Phase Equilibrium States in the <Emphasis Type="Italic">n</Emphasis>-Dodecane–<Emphasis Type="Italic">n</Emphasis>-Hexadecane–Cyclododecane System

A three-component system comprising cyclododecane and n-alkanes is studied by means of differential thermal analysis on a differential scanning microcalorimeter. It is concluded that the investigated system is of the eutectic type and the n-dodecane–n-hexadecane–cyclododecane eutectic mixture system is 73.0 wt % n-С₁₂Н₂₆, 9.0 wt % n-С₁₆Н₃₄, and 18.0 wt % С₁₂Н₂₄. Its melting point is found to be ?17.7°C.     

Synthesis of nitrogen-containing carbon materials for solid polymer fuel cell cathodes

The following nitrogen-containing supports with various nitrogen contents and structure and texture properties were synthesized: carbon nanofibers (N-CNFs) and amorphous microporous carbon materials (N-AMCMs). It was found that the above characteristics can be regulated by varying synthesis conditions: precursor compositions and reaction temperature and time. Mesoporous nitrogen-containing CNFs with a specific surface area of 30–350 m²/g and a pore volume of 0.10–0.83 cm³/g were formed by the catalytic decomposition of a mixture of ethylene with ammonia at 450–675°C. Microporous materials (N-AMCMs) with a specific surface area of 472–3436 m²/g and a micropore volume of 0.22–1.88 cm³/g were prepared by the carbonization of nitrogen-containing organic compounds at 700–900°C. An increase in the carbonization temperature and reaction time resulted in an increase in the specific surface area and microporosity of N-AMCMs, whereas lower temperatures of 450–550°C and reaction times of 1–3 h were optimal for the preparation of N-CNFs with a developed texture. It was found that milder synthesis conditions and higher nitrogen contents of precursors were required for obtaining high nitrogen concentrations in both N-CNFs and N-AMCMs. The synthetic method developed allowed us to prepare carbon supports with nitrogen contents to 8 wt %.     

Synthesis and van Alphen–Hüttel rearrangement of substituted 3<Emphasis Type="Italic">H</Emphasis>-pyrazoles,adducts of 1,3-dipolar cycloaddition of 9-diazofluorene and diphenyldiazomethane to trimethyl(tosylethynyl)silane

Trimethyl(tosylethynyl)silane reacted in ethyl ether at 20°С with diphenyldiazomethane affording 3Н-pyrazole, a product of 1,3-dipolar cycloaddition against Auwers rule. The reaction with 9-diazofluorene is less selective, but its regioselectivity is also governed by the steric effect of the bulky trimethylsilyl substituent at the triple bond С≡С. The adduct with diphenyldiazomethane at boiling in methanol or keeping in glacial acetic acid in the presence of a catalytic quantity of conc. H₂SO₄ undergoes the Van Alphen–Hüttel rearrangement by the migration of the phenyl substituent to the atom N² in the 1Н-pyrazole. The same 1Н-pyrazole together with a product of nitrogen elimination, trimethylsilyl substituted cyclopropane, is formed in the 2: 1 ratio at boiling in benzene. A similar behavior is observed in the glacial acetic acid for the anti-Auwers adduct of 9-diazofluorene. It suffers nitrogen elimination at boiling in benzene converting in spirocyclic cyclopropene. The Auwers adduct of 9-diazofluorene at boiling in methanol transforms due to the van Alphen–Hüttel rearrangement into the corresponding 4Н-pyrazole that undergoes a hydrodesilylation to give a derivative of 1Н-pyrazole, 3-tosyl-1(2)H-dibenzo[e,g]indazole.     

Preparation and TG—DTA analysis of manganese silicon nitride

Manganese silicon nitride was prepared quantitatively as a precipitated phase by treating a Mn; Si-alloy (Mn: 1.84 w/o, Si: 1.12 w/o) in a mixture of 2% NH₃ and H₂ at 700°C. Nitriding was carried out in situ in a thermobalance and the nitrogen uptake was recorded as a function of time. The nitride phase was isolated and investigated by means of the combined TG-DTG-DTA technique both in an atmosphere of nitrogen at 25–1600°C and in a mixture of Ar+O₂ (p_O2 = 0.20 atm) at 25–1000°C. In the nitrogen atmosphere MnSiN₂ appears to be stable up to 1000°C. Oxidising the nitride in the Ar/O₂ mixture caused three distinct exothermic processes to occur at characteristic temperatures. The final oxidation products as identified by diffractometry and IR-spectroscopy are manganese oxide silicate (braunite) and silicon dioxide.     

Purified oxygen- and nitrogen-modified multi-walled carbon nanotubes as metal-free catalysts for selective olefin hydrogenation

Oxygen- and nitrogen-functionalized carbon nanotubes (OCNTs and NCNTs) were applied as metal-free catalysts in selective olefin hydrogenation. A series of NCNTs was synthesized by NH₃ post-treatment of OCNTs. Temperature-programmed desorption, N₂ physisorption, Raman spectroscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were employed to characterize the surface properties of OCNTs and NCNTs, aiming at a detailed analysis of the type and amount of oxygen- and nitrogen-containing groups as well as surface defects. The gas-phase treatments applied for oxygen and nitrogen functionalization at elevated temperatures up to 600 °C led to the increase of surface defects, but did not cause structural damages in the bulk. NCNTs showed a clearly higher activity than the pristine CNTs and OCNTs in the hydrogenation of 1,5-cyclooctadiene, and also the selectivity to cyclooctene was higher. The favorable catalytic properties are ascribed to the nitrogen-containing surface functional groups as well as surface defects related to nitrogen species. In contrast, oxygen-containing surface groups and the surface defects caused by oxygen species did not show clear contribution to the hydrogenation catalysis.     

The effect of annealing temperatures on surface properties,hydroxyapatite growth and cell behaviors of TiO2 nanotubes

Well‐ordered TiO₂ nanotubes were prepared by the electrochemical anodization of titanium in an ethylene glycol electrolyte containing 1 wt% NH₄F and 10 wt% H₂O at 20 V for 20 min, followed by annealing. The surface morphology and crystal structure of the samples were examined as a function of the annealing temperature by field emission scanning electron microscopy (FE‐SEM) and X‐ray diffraction (XRD), respectively. Crystallization of the nanotubes to the anatase phase occurred at 450 °C, while rutile formation was observed at 600 °C. Disintegration of the nanotubes was observed at 600 °C and the structure vanished completely at 750 °C. Electrochemical corrosion studies showed that the annealed nanotubes exhibited higher corrosion resistance than the as‐formed nanotubes. The growth of hydroxyapatite on the different TiO₂ nanotubes was also investigated by soaking them in simulated body fluid (SBF). The results indicated that the tubes annealed to a mixture of anatase and rutile was clearly more efficient than that in their amorphous or plain anatase state. The in vitro cell response in terms of cell morphology and proliferation was evaluated using osteoblast cells. The highest cell activity was observed on the TiO₂ nanotubes annealed at 600 °C. Copyright © 2010 John Wiley & Sons, Ltd.     

Phase Diagrams of the <Emphasis Type="Italic">n</Emphasis>-Decane–<Emphasis Type="Italic">n</Emphasis>-Hexadecane–Cyclododecane, <Emphasis Type="Italic">n</Emphasis>-Decane–Cyclododecane,and <Emphasis Type="Italic">n</Emphasis>-Hexadecane–Cyclododecane Systems

The n-decane–n-hexadecane–cyclododecane, n-decane–cyclododecane, and n-hexadecane–cyclododecane systems are studied by means of low-temperature differential thermal analysis using a differential scanning heat flow calorimeter. It is noted that all studied systems belong to the eutectic type. It is concluded that in the n-decane–n-hexadecane–cyclododecane system, the eutectic composition contains 85.0 wt % n-С₁₀Н₂₂, 4.0 wt % n-С₁₆Н₃₄, and 11.0 wt % С₁₂Н₂₄. It has a melting point of ?35.0°C.     

Magnetic resonance study of carbon encapsulated Ni nanoparticles

Magnetic resonance study of six samples consisting of carbon encapsulated nickel nanoparticles or carbon nanotubes ended with such nickel nanoparticles was carried out at room temperature. Samples of Ni/C were prepared by carburization of nanocrystalline nickel by ethylene (C₂H₄) and methane (CH₄). Hydrocarbons decomposition on nickel nanoparticles was done at temperatures 500, 600 and 700°C. Magnetic resonance spectra of samples designated as CH₄/500, CH₄/600, CH₄/700, C₂H₄/500, C₂H₄/600 and C₂H₄/700 were obtained by Bruker E 500 spectrometer. The integrated intensities of the resonance spectra were correlated with the carburization conditions (temperature, type of hydrocarbon) during samples preparation. A core-shell model of the investigated samples allowed rough estimation of appropriate shell sizes.      

The features of ignition of hydrogen–methane and hydrogen–isobutene mixtures with oxygen over Rh and Pd at low pressures

The flammability limits of stoichiometric mixtures (20–80% H₂ + 80–20% CH₄) + O₂ over Rh and Pd were determined in the pressure range 0–200 Torr and the temperature range 200–500 °C. It has been shown that the dark reaction in the mixture (80% H₂ + 20% C₄H₈)_stoich + O₂ leads to the formation of carbon nanotubes with a mean diameter of 10–100 nm.     

Coprecipitation of calcium hydroxyapatite,graphene oxide,and chitosan from aqueous solutions

We determined the character of interactions between calcium hydroxyapatite Са₁₀(РO₄)₆(ОН)₂ (HA), graphene oxide (GO), and chitosan (С₆Н₁₁NO₄) _n (CHT) to yield HA/CHT/GO nanocomposites (NCs) in the СаС1₂–(NH₄)₂НРО₄–NH₃–Н₂О–(С₆Н₁₁NO₄) _n –GO system (25°С). A set of physicochemical methods helped us to elucidate composition–synthesis parameters–structure–particle size–properties correlations for the prepared NCs and to prove the feasibility to manufacture NCs with tailored HA, CHT, and GO contents, described by the bulk formula Са₁₀(РО₄)₆(ОН)₂ · х(С₆Н₁₁NO₄) _n · yGO · zН₂О, where х = 0.1, 0.2, 0.3; y = 0.6, 1.2, 2.4; and z = 6.0–7.4.     

Adsorption-Induced Deformation of Adsorbents

Adsorption-induced deformation of AR-V and AUK carbon adsorbents and NaX zeolite has been studied upon adsorption of n-С₅Н₁₂, n-С₆Н₁₈, n-С₇Н₁₆, and CO₂ at temperatures of 193?423 K. It has been shown that adsorption-induced deformation is positive upon the physical adsorption of gases and vapors on the surface of a nonporous (macroporous) solid when the excess adsorption is positive. When calculating the adsorption-induced deformation in the region of the capillary-condensation filling of mesopores, the additional pressure in capillaries, which is negative (contraction of an adsorbent), must be taken into account in the case of wetting a solid surface with a liquid adsorbate. The compressibility of AUK microporous carbon adsorbent as a porous solid is almost independent of the temperature and the properties of an adsorbate, and, for adsorption of n-C₅H₁₀ and n-C₇H₁₆ hydrocarbons and CO₂, it is γ_а = (5.6 ± 0.6) × 10^?6 bar^?1. The compressibility of AUK adsorbent appears to be 87% higher than that of nonporous graphite.     

Enhanced methane decomposition over transition metal-based tri-metallic catalysts for the production of COx free hydrogen

In this study, COx-free hydrogen production via methane decomposition was studied over Cu–Zn-promoted tri-metallic Ni–Co–Al catalysts. The catalysts have been prepared by the constant pH co-precipitation method, and the nominal Ni metal loading was fixed at 50 wt % along with other metals at 10 wt% each. The catalyst activity for methane decomposition reaction was examined in a reactor between 400 °C and 700 °C and at atmospheric pressure. Different techniques such as N₂-physisorption, X-ray diffraction, H₂-TPR SEM, TEM, ICP-MS, TGA, and Raman spectroscopy were applied to characterize the catalysts. The relation between the catalyst composition and their catalytic activity has been investigated. The controlled synthesis has resulted in a series of catalysts with a high surface area. Ni–Co–Cu–Zn–Al was the most active and productive catalyst. Various characterizations indicate that the promotional effects of Cu–Zn interaction were the critical factor in catalysts' activity and stability. Ni–Co–Cu–Zn catalyst gave the highest methane conversion of 85% at 700 °C. Zn addition improves the stability of the catalyst by retaining the active metal size during the decomposition reaction. The catalyst was active for 80 h of stability study. The rapid deactivation of the Ni–Co catalyst was due to the sintering of the catalyst at 650 °C. Moreover, carbon species accumulated during the methane decomposition reaction depend on the catalysts' composition. Zn promotes the growth of reasonably long and thin carbon nanotubes, whereas the diameter of carbon nanotubes on unpromoted catalysts was large.     

Phase Equilibria in the K,Cа∥SO<Subscript>4</Subscript>,CO<Subscript>3</Subscript>,HCO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O System at 25°С

Phase equilibria in the system K,Cа∥SO₄,CO₃,HCO₃–H₂O have been studied at 25°С. This system at 25°С involves 7 invariant points, 21 monovariant curves, and 22 divariant fields. The data gained served to plot the first phase diagram (phase complex) of the studied system at 25°С.     

Neutron diffraction study of dehydrogenation of titanium carbohydrides TiC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

The possibility of the synthesis of hydrogen-nonstoichiometric cubic titanium carbide ТiС _х of high purity from powdery nonstoichiometric cubic titanium carbohydride ТiС _х H _y or nonstoichiometric titanium carbide with admixture hydrogen by annealing in a continuously maintained vacuum of no worse than 1.33 × 10^–3 Pa at temperatures of 600–750°C for several hours has been shown. Similar annealing at higher temperatures (T ≥ 800°C) does not lead to the complete removal of hydrogen from a sample due to intensive sintering. In this case, it seems that pores between sintered particles are hydrogen traps, and the release of hydrogen through the surface of sintered particles is hindered.     

Charge Transfer and Defect Structure in BaCeO<Subscript>3</Subscript>

Electrical conductivity (at 460–990°С) and ion and proton transference numbers (at 550–950°С) of nominally undoped BaCeO₃ have been studied as dependent on temperature, pO₂ (2.1 × 10^–4 to 10–15 Pa), and pН₂O (40–2340 Pa). For determining the defect model, small additives of aliovalent dopants Nd³⁺ (up to 1 at %) and Ta⁵⁺ (up to 0.5 at %) were used. The effect of cationic nonstoichiometry of barium cerate on the electrical conductivity and reaction with the gas phase has been considered. Charge transfer in ВаСеО₃ is explained using the model of defect formation in the reaction of ВаСеО₃ with the gas phase.     

Effect of oxidative treatment on the electrochemical properties of aligned multi-walled carbon nanotubes

Vertically aligned multi-walled carbon nanotubes (MWNTs) were grown on the surface of electroconductive silicon substrate by catalytic chemical vapor deposition (CCVD) of a mixture of toluene and ferrocene vapors at 800°С. The anisotropic structure of the array that is due to the mutual orientation of MWNTs makes such materials attractive for use as supercapacitor electrodes. The effect of iron nanoparticles encapsulated in MWNTs as a result of synthesis on the electrochemical capacity of the sample in a 1 М H₂SO₄ solution was studied. Iron was removed during the thermal treatment of the MWNT array in a 20% H₂SO₄ solution under the normal or hydrothermal conditions. The contribution of redox processes involving iron was shown to be comparable to the contribution of the double-layer capacity of MWNTs. The hydrothermal treatment allows easy separation of the array from the silicon substrate without any loss of electric coupling of MWNTs.     

CO oxidation by oxygen of the catalyst and by gas-phase oxygen over (0.5–15)%CoO/ZrO<Subscript>2</Subscript>

CO adsorption on (0.5–15)%CoO/ZrО₂ catalysts has been investigated by temperature-programmed desorption and IR spectroscopy. At 20°С, carbon monoxide forms carbonyl and monodentate carbonate complexes on Co _m ²⁺ O _n ^2- clusters located on the surface of crystallites of tetragonal ZrO₂. With an increasing CoO content of the clusters, the amount of these complexes increases and the temperature of carbonate decomposition, accompanied by CO₂ desorption, decreases from 400 to 304°С. On the 5%CoO/ZrО₂ sample, the carbonyls formed on the Со²⁺ and Со⁺ cations and Со⁰ atoms decompose at 20, 90, and 200–220°С, respectively, releasing CO. At 20°С, they are oxidized by oxygen to monodentate carbonates, which decompose at 180°С. Adsorbed oxygen decreases the temperature of their decomposition on oxidation sites by ~40°C, and the sample remains in an oxidized state ensuring the possibility of subsequent CO adsorption and oxidation. The rate of the oxidation of 5%CoO/ZrО₂ containing adsorbed CO by oxygen is higher than the rate of the oxidation of the same sample reduced by carbon monoxide, because the latter reaction is an activated one. In view of the properties of the complexes, it can be concluded that the carbonates decomposing at 180°С are involved in CO oxidation by oxygen from the gas phase in the presence of hydrogen, a process occurring at 50–200°С. The rate-limiting step of this process the decomposition of the carbonates, which is characterized by an activation energy of 77–94 kJ/mol.     

Polyacrylonitrile-based FeCo/C nanocomposites: Preparation and magnetic properties

Metal–carbon nanocomposites that represent FeCo alloy nanoparticles uniformly distributed over the carbon matrix, were prepared by the IR pyrolysis of precursors comprising polyacrylonitrile (PAN), iron acetylacetonate, and cobalt acetate (the metal ratio in the precursors was Fe: Co = 1: 1, 3: 1). The composition of FeCo alloy nanoparticles satisfies the tailored ratio Fe: Co. The FeCo phase is formed at synthesis temperatures in the range 500–600°С; at T ≤ 500°С only FCC-Co-base solid solutions are observed. The nanocomposites prepared at T ≥ 600°С simultaneously contain FeCo intermetallic nanoparticles and an insignificant amount of a FCC-Co phase or a cobalt-base solid solution phase. The saturation magnetization of FeCo/C metal–carbon nanocomposites is determined by the mean nanoparticle size and the alloy composition, and ranges from 36 to 64 (A m²)/kg (when Fe: Co = 1: 1) and from 35 to 52 (A m²)/kg (when Fe: Co = 3: 1) at synthesis temperatures in the range 600–800°С.     

Formation of carbon nanotubes from a silicon carbide/carbon composite

The reaction of a SiC/C composite powder in an arcing plasma forms carbon nanotubes in good yield. Besides carbon nanotubes, a Si/C composite composed of β SiC covered with a shell of graphite is formed. The graphitic carbon surface layers of the carbon shell of this composite reacts further to form carbon nanotubes when heated to 600 °C. This process seems highly effective since only a small overall low weight loss, indicative for a complete carbon shell oxidation is observed by thermal analysis. The formation of the carbon nanotubes from SiC is unlikely since no SiO₂ has been found when heating the SiC/C core shell composite to its reaction temperature of 600 °C under O₂. The CNTs formed are of good quality with 3 to 6 concentric walls and high aspect ratio. Occasionally even single walled carbon naotubes have been observed.     

Conducting carbon-nitrogen pyropolymers derived from cyanogen

Electropolymerization of cyanogen in acetonitrile containing an electrolyte yields a poly(cyanogen). Its structure involves an open-structured dimer derived from the heterocyclic anion C₇N₇? mixed with a sequence of nitrile-substituted, conjugated carbon–nitrogen bonds. Although this polymer is an insulating solid, pyrolysis in vacuo to 700°C leads to highly conducting carbon–nitrogen pyropolymers via crosslinking and nitrogen elimination. The 700° pyropolymer has a carbon–nitrogen ratio of 5:1, a room temperature conductivity of 1 Ω^?1 cm^?1, and an activation energy for conduction of ～0.03 eV.