Viscosity Of Pitch Research Articles

Effect of Coal Tar Pitch Viscosity on Impregnation for Manufacture of Carbon Blocks with High Density

Effect of Coal Tar Pitch Viscosity on Impregnation for Manufacture of Carbon Blocks with High Density

Viscosity and Wetting Properties of Pitch

The viscosity, wetting properties, and fluidity threshold of coal and other pitches are considered. The fluidity threshold of coal pitch is determined, and the influence of heat treatment on this temperature is studied. The softening temperature and fluidity threshold of the pitch samples are compared. The relation between the viscosity of pitch and its composition, wetting properties, and mass loss on heating to 360°C is analyzed.

Thermo-rheological properties of coal-tar pitch modified with phenol-formaldehyde resin

Test results of changing the thermo-rheological properties of coal-tar pitch under influence of phenol-formaldehyde resin are presented in this research work. Influence of modifying agent amount and crosslinking conditions (time) of resin in bitumen was evaluated. Tests were carried out using the rheometer in oscillation mode. They enabled the evaluation of changes in bitumen viscous and elastic properties and draw the conclusions about changes in bitumen structure on that basis. Compositions of the coal-tar pitch with phenol-formaldehyde resin show increased thermal and mechanical resistance. Furthermore, phenol-formaldehyde resin has an effect on increase in the coal-tar pitch viscosity. It probably results from the increased content of components of higher average molecular mass in the pitch and lower solubility in organic solvents.

The wettability of coke by pitches with different quinoline-insoluble contents

The properties of pitch as the binder material for carbon anode manufacturing strongly affect the anode properties. Pitches show significant differences in their chemical composition depending on their origin. In this study, five coal tar pitches with different quinoline-insoluble (QI) contents were studied to understand the wettability of one calcined petroleum coke by these pitches using the sessile-drop test. The chemical properties of the coke and pitch were studied using XPS and FT-IR to investigate their wetting mechanism and their interactions. The structures of different pitches and the pitch-coke interface were characterized by optical microscopy and SEM, respectively. The results showed that not only the chemical but also the physical properties of the pitches contribute to the wettability of coke. The wettability increases with increasing heteroatom content in the pitch. The viscosity of pitch is a key parameter controlling the wetting behavior of pitch. The QI content, the solid particle size and their distribution in the pitches play a significant role in the wettability of coke by pitch.

Coal Tar Pitch Modification Methods: Effect of Surfactant Substances and Carbon Additives on Binder Properties

The effect of modifying coal tar pitch with different additives is studied; surfactant substances (SAS), carbon-containing modifiers, and high-temperature binder additives. Using SAS a reduction is observed in viscosity for a system of original pitch–modifier, and with a concentration of 7 wt.% it is most effective to use oleic acid, but with a concentration of 10 wt.% to use myristic acid. In both cases viscosity is reduced by almost a factor of ten with respect to original pitch viscosity. In the case of carbon-containing additives viscosity increases, the same as with use of a high-temperature binder. The effect of modifiers on coke residue yield is studied. On modifying pitch with SAS the reduction in coke residue obeys an additivity rule, which is explained by total removal of SAS from a pitch–modifier system. With use of carbon-containing modifiers and high-temperature binder the coke residue also increases by an additive rule.

Coke–pitch interactions during anode preparation

The information on the interactions between coke and pitch is of great value for the aluminum industry. This information can help choose the suitable coke and pitch pairs as well as the appropriate mixing parameters to be used during the production of anodes. In this study, the interaction mechanisms of pitch and coke at the mixing stage were studied by a sessile-drop test using two coal-tar pitches as the liquid and three petroleum cokes as the substrate. The results showed that the coke–pitch interactions are related to both pitch and coke chemical compositions. The contact angle of different coke–pitch systems decreased with increasing time and temperature. At high temperatures, decreasing the pitch viscosity facilitated the spreading of pitch and its penetration into the coke bed. The chemical behavior of petroleum cokes and coal tar pitches were studied using the FT-IR spectroscopy and XPS. The results showed that the wettability behavior of cokes by pitches depends on their physical properties as well as the presence of surface functional groups of coke and pitch which can form chemical bonds.

Wetting of carbon fibers by coal-tar pitch melts

The wettability of carbon fibers from different manufacturers with finish, rinsed of finish, and heat treated at 2000°C by the model liquids water and octane was studied comprehensively. The polar and dispersion components of the carbon-fiber surface free energy were calculated. It was shown that finished fiber had a polar nature whereas removal of the finish could increase or decrease the surface polarity. This could be related to the fiber preparation method. The surface tension of pitch melts was measured and factored into its components. It was shown that the contribution of the polar component to the pitch surface tension was always at least 50% for the studied pitches. The surface tension correlated well with the pitch viscosity but was not related to the softening temperature. Edge wetting angles of the carbon fibers by pitch were calculated based on the experimental results. Fibers for which the contribution of the surface-energy polar component was greater demonstrated better wettability.

The viscosity of pitches and coke pitch compositions

The viscosity of three coal pitches that have softening temperatures of 361, 386, and 393 K and dust pitch compositions containing a fine fraction (−0.074 mm) of baked oilcoke in amounts of 15, 30, and 50% is measured on a vibratory viscosimeter at T = 430–750 K. The characteristics of the viscous flow of these materials are determined based on the results of this investigation. This allowed specialists working in the aluminum industry to come to some practical conclusions.

Influence of heat and pressure treatment on the rheological behavior of petroleum pitches

Pitch rheological properties are extremely important during the manufacturing process of carbon materials, in mesophase formation, and with regard to the final properties of the carbon products. In this work, pitch samples have been prepared from three different FCC decant oils by heat-treatment, under 0.9 MPa pressure, in a reactor at 390 °C, 410 °C, and 430 °C. These samples were analyzed in a rotational rheometer using a parallel-plate sensor. The rheometric softening points matched the results obtained using conventional equipment and exponential relationships were found to exist between these softening points and the pitch cosity when the former approached 180 °C. The quinoline-insoluble content (QI) has been shown to be more important in increasing the pitch viscosity than the toluene-insoluble content (TI). Oscillatory rheometry analysis has shown that an elastic response is not always found in creep and recovery tests, even when the elastic modulus G′ is dominant over the viscous modulus G′′. Pitch elasticity was found to be independent of the mesophase, and this pitch property was either only observed when the cross-over point occurred at very high frequencies or did not occur at all within the frequency range studied.

Pitch/coke wetting behaviour

The mechanisms of pitch/coke interactions at the mixing stage were studied by a spreading drop test, using a bed of calcined petroleum coke as substrate. For this purpose, three petroleum pitches and a binder coal–tar pitch, which was selected as a reference, were used. The results show that pitch wetting behaviour is related to both pitch surface tension and pitch viscosity. Low values of surface tension and viscosity are required for the pitch to spread and penetrate into the coke bed at temperatures below 160 °C. The non-wetting behaviour observed in some petroleum pitches was ascribed to oxidation processes, as demonstrated by the fact that the non-wetting pitch behaviour can be improved by using an inert atmosphere and/or increasing the heating rate during the spreading drop test. Additionally, the use of blends of wetting and non-wetting pitches and the addition of active surface agents contributes significantly to modifying the wetting behaviour of non-wetting pitches. From the results obtained, a relationship between surface tension–viscosity and pitch wetting behaviour was established.

Rheological investigations of pitch material

Abstract Fluid behavior of carbonaceous pitch materials, such as A240 and ARA-24, is evaluated using the high-temperature, high-pressure (HTHP) viscometer. The measured viscosity of A240 pitch using the HTHP viscometer shows excellent agreement with that obtained using a Brookfield viscometer (DV III+). Further, the viscosity of ARA-24 (mesophase) pitch is measured and reported as a function of temperature at elevated temperature. Finally, the viscosity of pitch materials, both A240 and ARA-24, is modeled using the modified William–Landel–Ferry (WLF) equation. The shear activation energy for the 100% mesophase pitch (ARA-24 pitch) increased with the shear rate while that for the A240 pitch remained constant. Moreover, the shear activation energy for ARA-24 pitch was higher than that for A240 pitch at the shear rates investigated.

Simulation of melt spinning of pitches

Effects of process variables and material properties on melt spinning of pitches have been studied based on simulation using governing equations by Kase and Matsuo. It is shown that the tension F in a filament depends on spinning conditions as well as viscosity of pitch in the form of F∝μ0W1/6f1(v0,vL,vA)/f2(T0,TS, TA,E). Here, W, v0, vL, and vA are mass flow rate, velocity at the spinnerette, winding speed and cross‐flow air velocity respectively, and T0, TS, and TA denote temperatures at the spinnerette, at the solidification point and of air. Temperature dependence of viscosity is simplified by an Arrhenius type equation with a pre‐exponential factor μ0 and a flow activation energy E. To improve spinnability, the maximum tensile stress σL should be decreased by increasing W, T0 and TA or by decreasing vL, vA, TS, μ0 and E. In other words, slower cooling of the filament with larger diameter for a pitch with smaller activation energy is preferable to better spinnability. Effects of these factors on diameter, temperature and strain rate of the spinning filament are also discussed.

Simulation of Melt Spinning of Pitches

Effects of process variables and material properties on melt spinning of pitches have been studied based on simulation using governing equations by Kase and Matsuo. It is shown that the tension F in a filament depends on spinning conditions as well as viscosity of pitch in the form of F∝μ0W1/6ƒ1(v0, vL, vA)/ƒ2 (T0, Ts, TA, E). Here, W, v0, vL and vA are, mass flow rate, velocity at the spinnerette, winding speed and cross-flow air velocity respectively, and T0, Ts and TA denote temperatures at the spinnerette, at the solidification point and of air. Temperature dependence of viscosity is simplified by an Arrhenius type equation with a pre-exponential factor μ0 and a flow activation energy E. To improve spinnability, the maximum tensile stress σL should be decreased by increasing W, T0 and TA or by decreasing vL, vA, Ts, μ0, and E. In other words, slower cooling of the filament with larger diameter for a pitch with smaller activation energy is preferable to better spinnability. Effects of these factors on diameter, temperature and strain rate of the spinning filament are also discussed.

Modeling of the apparent viscosity of pitches and mesophases at linear temperature increase up to 500°C

During the heating of pitch or mesophase, the viscosity first decreases and then increases. The viscosity decrease is a net physical effect and reversible. The viscosity increase is caused by chemical changes and thus it is irreversible. This viscosity behaviour with increasing temperature is important for the spinning of mesophase, for the infiltration of carbon fibre preforms and especially for the sintering of pressed mesophase powders. By modeling the viscosity changes apparent activation energies for the reversible viscosity decrease E rev and also for the irreversible viscosity increase E irr were obtained. The E irr values were in the range between 120 and 160 kJ mol −1, and thus not strongly different from one material to another. Significant differences were found for the E rev values, namely from 160 to 250 kJ mol −1, and it is explained that a low E rev value is very important for the sintering properties of a mesophase.

Preferred orientation of pitch precursor fibers and carbon fibers prepared from isotropic pitch

The preferred orientation of pitch precursor fibers and carbon fibers from an isotropic pitch was studied using x-ray diffraction techniques. The φ scan profile of a pitch precursor fiber was divided into two parts: φ scan-dependent (anisotropic) and φ scan-independent (isotropic) profiles. The half width at half maximum (HWHM) intensity of the anisotropic part became smaller as the pitch viscosity increased during spinning and as the filament diameter decreased. The area ratio of the anisotropic part to the total area increased when spinning at higher pitch viscosities and when making the diameter thinner; no preferred orientation existed for pitch precursor fibers with very large diameters. A thermodynamic model is proposed for the preferred orientation formation when spinning an isotropic pitch. The carbon fiber exhibited no skin-core difference in preferred orientation. A crystallite with a larger crystallite size Lc(002) in the carbon fiber was shown to be better aligned along the fiber axis than that with a smaller Lc(002). Furthermore, a well-aligned crystallite possessed a larger Lc(002) than one that was misaligned. The pitch precursor fiber also exhibited such a correlation between Lc(002) and the preferred orientation, but the correlation was weak.

Preferred orientation of pitch precursor fibers

Spinning condition dependences of the microstructures of a pitch precursor fiber which is a raw material for carbon fiber preparation were studied in detail. The degree of preferred orientation of the molecules in a pitch precursor fiber along the fiber axis was higher when spinning was done at a lower mesophase pitch viscosity. An intermediate diameter gave the highest degree of preferred orientation. The degree of preferred orientation of the molecules in an extruded pitch rod was especially low. The crystallite size Lc(002) of the pitch precursor fiber also was varied by controlling the spinning conditions, and exhibited a good correlation with the degree of preferred orientation. Mesophase pitch at a higher temperature possessed a smaller Lc(002) and a larger d002. The small Lc(002) observed at high temperature was maintained by a rapid cooling to room temperature, but the large d002 relaxed to a small value at room temperature, even with rapid cooling. A qualitative model for the formation of a preferred orientation through spinning is proposed.

In situ ESR measurement of mesophase formation during the heat treatment and cooling processes of pitches

Both heating and cooling processes for mesophase formation from various pitches have been followed by in situ ESR measurements. In addition to signal intensity and linewidth, the saturation phenomenon of the signal intensity with changing microwave power was measured during heat treatment and cooling processes. As a convenient measure of the saturation factor, l/ P max ( P max is the microwave power at which the signal shows maximum intensity) was employed. In general, 1/ P max decreased with an increase in heat-treatment temperature; this change seems to correspond to a decrease in the viscosity of pitch. When pitches were heat treated at 500°C for 2 h, the carbonization reactions and the rearrangement of molecules may occur, which irreversibly changes 1/ P max . Pronounced differences in the behavior of 1/ P max measured during cooling of the heat-treated pitches were found to depend upon pitch optical texture (isotropic, flow and mosaic).

Transverse structure of pitch fiber from coal tar mesophase pitch

The transverse structure of pitch fiber has been successfully controlled by changing the pitch flow conditions at the upper portion of the capillary in spinning. The mean size of mesophase domains in the transverse section of pitch rod extruded from the capillary was found to decrease monotonously with decreasing rod diameter and with increasing pitch viscosity. Also, the stirring of molten pitch located just above the capillary gave rise to a decrease of the mesophase domain size. It has been revealed that the graphitizability of the pitch fiber depends mainly on the mean domain size in the transverse section, as long as the degree of preferred orientation is the same.

The pitch drop experiment

In the foyer of the Department of Physics at the University of Queensland in Brisbane is an experiment to illustrate, for teaching purposes, the fluidity and the very high viscosity of pitch, set up in 1927 by Professor Thomas Parnell, the first Professor of Physics there. An account is given of the experiment to illustrate the fluidity of pitch.

Viscosity of coal tar pitch at elevated temperatures

At temperatures up to about 200 ° the viscosity of pitch, of approximately 100 °C Ring and Ball Softening Point, follows a predictable variation with temperature. Above 200 °C, variations occur depending on the source of the pitch, although a minimum viscosity is always achieved between 320 and 400 °C, followed by a rise. On heat treating at a constant temperature of 400 °C the viscosity rises. Although some preliminary work on two low-temperature pitches indicates a different regime, the work on coke-oven pitches shows a clear relation between viscosity rise and the formation of toluene- and quinoline-insolubles by what appears to be consecutive reactions from tar oils, during which the rheological behaviour becomes increasingly pseudoplastic.