Rheological behavior and thermal properties of pitch/poly(vinyl chloride) blends

The effect of adding poly(vinyl chloride) (PVC) and coke filler on the rheological behavior and thermal properties of a coal tar pitch was investigated with a view to developing an appropriate viscoelastic binder for the injection molding of graphite components. Dynamic mechanical analysis revealed that the pitch formed compatible blends with PVC featuring a single glass transition temperature (Tg) intermediate to the two parent Tg’s. Adding PVC to the pitch increased melt viscosity substantially and resulted in strong shear thinning behavior at high PVC addition levels. Adding coke powder as filler increased the melt viscosity even further and enhanced shear thinning trends. Pyrolysis conducted in a nitrogen atmosphere revealed interactions between the PVC and pitch degradation pathways: the blends underwent significant thermal decomposition at lower temperatures but showed enhanced carbon yields at high temperatures. Pyrolytic carbon yield at 1000 °C was further improved by a heat treatment (temperature scanned to 400 °C) in air or oxygen. However, carbon yield decreased with addition of PVC. In addition, the degree of ordering attained following a 1 h heat treatment at 2400 °C also decreased with increasing PVC content.     

Mechanical and functional properties of Al2O3–ZrO2–MWCNTs nanocomposites

Multi-walled carbon nanotubes (MWCNTs) are often reported as additives improving mechanical and functional properties of ceramic composites. However, despite tremendous efforts in the field in the past 20 years, the results are still inconclusive. This paper studies room temperature properties of the composites with polycrystalline alumina matrix reinforced with 0.5–2 vol.% MWCNTs (composites AC) and zirconia toughened alumina with 5 vol.% of yttria partially stabilised zirconia (3Y-PSZ) containing 0.5–2 vol.% of MWCNTs (composites AZC). Dense composites were prepared through wet mixing of the respective powders with functionalised MWCNTs, followed by freeze granulation, and hot-pressing of granulated powders. Room temperature bending strength, Young's modulus, indentation fracture toughness, thermal and electrical conductivity of the composites were studied, and related to their composition and microstructure. Slight increase of Young's modulus, indentation fracture toughness, bending strength, and thermal conductivity was observed at the MWCNTs contents ≤1 vol.%. At higher MWCNTs contents the properties were impaired by agglomeration of the MWCNTs. The DC electrical conductivity increased with increasing volume fraction of the MWCNTs.     

Thermal analysis of drying process of durum wheat dough under the programmed temperature-rising conditions

The effects of temperature and moisture content on the drying rate of durum wheat pasta were examined using thermogravimetry and differential scanning calorimetry (DSC) at temperature-rising rates of 0.2–1.0 °C/min. The activation energy for the mass transfer coefficient of drying was estimated to be ca. 32 kJ/mol at a moisture contents of 0.14 kg-H₂O/kg-d.m. or higher, but increased rapidly as the moisture content dropped below this level. The conclusion temperature of the endothermic peak in the DSC and the temperature of the inflection point of the drying characteristics curve were located near the glass transition curve of the durum semolina flour.     

Liquid crystallinity in trimer oligomers isolated from petroleum and pyrene pitches

The first unsubstituted, monodisperse polycyclic aromatic hydrocarbon (PAH) to form a liquid crystalline phase (100% mesophase) has been isolated. With a molecular weight of 598 Da and consisting of only 14 aromatic rings, this pyrene trimer is also the lowest molecular weight (mol wt) PAH species for which the existence of liquid crystallinity has been reported. Multiple isomers of the pyrene trimer exist, providing the melting-point depression (mpt = 290 °C) necessary for the existence of a liquid phase and the possibility of mesophase formation. The trimer cut of M-50 pitch (mol wt = 645–890 Da; mpt = 330 °C) has also been isolated and was found to consist of ∼40% mesophase. This trimer is the lowest average mol wt carbonaceous pitch for which significant mesophase formation has been reported. Both trimers were isolated from their starting pitches via packed-column supercritical extraction, using toluene and N-methylpyrrolidone (NMP) mixtures as the extractive solvent. Mass spectrometry and UV–vis and fluorescence spectroscopy were used for molecular characterization. The results of this study indicate that for PAHs, the molecular weight for which liquid crystallinity occurs can be significantly reduced by creating PAH oligomers with lower polydispersity and increased monomer-unit homogeneity.     

The effect of changes in synthesis temperature and acetylene supply on the morphology of carbon nanocoils

Carbon nanocoils (CNCs) with controlled shape, coil diameter and coil pitch have been synthesized in a chemical vapor deposition (CVD) system by changing the reaction temperature and acetylene flow rate. It is found that three-dimensional CNCs are produced at a lower temperature (700–770 °C), while a higher temperature (810 °C) leads to the growth of straight carbon nanofibers (CNFs). CNC–CNF hybrid structures are produced by increasing growth temperature from 750 to 810 °C during a single synthesis run, while CNF–CNC hybrid structures are produced by decreasing the temperature from 810 to 750 °C. Similarly, by changing growth temperature from 750 to 810 °C and then back to 750 °C during a single run, CNC–CNF–CNC complex hybrid structures can be obtained. During the CVD process, the pulsing of acetylene and the changing of acetylene flow rate are also found to be effective in controlling the structure of CNCs. CNCs with periodic helical structures can be produced by interrupting the acetylene flow or changing its flow rate periodically. It is found that the higher the flow rate of acetylene, the smaller the coil pitch and diameter of the grown CNCs.     

Pitch-based ribbon-shaped carbon-fiber-reinforced one-dimensional carbon/carbon composites with ultrahigh thermal conductivity

Ribbon-shaped carbon fibers have been prepared from mesophase pitch by melt-spinning, oxidative stabilization and further heat treatment. The internal graphitic layers of ribbon-shaped carbon fibers graphitized at 2800 °C show a highly preferred orientation along the longitudinal direction. Parallel stretched and unidirectional arranged ribbon-shaped carbon fibers treated at about 450 °C were sprayed with a mesophase pitch powder grout, and then hot-pressed at 500 °C and subsequently carbonized and graphitized at various temperatures to produce one-dimensional carbon/carbon (C/C) composite blocks. The shape and microstructural orientation of ribbon fibers have been maintained in the process of hot-pressing and subsequent heat treatments and the main planes of the ribbon fibers are orderly accumulated along the hot-pressing direction. Microstructural analyses indicate that the C/C composite blocks have a typical structural anisotropy derived from the unidirectional arrangement of the highly oriented wide ribbon-shaped fibers in the composite block. The thermal conductivities of the C/C composites along the longitudinal direction of ribbon fibers increase with heat-treatment temperatures. The longitudinal thermal conductivity and thermal diffusivity at room temperature of the C/C composite blocks graphitized at 3100 °C are 896 W/m K and 642 mm²/s, respectively.     

Mechanical and physical behaviors of short pitch-based carbon fiber-reinforced HfB2–SiC matrix composites

Short Pitch-based carbon fiber-reinforced HfB₂ matrix composites containing 20 vol% SiC, with fiber volume fractions in the range of 20–50%, were manufactured by hot-press process. Highly dense composite compacts were obtained at 2100 °C and 20 MPa for 60 min. The flexural strength of the composites was measured at room temperature and 1600 °C. The fracture toughness, thermal and electrical conductivities of the composites were evaluated at room temperature. The effects of fiber volume fractions on these properties were assessed. The flexural strength of the composites depended on the fiber volume fraction. In addition, the flexural strength was significantly greater at 1600 °C than at room temperature. The fracture toughness was improved due to the incorporation of fibers. The thermal and electrical conductivities decreased with the increase of fiber volume fraction, however.     

Single domain oval carbon nanofiber prepared from a polymer blend process

Single domain graphite fibers of 50–500 nm in diameter were prepared from a mesophase pitch mixed with a matrix polymer to form a polymer alloy. The alloy was then spun, stabilized, carbonized, and graphitized at 2900 °C. The carbonized fiber had a circular or Y-shaped cross-section, but all of the graphitized carbon nanofiber (CNF) changed into an elliptical cross-section with an aspect ratio (major axis/minor axis) of 2.47. The CNF consisted of well-developed graphite layers ordered throughout the cross-section, as observed in a single crystal and the layer edges formed loops consisting of 5–10 layers.     

Characterization of particles packing in alumina green tape

Aqueous alumina slurry was prepared with a commercial powder of elongated particles, which has the aspect ratio ranging from 1 to 3.5 with the mean of 1.6, to examine the effect of forming conditions on the particle alignment in green tapes. The slurry appeared pseudoplastic with a yield stress, but showed no thixotropic behavior. Its flow curve fitted very well to the Herschel–Bulkley model approximation, which suggested shear-thinning constant of 0.54. Polarized microscopy with the liquid immersion technique was applied to examine the particle orientation through the direction along the tape thickness. In the absence of coquette flow, randomly oriented particles were noted in the tape. At the top surface, particles were aligned with their long-axes (a-axis) along the casting direction. The variation in the degree of orientation was 6.8 ± 1.2. In the area near the Mylar carrier, a-axis of particle made an angle to the carrier surface with the degree of orientation about 5.8 ± 1.0. As the combination of pressure flow and coquette flow, tape cast with casting velocity of 2.5 and 91.5 cm/min, which respectively resulted in shear rate of 1.38 and 50.8 s^?1, were observed. The orientation was significant near the top surface and was higher than that above the carrier surface. The a-axis of particles above the carrier surface was inclined to the surface at low shear rate (1.38 s^?1), but was nearly parallel at high shear rate (50.8 s^?1). Nevertheless, the orientation varies with the location in the tape prepared at the shear rate of 50.8 s^?1.     

A comparison of the effect of graphitization on microstructures and properties of polyacrylonitrile and mesophase pitch-based carbon fibers

Polyacrylonitrile (PAN) and mesophase pitch (MPP)-based carbon fibers were heat treated in the temperature range of 1300–2700 °C. After high-temperature heat treatment (HHT), the microstructures and mechanical properties of PAN and MPP-based carbon fibers were investigated. For both series of carbon fibers, the Young’s modulus increased with heat treatment temperature increasing. The tensile strength of PAN-based carbon fibers decreased, while that of MPP-based carbon fibers increased. After HHT at 2700 °C, the tensile strength of MPP-based carbon fibers exceeded that of PAN-based carbon fibers. The results could be ascribed to the variously original structures and the different routines of structural evolution. The physical entanglements and covalent cross-links of carbon ribbons in PAN-based carbon fibers contributed to a higher shear stress between the graphene layers, however, tended to generate voids and cracks during HHT due to an extensive transformation from turbostratic to ordered structure along with nitrogen removing. For MPP-based carbon fibers, they displayed a radial texture with ordered and parallel packing of layers in the transverse section. Thus, it was easier for the graphene layers to stack and bond to the adjacent ones without strong rotations, leading to fewer voids and cracks.     

An insight into pitch/substrate wetting behaviour. The effect of the substrate processing temperature on pitch wetting capacity

Pitch/substrate interactions at the mixing stage (<200 °C) were studied by means of a drop spreading wetting test. The substrates were obtained from a petroleum pitch by thermal treatment in the temperature range of 300–1900 °C. The results show that thermal treatment has a significant influence on the physical and chemical properties of the substrates, and consequently, on pitch/substrate wetting behaviour. Substrates with plastic properties (softening point below 350 °C) deform and/or agglomerate during the wetting experiment and thereby stop pitch penetrating. Moreover, the presence of aliphatic hydrogen in these substrates facilitates oxidative stabilization, which in turn facilitates pitch/substrate wetting behaviour. Substrates obtained above 400 °C are wetted by the pitch. However, the pre-graphitic order obtained on carbonization does not seem to have a significant effect on pitch wetting capability under the conditions used in this study. The oxidative stabilization of the substrates does not exert a significant influence on unfused substrates. However, in the case of plastic substrates, pitch wetting capacity is greatly affected by oxidation.     

The structure and properties of ribbon-shaped carbon fibers with high orientation

Using a naphthalene-derived mesophase pitch as a starting material, highly oriented ribbon-shaped carbon fibers with a smooth and flat surface were prepared by melt-spinning, oxidative stabilization, carbonization, and graphitization. The preferred orientation, morphology, and microstructure, as well as physical properties, of the ribbon-shaped carbon fibers were characterized. The results show that, the ribbon-shaped fibers possessed uniform shrinkage upon heat treatment, thereby avoiding shrinkage cracking commonly observed in round-shaped fibers. As heat treatment progressed, the ribbon-shaped graphite fibers displayed larger crystallite sizes and higher orientation of graphene layers along the main surface of the ribbon-shaped fiber in comparison with corresponding round-shaped fibers. The stability of the ribbon-shaped graphite fibers towards thermal oxidation was significantly higher than that of K-1100 graphite fibers. The longitudinal thermal conductivity of the ribbon fibers increased, and electrical resistivity decreased, with increasing the heat treatment temperatures. The longitudinal electrical resistivity and the calculated thermal conductivity of the ribbon-shaped fibers graphitized at 3000 °C are about 1.1 μΩ m and above 1100 W/m K at room temperature, respectively. The tensile strength and Young’s modulus of these fibers approach 2.53 and 842 GPa, respectively.     

Structural parameters and oxygen ion conductivity of Y2O3–ZrO2 and MgO–ZrO2 at high temperature

The oxygen ion conductivity of zirconia-based solid electrolytes doped with 8 mol% Y₂O₃–ZrO₂ (YSZ) and 9 mol% MgO–ZrO₂ (Mg-PSZ) at high temperature was investigated in terms of their thermal behavior and structural changes. At room temperature, YSZ showed a single phase with a fluorite cubic structure, whereas Mg-PSZ had a mixture of cubic, tetragonal and some monoclinic phases. YSZ exhibited higher ionic conductivity than Mg-PSZ at temperatures from 600 °C to 1250 °C because of the existence of the single cubic structure and low activation energy. A considerable increase in the conductivity with increasing temperature was observed in Mg-PSZ, which showed higher ionic conductivity than YSZ within the higher temperature range of 1300–1500 °C. A monoclinic-to-tetragonal phase transformation was found in Mg-PSZ and the lattice parameter of the cubic phase increased at 1200 °C. The phase transformation and the large lattice free volume contributed to the significant enhancement of the ionic conductivity of Mg-PSZ at high temperatures.     

Electrochemical behaviour of LaCl3 at tungsten and aluminium cathodes in LiCl–KCl eutectic melt

The electrochemical behaviour of lanthanum was studied at inert tungsten electrode and reactive aluminium electrode in LiCl–KCl eutectic melt in the temperature range 698–798 K using transient electrochemical techniques. Reduction of La(III) to La(0) at the tungsten electrode takes place in a single step. The reduction shows quasi-reversible behaviour for polarization rates, 25 ≤ ν ≤ 150 mV s^?1 and is predominantly controlled by charge transfer of La(III) ions for scan rates higher than 75 mV s^?1. The heterogenous rate constant of the process was estimated from impedance spectroscopy and from the semi-integrals of the cyclic voltammograms. The redox potential of the La(III)/La couple at the Al electrode was observed to be more positive than that at the inert electrode. This potential shift is due to the lowering of the activity of La in the metal phase caused by the formation of the intermetallic compound Al₁₁La₃. Thermodynamic properties such as Gibbs energy of formation of Al₁₁La₃, excess Gibbs energy and the activity coefficient of La in Al were calculated from the open circuit potential measurement.     

Pressure–temperature–viscosity relationship for heavy petroleum fractions

This paper deals with the influence that both pressure and temperature exert on the viscosity of heavy petroleum fractions, such as bitumen of different penetration grades, in temperature and pressure ranges comprised between 60 °C and 160 °C and 0–400 bars, respectively. From the viscous flow tests carried out, it is apparent that bitumen behaves as a Newtonian liquid in the above-mentioned range of temperature and pressure. The temperature–pressure–viscosity relationship for bitumen of different penetration grades, mainly used for paving applications, can be modelled using a modified WLF model, the FMT model. This model includes different physical parameters, such as material compressibility and expansivity, which have been obtained from pressure–volume–temperature (PVT) measurements.     

Phase equilibria of the propylene glycol/CO2 and propylene glycol/ethanol/CO2 systems

The high-pressure vapour–liquid phase equilibria (P–T–x–y) of the binary mixture propylene glycol/CO₂ have been experimentally investigated at temperatures of (398.2, 423.2 and 453.2) K over the pressure range from (2.5 to 55.0) MPa using a static-analytic method. Furthermore, the high-pressure vapour–liquid phase equilibria (P–T–x–y) of the ternary mixture propylene glycol/CO₂/ethanol at constant temperatures of (398.2, 423.2 and 453.2) K and at constant pressure of 15.0 MPa have been determined using a static-analytic method. Initial concentrations of components in propylene glycol (PG)/ethanol (EtOH) mixture vary from 10 up to 90 wt.%. In general, for binary system it was observed that the solubility of CO₂ in the heavy propylene glycol reach phase increases with increasing pressure at constant temperature. On the contrary, the composition of gaseous phase is not influenced by the pressure or the temperature. On average the solubility of PG in light phase of CO₂ amounts to 30 wt.%. The system behaviour at temperature of 398.2 K was investigated up to 70.0 MPa and a single-phase region was not observed. Above the pressure 60.0 MPa a single-phase region of the system was observed for the temperature of 423.2 K. For the temperature of 453.2 K the single-phase was observed above the pressure of 48.0 MPa. For ternary system it was observed that the composition of heavy phase is slightly influenced by the temperature when the mass fraction of EtOH in initial mixture is higher than 50 wt.%. If the mass fraction of PG in initial mixture is higher than 50 wt.%, the composition of heavy phase is not influenced by the temperature anymore. The composition of the PG, EtOH and CO₂ in light phase remains more or less unchanged and it is not influenced by the conditions.     

Enhanced electrokinetic,dielectric and electrorheological properties of covalently bonded nanosphere-TiO2/polypyrrole nanocomposite

Nanosphere-TiO₂ was synthesized, surface functionalized with (3-aminopropyl) triethoxysilane (APTS) and then covalently bonded with polypyrrole (PPy) with bottom-up surface engineering strategy to obtain nanosphere-TiO₂/PPy core/shell hybrit nanocomposite. All the materials were subjected to full chemical and morphological characterizations by using various techniques. The presence of NaCl, AlCl₃, cetyltrimethyl ammonium bromide and sodium dodecylsulfate observed to cause high colloidal stabilities of the nanocomposite dispersions by reaching to zeta(ζ)-potential values of ζ > + 30 mV and ζ < − 30 mV. A series of suspensions were prepared by dispersing nanosphere-TiO₂ and nanosphere-TiO₂/PPy particles in insulating silicone oil (SO) and dielectric properties were determined using an LCR meter. Antisedimentation stabilities of these suspensions were determined against gravitational forces and 54% colloidal stability was achieved with the nanocomposite after 30 days. Polarizabilities of the suspended particles were observed using an optical microscope under externally applied electric field strength. Then the suspensions were subjected to electrorheological measurements by investigating the effects of shear rate, particle volume fraction, shear stress, and electric field strength. Non-Newtonian shear thinning behaviors were observed for the samples. Further, vibration damping characteristics of the materials were determined with shear stress and frequency oscillation measurements. Enhanced reversible viscoelastic deformations were observed for the dispersions from creep-recovery tests and 64% creep-recovery was obtained for nanosphere-TiO₂/PPy/SO system under E = 3.5 kV/mm.     

Influence of particle size on the analytical and chemical properties of two energy crops

Two energy crops (switchgrass and reed canary grass) have been processed using ball mills and divided into two size fractions (<90 μm and 90–600 μm) and analysed using an array of analytical techniques including proximate and ultimate analysis, metal analysis, calorific value determination, and plant component analysis (cellulose, lignin and hemicellulose contents). The results indicate that smaller particles of the two grasses have a significantly higher concentration of inorganic matter and moisture content than larger particles. In contrast the larger size fractions had a higher carbon content, and lower nitrogen content, with a resulting higher calorific value. The volatile content was also higher in the larger size fraction. The composition of the organic content varied between the two size fractions, most noticeable was the difference in cellulose concentration which was approximately 50% higher in the >90 μm sample. Two laboratory scale techniques, thermogravimetric analysis (TGA) and pyrolysis–GC–MS (py–GC–MS), were used to study the significance of these differences in thermal conversion. In py–GC–MS of reed canary grass, and switchgrass to a lesser extent, the amounts of cellulose and lignin decomposition products were higher for the larger particle size fraction. The differences in cellulose contents were also apparent from the TGA studies, where different mass losses were seen in the cellulose decomposition region of the two size fractions. From the results of these two techniques it was concluded that the differences in ash, and therefore catalytic metal contents, between the two size fractions, resulted in lower pyrolysis temperatures, lower char combustion temperatures, and higher yields of catalytic pyrolysis decomposition products for the smaller size fractions. The implications of the results are discussed in terms of the bio-oil quality in fast pyrolysis and the predicted behaviour of the ash in combustion. It is suggested that pre-treatment by milling is one route that might be used routinely as a feedstock quality improvement strategy in integrated biomass conversion processes.     

Thermal-diffusivity measurement of 3D-stitched C–SiC composites

Effect of siliconization conditions on thermal diffusivity of 3D-stitched fiber architecture-based C–SiC composites was investigated to select desired conditions. Several 3D-stitched C–SiC composite blocks were prepared using coal–tar pitch as a carbon precursor and siliconization was carried out at 1450 and 1650 °C for 10 and 120 min. Thermal diffusivity of blocks was investigated using laser-flash equipment in in-plane and through-thickness directions. It varies from 77 mm²/s at room-temperature to 14.7 mm²/s at 1500 °C in in-plane and 36–6.1 mm²/s in through-thickness direction. A model was developed to estimate thermal diffusivity in in-plane and through-thickness directions based on the volume fraction of the constituents and porosity of the composite blocks. The estimated thermal-diffusivity values were compared with the measured values. The values were found to be close to the experimental values in entire testing temperature range at all the siliconization conditions.     

Graphite foam from pitch and expandable graphite

Graphite foams were prepared from a coal tar pitch that was partially converted into mesophase. Expandable graphite was used instead of an inert gas to “foam” the pitch. The resulting foam was subjected to a series of heat treatments with the objective of first crosslinking the pitch, and thereafter carbonizing and graphitizing the resulting foam. XRD confirmed that the graphitization at 2600 °C resulted in a highly graphitic material. The porosity of this foam derives from the loose packing of the vermicular exfoliated graphite particles together with their internal porosity. During the foaming process the pitch tends to coat the outside surface of the expanding graphite flakes. It also bonds them together. The graphite foam prepared with 5 wt.% expandable graphite had a bulk density of 0.249 g cm⁻³, a compressive strength of 0.46 MPa and a thermal conductivity of 21 W m⁻¹ K⁻¹. The specific thermal conductivity (thermal conductivity divided by the bulk density) of this low-density carbon foam was 0.084 W m² kg⁻¹ K⁻¹ which is considerably higher than that of copper metal (0.045 W m² kg⁻¹ K⁻¹) traditionally used in thermal management applications.