Influence of the physicochemical parameters of synthesis on the growth of nanotubes of the Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> composition under hydrothermal conditions

The growth of nanotubes of the Mg₃Si₂O₅(OH)₄ composition with a chrysotile structure has been investigated under hydrothermal conditions. It has been established that the nanotubes in the axial and radial directions grow through the step mechanism due to the recrystallization and mass transfer of the components. The introduction of seeds considerably promotes the growth process, especially at the nanotube ends. The evolution of chrysotile nanotubes with a variation in different physicochemical parameters of synthesis, such as the temperature, time, NaOH concentration in the reaction medium, and introduction of seeds, has been traced. It has been demonstrated that the controllable variation in these parameters makes it possible to perform a controlled hydrothermal synthesis of chrysotile nanotubes with specified lengths and aspect ratios.     

Regularities of the filling of Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> hydrosilicate nanotubes with solutions of sodium hydroxide and sodium chloride

The filling of nanotubes of the synthetic magnesium hydrosilicate Mg₃Si₂O₅(OH)₄ with a chrysotile structure by solutions of sodium hydroxide and sodium chloride has been investigated under different temperature-time conditions.     

Effect of the thermal prehistory of components on the hydration and crystallization of Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes under hydrothermal conditions

The influence of the thermal prehistory of precursors on the phase transformations occurring in the MgO-SiO₂-H₂O(NaOH) system during hydrothermal synthesis of nanotubular magnesium hydrosilicates Mg₃Si₂O₅(OH)₄ with a chrysotile structure is investigated by in situ Calvet calorimetry. It is demonstrated that the preliminary dehydration of the initial solid-phase reactants substantially affects the kinetics of their hydration and subsequent formation of nanotubes with a chrysotile structure.     

Effect of temperature on the synthesis of nanoparticles with different morphology in the system MgO–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O under hydrothermal conditions

Nanoparticles with different morphology have been obtained by hydrothermal method in the system MgO–SiO₂–TiO₂–H₂O. It has been found that in the investigated temperature–time interval the formation of nanotubes of hydrosilicate with the structure of chrysotile with a small amount of impurity phases predominantly takes place.     

Mechanism of formation of the complex oxide Na<Subscript>2</Subscript>Nd<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>10</Subscript>

The processes of phase formation in the Nd₂O₃-TiO₂-Na₂CO₃ system have been investigated in the temperature range 500–1100°C. The mechanism of the high-temperature solid-phase reaction of formation of the complex oxide Na₂Nd₂Ti₃O₁₀ has been studied. It has been established that the Na₂Nd₂Ti₃O₁₀ compound is formed from the intermediate product Na_0.5Nd_0.5TiO₃ with a perovskite structure in the temperature range 830–890°C and from the NaNdTiO₄ oxide with a perovskite-like layered structure in the temperature range 960–1100°C.     

Structure formation during gas-detonation spraying of coatings from composite powders TiAl<Subscript>3</Subscript> and Ni<Subscript>3</Subscript>Al

This paper considers the mechanisms of structure formation during gas detonation spraying of coatings of TiAl₃ and Ni₃Al intermetallic compounds produced under equilibrium and nonequilibrium synthesis conditions. The coating sprayed from TiAl₃ has the same phase composition as the initial powder, regardless of the synthesis conditions. During spraying of Ni₃Al, the structure of the coating also does not depend on the synthesis conditions and consists of two phases — Ni₃Al and NiAl, with the crystal structure varying along the coating thickness. Comparative impact abrasion tests of the coatings showed advantages of TiAl₃ coatings over coatings based on Ni₃Al and titanium diboride. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 106–111, September–October, 2008.     

Thermochemical modification of Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> hydrosilicate nanotubes by silver nitrate solutions

The interaction of an aqueous solution of silver nitrate with Mg₃Si₂O₅(OH)₄ hydrosilicate nanotubes under atmospheric conditions at 50 and 80°C and under dynamic conditions with subsequent annealing at 300°C has been investigated. The intercalation of AgNO₃ solutions into the internal channel and interlayer spaces of the nanotube structure and the crystallization of the silver particles of the spherical shapes on the nanotube surface have been established.     

On the Photomagnetic Properties of the Binuclear Spin Crossover Complexes {[Fe(bt)(NCSe)<Subscript>2</Subscript>]<Subscript>2</Subscript>(bpym)} and {[Fe(bpym)(NCSe)<Subscript>2</Subscript>]<Subscript>2</Subscript>(bpym)}

Infrared and visible light irradiation effects on the spin state of iron(II) ions have been investigated in the binuclear molecules {[Fe(bt)(NCSe)₂]₂(bpym)} (4) and {[Fe(bpym)(NCSe)₂]₂(bpym)} (2). For compound 2 we could observe LIESST and partial reverse-LIESST effects under visible and infrared light irradiation, respectively. Compound 4 exhibits a wavelength-selective photoconversion at 10 K from the low spin (LS–LS) ground state of the binuclear molecule to the metastable high spin (HS–HS) state under visible (785 or 532 nm) light irradiation or to the metastable HS–LS state under infrared (1,342 nm) light irradiation. In addition we also observed the reverse (HS–HS → HS–LS) and the cascade (LS–LS → HS–LS → HS–HS) photoconversions as well. These phenomena lead to complex and original photomagnetic behaviour due to the intramolecular magnetic coupling. This article is dedicated to Professor Didier Astruc in honor of his scientific achievements, with friendship and sincere respect.     

The system SiC–W<Subscript>2</Subscript>B<Subscript>5</Subscript>–LaB<Subscript>6</Subscript>

Experiments and calculations have been applied to the structure of the triple eutectic system SiC–W₂B₅–LaB₆(T _eu = 1900 ± 40°C), composition in mol.%: 10 LaB₆, 44 SiC, 46 W₂B₅, error ±2–3%, which opens up prospects for making ceramic materials for various purposes.     

Oxidative reforming of methane on structured Ni-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite catalysts

The catalytic properties of Ni/Al₂O₃ composites supported on ceramic cordierite honeycomb monoliths in oxidative methane reforming are reported. The prereduced catalyst has been tested in a flow reactor using reaction mixtures of the following compositions: in methane oxidation, 2–6% CH₄, 2–9% O₂, Ar; in carbon dioxide and oxidative carbon dioxide reforming of methane, 2–6% CH₄, 6–12% CO₂, and 0–4% O₂, and Ar. Physicochemical studies include the monitoring of the formation and oxidation of carbon, the strength of the Ni-O bond, and the phase composition of the catalyst. The structured Ni-Al₂O₃ catalysts are much more productive in the carbon dioxide reforming of methane than conventional granular catalysts. The catalysts performance is made more stable by regulating the acid-base properties of their surface via the introduction of alkali metal (Na, K) oxides to retard the coking of the surface. Rare-earth metal oxides with a low redox potential (La₂O₃, CeO₂) enhance the activity and stability of Ni-Al₂O₃/cordierite catalysts in the deep and partial oxidation and carbon dioxide reforming of methane. The carbon dioxide reforming of methane on the (NiO + La₂O₃ + Al₂O₃)/cordierite catalyst can be intensified by adding oxygen to the gas feed. This reduces the temperature necessary to reach a high methane conversion and does not exert any significant effect on the selectivity with respect to H₂.     

Aqueous solutions of cesium salts and cesium hydroxide in hydrosilicate nanotubes of the Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> composition

This paper reports on the results of studies on the filling of nanotubes of the Mg₃Si₂O₅(OH)₄ composition with aqueous solutions of hydroxide, chloride, and nitrate of cesium under different temperature-time conditions. It has been established that the nanotubes differently interact with solutions of different chemical nature.     

Sol-gel synthesis and features of the structure of Au-In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites

The specific features of the chemical state of gold and indium oxide in Au-In₂O₃ (0.01–1.0 wt % Au) nanocomposites have been investigated by the methods of X-ray diffraction analysis, electron microscopy, infrared and optical spectroscopy, electron paramagnetic resonance, and thermal analysis. Xerogels, powders, and films obtained by the introduction of HAuCl₄ into the indium hydroxide sol and thermal treatment at 50–700°C have been studied. The mutual influence of the components on the size of the Au and In₂O₃ particles and the state of their surface has been established. It has been shown that the synthesis of Au-In₂O₃ by the sol-gel method leads to the formation of nanosized indium oxide particles with the high concentration of hydroxyl groups on surfaces and favors the stabilization of gold in the form of nanoclusters and ion forms.     

Temperature programmed desorption of oxygen from Pd films interfaced with Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped ZrO<Subscript>2</Subscript>

The origin of the effect of non-faradaic electrochemical modification of catalytic activity (NEMCA) or Electrochemical Promotion was investigated via temperature-programmed-desorption (TPD) of oxygen, from polycrystalline Pd films deposited on 8 mol%Y₂O₃–stabilized–ZrO₂ (YSZ), an O²⁻ conductor, under high-vacuum conditions and temperatures between 50 and 250 °C. Oxygen was adsorbed both via the gas phase and electrochemically, as O²⁻, via electrical current application between the Pd catalyst film and a Au counter electrode. Gaseous oxygen adsorption gives two adsorbed atomic oxygen species desorbing at about 300 °C (state β₁) and 340–500 °C (state β₂). The creation of the low temperature peak is favored at high exposure times (exposure >1 kL) and low adsorption temperatures (T_ads < 200 °C). The decrease of the open circuit potential (or catalyst work function) during the adsorption at high exposure times, indicates the formation of subsurface oxygen species which desorbs at higher temperatures (above 450 °C). The desorption peak of this subsurface oxygen is not clear due to the wide peaks of the TPD spectra. The TPD spectra after electrochemical O²⁻ pumping to the Pd catalyst film show two peaks (at 350 and 430 °C) corresponding to spillover O_ads and according to the reaction:

Effect of the addition of triphenylphosphine oxide,hexabromocyclododecane, and ethyl bromide on a CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript> flame at atmospheric pressure

The chemical and thermal structure of a Mache-Hebra burner stabilized premixed rich CH₄/O₂/N₂ flame with additives of vapors of triphenylphosphine oxide [(C₆H₅)₃PO], hexabromocyclododecane (C₁₂H₁₈Br₆), and ethyl bromide (C₂H₅Br) was studied experimentally using molecular beam mass spectrometry (MBMS) and a microthermocouple method. The concentration profiles of stable and active species, including atoms and free radicals, and flame temperature pro.les were determined at a pressure of 1 atm. A comparison of the experimental and modeling results on the flame structure shows that MBMS is a suitable method for studying the structure of flames stabilized on a Mache-Hebra burner under near-adiabatic conditions. The relative flame inhibition effectiveness of the added compounds is estimated from changes in the peak concentrations of H and OH radicals in the flame and from changes in the flame propagation velocity. The results of the investigation suggest that place of action of the examined flame retardants is the gas phase. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 12–20, September–October, 2007.     

Glass formation region and order of formation of crystalline phases in the SrO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The glass formation region in the SrO-B₂O₃-SiO₂ system has been refined. The order of formation of crystalline phases in the system has been investigated at SrO contents of 50–75 mol %. It has been demonstrated that, at low temperatures, the 2SrO · SiO₂ and 3SrO · B₂O₃ phases crystallize first irrespective of the composition. The congruent melting temperature of the 3SrO · B₂O₃ · SiO₂ compound is determined to be 1180 ± 10°C. The triangulation previously performed for the SrO-B₂O₃-SiO₂ system in the concentration range 50–75 mol % SrO has been confirmed.     

Experimental study of the structure of a lean premixed indane/CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/Ar flame

In order to better understand the chemistry involved during the combustion of diesel fuel components, the structure of a laminar lean premixed methane flame doped with indane has been investigated. This flame contains 7.1% (molar) of methane, 36.8% of oxygen, and 0.90% of indane, corresponding to an equivalence ratio of 0.74 and a C₉H₁₀/CH₄ ratio of 12.75%, with argon used as a dilutant. The flame has been stabilized on a burner at a pressure of 6.7 kPa, with the gas velocity at the burner exit equal to 49.2 cm/sec at 333 K. Quantified species include usual methane combustion products C₀–C₂, but also eleven C₃–C₅ hydrocarbons and three C₁–C₃ oxygenated compounds, as well as 17 aromatic products, namely benzene, toluene, phenylacetylene, styrene, ethylbenzene, xylenes, trimethylbenzenes, ethyltoluenes, indene, methylindane, methylindene, naphthalene, phenol, benzaldehyde, and benzofuran. The temperature has been measured by a PtRh(6%)-PtRh(30%) thermocouple settled inside the enclosure: from 800 K close to the burner up to 2000 K in the burned gases.     

Electrochemical promotion of CO<Subscript>2</Subscript> hydrogenation on Rh/YSZ electrodes

The electrochemical promotion of the CO₂ hydrogenation reaction on porous Rh catalyst–electrodes deposited on Y₂O₃-stabilized-ZrO₂ (or YSZ), an O²⁻ conductor, was investigated under atmospheric total pressure and at temperatures 346–477 °C, combined with kinetic measurements in the temperature range 328–391 °C. Under these conditions CO₂ was transformed to CH₄ and CO. The CH₄ formation rate increased by up to 2.7 times with increasing Rh catalyst potential (electrophobic behavior) while the CO formation rate was increased by up to 1.7 times with decreasing catalyst potential (electrophilic behavior). The observed rate changes were non-faradaic, exceeding the corresponding pumping rate of oxygen ions by up to approximately 210 and 125 times for the CH₄ and CO formation reactions, respectively. The observed electrochemical promotion behavior is attributed to the induced, with increasing catalyst potential, preferential formation on the Rh surface of electron donor hydrogenated carbonylic species leading to formation of CH₄ and to the decreasing coverage of more electron acceptor carbonylic species resulting in CO formation.     

Synthesis and characterization of zeolite mazzite analogue in Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–Piperazine–H<Subscript>2</Subscript>O

Zeolite Mazzite (MAZ) analogue was synthesized directly using piperazine as a structure directing agent. The reactive gel composition used was (5.0–7.0) piperazine:(6.0–7.0) Na₂O:Al₂O₃:20.0SiO₂:400H₂O. Using this composition, the reaction time was shortened greatly to 4 days and the crystallization time was reduced as well. The DTA data showed that piperazine, in as-synthesized zeolite omega decomposed easily. The decomposition of the piperazine occurred at 400–480°C. NH₃-TPD analysis proved that zeolite H-omega from piperazine had strong surface acidity with ammonia desorption temperature up to 590°C.     

Facile Solvothermal Synthesis Ni(OH)<Subscript>2</Subscript> Nanostructure for Electrochemical Capacitors

Nickel hydroxide nanosheets were successfully synthesized by facile solvothermal method without any template. The structure and morphology of the as-prepared sample were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The observations revealed the formation of hexagonal phase β-Ni(OH)₂ nanosheets with an average diameter of about 100–120 nm. Electrochemical studies were carried out using cyclic voltammetry and galvanostatic charge–discharge tests, respectively. A maximum specific capacitance of 2,342 F g⁻¹, which is the highest reported for a β-Ni(OH)₂ electrode, could be achieved in 6 mol L⁻¹ KOH electrolyte within the potential range of 0–0.50 V (vs. SCE) for the obtained β-Ni(OH)₂ electrode at 0.4 A g⁻¹, suggesting its potential application in the electrode material for electrochemical capacitors.     

Structure and properties of solid solutions of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Pr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>BaCuFeO<Subscript>5 + δ</Subscript>

The effect of replacing lanthanum with praseodymium on the crystal chemistry parameters of solid solutions of La_{1 − x} Pr _x BaCuFeO_{5 + δ} has been investigated using X-ray powder diffraction analysis and IR spectroscopy. The thermal expansion, electroconductivity, and thermopower of these phases have been studied in air in the temperature range 300–1100 K. The values of linear thermal expansion coefficients (LTEC) of ceramics in different temperature ranges have been determined, and the values of electric transfer parameters in the above oxides have been calculated. It has been established that replacing lanthanum with praseodymium resulted in the compression of the elementary oxide unit La_{1 − x} Pr _x BaCuFeO_{5 + δ}, decrease in the content of labile oxygen in them (δ), decrease in nonmonotonic electroconductivity, increase in thermopower, decrease in LTEC, and difficulties in charge transfer in these phases.