Marcos Granda

Towards a Further Generation of High‐Energy Carbon‐Based Capacitors by Using Redox‐Active Electrolytes

This work was supported by MICINN (Project MAT2007-61467). S.R. thanks MICINN for an FPI doctoral grant.

Modification of coal-tar pitch by air-blowing — I. Variation of pitch composition and properties

Abstract Pitch oxidation by air-blowing has been studied as a possible method to modify pitch properties for composite preparation. Two commercial coal-tar pitches, an impregnating pitch and a binder pitch, were air-blown at temperatures between 250–300 °C, for 18 and 14 h, respectively, to produce pitches of similar softening point ranging from 148 to 223 °C. Parent and treated pitches were characterized by elemental analysis, FTIR, thermal analysis (TMA, TGA, and DTA), solubility in toluene and quinoline, XPS, X-ray diffraction, and optical microscopy. Additionally, parent pitches were also characterized by extrography. Pyrolysis products of parent and treated pitches, obtained at 450 °C, were characterized by optical microscopy to monitor the influence of air-blowing on mesophase formation. Results show that pitch modification by air-blowing produces a significant increase in carbon yield, without restricting the fluidity necessary to pitch for impregnation. During air-blowing, the reactions of dehydrogenative polymerization and crossing-linking of oligomers occur.

Influence of fibre–matrix interface on the fracture behaviour of carbon-carbon composites

Abstract This paper studies the fracture behaviour of unidirectional carbon fibre reinforced carbon matrix composites and its relation with the type of fibre–matrix interface developed in the composite. Model unidirectional carbon–carbon composites were prepared using the same type of fibre and different pitches as matrix precursors. These included both commercial pitches and synthesized in the laboratory ones. The chemical composition of the matrix precursor determined the type of microstructure developed in the composite, this microstructure seems to govern the fibre-matrix bonding and in turn controls the fracture behaviour of the composite. In general, a matrix texture of mosaic (small size) seems to yield a good fibre-matrix bonding, making the materials to have higher interlaminar shear strength but having at the same time brittle fracture behaviour. On the other hand, composites where larger textures were developed in the matrix seem to have a poorer fibre-matrix bonding. This made the composites to have lower strength, but it allowed debonding of fibre and matrix during fracture. As a result, these materials showed pseudo-plastic failure behaviour. Other examples of both types of fracture behaviour associated with the change in microstructure and fibre–matrix interface are discussed.

Application of extrography for characterization of coal tar and petroleum pitches

Extrography has been used for fractionation of coal tar and petroleum pitches into six fractions of increasing polarity by a given sequence of solvents. Sample recovery, composition of the fractions and reproducibility of separation into distinct classes of compounds were determined. The results of several samples show the efficiency of extrography for the characterization of pitches of different origin. FT-i.r. and gas chromatography were used to evaluate the separation. Extrography is a rapid, simple and reproducible technique for the characterization of pitch materials.

A study of pitch-based precursors for general purpose carbon fibres

Abstract The isotropic phase isolated from a thermally treated coal-tar pitch was studied as a possible precursor for carbon fibres. Extraction with different solvents was performed in order to increase its softening point and so enable higher stabilisation temperatures to be used, with a significant reduction in time. The extraction conditions were selected studying the softening temperatures of the residues, the results of their thermogravimetric analysis and reactivity in air studied by means of differential scanning calorimetry. The residue obtained with a mixture of 40% acetone–60% acetonitrile was found to be the most suitable precursor for the fibres. The carbonised fibres showed a homogeneous surface and diameter, and had tensile properties comparable to other isotropic fibres described in the literature.

Graphite Felt Modified with Bismuth Nanoparticles as Negative Electrode in a Vanadium Redox Flow Battery

A graphite felt decorated with bismuth nanoparticles was studied as negative electrode in a vanadium redox flow battery (VRFB). The results confirm the excellent electrochemical performance of the bismuth modified electrode in terms of the reversibility of the V(3+) /V(2+) redox reactions and its long-term cycling performance. Moreover a mechanism that explains the role that Bi nanoparticles play in the redox reactions in this negative half-cell is proposed. Bi nanoparticles favor the formation of BiHx , an intermediate that reduces V(3+) to V(2+) and, therefore, inhibits the competitive irreversible reaction of hydrogen formation (responsible for the commonly observed loss of Coulombic efficiency of VRFBs). Thus, the total charge consumed during the cathodic sweep in this electrode is used to reduce V(3+) to V(2+) , resulting in a highly reversible and efficient process.

High performance activated carbon for benzene/toluene adsorption from industrial wastewater

A coal-tar-derived mesophase was chemically activated to produce a high surface area (~3200 m(2)/g) carbon with a porosity made up of both micropores and mesopores. Its adsorption capacities were found to be among the highest ever reported in literature, reaching values of 860 mg/g and 1200 mg/g for the adsorption of benzene and toluene, respectively, and 1200 mg/g for the combined adsorption of benzene and toluene from an industrial wastewater. Such high values imply that the entire pore system, including the mesopore fraction, is involved in the adsorption process. The almost complete pore filling is thought to be due to the high relative concentrations of the tested solutions, resulting from the low saturation concentration values for benzene and toluene, which were obtained by fitting the adsorption data to the BET equation in liquid phase. The kinetics of adsorption in the batch experiments which were conducted in a syringe-like adsorption chamber was observed to proceed in accordance with the pseudo-second order kinetic model. The combined presence of micropores and mesopores in the material is thought to be the key to the high kinetic performance, which was outstanding in a comparison with other porous materials reported in the literature.

Suitability of thermogravimetry and differential thermal analysis techniques for characterization of pitches

Abstract The pyrolysis of a number of coal tar and petroleum pitches was studied by means of thermogravimetry, derivative thermogravimetry and differential thermal analysis (DTA). Acenapthylene was used as a model compound to interpret the results of pitch pyrolysis. DTA exo- and endothermal peaks were assigned to different types of phenomena such as devolatilization, polymerization, condensation and cracking. It was found that endothermal phenomena (devolatilization) are prevalent for binder coal tar pitches, whereas exothermal phenomena predominate for petroleum pitches. Results obtained with various pitch fractions provided evidence of interactions among constituents of fractions.

Catalytic polymerization of anthracene oil with aluminium trichloride

Abstract A commercial anthracene oil was polymerized with anhydrous aluminium trichloride in the temperature range of 250–325°C. The kinetics of the process and the conversion of anthracene oil were monitored by thermogravimetric analysis, solubility parameters and carbon yield. The reactivity of the major anthracene oil components was monitored by gas chromatography. The cokes obtained at 900°C from reaction products were characterized in terms of optical texture and air reactivity. The results showed that the treatment of anthracene oil with aluminium trichloride led to pitch-like materials, temperature and aluminium trichloride concentration being the controlling parameters of anthracene oil conversion. The residue obtained by thermogravimetric analysis at 350°C was used as a measure of the degree of anthracene oil conversion. Cokes obtained by carbonization of reaction products, in which aluminium trichloride had previously been removed, showed an optical texture of a larger size and a lower air reactivity than cokes from reaction products where aluminium trichloride was present.

Mass spectrometric characterization of polynuclear aromatic nitrogen compounds in coal tar pitches separated by extrography

Abstract Extrography is a rapid technique for fractionating relatively large quantities of coal tar and petroleum pitches. Mass spectrometry (m.s.) and gas chromatography (g.c.)-m.s. have confirmed that the technique separates non-basic heterocyclic nitrogen compounds from aza bases in coal tar pitches. However, the nitrogen-containing fractions also contain higher molecular weight (MW) polynuclear aromatic compounds. Azabenzopyrenes are the major low-MW bases present. A range of mixed heterocyclic compounds were identified, including basic quinones.