JP2011153038A - Refractory using refractory raw material coated with nanocarbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve especially the hot strength in a refractory using a refractory raw material coated with nanocarbon. <P>SOLUTION: The refractory is produced by adding an organic resin to a refractory raw material mixture containing a refractory raw material coated with nanocarbon in which at least a part of the surface of a refractory raw material particle is coated with carbon nanofibers and/or carbon nanotubes and kneading, and heat-treating the obtained body after molding, where the refractory raw material coated with nanocarbon having an amount of residual carbon obtained from the organic resin which is 1.2 mass% or more and 10.0 mass% or less to the mass of the whole refractory raw material mixture is used for the refractory. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a refractory used for high-temperature processes such as for molten metals and incinerators, and refractory used mainly for steel.

  As refractories used for steel, 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. Widely used as lining materials such as ladle, kneading car or vacuum degassing furnace, nozzles for continuous casting such as immersion nozzles and sliding nozzles, or repair materials such as baking materials.

  These refractories may be reduced in carbon in order to improve corrosion resistance and prevent carbon pick-up in molten steel. However, since thermal shock resistance is lowered in this case, methods for improving thermal shock resistance are being investigated. .

  On the other hand, the inventors disclosed in Patent Document 1 a nanocarbon coating in which the surface of the refractory raw material particles is coated with carbon nanotubes (hereinafter referred to as “CNT”) or carbon nanofibers (hereinafter referred to as “CNF”). It has been disclosed that the thermal shock resistance is greatly improved by including the refractory raw material in the refractory raw material composition.

  However, when the refractory disclosed in Patent Document 1 is used in a portion where the molten steel flow or gas flow is intense or a portion subjected to an impact due to the falling of scrap, there is a case where wear damage or damage due to the impact is severe. As a result of examining the cause, it was found that the strength of the refractory in the heat was not always sufficient.

JP 2008-133177 A

  The problem to be solved by the present invention is to improve the hot strength particularly in a refractory using a nanocarbon-coated refractory raw material.

  CNF and CNT, which are nanocarbon-coated refractory raw materials used in the present invention, have been widely applied industrially, and are often used for the purpose of imparting strength. Therefore, the same effect was expected when applied to refractories, but no application example has been reported. The present inventors have disclosed in Patent Document 1 that it is very effective to coat the surface of the refractory raw material particles in order to uniformly disperse CNF and CNT in the structure of the refractory. Furthermore, in order to firmly fix these in the structure, it is necessary to sufficiently give the remaining carbon content generated from the organic resin, and the residual carbon amount at that time is based on the total mass of the refractory raw material composition The present invention has been completed by finding that it is necessary to be 1.2% by mass or more and 10.0% by mass or less.

  That is, the present invention is obtained by adding and kneading an organic resin to a refractory raw material composition containing a nanocarbon-coated refractory raw material in which carbon nanofibers and / or carbon nanotubes are coated on at least a part of the surface of the refractory raw material particles. A refractory produced by heat-treating the kneaded clay after molding, and the amount of residual carbon obtained from the organic resin is 1.2% by mass or more and 10.0% by mass or less with respect to the total mass of the refractory raw material composition. It is characterized by being.

  Since the method of coating the surface of the refractory raw material particles with CNF or CNT as nanocarbon is described in Patent Document 1, it is omitted. In addition, since CNF and CNT exhibit the same effect, they may be either a single coating or a coating in a state where both are mixed. Moreover, it is most preferable that the coating covers the entire refractory raw material particles, but the effect can be exhibited even with a partial coating.

  The average diameter of the refractory raw material particles whose surface is coated with CNF and / or CNT is more effective when the average diameter is 300 μm or less, and the effect is smaller with particles coarser than this. More preferably, it is 100 micrometers or less.

  The coating amount of CNF and / or CNT is not particularly limited, but is suitably 0.1% by mass or more and 30% by mass or less with respect to the entire refractory raw material particles. When the amount is less than 0.1% by mass, the effect of strengthening the structure is small, and when the amount is more than 30% by mass, a dense refractory is hardly obtained and the corrosion resistance is greatly reduced. Preferably they are 1 mass% or more and 20 mass% or less, More preferably, they are 3 mass% or more and 10 mass% or less. The coating amount is an average value of the entire nanocarbon-coated refractory raw material.

  The refractory raw material that is mixed with the refractory raw material particles that coat CNF and / or CNT and the nanocarbon-coated refractory raw material particles to constitute the refractory raw material mixture is particularly limited as long as it is a raw material that is generally used for refractories. For example, magnesia, alumina, silica, spinel, mullite, calcia, dolomite, zirconia, zircon, chromia, and compounds and composites thereof can be used.

  As the organic resin for imparting a residual carbon content, a phenol resin, a furan resin, or an organic resin having a high residual carbon ratio in which a pitch component is dissolved therein is preferable. In the case of a phenol resin, either a novolak type or a resol type may be used. Particularly in the case of the novolak type, an appropriate amount of hexamethylenetetramine is added as a curing accelerator as usual. As the solvent, an alcohol solvent such as ethylene glycol or furfural can be used, and the pitch component can also be dissolved. There is also a method of using a powdered novolac resin together with an appropriate amount of solvent. The residual carbon ratio of these organic resins is suitably 10% by mass or more, preferably 35% by mass or more. If it is less than 10% by mass, a dense refractory cannot be obtained due to an increase in volatile content, and the corrosion resistance is greatly reduced.

  The reason why the amount of residual carbon obtained from the organic resin is 1.2% by mass or more is that if the amount is less than 1.2% by mass, the effect of improving the hot strength is small, and if it is more than 10.0% by mass, a large amount of organic resin is used. This is because the refractory material may crack when heated due to an increase in volatile content, expansion or contraction of the organic resin, and the hot strength may be reduced.

  The organic resin is polymerized while being decomposed during the heat treatment of the clay molded body to form a carbon network. It is considered that this carbon network is combined or physically entangled with CNF and CNT, so that the connective tissue is strengthened and the hot strength is improved.

  In order to further enhance the effect of increasing the strength, it is effective to add aluminum, silicon, magnesium and alloys thereof (hereinafter collectively referred to as “specific metals”) together. Although these specific metals generate carbides in the process of reacting with carbon, CNF and CNT act very effectively as carbon sources to be subjected to this reaction. That is, when these specific metals react with CNF and CNT, carbides much finer than those conventionally produced are formed, and this strengthens the connective tissue, thereby further improving the hot strength. It is done.

  These specific metals may be used alone or in combination of two or more, and the effect can be exhibited. The addition amount is preferably 0.1% by mass or more and 6.0% by mass or less based on the total mass of the refractory raw material composition. When the amount is less than 0.1% by mass, the added effect does not appear clearly, and when the amount exceeds 6.0% by mass, the connective structure is excessively strengthened and the thermal shock resistance is lowered.

  It is also useful to add borides to these specific metals. Examples of borides include boron carbide, calcium boride, zirconium boride, and magnesium boride. The addition amount is preferably 0.1% by mass or more and 3% by mass or less based on the total mass of the refractory raw material composition.

  In the present invention, the nanocarbon-coated refractory raw material is used as a part of the refractory raw material, the organic resin is added and kneaded, and the obtained clay is molded and heat-treated to be produced from the organic resin. By making the amount of residual charcoal 1.2 mass% or more and 10.0 mass% or less with respect to the mass of the whole refractory raw material mixture, the hot strength is dramatically improved.

  In addition, this effect is achieved by 0.1% by mass or more and 6.0% by mass of one or more selected from aluminum, silicon, magnesium and alloys thereof with respect to the total mass of the refractory raw material composition. It is further improved by adding up to 10%.

As a result, a refractory excellent in hot strength and thermal shock resistance can be obtained. For example, as a MgO-C brick, in a converter, the life of the charging wall directly hit by scrap in the converter is increased, and the molten steel flow passes. This can contribute to the improvement of the service life of a steel hole sleeve that is likely to break due to wear and external stress. Alternatively, as an Al ₂ O ₃ -C-based brick, it can contribute to the improvement of life and prevention of troubles by applying it to long nozzles with long inner hole wear due to molten steel flow and long immersion nozzles and long stoppers that are easy to break. .

The relationship between the amount of residual coal and hot strength is shown.

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

  Table 1 shows the results of evaluating the blending ratio of the blends used in the examples and comparative examples of the present invention, the amount of residual carbon of the organic resin, and various physical properties.

  In Table 1, CNF and CNT-covered magnesia as nanocarbon-coated refractory raw materials were immersed in an aqueous solution in which iron nitrate and ammonium molybdate were dissolved in an electrofused magnesia (purity 98 mass%) having an average particle size of 70 μm as a simple substance and filtered. It was obtained by carrying out a CVD treatment after supporting the catalyst by drying. The CVD treatment was carried out in a methane stream at 850 ° C. to generate CNF and CNT and coat the refractory raw material particles (electrofused magnesia particles). The coating amount of CNT was 6% by mass. The coating amount of CNF and CNT was calculated from the weight difference before and after the CVD process by correcting the amount of the catalyst that decreases during the process from the weight after the CVD process. In addition, the particle size of the electrofused magnesia used was measured with a laser diffraction particle size distribution analyzer.

  As shown in Table 1, an organic resin is blended into a fireproof raw material blend containing 80% by mass of magnesia having a purity of 98%, 15% by mass of scaly graphite having a purity of 99%, and 5% by mass of the above CNF and CNT-coated magnesia. As follows: A novolak resin diluted with ethylene glycol, a liquid phenol resin having a residual carbon ratio of 40% by mass, a novolac powder phenol resin having a residual carbon ratio of 60% by mass, appropriate amounts of hexamethylenetetramine and methanol were added and kneaded in a mixer. I got dredged soil. This clay was press-molded into a normal shape and heated at 250 ° C. for 5 hours.

  About the residual carbon amount of organic resin, the residual carbon rate of organic resin is calculated from the measurement based on the measurement method of the fixed carbon content described in 5.20 of JIS-K6910, and the added amount and residual carbon rate to the refractory raw material composition From this, the amount of residual carbon of the organic resin was calculated.

The test bricks thus obtained were evaluated for hot bending strength, corrosion resistance and thermal shock resistance. About hot bending strength, it measured at 1400 degreeC in nitrogen atmosphere based on JIS-R2656. Regarding the corrosion resistance, CaO / SiO ₂ = 3.0 (mass ratio), T.R. The test was conducted at 1700 ° C. for 5 hours using Fe = 16% by mass of slag. The evaluation results were expressed as an index, with the erosion dimension of Example 1 being 100. The smaller the number, the better the corrosion resistance. For thermal shock resistance, a 40 × 40 × 230 mm sample was immersed in 1500 ° C. hot metal for 3 minutes, then air-cooled for 15 minutes, and the size of the crack was visually observed after repeating this operation 10 times. Evaluation was made in four stages: no crack, fine, medium and large.

  FIG. 1 shows the relationship between the amount of residual carbon of the organic resin and the hot bending strength. In FIG. 1, ◇ indicates an example in which CNF and CNT-coated magnesia are blended (indicated as “use of CNF and CNT-coated raw material” in FIG. 1), and corresponds to each example in the upper part of Table 1. The Δ mark is an example in which aluminum is added as a specific metal in addition to CNF and CNT-coated magnesia (indicated as “addition of the same aluminum” in FIG. 1), and corresponds to each example in the middle of Table 1. □ is an example in which CNF and CNT-coated magnesia are not blended (indicated as “conventional product” in FIG. 1), and corresponds to each example in the lower part of Table 1.

  From Table 1 and FIG. 1, it can be seen that, first, bricks containing CNF and CNT-coated magnesia have significantly improved hot strength as compared with the case where they are not blended. It can also be seen that the hot strength is further improved by adding aluminum in addition to CNF and CNT-coated magnesia. However, when the amount of remaining coal is less than 1.2% by mass, the improvement effect is small, and when it exceeds 10.0% by mass, the strength is decreased. This is because a crack occurred in the brick during the heat treatment. Moreover, when the amount of residual coal exceeds 10.0 mass%, a corrosion-resistant fall will also be remarkable. Therefore, the amount of residual coal needs to be 1.2 mass% or more and 10.0 mass% or less. Incidentally, in all the examples of Patent Document 1, the amount of the organic resin is 2% by mass, but this corresponds to 0.8% by mass in terms of the amount of residual carbon, so the hot strength is low.

  From the viewpoint of thermal shock resistance, when Examples 1-6 and Comparative Examples 9-14 without addition of aluminum are compared with those of Comparative Examples 9-14, although the thermal shock resistance generally decreases as the strength increases, The thermal shock resistance is equal to or higher than that of the comparative example, and it can be seen that the product of the present invention has high hot strength and excellent thermal shock resistance.

  Next, in order to investigate the influence of the addition amount and the kind of the specific metals, as shown in Table 2, 80% by mass of alumina having a purity of 99%, 15% by mass of scaly graphite having a purity of 99%, 6% of CNF and CNT 6% by mass of a liquid phenolic resin having a residual carbon ratio of 40% by mass obtained by diluting a novolac-type resin as an organic resin with ethylene glycol in a refractory raw material formulation in which 5% by mass of alumina (CNF and CNT-coated alumina) coated with 5% by mass is mixed. Further, 1% by mass of a novolac-type powdered phenol resin having a residual carbon ratio of 60% by mass and appropriate amounts of hexamethylenetetramine and methanol were added and kneaded by a mixer to obtain a clay. This clay was press-molded into a normal shape and heated at 250 ° C. for 5 hours.

The test bricks thus obtained were evaluated for hot bending strength and thermal shock resistance in the same manner as described above. Regarding the corrosion resistance, CaO / SiO ₂ = 1.2 (mass ratio), T.R. The test was conducted at 1700 ° C. for 5 hours using Fe = 10 mass% slag. The evaluation results were expressed as an index with the melt damage size of Example 13 as 100. The smaller the number, the better the corrosion resistance.

  From Examples 13 to 16 in Table 2, it can be seen that the hot strength is greatly improved by adding 0.1% by mass or more of aluminum. However, as shown in Example 17, if it exceeds 6.0% by mass, the thermal shock resistance may decrease, so 6.0% by mass or less is preferable.

  Further, as shown in Examples 18 to 22, it can be seen that the hot strength is greatly improved by adding or using silicon, an aluminum / magnesium alloy, or using it together with a boride.

Claims (2)

  Add the organic resin to the refractory raw material composition containing the nanocarbon-coated refractory raw material with carbon nanofibers and / or carbon nanotubes coated on at least a part of the surface of the refractory raw material particles, knead and mold the resulting clay A refractory produced by post-heat treatment, characterized in that the amount of residual carbon obtained from the organic resin is 1.2% by mass or more and 10.0% by mass or less with respect to the total mass of the refractory raw material composition. Refractory using nano carbon coated refractory raw material.   Claims in which one or more selected from aluminum, silicon, magnesium and alloys thereof are added in an amount of 0.1% by mass or more and 6.0% by mass or less based on the total mass of the refractory raw material composition Item 2. A refractory using the nanocarbon-coated refractory raw material according to item 1.

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