content in the Ni + Al + xCo mixtures led to a decrease in the size of composite particles after MA, elongation of product samples, and the maximum synthesis temperature. After MA, the elongation of the product samples and combustion velocity increased many times, and the maximum synthesis temperature increased. With an increase in the cobalt content in the Ni + Al + Co mixture, the combustion velocity first increases (at Co content of 10%), then decreases. Solid solutions based on NiAl and Ni₃Al intermetallic compounds are synthesized by the self-propagating high-temperature synthesis (SHS) method.

Hydrogen fuel is a promising route to remark on the energy and environmental challenges facing the world today. Therefore, hydrogen storage has become enhancing essential for progressing cleaner and more sustainable technologies. Recent research has recognized metal and metalloid hydrides as a promising alternative that might suggest some benefits over compressed storage. In this work, a profound study on the adsorption of hydrogen by nanocone carbides of main group elements including Si, Ge, Sn and Pb has been done including both geometrical and electronic properties using density functional calculations. The effect of substituting silicon (Si) in silicon carbide by germanium (Ge), tin (Sn) or lead (Pb) elements on the geometrical structure and H atom adsorption behavior were investigated. The results show that when Si atoms are replaced by a Ge, Sn or Pb atoms, the hydrogen adsorption energy is greatly enhanced. Thermochemical, electric and magnetic properties of SiC, GeC, SnC and PbC nanocones and SiC–6H, GeC–6H, SnC–6H and PbC–6H nanocones hydrides are studied by the first-principles methods based on the density functional theory for adsorbing hydrogen atoms. The assumption of the chemical adsorption has been approved by the projected density of states and charge density difference plots. Charge density difference calculations also indicate that the electronic densities were mainly accumulated on the adsorbate of hydrogen atoms. Therefore, these results indicate that the SiC, GeC, SnC and PbC nanocones can be considered as good candidates for hydrogen adsorption and might be helpful for fabricating nano-devices such as hydrogen storage nanomaterials.

The temperature and pH responsive hydrogels of the polymer(N-vinylcaprolactam-crotonic acid-2-hydroxyethyl acrylate) and polymer(N-vinylcaprolactam-crotonic acid-2-hydroxyethyl methacrylate) were prepared by free radical polymerization using N-vinylcaprolactam, crotonic acid, 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate as raw materials. In the polymer(N-vinylcaprolactam-crotonic acid-2-hydroxyethyl acrylate/2-hydroxyethyl methacrylate) hydrogels, N-vinylcaprolactam is the temperature sensitive component, and crotonic acid is pH sensitive component. Six the polymer(N-vinylcaprolactam-crotonic acid-2-hydroxyethyl acrylate/2-hydroxyethyl methacrylate) hydrogels with different 2-hydroxyethyl acrylate/2-hydroxyethyl methacrylate contents were prepared. The chemical structure and morphology of the polymer(N-vinylcaprolactam-crotonic acid-2-hydroxyethyl acrylate/2-hydroxyethyl methacrylate) hydrogels were characterized by fourier transform infrared spectrum and scanning electron microscopy, respectively. The swelling kinetic curves and equilibrium swelling ratios under different temperature and pH of the polymer(N-vinylcaprolactam-crotonic acid-2-hydroxyethyl acrylate/2-hydroxyethyl methacrylate) hydrogels were tested. Mechanical properties of the two hydrogels were determined by compressive testing. Results show that the 2-hydroxyethyl acrylate/2-hydroxyethyl methacrylate content in the polymer(N-vinylcaprolactam-crotonic acid-2-hydroxyethyl acrylate/2-hydroxyethyl methacrylate) hydrogels affects the pore size, swelling ratio and mechanical properties. Compared with the polymer(N-vinylcaprolactam-crotonic acid-2-hydroxyethyl methacrylate) hydrogel, the polymer(N-vinylcaprolactam-crotonic acid-2-hydroxyethyl acrylate) hydrogel has higher swelling properties and mechanical properties due to its uniform network structure.

Earlier, by comparing the results of mathematical modeling with experimental data on the nonideal detonation velocities of triple mixtures of nitromethane (NM) and ammonium perchlorate (AP) with an excess of aluminum (Al), the rates of exothermic reactions and the consumption degree of components within the detonation wave reaction zone were determined. A quasi-one-dimensional model of steady detonation is used for the calculations in which all components have a common pressure and move with a common mass velocity, and exothermic conversion is carried out in three stages, which include the decomposition of NM and AP and the diffusion combustion of Al. To confirm the obtained results and the applicability of the relatively simple theoretical model, calculations of the mass velocity profile during detonation of one of the triple mixtures with 17% NM are carried out. The calculation results are in agreement with the measured mass velocity profile concerning the shape of the profile, the amplitude, and the rate of decrease of the mass velocity along the detonation reaction zone. The rise time of the sensor signal is estimated, taking into account the calculated curvature of the shock front of the detonation wave.

The thermal stability of the propargyl derivatives of 7H-difurazanofuroxanoazepine and 7H-trifurazanoazepine in the isothermal and nonisothermal modes is studied. Formal kinetic regularities of the decomposition and temperature dependencies of the reaction rate constants are determined. The thermal stability of propargyl, cyanomethyl, allyl, and amine derivatives of azepines is compared.