Polyaromatic Mesophase Research Articles

Graphitic mesoporous carbon based on aromatic polycondensation as catalyst support for oxygen reduction reaction

Mesoporous carbon is constructed by monolithic polyaromatic mesophase deriving from the hexane insoluble of coal-tar pitch. This carbon material exhibits spherical morphology and layered crystallite, and thereby can be graphitized at 900 °C without destroying the mesoporous structure. Electrochemical measurements indicate that graphitic mesoporous carbon (GMC) support not only improves the activity of Pt electrocatalyst to oxygen reduction reaction (ORR), but also shows higher corrosion resistance than commercial XC-72 carbon black in the acid cathode environment.

Isotropic graphyte produced from coke to automotive aplications

The graphite is an allotropic form of the element carbon consisting of layers of hexagonally arranged carbon atoms in a planar condensed ring system. Coke particles used for conventional synthetic graphite products are long and narrow. These particles produce a preferred structural orientation in the product after the conventional uniaxial pressing or extrusion with high anisotropy. With a properly election of raw materials and process is possible reduce the anisotropy to obtain isotropic graphite. Repsol-YPF has produced a binderless polyaromatic mesophase from petroleum pitch, which has shown to be very appropriated as raw material for production of high strength isotropic graphite with high performance and low cost. This graphite have offered thermal, mechanical, chemical and wear properties higher than conventional graphite. The isotropic graphite obtained is suitable for making pistons, valves, turbojoints and other automotives components. The pistons design with this isotropic graphite has been developed for an automotive petrol engine. Piston prototypes were manufactured and tested in engines at full power and at full torque. This paper analysed the physical, mechanical and fracture properties of the isotropic graphite obtained.

Production of High-Strength Carbon Artifacts from Petroleum Residues: Influence of the Solvent Used to Prepare Mesophase Powder

The preparation process and sintering behavior of different binderless polyaromatic mesophase (BPAM) powders, obtained by extraction of a semicoke (product of pyrolysis of a petroleum residue) with...

Synthesis of boron-substituted polyaromatic mesophase

Synthesis of boron-substituted polyaromatic mesophase

Modification of the sintering behaviour of mesophase powder from a petroleum residue

The effect of preparation conditions on the sintering behaviour of different binderless polyaromatic mesophase (BPAM) powders, obtained by extraction with different solvents of four petroleum semicokes of increasing carbonisation degree, is described. The analyses of the powders indicate that large differences in composition and structure are obtained when changing the semicoke. Increasing carbonisation degree of the semicoke produces a decrease in the amount of β-resins, increase in mesophase content, C/H ratio and aromaticity, but decreases the thermofusibility of BPAM. Increasing extraction strength of the solvent reduces the amount of light material, and thermofusibility of BPAM, being more evident with low carbonised semicokes. Selection of carbonisation conditions and solvent permits to adjust fusibility of the powders and to improve sintering. Graphitised compacts exhibited the best properties when they are produced from low carbonisation degree semicokes. In this case solvents of low extraction strength provide large thermofusibility to the material, and compacts may swell. When using semicokes of higher carbonisation degree there is a reduction of the sintering abilities of the powders, this being more evident as the strength of the solvent increases.

Sintering of powders of polyaromatic mesophase to high-strength isotropic carbon-IV powders based on boron-substituted mesophase

Boron-substituted polyaromatic mesophases were synthesized by co-pyrolysis of a coal tar pitch with pyridine–borane using boron contents of 0.5 and 1%. After removal of residual isotropic material by extraction with tetrahydrofuran, the mesophases were milled to a particle size of d≤10 μm and compacted to bodies. These bodies were sintered at 1300°C and subsequently high-temperature treated at 1600, 1800, and 2000°C. The treated bodies were investigated to determine boron content, bulk density, crystallite parameters, and mechanical properties. Boron catalyzes graphitization already above 1300°C; an influence of boron concentration was detected only above 1800°C. Carbons produced with a low boron content exhibit a flexural strength of 135 MPa, a Young's modulus of 14 GPa and a strain-to-failure of 1% without optimization of the process steps. These properties exist over the total temperature range investigated, i.e. they are not lowered by progressive graphitization. Carbons with a high boron content show decreasing strength and modulus, but a constant strain-to-failure of about 0.95%.

98/02127 Pyrolyzable composition for preparing boron-containing polyaromatic mesophase, polyaromatic mesophase pitch, and carbon products by liquid-phase pyrolysis at 350–1000°

98/02127 Pyrolyzable composition for preparing boron-containing polyaromatic mesophase, polyaromatic mesophase pitch, and carbon products by liquid-phase pyrolysis at 350–1000°

Element-substituted polyaromatic mesophases: II a comparison of various synthesis routes for boron substitution

The synthesis of boron-substituted polyaromatic mesophase was studied by (1) co-pyrolysis of a filtered coal tar pitch with three different borane complexes, (2) pyrolysis of a boron-containing polymer produced by co-polymerisation of divinylbenzene with borane, and (3) pyrolysis of boron-substituted/crosslinked acenaphthylene, produced by hydroboronation of acenaphthylene. The pyrolyses were performed at an argon gas pressure of 1 MPa to suppress the evaporation of volatile products. All synthesis routes are attractive due to possible boron yields in the range of 100%. In the co-pyrolysis route, this result is only obtained with pyridine-borane and not with other borane complexes like trimethylamine-borane and piperazine borane.

97/02825 Sintering of powders of polyaromatic mesophase to high-strength isotropic carbons. 111. Powders based on an iron-catalyzed mesophase synthesis

97/02825 Sintering of powders of polyaromatic mesophase to high-strength isotropic carbons. 111. Powders based on an iron-catalyzed mesophase synthesis

96/05930 Tangential stream method for production of synthesis gas in modified wet bottom generators

The effect of preparation conditions on the sintering behaviour of different binderless polyaromatic mesophase (BPAM) powders, obtained by extraction with different solvents of four petroleum semicokes of increasing carbonisation degree, is described. The analyses of the powders indicate that large differences in composition and structure are obtained when changing the semicoke. Increasing carbonisation degree of the semicoke produces a decrease in the amount of β-resins, increase in mesophase content, C/H ratio and aromaticity, but decreases the thermofusibility of BPAM. Increasing extraction strength of the solvent reduces the amount of light material, and thermofusibility of BPAM, being more evident with low carbonised semicokes. Selection of carbonisation conditions and solvent permits to adjust fusibility of the powders and to improve sintering. Graphitised compacts exhibited the best properties when they are produced from low carbonisation degree semicokes. In this case solvents of low extraction strength provide large thermofusibility to the material, and compacts may swell. When using semicokes of higher carbonisation degree there is a reduction of the sintering abilities of the powders, this being more evident as the strength of the solvent increases.

96/05937 Carbon fibers with superhigh elasticity and their manufacture

The effect of preparation conditions on the sintering behaviour of different binderless polyaromatic mesophase (BPAM) powders, obtained by extraction with different solvents of four petroleum semicokes of increasing carbonisation degree, is described. The analyses of the powders indicate that large differences in composition and structure are obtained when changing the semicoke. Increasing carbonisation degree of the semicoke produces a decrease in the amount of β-resins, increase in mesophase content, C/H ratio and aromaticity, but decreases the thermofusibility of BPAM. Increasing extraction strength of the solvent reduces the amount of light material, and thermofusibility of BPAM, being more evident with low carbonised semicokes. Selection of carbonisation conditions and solvent permits to adjust fusibility of the powders and to improve sintering. Graphitised compacts exhibited the best properties when they are produced from low carbonisation degree semicokes. In this case solvents of low extraction strength provide large thermofusibility to the material, and compacts may swell. When using semicokes of higher carbonisation degree there is a reduction of the sintering abilities of the powders, this being more evident as the strength of the solvent increases.

Element-substituted polyaromatic mesophases: I. Boron-substitution with the pyridine-borane complex

The synthesis of a boron-substituted polyaromatic mesophase was studied by copyrolysis of a filtered coal tar pitch with pyridine-borane under a 1 MPa argon atmosphere. The pyrolysis temperature was varied between 360 and 420 °C, the boron content of the pitch-pyridine-borane mixture was increased step by step up to 5%. Pyridine-borane is decomposed above 120 °C; the pyridine is volatilized, and the highly volatile borane immediate reacts with the aromatics, preferentially by hydroboronation. Formation of the mesophase is accelerated; it is already high-grade spherulitic with small boron additions; with 5% boron the pyrolysis product is nearly isotropic. These boron-substituted mesophases are potential precursors for the production of boron-substituted sintered carbons.

Sintering of powders of polyaromatic mesophase to high-strength isotropic carbons: III. Powders based on an iron-catalyzed mesophase synthesis

A spherulitic mesophase pitch with about 50 vol% mesophase has been synthesized by an iron-catalyzed pyrolysis of a coal tar pitch. The isotropic pitch is removed to various extents by solvent extraction. The thermoplasticity of the resulting raw mesophase powders is adjusted by treatment with oxygen with respect to optimum sintering properties. After milling of these powders to a particle size d ⪯ 10 μm they were compacted with various molding pressures, sintered and graphitization-treated with various heating programs. The individual process steps and intermediate products were analyzed. Carbons sintered at 1300 °C show flexural strengths up to 225 MPa and strains-to-failure up to 1.25%. After graphitization treatment at 2400 °C, carbons with a flexural strength of about 170 MPa and a strain-to-failure of about 1% were obtained.

Sintering of powders of polyaromatic mesophase to high-strength isotropic carbons—II. Influences of the synthesis conditions of the mesophases and the preparation of the powders

Mesophase pitches with mesophase contents of 22, 45, 47 and 68 vol% were produced from the Ashland A 240 pitch using a discontinuous stirred tank reactor. For synthesis of the mesophase pitch with 47 vol% mesophase ferrocene was used as a soluble catalyst precursor of iron. The mesophase pitches were milled to a particle size of d max ≤ 100 μm and afterwards extracted with tetrahydrofuran. The residues were treated at 200°C with oxygen in order to adjust their thermoplasticity for sintering. For the sintering of compacted powders the particle size of the raw powder was reduced to d max ≤ 32 μm and d max ≤ 10 μm. By optimizing the thermoplasticity and the sintering conditions, nearly equal mechanical properties were obtained after sintering at 1000°C for all mesophase powders produced from pitches with mesophase contents below 50 vol%. After the stepwise high-temperature treatment of the sintered carbons up to 2440°C, two effects were observed: 1. (a) a strong decrease of the flexural strength between 1300 and 1800°C of such carbons obtained from the mesophase pitches produced without ferrocene; this strength decrease is caused by sulfur puffing; 2. (b) a similar strength decrease was found between 1800 and 2440°C for the carbons obtained from the mesophase pitch produced with ferrocene. The different behaviour of this material is ascribed to the formation of iron sulfide during pyrolysis and evaporation of iron, sulfur and/or carbon disulfide above 1800°C as a consequence of dissociation and/or reduction of the iron sulfide by carbon.

Sintering of powders of polyaromatic mesophase to high-strength isotropic carbons—I. Influence of the raw material and sintering conditions on the properties of the carbon materials

The sintering of compacted mesophase powders of varying nature and particle size was studied. The sintered carbons were stepwise heat-treated to 2600°C, and their properties were determined after each step. The sintering process is composed of a transient liquid-phase sintering step and a subsequent reaction sintering step in the solid state. The investigation of both process steps and the properties of the heat-treated carbons indicate that the initial transient liquid-phase sintering is the decisive step, and thus predetermines the properties of the heat-treated carbons. After graphitization treatment of sintered carbons at 2400°C, flexural strength values up to 160 MPa were obtained. Criteria for the selection of the mesophase, the particle size, and the sintering conditions are discussed.

Carbon-fiber-reinforced carbon composites fabricated with mesophase pitch

This study is concerned with the production of carbon-fiber-reinforced carbon with polyaromatic mesophase as matrix precursor. Carbon fibers from several manufacturers and with specific surface treatments were infiltrated at various pressures and temperatures using pitches with mesophase contents from 15 to 75 vol%. The resulting matrix shows a significantly increased mesophase content of about 80 vol% even if a starting pitch with only 40 vol% mesophase is used. Carbonization of composites without swelling was only possible after a well defined stabilization treatment of the green composites in oxygen. Mechanical testing of the carbonized composites (1000°C) showed four modes of failure behaviour, depending on the surface treatment of the carbon fibers and the stabilization treatment of the matrix. After a graphitization treatment at 2100°C, flexural strengths up to 650 MPa were found; a composite made of surface-activated fibers and a stabilized matrix displayed the greatest strength.