Synthesis and properties of the composite ceramics from nanocrystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-30% Y<Subscript>0.1</Subscript>Zr<Subscript>0.9</Subscript>O<Subscript>2</Subscript> prepared from a water-alcohol solution

The hydrogel of the mixed oxide Al₂O₃-30% Y_0.1Zr_0.9O₂ was prepared by precipitation of ammonia from a water-alcohol mixture (1 : 5). The Al₂O₃-30% Y_0.1Zr_0.9O₂ compound thus synthesized was characterized using differential scanning calorimetry, transmission electron microscopy, and the BET adsorption method. The obtained sample consisted of spherical particles with an average size of 16–20 nm and a specific surface area of 167 m²/g. The Al₂O₃-30% Y_0.1Zr_0.9O₂ powder was pressed at 300 MPa and then calcinated at 1600°C for 2 h in air. The topographic and structural features of the prepared ceramics were determined using atomic force microscopy and X-ray electron probe microanalysis. The porosity, the Vickers microhardness, and the tensile strength were determined by mercury porometry.     

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.     

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.     

Study on the properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-BaO lead-free glass using in the electronic pastes

The Sb₂O₃ doping lead-free glass in Bi₂O₃-B₂O₃-BaO ternary system were prepared in the composition of several different subsystem, and the glass powder was produced through the process of water quenching. Glass transition temperatures (T _g ), glass soften temperatures(T _s ), the volume resistivity (ρ) in the temperature range of 80–200°C, and linear thermal coefficients of expansion in the temperatures range of 25–300°C (α_25–300) were measured for subsystems along with the different ratio of Bi₂O₃, B₂O₃ and BaO. For these subsystems, T _g ranged from 458 to 481°C, and T _s ranged from 490 to 512°C, both decreasing with the increasing of Bi₂O₃/B₂O₃ ratio, and increasing with the increasing of BaO/B₂O₃ ratio. The measured α_25–300 ranged from 65.3 to 76.3 × 10⁻⁷ K⁻¹, with values increasing with increasing Bi₂O₃/B₂O₃ and BaO/B₂O₃ ratio. The volume resistivity remains at a high standards, which may caused by it’s non-alkali composition, and it fluctuated from 10¹³ to 10¹¹ Ω cm with the temperature varied from 80–200°C. The structure of Bi₂O₃-B₂O₃-BaO ternary leadfree glass system was mearsured by FT-IR. The IR studies indicate that these glasses are made up of [BiO₆], [BO₃], and [BO₄] basic structural units, and it appears that Ba²⁺ acts as a glass-modifier in this ternary system, but the Bi³⁺ has entered the glass network when it is in relative high content so as to change the α_25–300, T _s and T _g .     

Sintering of SHS-produced α-Si<Subscript>3</Subscript>N<Subscript>4</Subscript>, α-SiAlON,and β-SiAlON

Explored was the sintering of SHS-produced α-Si₃N₄, α-SiAlON, and β-SiAlON in the presence of sintering aids such as Y₂O₃ and Al₂O₃. Process conditions were optimized to prepare sintered sialon ceramics with a high relative density and good strengths characteristics.     

Investigation of the conditions for synthesis of Ce<Subscript>0.9</Subscript>Y<Subscript>0.1</Subscript>O<Subscript>2</Subscript> dense coatings

The conditions for preparation of Ce_0.9Y_0.1O₂ (CYO) oxide coatings on La_0.8Sr_0.2MnO₃ (LSM) ceramic substrates by screen printing were investigated. The CYO compound was synthesized by the pyrolysis of polymer-salt composites with the aim of producing submicron powders with a uniform size distribution. Transmission electron microscopy of the microstructure of the CYO compound synthesized with ethylene glycol revealed that the synthesis product consists of ultrafine crystalline particles with an average size of 5–15 nm. The use of CYO nanopowders made it possible to prepare rather dense single-layer coatings on LSM substrates. It was demonstrated that annealing of the coatings at high temperatures leads to the recrystallization and coarsening of particles.     

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.     

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:

Hydrothermal synthesis of nanotubes based on (Mg,Fe,Co,Ni)<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> hydrosilicates

Hydrosilicate nanotubes of the variable composition (Mg,Fe,Co,Ni)₃Si₂O₅(OH)₄ with a chrysotile structure have been synthesized under hydrothermal conditions at temperatures of 250–450°C and pressures of 30–100 MPa in media of different compositions. The conditions and ranges of formation of nanotubular hydrosilicates of the compositions under investigation have been determined. It has been demonstrated that the type of cation of the octahedral layer in the chrysotile structure has a decisive effect on the physicochemical conditions, mechanism, and rate of formation of nanotubes, as well as on their structure, morphology, and sizes.     

The Effect of Sulfur on ZrO<Subscript>2</Subscript>-Based Biomass Gasification Gas Clean-Up Catalysts

The effect of sulfur on biomass gasification gas clean-up over ZrO₂, Y₂O₃–ZrO₂ and SiO₂–ZrO₂ catalysts was examined. Experiments were carried out at the temperature range of 600–900 °C with sulfur free and 100 ppm H₂S containing simulated gasification gas feeds. A mixture of toluene and naphthalene was used as a tar model compound. Results revealed that the sulfur addition affected positively on the catalyst properties mainly at 600 and 700 °C: over Y₂O₃–ZrO₂ and ZrO₂ sulfur addition improved naphthalene and ammonia conversion. However, over SiO₂–ZrO₂ no clear effect with H₂S addition was observed. The effect of sulfur addition on the catalyst properties was connected to the formation of SO₂ from H₂S when oxygen was available. The intensity of the sulfur effect increased with the Lewis basicity strength of the catalysts. This indicates that the sulfur adsorption has a role in generating new type of active sites and/or plays role in changing the redox properties of the zirconia. Since the biomass gasification gas contains usually significant amounts of H₂S the sulfur tolerance of the zirconia based catalysts is a remarkable benefit.     

Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

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.     

Properties of unsupported MoS<Subscript>2</Subscript> species produced in the preparation of MoS<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> using a sonochemical method

Unsupported MoS₂ particles, which were produced in the preparation of MoS₂/Al₂O₃ using a sonochemical method, were successfully separated from the prepared sample catalyst by adding oleylamine as an agent for dispersing the unsupported particles. The fraction of the unsupported MoS₂, which was estimated based on Mo balance, varied between 0.03 and 0.4, independent of the Mo loading levels investigated (6–54 wt% of Mo). The activity of the unsupported MoS₂ for the hydrodesulfurization of dibenzothiophene was nearly the same as that of the Al₂O₃-supported MoS₂, indicating that the activity of the prepared catalyst was not affected by the presence of the unsupported MoS₂ particles.     

Synthetic spinels of the system MgO-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Synthetic spinels of the system MgO-Cr₂O₃-Al₂O₃-Fe₂O₃ are considered and the desirability of organizing their production for the refractory industry is demonstrated. Translated from Novye Ogneupory, No. 6, pp. 32–35, June 2008.     

Research of mica/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> pearlescent pigment by co-precipitation

Experiments on preparation of mica/Fe₃O₄ pearlescent pigment were performed to discuss influences of several crucial parameters on final products. The samples were characterized by XRD, HRSEM, FTIR and color measurement, the content of Fe₃O₄ on the mica surface was also analyzed by XPS. It was found that the smoothness, compactness and colour deepness of the coating were influenced by different pH values and temperatures. The optimum preparation parameters of mica/Fe₃O₄ pearlescent pigment were obtained: the value of pH ≥ 9.2; the concentration of sodium hydroxide was 0.5 mol/l; the concentration ratio of Fe³⁺ to Fe²⁺ was 1.6 : 1; the velocity of magnetic stirring was 138 ≤ v ≤ 151 r/min; reaction temperature was 70–80°C; calcination temperature was 350°C and calcination time was 3 h.     

Electrochemical properties of microwave-assisted reflux-synthesized Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles in different electrolytes for supercapacitor applications

The nanosized Mn₃O₄ particles were prepared by microwave-assisted reflux synthesis method. The prepared sample was characterized using various techniques such as X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), Raman analysis, and transmission electron microscopy (TEM). Electrochemical properties of Mn₃O₄ nanoparticles were investigated using cyclic voltammogram (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge analysis in different electrolytes such as 1 M KCl, 1 M Na₂SO₄, 1 M NaNO₃, and 6 M KOH electrolytes. XRD pattern reveals the formation of single-phase Mn₃O₄ nanoparticles. The FT-IR and Raman analysis also assert the formation of Mn₃O₄ nanoparticles. The TEM image shows the spherical shape particles with less than 50 nm sizes. Among all the electrolytes, the Mn₃O₄ nanoparticles possess maximum specific capacitance of 94 F g⁻¹ in 6 M KOH electrolyte calculated from CV. The order of capacitance obtained by various electrolytes is 6 M KOH > 1 M KCl > 1 M NaNO₃ > 1 M Na₂SO₄. The EIS and galvanostatic charge–discharge results further substantiate with the CV results. The cycling stability of Mn₃O₄ electrode reveals that the prepared Mn₃O₄ nanoparticles are a suitable electrode material for supercapacitor application.     

Effect of surface modification of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles on the preparation of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/polystyrene composite particles via miniemulsion polymerization

Fe₃O₄ nanoparticles were modified by n-octadecyltrimethoxysilane (C18TMS) and 3-trimethoxysilylpropylmethacrylate (MPS). The modified Fe₃O₄ nanoparticles were used to prepare Fe₃O₄/polystyrene composite particles by miniemulsion polymerization. The effect of surface modification of Fe₃O₄ on the preparation of Fe₃O₄/polystyrene composite particles was investigated by transmission electron microscopy, Fourier transform infrared spectrophotometer (FT-IR), contact angle, and vibrating sample magnetometer (VSM). It was found that C18TMS modified Fe₃O₄ nanoparticles with high hydrophobic property lead to the negative effect on the preparation of the Fe₃O₄/polystyrene composite particles. The obtained composite particles exhibited asymmetric phase-separated structure and wide size distribution. Furthermore, un-encapsulated Fe₃O₄ were found in composite particles solution. MPS modified Fe₃O₄ nanoparticles showed poor hydrophobic properties and resulted in the obtained Fe₃O₄/polystyrene composite particles with regular morphology and narrow size distribution because the ended C=C of MPS on the surface of Fe₃O₄ nanoparticles could copolymerize with styrene which weakened the phase separation distinctly.     

Thermomechanical properties of refractory materials of AL<Subscript>2</Subscript>O<Subscript>3</Subscript>–Si<Subscript>3</Subscript>N<Subscript>4</Subscript>–C compositions based on acpb after impregnation with a sol-gel composition

Comparative characteristics are presented for the physicomechanical properties and oxidation resistance of refractory materials of Al₂O₃–Si₃N₄–C composition based on an ACPB for the original materials (fired at 1400°C) and after impregnation with a sol-gel composition and heat treatment at 800°C. Areduction in material porosity, increase in strength and reduction in carbon burn-off are due to development of a glassy phase in the pore space and on graphite flakes due to SiO₂formation with thermal destruction of the organosilicon substance.     

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.