Investigation of the Reaction of Roasted Serpentine Ore with Some Ammonium Salts

The reaction between roasted serpentine ore and ammonium sulfate was studied at the range of temperature 250–1000°C using different molar ratios to determine the maximum extraction of magnesia and also to characterize the different reaction products. The maximum extraction of MgO from the roasted ore reached 92.4% at 400°C. It was found from XRD that ammonium magnesium sulfate [(NH₄)₂Mg₂(SO₄)₃] was produced as the main product at 400°C, which decomposes to magnesium sulfate at 500–600°C. The last compound decomposes to magnesium oxide at 900–1000°C. Thermal analysis of the reaction mixture confirmed the results obtained by XRD. Extraction of magnesia by ammonium chloride at 300–400°C showed low percentage of extraction (7.8%). Comparison was made between using ammonium chloride instead of sulfate taking into consideration the thermal decomposition products of both ammonium salts. Extraction of magnesia from the roasted ore by aqueous ammonium sulfate or ammonium chloride showed good results.     

Surfactants for CNTs dispersion in zirconia-based ceramic matrix by sol–gel method

Zirconium oxide is a ceramic material widely studied due to its mechanical and electrical properties that can be improved with the use of carbon nanotubes (CNTs) as reinforcement. The synthesis of CNT/zirconia composites by sol–gel method is still very scarce, due to the hydrophobic nature of the CNTs, being their dispersion in aqueous medium an intrinsic difficulty to the synthesis. In this work, we present a sol–gel synthesis for MWCNTs/zirconia composites, where two kinds of surfactants, sodium and ammonium stearates dissolved in water (1 g/100 mL), were used as dispersant agents for multiwall carbon nanotubes (MWCNTs). They are cheap and easy to prepare, and were very effective in dispersing the MWCNTs. Different quantities of MWCNTs (up to 5 wt%) were added in the solution of stearate/water and this solution with the highly dispersed MWCNTs was added to the zirconia sol–gel, producing composites of MWCNTs/zirconia with different concentrations of MWCNTs. All the powders were heat treated at 300 and 500 °C and the powder characterization was performed by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and infrared spectroscopy (FTIR). The composite MWCNTs/zirconia remained amorphous at 300 °C and presented a tetragonal phase at 500 °C with an average grain size of about 20 ± 3 nm, determined by the Scherrer equation from the XRD patterns. For these crystalline samples, TEM images suggest a more effective interaction between MWCNTs with ZrO₂ matrix, where it can be observed that the carbon nanotubes are fully coated by the matrix.     

THERMAL REACTIONS IN SYNTHETIC APATITE–AMMONIUM SULFATE MIXTURE

The thermal reactions in the mixtures of hydroxylapatite or fluorapatite and (NH₄)₂SO₄up to 500°C were studied with the purpose of elaborating the conditions of obtaining calcium–ammonium cyclophosphate that could be used as fertilizer. Thermal analysis with a simultaneous FTIR analysis of the evolved gases as well as the analyses of chemical and phase composition of solid products were performed. The thermal changes in the mixtures could be divided into three steps: (1) decomposition of (NH₄)₂SO₄and reactions of apatite with these products at 250–420°C, (2) calcium ammonium polyphosphate formation at 290–450°C, and (3) reaction of CaSO₄with CaNH₄P₃O₉at 320–500°C. Higher concentrations of NH₃in the gas phase promote the formation of CaNH₄P₃O₉and increase its stability. Calcination at temperatures above 350°C causes decomposition of CaNH₄P₃O₉with a decrease in the content of water-soluble phosphorus and evolvement of SO₂.     

From green algae to calcium inside buckyballs

Coorongite and carbonaceous residues from coorongite pyrolysis at 450 and 500°C were studied by laser ablation Fourier transform mass spectrometry. Raw coorongite gave positive-ion spectra having mainly protonated species of m/z 80–300 when laser ablated with a high laser power density. Endohedral fullerene positive ions of calcium were observed during the laser ablation of coorongite pyrolysis residues. Pyrolysis of the raw coorongite at 450 and 500°C produced residues which on laser ablation using the fundamental frequency of an Nd: YAG laser (1064 nm) gave a series of calcium fullerides. These ions were observed using low laser power densities (100–600 kW cm^–2) Mixing the coorongite pyrolysis residue with barium sulphate gave M@C_n⁺ ions

1 The symbol ‘@’, as in Ca@₆₀, is used to represent an endohedral complex, i.e. the adduct is located inside the carbon cage.

where M = calcium or barium. Mixing the coorongite pyrolysis residue with strontium oxalate also gave M@C_n⁺ ions where M = calcium or strontium. No ions containing two or more metals were detected.     

Influence of a Fe/activated carbon catalyst and reaction parameters on methane decomposition during the synthesis of carbon nanotubes

In our experimental work on carbon nanotubes synthesis, the influence of pre-treatment and reaction temperature conditions over Fe catalyst loaded on low-cost activated carbon (AC) in the catalytic chemical vapor deposition of methane was studied. Catalyst with the metal concentration of 5 mass % calcined at 350°C and reduced at 450°C was effective in CH₄ decomposition giving 98 % conversions. TEM images showed that thin multi-walled carbon nanotubes (MWNTs) with the average internal diameter of ∼ 8 nm and the wall thickness of ∼ 2.5 nm were obtained over unreduced Fe/AC catalyst at the reaction temperature of 850°C. On the other hand, broader filamentous nanostructures with the diameter of ∼ 22 nm and the wall thickness of ∼ 3.72 nm were observed over reduced catalyst.     

Fullerenes from kerogen by laser ablation fourier transform ion cyclotron resonance mass spectrometry

Raw oil shale, kerogen (demineralized shale) and carbonaceous residues from kerogen pyrolysis in the range 350–700°C (at 50°C intervals) were studied by laser ablation Fourier transform ion cyclotron resonance mass spectrometry using the fundamental frequency of Nd: YAG laser (1064 nm). Normally, pyrolysis of the raw materials produces oil and the resulting residues have decreased hydrogen to carbon ratios and exhibit relative increases in aromatic carbons. Raw shale and kerogen give positive-ion spectra with mainly protonated species of m/z 100–400. Laser ablation positive-ion mass spectra of the pyrolysis products of the kerogen show the presence of C₆₀, C₇₀ and other fullerene ions with a distribution of higher mass fullerene ions up to m/z 4000. Using high laser powers (100–3000 MW cm^?2), the residue from pyrolysis at 350°C initially did not produce any fullerene ions (apart from traces of C₆₀ and C₇₀), but after continued ablation a cavity was formed in the target and a wide distribution of fullerene ions was obtained with subsequent laser pulses. Residues obtained from the pyrolysis of kerogen at 400–500°C produced fullerene ions at both low (4–200 kW cm^?2) and high laser powers. The 550°C pyrolysis residue gave only small amounts of C₆₀ and C₇₀ positive ions at low laser power whereas residues from the pyrolysis of kerogen above 550°C did not give fullerene ions over a wide range of laser powers. It is proposed from the above results that the changes in the aromatic nature of the kerogen residues with increasing pyrolysis temperature are directly related to the ease of fullerene formation. This is possibly due to the formation of large polycyclic aromatic systems at pyrolysis temperatures above 400°C, formed in the residues. It should be noted that the shale samples (raw or pyrolysed) did not generate fullerene ions under any of the conditions employed in these experiments.     

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.     

Selective Template Removal by Thermal Depolymerization to Obtain Mesostructured Molybdenum Oxycarbide

The carbon content of mesostructured organic‐inorganic hybrid material of a cylindrical block copolymer template of poly(2‐vinylpyridine)‐block‐poly(allyl methacrylate) (P2VP‐b‐PAMA) and ammonium paramolybdate (APM) could be reduced by thermal depolymerization. By calcination in vacuo at 320 °C the PAMA core can be completely removed while the remaining P2VP brush preserves the mesostructure. The P2VP‐APM composite can then be carburized in‐situ to MoO_xC_y in a second pyrolysis step without any additional carbon source but P2VP. The molybdenum oxycarbide nanotubes obtained, form hierarchically porous non‐woven structures, which were tested as catalyst in the decomposition of NH₃. They proved to be catalytically active at temperatures above 450 °C. The activation energy was estimated from an Arrhenius Plot to be 127 kJ · mol^–1.     

Carbon deposits on a resistive FeCrAl catalyst for the suboxidative pyrolysis of methane

The carbon deposits forming upon the suboxidative pyrolysis of methane on resistive FeCrAl catalysts heated with electric current were studied. The suboxidative pyrolysis of methane was carried out in a flow reactor at the ratio CH₄: O₂ = 15: 1 in a catalyst-coil temperature range of 600–1200°C; a cold reaction mixture (～20°C) was supplied. The morphology and structure of the carbon deposits and changes in the composition and structure of the catalyst were characterized by scanning electron microscopy, transmission electron microscopy with EDX analysis, Raman spectroscopy, and X-ray diffraction analysis. Various forms of carbon deposits, including branched nanotubes, and metal carbides formed by catalyst constituents were detected. It was found that the carbon deposits on the catalyst surface were morphologically different from the deposits on quartz reactor walls. The reasons for these differences were considered.     

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.     

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.     

Producing carbon nanotube dispersions using polynuclear zirconium benzoate

Aqueous dispersions of polynuclear zirconium benzoate with molar ratios of Zr: C₆H₅COO = 3–6, stable at pH 3.25–3.87 and having “solubilities” of up to 20 mg/mL by ZrO₂, are prepared; in such dispersions, benzoate decomposes to ZrO₂ at 500°C. Adding thin multiwalled carbon nanotubes to these dispersions makes it possible to isolate stable dispersions that contain both zirconium and nanotubes, mixtures suitable for producing composite coatings. It is shown that the concentration of nanotubes in mixtures with ZrO₂ can vary within 1.7–50.6 wt %.     

Surface modification of single-walled carbon nanotubes by functional nitrogen-containing groups and study of their properties

Treatment of single-walled carbon nanotubes (SWCNT) in a gaseous 40%NH₃–1%С₂Н₂–C₂H₄ mixture at 600 and 700°С led to “nitrogen-containing carbon coating–single-wall carbon nanotubes” composites. Single-walled carbon nanotubes after etching in aqua regia (SWCNTetch) and doped with nitrogen (N-SWCNT) were studied by XPS, electron microscopy, and IR spectroscopy. It was found that the initial SWCNTetch surface contains various oxygen-containing functional groups. Treatment of SWCNTetch in a 40%NH₃–1%С₂Н₂–C2H₄ mixture led to the formation of a thin carbon coating on the carbon nanotube surface due to polymerization and condensation of hydrocarbons. After treatment at 600°C, the formation of nitrogen-containing functional groups is insignificant; however, when the treatment temperature is increased to 700°C, the nitrogen content reaches 0.5 at % of the weight of the N-SWCNT sample.     

A simple routine method for the rapid determination of organic and inorganic carbon in oil shale

A procedure for the rapid determination of organic and inorganic carbon in oil shale samples is proposed. Oil shale samples are decomposed in an oxygen stream at three different temperatures (450°C, 550°C, 900°C). The resulting CO₂ is determined after absorption in 0.02 M NaOH in a relative conductometric detection unit. Temperature. differentiated carbon analysis was used to establish the decomposition temperatures of the organic material (450°C) and the inorganic fractions (550°C and 900°C). The method was tested for samples weighing 2–4 mg. Oil shales with organic carbon contents of 8–20% were determined with good reproducibility (r.s.d. 0.4–1.3%). The accuracy was tested with a standard oil shale sample. One determination requires 8 min.     

Synthesis of CuO nanoparticles via one-pot wet-chemical method and its catalytic performance on the thermal decomposition of ammonium perchlorate

Sphere-like CuO products aggregated by numerous nanoparticles were fabricated by a low-temperature (50°C) wet chemical method using CuSO₄·5H₂O as precursor. The possible formation processes of CuO were investigated by a series of single-factor experiments. The CuO was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, selectedarea electron diffraction. Furthermore, the application of CuO nanoparticles on the thermal decomposition of ammonium perchlorate was studied with 2 wt % CuO nanoparticles at heating rates of 10, 15, 20, and 25°C min^–1 from 35 to 500°C.     

Study Kinetics of Thermal Decomposition and Electrochemical Oxidation by Using Nanocomposite Paste of Novel Poly(amide-ether)s Derived from Asymmetric Diamine

A new asymmetric diamine containing diarylimodazole pendant was synthesized from the nucleophilic substitution reaction of 1-fluoro-4-nitrobenzene and 2,4-dihydroxy benzaldehyde in the presence of K₂CO₃, followed by reaction with benzil and ammonium acetate for the preparation of imidazole ring. This novel diamine was used to prepare poly(amide-ether) (PAE) in reaction with different commercially available dicarboxylic acids via direct polycondensation using triphenyl phosphite and pyridine (Py) as catalyst. The PAEs were fully characterized and their properties such as inherent viscosity, solubility, optical, thermal and kinetics of thermal decomposition, and electrochemical oxidation were investigated. The polymers had inherent viscosity in the range of 0.47–0.65 dL/g and were noncrystalline with excellent solubility in various polar aprotic organic solvents. Their T_g values ranged from 200 to 355°C and 10% weight loss temperature above 450°C in nitrogen and left more than 70% residue at 650°C. The kinetic parameters of thermal degradation such as activation energy, entropy, enthalpy and Gibbs free energy of thermal decomposition have been evaluated using different equations. We also report electrochemical oxidation of the resulting polymers in aqueous solution by using cyclic voltammetry technique on the multi-walled carbon nanotube-modified glassy carbon electrode.     

Graphene Grown from Flat and Bowl Shaped Polycyclic Aromatic Hydrocarbons on Cu(111)

The growth of carbon layers, defective graphene, and graphene by deposition of polycyclic aromatic hydrocarbons (PAHs) on Cu(111) is studied by scanning tunneling microscopy and X-ray photoelectron spectroscopy. Two different PAHs are used as starting materials: the buckybowl pentaindenocorannulene (PIC) which contains pentagonal rings and planar coronene (CR). For both precursors, with increasing sample temperature during deposition, porous carbon aggregates (350 °C), dense carbon layers (400–450 °C), disordered defective graphene (500 °C–550 °C), and extended graphene (≥600 °C) are obtained. No significant differences for defective graphene grown from PIC and CR are observed. C 1s X-ray photoelectron spectra of PIC and CR derived samples grown at 350–550 °C exhibit a characteristic C−Cu low binding energy component. Preparation at ≥600 °C eliminates this C−Cu species and only C−C bonded carbon remains.     

Kinetic features of the carbon erosion of a bulk NiCr alloy during the catalytic decomposition of 1,2-dichloroethane

Kinetic features for the carbon erosion (CE) of bulk NiCr alloy (NiCrA, nichrome wire 0.1 mm in diameter) were studied at 450–750°C under conditions of the catalytic decomposition of 1,2-dichloroethane vapor in a reductive atmosphere (H₂). It was found that the CE process takes place more efficiently in the temperature range from 550 to 720°C, leading to the disintegration of the bulk alloy with the formation of a fibrous carbon product. The apparent activation energy of the process was estimated to be 16.8 ± 0.9 kJ/mol. The realization of CE is hampered outside the optimal temperature range because of chlorination (T < 500°C) or blocking of the alloy’s surface by carbonaceous deposits (T > 720°C). The kinetics of the process is characterized by the existence of an induction period, whose duration decreases with an increasing temperature (from 40 min at 550°C to 6 min at 710°C). According to scanning and transmission electron microscopy data, the submicron metallic particles (0.2–0.4 μm) catalyzing the growth of carbon fibers with disordered structure result from the disintegration of the NiCr alloy.     

Solubility of fullerenes in n-alkanoic acids C2–C9

The solubility of fullerene C₆₀ and a fullerene mixture [C₆₀ (75%), C₇₀ (24%), C_76–80 (1%)] in linear alkanoic acids (C₂–C₉) was determined at 20°C. The solubilities of C₆₀ and a fullerene mixture in carboxylic acids were examined in relation to the number of carbon atoms in the carboxylic acid.     

Effect of carbon nanostructures on the carbonization of polyacrylonitrile

Composite materials based on polyacrylonitrile with carbon nanofillers (technical-grade carbon, thermally expanded graphite, carbon nanotubes) were synthesized. A carbonization of film and fiber composite samples in the temperature range 20–1000°C provided a noticeable increase in the thermal stability of fibers and a rise in the electrical conductivity of the composite material. Dependences of the degree of carbonization on the concentration of nanostructures, type of material, and nature of modifier were determined. Differential-thermal and X-ray diffraction analyses revealed the formation of oriented nucleus structures of turbostratic carbon in the temperature range 450–550°C.