Graphitization Of Coke Research Articles

Characterization of Thermal Annealing Effects on the Evolution of Coke Carbon Structure Using Raman Spectroscopy and X-ray Diffraction

An experimental study was conducted to monitor the evolution of coke carbon structure during thermal annealing in a temperature range from 1273 to 2473 K in a bench-scale reactor. Coke carbon structure was characterized by using Raman Spectroscopy and the X-ray Diffraction. The Raman spectra of most of the cokes displayed two broad peaks G* (1620 cm−1) and D* (1360 cm−1). Both Raman peaks were deconvoluted into five peaks namely G, D, D′, R1 and R2. On the basis of area under the respective band peaks, new structural parameters were obtained to quantify graphitic (G), graphitic defect (D) and random (R) carbon fractions of cokes.XRD analysis was used to show that stack height carbon crystallite, Lc, of coke increases with increasing annealing temperature while the impact of annealing duration was not significant particularly up to 1873 K. On the other hand, average carbon crystallite width, La, did not improve significantly up to 1873 K, and increased rapidly after subsequent rise in the annealing temperature. It appears that during annealing up to 1873 K, modification of coke carbon structure could occur due to loss of basal carbon as a consequence of in-situ gasification.The lateral expansion of carbon crystallite, La, was related to relative intensity or shape of Raman band peaks such that both parameters did not change significantly up to an annealing temperature of 1873 K. At higher annealing temperatures, La values of coke increased with decreasing D/G ratio. Lateral expansion of carbon crystallite was attributed to progressive reduction of defects of graphitic carbon of coke, which can be monitored by D fraction of Raman Analysis. Combined Raman and XRD analysis suggested that rapid graphitization of coke may not occur along all dimensions until the annealing temperature exceeds 1873 K.Combining XRD and Raman analysis would provide a comprehensive evaluation of the evolution of coke carbon structure at different temperatures and their subsequent implications on the efficiency of various ironmaking operations.

The effect of boron doping on lithium intercalation performance of boron-doped carbon materials

Boron-doped carbons were prepared by pyrolysis of phenolic resin and of pitch with boric acid. The charge–discharge performance of those carbons as an anode electrode material of lithium-ion batteries is here reported. Results showed that the reversible capacity of carbon from pyrolysis of boron-doped phenolic resin was 176.6 mA h g −1 and its charge–discharge efficiency during the first cycle did not change apparently, while that of carbon from pitch was 258.5 mA h g −1, and its charge–discharge efficiency during the first cycle was 92.2%. XRD analysis for the present boron-doped materials showed that the distance between carbon layers was lowered by a proper amount of doped boron. XPS analysis with Ar bombardment showed that boron mainly stays on the surface of carbon from pitch, and the increase of surface content of oxygen and nitrogen was also observed. The influence of boron doping on the graphitization of pitch coke and the behavior of lithium intercalation was regarded as surface effect, thus elucidating the increases of graphitization degree and lithium intercalation capacity, and the decrease of irreversible capacity by boron doping.

95/01707 Effects of unconverted pulverized coal on the degrees of graphitization of coke

95/01707 Effects of unconverted pulverized coal on the degrees of graphitization of coke

Mechanism of puffing and the role of puffing inhibitors in the graphitization of electrodes from needle cokes

A mechanism of puffing that occurs during graphitization of needle coke in the electrode is proposed based on the experimental results in the literature. Gases may evolve from within needle coke grains via porosity, causing pore walls to expand irreversibly when they are softened during graphitization. Hence, extents of puffing are influenced by rate and temperature range of gas evolution, the nature of evolved gases, location of the evolved heteroatoms such as sulfur and nitrogen in the coke, and the structure (especially grain size), porosity (pores and cracks), and preferred orientation of the coke, because these factors are related to the pressure induced by the evolved gas, timing for the softening of the coke and gas evolution and the resistivity of the wall against the pressure. Porosity within a coke grain can be modified by the coke derived from binder and impregnation pitches that can diffuse into the porosity of filler coke in the electrode. The graphitization also leads to shrinkage of the carbon. Hence, the size of the electrode is influenced by both puffing and shrinkage, these having opposing effects. The extent of puffing can be described semi-quantitatively in terms of influential factors described above. Thus, it is understandable that the puffing increased the porosity in a certain range (0.1–1 μm) and that puffing is suppressed by the increased porosity of 1–100μm. Based on the mechanism, procedures for puffing inhibition are suggested including: 1. 1. moderate acceleration of graphitization 2. 2. capture of heteroatoms to be liberated 3. 3. controled gasification to increase porosity of the filler cokes 4. 4. removal of heteroatoms from the needle coke or its starting feedstock The roles of puffing inhibitors are discussed based on the mechanism of puffing.

Coke deposits on Pt/Al2O3 catalysts of varying dispersities

Coke deposition during cyclopentane reaction was investigated on Pt/Al2O3 catalysts of varying dispersity. For all working pressures the higher the metallic accessibility, the higher the amount of coke deposited on the catalyst. Nevertheless, coke deposited on the less dispersed catalysts is more toxic for the metallic function. An increasing metal accessibility improves the graphitization of coke on the support and so, prevent the deactivation of the metal of a bifunctional catalyst.

Deactivation by Coking of Platinum/Alumina Catalysts: Effects of Operating Temperature and Pressure

Coke deposition is a complex reaction that results from the production of coke precursors and from their destruction. At low temperatures, when the destruction reaction (high apparent activation energy) is negligible, the coking rate is increased owing to increasing metal accessibility. In contrast, at high temperatures the coking reaction is hindered by an increasing metal loading. A change in the coking temperature does not alter the chemical nature of the carbonaceous deposits and their distribution between the metallic and acidic phases of a bifunctional catalyst. On the other hand, an increase in coking pressure (with a constant hydrogen:hydrocarbon molar ratio) promotes the graphitization of coke on the support, protecting the catalytic activity of the metallic phase.

Graphitization of pitch coke: Changes in mean interlayer spacing, strain and weight

Studies of the average interlayer spacing, d ̄ 002 , strain parameter, ϵ, and fractional weight changes, Δw w , were made of a pitch coke heat treated at temperatures in the range 1250–2300°C for periods up to 25 h in inert atmosphere. Application of the superposition technique to the change in d ̄ 002 , gave an activation energy of 65 ± 5 kcal/mole between 1500°C and 2000°C and 220 ± 30 kcal/mole between 2000°C and 2300°C. The weight loss was thermally activated with an activation energy of about 100 ± 5 kcal/mole. The interlayer spacing decreases sharply at a critical value of weight loss, and this is attributed to removal of an interlayer chemical species, most likely interstitial carbon.

292. Structural changes during graphitization of petroleum coke

292. Structural changes during graphitization of petroleum coke

The Properties of Coke at High Temperature

The degree of graphitization of coke is increased at higher temperature than the carbonization temperature. As the heat treatment temperature (H. T. T.) increase, the three dimension crosslinkage of layers develope to the second dimensional graphite like net structures (so called the turbostratic ones) and finally the graphite crystal structure is completed. The physical and chemical properties of coke is reviewed in the coures of graphitization at high temperature:1) The most properties of coke is highly dependent on the H. T. T.2) The higher H.T.T. cause the reduction of hetero atoms (S. N. P. H) making coke inert but the ash components behave sometimes as catalysts to increase the reactivity of coke at higher than 1700°C.3) The electromagnetic properties of coke show clearly the progress of the graphitization when the H. T. T. increasing.4) The mechanical properties of coke: The intrinsic strength, determined with such as knoop hardness, is reduced as the higher temperature. On the other hand, the structural strength is high below the carbonization temperature and over the carbonization temperature it become weak mainly due to the shrinkage.

Effects of Holding Time and Pressure of Hot-pressing on Sintering and Graphitization of Coke with B2O3 Addition

Effects of holding time and pressure of hot-pressing were investigated on some properties of the coke compacts made by hot-pressing at 2000°C and 2200°C from a calcined pitch coke powder mixed with 10 wt% B2O3. The holding time was changed from 0 to 4 hr and the pressure from 70 to 400kg/cm2.Bulk density and mechanical strength of the compacts increased and also their graphitization measured from the interlayer spacing d (002) and the appearance of 112 diffraction proceeded with the increase of holding time up to 1 hr.Above 1 hr, however, they showed almost constant values. The hot-pressing pressure gave a remarkable effect on densification and strength of the compacts, but almost no effect on graphitization.The compact with the bulk density of 2.13 g/cm3, the bending strength of 490 kg/cm2 and the d (002) spacing of 3.360A was obtained under the condition of the pressure of 400 kg/cm2 at 2200°C. The hot-pressing temperature and pressure were known to be very important factors to prepare the dense and strong compact from the coke with B2O3 addition.

Effect of Hot-pressing Temperature on Sintering and Graphitization of Coke with B2O3 Addition

Effect of hot-pressing temperature was investigated on some properties of polycrystalline coke compacts made from calcined pitch coke powder with 10% B2O3 addition at various temperatures from 1200 to 2200°C under a pressure of 200kg/cm2.Bulk density was almost constant as 1.6g/cm3 up to 1800°C, and increased rapidly to about 2.0 g/cc above 2000°C.Mechanical strength once decreased at temperature range from 1600 to 1800°C, and it increased again above 2000°C.Graphitization proceeded remarkably above 2000°C.B4C was formed at 1600°C and amount of B4C decreased with increase of temperature.The hot-pressed compacts could be classified into three types.The first is the one made below 1400°C in which coke particles adhered each other with B203 glass phase, the second is the one made between 1600 and 1800°C which consist of the mixture of coke particle and small amount of B4C exist independently, and the last is the one made above 2000°C of which boron is considered to give strong influence for sintering and graphitization of coke by its diffusion into coke structure.

Polycrystalline Graphite made from Coke Powder in addition of Boron Carbide (1)

Polycrystalline graphite compacts were made from calcined pitch coke powder with boron carbide of 4.8wt% by hot-pressing at variou temperatures from 1400 to 2200°C under a pressure of 200kg/cm2.Effect of boron carbide and hot-pressing temperature on some propertiesof the compacts were investigated by comparing the ones made from the coke powder with no addition under the same conditions. As the results, with boron carbide, density, mechanical strength and graphitization degree of the compact were remarkably increased above about 2000°C, and at 2200°C the compact with bending strength of 200-300kg/cm2, relative density of 89%, d (002) spacing of 3.358 A and electric resistivity of about 1×10-3Ω-cm was obtained.It was known that boron carbide addition has remarkable influence for acceleration of both densification and graphitization of coke above about 2000°C under the pressure.

Graphitization of Coke Investigated with Magnetoresistance Technique

Graphitization of Coke Investigated with Magnetoresistance Technique

人造黒鉛混合成形試料のX線回折線図形

The (001) diffraction line profiles of electrographitized carbon products were graphically separated into profiles of their component carbons. The products used for this experiment were made from a petroleum coke, a thermal black, or a furnace black and a binder pitch. The ratios of the integrated difiraction intensities of the component carbons were in good agreement with the mixing ratios of components, when the intensity of diffraction was corrected for the effect of preferrential orientation of graphite crystallities and for the weight loss in the process of graphitization. The lattice constant c/sub o/ and size of graphite crystallities L/sub c/ of graphitized coke derived from the binder pitch in the carbon products were found to be 6.74 approximates 6.83A and 280 approximates 130A, respectively, while c/sub o/ and L/sub c/ of coke derived from the same pitch without the admixture of carbon materials were 6.71 and 340A, respectively. The degree of graphitization of coke from the binder pitch in the cokebase products was found to be larger than that of coke from the binder pitch in the carbon black-base products. (auth)