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.     

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.     

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.     

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.     

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.     

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.     

Fast pyrolysis of chicken litter and turkey litter in a fluidized bed reactor

Disposal of poultry litter such as chicken litter and turkey litter is becoming a major problem in the USA poultry industry because of environmental pressures and health concerns. Poultry litters form wood chips, chicken litter (flock 1, flock 2 and broiler) and turkey litter were converted into bio-oil, gas and char in a fluidized bed reactor at the temperature ranges of 450–550 °C. The bio-oil yield of poultry litter was relatively low (15–30 wt%) compared to wood derived bio-oil (34–42 wt%). The gas yield was increased from 32 to 61 wt% with increasing reaction temperature, and char yield was between 22 and 45 wt% depending on age and reaction conditions. The higher heating value (HHV) of the poultry litter bio-oil were between 26 and 29 MJ/kg, whereas that of the bedding material (wood chips) was 24 MJ/kg. The dynamic viscosities of bio-oil were varied from 0.01 to 27.9 Pa s at 60 °C, and those of values were decreased with increasing shear rate.     

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.     

Ferroelastic deformation of La0.58Sr0.4Co0.2Fe0.8O3−δ under uniaxial compressive loading

The mechanical deformation of lanthanum strontium cobalt ferrite under uniaxial compression was investigated at various temperatures. The material revealed a rather complex mechanical behaviour related to its ferroelasticity and stress–strain curves obtained in the 1st and 2nd loading cycles were completely different. A distinctive ferroelastic creep was observed at 293 K whilst typical ferroelastic stress–strain curves were obtained in the temperature range from 473 K to 873 K. At 1073 K, high-temperature creep deformation was observed instead of the ferroelastic deformation. The apparent Young's modulus was evaluated in various ways; the modulus determined from the last unloading curve ranged between 85 and 120 GPa. The obtained critical stress monotonically decreases from about 80 MPa to zero with increasing temperature, corresponding to the behaviour of the remnant strain. The presented results indicate that the importance of an appropriate consideration of the loading history in the practical application of these ferroelastic materials.     

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.     

Low temperature synthesis of anorthite based glass-ceramics via sintering and crystallization of glass-powder compacts

Anorthite based glass-ceramics were synthesized. The investigated glass compositions are located close to the anorthite-rich corner of the fluorapatite–anorthite–diopside ternary system. Glass powder compacts with mean particle size of 2 and 10 μm were prepared. Sintering behaviour, crystallization and the properties of glass-ceramics were investigated between 800 and 950 °C. In the case of specimens made from the finer particles, complete densification was achieved at a remarkably low temperature (825 °C) and the highest mechanical strength was obtained at 850 °C, but density significantly decreased at higher temperatures. The samples prepared from the larger particles exhibited higher values of density, shrinkage and bending strength within a wider temperature range (825–900 °C). Anorthite was predominantly crystallized between 850 and 950 °C, along with traces of fluorapatite. Diopside was detected only in the MgO richer compositions.     

Pitch carbon and LiF co-modified Si-based anode material for lithium ion batteries

To improve the electrochemical performance of silicon-based anode material, lithium fluoride (LiF) and pitch carbon were introduced to co-modify a silicon/graphite composite (SG), in which the graphite acts as a dispersion matrix. The pitch carbon helps to improve the electronic conductivity and lithium ion transport of the material. LiF is one of the main components of the solid electrolyte interphase (SEI) formed on the silicon surface, helping to tolerate the large volume changes of Si during lithiation/delithiation. The modified SG sample delivered a capacity of over 500 mA h g⁻¹, whereas unmodified SG delivered a capacity of lower than 50 mAh g⁻¹ after 100 cycles at 100 mA g⁻¹. When performed at 4 A g⁻¹, the reversible capacity of the modified SG was 346 mAh g⁻¹, much higher than that of SG (only 37 mA h g⁻¹). The enhanced cycling and rate properties of the modified SG can be attributed to the synergetic contribution of the pitch carbon and LiF which help accommodate the volume change, reduce the side reaction, and form a stable solid electrolyte interface layer.     

Determination of the particle interactions,rheology and the surface roughness relationship for dental restorative ceramics

The effect of inter-particle interactions on the slurry properties and the final surface roughness of the dental ceramic restoratives was investigated. A commercial dental ceramic powder, IPS Empress 2 veneer, was used as the raw material.The magnitudes of the particle–particle interactions were computed by the DLVO theory for the ceramic slurries of different electrolyte solutions (0.1 M, 0.25 M, 0.5 M, 0.75 M, 1 M NaCl and CaCl₂). As expected, the energies of particle–particle interactions were influenced significantly by the presence of electrolytes. These computations demonstrated that addition of electrolytes leads to a progressive depression of the repulsive double layer forces. The absence of these forces should inevitably lead to agglomeration caused by the ever-present van der Waals forces.The rheological measurements carried out using the slurries with same solution properties supported the findings of the DLVO computations. It was found that dental ceramic slurries showed a Newtonian behavior in the absence of electrolytes, which is indicative of little or no agglomeration in the slurry. On the other hand, the same slurries displayed a non-Newtonian, shear thinning behavior in the presence of electrolytes which can be attributed to agglomeration or gelation.Roughness of the ceramic surfaces produced from these slurries was studied by SEM analysis and profilometer measurements. Contact angle studies were also carried out on the same surfaces. It was observed that the surface became rougher initially with electrolyte addition to a maximum, most probably due to formation of isolated agglomerates due to a reduction of the repulsive double layer forces. After reaching a maximum, surface roughness decreased to a much lower value with further increase in electrolyte concentration. This was most probably caused by the formation of a relatively homogeneous, gel-like structure within the extensively agglomerated slurry due to a complete collapse of the double layer.     

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.     

Effect of pyrolysis temperature on the pore structure evolution of polysiloxane-derived ceramics

Homogeneous silicon oxycarbide (SiOC) ceramic powders were prepared by pyrolysis of cross-linked polysiloxane at different temperatures (1250–1500 °C) under vacuum. The effect of pyrolysis temperature on the pore structure evolution was investigated by means of N₂ adsorption, SEM, XRD, IR and element analysis (EA). Studies showed that predominate mesoporous ceramics with the average pore size in the range of 2–13 nm were obtained after pyrolysis in this temperature range. The pore structure transformation is strongly correlated with the thermolytic decomposition process of the used precursor, such as phase separation and carbothermal reduction. At relatively lower temperature (1250–1350 °C), the ceramics had a relative small specific surface areas (35 m²/g) owing to the low degree of carbothermal reduction. However, as the carbothermal degree had an obvious augment at relative higher temperature (1400–1450 °C), the specific surface areas and total pore volume increased and reached to the maximum of 66 m²/g and 0.214 cm³/g, respectively, and subsequently decreased rapidly after 1500 °C for the reason of partial sintering of the nano-sized SiC derived from polysiloxane.     

Kinetics,aggregation behavior and optimization of the fractionation of whey protein isolate with hydrochloric acid

Concentrated WPI solutions (10%, w/w) containing approximately 50% beta-lactoglobulin (β-LG) and 26% alpha-lactalbumin (α-LA) were fractionated with HCl at acidic pH and moderate temperature to obtain enriched α-LA and β-LG fractions. Aggregation behavior and kinetics of protein precipitation and aggregate formation were analyzed as a function of four process parameters: pH (3.0–5.5), temperature (50–70 °C), reaction time (0–180 min) and protein concentration (10–29%). The precipitation and aggregation of α-LA appeared rate-limited, with a logarithmic dependence of time and possible bimodal nucleation rate, and varied considerably with pH and temperature. Aggregates as large as ～300 μm were noted after 120 min at pH 4, 60 °C. Processing parameters were optimized to obtain both a high aggregate yield and optimal composition of the aggregate fraction. The optimally enriched solid and liquid fractions contained 58% α-LA and 76% β-LG, respectively, with 99% and 74% recovery ratios. Over the pH range studied, β-LG aggregation was found negligible at 60 °C and β-LG recovery in the aggregates attributed to liquid holding. Increasing WPI concentration accelerated α-LA aggregation, demonstrating a concentration-dependent aggregation mechanism, and reduced aggregate purity. Enriched whey protein fractions are valuable health-enhancing food ingredients.