Mixtures Of Pitch Research Articles

Preparation and Structures of Mesocarbon Microbeads

MCMB were prepared from coal-tar pitch by pyrolysis condensation in the presence of graphite. The characteristics of the MCMB were studied by BET and optical textures of the pitch mixtures were characterized by polarized-light microscopy. Results show that the graphite addition contributes to an increase of MCMB yield. The pyrolysis conditions and content of graphite have notable effect on the structure and yields of MCMB. When content of graphite reaches 3% and the pitch are pyrolysated at 450°C for 4 h, the MCMB yield arrive at 32wt%.

Microstructure and thermal/mechanical properties of short carbon fiber-reinforced natural graphite flake composites with mesophase pitch as the binder

Short carbon fiber reinforced graphite blocks (SFGs) were fabricated from a mixture of mesophase pitch, natural graphite flakes and short carbon fibers by hot-pressing at 2773K. The effect of fiber content on the structure and thermal/mechanical properties of the SFGs was investigated. It was found that introducing the fibers lowered the densification, and also changed the pore structure and pore size distribution. Compared with the pristine block, all the SFGs earned improved in-plane thermal conductivity and mechanical strength. The formation of a heat flow network and the increase of crystalline sizes made a synergistic effect on the promotion of in-plane thermal conductivity. In-plane thermal conductivity reached the maximum when the fiber content was 6wt.%. The increase of mechanical strength was mainly attributed to the pull-out of fibers from the matrix. The bend and compressive strength in the direction perpendicular to graphite layers reached the maximum values of 39.6MPa and 65.5MPa for fiber content of 8wt.%, respectively.

CO2 adsorption on zeolite X/activated carbon composites

Two series of zeolite X/activated carbon composites with different ratios of zeolite and activated carbon were prepared through a combination process of CO2 activation of the mixtures of elutrilithe and pitch and subsequent hydrothermal crystallization in alkaline solution. An additional surface modification was achieved in diluted NH4Cl solution. CO2 and N2 uptakes on the composites before and after modification were determined for pressures up to 101 kPa at 273 and 298 K, respectively. Langmuir-Freundlich and Toth adsorption models were used to describe the adsorption isotherms of CO2 and the corresponding heats of adsorption were estimated with the Clausius-Clapeyron equation. Both before and after modification, all composites exhibited a remarkable preferential adsorption of CO2 compared to N2, with the modified composites showing a higher adsorption selectivity to CO2 over N2 than the unmodified composites. With an increasing ratio of zeolite in the composites, adsorption capacity and adsorption heat of CO2 on the composites increased simultaneously. Lower adsorption heat was observed both before and after modification especially at the low-loading region and when there was less energetic heterogeneity on the surface of the modified composites. The results may be attributed to the elimination of strong basic sites on the modified composites, which is favorable for desorption of CO2 on the adsorbents and application in pressure swing adsorption processes.

Microstructure, Properties and Lignin-Based Modification of Wood–Ceramics from Rice Husk and Coal Tar Pitch

Wood–Ceramics are prepared from a shaped mixture of rice husk and high-temperature coal tar pitch by pyrolysis at different temperatures. Subsequently, the wood–ceramics are modified by pyrolysis of different mixture precursors with adding lignin. The effect of pyrolysis temperature, lignin content and lignin types on the microstructure, yield, volume shrinkage, open porosity ratio and bending strength of the wood–ceramics is discussed, respectively. The results show that the microstructure, volume shrinkage ratio, and bending strength of wood–ceramics are significantly dependent on the pyrolysis temperature, lignin content and types. When the pyrolysis temperature increases from 500 to 1200 °C, the (002) crystal planes peaks of the wood–ceramics move to a higher diffraction angle and the intensity of these peaks increase. The volume shrinkage ratio and bending strength of the wood–ceramics increase from 41.2 to 55.5 % and 10.2 to 31.2 MPa, respectively. Moreover, the open porosity ratio first decreases from 35.6 to 26.2 %, and then increases to 30.1 %. The enzymatic hydrolysis lignin (EHL) plays an important role in improving the order and graphitization, porous content and open porosity of the EHL-modified wood–ceramics, whereas the lignosulfonate causes the bending strength of the lignosulfonate-modified wood–ceramics to decrease.

Influence of Electroless Copper Deposition on the Electrochemical Performance of Si/MCMB

Si-Cu alloys have been prepared by electroless depositions with different process. Si-Cu/MCMB materials have been prepared by carbonization of the mixture of Si-Cu, MCMB and mesophase pitch. The influences of electroless deposition condition and heat-treatment temperature on the anodic performance of Cu-Si/MCMB have been studied. Compared with Si/MCMB, Si-Cu/MCMB has more stable cyclical performance. Furthermore, the Si-Cu/MCMB sample produced by cleaning and then electroless deposition on Si shows the better anodic performance than the Si-Cu/MCMB sample produced by direct electroless deposition on Si, because the former sample has more Cu contents than the latter sample.

Effect of activated carbons derived from different precursors on the hydrogen sorption properties of magnesium

The absorption–desorption characteristics towards hydrogen of obtained by ball milling under argon atmosphere magnesium based composites (containing respectively 95 wt% Mg and 5 wt% activated carbon (AC) derived from bean pods (BP), apricot stones (AS) and mixture of coal tar pitch and furfural (CTPF)), were investigated. Actually there is no substantial difference between the rate of hydriding and the absorption capacity for magnesium composite with AC derived from apricot stones, and for magnesium composite with AC derived from a mixture of coal tar pitch and furfural — the capacity is 6.13 wt% for the former and 5.98 wt% for the latter. More significant difference between the investigated composites was observed for the dehydriding process. The magnesium composite with synthetic carbon (from furfural and coal tar pitch) desorbs at 623 K and 0.15 MPa and the absorbed hydrogen about twice faster than magnesium composite with AC from bean pods. The activated carbon derived from a mixture of coal tar pitch and furfural has the highest specific surface area, and obviously this characteristic has important influence especially on the dehydriding kinetics of magnesium.

Synthesis and electrochemical properties of activated carbons and Li4Ti5O12 as electrode materials for supercapacitors

New activated nanoporous carbons, produced by carbonization of mixtures of coal tar pitch and furfural with subsequent steam activation, as well as electrochemically active oxide Li4Ti5O12, prepared by thermal co-decomposition of oxalates, were tested and characterized as electrode materials for electrochemical supercapacitors. The phase composition, microstructure, surface morphology and porous structure of the materials were studied. Pure carbon electrodes as well as composite electrodes based on these materials obtained were fabricated. Two types of supercapacitor (SC) cells were assembled and subjected to charge–discharge cycling study at different current rates: (1) symmetric sandwich-type SC cells with identical activated carbon electrodes and different organic electrolytes, and (2) asymmetric hybrid SC cell composed by activated graphitized carbon as a negative electrode and activated carbon–Li4Ti5O12 oxide composite as a positive electrode, and an organic electrolyte (LiPF6–dimethyl carbonate/ethylene carbonate (DMC/EC). Four types of carbons with different specific surface area (1,000–1,600 m2 g−1) and texture parameters, as well as three types of organic electrolytes: Et4NBF4–propylene carbonate (PC), LiBF4–PC and LiPF6–DMC/EC in the symmetric SC cell, were tested and compared with each other. Capacitance value up to 70 F g−1 for the symmetric SC, depending on the electrolyte microstructure and conductivity of the carbon material used, and capacitance of about 150 F g−1 for the asymmetric SC cell, with good cycleability for both supercapacitor systems, were obtained.

Synthesis of nanoporous carbons from mixtures of coal tar pitch and furfural and their application as electrode materials

Synthetic nanoporous carbons are prepared by polymerization of mixtures containing coal tar pitch and furfural in different proportions, followed by carbonization of obtained solid product and steam activation of the carbonizate. The chemical composition of the initial mixture significantly affects the physicochemical properties (surface area, pore structure, electro resistance and amount of oxygen-containing groups on the surface) of the obtained materials. The incorporation of oxygen in the precursor mixture by means of furfural, has a strong influence in the synthetic step; increasing the furfural content facilitates the formation of a solid product characterized by a large oxygen content. Moreover, the solid product is more reactive towards activation as the furfural content increases, giving rise to nanoporous carbons with large surface areas and unique chemical features (high density of oxygen functionalities of basic nature). These nanoporous carbons have been investigated as electrodes in electrochemical applications.

Influence of fiber content on the structure and properties of short carbon fiber reinforced carbon foam

A novel carbon foam with high strength was produced from mixtures of short carbon fibers and Mitsubishi naphthalene-based mesophase pitch. These mixtures subsequently underwent foaming, carbonization and graphitization. Investigations were carried out to determine the effect on the structure and properties of the carbon foam through the addition of fibers to carbon foam. The results have shown that compressive strength increased linearly with fiber fraction, but decreased at higher fiber fractions. Thermal conductivity increased at lower fiber fraction, but dropped with more fibers addition to carbon foam. The predominant strengthening mechanism was attributed to the pulling-out effect based on the fiber–matrix interface.

Templated mesoporous carbons and their performance for electric double layer capacitors

Templated mesoporous carbons with high surface area were successfully prepared by the carbonization of a mixture of thermoplastic precursor pitch with MgO precursors (magnesium acetate and citrate) at 950 °C in a N 2 atmosphere. The BET surface area of the carbons obtained reached a very high value without any activation process. The carbons were rich in mesopores. The electrochemical performance of mesoporous carbons prepared as electrode materials for electric double layer capacitors were also investigated. Measurement of capacitance was carried out in a mass fraction 30% KOH electrolyte. Results showed that the mesoporous carbons had a high specific capacitance and perfect rate performance. In particular, the sample prepared with a mass ratio of MgO to pitch of 4 for the magnesium citrate template showed a fairly high capacitance, about 284 F·g −1 at a current density of 20 mA·g −1 and 236 F·g −1 at 1 000 mA·g −1. The impedance of all the capacitors was smaller than 3.5 Ω.

Carbon Foams with High Compressive Strength Derived from Mixtures of Mesophase Pitch and Si Particles

Carbon foam with relatively high compressive strength and high porosity was prepared from a mixture of mesophase pitch and Si particles by foaming and carbonization. The influence of Si content on the microstructures and properties of the carbon foam was studied. Results show that the pore number decreases and the strut thickness increases with an increasing of Si content. In addition, bulk density also increases with increasing Si content but the porosity decreases. Si addition to the mesophase pitch reduces the number of microcracks on the cell wall of the carbon foam remarkably which results in an increase of compressive strength for the carbon foams. Compressive strengths improve by 46%, 176% and 339% at Si additions of 30%, 40% and 50% (wt %), respectively. Carbon foam with a relatively high compressive strength of 24.6 MPa and a porosity of 61% are obtained when 50 wt% Si is added.

Microstructure and electrochemical performance of Si–SiO 2–C composites as the negative material for Li-ion batteries

Si–SiO 2–C composites are synthesized by ball milling the mixture of SiO, graphite and coal pitch, and subsequent heat treatment at 900 °C in inert atmosphere. The electrochemical performance and microstructure of the composites are investigated. XRD and TEM tests indicate that the carbon-coating structure of Si–SiO 2–C composites form in pyrolysis process, which can remarkably improve the electrochemical cycling performance. The coal pitch as carbon precursor and graphite demonstrate the same important effect on the Li-alloying/de-alloying property of the Si–SiO 2–C composites. The Si–SiO 2–C composites exhibit the electrochemical reversible Li-alloying/de-alloying capacity of 700 mAh g −1 and excellent cyclic stability even at about the 90th cycle.

Effect of zirconium addition on the microstructure and performance of carbon foam

A novel carbon foam was prepared from mixtures of mesophase pitch and dopant (zirconium), followed by foaming, carbonization and graphitization. The influence of Zr on the microstructure and properties of these foams was analyzed. Results have shown that Zr can promote the graphitization degree of carbon foams, which lead to an increase of thermal conductivity. The high bulk thermal conductivity of 63 W/m K was achieved with an addition of 3 wt% at heat treatment temperature of 2573 K. The d 0 0 2 spacings of graphitic foams are found to decrease with the increase of dopant concentration in the pitch. SEM analysis also showed micro-cracks at the ligament of the doped graphitic foam, which might be responsible for the decrease of the compressive strength.

Orthopedics in the Graeco - Roman era

In this study the evolutionary development of orthopedics (management of diseases of bones and joints), which commenced in early Mesopotamia and Egypt, is followed through Classical times.The Greek infl uence probably commenced in the 6thcentury BC with Democedes of Croton who cured the Persian king’s dislocated ankle. The Corpus Hippocraticum laid the foundation of orthopedic practice in antiquity. Although knowledge of anatomy was limited, its four books on orthopedics (The Nature of Bones, Mochlicon, On Fractures, On Joints) count amongst the outstanding contributions of Hippocratic writers. In systematic manner the general recognition and management of fractures and dislocations are covered, followed by the handling of individual lesions. Hippocrates differentiated between closed and open fractures (with overlaying skin wounds). Closed fractures were reduced to as normal a position as possible – manually where possible, but with large bones and in the presence of formidable muscle mass, mechanical traction was often employed (e.g. the Hippocratic bench and the bizarre succusion ladder for spinal deformities). There is no mention of the use of analgetic drugs. After application of cerate (mixture of olive oil, soda and pitch) to the skin, the fracture was immobilized by a combination of plasters and compresses (often fi rmed up with gum-mixtures) – but never very fi rmly. On the 3rd, 6/7th, 9thand 12th days the bandaging was removed, the lesion inspected and if considered necessary, re-aligned, A variety of splints were then applied. Strict bed rest was enforced, as well as a light diet (no wine or meat for 10 days). It was believed that fractures of the feet, clavicle, ribs and jaw healed after 20 days, of the forearm after 30 days, and fractures of the upper arm and leg after 40 days. Open fractures were considered very serious injuries, and reduced very carefully. Protruding bone fragments were removed (sawn off if necessary) and the wound was covered with black cerate, compresses and light bandages. Pressure and heavy splints were thought to induce infection and gangrene and thus avoided. Dislocations were reduced as soon and as effectively as possible, before muscle spasm set in. As with fractures manual reduction was, where necessary, complemented by mechanical traction. After extensive washing of the joint area with warm water, cerate was applied to the wound and specialised bandaging (even splints) ensured immobilization. Open dislocations like open fractures were considered very serious and reduction was not attempted. Again all pressure bandaging was avoided. A non-functional joint was commonly the end result. The management of 18 specifi c fractures is described in detail. Jaw fractures were fi xed by the binding of contiguous teeth. Fractures of the spinal column clearly presented a major problem. Although knowledge of spinal anatomy was surprisingly good, the diagnosis of fractures was very difficult and its association with spinal curvatures presented almost insurmountable problems of management. It was recognized that rib fractures could cause serious damage to the lung and pleura. Complex problems caused by arm fractures involving the elbow or shoulder joints, and combined radius and ulna fractures, are addressed. Femur fractures presented major problems and permanent leg deformity was very common. Open femur fractures were extremely serious and Hippocrates even stated that a physician who could ethically avoid becoming involved in treating such an injury, should do so. Fractures of femur necks were not recognised. The Hippocratic work, Wounds of the head, dealing with fractures of the skull, is not covered in this study.Management of the major joints are individually described. Seven different techniques of reducing a dislocated shoulder joint are mentioned The original description of the management of the dislocation of the wrist and hand is lost. Proper reduction of hip-dislocation was essential to avoid muscle atrophy and life-long limping, and was achieved by intricate mechanical suspension. Strangely enough, lateral dislocation of the knee was a common occurrence and not seen as a serious problem. Congenital club feet were effectively treated by prolonged fi xation in the correct position by way of tight bandaging with compresses stiffened in glue-mixtures.There is abundant skeletal evidence of osteo-arthritis in Neolithic man, but no clear description of it in the Corpus Hippocraticum. Gout is repeatedly mentioned in the Corpus but without detailed descriptions of the disease. In the Roman era authors like Heliodorus, Antyllus and Celsus in particular, wrote authoritatively on orthopedic subjects, Osteo-archaeological evidence is that fractures were treated expertly in the Roman army. Conditions consistent with degenerative osteoarthritis and true gout (as podagra and chiragra) were described by Celsus and Aretaeus of Cappadocia. Soranus, Rufus of Ephesus and Galen also wrote on orthopedic subjects. We will today differ from many statements made in the Corpus Hippocraticum, but it is clear that the orthopedic basis laid by those documents was not seriously challenged for 1 000 years.

Chemical investigation on black pigments in the carved decoration of sixteenth century alabaster tombs from Zaragoza (Spain)

An analytical protocol based on optical microscopy (OM), scanning electron microscopy (SEM) observation, energy-dispersive X-ray (EDX) analyses, analytical pyrolysis in the presence of hexamethyldisilazane followed by gas chromatographic/mass spectrometric analysis (Py-silylation-GC/MS) and gas chromatography/mass spectrometry (GC/MS) after alkaline hydrolysis, solvent extraction and trimethylsilylation was used to study the origin and nature of black pigments from the carved inscriptions of several panels of two alabaster tombs dated from the mid-sixteenth century. Optical microscopy and SEM observation showed the presence of an amorphous very dark-brown substance, from translucent to opaque. EDX analyses revealed that the samples were mainly made up of C and O, thus highlighting the organic nature of the material used in the inscriptions. Py-silylation-GC/MS and GC/MS analyses provided detailed molecular compositions, highlighting the presence of a wide range of compound classes including diterpenoid acids, tricyclic abietanes, mid- and long-chain monocarboxylic fatty acids, n-alkanols and nalkanes. The pyrograms, the chromatographic profiles and the presence of characteristic biomarkers indicated that a mixture of pine pitch and beeswax had been used to make the black inscriptions.

High rate capability of carbonaceous composites as anode electrodes for lithium-ion secondary battery

Anode materials with high rate capability for Li-ion secondary batteries were investigated by using the mixture of graphite, cokes, and petroleum pitch. Since obvious potential plateaus were obtained at graphite contents above 40 wt.%, which would cause difficulties in perceiving the capacity variations as a function of electrical potential, the graphite content were determined at 20–30 wt.%. The composites with a given content of graphite and remaining content of petroleum pitch/cokes mixtures at 1:4, 1:1, and 4:1 mass ratios were heated at a temperature range of 800–1200 °C. For a given composition of carbonaceous composite, the discharge rate capability improved but the reversible capacity decreased with increasing the heat treatment temperature. Although the reversible capacity increased with increasing content of the petroleum pitch for given graphite content and heat treatment temperature, the discharge rate capability decreased. The carbonaceous composites prepared by the mixture of 30 wt.% graphite and 70 wt.% petroleum pitch/cokes mixture at 1:4 mass ratio with the heat treatment at 800 °C showed relatively high electrochemical properties, of which reversible capacity, initial efficiency, discharge rate capability (retention of discharge capacity in 5 C/0.2 C) and charge capacity at 5 C were 312 mAh/g, 79%, 89% and 78 mAh/g, respectively.

Investigation of pitch–sulphur mixtures used as binder in the preparation of black ceramics

Since tens of years, sulphur is a very classical additive in the composition of black ceramics because, if added in small amounts (i.e., less than 10 wt.% of the binder), it improves their mechanical properties without strongly degrading their graphitability and their conductivity. Macroscopic properties of black ceramics strongly depend on the quality of the interfaces between grains of solid filler (graphite, carbon black) and coke originating from the pyrolysis of the binder; thus, the binder should correctly wet the filler prior to the carbonisation process. Coal-tar pitch usually exhibits a high affinity for carbon grains. In the present work, the effect of the amount of sulphur on the viscosity of the molten binder and on the way it wets the solid filler was investigated. For that purpose, the penetration of mixtures of coal-tar pitch and sulphur inside a bed of carbon particles was studied as a function of temperature. The influence of the sulphur content on composition, optical texture, and transport properties of the derived black ceramics, as well as the way it was mixed with the other constituents, were also examined. It was found that the preparation of black ceramics may be achieved easily and in safe conditions, without evolution of H 2S, using pitch–sulphur mixtures first molten in a bladed mixer, and having sulphur contents within the range 10–20 wt.%. The presence of sulphur increases the coke yield but lowers the ability to graphitise, thus limiting the transport properties of the resultant black ceramic. The optimal concentration of sulphur should thus be a compromise between mechanical strength and other physical properties.

Porous Silicon Carbide Ceramics Produced by a Carbon Foam Derived from Mixtures of Mesophase Pitch and Si Particles

Carbon foam templates were prepared from a mixture of mesophase pitch (MP) and Si particles, followed by foaming and carbonization. Subsequent molten Si infiltrated into the carbon foam at 1500°C for 4 h in an inert atmosphere resulted in the formation of porous SiC ceramics. Micrographs were investigated by a scanning electron microscope (SEM), and phase identification of porous SiC ceramics was performed by X‐ray diffraction (XRD). The flexural strength and bulk density of porous SiC ceramics were also measured and calculated. The results revealed that the flexural strength of porous SiC ceramics increases with increasing Si content and decreasing porosity. The addition of Si in MP results in an increased densification of porous SiC struts. With 50 wt% Si, porous SiC ceramics with a high flexural strength of 23.9 MPa and a porosity of 55% were obtained.

Spherical natural graphite coated by a thick layer of carbonaceous mesophase for use as an anode material in lithium ion batteries

A method for coating a thick layer of carbonaceous mesophase was developed to treat spherical natural graphite (SNG) for use as anodes in lithium ion batteries. The carbonaceous mesophase layer was fabricated by heat treatment of a mixture of SNG and coal tar pitch. The thickness of the carbonaceous mesophase on the surface of the SNG was approximately 2.5 μm, which is effective for enhancing the strength of the carbonaceous mesophase shell and for allowing the shell to maintain good integrity at a high anode density (1.6 g cm−3). The mesophase layer increased the initial columbic efficiency from approximately 90% to 95%, dramatically improved the capacity retention and reduced the irreversible capacity by greatly decreasing the SNG surface area. The initial efficiency, cycle life and rate capability for the SNG anode covered by a thick mesophase layer gave comparable results as the mesocarbon microbeads (MCMB) anode, while the SNG anode reversible capacity of 341 mAh g−1 was higher than that of MCMB, 319 mAh g−1. Electrochemical measurements showed that SNG particles coated by a thick carbonaceous mesophase layer are strong candidates for use as possible anode materials in high energy density lithium ion batteries.

Eucalyptus Tar Pitch Substitution of Phenol in the Preparation of Novolak-Type Resins Cured with Hexamethylenetetramine

Abstract Wood tar pitch, sometimes referred to as biopitch, is the residue from the distillation of tar recovered during charcoal making processes. The biopitch from Eucalyptus tar, which has guaiacyl and syringyl units in its molecular structure, exhibits novolak behavior and this phenolic oligomer can be cured with hexamethylenetetramine (HMTA). In this work, mixtures of commercial phenolic resins and Eucalyptus tar pitch were cured and characterized by infrared spectroscopy, elemental and thermogravimetric analyses. Their acetone-insoluble contents were determined and their electrical properties were investigated. The effects of pitch and HMTA contents on phenolic resin properties were modelled using statistical techniques. The regions of optimum formulations were indicated. The results showed that pitch decreases the thermal stability and the acetone-insoluble content of the phenolic blends, whereas HMTA addition had an opposite effect. The statistical model applied indicated that, in terms of acetone-insoluble content, phenolic resin can be substituted for pitch up to a composition of 50 wt %. Electrical studies showed that pitch–phenolic blends have insulating properties.