JP5192774B2 - Nanocarbon-coated refractory raw material and production method thereof, and refractory using the same and production method thereof - Google Patents

Description

  The present invention relates to a refractory material used for a refractory for molten metal, mainly steel, and a refractory using the same.

  Carbon-containing refractories containing carbon raw materials such as graphite, pitch, carbon black, or phenol resin are excellent in thermal shock resistance and slag resistance. For example, converters, ladle, kneading cars, or vacuum degassing. Brick as a lining material for furnaces is widely used as an irregular refractory material, a continuous casting nozzle such as an immersion nozzle, or a repair material such as a baking material.

  By the way, in recent years, higher quality of steel products and stricter composition control have been required in the steelmaking process. Therefore, the problem of contamination of molten steel due to the phenomenon that carbon contained in the refractory containing carbon dissolves into molten steel (hereinafter referred to as “carbon pickup”) has become apparent. In particular, magnesia-carbon bricks used in converters, vacuum degassing equipment, ladles, etc. originally contain 10 to 30% by mass of graphite, and there is a great demand from users to reduce this graphite. Strong. In order to suppress such a carbon pickup, it is necessary to reduce the carbon of the carbon-containing refractory.

  Furthermore, because carbon has a high thermal conductivity, heat loss such as a drop in molten steel temperature, deformation of the iron core of the container, and problems such as the release of CO gas accompanying the combustion of carbon can reduce the refractory's carbon content. It is requested.

  However, there is a problem that the thermal shock resistance decreases when the carbon content is lowered, and various methods for improving this have been studied in the past.

  For example, Patent Document 1 discloses an MgO—C non-fired brick containing 10 to 50% by volume of magnesia particles around which a layer having a thickness of 5 to 100 μm composed of voids and pitches is formed. In this unfired brick, voids existing around the magnesia particles in the structure and graphite having low crystallinity prevent the propagation of cracks generated by thermal shock. It is said that this blocking action does not develop into a crack large enough for the brick to peel off.

  Moreover, in patent document 2, since carbon nanofiber produces | generates in a structure | tissue by using fullerenes as a raw material, and an intensity | strength and a thermal shock resistance improve dramatically, it reduces carbon amount in a carbon containing refractory. It is stated that you can. In particular, it is said that a remarkable effect is obtained in a carbon-containing refractory having an amount of graphite used of 10% by mass or less.

  Furthermore, Patent Document 3 describes that carbon nanofibers are generated in a refractory using a mesophase pitch and a thermosetting resin, and as a result, excellent thermal shock resistance is obtained.

Furthermore, in recent years, various methods for synthesizing carbon nanotubes or carbon nanofibers have been studied. For example, in Patent Document 4, a solution in which an organic metal salt or an inorganic metal salt of a catalyst metal is dispersed or dissolved in a solvent is applied to the substrate surface and reduced to form catalytic metal fine particles, and then carbon nanotubes are formed by CVD or the like. It is disclosed to synthesize.
JP-A-6-321625 JP 2006-8504 A JP 2005-139062 A WO2004 / 071654

  However, in order to reduce the carbon without lowering the thermal shock resistance, there are various problems with the above-described improvement methods studied in the past.

  For example, in the method of forming voids and pitches around the refractory particles described in Patent Document 1, slag is likely to enter the voids around the magnesia particles during use, and the corrosion resistance to the slag is reduced.

  In addition, the method of using fullerenes described in Patent Document 2 as a raw material is extremely laborious and expensive in order to uniformly disperse nano-sized and extremely small fullerenes in a refractory material without agglomeration. become.

  Moreover, in the methods of Patent Document 2 and Patent Document 3, the thermal shock resistance is improved by the effect of carbon nanofibers, so that a low carbon-containing refractory with a low graphite content can be obtained. Since the slag penetrated and the structure melted and was worn out, corrosion resistance became a bottleneck.

  The problem to be solved by the present invention is that carbon nanotubes or carbon nanofibers can be dispersed relatively easily and uniformly in a refractory, and a refractory excellent in thermal shock resistance and slag resistance is obtained. An object of the present invention is to provide a refractory raw material that can be used and a method for producing the same, and a refractory using the refractory raw material and a method for producing the same.

The present invention is a nanocarbon-coated refractory material for molten metal in which the surface of refractory material particles is coated with carbon nanotubes or carbon nanofibers. Hereinafter, the carbon nanotube is referred to as CNT, and the carbon nanofiber is referred to as CNF.

  The state where the surface of the refractory raw material particles is coated with CNT or CNF refers to a state where the refractory raw material particles are adhered and adhered without being peeled off during storage or transportation. Further, the entire surface of the refractory raw material may be covered in a dense state, but it may be in a rough state or a partial state.

  Among the CNTs or CNFs covering the surface of the refractory raw material particles, CNTs are single-wall and double-wall carbon nanotubes having a diameter of several to several tens of nm, or so-called multi-walls (multi-walls) having two or more carbon area layers. ) Consists mainly of carbon nanotubes. CNF, on the other hand, has a diameter of several nanometers to several hundreds of nanometers, a length of several μm, a carbon network surface parallel to the fiber axis, and a herring-bone whose carbon network surface is inclined with respect to the fiber axis. ) Type and tubular type whose carbon mesh surface is parallel to the fiber axis.

  The particle diameter of the refractory raw material particles to be coated with CNT or CNF is not particularly limited, but for the purpose of uniformly dispersing in the refractory, the average particle diameter is preferably 100 μm or less, more preferably the average particle diameter is 50 μm or less and 1 μm or more. When the average particle diameter exceeds 100 μm, the effect of uniformly dispersing CNT or CNF in the refractory decreases, and the effect of improving the thermal shock resistance is limited. Also, when the average particle size is 50 μm or less, the effect of uniform dispersion of CNT or CNF in the refractory is enhanced, so that the thermal shock resistance is excellent. Become. Here, the average particle diameter is the median diameter, and the particle diameter (range) and weight ratio obtained by measuring the particle diameter distribution of the refractory raw material particles before coating are plotted on a graph, and the particle diameter when the integrated ratio is 50%. Is the average particle size. Examples of the particle size distribution measuring method include a laser diffraction particle size distribution measuring apparatus.

The coating amount of CNT or CNF is 3 to 40 % by mass relative to the nanocarbon-coated refractory raw material. If the coating amount of CNT or CNF is less than 3% by mass, it is difficult to obtain an expansion absorption effect (improvement effect of thermal shock resistance), and if it exceeds 40 % by mass, the mixing ratio of coated refractory raw material particles must be lowered. CNT or CNF cannot be uniformly dispersed in the refractory.

  As the refractory raw material particles coated with CNT or CNF, one or more of the group consisting of magnesia, alumina, spinel, calcia, dolomite, silica, chromia, zirconia, titania and mullite are used as refractories. It is preferable from the viewpoint of excellent metal oxide. These refractory raw material particles are generally used as a refractory raw material. These refractory raw materials have a tendency to deteriorate in thermal shock resistance as they are repeatedly used because the refractory raw material particles sinter due to heat during use, but in the present invention, the surface CNT or CNF An effect of suppressing sintering is obtained. On the other hand, it is conceivable to form a CNT or CNF by coating a catalyst on the surface of non-oxide raw materials such as silicon carbide and scaly graphite. Since sintering does not occur, the effect of improving thermal shock resistance by preventing oversintering cannot be expected.

  When coating the surface of the refractory raw material particles with CNT or CNF, for example, refractory raw material particles whose average particle size is adjusted to 100 μm or less in advance are used, and these surfaces are coated with CNT or CNF. This is because if the refractory raw material particles are pulverized after being coated with CNT or CNF, the CNTs or CNF are peeled off during the pulverization.

  Specifically, as a method of coating CNT or CNF on the surface of the refractory raw material particles, a method of applying or applying CNT or CNF, such as a method of applying a solution in which CNT or CNF is dispersed to the surface of the refractory raw material particles and then drying, Alternatively, a method of directly growing CNT or CNF on the surface of the refractory raw material particles can be considered.

  Among these, the method of growing CNT or CNF on the surface of the refractory raw material particles is preferable because CNT or CNF uniformly and firmly adheres to the surface of the refractory raw material particles. That is, the bond between the carbon bond and the refractory raw material particles can be made stronger in the refractory structure.

  Specifically, first, the catalyst is supported on the surface of the refractory raw material particles by immersing the refractory raw material particles in a liquid in which the catalyst is dispersed in the liquid or the catalyst precursor is dissolved, and the liquid is removed. Next, the refractory raw material particles carrying a catalyst for growing CNT or CNF are heat-treated in contact with a carbon compound to synthesize CNT or CNF on the surface. For example, single wall and double wall CNTs can be obtained by performing heat treatment in a methane stream at 850 ° C. by CVD. The coating amount of CNT or CNF on the refractory raw material particles can be controlled, for example, by changing various conditions of the CVD method. At this time, when heat treatment is performed in a 700 ° C. ethylene / hydrogen or 900 ° C. methane stream, multilayer (multi-wall) CNTs are mainly obtained. Furthermore, CNF can be obtained by heat treatment in 450 ° C. methane, ethylene / hydrogen or carbon monoxide / hydrogen stream.

  The carbon compound to be brought into contact with the refractory raw material particles supporting the catalyst is not particularly limited, and a carbon compound usually used for the synthesis of CNT or CNF can be used. Preferably, hydrocarbon or carbon monoxide is used.

  The catalyst can be used without any problem as long as it is generally used for the synthesis of CNT or CNF. Among them, V, Fe, Co, Ni, Cu, Mo, Pd, Rh, W and Pt can be used. One or two or more metals, oxides or metal salts of the metals in the group consisting of these are preferred from the point of not adversely affecting the refractory. In the present invention, even if the catalyst is a metal oxide or metal salt, the metal oxide is reduced because it is subsequently heated in the presence of a reducing gas, so that the function as the catalyst is sufficiently obtained.

  As described above, in the present invention, since CNT or CNF is present on the surface of the refractory raw material particles, the thermal shock resistance is improved by absorbing the expansion of the refractory material and suppressing the sintering of the refractory raw materials by its flexibility. I think that. Furthermore, since CNT or CNF is familiar with the organic binder, it is considered that a strong bond is formed without generating a gap between the carbon bond generated by the heat treatment and the refractory raw material particles. For this reason, it is estimated that slag resistance is also improved. And since the refractory raw material particle | grains coat | covered with CNT or CNF are uniformly disperse | distributed in a refractory as a fine powder, CNT or CNF will also be disperse | distributed uniformly in a refractory. As a result, it is considered that the effect can be further enhanced. On the other hand, materials such as pitch with a large amount of volatile matter and expanded graphite in which the graphite layer expands can form large voids around the aggregate, resulting in thermal shock resistance but reduced corrosion resistance. On the other hand, in this invention, since this space | gap can be reduced, the fall of corrosion resistance is small.

  The nanocarbon-coated refractory raw material of the present invention can be used as a part of a refractory raw material composition when producing a conventional refractory, whereby CNT or CNF can be uniformly dispersed in the refractory. Therefore, it can be used for any carbon-containing refractory. For example, it can be used for refractories having carbon bonds that are widely used for steel. Specifically, alumina-carbon, alumina-silicon carbide-carbon, alumina-spinel-carbon, zirconia-carbon, magnesia-carbon, magnesia-spinel-carbon, silicon carbide-carbon, silicon nitride -Carbon type, magnesia-calcia-carbon type and the like. As carbon content, it is preferable to contain 1-30 mass% as fixed carbon. If the content of fixed carbon is less than 1% by mass, the effect of improving the slag resistance is small, and if it exceeds 30% by mass, the effect of improving the thermal shock resistance is small. Here, the amount of fixed carbon is measured in accordance with JIS-M8812.

  Furthermore, the present invention is more effective when applied to a fixed refractory having higher required levels of thermal shock resistance and slag resistance than an irregular refractory. The regular refractory is denser with a lower porosity than the amorphous refractory (high elasticity), and by containing CNT or CNF, it becomes less elastic due to the above-described action, so the carbonization is further reduced. can do. The fixed refractory is a so-called brick obtained by press-molding the kneaded material with a press or the like, such as a brick for lining a molten metal container, a nozzle for continuous casting, or the like.

  In particular, to obtain a nanocarbon-containing refractory excellent in thermal shock resistance and corrosion resistance by adding an organic binder to a refractory raw material composition containing 1-30% by mass of a nanocarbon-coated refractory raw material, kneading, molding, and heat treating Can do. If the content of the nanocarbon-coated refractory raw material is less than 1% by mass, the effect of improving thermal shock resistance and corrosion resistance is insufficient, and if it exceeds 30% by mass, the amount of carbon is excessive. The organic binder is used to generate a carbon bond, and when used in combination with CNT or CNF, a bond having low elasticity and high strength can be formed. Specifically, as the organic binder, one or more members selected from the group consisting of phenol resins, furan resins, pitches, phenols, furfuryl alcohols and furfuryl aldehydes are preferable from the viewpoint of forming a strong carbon bond.

  Furthermore, especially when applied to magnesia-carbon bricks among the refractories to be applied, even if the amount of graphite is reduced, it is possible to suppress a decrease in thermal shock resistance, and a high durability low carbon magnesia-carbon brick. Can be obtained.

  Specifically, an organic binder is added to the refractory raw material composition containing 60 to 99% by mass of the magnesia raw material and 1 to 30% by mass of the nanocarbon-coated refractory raw material of the present invention, followed by heat treatment after kneading and molding. Can be obtained at The nanocarbon-coated refractory raw material used at this time is preferably magnesia. Scalar graphite does not have to be used, but when used, it is less than 15% by mass, more preferably less than 10% by mass, so that it can be used for conventional converter or secondary refining magnesia-carbon. Can be used in the same way as brick.

  The nanocarbon-containing refractory of the present invention may be an unfired refractory or a fired refractory. When the non-fired refractory is used, the heat treatment is performed by heating the carbon-containing refractory raw material at 100 ° C. or higher and lower than 800 ° C. Moreover, when setting it as a fired refractory, the molded object of a carbon containing refractory raw material is heated at 800 degreeC or more and less than 1600 degreeC.

  By using the nanocarbon-coated refractory raw material of the present invention as a part of a refractory raw material composition of a carbon-containing refractory, CNT or CNF can be uniformly dispersed in the refractory. For this reason, sintering of a refractory raw material is suppressed by CNT or CNF, the stress of a refractory can be absorbed, and a carbon bond is strengthened.

  As a result, the thermal shock resistance and slag resistance are improved, and the life of the refractory is greatly improved. Moreover, since the amount of carbon of the carbon-containing refractory can be reduced, carbon pickup during use can be suppressed.

  Furthermore, the thermal insulation of the furnace can be improved by optimizing the thermal conductivity of the refractory.

  Hereinafter, embodiments of the present invention will be described based on examples.

  Table 1 shows the composition of the nanocarbon-coated refractory material used in the examples of the present invention and the refractory material used in the comparative examples.

  In Table 1, the nanocarbon-coated refractory raw materials A to H are magnesia (purity of 97 mass% for electrofused magnesia) or alumina (purity of 99 mass% for electrofused alumina) previously adjusted to a predetermined average particle size as a carrier. After immersing in an aqueous solution in which iron nitrate and ammonium molybdate were dissolved, filtering and drying, the catalyst was supported, and then CVD treatment was performed.

  In the CVD process, when heat treatment was performed in a methane gas stream at 850 ° C., single-wall and double-wall CNTs were generated, and the refractory material could be coated (nanocarbon-coated refractory materials A to F). In addition, in the CVD process, heat treatment was performed with 700 ° C. ethylene / hydrogen or 900 ° C. methane / hydrogen to obtain a multilayer (multi-wall) CNT coated (nanocarbon coated refractory raw material G). Further, in the CVD process, a CNF-coated product was obtained by performing a heat treatment in an ethylene / hydrogen stream at 450 ° C. (nanocarbon-coated refractory raw material H).

  The average particle diameters of magnesia and alumina used are shown in Table 1, respectively. The particle size was measured with a laser diffraction particle size distribution analyzer. The coating amount of CNT or CNF was calculated by heating the obtained nanocarbon-coated refractory raw material at 1200 ° C. for 2 hours in an oxidizing atmosphere and measuring the mass before and after that.

  FIG. 1 shows the result of observing the nanocarbon-coated refractory material A in Table 1 with a TEM. It is observed that single-wall and double-wall CNTs 2 are formed on the surface of the magnesia particles 1 without any gaps.

  2 and 3 show the results of observing the nanocarbon-coated refractory raw material G in Table 1 with a TEM. It is observed that the magnesia particles 3 have a structure covered with multilayer (multiwall) CNT4.

  4 and 5 show the results obtained by observing the nanocarbon-coated refractory raw material H in Table 1 with a TEM. It is observed that the magnesia particles 5 have a structure covered with a herring-bone type CNF6.

  On the other hand, in Table 1, the pitch-coated raw material is coated with pitch on the surface of the refractory raw material particles by mixing the pitch with a softening point of 120 ° C. and the refractory raw material particles in a container while heating until the pitch flows. It is a thing. The carbon black-coated refractory raw material is prepared by dispersing carbon black having a particle size of 10 μm or less in methanol containing a small amount of an organic binder, and volatilizing ethanol while mixing and mixing the refractory raw material particles on the surface of the refractory raw material particles. Carbon black is coated. Each coating amount was measured by the same method as in the case of the nanocarbon-coated refractory raw material.

  Tables 2 and 3 show the compositions of the refractory raw material blends in each example and the test results. In each example, a phenol resin was added as an organic binder to the refractory raw material blends shown in Tables 2 and 3 and kneaded. After pressing in parallel with a friction press, the mixture was heated at 250 ° C. for 24 hours. The phenol resin used was diluted with a solvent containing ethylene glycol as a main component and adjusted in viscosity. The refractory raw material composition in the table had a maximum particle size of 3 mm and a particle size configuration suitable for general refractory bricks (parallel shape). The test refractories thus obtained were measured for thermal shock resistance and corrosion resistance. The thermal shock resistance was immersed for 3 minutes in hot metal at 1500 ° C., then air-cooled for 15 minutes, and the size of the crack was visually measured after repeating this operation 10 times. Corrosion resistance was measured by a rotary erosion method using a converter slag at 1700 ° C. for 5 hours. The erosion dimension was measured, and in Table 2, Example 1 was 100, and in Table 3, Example 5 was 100. Moreover, it used for the lining of the converter as an actual machine test. In addition, the refractory of Example 1 had a bulk specific gravity of 3.15, an apparent porosity of 3.0, a hot bending strength of 15 MPa at 1400 ° C., and fixed carbon of 4.7 mass%.

  As is apparent from Tables 2 and 3, the refractories obtained by the examples of the present invention have significantly improved thermal shock resistance, and the corrosion resistance has a numerical value equal to or higher than that of the comparative example corresponding to the conventional product. Obtained. As a result, in the actual machine test, the useful life of Example 2 was about 1.2 times that of Comparative Example 3.

  Examples 1 to 4 differ only in the average particle diameter of the refractory raw material particles before coating the CNTs, and the smaller the average particle diameter, the better the thermal shock resistance. Further, in comparison between Example 2 and Example 3, it can be seen that Example 3 has a large thermal shock resistance level.

  Comparative Example 1 is an example in which pitch is coated with refractory raw material particles, and Comparative Example 2 is an example in which carbon black is coated with refractory raw material particles, but the corrosion resistance and thermal shock resistance are considerably inferior to those of Examples. I understand. Moreover, although the comparative example 3 is an example which added the mesophase pitch, it turns out that both corrosion resistance and thermal shock resistance are also inferior. Comparative Example 4 is a conventional alumina-carbon refractory, but is inferior in both corrosion resistance and thermal shock resistance to Examples 7 and 8 of the same alumina-carbon refractory.

The result of having observed the nanocarbon covering refractory raw material A of Table 1 by TEM is shown. The result of having observed the nanocarbon covering refractory raw material G of Table 1 by TEM is shown. The result of having observed the nanocarbon covering refractory raw material G of Table 1 by TEM is shown. The result of having observed the nano carbon covering refractory raw material H of Table 1 by TEM is shown. The result of having observed the nano carbon covering refractory raw material H of Table 1 by TEM is shown.

Explanation of symbols

1 magnesia particles 2 single wall and double wall CNT
3 Magnesia particles coated with multi-walled CNTs 4 Multi-walled CNTs coated with magnesia particles
5 magnesia particles coated with CNF 6 herring-bone type CNF coated with magnesia particles

Claims (5)

The surface of the refractory raw material particles consisting of one or more of the group consisting of magnesia, alumina, spinel, calcia, dolomite, silica, chromia, zirconia, titania and mullite is coated with carbon nanotubes or carbon nanofibers. A nanocarbon-coated refractory raw material for molten metal having an amount of 3 to 40% by mass.   The nanocarbon-coated refractory raw material according to claim 1, wherein the average particle diameter of the refractory raw material particles is 100 μm or less. A catalyst is supported on refractory raw material particles having an average particle size of 100 μm or less, consisting of one or more members selected from the group consisting of magnesia, alumina, spinel, calcia, dolomite, silica, chromia, zirconia, titania and mullite. Nanocarbon coating for molten metal that coats the surface of refractory raw material particles with carbon nanotubes or carbon nanofibers so that the coating amount is 3 to 40% by mass by heat-treating the refractory raw material particles in contact with a carbon compound A method for producing refractory raw materials. A nanocarbon-containing refractory for molten metal, comprising 1 to 30% by mass of the nanocarbon-coated refractory material according to claim 1 or 2 in a refractory material composition. A nanocarbon-coated refractory raw material obtained by the method for producing a nanocarbon-coated refractory raw material according to claim 3 is blended in an amount of 1 to 30% by mass in the refractory raw material composition, an organic binder is added and kneaded, and after molding A method for producing a nanocarbon-containing refractory for molten metal to be heat-treated.