Soot-free synthesis of C60

A new synthetic medium for the production of C₆₀ has been found that does not produce soot. C₆₀ was produced in the liquid phase of an aerosol of precursor soot at 700 °C. The precursor soot aerosol, a high temperature stable form of hydrocarbon, was produced by pyrolysis of acetylene at atmospheric pressure in a flow tube reactor. At 700 °C, the effluent particles were found to contain PAHs, small hydrocarbons and fullerenes but no observable black material. However, when the reactor temperature was changed to 800 °C, soot was also produced in the effluent particles along with PAHs and other small hydrocarbons, and the fullerene product disappeared. These results show a clear competition between the production of fullerenes and other forms of carbon. The filter-collected effluent was shown to be completely soluble in conventional solvents suggesting the possibility of an efficient cyclic synthetic process. Fullerenes were only found in the particle phase implying the first observed liquid phase synthesis of C₆₀.     

Soot-free synthesis of C60

A new synthetic medium for the production of C₆₀ has been found that does not produce soot. C₆₀ was produced in the liquid phase of an aerosol of precursor soot at 700 °C. The precursor soot aerosol, a high temperature stable form of hydrocarbon, was produced by pyrolysis of acetylene at atmospheric pressure in a flow tube reactor. At 700 °C, the effluent particles were found to contain PAHs, small hydrocarbons and fullerenes but no observable black material. However, when the reactor temperature was changed to 800 °C, soot was also produced in the effluent particles along with PAHs and other small hydrocarbons, and the fullerene product disappeared. These results show a clear competition between the production of fullerenes and other forms of carbon. The filter-collected effluent was shown to be completely soluble in conventional solvents suggesting the possibility of an efficient cyclic synthetic process. Fullerenes were only found in the particle phase implying the first observed liquid phase synthesis of C₆₀.     

Sintering behavior and microwave dielectric properties of Bi2O3–ZnO–Nb2O5-based ceramics sintered under air and N2 atmosphere

The sintering behavior and dielectric properties of the monoclinic zirconolite-like structure compound Bi₂(Zn_1/3Nb_2/3)₂O₇ (BZN) and Bi₂(Zn_1/3Nb_2/3−xV_x)₂O₇ (BZNV, x = 0.001) sintered under air and N₂ atmosphere were investigated. The pure phase were obtained between 810 and 990 °C both for BZN and BZNV ceramics. The substitution of V₂O₅ and N₂ atmosphere accelerated the densification of ceramics slightly. The influences on microwave dielectric properties from different atmosphere were discussed in this work. The best microwave properties of BZN ceramics were obtained at 900 °C under N₂ atmosphere with _r = 76.1, Q = 850 and Q_f = 3260 GHz while the best properties of BZNV ceramics were got at 930 °C under air atmosphere with _r = 76.7, Q = 890 and Q_f = 3580 GHz. The temperature coefficient of resonant frequency τ_f was not obviously influenced by the different atmospheres. For BZN ceramics the τ_f was −79.8 ppm/°C while τ_f is −87.5 ppm/°C for BZNV ceramics.     

Improving sintering behavior of MWCNT/BaTiO3 ceramic nanocomposite with Bi2O3-B2O3 addition

The present research systematically investigated the novel low-temperature fabrication of a multi-walled carbon nanotube (MWCNT)/barium titanate nanocomposite using a two-step mixing technique. The synthesis was conducted using different amounts of MWCNT (0.25%, 0.5%, 1%, 2%, 4%, and 8% wt) with different compositions of (Bi₂O₃ + B₂O₃) as a sintering aid. Scanning and transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, three-point bending strength, Vickers hardness indentation and Archimedean technique were used to characterize the as-synthesized specimens. It was found that the appropriate content of sintering aid (Bi₂O₃+B₂O₃) strongly decreased the sintering temperature from 1200 °C to 950 °C. The results also revealed that any sintering aid with the optimum composition that included 30% (mol) Bi₂O₃ was optimal for a sintering aid content of 6% (wt). Consequently, the highest values of the flexural strength and fracture toughness were achieved by applying the optimal amounts of MWCNT (1% wt) and sintering aid (6% wt).     

Preparation and characterization of tetragonal-ZrO2 nanopowders by a molten hydroxides method

Pure tetragonal-ZrO₂ nanopowders are prepared by a molten hydroxides method, using hydrated zirconium nitrate as the starting material at 200 °C. X-ray diffraction analysis and transmission electron microscopy observation reveal that the nanopowders exhibit poor crystalline quality. After heat treated at 400 °C for 10 h in air, the nanopowders are crystalline with size range of ∼10–12 nm and most of them are agglomerated. The formation mechanism of the ZrO₂ nanopowders has been proposed. The heat treated nanopowders have a BET surface area of ∼27.3 m²/g due to agglomeration. The photoluminescence of the heat treated nanopowders has been investigated at room temperature.     

Growing carbon nanotubes on patterned submicron-size SiO2 spheres

Growing carbon nanotubes (CNTs) perpendicularly to the surface of submicron-size SiO₂ spheres by pyrolyzing iron(II) phthalocyanine (FePc) is reported for the first time in this paper. The large curvature isolates the nanotubes and forms unique structures. The density, lengths and morphology of CNTs on SiO₂ spheres can be controlled by varying the experimental conditions. A method of growing CNTs on patterned SiO₂ spheres on conducting surface by photolithography is further developed based on the selective growth of CNTs. This may offer an effective way to control the density of patterned, aligned CNTs on conducting substrates for various applications, particularly for field emission.     

In-situ formation of carbon nanotubes in an alumina-nanotube composite by spray pyrolysis

Alumina (Al₂O₃)-carbon nanotube composite materials were synthesized by spraying a slurry of ferrocene (Fe(C₅H₅)₂) and alumina in xylene, at 1000±50 °C, using argon (≤1.5 bar) as carrier gas. The as-prepared materials were formed in large flakes (ca. 2 cm) and consist of nanotubes intricately matted in a glassy alumina matrix. Based on the structural and microstructural investigations done by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), a possible growth mechanism has been suggested.     

Soot surface area evolution during air oxidation as evaluated by small angle X-ray scattering and CO2 adsorption

The total surface area of two diesel engine produced soots, a high volatile content NIST standard (termed NIST) and a low volatile content soot (termed NEU), were determined with CO₂ adsorption and small angle X-ray scattering (SAXS), as a function of the extent of oxidation. During initial volatilization of condensables of the NIST and NEU soots in a thermogravimetric analyzer, in helium at 1073 K, their CO₂ surface areas increased sharply from 49 m²/g to 273 m²/g and from 96 m²/g to 367 m²/g, respectively. During oxidation, the CO₂ surface area increased by an additional 100-150 m²/g, until 50% conversion was reached. Thereafter, the CO₂ surface area was relatively constant with conversion for the NIST soot, but decreased to 150 m²/g for the NEU soot. Three porosity regimes were assumed for the calculation of SAXS areas; they were based on (a) constant density (shrinking core), (b) constant diameter, and (c) an observed (with a TEM) diameter variation. The best agreement between the CO₂ and SAXS surfaces area occurred for the constant density assumption, in contrast to the actual measured diameter variation. By applying fractal surface analysis to the SAXS data, this discrepancy is ascribed to the opening up of internal volume to reaction volatilization of condensables and oxidation.     

Separation of CO2/CH4 through carbon molecular sieve membranes derived from P84 polyimide

The separation of CO₂/CH₄ separation is industrially important especially for natural gas processing. In the past decades, polymeric membranes separation technology has been widely adopted for CO₂/CH₄ separation. However, polymeric membranes are suffering from plasticization by condensable CO₂ molecules. Thus, carbon molecular sieve membranes (CMSMs) with excellent separation performance and stability appear to be a promising candidate for CO₂/CH₄ separation. A commercially available polyimide, P84 has been chosen as a precursor in preparing carbon membranes for this study. P84 displays a very high selectivity among the polyimides. The carbonization process was carried out at 550–800 °C under vacuum environment. WAXD and density measurements were performed to characterize the morphology of carbon membranes. The permeation properties of single and equimolar binary gas mixture through carbon membranes were measured and analyzed. The highest selectivity was attained by carbon membranes pyrolyzed at 800 °C, where the pyrolysis temperatures significantly affected the permeation properties of carbon membranes. A comparison of permeation properties among carbon membranes derived from four commercially available polyimides showed that the P84 carbon membranes exhibited the highest separation efficiency for CO₂/CH₄ separation. The pure gas measurement underestimated the separation efficiency of carbon membranes, due to the restricted diffusion of non-adsorbable gas by adsorbable component in binary mixture.     

Na2O, K2O, SiO2 and Al2O3 release from potassic and calcic-sodic feldspars into alkaline solutions

The potential release of elements from potassic and calcic-sodic feldspars into the concrete pore solution was evaluated by ICP-MS using 1 N NaOH and KOH solutions at 80 °C in accordance with the conditions set in the chemical test method. Materials were characterized by petrography, XRD and by XRF analysis. The influence of textural and microstructural characteristics on the leaching process was also analyzed by immersing polished plates of each mineral in 1 N NaOH at 80 °C for 7 days. Optical microscope and SEM observations indicate that microstructural characteristics, such as cleavage zones, twins, grain-grain contact and the finer and less abundant phases in perthites, play a key role in the leaching process under alkaline conditions. Na₂O, K₂O, SiO₂ and Al₂O₃ are supplied by hydrolysis, although the participation of other processes cannot be ruled out.     

Carbon-encapsulated Fe nanoparticles from detonation-induced pyrolysis of ferrocene

Carbon-encapsulated Fe nanoparticles with size between 5 and 20 nm were synthesized via a picric acid-detonation-induced pyrolysis of ferrocene, which is characterized by a self-heating and extremely fast process. The nanoparticles exhibit well-constructed core-shell structures, with bcc-Fe cores and graphitic shells. The graphitic shells can protect effectively the cores against the attack of HNO₃ solution. The formation of the core-shell nanoparticles can be selectively controlled by adjusting the composition of the picric acid-ferrocene mixture, which determines C/Fe atomic ratio of the reaction system. The core-shell nanoparticles are preferably formed at low C/Fe atomic ratios, while tubular structures are formed at high C/Fe ratio. The possible pathway for the carbon-encapsulated Fe nanoparticles formation is discussed briefly.     

Impedance spectroscopic studies on NiFe2O4 with different morphologies: Microstructure vs. dielectric properties

NiFe₂O₄ powders were prepared by combustion synthesis, polyol-mediated and sol–gel methods. Morphological characterization of sintered disks was carried out using scanning electron microscopy (SEM). Dielectric properties of NiFe₂O₄ synthesized by different routes were investigated over the frequency range of 100 Hz–5 MHz at room temperature. A difference in dielectric constant (ε_r) and dissipation factor (tan δ) of NiFe₂O₄ samples obtained by different synthesis methods has been observed. The observed dissimilarity in the behavior originates from the variation in the microstructure of the samples that is evident in the Cole–Cole plot results.     

Effects of phase and chemical composition of precursor on structural and morphological properties of (Lu0.95Eu0.05)2O3 nanopowders

Europium-doped lutetium oxide nanopowders have been synthesized by the co-precipitation technique using ammonium hydrogen carbonate as a precipitant. Effects of chemical and phase composition of carbonate precursors on the morphology and sinterability of (Lu_0.95Eu_0.05)₂O₃ nanopowders have been studied. Two types of precursors have been obtained differing by the molar ratio R=NH₄HCO₃/Lu³⁺: a mixture of crystalline Lu_0.95Eu_0.05(OH)(CO₃)·4H₂O and unidentified amorphous phases at R=4–7 and crystalline Lu_0.95Eu_0.05(H₂O)_x(HCO₃)₃·nH₂O precursor at R=8–20. The two-phase precursor consists of spherulite-like aggregates, while the crystalline one is characterized by plate-like morphology. Calcination of Lu_0.95Eu_0.05(H₂O)_x(HCO₃)₃·nH₂O leads to formation of (Lu_0.95Eu_0.05)₂O₃ nanopowders that inherit the precursor morphology, while no morphology succession is observed for (Lu_0.95Eu_0.05)₂O₃ nanopowders obtained by heat treatment of the two-phase precursor. Calcination of the two-phase mixture leads to breakdown of the spherulites and to formation of equiaxed particles with an average diameter of 40 nm with the standard deviation of particle size distribution of about 15%. The obtained low-agglomerated nanopowders were used in vacuum sintering to produce (Lu_0.95Eu_0.05)₂O₃ optical ceramics with in-line transmittance of 41% at 611 nm.     

Multi-wall carbon nanotubes with uniform chirality: evidence for scroll structures

Multi-wall carbon nanotubes (MWCNT) obtained by catalytic decomposition of iron phthalocyanine are investigated by high resolution electron microscopy and electron diffraction (ED). The evaluation of the ED patterns shows that all MWCNTs studied have a uniform chirality, i.e. all tubes of a given MWCNT show the same chiral angle. The conditions for the formation of nested tubes are discussed. A comparison of the values of the chiral angles with those of the corresponding interwall spacings, both obtained from the ED patterns, leads to the conclusion that these MWCNTs have a scroll structure, very probably consisting of one single rolled-up graphene sheet.     

Low temperature sintering and microwave dielectric properties of Ce2(WO4)3 ceramics

Ce₂(WO₄)₃ ceramics have been synthesized by the conventional solid-state ceramic route. Ce₂(WO₄)₃ ceramics sintered at 1000 °C exhibited ?_r = 12.4, Qxf = 10,500 GHz (at 4.8 GHz) and τ_f = −39 ppm/°C. The effects of B₂O₃, ZnO–B₂O₃, BaO–B₂O₃–SiO₂, ZnO–B₂O₃–SiO₂ and PbO–B₂O₃–SiO₂ glasses on the sintering temperature and microwave dielectric properties of Ce₂(WO₄)₃ were investigated. The Ce₂(WO₄)₃ + 0.2 wt% ZBS sintered at 900 °C/4 h has ?_r = 13.7, Qxf = 20,200 GHz and τ_f = −25 ppm/°C.