Carbon Black Mixture Research Articles

Positive‐temperature‐coefficient/negative‐temperature‐coefficient effect of low‐density polyethylene filled with a mixture of carbon black and carbon fiber

AbstractLow‐density polyethylene (LDPE) filled with carbon black (CB) and carbon fiber (CF) composites were prepared by a conventional melt‐mixing method. The effects of a mixture of CB and CF on the positive‐temperature‐coefficient (PTC) effect and the negative‐temperature‐coefficient (NTC) effect, as well as the percolation threshold, were examined in detail. A synergy effect between CB and CF occurred, in that continuous conductive pathways formed within the CB/CF‐filled composite. The percolation threshold was moved to a reduced filler content with the addition of CF to an LDPE/CB composite. A model was proposed to explain the difference in the PTC behavior of composites containing CB and CF and composites containing only CB or CF. In addition, the NTC effect was weakened with a mixture of CB and CF, and a relatively small radiation dose was required to eliminate the NTC phenomenon in LDPE/CB/CF composites. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3094–3101, 2003

Induced effect of Mn3O4 on formation of MnO2 crystals favourable to catalysis of oxygen reduction

Catalysts prepared from a mixture of Mn3O4 powders and carbon blacks carrying pyrolytic MnO2 were investigated for catalysis of oxygen reduction. It was found that the introduction of Mn3O4 to the pyrolysis process of manganous nitrate carried out on carbon blacks improved the performance of air electrodes as the amount of Mn3O4 was controlled within 15 wt% relative to the weight of carbon carrier. The mechanism of this improved behaviour was also investigated using X-ray diffraction (XRD). The results showed that Mn3O4 induced the formation of favourable MnO2 crystalline grains during the pyrolysis of manganous nitrate. The induced effect and the blocking effect of Mn3O4 on the catalysis of air electrodes catalysed by pyrolytic MnO2 were demonstrated both on carbon black and porous carbon carriers.

Dielectric properties of periodic heterostructures: A computational electrostatics approach

The dielectric properties of heterogeneous materials for various condensed-matter systems are important for several technologies, e.g. impregnated polymers for high-density capacitors, polymer carbon black mixtures for automotive tires and current limiters in circuit protection. These multiscale systems lead to challenging problems of connecting microstructural features (shape, spatial arrangement and size distribution of inclusions) to macroscopic materials response (permittivity, conductivity). In this paper, we briefly discuss an ab initio computational electrostatics approach, based either on the use of the field calculation package FLUX3D (or FLUX2D) and a conventional finite elements method, or the use of the field calculation package PHI3D and the resolution of boundary integral equations, for calculating the effective permittivity of two-component dielectric heterostructures. Numerical results concerning inclusions of permittivity e 1 with various geometrical shapes periodically arranged in a host matrix of permittivity e 2 are provided. Next we discuss these results in terms of phenomenological mixing laws, analytical theory and connectedness. During the pursuit of these activities, several interesting phenomena were discovered that will stimulate further investigation.

Electrical properties of polyethylene highly filled with carbon

Carbon-filled polyethylene composites were fabricated and tested to establish the practical lower limit of their electrical resistivity at room temperature and to investigate the trade-offs between low resistivity and the magnitude of the resistance anomaly (i.e., a large positive temperature coefficient of resistivity) that appears when such composites are heated through the polyethylene crystalline melting transition. Carbon blacks with large particle size and low surface area provided low-resistivity composites having large resistance anomalies. The largest resistance anomalies were found in composites that were well mixed, but the room-temperature resistivity also increased in composites that were cycled repetitively through the crystalline-melting transition. A mixture of carbon blacks of two different sizes provided a lower resistance than was found in a material with the same fill of only the coarser black. By controlling the composition and the processing, composites were made with room-temperature resistivities lower than 0.2 ohm cm and resistance changes of at least 2 orders of magnitude. A resistance change of as much as 5 orders of magnitude was obtained for composites with room-temperature resistivities of only 1 ohm cm.

Formation of SiC from rice husk silica-carbon black mixture: Effect of rapid heating

Formation of SiC from rice husk silica and carbon black mixture with Co catalyst, and without any catalyst, has been studied by rapid heating to 1300–1600 °C. Formation of SiC in CoCl 2 treated mixture was rapid at and above 1400 °C. However, in the untreated mixture considerable quantities of SiC has formed only above 1500 °C. Total SiC content and SiC whisker yield in the treated mixture were higher than that in the untreated mixture.

Preparation of porous electrodes and laminated electrode-membrane structures for polymer electrolyte fuel cells (PEFC)

Porous Nafion-PTFE-bonded gas-diffusion electrodes (GDEs), for use in (PEFC), were prepared by a cold rolling process. In this process, no solvents are required. The raw material for the production of these electrodes is a ternary mixture of Nafion, PTFE and Platinum-loaded carbon blacks. Development goal of our recent activities is the optimisation of the raw material composition with respect to the structural and electrochemical properties of the electrode.

Microstructure of Composite Materials Using Small-Angle Neutron Scattering and Contrast Variation: Approaches toward Understanding the Structure of Carbon Black-Elastomer Mixtures

Mixed composites of rubber and carbon black are of fundamental importance to rubber technology, and neutron scattering provides a unique view of structure in these interesting and complex systems. This is due, in part, to the nature of the interaction of the neutron with nuclei, which is a function of the specific nucleus, not on atomic number, per se. This allows neutrons to be used to probe fluctuations in chemical and isotopic composition and density in a manner that is a distinct from x-rays or electrons. This aspect of neutron scattering has been used extensively in the study of multicomponent systems, even when components have elements of similar atomic numbers. The large difference in scattering from some isotopes—hydrogen and deuterium being the most important example—can be used to enhance fluctuations in these systems and thus to probe structures that are not accessible by other methods. We describe the use of small-angle neutron scattering in carbon black, elastomer and carbon black elastomer mixtures using the method of contrast variation. In this approach the sample is suspended in solvents containing different proportions of perdeuterated and protonated molecules. The variation in scattering observed as a function of solvent scattering power gives information on the distribution of components within the sample. Our first experiences using this approach show the potentials of the technique. The use of solvents near the average scattering length density of the carbon black allows observation of non-uniformity in carbon black particles that has not been previously noted. Further, we have established that the shape of the scattering curves in N762 carbon black can be explained as scattering from spherical particles of size and polydispersity measured by electron microscopy. In N121, in which the particle sizes are smaller than N762, contribution to the scatter from the carbon black particle interactions is observable. In gels of solvent extracted carbon black and elastomer we find that the scattering is dominated by carbon black density fluctuations. We find further that the elastomer coats the carbon black particles, at least in N762. There are differences in the association of the carbon blacks in solvent extracted mixtures compared to the carbon blacks suspended in cyclohexane. There may be changes, as well, in the elastomer conformation in the mixtures compared to the polymer alone in cyclohexane. These differences are small in gels containing low concentrations of polyisoprene and carbon black, but are quite profound in a gel containing styrene butadiene rubber with high concentrations of components. Further measurements and modelling of die data will be needed to come to a more satisfactory picture of carbon black morphology and elastomer conformation in the solvent extracted mixtures.

Microstructure of Composite Materials Using Small-Angle Neutron Scattering and Contrast Variation: Approaches toward Understanding the Structure of Carbon Black-Elastomer Mixtures

Mixed composites of rubber and carbon black are of fundamental importance to rubber technology, and neutron scattering provides a unique view of structure in these interesting and complex systems. This is due, in part, to the nature of the interaction of the neutron with nuclei, which is a function of the specific nucleus, not on atomic number, per se. This allows neutrons to be used to probe fluctuations in chemical and isotopic composition and density in a manner that is a distinct from x-rays or electrons. This aspect of neutron scattering has been used extensively in the study of multicomponent systems, even when components have elements of similar atomic numbers. The large difference in scattering from some isotopes—hydrogen and deuterium being the most important example—can be used to enhance fluctuations in these systems and thus to probe structures that are not accessible by other methods. We describe the use of small-angle neutron scattering in carbon black, elastomer and carbon black elastomer mixtures using the method of contrast variation. In this approach the sample is suspended in solvents containing different proportions of perdeuterated and protonated molecules. The variation in scattering observed as a function of solvent scattering power gives information on the distribution of components within the sample. Our first experiences using this approach show the potentials of the technique. The use of solvents near the average scattering length density of the carbon black allows observation of non-uniformity in carbon black particles that has not been previously noted. Further, we have established that the shape of the scattering curves in N762 carbon black can be explained as scattering from spherical particles of size and polydispersity measured by electron microscopy. In N121, in which the particle sizes are smaller than N762, contribution to the scatter from the carbon black particle interactions is observable. In gels of solvent extracted carbon black and elastomer we find that the scattering is dominated by carbon black density fluctuations. We find further that the elastomer coats the carbon black particles, at least in N762. There are differences in the association of the carbon blacks in solvent extracted mixtures compared to the carbon blacks suspended in cyclohexane. There may be changes, as well, in the elastomer conformation in the mixtures compared to the polymer alone in cyclohexane. These differences are small in gels containing low concentrations of polyisoprene and carbon black, but are quite profound in a gel containing styrene butadiene rubber with high concentrations of components. Further measurements and modelling of die data will be needed to come to a more satisfactory picture of carbon black morphology and elastomer conformation in the solvent extracted mixtures.

Studies on the formation of SiC whiskers from pulverized rice husk ashes

Conversion of rice husk precursors (raw husks, pulverized black ash and mixtures of white ash and carbon black) to silicon carbide through vacuum pyrolysis over a wide temperature range, has been studied. The products of the pyrolysis (SiC whiskers and particles) were analyzed with the help of XRD, SEM and chemical analysis. The present study indicates that a temperature range of 1250–1370°C, carbonaceous substrate, sufficient void space, controlled release of SiO vapour, and the presence of CO are favourable conditions that tend to maximize the formation of SiC whiskers. Under similar experimental conditions, the formation of SiC (w) from rice husk precursors has been observed to increase in the following order: the lowest from the pulverized black ash, intermediate from the white ash and carbon black mixtures, and the highest from the raw rice husks.

Carbothermal Reduction of the Molybdenum Oxide/Phenanthroline Complex

Samples of an MoO3/phenanthroline complex and an MoO3/carbon black mixture were heated below 1400°C in nitrogen to characterize the carbothermal reduction process of the complex. The conversion of crystalline phases by carbothermal reduction followed substantially the same process in both samples but occurred at a temperature 100° to 150°C lower in the complex than in the carbon black mixture. Two possible explanations for this difference are theorized: (1) The complex may provide more intimate contact between the MoO3 and the intercalated reducing material. (2) The intercalated reducing agents may have a higher reactivity than does the carbon black.

Positive temperature coefficient of resistance in some copper phthalocyanine — carbon black mixtures

Copper phthalocyanine — carbon black mixtures in which carbon black content is closed to the percolation threshold as the material is heated show regions of negative and positive temperature coefficients of resistivity. The model explaining mechanism PTC of resistance in these mixtures is proposed.

An explanation of electrical conductivity data for copper phthalocyanine- acetylene carbon black mixtures

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Hydrogen fuel cells as direct energy converters

Electrochemical energy converters have a principal advantage over heat engines: they can utilize the chemical energy of fuels with a higher efficiency. Several systems have evolved since the feasibility of fuel cells was demonstrated early in this century. The alkaline fuel cells operate at ambient temperature and atmospheric pressure. During the last decade the catalyst cost picture has improved drastically, mass-production possibilities have opened up and the near-future chances for hydrogen fuel cell systems look promising. The breakthrough in cost can be expected from new designs and components. the replacement of expensive metals as current collectors and construction materials by carbon. In this paper it is intended to give a comparison of the new bipolar design of alkaline cells with the “edge-current” construction. Also, hydrophobic electrodes made the classical way from PTFE-bonded carbon black mixtures are compared with supported electrodes based on hydrophilic graphite as catalyst carrier.

Cathode Performance Improvement in Calcium‐Thionyl Chloride Cells

Carbon cathode performance in calcium‐thionyl chloride cells was markedly improved with a cathode comprised of a mixture of high and low surface area carbon blacks. Addition of sulfur dioxide gas to the electrolyte further enhanced cathode performance and electrolyte conductivity. Load potentials and cathode life were nearly equal to that of the analogous lithium based system. The advantage of the calcium based system is its potential for greater safety.

Electrical properties of carbon black filled crosslinked polyethylene

AbstractThe electrical resistivity of peroxide and radiation crosslinked polyethylene/carbon black compounds was studied as a function of black concentration and, temperature in heating/cooling cycles. Different carbon blacks in compounds with polyethylene responded differently, regarding electrical resistivity, to the effect of crosslinking. In one case (fine black) the resistivity and PTC (positive temperature coefficient) effect did not significantly change, whereas in another case (coarse black) the effect of crosslinking‐was to significantly increase the resistivity and reduce the PTC effect. The main advantages of crosslinking were to give compounds having good electrical reproducibility and to practically eliminate the NTC (negative temperature coefficient) effect in compounds containing fine, coarse, or mixtures of carbon blacks. Crosslinked compounds containing mixtures of carbon blacks have shown good conductivity, electrical reproducibility, and switching properties.

ESR study of rubber‐carbon black interaction

AbstractBenzene extract ESR spectra of natural rubber/various kinds of carbon black mixtures have been examined. Existence of two types of rubber radicals has been found, i.e. the radicals of unbound rubber and rubber radicals stabilized by interaction with carbon black particles. It has been demonstrated that bounding of rubber macromolecules with carbon black particles takes place always in the same ratio determined by the number of polymer chain structural units and active sites of carbon black particles.

Electrical properties of carbon black filled polyethylene

AbstractResistivity and dielectric constant of polyethylene/carbon black compounds were measured from room temperature to 140°C. Within the polyethylene melting region a PTC/NTC (positive followed by negative temperature coefficients) phenomenon is observed, whose intensity depends on the type of carbon black, its concentration and other parameters. Reproducibility of the PTC phenomenon in polyethylene compounds containing a single type of carbon black is rather low. However, by using mixtures of carbon blacks differing appreciably in their particle size, remarkable reproducibility improvements can be achieved. Several other aspects are also discussed in the present paper covering current‐voltage relationships in these materials, comparison of PTC curves with DSC thermograms upon heating and cooling, and dielectric constant‐temperature relations. The carbon black concentration giving the optimum PTC intensity can be predicted approximately from room temperature data.

Dielectric Properties of Polar Rubber Mixtures Perbunan Rubber- Carbon Black Mixtures

Article Dielectric Properties of Polar Rubber Mixtures Perbunan Rubber- Carbon Black Mixtures was published on February 1, 1973 in the journal Zeitschrift für Physikalische Chemie (volume 252O, issue 1).

Pressure effects on color centers in RbF, RbCl, RbBr, and CsI

Pure scheelite (CaWO4) and carbon black mixtures, containing either 0–6 wt% cobalt or 0–2 wt% nickel were prepared by 24 h planetary ball milling (PBM). CaWO4:C mixtures were then subjected to 1 h annealing at 1200 or 1400 °C in tubular furnace under flowing Ar (heating ramp: 3 °C/min). Following the carbothermic reduction, the obtained powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).CaWO4:C mixtures with no added metal gave an almost quantitative WC yield (≥ 96%) after 1 h annealing at both temperatures. All mixtures containing Co or Ni gave rise to a WC yield exceeding 99% after annealing at 1400 °C. Mixtures annealed at 1200 °C exhibited a slightly lower yield, being the estimated percentage of WC ≥ 98% with cobalt dopant, and 95% with 2 wt% Ni.For the first time we here show that Co or Ni addition has a noteworthy effect on the size of WC particles produced by carbothermic reduction of CaWO4 and subsequent leaching with diluted hydrochloric acid. In particular, the size of WC particles could be tailored from 0.2–0.3 μm to 2–3 μm when Co was increased from 0 to 5–6 wt% and the reaction temperature raised to 1400 °C.These findings are particularly appealing from both industrial and sustainability point of view, since they further validate the carbothermic reduction of scheelite as a simpler, cheaper and less energy-intensive process for the synthesis of nano- and micro-structured WC powders to be employed for manufacturing different hardmetal grades.

Abrasion of Butyl Rubber

Abstract By using the Lambourn abrader, a concept of abrasion has been proposed that fits the performance of a wide variety of compounds. The ability of this type of machine to give varying degrees of slip and braking forces has aided in the selection of the proper conditions for abrasion studies. By using a small tread pattern on the sample wheel, laboratory results are brought into closer agreement with actual road wear tests. The work of Schallamach and the analysis of abrasion by a needle abrader have been extended to an abrasive surface. To the considerations of compound strength and surface friction or traction has been added the consideration of dynamic hardness. The abrasion of rubber has then been related to a ratio of dynamic modulus over rupture energy. Thus if a compound is made dynamically softer or more conformable without a sacrifice of its resistance to rupture, a superior abrading tread will result. In simple terms, what is needed for best abrasion resistance is the softest toughest material. Butyl owes its comparable or superior abrasion resistance (compared to other rubbers) to the fact that its vulcanizates are dynamically softer. The heat treatment of Butyl carbon black mixtures produces vulcanizates that are still softer in relation to their rupture energy. This is the sole advantage of such a mixing procedure. Other polymer and compounding variables that tend to decrease the ratio of dynamic hardness to rupture energy improve abrasion resistance. These changes include increasing the molecular weight of the polymer and reducing somewhat the unsaturation. A certain quantity of plasticizer to increase softness and a reduction of the state of cure have been shown to be beneficial. The latter change produced by a reduction of the amount of sulfur in the compound, which limits the extent of cross-linking, has resulted in distinctly superior tire treads.