Needle coke for graphite electrode, method for producing the same, and suppressor

Abstract

The present invention aims to provide a needle coke for graphite electrodes, a manufacturing method therefor, and an inhibitor, which suppresses the crystal expansion of needle coke without incurring a large cost in manufacturing the needle coke, and which improves the manufacturing yield and characteristics of graphite electrodes. An inhibitor for graphite electrode manufacturing, which contains at least one of a metal composed of an element (Mβ) and an oxide having the element (Mβ), or at least one of a metal composed of the element (Mβ) and a compound having the element (Mβ), the inhibitor for graphite electrode manufacturing being volatilized at a temperature of 2100°C to 6000°C, the element (Mβ) being at least one element selected from the group consisting of a long-period type periodic table Group 4 element, a Group 8 element, a Group 9 element, a Group 10 element, a Group 13 element, a Group 14 element, and a Group 15 element.

Description

Technical Field

[0001] This invention relates to needle coke for graphite electrodes, its manufacturing method, and inhibitors.

[0002] This application claims priority based on Japanese Patent Application Nos. 2021-066201, 2021-066203 and 2021-066639, filed on April 9, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] Coal tar, a byproduct of coal dry distillation, is largely composed of condensed polycyclic aromatic compounds and has long been used as a raw material for various carbon products. The composition of coal tar-based products is approximately 30% from creosote oils and naphthalene, derived from distillate components, and the remaining 70% from coal tar pitch, a heavy component that is not distillate. Needle coke, manufactured from coal tar pitch, occupies an important position as a product with particularly high added value, primarily used as aggregate for graphite electrodes in electrical steel production. In the graphite electrode manufacturing process, needle coke particles and binder pitch are first mixed in a predetermined ratio, heated and kneaded, and then extruded to produce green electrodes. These green electrodes are then sintered, graphitized, and processed to obtain finished graphite electrode products.

[0004] These graphite electrodes are used under harsh high-temperature conditions, thus requiring extremely high thermal shock resistance. To manufacture graphite electrodes with high thermal shock resistance, needle coke with a low coefficient of thermal expansion is needed. Needle coke made from coal tar pitch (hereinafter, sometimes referred to as pitch-based needle coke) has the lowest coefficient of thermal expansion among all cokes, making it the most preferred raw material for graphite electrodes. However, while pitch-based needle coke provides graphite electrodes of acceptable quality, it conversely, during the graphitization process of electrode manufacturing, it easily induces an irreversible expansion phenomenon known as crystal expansion. Under rapid graphitization conditions, this leads to the disadvantage of cracking in the finished product and a significant reduction in yield.

[0005] Therefore, the graphitization process requires prolonged heating for graphitization, significantly reducing productivity. This crystal expansion phenomenon is believed to be primarily due to the abnormal expansion caused by the rapid detachment and volatilization of nitrogen and sulfur contained in pitch-based needle coke within the 1500℃–2100℃ and 2500℃–2800℃ regions of the graphitization process.

[0006] To eliminate this crystal expansion phenomenon, several methods have been adopted in the manufacturing process of graphite electrodes. For example, one method involves adding small amounts of iron oxides, nickel compounds, and titanium dioxide as crystal expansion inhibitors during the mixing of pitch-based needle coke and the binder pitch. These inhibitors form stable metallic compounds with the sulfur components in the coke during graphitization, thus suppressing crystal expansion by staggering the release time to its decomposition temperature. Another method involves adjusting the bulk density of the graphite electrode during the forming process to facilitate the volatilization of gases generated during graphitization. However, while the former method has some effect on reducing expansion originating from sulfur, no effect on reducing expansion originating from nitrogen has been observed. The latter method suffers from a decrease in the mechanical strength of the graphite electrode due to the reduction in bulk density.

[0007] In addition to the above, various methods for suppressing crystal expansion when manufacturing graphite electrodes using needle coke have been proposed. For example, Patent Documents 1 and 2 propose a method to reduce crystal expansion by denitrifying the pitch coke through heat treatment at temperatures above 1500°C. Furthermore, Patent Document 3 discloses a method of heat-treating the raw coke at a normal calcination temperature after pretreatment such as oxidation. These methods have the following drawbacks: the former involves increased energy consumption due to high-temperature heating, and the latter involves more complex procedures compared to conventional methods.

[0008] Furthermore, it was proposed that by adding a metal compound used as a crystal swelling inhibitor only to the surface of block and granular coke in a solution state before mixing with binder asphalt, and then performing heat treatment, the crystal swelling inhibition effect was increased despite reducing the amount of inhibitor added (Patent Document 4).

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 60-33208

[0012] Patent Document 2: Japanese Patent Application Publication No. 60-208392

[0013] Patent Document 3: Japanese Patent Application Publication No. 63-135486

[0014] Patent Document 4: Japanese Patent Application Publication No. 2001-329271 Summary of the Invention

[0015] The problem the invention aims to solve

[0016] However, in all cases, the manufacturing methods of these low-crystal-expansion needle cokes are economically difficult, and there are problems such as not being able to achieve practical application or not being able to obtain sufficient crystal expansion reduction effect.

[0017] The present invention was made in view of the above-mentioned situation, and its object is to provide: a needle coke for graphite electrodes that suppresses crystal expansion of needle coke and improves the manufacturing yield and characteristics of graphite electrodes without incurring high costs in manufacturing needle coke, a method for manufacturing the same, and an inhibitor.

[0018] Solution for solving the problem

[0019] The inventors of this invention have repeatedly conducted focused research in order to solve the above-mentioned problems, and as a result, they discovered that by using a graphite electrode manufacturing inhibitor that contains at least one of a metal composed of the element (Mβ) described later and an oxide having the element (Mβ) described later, or by using a graphite electrode manufacturing inhibitor that contains at least one of a metal composed of the element (Mβ) described later or a compound having the element (Mβ) and volatilizes at a temperature of 2100°C to 6000°C, the crystal expansion suppression effect is increased, and the present invention is thus completed.

[0020] In the case of a graphite electrode manufacturing inhibitor comprising at least one of a metal composed of element (Mβ) and an oxide having element (Mβ), the crystal expansion suppression effect is further increased. Therefore, a graphite electrode manufacturing inhibitor comprising a composite oxide having element (Mα) and element (Mβ) as described later, or a graphite electrode manufacturing inhibitor comprising an oxide having element (Mα-1) as described later and an oxide having element (Mβ) as described later, is preferred.

[0021] That is, the present invention is based on the following [1] to

[24] .

[0022] [1] An inhibitor for manufacturing graphite electrodes, comprising at least one of a metal composed of element (Mβ) and an oxide having element (Mβ),

[0023] Element (Mβ): Selected from at least one element from the group consisting of elements from Group 4, Group 8, Group 9, Group 10, Group 13, Group 14 and Group 15 of the long-period periodic table.

[0024] [2] The inhibitor for manufacturing graphite electrodes according to [1], wherein the element (Mβ) is at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe and P.

[0025] [3] The inhibitor for manufacturing graphite electrodes according to [1] or [2], wherein the oxide having element (Mβ) is a composite oxide having element (Mα) and said element (Mβ),

[0026] Element (Mα): At least one metallic element (except for element (Mβ)).

[0027] [4] The inhibitor for manufacturing graphite electrodes according to [3], wherein the element (Mα) is at least one metal element selected from the group consisting of K, Sc, alkaline earth metals and rare earth metals.

[0028] [5] The inhibitor for manufacturing graphite electrodes according to [3] or [4], wherein the composite oxide has the following formula (1):

[0029] Mα 3-x Mβ 1-y O 5-z …(1)

[0030] (In the formula, x ≤ 3, y ≤ 1, z ≤ 5.)

[0031] [6] The inhibitor for manufacturing graphite electrodes according to [1] or [2] further comprises at least one of a metal consisting of element (Mα) and an oxide having element (Mα).

[0032] Element (Mα): At least one metallic element (except for element (Mβ)).

[0033] [7] The inhibitor for manufacturing graphite electrodes according to [6], wherein the element (Mα) is at least one metal element selected from the group consisting of K, Sc, alkaline earth metals and rare earth metals.

[0034] [8] The inhibitor for manufacturing graphite electrodes according to [6] or [7], wherein the oxide having element (Mα) has the following formula (2):

[0035] Mα 3-x1 O 3-z1 …(2)

[0036] (In the formula, Mα is an element (Mα), where 0≤x1<3 and 0≤z1<3.)

[0037] [9] An inhibitor for manufacturing a graphite electrode according to any one of [6] to [8], wherein the oxide having element (Mβ) has the following formula (3):

[0038] Mβ 1-y1 O 2-z2 …(3)

[0039] (In the formula, Mβ is an element (Mβ), where 0≤y1<1, 0≤z2<2.)

[0040]

[10] An inhibitor for manufacturing graphite electrodes, comprising at least one of a metal composed of an element (Mβ) and a compound having the element (Mβ).

[0041] The inhibitor used in the manufacture of graphite electrodes volatilizes at temperatures ranging from 2100°C to 6000°C.

[0042] Element (Mβ): Selected from at least one element from the group consisting of elements from Group 4, Group 8, Group 9, Group 10, Group 13, Group 14 and Group 15 of the long-period periodic table.

[0043]

[11] The inhibitor for manufacturing graphite electrodes according to

[10] , wherein when the proportion (by weight%) of the inhibitor added to the needle coke is set as X and the proportion (by weight%) of the inhibitor after heat treatment at 2800°C for 30 minutes is set as Y, Y / X < 0.01.

[0044]

[12] The inhibitor for manufacturing graphite electrodes according to

[10] or

[11] , wherein the element (Mβ) is at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe and P.

[0045]

[13] An inhibitor for manufacturing graphite electrodes according to any one of

[10] to

[12] , which reacts with a sulfur compound.

[0046]

[14] An inhibitor for manufacturing graphite electrodes according to any one of

[10] to

[13] , which reacts with a nitrogen compound.

[0047]

[15] An inhibitor for manufacturing a graphite electrode according to any one of

[10] to

[14] , wherein the oxide having element (Mβ) further has the following element (Mα-1),

[0048] Element (Mα-1): At least one alkaline earth metal element (except for element (Mβ)).

[0049]

[16] The inhibitor for manufacturing graphite electrodes according to any one of

[10] to

[15] further comprises at least one of a metal composed of an element (Mα-1) or a compound having an element (Mα-1).

[0050] Element (Mα-1): At least one alkaline earth metal element (except for element (Mβ)).

[0051]

[17] An inhibitor for manufacturing graphite electrodes according to any one of

[10] to

[16] , wherein the element (Mα-1) is at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements and rare earth metal elements.

[0052]

[18] An inhibitor for manufacturing graphite electrodes according to any one of [1] to

[17] , wherein the crystal expansion value P of the test piece prepared by the following evaluation test (i) is calculated using the following formula (I). 2100 Below 1.00%

[0053] P 2100 = (L2-L1) / L1×100…(I)

[0054] In equation (I), L1 and L2 have the following meanings:

[0055] L1: Thickness of the test piece before firing (mm)

[0056] L2: Thickness (mm) of the test piece after firing at 2100℃

[0057] <Evaluation Experiment (i)>

[0058] Coal-based needle coke, binder pitch (30% by weight relative to the amount of coal-based needle coke), and inhibitor were mixed and kneaded at 165°C for 5 minutes. The mixture was then molded into circular plates of 20mm diameter × 3mm–15mm and calcined at 1000°C for 3 hours in a firing furnace to burn off the binder pitch, thus producing test pieces. The test pieces were then heated to 2100°C at a rate of 20°C / min and fired. The L1 and L2 values ​​of the test pieces before and after firing were measured.

[0059]

[19] A composition comprising any one of the graphite electrode manufacturing inhibitors described in [1] to

[18] and needle coke.

[0060]

[20] A needle coke for a graphite electrode comprising the composition described in

[19] .

[0061]

[21] A graphite electrode, which is formed by calcining the graphite electrode described in

[20] with needles.

[0062]

[22] A method for manufacturing needle coke for graphite electrodes, wherein the needle coke for graphite electrodes comprises a composition in which an inhibitor is directly attached to the surface of the needle coke.

[0063] In the method, the graphite electrode manufacturing inhibitor described in any one of [1] to

[18] is added in solution or molten state to the needle coke before it is mixed with the binder bitumen, so that the graphite electrode manufacturing inhibitor is directly attached to the surface of the needle coke.

[0064]

[23] A method for manufacturing a graphite electrode, wherein the graphite electrode described in

[20] is calcined using needle coke.

[0065]

[24] In the method for manufacturing the graphite electrode according to

[23] , the firing temperature is 300℃~1500℃.

[0066] The effects of the invention

[0067] According to the present invention, by using specific inhibitors to manufacture graphite electrodes, it is possible to provide graphite electrodes that maintain low thermal expansion while having low crystal expansion. Attached Figure Description

[0068] Figure 1 This is a graph showing the results of plotting the cold crystal expansion values ​​relative to the amount of Ca3SiO5 added for Examples A3, A12 to A14 and Comparative Example A1.

[0069] Figure 2 This is a graph showing the nitrogen determination results of TPD-MS at 1700°C in Examples A3, A12-A14 and Comparative Example A1.

[0070] Figure 3 This is a graph showing the results of powder X-ray diffraction at 2θ = 24° to 27° after TPD-MS measurement in Examples A3, A12 to A14 and Comparative Example A1, normalized to the peak.

[0071] Figure 4 This is a graph showing the measurement results of crystal expansion values ​​at 1000℃ to 2650℃ in Example A21 and Comparative Example A8.

[0072] Figure 5 The graph shows the cold crystal expansion values ​​of Examples B1, B2 and Comparative Examples B1, B2 when fired to 2100°C and when fired to 2800°C. Detailed Implementation

[0073] The present invention will now be described in detail, but the present invention is not limited to the following description. It can be implemented in any way without departing from the spirit of the present invention.

[0074] In the following description, "weight%" and "mass%" are synonymous, as are "parts by weight" and "parts by mass". It should be noted that in this invention, "asphalt series" and "coal series" are treated as synonymous terms.

[0075] In this invention, the "sulfur content of coke" refers to the value measured according to JIS M8813. Furthermore, the "nitrogen content of coke" refers to the value measured according to JIS M8819.

[0076] 1. Inhibitor for graphite electrode manufacturing

[0077] The graphite electrode manufacturing inhibitor of the present invention (hereinafter sometimes simply referred to as "inhibitor") is used to obtain a graphite electrode by simultaneous firing with needle coke.

[0078] One embodiment of the present invention includes an inhibitor comprising at least one of a metal composed of element (Mβ) and an oxide having element (Mβ).

[0079] Element (Mβ): Selected from at least one element from the group consisting of Group 4 (Ti, Zr, Hf), Group 8 (Fe, Ru, Os), Group 9 (Co, Rh, Ir), Group 10 (Ni, Pr, Pt), Group 13 (B, Al, Ga, In), Group 14 (Si, Ge, Sn), and Group 15 (P, Sb, Bi) of the long-period periodic table.

[0080] 1.1. First Implementation Method

[0081] The inhibitor of the first embodiment comprises a complex oxide having elements (Mα) and (Mβ).

[0082] Element (Mα): At least one metallic element (except for element (Mβ)).

[0083] Element (Mβ): Selected from at least one element from the group consisting of Group 4 (Ti, Zr, Hf), Group 8 (Fe, Ru, Os), Group 9 (Co, Rh, Ir), Group 10 (Ni, Pr, Pt), Group 13 (B, Al, Ga, In), Group 14 (Si, Ge, Sn), and Group 15 (P, Sb, Bi) of the long-period periodic table.

[0084] As an element (Mα), from the perspective of easily reducing crystal swelling, it is preferably at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements (Mg, Ca, Sr, Ba) and rare earth metal elements (Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), more preferably at least one metal element selected from the group consisting of alkaline earth metals and rare earth metals, particularly preferably at least one metal element selected from the group consisting of alkaline earth metals and rare earth metals, and most preferably an alkaline earth metal.

[0085] As an element (Mβ), from the perspective of easily reducing crystal expansion, it is preferably selected from at least one element in the group consisting of Si, Ge, Al, B, Ti, Fe and P, more preferably at least one element in Si and Ge, and most preferably Si.

[0086] The composition of the inhibitor in the first embodiment is not particularly limited, but from the viewpoint of easily reducing crystal swelling, the following formula (1) is preferred.

[0087] Mα 3-x Mβ 1-y O 5-z …(1)

[0088] (In the formula, x ≤ 3, y ≤ 1, z ≤ 5.)

[0089] In the formula, from the perspective of easily reducing crystal swelling, x is preferably 0≤x<3, more preferably 0.05≤x≤2.5, and particularly preferably 0.1≤x≤2.

[0090] In the formula, from the perspective of easily reducing crystal swelling, y is preferably 0≤y<1, more preferably 0.01≤y≤0.8, and particularly preferably 0.1≤y≤0.5.

[0091] In the formula, from the perspective of easily reducing crystal swelling, z is preferably 0≤z<5, more preferably 0.05≤z≤4, and particularly preferably 0.1≤z≤3.

[0092] Specific examples of composite oxides having elements (Mα) and (Mβ) include MgSi3O7, Mg3SiO5, and Mg 14 Si5O 24 , MgO, Ca3SiO5, Ca2SiO4, CaSiO3, Ca8Si5O 18 , CaSi2O5, CaO, CaCO3, Ca(OH)2, SrSiO3, Sr3SiO5, SrSi2O5, Sr2SiO4, Ba3SiO5, Ba2SiO4, BaSiO3, BaSi2O5, Ba2Si3O8, Ba5Si8O 21 Ba3Si5O 13 , Ba2SiO4, BaO, BaCO3, Ce2SiO5, Ce2Si2O7, Ce2Si4O 11 , CeSi3O8, Ce3SiO8, Ce6Si6O 21 La5Si3O 13.5 La6Si6O 21 La2SiO5, La2Si4O 11 La2Si6O 16 Pr 4.67 Si3O 13 Pr2Si2O7, Pr6Si2, Pr6Si 12 O 25 Eu5Si3O 13Eu2Si2O7, Eu2SiO4, Eu6Si 12 O 33 、CaGe2O5、Ca3GeO5、Ca2GeO4、Ca5Ge3O 11 CaGeO3, Ca2Ge7O 16 CaAl 12 O 19 CaAl4O7, Ca4Al6O 13 Ca5Al6O 14 Ca6Al7O 16 Ca2Al2O5, Ca3Al2O6, CaFeO2, Ca2Fe2O5, CaFeO3, CaFe2O4, CaFe3O5, CaFe4O6, CaFe5O7, CaFe6O8, CaTi2O4, CaTi2O5, Ca3Ti2O7, Ca4Ti3O 10 CaTiO3, CaTi5O 11 、Mg2Al4O8、MgAl2O4、Mg2Al2O5、MgGe2O4、Mg2TiO4、MgTiO3、MgTi2O4、MgTi2O5、MgFe2O4、SrAl 12 O 19 SrAl4O7 Sr4Al 14 O 25 Sr 12 Al 14 O 33 Sr3Al2O6 Sr 10 Al6O 19 、Sr3GeO、SrGe4O9、SrGeO3、Sr3GeO5、SrTi 11 O 20 Sr2Ti6O 13 SrTiO3, Sr4Ti3O 10 Sr3Ti2O7, Sr2TiO4, SrFe 12 O9, SrFe2O4, Sr2Fe3O6, SrFeO2, Sr4Fe6O 13 Sr2Fe2O5, Sr3Fe2O5, Sr4Fe4O 11 、SrFeO3、Sr3Fe2O6、Sr2FeO3、Sr3Fe2O7、SrFeO4、Sr2FeO4、BaAl 12 O 19 BaAl4O7, BaAl2O4, Ba3Al2O6, Ba4Al2O7, Ba7A l2 O 10 Ba17 Al3O7, Ba 21 Ge2O5, Ba3GeO, Ba3GeO5, Ba 10 Ge7O3, BaGeO3, BaGe2O5, Ba2Ge5O 12 , BaGe4O9, Ba3TiO5, Ba2TiO4, Ba4Ti5O 10 Ba4Ti4O 11 , BaTiO3, BaTi2O5, BaTi4O9, Ba2Ti9O 20 BaTi5O 11 Ba2Ti 13 O 22 , Ba3FeO5, Ba2FeO4, BaFeO2, Ba2Fe2O5, Ba8Fe8O 21 Ba5Fe5O 14 BaFeO3, BaFe2O4, Ba2Fe6O 11 BaFe4O7, BaFe7O 11 BaFe 12 O 19 BaFe 15 O 23 The inhibitor in the first embodiment may contain one or more complex oxides.

[0093] From the perspective of easily suppressing the crystal expansion of needle-shaped coke during the manufacture of graphite electrodes, the inhibitor of the first embodiment is preferably the crystal expansion value P calculated by the following formula (I) from the test piece prepared by the following evaluation test (i). 2100 It is below 1.00%.

[0094] P 2100 = (L2-L1) / L1×100…(I)

[0095] In equation (I), L1 and L2 have the following meanings.

[0096] L1: Thickness of the test piece before firing (mm)

[0097] L2: Thickness (mm) of the test piece after firing at 2100℃

[0098] <Evaluation Experiment (i)>

[0099] Coal-based needle coke, binder pitch (30 parts by weight relative to the amount of coal-based needle coke, i.e., 30 parts by weight of binder pitch relative to 100 parts by weight of coal-based needle coke), and inhibitor were mixed and kneaded at 165°C for 5 minutes. The mixture was then molded into circular plates of 20mm diameter × 3mm to 15mm and calcined at 1000°C for 3 hours in a firing furnace to burn off the binder pitch, thus producing test pieces. The test pieces were then heated to 2100°C at a rate of 20°C / min and fired. The L1 and L2 values ​​of the test pieces before and after firing were measured.

[0100] Crystal expansion value P 2100 Preferably, it is 1.00% or less, more preferably 0.00% or less, further preferably -1.00% or less, particularly preferably -2.00% or less, and most preferably -3.00% or less. Furthermore, the crystal expansion value P... 2100 There is no particular limitation on the lower limit value, but it is preferably -30% or higher, more preferably -20% or higher, particularly preferably -15% or higher, and most preferably -10% or higher. The crystal expansion value P... 2100 The lower and upper limits can be combined arbitrarily, for example, preferably above -30% and below 1.00%.

[0101] From the perspective of easily suppressing the crystal expansion of needle-shaped coke during the manufacture of graphite electrodes, the inhibitor of the first embodiment is preferably the crystal expansion value P calculated by the following formula (II) from the test piece prepared by the following evaluation test (ii). 2800 It is below 2.9%.

[0102] P 2800 = (L3-L1) / L1×100…(II)

[0103] In equation (II), L1 and L3 have the following meanings.

[0104] L1: Thickness of the test piece before firing (mm)

[0105] L3: Thickness (mm) of the test piece after firing at 2800℃

[0106] <Evaluation Test (ii)>

[0107] Coal-series needle coke, binder pitch (30% by weight relative to the amount of coal-series needle coke), and inhibitor were mixed and kneaded at 165°C for 5 minutes. The mixture was then molded into circular plates of 20mm diameter × 3mm–15mm and calcined at 1300°C for 3 hours in a firing furnace to burn off the binder pitch, thus producing test pieces. The test pieces were then heated to 2800°C at a rate of 20°C / min and fired. The L1 and L3 values ​​of the test pieces before and after firing were measured.

[0108] Crystal expansion value P2800 Preferably, it is 2.9% or less, more preferably 2.5% or less, particularly preferably 2.2% or less, and most preferably 2.0% or less. Additionally, the crystal expansion value P... 2800 There is no particular limitation on the lower limit value, but it is preferably -5.0% or higher, more preferably -3.0% or higher, particularly preferably -1.0% or higher, and most preferably 0% or higher. The crystal expansion value P... 2800 The lower and upper limits can be combined arbitrarily, for example, preferably above -5.0% and below 2.9%.

[0109] The method for manufacturing the inhibitor according to the first embodiment is not particularly limited. For example, a method can be exemplified by measuring and mixing the compound as a raw material in a compositional ratio that becomes the target composite oxide, and calcining it in an atmospheric atmosphere and a reducing atmosphere at a temperature range of 1000°C to 1500°C. Furthermore, the upper limit of the particle size of the obtained inhibitor is not limited, but is more preferably 10000 μm or less, particularly preferably 1000 μm or less, and most preferably 100 μm or less. The lower limit of the particle size is also not particularly limited, but is more preferably 1 nm or more, particularly preferably 10 nm, and most preferably 100 nm or more. By controlling the particle size within this range, it is easy to disperse uniformly, and it is also expected that the crystallinity of the obtained inhibitor can be maintained, thus improving the crystal expansion effect.

[0110] It should be noted that, in this specification, "particle size of the inhibitor" refers to the mode diameter determined by using a laser diffraction particle size analyzer MT3300EX (manufactured by Microtrac BEL) in a dispersion medium with ethanol.

[0111] By using the inhibitor of the first embodiment, which comprises a composite oxide having elements (Mα) and (Mβ), the crystal expansion suppression effect is increased, and the manufacturing yield and characteristics of the graphite electrode are improved. The reason why the inhibitor of the first embodiment achieves such an effect is not yet clear, but it is speculated as follows.

[0112] It is speculated that by adding the inhibitor of the first embodiment during the sintering of the graphite electrode with needle coke, a nitrogen-containing composite compound or a sulfur-containing composite compound is formed at a temperature lower than the temperature at which nitrogen is removed from the graphite electrode. The timing of denitrification and desulfurization is staggered compared to the system without the inhibitor, thus suppressing crystal expansion. That is, it is speculated that since the inhibitor of the first embodiment contains a composite oxide containing elements (Mα) and (Mβ), it reacts with nitrogen or sulfur in the coke during the heating process of sintering to form composite compounds (nitrides, nitrogen oxides, sulfides, oxysulfides), thus achieving the effect of the first embodiment.

[0113] 1.2. Second Implementation Method

[0114] The inhibitor of the second embodiment comprises a metal composed of element (Mα) or an oxide containing element (Mα), and a metal composed of element (Mβ) or an oxide containing element (Mβ). From the viewpoint of easily reducing crystal swelling, the inhibitor of the second embodiment preferably comprises an oxide containing element (Mα) and an oxide containing element (Mβ).

[0115] Element (Mα): At least one metallic element (except for element (Mβ)).

[0116] Element (Mβ): Selected from at least one element from the group consisting of elements from Group 4, Group 8, Group 9, Group 10, Group 13, Group 14 and Group 15 of the long-period periodic table.

[0117] (Metals composed of element (Mα) or oxides containing element (Mα))

[0118] As an element (Mα), from the perspective of easily reducing crystal expansion, it is preferably at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements and rare earth metal elements, more preferably at least one metal element selected from the group consisting of Sc, alkaline earth metals and rare earth metal elements, particularly preferably at least one metal element selected from the group consisting of alkaline earth metals and rare earth metal elements, and most preferably an alkaline earth metal.

[0119] There are no particular limitations on the composition of the oxide containing the element (Mα), but from the perspective of easily reducing crystal swelling, the following formula (2) is preferred.

[0120] Mα 3-x1 O 3-z1 …(2)

[0121] (In the formula, Mα is an element (Mα), where 0≤x1<3 and 0≤z1<3.)

[0122] In the formula, from the perspective of easily reducing crystal swelling, x1 is preferably 0≤x1<3, more preferably 0.05≤x1≤2.5, and particularly preferably 0.1≤x1≤2.

[0123] In the formula, from the perspective of easily reducing crystal expansion, z1 is preferably 0≤z1<3, more preferably 0.05≤z1≤2.5, and particularly preferably 0.1≤z1≤2.

[0124] As specific examples of the metal formed of element (Mα) or the oxide containing element (Mα), examples include CaO, Ca(OH)₂, CaCO₃, Ca, MgO, MgCO₃, Mg(OH)₂, Mg, SrO, SrCO₃, Sr(OH)₂, Sr, BaO, BaCO₃, Ba(OH)₂, Ba, CeO₂, Ce, Pr₆O 11 , Pr, Eu₂O₃, Eu. The oxide containing element (Mα) contained in the inhibitor of the second embodiment may be one kind, or two or more kinds.

[0125] (Metal formed of element (Mβ) or oxide containing element (Mβ))

[0126] As element (Mβ), from the viewpoint of easily reducing crystal expansion, it is preferably at least one element selected from the group consisting of Si, Ge, Al, B, Ti, Fe and P, more preferably at least one of Si and Ge, and most preferably Si.

[0127] There is no particular limitation on the composition formula of the oxide containing element (Mβ), but from the viewpoint of easily reducing crystal expansion, the following formula (3) is preferred.

[0128] Mβ 1-y1 O 2-z2 …(3)

[0129] (in the formula, Mβ is element (Mβ), 0≤y1<1, 0≤z2<2.)

[0130] In the formula, from the viewpoint of easily reducing crystal expansion, y1 is preferably 0≤y1<1, more preferably 0.01≤y1≤0.8, and particularly preferably 0.1≤y1≤0.5.

[0131] In the formula, from the viewpoint of easily reducing crystal expansion, z2 is preferably 0<z2≤2, more preferably 0.05≤z2≤0.15, and particularly preferably 0.1≤z2≤0.2.

[0132] As specific examples of the metal formed of element (Mβ) or the oxide containing element (Mβ), examples include SiO₂, Si, SiO x , GeO₂, Ge, Al₂O₃, Al, B₂O₃, P₂O₅. The oxide containing element (Mβ) contained in the inhibitor of the second embodiment may be one kind, or two or more kinds.

[0133] From the viewpoint of easily inhibiting the crystal expansion of needle coke during the production of graphite electrodes, the crystal expansion value P calculated by said formula (I) of the test piece prepared by said evaluation test (i) for the inhibitor of the second embodiment is preferably 2100It is below 1.00%.

[0134] Crystal expansion value P 2100 Preferably, it is 1.00% or less, more preferably 0.50% or less, even more preferably 0.00% or less, particularly preferably -1.00% or less, and most preferably -2.00% or less. Additionally, the crystal expansion value P... 2100 There is no particular limitation on the lower limit value, but it is preferably -30% or higher, more preferably -20% or higher, particularly preferably -15% or higher, and most preferably -10% or higher. The crystal expansion value P... 2100 The lower and upper limits can be combined arbitrarily, for example, preferably above -30% and below 1.00%.

[0135] From the perspective of easily suppressing the crystal swelling of needle-shaped coke during the manufacture of graphite electrodes, the inhibitor of the second embodiment is preferably the crystal swelling value P calculated by the above formula (II) from the test piece prepared by the evaluation test (ii). 2800 It is below 2.9%.

[0136] Crystal expansion value P 2800 Preferably, it is 2.9% or less, more preferably 2.5% or less, particularly preferably 2.2% or less, and most preferably 2.0% or less. Additionally, the crystal expansion value P... 2800 There is no particular limitation on the lower limit value, but it is preferably -5.0% or higher, more preferably -3.0% or higher, particularly preferably -1.0% or higher, and most preferably 0% or higher. The crystal expansion value P... 2800 The lower and upper limits can be combined arbitrarily, for example, preferably above -5.0% and below 2.9%.

[0137] The method for manufacturing the inhibitor according to the second embodiment is not particularly limited. For example, a method can be described as follows: elements (Mα) and (Mβ) are measured and mixed in a target ratio, and calcined in an atmospheric and reducing atmosphere at a temperature range of 1000°C to 1500°C to obtain an inhibitor composed of an oxide containing element (Mα) and an oxide containing element (Mβ). Alternatively, an oxide containing element (Mα) and an oxide containing element (Mβ) can be mixed to prepare the inhibitor. The particle size of the composite inhibitor is not particularly limited, but is more preferably 10000 μm or less, particularly preferably 1000 μm or less, and most preferably 100 μm or less. The lower limit of the particle size is also not particularly limited, but is more preferably 1 nm or more, particularly preferably 10 nm, and most preferably 100 nm or more. By controlling the particle size within this range, it is easy to disperse uniformly, and it is expected to improve the crystal expansion effect.

[0138] The mixing ratio of oxides containing element (Mα) and oxides containing element (Mβ) is not particularly limited, but in order to achieve low crystal expansion, the lower limit of the weight ratio of oxides containing element (Mβ) to oxides containing element (Mα) is generally 0.01 or more, preferably 0.05 or more, more preferably 0.1 or more, and on the other hand, the upper limit is generally 1 or less, preferably 0.7 or less, more preferably 0.5 or less.

[0139] By using the inhibitor of the second embodiment, which comprises a metal consisting of element (Mβ) or an oxide containing element (Mα), and a metal consisting of element (Mβ) or an oxide containing element (Mβ), the crystal expansion suppression effect is increased, and the manufacturing yield and characteristics of the graphite electrode are improved. The reason why the inhibitor of the second embodiment achieves such an effect is not yet clear, but it is speculated as follows.

[0140] It is speculated that by adding the inhibitor of the second embodiment during the sintering of the graphite electrode with needle coke, a nitrogen-containing composite compound or a sulfur-containing composite compound is formed at a temperature lower than the temperature at which nitrogen is removed from the graphite electrode. The timing of denitrification and desulfurization is staggered compared to the system without the inhibitor, thus suppressing crystal expansion. That is, it is speculated that since the inhibitor of the second embodiment contains oxides containing element (Mα) and oxides containing element (Mβ), it reacts with nitrogen or sulfur in the coke during the heating process of sintering to form composite compounds (nitrides, nitrogen oxides, sulfides, oxysulfides), thus achieving the effect of the second embodiment.

[0141] 1.3. Third Implementation Method

[0142] Hereinafter, another example of an embodiment of the inhibitor of the present invention will be described.

[0143] The inhibitor of the third embodiment of the present invention comprises at least one of a metal consisting of element (Mβ) or a compound having element (Mβ), which volatilizes at a temperature of 2100°C to 6000°C.

[0144] Element (Mβ): Selected from at least one element from the group consisting of elements from Group 4, Group 8, Group 9, Group 10, Group 13, Group 14 and Group 15 of the long-period periodic table.

[0145] Regarding the temperature at which the inhibitor volatilizes, from the perspective of easily reducing crystal swelling, it is preferably 2100℃ or higher, more preferably 2400℃ or higher, even more preferably 2600℃ or higher, particularly preferably 2700℃ or higher, and most preferably 2800℃ or higher. To reduce crystal swelling, the upper limit of the inhibitor volatilization temperature is preferably below 6000℃, more preferably below 5000℃, even more preferably below 4000℃, particularly preferably below 3500℃, and most preferably below 3000℃. The lower and upper limits of the inhibitor volatilization temperature can be combined arbitrarily.

[0146] The inhibitor of the third embodiment is added to the needle coke. The ratio (by weight) of the inhibitor to the total amount of needle coke is set as X, and the ratio (by weight) of the inhibitor to the total amount of needle coke after heat treatment at 2800°C for 30 minutes is set as Y. In this case, from the viewpoint of easily reducing crystal swelling, Y / X < 0.01 is preferred.

[0147] The value of Y / X is more preferably 0.004 or less, particularly preferably 0.0005 or less. Regarding the lower limit of the value of Y / X, from the viewpoint of easily reducing crystal swelling, it is preferably 0.000001 or more, more preferably 0.00001 or more.

[0148] As an element (Mβ), from the perspective of easily reducing crystal expansion, it is preferably selected from at least one element in the group consisting of Si, Ge, Al, B, Ti, Fe and P, more preferably at least one element in Si and Ge, and most preferably Si.

[0149] From the perspective of easily reducing crystal swelling, oxides containing element (Mβ) are preferred as compounds. There is no particular limitation on the composition of the oxide containing element (Mβ), but from the perspective of easily reducing crystal swelling, the following formula (4) is preferred.

[0150] Mβ 1-y2 O 2-z3 …(4)

[0151] (In the formula, Mβ is an element (Mβ), where 0≤y2<1 and 0≤z3<2.)

[0152] In the formula, from the perspective of easily reducing crystal expansion, y2 is preferably 0≤y2<1, and more preferably 0.001≤y2≤0.1.

[0153] In the formula, from the perspective of easily reducing crystal expansion, z3 is preferably 0≤z3<2, and more preferably 0.001≤z3≤0.1.

[0154] Specific examples of oxides containing the element (Mβ) include SiO2, Si, and SiO.x GeO2, Ge, Al2O3, Al, B2O3, P2O5. The inhibitor in the third embodiment may contain one or more compounds having the element (Mβ).

[0155] Compounds containing element (Mβ) may also contain the following elements (Mα-1).

[0156] Element (Mα-1): At least one alkaline earth metal element (except for element (Mβ)).

[0157] As an element (Mα-1), from the perspective of easily reducing crystal expansion, it is preferably at least one metal element selected from the group consisting of K, Sc, alkaline earth metal elements and rare earth metal elements, more preferably at least one metal element selected from the group consisting of alkaline earth metal elements and rare earth metal elements, and most preferably an alkaline earth metal.

[0158] From the perspective of easily reducing crystal swelling, composite oxides having elements (Mα-1) and (Mβ) are preferred as compounds. The compositional formula of composite oxides having elements (Mα-1) and (Mβ) is not particularly limited, but from the perspective of easily reducing crystal swelling, the following formula (5) is preferred.

[0159] Mα 3-x2 Mβ 1-y3 O 5-z4 …(5)

[0160] (In the formula, Mα is element (Mα-1), Mβ is element (Mβ), and 0≤x2<3, 0≤y3<1, 0≤z4<5.)

[0161] In the formula, from the perspective of easily reducing crystal swelling, x2 is preferably 0≤x2<3, more preferably 0.05≤x2≤2.5, and particularly preferably 0.1≤x2≤2.

[0162] In the formula, from the perspective of easily reducing crystal swelling, y3 is preferably 0≤y3<1, more preferably 0.01≤y3≤0.8, and particularly preferably 0.1≤y3≤0.5.

[0163] In the formula, from the perspective of easily reducing crystal expansion, z4 is preferably 0≤z4<5, more preferably 0.05≤z4≤4, and particularly preferably 0.1≤z4≤3.

[0164] Specific examples of composite oxides having elements (Mα-1) and (Mβ) include MgSi3O7, Mg3SiO5, and Mg 14 Si5O 24、MgO、Ca3SiO5、Ca2SiO4、CaSiO3、Ca8Si5O 18 、CaSi2O5、CaO、CaCO3、Ca(OH)2、SrSiO3、Sr3SiO5、SrSi2O5、Sr 2SiO4、Ba3SiO5、Ba2SiO4、BaSiO3、BaSi2O5、Ba2Si3O8、Ba5Si8O 21 Ba3Si5O 13 、Ba2SiO4、BaO、BaCO3、Ce2SiO5、Ce2Si2O7、Ce2Si4O 11 、CeSi3O8、Ce3SiO8、Ce6Si6O 21 La5Si3O 13.5 La6Si6O 21 La2SiO5, La2Si4O 11 La2Si6O 16 Pr 4.67 Si3O 13 Pr2Si2O7, Pr6Si2, Pr6Si 12 O 25 Eu5Si3O 13 Eu2Si2O7, Eu2SiO4, Eu6Si 12 O 33 、CaGe2O5、Ca3GeO5、Ca2GeO4、Ca5Ge3O 11 CaGeO3, Ca2Ge7O 16 CaAl 12 O 19 CaAl4O7, Ca4Al6O 13 Ca5Al6O 14 Ca6Al7O 16 Ca2Al2O5, Ca3Al2O6, CaFeO2, Ca2Fe2O5, CaFeO3, CaFe2O4, CaFe3O5, CaFe4O6, CaFe5O7, CaFe6O8, CaTi2O4, CaTi2O5, Ca3Ti2O7, Ca4Ti3O 10 CaTiO3, CaTi5O 11 、Mg2Al4O8、MgAl2O4、Mg2Al2O5、MgGe2O4、Mg2TiO4、MgTiO3、MgTi2O4、MgTi2O5、MgFe2O4、SrAl 12 O 19 SrAl4O7 Sr4Al 14 O 25、Sr 12 Al 14 O 33 Sr3Al2O6, Sr 10 Al6O 19 , Sr3GeO, SrGe4O9, SrGeO3, Sr3GeO5, SrTi 11 O 20 Sr2Ti6O 13 SrTiO3, Sr4Ti3O 10 Sr3Ti2O7, Sr2TiO4, SrFe 12 O9, SrFe2O4, Sr2Fe3O6, SrFeO2, Sr4Fe6O 13 , Sr2Fe2O5, Sr3Fe2O5, Sr4Fe4O 11 , SrFeO3, Sr3Fe2O6, Sr2FeO3, Sr3Fe2O7, SrFeO4, Sr2FeO4, BaAl 12 O 19 , BaAl4O7, BaAl2O4, Ba3Al2O6, Ba4Al2O7, Ba7A l2 O 10 Ba 17 Al3O7, Ba 21 Ge2O5, Ba3GeO, Ba3GeO5, Ba 10 Ge7O3, BaGeO3, BaGe2O5, Ba2Ge5O 12 , BaGe4O9, Ba3TiO5, Ba2TiO4, Ba4Ti5O 10 Ba4Ti4O 11 , BaTiO3, BaTi2O5, BaTi4O9, Ba2Ti9O 20 BaTi5O 11 Ba2Ti 13 O 22 , Ba3FeO5, Ba2FeO4, BaFeO2, Ba2Fe2O5, Ba8Fe8O 21 Ba5Fe5O 14 BaFeO3, BaFe2O4, Ba2Fe6O 11 BaFe4O7, BaFe7O 11 BaFe 12 O 19 BaFe 15 O 23 The inhibitor in the third embodiment may contain one or more compounds.

[0165] The inhibitor of the third embodiment may also contain, in addition to containing at least one of a metal composed of element (Mβ) or a compound containing element (Mβ), a metal composed of element (Mα-1) or a compound containing element (Mα-1). In this case, the preferred element (Mα-1) is the same as the preferred element (Mα-1) in compounds containing both element (Mα-1) and element (Mβ).

[0166] From the perspective of easily reducing crystal swelling, oxides containing element (Mα-1) are preferred as compounds containing element (Mα-1). The compositional formula of the oxide containing element (Mα-1) is not particularly limited, but from the perspective of easily reducing crystal swelling, the following formula (6) is preferred.

[0167] Mα 3-x3 O 3-z5 …(6)

[0168] (In the formula, Mα is the element (Mα-1), where 0≤x3<3 and 0≤z5<3.)

[0169] In the formula, from the perspective of easily reducing crystal swelling, x3 is preferably 0≤x3<3, more preferably 0.05≤x3≤2.5, and particularly preferably 0.1≤x3≤2.

[0170] In the formula, from the perspective of easily reducing crystal swelling, z5 is preferably 0≤z5<3, more preferably 0.05≤z5≤2.5, and particularly preferably 0.1≤z5≤2.

[0171] Specific examples of oxides having element (Mα-1) include CaO, Ca(OH)2, CaCO3, Ca, MgO, MgCO3, Mg(OH)2, Mg, SrO, SrCO3, Sr(OH)2, Sr, BaO, BaCO3, Ba(OH)2, Ba, CeO2, Ce, and Pr6O. 11 Pr, Eu2O3, Eu. The inhibitor in the third embodiment may contain one or more compounds having the element (Mα-1).

[0172] From the perspective of easily reducing crystal swelling, the inhibitor in the third embodiment preferably reacts with a sulfur compound. Here, "reaction of inhibitor with sulfur compound" means that, under the condition of adding an inhibitor to the needle coke, other compounds are formed through the reaction of the inhibitor with a sulfur compound.

[0173] From the perspective of reducing crystal swelling, the inhibitor in the third embodiment preferably reacts with a nitrogen compound. Here, "reaction of the inhibitor with a sulfur compound" means that, under conditions where an inhibitor is added to the needle coke, other compounds are formed through the reaction of the inhibitor with a nitrogen compound.

[0174] From the perspective of easily suppressing the crystal expansion of needle-shaped coke during the manufacture of graphite electrodes, the inhibitor of the third embodiment is preferably the crystal expansion value P calculated by the above formula (I) from the test piece prepared by the evaluation test (i). 2100 It is below 1.00%.

[0175] Crystal expansion value P 2100 Preferably, it is 1.00% or less, more preferably 0.50% or less, even more preferably 0.00% or less, particularly preferably -1.00% or less, and most preferably -2.00% or less. Additionally, the crystal expansion value P... 2100 There is no particular limitation on the lower limit value, but it is preferably -30% or higher, more preferably -20% or higher, particularly preferably -15% or higher, and most preferably -10% or higher. The crystal expansion value P... 2100 The lower and upper limits can be combined arbitrarily, for example, preferably above -30% and below 1.00.

[0176] From the perspective of easily suppressing the crystal expansion of needle-shaped coke during the manufacture of graphite electrodes, the inhibitor of the third embodiment is preferably the crystal expansion value P calculated by the above formula (II) from the test piece prepared by the evaluation test (ii). 2800 It is below 2.9%.

[0177] P 2800 = (L3-L1) / L1×100…(II)

[0178] In equation (II), L1 and L3 have the following meanings.

[0179] L1: Thickness of the test piece before firing (mm)

[0180] L3: Thickness (mm) of the test piece after firing at 2800℃

[0181] Crystal expansion value P 2800 Preferably, it is 2.9% or less, more preferably 2.5% or less, particularly preferably 2.2% or less, and most preferably 2.0% or less. Additionally, the crystal expansion value P... 2800 There is no particular limitation on the lower limit value, but it is preferably -5.0% or higher, more preferably -3.0% or higher, particularly preferably -1.0% or higher, and most preferably 0% or higher. The crystal expansion value P... 2800 The lower and upper limits can be combined arbitrarily, for example, preferably above -5.0% and below 2.9%.

[0182] The method for manufacturing the inhibitor in the third embodiment is not particularly limited. For example, if it is an oxide, an example can be a method in which raw materials are measured and mixed in a compositional ratio that is the target oxide, and then calcined in an atmospheric atmosphere and a reducing atmosphere at a temperature range of 1000°C to 1500°C. Furthermore, the upper limit of the particle size of the obtained inhibitor is not limited, but is more preferably 10000 μm or less, particularly preferably 1000 μm or less, and most preferably 100 μm or less. The lower limit of the particle size is also not particularly limited, but is more preferably 1 nm or more, particularly preferably 10 nm, and most preferably 100 nm or more. By controlling the particle size within this range, it is easy to disperse uniformly, and it is also expected that the crystallinity of the obtained inhibitor can be maintained, thus improving the crystal expansion effect.

[0183] 2. Needle coke for graphite electrodes

[0184] The needle coke for graphite electrodes of the present invention comprises a composition containing one or more inhibitors and needle coke according to embodiments of the present invention.

[0185] 2.1. Composition

[0186] The composition of the present invention is not particularly limited as long as it contains one or more inhibitors according to embodiments of the present invention and needle coke. From the viewpoint of increasing the crystal swelling suppression effect while reducing the amount of inhibitor added, a composition formed by directly adhering one or more inhibitors according to embodiments of the present invention to the surface of needle coke is preferred.

[0187] The inhibitor content relative to 100 parts by weight of needle coke in the composition is preferably 0.1 to 15 parts by weight, more preferably 0.5 to 3 parts by weight, based on the ash content (metal component or metal oxide). If the inhibitor content is within this range, the crystal expansion reduction effect can be easily and sufficiently obtained, and there is almost no residual ash affecting the electrode product.

[0188] The method for manufacturing the composition is not particularly limited. For example, it is preferable to add the inhibitor of the present invention in a solution or molten state to needle coke before mixing with binder bitumen, so that the inhibitor of the present invention directly adheres to the surface of the needle coke, and then perform heat treatment at 300°C to 1500°C. As needle coke, blocky and granular calcined coke, i.e., coarse coke without particle size adjustment, can be used. When adding the inhibitor in a solution state, it can also be added in the form of an aqueous solution. If the inhibitor is insoluble in water, it can also be dissolved in volatile solvents such as alcohol or benzene for addition.

[0189] The composition obtained by the manufacturing method does not undergo particle size adjustment. Therefore, it is preferable to mix micronized coke or the like into the obtained composition to produce needle coke for graphite electrodes with particle size adjustment before the binder pitch is mixed. In this case, the total amount of micronized coke mixed relative to the total amount of needle coke for graphite electrodes is preferably 50% by weight or less, more preferably 30% by weight or less.

[0190] It should be noted that inhibitors can also be added to coarse coke without particle size adjustment, followed by a pulverization process after heat treatment. This pulverization process produces fine coke powder. In this case, the fine coke powder without inhibitors can be further mixed, or it can be left unmixed. Since fine coke powder is not directly related to the reduction of crystal expansion, the mixing of fine coke powder should be appropriately determined considering electrode quality factors such as ash content and economic efficiency.

[0191] 2.2. Needle-shaped char

[0192] The needle coke used in this invention will now be described in further detail.

[0193] The needle coke used in this invention is not particularly limited, but pitch-based needle coke is preferred due to its low sulfur and nitrogen content, small coefficient of thermal expansion, and ease of suppressing crystal expansion. Pitch-based needle coke is suitable as aggregate for graphite electrodes used in electric arc furnace steelmaking. Pitch-based needle coke can be manufactured by hydrogenating raw coal tar pitch to obtain hydrogenated coal tar pitch, and then coking the hydrogenated coal tar pitch.

[0194] Hydrogenated coal tar pitch is obtained by hydrogenating raw coal tar pitch (hydrogenation process) and separating light oil from the resulting hydrogenated coal tar pitch (separation process). The light oil separated in the separation process can be fed back to the hydrogenation process for recycling. There are no particular limitations on the method for hydrogenating the raw coal tar pitch and the method for separating light oil from the hydrogenated coal tar pitch; known methods can be used.

[0195] There are no particular limitations on the raw material coal tar pitch. There are also no particular limitations on the manufacturing method (pre-adjustment method) of the raw material coal tar pitch; for example, a method for substantially removing quinoline-insoluble components from coal tar-based heavy oils can be used. As a means of removing quinoline-insoluble components, known methods can be applied, preferably methods using solvents of aromatic or aliphatic oils, or methods using a mixed solvent of aromatic and aliphatic oils. Specifically, under suitable conditions, the solvent is mixed with coal tar-based heavy oil, heated, and allowed to stand as needed. The mixture is then distilled to remove low-boiling-point components, thereby obtaining raw material coal tar pitch that is almost free of quinoline-insoluble components. As aliphatic oils, alicyclic compounds such as cyclohexane and cyclopentane, compounds with carbonyl groups such as acetone and ethers, and light oils can be used. As aromatic oils, tar-based cleaning oils and anthracene oils can be used.

[0196] In the manufacture of hydrogenated coal tar pitch, petroleum-based heavy oil can also be mixed with the raw coal tar pitch. When mixing petroleum-based heavy oil, quinoline-insoluble components can be removed after mixing the coal tar-based heavy oil and petroleum-based heavy oil to produce a mixture of raw coal tar pitch and petroleum-based heavy oil. Alternatively, the raw coal tar pitch and petroleum-based heavy oil can be mixed and then the light oil can be separated and used in the hydrogenation process. Furthermore, the light oil obtained from separating the light oil can be separated from the coal tar pitch and mixed with the petroleum-based heavy oil for use in the hydrogenation process.

[0197] As a petroleum-based heavy oil, there are no particular limitations. Examples include fluidized bed catalytic cracking oil, atmospheric distillation residue, vacuum distillation residue, shale oil, tar sands pitch, Orinoco tar, coal liquefaction oil, ethylene bottom oil, and heavy oils obtained by hydrogenation and refining them. In addition, it may also contain relatively light oils such as straight-run light oil, vacuum light oil, desulfurized light oil, and desulfurized vacuum light oil.

[0198] There are no particular limitations on the method for coking hydrogenated coal tar pitch. Examples include delayed coking, viscosity-reducing cracking, flexible coking, and the Eureka process. Among these, delayed coking is preferred from the perspectives of needle coke productivity and quality stability.

[0199] In the delayed coking process, hydrogenated coal tar pitch is rapidly passed through a heating tube while being heated, and then introduced into a coke pot for coking. There are no particular restrictions on coking conditions, but the preferred temperature is 400℃ to 600℃, and the preferred coking time is 18 to 72 hours.

[0200] The coke obtained in this way is preferably calcined in a rotary kiln or vertical shaft furnace. The preferred calcination temperature is 1000℃~1500℃, and the preferred calcination time is 1 hour~6 hours.

[0201] It should be noted that, as a raw material for coking, it can also be used in combination with other raw materials, such as hydrogenated coal tar pitch. There are no limitations on such raw materials; for example, petroleum-based heavy oils can be listed.

[0202] 3. Graphite electrode

[0203] The graphite electrode of the present invention is a graphite electrode formed by calcining the graphite electrode of the present invention with needle coke. For example, the graphite electrode of the present invention is obtained by graphitizing a green electrode obtained by mixing a raw material containing an appropriate amount of binder pitch with needle coke, and then calcining the green electrode. In the manufacture of the graphite electrode, further processing can be performed after graphitization as needed.

[0204] As a specific example of the manufacturing method of the graphite electrode of the present invention, for example, a method can be implemented by mixing (kneading) binder pitch into needle coke for graphite electrodes of the present invention, further adding iron oxide as needed, and then performing extrusion molding, primary firing, impregnation, secondary firing, graphitization, etc. The use of iron oxide can be omitted, but if iron oxide is used, a further reduction in crystal expansion can be obtained; therefore, it can be appropriately determined considering the requirements for quality and economy.

[0205] There is no particular limitation on the firing temperature, but for the purpose of burning off the binder bitumen, it is preferably 300℃~1500℃, and more preferably 400℃~1400℃.

[0206] 4. Experimental Results

[0207] The present invention will be specifically described below through examples, but the present invention is not limited to the following description.

[0208] (1) Synthesis methods of inhibitors

[0209] Each compound was measured in the proportions specified in the examples, mixed using a mortar, and calcined at temperatures ranging from 1000°C to 1500°C under both atmospheric and reducing atmospheres. The resulting compounds were then pulverized to below 100 μm using a mortar and used as inhibitors.

[0210] (2) Crystal expansion measurement method - 1 (cold crystal expansion method)

[0211] In each example, coal-based needle coke pulverized to a predetermined particle size, binder pitch added at 30% by weight relative to the coal-based needle coke, and inhibitors added in amounts listed in Tables 1-3 were mixed and kneaded at 165°C for 5 minutes. The mixture was then molded into a circular plate of 20mmΦ × 3mm-15mm and calcined in a firing furnace at 1000°C or 1300°C for 3 hours to burn off the binder pitch, serving as a test piece for crystal expansion determination. The test piece was heated to 2100°C or 2800°C at a heating rate of 20°C / min for firing (formal firing). The irreversible shrinkage rate before and after firing was calculated using formula (I) or formula (II) and expressed as the cold crystal expansion value. The cold crystal expansion value at a calcination temperature of 1000°C and a formal firing temperature (the highest formal firing temperature) of 2100°C is the crystal expansion value P. 2100 The cold crystal expansion value P is the crystal expansion value when the calcination temperature is 1300℃ and the formal firing temperature (the highest formal firing temperature) is 2800℃. 2800 .

[0212] (3) Determination of crystal expansion - 2 (thermal crystal expansion)

[0213] Calcined coke is pulverized and adjusted to a specific particle size. Coal-based binder pitch, at a ratio of 30% by weight relative to the calcined coke, is added and mixed at 165°C. The mixture is then extruded to form cylindrical bodies. These bodies are fired in a furnace at 1000°C for 3 hours to produce test pieces (cylinders). The test pieces are heated from room temperature to 2800°C at a rate of 20°C / min. The elongation of the sample along its length is measured using a pusher-type dilatometer and calculated as the thermal expansion value. It should be noted that the elongation of the test piece (cylinder) along its length corresponds to the elongation in the direction perpendicular to the extrusion direction. A lower thermal expansion value is preferred.

[0214] Thermal expansion value (%) = (ΔL / L) × 100

[0215] (In the formula, L is the length of the test piece before the test, and ΔL is the elongation of the test piece in the length direction during the heating period to 2800℃.)

[0216] (4) Methods for determining graphitized BD

[0217] For the test piece after firing by the above (2) method, the volume is calculated from its diameter and thickness. In addition, the weight of the test piece is measured, and the bulk density is calculated by dividing the weight by the volume, which is used as the bulk density BD.

[0218] (5) TPD-MS method

[0219] The calcined test piece obtained by the same method as described in (2) above was collected in a W crucible, and the collected amount was accurately weighed. It was placed in a quartz TPD tube in an infrared heating furnace, and heated to 1700°C at a flow rate of 100 ccm and 100°C / min, and held at 1700°C for 3 minutes before natural cooling. During this period, the gas exiting the quartz TPD tube was introduced into a time-of-flight mass spectrometer to monitor the trends of each gas component. Quantitative analysis was performed using the trend area-to-mass ratio of a standard sample, determined separately relative to the background area of ​​the obtained trend, or a standard curve of a standard gas.

[0220] (6) Powder X-ray diffraction

[0221] For the test pieces measured by TPD-MS as described above (5), X-ray diffraction was performed using an X-ray diffraction apparatus. The measurement conditions were set as CuKα, 40kV, 50mA, 2θ=10°-90°, and a sealed tube X-ray diffraction apparatus (Rigaku SmartLab SE) was used.

[0222] [Examples A1-A20, Comparative Examples A1-A7]

[0223] The inhibitor was synthesized using method (1), and test pieces were prepared using method (2). The cold crystal expansion value and the density BD of the molded body were measured. In Comparative Example A1, test pieces were prepared using the same method as (2), except that no inhibitor was added. The composition, amount added, calcination temperature, and final firing temperature of the inhibitors in each example are recorded in Tables 1-3.

[0224] The results of measuring the cold crystal expansion value and the density BD of the molded body for each example are shown in Tables 1 to 3. Furthermore, for Examples A3, A12 to A14, and Comparative Example A1, the results of plotting the cold crystal expansion value relative to the amount of Ca3SiO5 added are shown in Tables 1 to 3. Figure 1 Additionally, the results of TPD-MS measurements at 1700℃ are presented below. Figure 2 The powder X-ray diffraction results after TPD-MS determination are shown in... Figure 3 .

[0225] [Table 1]

[0226]

[0227] [Table 2]

[0228]

[0229] [Table 3]

[0230]

[0231] As shown in Table 1, in Examples A1 to A11 where the inhibitor of the first embodiment was added, compared with Comparative Example A1 where no inhibitor was added and Comparative Examples A2 to A5 where other inhibitors were added, the cold crystal swelling value was smaller and the crystal swelling suppression effect was higher. As shown in Table 3, in Examples A15 to A20 where the inhibitor of the first embodiment was added, the same was true; compared with Comparative Example A6 where no inhibitor was added and Comparative Example A7 where other inhibitors were added, the cold crystal swelling value was smaller and the crystal swelling suppression effect was higher.

[0232] Additionally, as shown in Table 2 and Figure 1 As shown, when comparing Comparative Example A1, Examples A3, and A12-A14, as the amount of inhibitor added increases, the cold crystal swelling value decreases and the crystal swelling suppression effect increases.

[0233] In addition, in Examples A1 to A20, the density BD of the molded body is also sufficiently high.

[0234] like Figure 2 As shown in the TPD-MS results, it was observed that the more the amount of inhibitor added in the first embodiment increased, the lower the denitrification temperature shifted. Additionally, as... Figure 3 As shown, the spectrum was normalized at the peak of powder X-ray diffraction at 2θ = 24°–27°, and the changes in the diffraction peaks were observed. The results confirmed that the more the amount of inhibitor added in the first embodiment increased, the smaller the half-width became, until in Example A14, a peak of the 002 plane of graphite crystals appeared. These results suggest that by adding the inhibitor of the first embodiment, graphite crystallization was promoted, and as graphite crystallization proceeded, denitrification occurred, thereby reducing crystal swelling.

[0235] [Example A21, Comparative Example A8]

[0236] Ca3SiO5 synthesized using method (1) was added at 2% by weight in method (2) to prepare test pieces, and the cold crystallization value was measured. In Comparative Example A8, test pieces were prepared using method (3) without the addition of inhibitors, and the hot crystallization temperature was measured. The results of the crystallization values ​​measured from 1000℃ to 2650℃ are shown below. Figure 4 .

[0237] In addition, since nitrogen expansion occurs at temperatures ranging from 1700℃ to 2100℃, the rate of change of shrinkage at firing temperatures of 1700℃ to 2100℃ and 1700℃ to 2600℃ were calculated separately to differentiate between nitrogen and sulfur expansion. The results are shown in Table 4.

[0238] [Table 4]

[0239]

[0240] like Figure 4 As shown in Table 4, it was confirmed that crystal expansion occurred rapidly starting from around 1900°C in Comparative Example A8. In contrast, crystal expansion did not occur in the temperature range where crystal expansion occurs in Example A21. The inhibitor of the first embodiment suppressed crystal expansion.

[0241] [Examples A22-A25]

[0242] Inhibitors were synthesized using method (1), and test pieces were prepared using method (2). The cold crystal expansion value and the density BD of the molded body were measured. The composition, amount added, calcination temperature, and final firing temperature of the inhibitors for each example are recorded in Table 5.

[0243] The results of the cold crystal expansion value and the density BD of the molded body for each example are shown in Table 5.

[0244] [Table 5]

[0245]

[0246] As shown in Table 5, in Examples A22 to A25 where the inhibitor of the first embodiment was added, the cold crystal swelling value was small and the crystal swelling suppression effect was high.

[0247] (7) Crystal expansion measurement method (cold crystal expansion method)

[0248] In each example, coal-based needle coke pulverized to a predetermined particle size, 30% by weight of binder pitch relative to the coal-based needle coke, and 2% by weight of inhibitor were mixed and kneaded at 165°C for 5 minutes. The mixture was then molded into a circular plate of 20mmΦ×3mm~15mm and calcined in a firing furnace at 1000°C or 1300°C for 3 hours to burn off the binder pitch, serving as a test piece for crystal expansion determination. The test piece was heated to 2100°C or 2800°C at a heating rate of 20°C / min for firing (formal firing). The irreversible shrinkage rate before and after firing was calculated using formula (I) or formula (II) and expressed as the cold crystal expansion value. The cold crystal expansion value at a calcination temperature of 1000°C and a formal firing temperature (the highest formal firing temperature) of 2100°C is the crystal expansion value P. 2100 The cold crystal expansion value P is the crystal expansion value when the calcination temperature is 1300℃ and the formal firing temperature (the highest formal firing temperature) is 2800℃. 2800 .

[0249] [Example B1]

[0250] Ca and Si were mixed in the molar ratio shown in Table 6 to synthesize an inhibitor for the CaO and SiO2 complexation using method (1). Using the obtained inhibitor, two test pieces were prepared by method (7) for determination based on the cold crystal expansion method. To differentiate between nitrogen and sulfur expansion, one test piece was fired at 2100°C (where nitrogen expansion occurs), while the other was fired to 2800°C. The cold crystal expansion value (P) at 2100°C was then determined. 2100 ) and cold crystal expansion value at 2800℃ (P 2800 ).

[0251] [Example B2]

[0252] CaO and SiO2 were mixed at a ratio of 75 mol% CaO and 25 mol% SiO2. This mixture was used as an inhibitor. Otherwise, two test pieces were prepared in the same manner as in Example B1, and the cold crystallization expansion value (P) at 2100°C was determined. 2100 ) and cold crystal expansion value at 2800℃ (P 2800 ).

[0253] [Comparative Example B1]

[0254] Except for the inhibitor consisting solely of CaO, two test pieces were prepared in the same manner as in Example B1, and the cold crystallization value (P) at 2100°C was determined. 2100 ) and cold crystal expansion value at 2800℃ (P 2800 ).

[0255] [Comparative Example B2]

[0256] Except for the inhibitor being composed solely of SiO2, two test pieces were prepared in the same manner as in Example B1, and the cold crystal expansion value (P) at 2100°C was determined. 2100 ) and cold crystal expansion value at 2800℃ (P 2800 ).

[0257] The results of the cold crystal expansion values ​​at 2100℃ and 2800℃ for each example are shown in Table 6 and... Figure 5 .

[0258] [Table 6]

[0259]

[0260] As shown in Table 6 and Figure 5 As shown, in Examples B1 and B2, where the inhibitor of the second embodiment was added, both crystal expansion at 2100°C and 2800°C were suppressed.

[0261] Furthermore, as shown in Comparative Examples B1 and B2, it is impossible to suppress crystal expansion at 2100°C and 2800°C when only a single-element metal is added. For example, Comparative Example B1 only confirmed the effect of suppressing nitrogen expansion at 2100°C.

[0262] That is, it is speculated that since the inhibitor of the second embodiment contains oxides having element (Mα) and oxides having element (Mβ), it reacts with nitrogen or sulfur in the coke during the heating process of firing to form a complex compound (nitride, nitrogen oxide, sulfide, oxysulfide), thus achieving the effect of the second embodiment.

[0263] (8) Crystal expansion measurement method - 3 (cold crystal expansion method)

[0264] In each example, coal-based needle coke pulverized to a predetermined particle size, 30% by weight of binder pitch relative to the coal-based needle coke, and 2% by weight of inhibitor were mixed and kneaded at 165°C for 5 minutes. The mixture was then molded into circular plates of 20mm Φ × 3mm to 15mm and calcined in a firing furnace at 1000°C for 3 hours to burn off the binder pitch, thus creating test pieces for crystal expansion determination. The test pieces were then fired (formal firing) at a heating rate of 20°C / min to 2100°C, 2650°C, or 2800°C. The irreversible shrinkage before and after firing was expressed as the cold crystal expansion value. The cold crystal expansion value at 2100℃ is calculated using the formula (I). The cold crystal expansion value at 2650℃ or 2800℃ is calculated by substituting the thickness (mm) of the test piece after firing at 2650℃ or 2800℃ as L2 in the formula (I).

[0265] (9) Method for determining graphitized BD

[0266] For the test piece fired by the above (8) determination method, the volume is calculated from its diameter and thickness. In addition, the weight of the test piece is measured, and the weight is divided by the volume to calculate the bulk density, which is taken as the bulk density BD.

[0267] (10) Compositional Analysis Methods

[0268] Compositional analysis was performed on the test pieces after calcination or firing in each example.

[0269] For the metallic elements (Ca, Si) in the test specimens, the specimens were dry-ashed at a maximum temperature of 750℃, and the ash was then subjected to alkali-salt melting decomposition. The ash was dissolved in dilute hydrochloric acid to prepare a certain volume, appropriately diluted, and analyzed using an inductively coupled plasma optical emission spectrometry (ICP) system (Thermo Fischer Scientific, iCAP7600 duo). Quantification was performed using the matrix matching standard curve method. For nitrogen and oxygen in the test specimens, an oxygen-nitrogen composition analyzer (LECO TCH600) was used for heating and extraction in a pulse furnace under an inert gas atmosphere. Oxygen was quantified using the NIR detection standard curve method, and nitrogen was quantified using the thermal conductivity detection standard curve method. For sulfur in the test specimens, a carbon-sulfur composition analyzer (LECO CS600) was used. The test specimens were burned in an oxygen stream using a high-frequency furnace, and quantification was performed using the NIR detection standard curve method.

[0270] [Example C1]

[0271] Using Ca3SiO5 synthesized by method (1) as an inhibitor, test pieces were prepared by method (8), and the composition of the calcined test pieces was analyzed by method (10). The results are shown in Table 7.

[0272] [Examples C2-C4]

[0273] Using Ca3SiO5 synthesized by method (1) as an inhibitor, test pieces were prepared by method (8). The calcined test pieces were heated to 2100℃, 2650℃ or 2800℃ for firing, and the cold crystal expansion value was measured. In addition, for these test pieces, the bulk density BD was measured by method (9), and the composition was analyzed by method (10). The results are shown in Table 7.

[0274] It should be noted that the units for each component in the composition analysis results in Table 6 are μmol / g.

[0275] [Table 7]

[0276]

[0277] As shown in Table 7, Examples C1 to C4, which used the inhibitor of the third embodiment, suppressed crystal swelling. Furthermore, in Example B4, the residual amount of inhibitor-derived material after graphitization treatment was extremely low. While this also depends on the application of the graphite electrode, lower residual inhibitor-derived material in the graphite electrode is advantageous in terms of reducing the degradation of the graphite electrode's performance and minimizing adverse environmental impacts.

Claims

1. The use of an inhibitor for manufacturing graphite electrodes to suppress crystal expansion of needle coke, said inhibitor comprising a composite oxide having elements Mα and Mβ, Element Mβ: Selected from at least one element in the group consisting of Si and Ge. The element Mα is selected from at least one metallic element chosen from the group consisting of Mg, Ca, Sr, Ba, and Ce.

2. The use according to claim 1, wherein, The composite oxide has the following formula (1): Mα 3-x Mβ 1-y O 5-z … (1) In the formula, 0≤x<3, 0≤y<1, and 0≤z<5.

3. The use of an inhibitor for manufacturing graphite electrodes to suppress crystal expansion of needle coke, said inhibitor comprising a composite oxide having elements Mα-1 and Mβ. The inhibitor used in the manufacture of graphite electrodes volatilizes at temperatures ranging from 2100°C to 6000°C. Element Mβ: Selected from at least one element in the group consisting of Si and Ge. The element Mα-1 is selected from at least one metallic element chosen from the group consisting of Mg, Ca, Sr, Ba, and Ce.

4. The use according to claim 3, wherein, When the percentage of inhibitor added to the needle coke, expressed as X, is set as X, and the percentage of inhibitor after heat treatment at 2800°C for 30 minutes, expressed as Y, is set as Y, Y / X < 0.

01.

5. The use according to claim 3, wherein it reacts with sulfur or sulfur compounds.

6. The use according to claim 3, wherein it reacts with nitrogen or a nitrogen compound.

7. The use according to claim 3, wherein, The crystallization expansion value P of the test piece produced from the evaluation test (i) below was calculated using the following equation (I) 2100 1.00% or less: P 2100 = (L2 - L1) / L1 x 100 (I) In equation (I), L1 and L2 have the following meanings: L1: Thickness of the test piece before firing, in mm. L2: Thickness of the test piece after firing at 2100℃, in mm. <Evaluation Experiment (i)> Coal-based needle coke, binder pitch (30% by weight relative to the coal-based needle coke), and inhibitor were mixed and mixed while heated at 165°C for 5 minutes. The mixture was then molded into a circular plate with a diameter of 20 mm × 3 mm to 15 mm. The plate was then calcined in a furnace at 1000°C for 3 hours to burn off the binder pitch, thus producing a test piece. The test piece was then heated to 2100°C at a rate of 20°C / min and calcined. The L1 and L2 values ​​of the test piece before and after calcination were measured.

8. A composition comprising the inhibitor for manufacturing graphite electrodes as described in any one of claims 1 to 7 and needle coke.

9. A needle coke for a graphite electrode, comprising the composition of claim 8.

10. A graphite electrode, which is formed by calcining the graphite electrode of claim 9 with needle-shaped calcination.

11. A method for manufacturing needle coke for graphite electrodes, wherein, The graphite electrode needle coke contains a composition in which an inhibitor is directly attached to the surface of the needle coke. In the method, the graphite electrode manufacturing inhibitor as described in any one of claims 1 to 7 is added in solution or molten state to the needle coke before it is mixed with the binder bitumen, so that the graphite electrode manufacturing inhibitor is directly attached to the surface of the needle coke.

12. A method for manufacturing a graphite electrode, wherein, The needle coke for firing the graphite electrode as described in claim 9.

13. The method for manufacturing a graphite electrode according to claim 12, wherein, The firing temperature is 300℃~1500℃.

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