graphite electrodes quality

graphite electrode - an overview | sciencedirect topics

Graphite electrodes serve to transfer the electrical energy from the power supply to the steel melt in the EAF bath. They are typically made using premium petroleum needle coke, coal tar pitch, and some additives (Fruehan, 1998). Specification of needle coke for the manufacture of large diameter graphite electrodes is shown in Table12.12.

Electrode consumption varies between 1.8 and 9.9kg/t of liquid steel (Parkash, 2010) depending on the process characteristics and electrode quality. Ameling et al. (2011) reported that the electrode consumption in Germany in 2010 was approximately 1.1kg per ton as a result of the reduction of time between the taps to 40min and consequently the lower electricity consumption (345 kWh/t). Electrodes are classified as regular grade or premium grade on the basis of their physical properties (International Iron and Steel Institute, 1983).

Composite graphite electrodes were studied by in situ AFM working in EC-dimethyl carbonate (EC-DMC) and EC-PC solutions of lithium bis(oxalato)borate (LiBOB), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4) in an attempt to follow any pronounced morphological changes in the graphite particles owing to the surface film formation in the course of the first cathodic polarization and during lithium insertion and desertion processes. Figure 22 gives AFM images obtained in situ from composite graphite electrodes at open-circuit voltage (3V) and after polarization to 0.3V (Li/Li+) in 1molL1 LiBOB and 1molL1 LiPF6 solutions. They show morphological changes owing to cathodic polarization of both electrodes connected with the formation of surface films. A rougher surface film was formed in the case of a LiPF6 solution.

Figure 22. Atomic force microscopy images (2mm2mm) of composite graphite electrodes obtained in situ in 1molL1 LiBOB and 1molL1 LiPF6 solution in ethylene carbonate:propylene carbonate 2:3 at open-circuit potential and after polarization to 0.3V (vs Li/Li+). Reproduced with permission from Larush-Asraf L, Biton M, Teller H, Zinigrad E, and Aurbach D (2007) On the electrochemical and thermal behavior of lithium bis(oxalato)borate (LiBOB) solutions. Journal of Power Sources 174(2): 400407.

Artificial graphite electrodes are currently a standard in EAF operations. Raw materials are petroleum coke (needle type is preferred) and coal tar pitch. They are mixed and processed at high temperature in several steps. Milestones of electrode technology are shown in Table 1.5.3.

Electrode water cooling was first adopted by Nippon Steel Corporation, and then most companies followed. Main advantage is to decrease side consumption. Large DC furnaces with only one electrode obliged to the development of very large electrodes, 800mm diameter. Some development work has been carried out recently to avoid some drawbacks of the nipple system joining two electrodes.

Fig.2. EC-AFM acquired on (A) HOPG immersed in H2SO4 at 0.3V, after a CV cycle up to 1.3V (A region of Fig.1A, see earlier); (B) HOPG immersed in HClO4 electrolyte at 0.3V, after the anion intercalation and blister formation (A region of Fig.1B, see earlier).

The Goss model predicts that steps are preferential intercalation sites and, consequently, areas close to the steps could be favored in surface swelling. This picture is partially true. For example, when the HOPG electrode is set to an EC potential greater than 1.0V in diluted perchloric electrolyte, some fractures appear on the surface and blisters decorate this regions, where the density of steps is higher, as reported in Fig.3.

Nonetheless, the chemical stability of the graphite basal plane in HClO4 electrolyte even just below 0.9V (B region) is critical and we observe carbon dissolution as a function of time, as reported in Fig.4.

Fig.4. EC-STM images (Itunnel=0.7nA; Vbias=0.8V) acquired on graphite in HClO4 solution at VEC just below 0.9V. The acquisition time for each image was 150s. The reported t refers to the elapsed time computed from the scanning start of the first image (A)to the scanning start of the 150s image (B)or the 300s image (C). The formation of damages (holes) on the graphite surface is marked by dashed circles. Pre-existing damages increase their sizes (see the dashed straight line). In addition, we observe that the terrace edges are smoothed and the corner eroded, as marked by the dashed squares.

In the image, the step is clearly eroded (see the area inside the dashed rectangle) and new defects in the surface basal plane are created due to the carbon dissolution in perchloric acid. Thus, even if the best quality of the HOPG crystal (e.g., -type) is used as WE, the electrode surface is not preserved from a massive intercalation process, due to the carbon dissolution process that starts just below the A region in the CV (see Fig.1).

A possible stratagem consists in covering the overall graphite surface with an ultrathin film, which can protect the carbon atoms, the crystal defects (steps, kinks, adatoms, etc.), and preserve a good EC exchange with the electrolyte. We found that free-base tetraphenyl porphyrin (H2TPP) forms a single molecule wetting layer on HOPG, when deposited in vacuum.54 The latter protects the HOPG from both dissolution and blistering damages during a CV in H2SO4, as reported in Fig.5.

Fig.5. AFM images (24m2) of a sample covered with a 0.5 thick layer of H2TPP. (A) Topography acquired in air in tapping mode before the EC process in H2SO4. The white dashed line represents the profile cross-section. (B) Phase-contrast image. The blue areas indicate the porphyrin wetting layer, while the yellow ones represent HOPG regions. (C) Image of the 0.5-thick H2TPP sample after anion intercalation acquired on a sample area (labeled as region A) where graphite is covered by porphyrins and no blisters are observed.

The ultrathin porphyrin film is hardly visible from the topography image (panel A), while it appears in the phase-contrast figure (panel B). After a CV sweep, the H2TPP film undergoes a molecular reassembling, but the HOPG substrate does not show any blister (panel C). The protective role of the porphyrin depends on the used electrolyte. Even if H2SO4 and HClO4 shows comparable effects on the pristine HOPG electrode, when the latter is covered by porpyrin, the perchloric acid is able to dissolve the organic film, intercalating inside the graphite and swelling the surface,55 strongly in contrast to what was previously observed in the sulfuric electrolyte (Fig.5).

Arc discharge between graphite electrodes was the first method to produce CNTs [42]. This technique involves establishing a direct current (DC) between a pair of graphite electrodes under an inert gas (helium or argon) at about 500torr [40,43]. MWCNTs are produced by arc discharge without any metal catalyst, while mixed metals catalysts (Fe, Co, and Ni) are required for the production of SWNCTs [44]. Usually, CNTs synthesized by arc discharge show a high degree of structural perfection [45]; however, a number of variables (temperature of the chamber, the composition and concentration of the catalyst, the presence of hydrogen, etc.) influence their size and structure [46]. Recently, other electrodes [47] and other chemicals [4850] have been employed for the synthesis of CNTs using arc discharge. Belgacem et al. [48] were able to produce MWCNTs doped with boron and nitrogen using the arc discharge method. Other research groups [49] have synthesized SWCNTSWCNT hybrids by arc discharge in open air at less cost.

Charge/discharge characteristics of natural graphite electrodes were investigated because fluorine compounds are electrochemically reduced at higher potentials than EC, PC, DMC, and DEC. Electrochemical reduction of fluorine compounds used in the study starts between 1.9 and 2.7V versus Li/Li+ [42,43]. These potentials are higher than the reduction potentials of EC (1.4V), PC (1.01.6V), DMC (1.3V), and DEC (1.3V) [56,62]. EC-based solvents should be used for high crystalline graphite such as natural graphite for the smooth formation of SEI on the electrode. Many fluorine compounds can be used for EC/DMC or EC/DEC electrolytes because EC easily forms SEI on natural graphite electrodes [42,4446]. First coulombic efficiencies obtained in fluorocarbonate-mixed electrolyte solutions are nearly the same as or slightly higher than those obtained in EC/DMC and EC/DEC electrolytes without fluorine compounds. If decomposed products of fluorine compounds facilitate SEI formation on graphite electrode, PC-containing electrolytes with low melting points can be also used. Figure 7.16 shows the first charge/discharge curves obtained using a natural graphite electrode (NG15 m) in 0.90, 0.78, and 0.67 molL1 LiClO4-EC/DEC/PC (1:1:1 vol) and -EC/DEC/PC/(A, B, D, E, or F) (1:1:1:0.33, 0.83 or 1.5 in vol, or 10.0, 21.7, or 33.3vol%, respectively) electrolytes as functions of the concentration of fluorocarbonate and current density [44]. The potential plateaus at 0.8V versus Li/Li+ indicate the reductive decomposition of PC. In EC/DEC/PC electrolyte without the fluorine compound, the potential plateau was prolonged with decreasing concentrations of LiClO4 and increasing current densities. According to these changes, the first columbic efficiency in the EC/DEC/PC electrolyte also decreased. On the other hand, in the fluorocarbonate-mixed solutions, the potential plateau was shortened with increasing concentrations of fluorocarbonate and current density. The difference in the EC/DEC/PC electrolytes with and without fluorine compound was clearly observed when fluorocarbonate was mixed by 33.3vol%. First coulombic efficiency in EC/DEC/PC/(A, B, D, E, or F) electrolyte increased, that is, irreversible capacity decreased with increasing concentrations of fluorocarbonate and current density. Fluorocarbonate B is the best among five fluorocarbonates, giving much higher first coulombic efficiencies, that is, lower irreversible capacities than others. For other fluorocarbonates except for B, much higher first coulombic efficiencies than those in the EC/DEC/PC electrolyte were also obtained by mixing of fluorocarbonates by 33.3vol%. Charge capacities are nearly the same as for each other in the electrolyte solutions with and without fluorocarbonates at 60 mAg1.

Figure 7.16. First charge/discharge curves of an NG15 m in 0.90, 0.78, and 0.67 molL1 LiClO4-EC/DEC/PC (1:1:1 vol) and 0.90, 0.78, and 0.67 molL1 LiClO4-EC/DEC/PC/(A, B, D, E, or F 1:1:1:0.33, 0.83 or 1.5 vol, 10.0, 21.7 or 33.3vol%, respectively) as functions of the concentration of fluorocarbonate and current density [44]. : EC/DEC/PC, : EC/DEC/PC/A, : EC/DEC/PC/B, : EC/DEC/PC/D, : EC/DEC/PC/E, : EC/DEC/PC/F.

Figure 7.17 shows charge/discharge potential curves at the first cycle in 1 molL1 LiPF6-EC/DMC (1:1:1 vol) and 1 molL1 LiPF6-EC/DMC/(A, B, G, or J) (1:1:1 vol) at 60 mAg1 [46]. Electrode potentials quickly decreased except that in 1 molL1 LiPF6-EC/DMC/G (1:1:1 vol), in which a short potential plateau indicating the reduction of G was observed. First coulombic efficiencies obtained in fluorine compound-mixed electrolyte solutions are similar to those obtained in 1 molL1 LiPF6-EC/DMC (1:1:1 vol) without fluorine compounds except that for 1 molL1 LiPF6-EC/DMC/G (1:1:1 vol). Contribution of G to SEI formation is slightly lower than others. The results indicate that fluorine compounds A, B, and J can be used for 1 molL1 LiPF6-EC/DMC (1:1:1 vol). The effect of mixing of fluorine compounds was also examined using PC-containing electrolytes. Figure 7.18 shows charge/discharge potential curves at the first cycle in 1 molL1 LiPF6-EC/EMC/PC/(A, B, or J) (1:1:1:0.33 or 1:1:1:1.5 vol) [46]. The potential plateau observed in 1 molL1 LiPF6-EC/EMC/PC (1:1:1 vol) indicates the electrochemical reduction of PC. However, the potential plateau almost disappeared in fluorine compound-mixed solutions. Table 7.4 gives electrochemical data obtained in PC-containing electrolytes. First coulombic efficiencies were largely increased by mixing of fluorine compounds without any decrease in capacities [46]. First coulombic efficiencies were in the range of 6974% when A, B, and J were mixed by 10vol%, but it reached 81% when J was mixed by 33vol%. The increments of first coulombic efficiencies were in the range of 1620% in 1 molL1 LiPF6-EC/EMC/PC/(A, B, or J) (1:1:1:0.33 vol), and 28% in 1 molL1 LiPF6-EC/EMC/PC/J (1:1:1:1.5 vol) at 60 mAg1. This means that fluorine compounds A, B, and J effectively facilitate SEI formation in PC-containing electrolyte solutions.

Figure 7.17. First charge/discharge curves of an NG15 m in 1 molL1 LiPF6-EC/DMC (1:1:1 vol) and 1 molL1 LiPF6-EC/DMC/(A, B, G, or J) (1:1:1 vol) at 60 mAg1 [46]. : EC/DMC, : EC/DMC/A, : EC/DMC/B, : EC/DMC/G, : EC/DMC/J.

Figure 7.18. First charge/discharge curves of an NG15 m at 60 mAg1 in 1 molL1 LiPF6-EC/EMC/PC (1:1:1 vol) and 1 molL1 LiPF6-EC/EMC/PC/(A, B, or J) (1:1:1:0.33 vol) (a), and in 1 molL1 LiPF6-EC/EMC/PC (1:1:1 vol) and 1 molL1 LiPF6-EC/EMC/PC/J (1:1:1:1.5 vol) (b) [46]. : EC/EMC/PC, : EC/EMC/PC/A, : EC/EMC/PC/B, : EC/EMC/PC/J.

Table 7.4. Charge/Discharge Capacities and Coulombic Efficiencies of NG15 m in 1 molL1 LiPF6-EC/EMC/PC (1:1:1 vol), 1 molL1 LiPF6-EC/EMC/PC/(A, B or J) (1:1:1:0.33 vol), and 1 molL1 LiPF6-EC/EMC/PC/J (1:1:1:1.5 vol) at 60 mAg1 [46]

Figure 7.19 shows charge/discharge potential curves at the first cycle in 0.90, 0.78, and 0.67 molL1 LiClO4-EC/DEC/PC with or without fluoroether [45]. In all cases, potential plateaus at 0.8V versus Li/Li+ indicating the electrochemical reduction of PC are reduced by mixing of fluoroethers. This trend becomes more distinct with increasing fluoroethers. Coulombic efficiencies are shown in Figure 7.20 as a function of cycle number [45]. Mixing of fluoroethers largely increases first coulombic efficiencies, which indicates that fluoroethers effectively facilitate SEI formation on natural graphite powder because electrochemical reduction of fluoroethers H and I starts at 2.1 and 2.3V versus Li/Li+, respectively [43], higher than 1.31.6V for PC, EC, and DEC [56,62]. The increments in first coulombic efficiencies by mixing of fluoroethers were approximately 1030%, 2040%, and 1050% at 60, 150, and 300 mAg1, respectively. The charge capacities obtained in fluoroether-mixed solutions are nearly the same as those in original electrolyte solutions without fluorine compounds at 60 mAg1; however, they slightly decrease at higher current densities.

Figure 7.19. Charge/discharge potential curves of an NG15 m at the first cycle, obtained in 0.90, 0.78, and 0.67 molL1 LiClO4-EC/DEC/PC (1:1:1 vol), and 0.90, 0.78, and 0.67 molL1 LiClO4-EC/DEC/PC/(H or I) (1:1:1:0.33, 0.83, or 1.5 vol) at current densities of 60, 150, and 300 mAg1 [45]. : EC/DEC/PC, : EC/DEC/PC/H, : EC/DEC/PC/I.

Figure 7.20. Coulombic efficiencies for an NG15 m as a function of cycle number, obtained in 0.90, 0.78, and 0.67 molL1 LiClO4-EC/DEC/PC (1:1:1 vol), and 0.90, 0.78, and 0.67 molL1 LiClO4-EC/DEC/PC/(H or I) (1:1:1:0.33, 0.83, or 1.5 vol) at current densities of 60, 150, and 300 mAg1 [45]. : EC/DEC/PC, : EC/DEC/PC/H, : EC/DEC/PC/I.

In LiPF6-containing electrolyte solutions, the first coulombic efficiencies are high in most of the cases. Figure 7.21 shows charge/discharge curves at the first cycle obtained in 1 molL1 LiPF6-EC/EMC/PC (1:1:1 vol) and 1 molL1 LiPF6-EC/EMC/PC/(H or I) (1:1:1:1.5 vol) [45]. In the PC-containing electrolytes, SEI formation is faster in fluoroether-mixed solutions than in the original one. First coulombic efficiencies obtained in fluoroethers H- and I-mixed solutions were 78 and 74%, respectively, >68% in the original solution. The results indicate that fluoroethers H and I also facilitate SEI formation in PC-containing electrolytes.

Figure 7.21. First charge/discharge curves of an NG15 m in 1 molL1 LiPF6-EC/EMC/PC (1:1:1 vol) and 1 molL1 LiPF6-EC/EMC/PC/(H or I) (1:1:1:1.5 vol.) at 60 mAg1 [45]. : EC/EMC/PC, : EC/EMC/PC/H, : EC/EMC/PC/I.

In the arc discharge method, two graphite electrodes separated by a distance of nearly 1mm are kept in an inert He atmosphere and a direct current is passed through them. The anode is consumed due to arcing and a cigar-like deposit is formed on the cathode. The outer shell of this deposit is gray and hard, with a black soft inner core that contains MWCNTs, polyhedral particles, and amorphous carbon [29]. SWCNTs may also be obtained but the synthesis of which requires mixed metal catalysts, such as Fe:Co and Ni:Y [30] that are inserted into the anode. SWCNTs are found distributed in the chamber as a fluffy web-like material [30]. In 2006, Ando and Zhao reported the synthesis of SWCNT nets of up to 2030cm in length by arc evaporation of a graphite rod containing a pure Fe catalyst in the chamber filled with a mixture of hydrogen and inert gas. Replacement of H2 by He resulted in the formation of MWCNTs with a very thin innermost tube of <0.4nm [31]. MWCNTs synthesized by arc discharge are highly crystalline and typically 20m long. They have an average outer diameter of around 10nm and have 2030 concentric graphitic walls. MWCNTs produced by the arc discharge method exhibit fewer defects than those produced by other methods. SWCNTs occur in bundles with diameters ranging from 1 to 2nm and due to the entanglement of the SWCNT bundles, it is really difficult to measure the SWCNT length accurately. The SWCNTs in the bundles exhibit a collection of different chiralities [30]. Along with the CNTs, the as-prepared material by arc discharge also contains substantial amounts of byproducts such as polyhedral carbon and amorphous carbon. Encapsulated metal catalyst particles may also be present in SWCNT samples [32, 33] (Fig. 16.4).

The carbon arc discharge evaporation method was used by Iijima in the discovery of CNTs [10]. The first obtained CNTs had diameters ranging from 4 to 30nm and a length up to 1mm. TEM analysis revealed that on each of these tubes, the carbon-atom hexagons were arranged in a helical fashion about the tube axis. The tips of the tubes were closed by curved polygonal or cone-shaped caps. The TEM study of the growth morphology revealed that there were many variations in shape, especially near the tube tips [7]. A topological model was constructed in which pentagons and heptagons played a key role in the tube tip shapes. For an open-ended growth, Iijima et al. proposed a model in which the carbon atoms are captured by the dangling bonds, resulting in layer-by-layer growth [13]. The large-scale synthesis of MWCNTs by the arc discharge technique was reported by Ebbesen and Ajayan [29].

The results reported here refer to a graphite electrode prepared by mixing 95wt.% of natural graphite with 5wt.% of poly(vinylidene fluoride) (PVdF)-binder. Graphite electrodes without PVdF-binder were also fabricated. The electrolyte was 1M LiPF6/ethylene carbonate (EC)+dimethyl carbonate (DMC) (1:1 v/v) and the counter electrode a Li metal sheet.

The cells were cycled between 0.01 and 1.5V with a relaxation period of 60min at the end of charge, at a constant current of 0.2mA/cm2. After two cycles in this condition, the cells were charged to 0V with the time limit of 372mAh/g to obtain a fully charged negative electrode.

Figure 20.2 shows DSC curves for fully lithiated or delithiated graphite (ad) and the electrolyte (e). Sample (a) shows a mild heat generation starting at 130C with a small peak at 140C. The mild heat generation continued until a sharp exothermic peak appeared at 280 C. From our experiments, the small peak at 140C is caused by SEI formation. There is already SEI on the sample (lithiated graphite), which is formed during cycling for sample preparation. This original SEI protects the reaction of the electrolyte and Li in graphite at a lower temperature, and there is no heat generation. However, at 140C, the protection effect of the original SEI is not sufficient, and a new, thicker SEI is formed. When this becomes thick enough, its formation speed decreases, and a small exothermic heat peak is observed at 140C. The mild heat generation continued until a sharp exothermic peak appeared at 280C, because the SEI formation continues with increase in temperature even if there is a protection effect of the SEI. If the original SEI formed during cycling is thick enough, the small peak at 140C does not appear because the protection effect of the original SEI is enough even at this temperature. Sample (b) is charged at a very low current density because PVdF-binder is not used to make the electrode. Therefore, SEI of sample (b) is very thick, and no peak appeared at 140C. Samples (c) and (d) did not show the small peak at 140C. Therefore, the lithiated graphite and the electrolyte are necessary to show the small peak at 140C. This fact also supports that the small peak at 140C is the formation of SEI. This peak is sometimes large and the peak temperature is different from 140C, because the thickness of original SEI is different (the charge current density is different).

FIGURE 20.2. DSC curves of (a) fully lithiated graphite with the electrolyte and PVdF (the usual graphite anode), (b) fully lithiated graphite with the electrolyte, (c) fully delithiated graphite with the electrolyte and PVdF (the usual graphite electrode), (d) fully lithiated graphite with PVdF (the usual graphite electrode), and (e) the electrolyte (1M LiPF6/EC+DMC) [6].

There is evidence [7] that the peak at 280C in Figure 20.2 is caused by decomposition of SEI with reaction of Li in graphite. DSC curves of charged electrode powder (without electrolyte) obtained after the 2nd charge are shown in Figure 20.3, together with that of discharged electrode powder (without electrolyte) after the 2nd discharge. No exothermic peak was seen at around 100130C. The heat values, which were evaluated by integrating DSC curves, were proportional to the amount of charged electrode powder. These results suggest that SEI formed on graphite during charging would react with charged graphite at 280C accompanied by exothermic heat.

As shown in Figure 20.3 no exothermic peak was visible at 100160C for charged graphite only, thus the electrolyte should be directly involved in the exothermic reaction at this temperature. To identify the effect of solvent and LiPF6 in the electrolyte separately, the thermal behavior of the charged graphite in solvent was studied firstly [8]. Figure 20.4(a) shows DSC curves for 4mg of Li0.92C6 mixed with a given amount of the EC+DMC solvent (from 0.25 to 4l). When the amount of the solvent was 0.25l, an exothermic peak was observed at 160C. When the amount of solvent increased from 0.25 to 2l, the heat values of the peak increased significantly. However, the heat value was almost constant when the amount of the coexisting solvent increased to 3 and 4l. Therefore, the exothermic peak at 160C is caused by the reaction between solvent and intercalated Li. The protection effect of original SEI, which was formed during sample preparation, has to be considered. The heat value of the peak increased with the increase of the solvent until the amount of solvent became to 3l. All the coexisting solvent was used for the reaction, and some of intercalated Li remained, because the reaction was limited by the amount of the solvent. With 4l, the heat value did not increase too much from that of 3l solvent, because the reaction was limited by the amount of intercalated Li. All the intercalated Li was consumed, and excess solvent remained after the reaction.

FIGURE 20.4. (a) DSC curves for mixtures of 4mg Li0.92C6 and given amounts of EC+DMC solvent; (b) DSC curves for mixtures of 4mg Li0.48C6 and given amounts of EC+DMC solvent [8]. (For color version of this figure, the reader is referred to the online version of this book.)

To confirm the above supposition of exothermic peak at around 160C, half-charged graphite (Li0.48C6) with solvent was also quantitatively studied by DSC. Figure 20.4(b) shows DSC curves for 4mg of Li0.48C6 mixed with a given amount of EC+DMC solvent (from 0.25 to 4l). Compared with the DSC curves of the mixtures of Li0.92C6 and solvent (Figure 20.4(a)), it was easy to find that the dominant peak was quite similar to that obtained for Li0.92C6 in the solvent, including peak position and peak shape. At the same time, similar tendency of the heat value was visible. The heat values in both cases increased with the increasing of the amount of solvent, and then remained almost constant when all the intercalated Li was consumed with excess solvent. The heat value became almost constant when the solvent was about 3l with 4mg of Li0.92C6, and the solvent was from 1 to 2l with 4mg of Li0.48C6. Furthermore, the largest heat value of Li0.48C6 was almost half the value of Li0.92C6. Based on these results, it was clear that the amount of solvent limits the reaction when its amount is small, and the amount of intercalated Li limits the reaction when the amount of solvent is large. LiPF6 in the electrolyte is needed to form SEI (with protection effect) on the charged graphite.

In 1998 [6], a graphite electrode, which was pretreated by lanthanum nitrate, was modified with 2,6-dichlorophenolindophenol (DCPI) through physical adsorption (DCPI-La). This electrode was then applied for the voltammetric detection of nicotinamide coenzyme (NADH) in a flow injection analysis system. NADH oxidized at bare electrodes at high potentials (from 450 to 1100mV based on the electrode materials). The oxidation reaction was irreversible and was affected from interferences from other oxidizable species at these high voltages. Hence, modifiers were needed to promote NADH oxidation at lower potentials. The role of La in the modified electrode was to enhance the analytic properties of the DCPI-modified electrode in terms of linear range and detection limit. Since the solubility of the DCPI-La was low (about Ksp<1010), DCPI remained better on the electrode surface, and the stability of the electrode was increased (about 20% higher after 6h of continuous operation in the flow injection system).

In 2000, [7] synthesized a lanthanide porphyrin complex and used it for the modification of an electrode to make an ethacrynic acid (EA) potentiometric sensor. The complex pentane-2,4-dionato(meso-tetraphenylporphinato)terbium [TbTPP(acac)] was applied as a sensing material in a polymeric membrane of the potentiometric sensor. Nernstian response to EA ion in the concentration range from 7.4106 to 1.0101mol L1, in a pH range from 3.2 to 6.8, with a fast response time of 30s was achieved. Lanthanide porphyrin complexes performed better than copper porphyrin complexes in the potentiometric sensor. The sensor was then successfully used in the analysis of EA in human urine samples.

In 2001, an electronic nose was introduced for discrimination among diverse virgin olive oils. In that work, a sensor array based on Langmuir-Blodgett (LB) films of lanthanide bisphthalocyanines (LnPc2) was used as a sensing material. A LB film consists of one or more monolayers of an organic material, deposited from the surface of a liquid onto a solid by immersing (or emersing) the solid substrate into (or from) the liquid. Bisphthalocyanines composed of unsubstituted bisphthalocyanines with a distinct central Ln atom (PrPc2 and LuPc2) and an octa-tert-butyl-substituted bisphthalocyanine (PrPc2t) were synthesized. The interaction of the sensors in the designed electronic nose (composed of an array five sensors) with the headspace of olive oil samples caused the chemisorption of the volatile organic compounds (VOCs) in the Ln-biphthalocyanine LB films and led to the formation of complexes, which changed the conductivity in the LB films. Other studies by the same group, related to a tobacco smoke sensor using LB films of Pr, Gd, and Yb diphthalocyanines and an octa-tert-butyl praseodymium diphthalocyanine [8] or to the application of lutetium bisphthalocyanine thin films as sensors for organic volatile components of aromas [9], have also contributed to evince the feasibility of using thin LB films or evaporated films of lanthanide bisphthalocyanines for the determination of volatile VOCs (e.g., alcohols, aldehydes, esters, and acids).

In 2004, a series of anion-selective potentiometric sensors were introduced by the application of lipophilic lanthanide tris(-diketonates) as sensing materials in a plasticized poly(vinyl chloride) membrane [10]. The designed sensors possessed high selectivity toward the chloride anion in the 1.0105101mol L1 concentration range with near-Nernstian slopes. A non-Hofmeister anion selectivity in the determination of Cl anion from NO3, ClO4, and other anions was observed, which was due to a 1:1 complex formation of lanthanide tris(-diketonates) with chloride.

In a study in 2009, a Ln-containing ionic liquid of [(C4H9)2-bim]3[La(NO3)6] (bim=benzimidazole) was synthesized and utilized as a modifier in a carbon paste electrode [11]. The results showed that the modified electrode had excellent electrocatalytic activities toward the reduction of H2O2, nitrite, bromate, and trichloroacetic acid.

In 2014 [12], Selvaraju and Ramaraj reported an electroactive sodium lanthanum hexacyanoferrate complex that was deposited on a glassy carbon electrode (GCE). The modified electrode was an excellent transducer for oxidation of neurotransmitter molecules: it enhanced the oxidation peak of dopamine by a factor of 50 as compared with the bare GCE.

In a study in 2016, a novel LB-film-based taste sensor for evaluating the quality of Japanese sake was developed by Hiroki et al. [13]. LB films were made of lanthanides coordinated to stearic acid (Tb-SA and Eu-SA). Three different kinds of Japanese sake were assessed by the sensors. The Ln-SA films increased the sensitivity of taste sensors.

A lanthanum MOF, [La(BTC)(H2O)(DMF)] (H3BTC=1,3,5-benzenetricarboxylic acid), was prepared through mild hydrothermal conditions [14]. The synthesized MOF showed an electrocatalytic activity toward H2O2 reduction in acidic media at ca. 0.7V. The modified electrode showed a linear range from 5M to 2.67mM with a detection limit of 0.73M.

In arc discharge method, two high purity graphite electrodes as anode and cathode are held at short distance apart under a helium atmosphere. Under these conditions, some of the carbon evaporated from the anode, re-condensed as a hard cylindrical deposit on the cathodic rod. The key point in the arcevaporation method is the current applied. Higher current application will result in a hard, sintered material with few free nanotubes. Therefore, the current should be kept as low as possible. Using arc-discharge method, individual carbon nanotubes could be achieved in generally several hundred microns long.

Arc discharge process has scale up limitations and also sometimes requires the addition of a small amount of metal catalysts, which increases the yield of nanotubes. So the resulting products contain some catalyst particles, amorphous carbons, and non-tubular fullerenes. Therefore, subsequent purification steps are required. High temperatures are also necessary for this technique. Arc discharge technique needs 6001000C, so, the differences in lattice arrangements could exist in the tubes and also there may be a difficulty in the control of chirality and diameter of the nanotubes.

rongsheng group - graphite electrode manufacturer

Rongsheng Group as a graphite electrode manufacturer, owns an in-depth raw material, production line, and engineering expertise, experienced applications on steelmaking furnaces, a comprehensive graphite based product portfolio, such as (RP, hp, UHP) graphite electrode, graphite electrodes nipples, graphite block, graphite powder, graphite tile, graphite crucible, graphite mould, carbon raiser, etc.More >

Know more about graphite electrode manufacturers, graphite electrode sellers, graphite electrode prices, high-quality graphite electrode prices, and for the price quoting of graphite electrodes, please contact us.

Graphite electrode as a major conduction material is mainly applied for the electric furnace smelting industry. Graphite electrodes are used in EAF, Submerged-arc furnace, Electric resistance furnace, etc.

The manufacturing process of graphite electrodes is from the preparation of the raw materials (a series of crushing, calcining, milling, sieving, and finally mixed together) to the kneading and pressing, and then baking, Impregnation, graphitizing, machining, and finally the graphite electrode products. MORE >

graphite electrodes for steel industrial with high quality real-time quotes, last-sale prices

1. SpecificationsGraphite Electrodes Used for steel making in arc furnace Dia:200mm-500mm Superquality Competitive price2. Specifications for RP, HP, UHP graphite electrodes with nipples:RPHPUHPElectrode:Bulk Density 1.56g/cm3 Specific Resistivity 8.5m Bending Strength 10.0MPa Elastic Modulus 9.3GPaThermal Expansion Coefficient 2.7x10 -6/CAsh 0.5%Nipple: Bulk Density 1.68g/cm3 Specific Resistivity 7.0m Bending Strength 14.0MPaElastic Modulus 13.7GPaThermal Expansion Coefficient 2.5 x10 -6/CAsh 0.5%Electrode:Bulk Density 1.65g/cm3 Specific Resistivity 6.5m Bending Strength 12.0MPa Elastic Modulus 10.0GPaThermal Expansion Coefficient 2.2x10 -6/CAsh 0.3%Nipple: Bulk Density 1.74g/cm3 Specific Resistivity 5.5m Bending Strength 16.0MPaElastic Modulus 14.0GPaThermal Expansion Coefficient 2.0 x10 -6/CAsh 0.3%Electrode:Bulk Density 1.68g/cm3 Specific Resistivity 5.8m Bending Strength 16.0MPa Elastic Modulus 14.0GPaThermal Expansion Coefficient 1.9x10 -6/CAsh 0.2%Nipple: Bulk Density 1.75g/cm3 Specific Resistivity 4.5m Bending Strength 18.0MPaElastic Modulus 16.0GPaThermal Expansion Coefficient 1.4 x10 -6/CAsh 0.2%3. Packing:In wooden cases strapped with steel bands.4.Pictures of Graphite Electrodes Factory5.FAQWehaveorganizedseveralcommonquestionsforourclientsmayhelpyousincerelyHowaboutyourWarrantyGraphite Electrodes with high power Our factory could produce qualified products and good delivery time, cause we have many graphite electrodes in stock to our clients. So we can offer you stock products if you need urgent.HowtoguaranteethequalityoftheproductsGraphite Electrodes with high powerWehaveestablished purchasing quality control system, and we have inspector in the factory to check the quality. each good should be appreoved by the inspectors ,then, could be permit to do shipment.Howlongcanwereceivetheproductafterpurchase?Inthepurchaseofproductwithinthreeworkingdays,Wewillarrangethefactory to do production or do deliveryas cusotmers' request.

Wehaveestablished purchasing quality control system, and we have inspector in the factory to check the quality. each good should be appreoved by the inspectors ,then, could be permit to do shipment.

uhp graphite electrode, eaf graphite electrode | hgraphite

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UHP graphite electrode are mostly made of 100% high-specification needle coke. Compared with HP and RP grades, UHP electrode requires highest technical expertise in each of the main process steps in making them, particularly baking, extrusion and graphitizing.

The electrodes come with a wide range of sizes, but diameter of 600mm and 700mm high performance. UHP graphite electrode is often used for ultra high power electric arc furnaces (EAF) with current density greater than 25 A/cm2.

The length of EAF graphite electrodes can be up to 2900mm. They are usually packed with pre-set graphite nipple, which allows one electrode to be joined together with another. In an EAF, three electrodes are often joined together to form a column, with new electrodes added to the top of a column as electrodes are consumed upwards from the tip. In a DC furnace, one column is used, but in an AC furnace three columns are used simultaneously.

The rate at which UHP graphite electrodes are consumed in an EAF depends on the steelmaking or other raw materials used, the grades of steel being produced, and the amount of supplemental (chemical) energy used. EAFs typically consume electrodes at a rate of around 2 kg per tonne of steel produced, with some specialty steel applications consuming at a slightly higher rate.

Hgraphites focus is being a very good partner with the steel industry and to foster long-term relationships with clients, delivering products to customers when and where they want them at a fair price.

Ultra-high-power (UHP) electrodes are often found inside of electric arc furnaces, or EAFs, which are used in most metal shops. Capable of reaching extremely high temperatures to melt even some of the hardest metals, ultra-high-power (UHP) electrodes play a vital role in melt-shop operations, yet they have never received that much attention when it comes to relevant markets, at least not until 2018.

Following calcination, the UHP must be kneaded, pressed, roasted, graphitized, machined, and finally released into an electric arc furnace (EAF) for the steelmaking process to begin. Graphite electrode quality is indicated by the name, ranging from ordinary power graphite electrode (lowest quality) to HP graphite electrode (mid-quality) to UHP graphite electrode (highest quality).

A few years back, the steel industry noted a shorted of UHP graphite electrodes and, as expected, the lack of supply in the face of imminent demand drove the prices up to critical highs. Meanwhile, steelmakers tried to secure a steady source of UHP to avoid production holdups. Of course, not every steel producer was able to do so, and many some steel production was slowed or halted until producers could secure more UHP.

Reportedly, the panic led to UHP electrode prices peaking at up to $30,000 per tonne. However, prices have since fallen, although they remain high when compared to the historical cost of UHP. Meanwhile, the global demand for UHP is estimated at around 785,000 tonnes per year. This has kept steel producers on their toes, since the global demand is very near to the annual global production capacity of 800,000 tonnes.

While China is capable of producing approximately 50,000 tonnes on top of the above estimate (and perhaps even more if they lower the quality), the current state of UHP electrodes is still on the edge. Today, the supply and demand equation for UHP remains in a careful balance, which is a far cry from the state of the market some years ago.

Back when the world steel markets were performing exceedingly poorly, UHP was in very low demand, and about 20% of UHP production stopped as a result of that. This is what experts say led to the unexpected shortage the markets witnessed just a few years back. However, although demand has picked up, UHP production remains bridled in light of materials shortages.

Needle coke is one such critical ingredient in the production of UHP that UHP producers are struggling to find. Experts estimated a global production of no more than 900,000 tonnes per year for this ingredient, and producing 1 tonne of UHP consumes about 1 tonne of needle coke.

With the most recent estimated need for UHP sitting at 820,000 tonnes per year (implying a 5% annual increase in demand), producing needle coke at full capacity is a critical element in avoiding another shortage. As we enter 2020, it awaits to be seen just how the market turns out for UHP production and its components.

graphite electrode, solutions for steel and foundries industry | hgraphite

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HGraphite has been in thegraphite electrode industry for 20 years, engaged in supplying graphite related products especially graphite electrode, electrode paste. Our associated manufacturing facilities were awarded byISO 9001:2008. With strong and continuous R&D, we offer high quality graphite electrodes and carbon products for various applications. We always intend to adopt all measures to improve our competitivenessbased on diverse manufacturing fields and technology. graphite electrode manufacturer

HGRAPHITE givea special offer for UHP Graphite Electrode Dia 450mm x Length 1600/1800mm for sale at stock: The offered item is ready for delivery in stock. We give the great discount for promotion purpose. It will go up to the original price after this promotion [...]

Recently, HGRAPHITE delivered 150MT of synthetic graphite powder to Indonesia. The client is an importer and service company of graphite based product. They have been in this business for 5 years offering consulting, research, and product development on graphite products for their local foundry, steel, [...]

green graphite electrodes | coidan graphite

We are committed to reducing our environmental footprint by recovering used and damaged electrodes and reconditioning them into green graphite electrodes. This energy-efficient production process not only dramatically reduces the amount of energy required to create high quality electrodes but also stops thousands of tonnes of graphite being sent to landfill sites.

As one of the few companies in this sector operating within Europe, we have years of experience in the recovery and reconditioning of broken or used graphite electrodes. Our MD was running an electrode reconditioning facility in the 1980s and consequently, we have a wealth of experience and contacts within the industry.

By recovering electrodes or using electrodes we have reconditioned, you save on the expense of purchasing new electrodes and help the environment by being involved in a recycling activity recovering an item that is highly energy intensive in its original manufacture.

Graphite manufacturing is highly energy intensive. Manufacturing one tonne of graphite requires 17MWhr of energy. This is equivalent to two households annual energy usage or 1.5 million charges of your mobile phone. Our reconditioning process uses less than 1% of the energy required to manufacture new electrodes. Not only does this process emit 99% less carbon emissions but it also stops damaged and used electrodes from being sent to landfill sites.

By recovering electrodes or using electrodes we have reconditioned, you save on the expense of purchasing new electrodes and help the environment by being involved in a recycling activity recovering an item that is highly energy intensive in its original manufacture.

The sudden rise in the price of graphite has led to the formation of many companies without the background knowledge and experience we have gained over the years, but luckily, our reconditioning process takes place within the controls and checks as laid out in our ISO 9001:2015 Quality System and significantly enhances the reliability of our product.

This reconditioning process takes place within the controls and checks as laid out in our ISO 9001:2015 Quality System so you can rest assured our green graphite electrodes are as reliable as a new one.

At Coidan Graphite, were committed to reducing our environmental footprint by recovering used and damaged electrodes and reconditioning them into green graphite electrodes. Our carbon footprint calculator explains exactly what is used to create green graphite electrodes in comparison to what is used to manufacture new graphite electrodes.

Our vision has remained the same throughout the years: to build an innovative, global graphite manufacturing company that offers our customers a full range of top quality carbon and graphite-based services. Moving together towards excellence, we aim to build our future, setting Coidan Graphite's standards as the benchmark for the niche carbon and graphite market we occupy.

high quality graphite electrode export - graphite electrodes for sale

In the production of high quality graphite electrode, we pay great attention to the product characteristics, from petroleum coke, asphalt, needle coke and other raw materials will be strictly controlled ash and sulfur content, to ensure the product performance from calcining, kneading, molding, roasting, maceration. Graphite electrode export, we pay attention to every detail of the product.

In electrode manufacturing, we know the importance of machining, so we use advanced CNC lathes to ensure the quality and performance of products. Because of our strict requirements, our graphite products have good conductivity, low ash, compact structure, good oxidation resistance and high mechanical strength.

From the polarization curve, the corrosion resistance of graphite oxide is better than that of expelable graphite, and the corrosion resistance of expelable graphite is better than that of natural graphite. The higher the purity of natural graphite, the better the corrosion resistance.

Graphite positive rod has good thermal conductivity and high temperature resistance. Easy to be machined, good chemical stability, resistance to acid and alkali corrosion, low ash content. Used for electrolysis of aqueous solution, preparation of chlorine, electrolysis of salt solution to make alkali. Or used for electroplating various metal and nonmetallic carrier. For example, graphite anode can be used as the conductive anode of caustic soda. Graphite electrode export can also be used for sewage treatment in chemical, electronic and textile industries.

When the graphite electrode is in use, the standby electrode should be hoisted above the electrode to be connected, and then the electrode hole should be aligned and slowly dropped down. Then make the spiral hook and the electrode rotate together to descend, when the distance between the two electrode end faces is close, clean the two electrode end faces and the joint part with compressed air again. After the electrode is completely lowered, do not be too strong, or it will be a violent collision, will cause damage to the electrode hole and joint thread. Graphite electrode export, quality is stable and reliable, the production experience is rich, welcome everybody to come to consult purchase.

Hot-SaleHP Graphite Electrode,RP Graphite Electrode,UHP Graphite Electrodes,Graphite Electrode Nipplefor sale cheap from RS Factory, which are widely used in metallurgy, nonferrous metals, chemicals, electricity and other industries. Any Interest? Send Us an Email for Price List Now!