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.     

Formation of fullerenes by pyrolysis of perchlorofulvalene and its derivatives

In a retro-synthetic approach, [60]fullerene might be accessible by condensing six fulvalene fragments. In order to explore the potential of such a route for direct synthesis of [60]fullerene we have investigated the pyrolysis of perchlorofulvalene (PCF). Low temperature pyrolysis of PCF at 250 °C resulted mainly in the formation of dimers, trimers, tetramers and products of subsequent intramolecular condensation of these oligomers. Increasing the temperature to 300-350 °C leads to the formation of perchlorinated polynuclear aromatic hydrocarbons. Pyrolysis at 400-450 °C gives a cross-linked polymer structure which is the result of intermolecular condensation of the polynuclear aromatic intermediates. Pyrolysis at higher temperatures (>500 °C) mainly leads to graphite. It was found that the two-step pyrolysis of PCF (heating first at 450 °C, after that at 750 °C) yielded a fullerene containing soot via an intermediate polynuclear aromatic net. High temperature rearrangement of the latter gave fullerenes C₆₀ and C₇₀. The best results were obtained when a PCF oligomer obtained by Ullmann condensation was used as a precursor. By two-step pyrolysis and further high vacuum sublimation of the soot the fullerenes C₆₀ and C₇₀ were obtained in extractable amounts.     

Experimental study on sawdust air gasification in an entrained-flow reactor

Experiments were performed in an entrained-flow reactor to better understand the processes involved in biomass air gasification. Effects of the reaction temperatures (700 °C, 800 °C, 900 °C and 1000 °C), residence time and the equivalence ratio in the range of 0.22-0.34 on the gasification process were investigated. The behavior of biomass gasification was discussed in terms of composition of produced gas. Four parameters, i.e. the low heating value, fuel gas production, carbon conversion and cold gas efficiency were used to evaluate the gasification. The results show that CO, CO₂ and H₂ are the main gasification products, while hydrocarbons (CH₄ and C₂H₄) are the minor ones. With the increase of the reaction temperature, the concentration of CO decreases, while the concentrations of CO₂ and H₂ increase. The concentrations of CH₄ and C₂H₄ reach their maximum value when the reaction temperature is 800 °C. The optimal reaction temperature is considered to be 800 °C and the optimal equivalence ratio is 0.28 in that the low heating value of the produced gas, carbon conversion and cold gas efficiency achieve their maximum values. The kinetic parameters of sawdust air gasification are calculated basing on the Arrhenius correlation.     

Hydrogen adsorption on partially truncated and open cage C60 fullerene

C₆₀ buckyball molecules were partially truncated by a controlled oxidation at 400 °C and 2 bar oxygen pressure to create unique pore textures suitable for hydrogen adsorption. Pore textural analysis and density measurement confirmed the success of cage-opening and the creation of pore structures accessible to gas molecules. The specific surface area of the C₆₀ sample were increased from below detection to a measurable value (BET: 85 m²/g). Raman spectral study showed that the three main bands of C₆₀, H_g(1), A_g(1) and A_g(2) remained and significant defects were created after the C₆₀ fullerenes were partially oxidized. XRD and SEM measurements suggested that the C₆₀ fullerenes lost their crystallinity and the crystal surfaces were etched after the oxidation step. Hydrogen adsorption on the C₆₀ fullerenes were measured at three temperatures (77, 143 and 228 K) and hydrogen pressures up to 150 bar. Hydrogen adsorption capacity on C₆₀ fullerenes at 77 K at 120 bar was more than tripled (from 3.9 to 13 wt.%) after the C₆₀ fullerenes were partially oxidized. The average heat of adsorption of hydrogen on the partially oxidized C₆₀ fullerene molecules (2.38 kJ/mol) is within the range of the reported values of heat of adsorption on other porous adsorbents.     

Self-assembled network structures in Al/C60 composites

A method is explored for the development of nano-network structures in aluminum-based composites containing C₆₀-fullerenes by annealing at 500 °C. During annealing, although carbon atoms are decomposed from fullerenes attempting to form carbides, they cannot readily form carbides because C₆₀-fullerenes are individually dispersed and the driving force for long-range diffusion of carbon atoms is not sufficient at 500 °C. Carbon atoms rather occupy the interstices of aluminum, providing a meta-stable supersaturated aluminum phase with distorted crystal structures. The supersaturated aluminum phases grow with a strong anisotropy derived from lattice mismatch, meet neighboring phases, and then self-assemble into network structures. These nano-scale network structures are extremely stable at 500 °C, and offer significant potential for the development of structural aluminum matrix composites with a GPa-level strength.     

Effect of Na2CO3 on hexagonal boron nitride prepared from urea and boric acid

Formation of hexagonal boron nitride (hBN) from a precursor obtained by the reaction of urea and boric acid was studied in nitrogen, ammonia and argon atmospheres in 700-1200 °C temperature range. Effect of sodium carbonate (Na₂CO₃) addition on this process was investigated. Reaction products were subjected to X-ray diffraction, particle size distribution, gravimetric and Fourier transformed infrared spectroscopy analyses. Particle size and crystallite thickness of the formed hBN were seen to increase from about 60 nm and 5 nm at 700 °C to 230 nm and 19 nm at 1200 °C, respectively in NH₃ atmosphere with Na₂CO₃ addition. Highest conversion of boron in the precursor into hBN was achieved as 73.6% when Na₂CO₃ added precursor was reacted at 1200 °C in NH₃. hBN powder with high yield and relatively large particle size was obtained at low temperature such as 1200 °C with Na₂CO₃ addition. Role of Na₂CO₃ addition was suggested to be formation of a sodium borate melt from which hBN crystallized via the reaction of borate and nitrogen ions in the melt. Obtained hBN has the potential for utilization as a clean starting material for synthesis of B or N containing compounds.     

Gas evolution kinetics of two coal samples during rapid pyrolysis

Quantitative gas evolution kinetics of coal primary pyrolysis at high heating rates is critical for developing predictive coal pyrolysis models. This study aims to investigate the gaseous species evolution kinetics of a low rank coal and a subbituminous coal during pyrolysis at a heating rate of 1000 °C s^− 1 and pressures up to 50 bar using a wire mesh reactor. The main gaseous species, including H₂, CO, CO₂, and light hydrocarbons CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈, were quantified using high sensitivity gas chromatography. It was found that the yields of gaseous species increased with increasing pyrolysis temperature up to 1100 °C. The low rank coal generated more CO and CO₂ than the subbituminous coal under similar pyrolysis conditions. Pyrolysis of the low rank coal at 50 bar produced more gas than at atmospheric pressure, especially CO₂, indicating that the tar precursor had undergone thermal cracking during pyrolysis at the elevated pressure.     

Hydrothermal reforming of bio-diesel plant waste: Products distribution and characterization

A viscous waste derived from a bio-diesel production plant, in the form of crude glycerol, was reacted under subcritical and supercritical water conditions and the product composition determined in relation to process conditions. Preliminary analysis of the original sample showed that the main constituent organic compounds were methanol (20.8 wt.%), glycerol (42.3 wt.%) and fatty acid methyl esters (33.1 wt.%). Uncatalyzed reforming experiments were carried out in a 75 ml Hastelloy-C batch reactor at temperatures between 300 °C and 450 °C and pressures between 8.5 MPa and 31 MPa. Oil/wax constituted more than 62 wt.% of the reactions products. At 300 °C, the main product was a waxy material containing mainly glycerol and fatty acid methyl esters. As the temperature increased to supercritical water conditions, low viscosity oils were produced and all of the glycerol was reacted. The oils contained mainly saturated and unsaturated fatty acid esters as well as their decomposition products. The gaseous products were carbon dioxide, hydrogen and methane and lower concentrations of carbon monoxide and C₂-C₄ hydrocarbons. No char formation was observed. However, during alkaline gasification with sodium hydroxide at 380 °C, the reaction products included a gaseous effluent containing up to 90% by volume of hydrogen, in addition to oil and significant amount of whitish solid residue (soap). Sodium hydroxide influenced the production of hydrogen via water-gas shift by the removal of carbon dioxide as sodium carbonate, but also decreased oil product possibly through saponification.     

Oxygen reducing activity of methanol-tolerant catalysts by high-temperature pyrolysis

This study demonstrates the feasibility of platinum-free catalysts, which exhibit not only a high activity in the oxygen reduction reaction (ORR) but also a high tolerance of methanol. A cobalt (II) tetramethoxyphenylporphyrin (CoTMPP) precursor was dispersed in N,N-dimethylmethanamide (DMF), which was ultrasonically stirred for 30 min to yield a homogeneous solution, and then filtered to remove the solvent. The CoTMPP precipitate was pyrolyzed at temperatures of 300, 500, 700 and 900 °C in N₂ atmosphere. Raman spectra include strong peaks at 1330 and 1550 cm^− 1, which are associated with the D- and G-peaks of pyrolyzed CoTMPP above 500 °C, revealing that the original porphyrin structure of CoTMPP yields a network structure of poly-aromatic hydrocarbons upon the pyrolysis. Pyrolyzed CoTMPP loaded on carbon blacks (CoTMPP/C) at 700 °C exhibits a higher ORR activity than other various pyrolysis temperatures. In a methanol-containing solution, pyrolyzed CoTMPP/C preferentially undergoes the ORR rather than the methanol oxidation reaction, and so exhibits a high tolerance of methanol. Pyrolyzed CoTMPP has the pyrrolic nitrogen, and part of the cobalt-containing nitrogen chelate is cleaved and bound to other atoms, forming Co―N_x―C_{y (x + y = 4),} which are responsible for the ORR activity and the high tolerance of methanol.     

Effects of PbO and SrO contents on crystallization and dielectric properties of PbO–SrO–Na2O–Nb2O5–SiO2 glass–ceramics system

PbO–SrO–Na₂O–Nb₂O₅–SiO₂ glass–ceramics were prepared via roll-quenching followed by controlled crystallization from 700 °C to 900 °C. The effects of PbO and SrO contents on crystallization and dielectric properties were investigated. The results show that Pb₂Nb₂O₇, Sr₂Nb₂O₇ and their solid solutions crystallize at 700 °C, NaNbO₃ is the primary phase at 800 °C, Pb₂Nb₂O₇ disappears and PbNb₂O₆ forms at 900 °C. The dielectric properties of the glass–ceramics formed through controlled crystallization has a strong dependence on the phase compositions that were developed during heat treatment. The highest dielectric constants (∼600) are found in samples with 6.0 mol% SrO annealed at 900 °C for 3 h. The dielectric–temperature characteristics of the samples show stability over the range from −60 °C to 180 °C, except the sample without SrO heated at 900 °C.     

Fullerenes synthesis in combustion

The early suggestion in fullerenes research that fullerenes might be produced in flames was soon supported by the observation of polyhedral carbon ions in flames and in 1991 was confirmed by the recovery and identification of fullerenes C₆₀ and C₇₀ from benzene/oxygen flames. Recent research has determined the effects of pressure, carbon/oxygen ratio, temperature and the type and concentration of diluent gas, on the yields of C₆₀ and C₇₀ in subatmospheric pressure premixed laminar flames of benzene and oxygen. Similar flames but with acetylene as fuel have also been found to produce fullerenes, but in smaller yields than with benzene fuel. The largest observed yields of C₆₀ + C₇₀ from benzene/oxygen flames are substantial, being 20% of the soot produced and 0.5% of the carbon fed. The largest rate of production of C₆₀ + C₇₀ was observed at a pressure of 69 Torr, a C/O ratio of 0.989 and a dilution of 25% helium. Several striking differences between fullerenes formation in flames as compared to the widely used graphite vaporization method include, in the case of flames, an ability to vary the C₇₀/C₆₀ ratio from 0.26 to 8.8 (cf., 0.02 to 0.18 for graphite vaporization) by adjustment of flame conditions and production of several isomers each of fullerenes C ₆₀, C₇₀, C₆₀O and C₇₀O. Many of the apparent isomers are thermally metastable, one C₆₀ converting to the most stable form with a half-life of 1h at 111°C. The structures of the apparent C₆₀ and C₇₀ isomers necessarily must include abutting five-membered rings, previously assumed to be disallowed because of their high strain energy. The chemistry of fullerenes formation in flames is in some ways similar to that of soot formation, but important differences are seen and assumed to reflect the effects of the curved, strained structures of fullerenes and their precursors.     

Interaction of boron suboxide with compacted graphite cast iron

The chemical interaction of boron suboxide (B₆O) with compacted graphite cast iron (CGI) was investigated using static interaction diffusion couples between B₆O and CGI at 700 °C, 900 °C and 1100 °C for 1 h. This interaction offers the possibility to evaluate the potential of B₆O as a cutting tool. The microstructures and phase compositions of the interaction zones were investigated. At 700 °C and 900 °C the chemical interaction was minimal. However, at 1100 °C, Fe₂B and SiO₂ were formed at the interface. Hence, machining at 1100 °C is likely to result in chemical wear.     

Effect of 1 wt% LiF additive on the densification of nanocrystalline Y2O3 ceramics by spark plasma sintering

Densification of nanocrystalline cubic yttria (nc-Y₂O₃) powder, with 18 nm crystal size and 1 wt% LiF as a sintering additive was investigated. Specimens were fabricated by spark plasma sintering at 100 MPa, within the temperature range of 700-1500 °C. Sintering at 700 °C for 5 and 20 min resulted in 95% and 99.7% dense specimens, with an average grain size of 84 and 130 nm, respectively. nc-Y₂O₃ without additive was only 65% dense at 700 °C for 5 min. The presence of LiF at low sintering temperatures facilitated rapid densification by particle sliding and jamming release. Sintering at high temperatures resulted in segregation of LiF to the grain boundaries and its entrapment as globular phase within the fast growing Y₂O₃ grains. The sintering enhancement advantage of LiF was lost at high SPS temperatures.     

Formation of nanosize ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate

Formation of ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate in air atmosphere has been investigated using XRD, DTA, FT-IR, and FE-SEM as experimental techniques. ZnO as a single phase was produced by direct heating at ≥200 °C. DTA in air showed an endothermic peak at 195 °C assigned to the ZnO formation and exothermic peaks at 260, 315 and 365 °C, with a shoulder at 395 °C. Exothermic peaks can be assigned to combustion of an acetylacetonate ligand released at 195 °C. ZnO particles prepared at 200 °C have shown no presence of organic species, as found by FT-IR spectroscopy. Particles prepared for 0.5 h at 200 °C were in the nanosize range from ∼20 to ∼40 nm with a maximum at 30 nm approximately. The crystallite size of 30 nm was estimated in the direction of the a₁ and a₂ crystal axes, and in one direction of the c-axis it was 38 nm, as found with XRD. With prolonged heating of ZnO particles at 200 °C the particle/crystallite size changed little. However, with heating temperature increased up to 500 or 600 °C the ZnO particle size increased, as shown by FE-SEM observation. Nanosize ZnO particles were also prepared in two steps: (a) by heating of zinc acetylacetonate monohydrate up to 150 °C and distillation of water and organic phase, and (b) with further heating of so obtained precursor at 300 °C.     

Effects of PVA content on the synthesis of LaFeO3 via sol-gel route

LaFeO₃ were synthesized via a sol-gel route based on polyvinyl alcohol (PVA). Differential scanning calorimetry (DSC), Thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM) techniques were used to characterize precursors and derived oxide powders. The effect of the ratios of positively charged valences to hydroxyl groups of PVA (Mⁿ⁺/-OH) on the formation of LaFeO₃ was investigated. XRD analysis showed that single-phase and well-crystallized LaFeO₃ was obtained from the Mⁿ⁺/-OH = 4:1 molar ratio precursor at 700 °C. For the precursor with Mⁿ⁺/-OH = 2:1, nanocrystalline LaFeO₃ with average particle size of ∼50 nm was formed directly in the charring procedure. With increase of PVA content to Mⁿ⁺/-OH = 1:1, phase pure LaFeO₃ was obtained at 500 °C.     

Hydroprocessed rapeseed oil as a source of hydrocarbon-based biodiesel

This paper deals with the hydroprocessing of rapeseed oil representing a perspective technological way for production of biocomponents in diesel fuel range. Rapeseed oil was hydroprocessed at various temperatures (260-340 °C) under a pressure of 7 MPa in a laboratory flow reactor. Three Ni-Mo/alumina hydrorefining catalysts were used. Reaction products were analyzed using several gas-chromatographic methods. Reaction products contained water, hydrogen-rich gas and organic liquid product (OLP). The main components of OLP were identified as C₁₇ and C₁₈n-alkanes and i-alkanes. At a low reaction temperature, OLP contained also free fatty acids and triglycerides. At reaction temperatures higher than 310 °C, OLP contained only hydrocarbons of the same nature as hydrocarbons present in diesel fuel. Influence of reaction temperature and catalyst on the composition of reaction products is discussed.     

Synthesis of spherical shape borate-based bioactive glass powders prepared by ultrasonic spray pyrolysis

Spherical shape borate-based bioactive glass powders with fine size were directly prepared by high temperature spray pyrolysis. The powders prepared at temperatures between 1200 and 1400 °C had mixed phase with small amounts of fine crystal and an amorphous rich phase. Glass powders with amorphous phase were prepared at a temperature of 1500 °C. The mean size of the glass powders prepared by spray pyrolysis was 0.76 μm. The glass powders prepared at a temperature of 1200 °C had two distinct exothermic peaks (T_c1 and T_c2) at temperatures of 588 and 695 °C indicating crystallization. The glass transition temperature (T_g) of the powders prepared at a temperature of 1200 °C was 480 °C. Phase-separated crystalline phases with spherical shape were observed from the surface of the pellet sintered at a temperature of 550 °C. Crystallization of the pellet was completely occurred at temperatures of 750 and 800 °C. The pellets sintered at temperatures below 700 °C had single crystalline phase of CaNa₃B₅O₁₀. The pellet sintered at a temperature of 800 °C had two crystalline phases of CaNa₃B₅O₁₀ and CaB₂O₄.     

Growth of carbon nanofilaments on coal foams

Nanofilamentous carbon was grown on a carbon foam by catalytic chemical vapour deposition (CVD) using the decomposition of ethylene/hydrogen mixtures over Ni. The carbon foam was obtained from a coal by a two-stage thermal process, with the first stage taking place at a temperature within the plastic region of the precursor coal. The extent of porosity and the pore size of the foam were mainly influenced by the pressure reached in the reactor during the first stage. In the CVD process, 700 °C was the optimum temperature for obtaining good yields of nanofilaments. A low ethylene/hydrogen ratio (1/4) in the reactive gas gave rise to almost only short and thin carbon nanostructures. A higher proportion of C₂H₄ (4/1, C₂H₄/H₂) gave better yields of nanofilaments, with good proportions of higher-length and higher-diameter (up to around 0.5 μm) structures. Among the carbon forms produced, transmission electron microscopy revealed the predominance of fishbone-type nanofibres, with some bamboo-like nanotubes being also observed.     

Hydroconversion of sunflower oil on Pd/SAPO-31 catalyst

This work presents results from the hydroconversion of sunflower oil on the bifunctional Pd/SAPO-31 catalyst as a perspective technological way for single-stage production of hydrocarbons in the diesel fuel range that have improved low-temperature properties. Transformation of sunflower oil was performed at temperatures of 310-360 °C and WHSV = 0.9-1.6 h⁻¹, under a pressure of 2.0 MPa in a laboratory flow reactor. Gaseous and liquid reaction products were analyzed by GC using an internal standard method as well as by ¹H and ¹³C NMR spectroscopy. At temperatures 320-350 °C, liquid reaction product contained only hydrocarbons, the main components were identified as C₁₇ and C₁₈n-alkanes and i-alkanes. Pd/SAPO-31 catalyst demonstrated high initial activity for the hydroconversion of the feed and good isomerizating properties, but its deactivation was followed after several hours of operation. Physico-chemical properties of both fresh and spent catalysts were compared. The influence of reaction conditions on the composition of the reaction products is also discussed.     

Influence of grain size on high temperature oxidation behavior of Cr2AlC ceramics

The influence of grain size on the oxidation behavior of Cr₂AlC at 1100 °C and 1200 °C for different times was investigated using fine grained (2 μm) and coarse grained (60 μm) samples. The two materials show a good oxidation resistance owing to the formation of a dense and continuous Al₂O₃ layer. The oxidation rate of the fine grained Cr₂AlC is relatively faster than that of the coarse grained Cr₂AlC. The microstructure and phase composition of scale was characterized. After oxidation at 1100 °C and 1200 °C for long times up to 100 h, only a dense and continuous α-Al₂O₃ oxide layer formed on both the fine grained and coarse grained Cr₂AlC. However, after oxidation at 1100 °C for a relatively short 2 h period, a Cr₇C₃ compound was detected beneath the α-Al₂O₃ oxide layer on the coarse grained Cr₂AlC, yet no Cr₇C₃ was found in the fine grained Cr₂AlC. The oxidation mechanism of the fine and the coarse grained Cr₂AlC was discussed.