KR101772031B1 - Method for improvement of oxidation resistance in graphite for MgO-C refractory through surface modification and MgO-C refractory by the same - Google Patents

Abstract

The present invention relates to a method for enhancing the antioxidative properties of graphite, and particularly relates to a method for improving surface oxidation of a graphite particle surface by an acid treatment before coating the graphite surface with an aluminum precursor to improve the efficiency of coating a metal precursor on the graphite surface The present invention relates to a method for enhancing the antioxidative activity of graphite contained in magnesia-carbon refractories through surface modification capable of enhancing the antioxidative properties of graphite, and to a magnesia-carbon refractory produced thereby.

Description

The present invention relates to a method for enhancing the antioxidative activity of graphite contained in magnesia-carbon refractories through surface modification, and a method for improving the oxidation resistance of graphite for MgO-C refractory by the same}

The present invention relates to a method for enhancing the antioxidative properties of graphite. Specifically, the present invention relates to a method for improving the antioxidative properties of graphite by acid-treating the surface of graphite particles before coating the graphite surface with an aluminum precursor, thereby improving the efficiency of coating the metal precursor on the graphite surface, The present invention relates to a method for promoting the antioxidation of graphite contained in magnesia-carbon refractories through surface modification capable of enhancing the properties and a magnesia-carbon refractory produced thereby.

Generally, magnesium carbon (MgO-C) refractories are widely used in basic lorna electric arc furnaces and metal ladles because of the corrosion resistance due to low wettability to molten metal and the presence of graphite used as carbon source, It is because of the characteristics.

However, the mechanical and thermal properties of the magnesia carbon (MgO-C) refractory are continually deteriorated by use, which is due to spalling and pore formation due to oxidation of graphite.

Therefore, in order to prevent the oxidation of the graphite, an antioxidant having considerable reactivity with oxygen is added to the graphite during the production process, and in theory, almost all of the graphite should not react with oxygen until the oxidation of the antioxidant proceeds considerably .

However, in reality, due to the phenomenon that pores are generated in the above-mentioned magnesia carbon (MgO-C) refractory, the antioxidant can not effectively inhibit the oxidation of graphite.

In order to solve such problems, conventionally, graphite was coated as a coating agent for a metal precursor (particularly, an aluminum precursor) to prevent oxygen from accessing graphite.

However, such conventional techniques have a problem in that the efficiency of coating the metal precursor on the graphite surface is low and it is difficult to enhance the antioxidative properties of the graphite.

On the other hand, the technique for preventing the oxidation of graphite as described above is widely used, and in particular, is described in the following prior art documents, so that detailed description and illustration thereof will be omitted.

United States Patent No. 4824733 United States Patent No. 6455159 United States Patent No. 6668984

 ZHANG S, LEE W E. Influence of additives on corrosion resistance and corroded microstructures of MgO-.C refractories [J]. Journal of the European Ceramic Society, 2001, 21: 2393-2405.  HASHEMI B, NEMATI ZA, FAGHIHI-SANI M A. Effects of resin and graphite content on density and oxidation behavior of MgO-.C refractory bricks [J]. Ceramics International, 2006, 32 (3): 313-319.  ZHANG S, MARRIOTT N J., LEE W E. Thermochemistry and microstructures of MgO-.C refractories based various antioxidants [J]. Journal of the European Ceramic Society, 2001, 21: 1037-. 1047.  SADRNEZHAAD S K, MAHSHID S, ASHEMI B H, NEMATI Z A. Oxidation mechanism of C in MgO-.C refractory bricks [J]. Journal of the American Ceramic Society, 2006, 89: 1308-. 1316.  KIM E H, JO G H, LIM H T, BYEUN Y K, JUNG Y G. Development of MgO-.C refractory having high oxidation resistance by metal coating process [J]. Journal of Nanoscience and Nanotechnology (In-press).  BUTTRY D, ANSON F. New strategies for electrocatalysis of polymer-coated electrodes reducton of dioxygen by cobalt porphyrins iImmobilized in nafion coatings on graphite electrodes [J]. Journal of the American Society, 1984, 106 (1): 59-64.  KIM E H, LEE D, PAIKI G, JUNG Y G. Effect of Ni-coated TiC particles on metal matrix composites [J]. Journal of Nanoscience and Nanotechnology, 2011, 11: 1746-.1749  J. Mol. Chem. Soc. J. Mol. Chem. Soc., Vol. 36, No. 3, pp. Progress in Organic Coatings, 2011, 70: 310-317.   PANDEY P C, UPADHYAY SI, SHUKLA N K, SHARMA S. Studies on the electrochemical performance of glucose biosensor based on ferrocene encapsulated ORMOSIL and glucose oxidase modified graphite paste electrode [J]. Biosensors and Bioelectronics, 2003, 18: 1257-1268.   HOU C H, LIANG C, YIACOUMI S, DAI S, TSOURIS C. Electrosorption capacitance of nanostructured carbon-based materials [J]. Journal of Colloid and Interface Science, 2006, 302: 54-61.   LIU X G, QU Z Q, GENG D Y, HAN Z, JIANG J J, LIU W, ZHANG Z D. Influence of a graphite shell on the thermal and electromagnetic properties of FeNi nanoparticles [J]. Carbon, 2010, 48: 891-897.   WANG Z, LIU J, LIANQ Q, WANG Y, LUO G. Carbon nanotubemodified electrodes for the simultaneous determination of doamine and ascorbic acid [J]. Analyst, 2002,127: 653-6558.   KNOX J H, WAN Q H. Chiral chromatography of amino- and hydroxy-acids on surface modified porous graphite [J]. Chromatographia, 1995, 40: 9-14.   ABIMAN P, CROSSLEY A, WILDGOOSE G G, JONES J H, COMPON R G. Investigating the thermodynamic causes behind the anomalous large shifts in pKa values of benzoic acid-modified graphite and glassy carbon surfaces [J]. Langmuir, 2007, 23: 7847-7852.   KIM E H, JUNG Y G, PAIKI G. Microstructure and mechanical properties of Al2O3 composites with surface-treated carbon nanotubes (CNTs): Dispersibility of modified carbon nanotubes (CNTs) on Al2O3 matrix [J]. Journal of Nanoscience and Nanotechnology, 2012,12: 1332-. 1336.

Accordingly, an object of the present invention is to solve the above-mentioned problems, and it is an object of the present invention to improve the efficiency of coating the surface of graphite on the surface of graphite by performing surface modification of the surface of graphite particles by acid treatment before coating the surface of graphite with aluminum precursor, The present invention provides a method for promoting the antioxidation of graphite contained in a magnesia-carbon refractory material through surface modification capable of enhancing the antioxidative properties of the magnesia-carbon refractory material.

In order to accomplish the above object, the present invention provides a method for producing a magnesium-carbon refractory comprising the steps of: (a) modifying a surface of graphite particles contained in a magnesium-carbon refractory material by acid treatment; and (S200) coating the surface of the graphite particle with an aluminum precursor There is a feature in a method for promoting the antioxidation of graphite contained in magnesia-carbon refractories through surface modification.

At this time, the reforming step (S100) may include an eleventh step (S110) of injecting the graphite particles into a mixture of sulfuric acid and nitric acid at a ratio of 3: 1 (volume ratio).

In addition, a twelfth step (S120) in which the mixture containing the graphite particles is ultrasonically treated for 3 hours and then stirred for 24 hours after the execution of the eleventh step (S110), a thirteenth step of washing the agitated graphite particles with distilled water (S130), and a fourteenth step (S140) of drying the washed graphite particles.

The step (S130) of washing the graphite particles with distilled water until the pH of the graphite particles reaches 7, the step (S140) of filtering the washed graphite particles, drying the particles at 80 ° C for 48 hours It is also possible to do.

The coating step (S200) In addition, it is also possible to include a first step 21 (S210) to the graphite particle subjected to the reforming step (S100) and the mixture stirred for Al (NO _{3) 3} solution.

In addition, step 22 (S220) of filtering and drying the mixed graphite particles after performing step 21 (S210), and step 23 (S230) of preheating the dried smoke particles to a specific temperature It is also possible to do.

The graphite particles mixed in the Al (NO 3) 3 solution are stirred at room temperature for 1 hour, and the 22nd step (S220) is dried at 80 ° C for 1 hour, Step 23 (S230) may be preheated to 300 DEG C for 1 hour in a hydrogen atmosphere.

Further, the present invention is further characterized by the magnesia-carbon refractory produced by the above-described method.

The features and advantages of the present invention will become more apparent from the following detailed description based on the accompanying drawings.

Prior to that, terms and words used in the present specification and claims should not be construed in a conventional and dictionary sense, and the inventor may properly define the concept of the term in order to best explain its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

According to the present invention, the surface of the graphite particles is modified by acid treatment to improve the efficiency of coating the surface of the graphite with the metal precursor, thereby enhancing the antioxidative properties of the graphite.

1 is a flowchart according to an embodiment of the present invention.
2 is a photograph showing the dispersibility of graphite particles by the method according to one embodiment of the present invention.
FIG. 3 is a SEM image of an EDS analysis of surface-modified graphite according to an embodiment of the present invention. FIG. 3a and FIG. 3b show the case where there is no coating layer. FIG. 3a shows the case before heat treatment at 1000.degree. C., Respectively. FIGS. 3C and 3D show the case where the coating layer is present, FIG. 3C shows the state before the heat treatment at 1000.degree. C., and FIG. 3D shows the state after the heat treatment at 1000.degree.
FIG. 4 is a graph showing the results of a combustion test on modified graphite particles with and without a coating layer according to an embodiment of the present invention. Numerals 1 to 4 are modified graphite particles, 2 is 700 ° C, 3 is 900 ° C, and 4 is a photograph after a combustion test at 1000 ° C. In addition, a1 to a4 are cases in which there is no coating layer, and b1 to b4 are cases in which there is a coating layer.
FIG. 5 shows the results of modified graphite XRD with and without a coating layer according to an embodiment of the present invention, wherein 5 (a) shows modified graphite without a coating layer before heat treatment and 5 (b) 5 (c) shows modified graphite with a coating layer after heat treatment at 500 ° C, 700 ° C and 900 ° C, and 5 (d) shows modified graphite after 1000 ° C And modified graphite with a coating layer after heat treatment at 1200 ° C.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In this process, the thicknesses of the lines and the sizes of the components shown in the drawings may be exaggerated for clarity and convenience of explanation.

In addition, the terms described below are defined in consideration of the functions of the present invention, which may vary depending on the intention or custom of the user, the operator. Therefore, definitions of these terms should be made based on the contents throughout this specification.

In addition, the following embodiments are not intended to limit the scope of the present invention, but merely as exemplifications of the constituent elements set forth in the claims of the present invention, and are included in technical ideas throughout the specification of the present invention, Embodiments that include components replaceable as equivalents in the elements may be included within the scope of the present invention.

Example

As shown in FIG. 1, a method (S10) for improving the antioxidative activity of graphite according to an embodiment of the present invention includes a modification step (S100) of acid-treating the surface of the graphite particles contained in the magnesia-carbon refractory material, And a coating step (S200) of coating the particle surface with an aluminum precursor.

That is, when the surface of the graphite particles is subjected to acid treatment before coating with the metal, that is, the aluminum precursor, the coating efficiency of the aluminum precursor can be improved and the antioxidative property of the graphite can be improved as described above.

At this time, the modification step (S100) includes an eleventh step (S110) of adding the graphite particles to a mixture of sulfuric acid and nitric acid at a ratio of 3: 1 (volume ratio) .

After the surface is acid-treated by the eleventh step (S110), the mixture into which the graphite particles have been introduced is subjected to ultrasonic treatment for 3 hours and then subjected to a twelfth step (S120) for stirring for 24 hours. Then, the thirteenth step (S130) of washing the agitated graphite particles with distilled water is performed. In the thirteenth step (S130), the graphite particles are preferably washed with distilled water until the pH of the graphite particles reaches 7.

In the 14th step (S140) of washing the graphite particles with the cleaned graphite particles in the 13th step (S130), the cleaned graphite particles are dried for the 14th step (S140) After filtering, it is possible to dry for 48 hours at 80 ° C.

After the surface is acid-treated by the modification step (S100) of the present invention as described above, the coating step (S200) is performed.

In this case, the coating step (S200) includes the steps of claim 21 (S210) of the graphite particles by acid treatment in the modification step (S100) and the mixture stirred for Al (NO _{3) 3} (aluminum nitrate) was added.

In this step 2110, an aluminum coating is formed on the surface of the graphite particles. At this time, the graphite particles mixed in the Al (NO ₃ ) ₃ solution are preferably stirred at room temperature for 1 hour.

After performing the twenty-first step (S210), the twenty-second step (S220) of filtering and drying the mixed graphite particles is performed, and the twenty-second step (S220) is preferably performed at 80 ° C for one hour .

In operation 23, the operation S230 of S230 is performed to pre-heat the dried smoke particles to a specific temperature after the operation S220. In operation S230, ) Is preferably preheated to 300 DEG C for 1 hour in a hydrogen atmosphere.

With respect to the effect of the present invention described above, the coating efficiency of the aluminum precursor on the graphite surface in the state of the surface modification and the state of no surface modification is examined through the degree of dispersion of the precursor. The oxidation behavior of the aluminum-coated graphite is examined by the microstructure and state analysis of the graphite after the combustion test.

First, a scanning electron microscope (SEM; Model JSM-5610; JEOL, Tokyo, Japan) and an energy dispersive x-ray spectrometer (EDS; energy resolution of 133 eV, Oxford Inst., Oxford, UK Respectively.

Further, as described later, a combustion test for the graphite particles modified with the aluminum precursor before or after coating with the aluminum precursor is performed for 1 hour at a temperature range of 500 ° C to 1000 ° C. The phase analysis after the combustion test is carried out by an X- (Model 3040 PW Philips X'pert MPD Eindhoven, The Netherlands).

As described above, in order to effectively inhibit the oxidation of graphite in the magnesia-carbon refractory, the aluminum precursor must be uniformly and uniformly coated on the graphite surface and the coating efficiency of the aluminum precursor should be enhanced.

For this purpose, a hydroxyl group of an anion should be provided on the graphite surface, and the surface of the graphite is modified with an acid to provide the hydroxyl group.

In order to confirm the effect of the surface modification, graphite particles in the case of being modified or not are dispersed in an aqueous solution containing aluminum-coated graphite particles, which will be explained with reference to Fig.

2 is a graph showing the dispersibility of graphite particles. Numeral 1 indicates graphite free of a coating layer, numeral 2 indicates graphite in a state where a coating layer is present, and numeral 3 indicates graphite in a state of having a coating layer. Graphite in the state of being aged. Further, a1, a2, and a3 denote original graphite that has not been surface-modified, and b1, b2, and b3 denote graphite that has undergone surface modification.

As shown in the figure, after the acid treatment, the surface-modified graphite was well dispersed without agglomeration (b1 in FIG. 2), indicating that a hydroxyl group having a negative charge on the graphite surface was generated by the acid,

On the other hand, as shown in (a1) of FIG. 2, it can be confirmed that the graphite which has not undergone the surface modification precipitates within a few minutes, and it is found that the surface modification by the acid treatment is necessary for improving the efficiency of the aluminum coating .

Particularly, as compared with the case of coating with an aluminum precursor, it can be confirmed that graphite (a2 in Fig. 2) that is not surface-modified precipitates faster than surface-modified graphite (b2 in Fig. 2) The advantage of coating can be confirmed again.

In other words, it can be seen that the aluminum precursor is better coated on the graphite surface modified by the present invention.

Referring to FIG. 3, the microstructure and elemental analysis results of the surface-modified graphite particles with and without the coating layer are examined through a heat treatment function.

FIG. 3 is a SEM photograph of the surface-modified graphite as an SEM image, and FIGS. 3A and 3B show the case where there is no coating layer. FIG. 3A shows a state before heat treatment at 1000.degree. C. and FIG. 3B shows a state after heat treatment at 1000.degree. FIGS. 3C and 3D show the case where the coating layer is present, FIG. 3C shows the state before the heat treatment at 1000.degree. C., and FIG. 3D shows the state after the heat treatment at 1000.degree.

In Fig. 3A, only O and C are detected in the graphite when there is no coating layer. Further, in FIG. 3C, aluminum element is additionally detected in graphite as a case without a coating layer, since the structure after the aluminum layer is preheated at 300 ° C. is amorphous.

On the other hand, the polygonal Al ₂ O ₃ particles converted from the amorphous aluminum layer after the heat treatment at 1000 ° C. under the premise that the aluminum precursor was uniformly coated on the graphite surface were completely covered with the graphite surface as shown in FIG. Review in detail.

Graphite particles with and without a coating layer after heat treatment at 1000 ° C exhibit different shapes. That is, as shown in FIG. 3B, when there is no coating layer, various impurities are detected in graphite, which indicates that graphite is easily decomposed in the absence of a coating layer.

However, only Al, O, and C elements are detected in graphite with the coating layer, and Al and O are increased and C is decreasing after heat treatment (FIG. 3D)

Therefore, it can be assumed that the graphite oxidation is suppressed by the aluminum layer (serving as the oxygen barrier layer) formed on the surface.

Referring to FIG. 4, the combustion test results for modified graphite particles with and without a coating layer will be examined below.

In FIG. 4, numerals 1 to 4 are modified graphite particles, 1 is a photograph after a combustion test at 500 ° C, 2 is 700 ° C, 3 is 900 ° C, and 4 is a photograph after a combustion test at 1000 ° C. In addition, a1 to a4 are cases in which there is no coating layer, and b1 to b4 are cases in which there is a coating layer.

As the temperature increases in the combustion test, graphite in the absence of a coating layer is decomposed and oxidized (see Fig. 4a) to exhibit gray color at 700 ° C and brown color at 900 ° C, respectively.

In fact, graphite without a coating layer starts to react at 700 ° C and reacts completely at 900 ° C.

However, as shown in Fig. 4 (b), graphite coated with an aluminum precursor exhibits favorable conditions in a 700 ° C combustion test and starts to react with oxygen at 900 ° C.

Finally, the aluminum-coated graphite (the coating layer starts a complete reaction at 1000 ° C with oxygen) represents a white color.

This means that the coating layer (aluminum precursor) has a considerable effect as an antioxidant which delays the oxidation of graphite by a continuous and homogeneous coating on the graphite surface.

In addition, the mass loss of aluminum coated graphite is less than 10% (mass fraction) after the combustion test. Therefore, it can be seen that the coating process strengthens the inhibition of oxidation of graphite even though mass acquisition by oxidation of the coating layer is considered.

Referring to FIG. 5, the modified graphite XRD results with and without a coating layer will be discussed below.

5 (a) of FIG. 5 represents modified graphite having no coating layer before heat treatment, 5 (b) represents modified graphite having no coating layer after heat treatment at 1000 ° C. for 1 hour, and 5 5 (d) shows modified graphite with a coating layer after heat treatment at 1000 ° C and 1200 ° C. Fig. 5 (d) shows modified graphite with a coating layer after heat treatment at 700 ° C, 700 ° C and 900 ° C.

In the absence of a coating layer, a graphite peak is detected before the heat treatment (FIG. 5 (a)), but disappears after the heat treatment at 1000 ° C. (FIG.

However, when a coating layer is present, graphite peaks are detected until the heat treatment is performed at 900 캜 (Fig. 5 (c)).

Peaks of alumina (Al ₂ O ₃ ) and graphite coexist after heat treatment at 1000 ° C. after heat treatment with amorphous peak characteristics, indicating that the graphite is decomposed and the coating layer is not completely crystallized (FIG. 5 (d)).

Finally, the aluminum-coated graphite is converted to alumina at 1200 ° C. The results are in good agreement with the results of the combustion test. As a result of the phase analysis, the oxidation resistance of graphite is enhanced by the coating of the aluminum precursor.

As described above, in the case of the present invention, graphite is acid-treated to improve the coating efficiency of the aluminum precursor. The surface-modified graphite exhibits improved dispersibility than the original graphite.

The modified graphite particles coated with the aluminum precursor precipitate with time because the charge due to the reaction between the cation of the aluminum precursor and the graphite anion disappears.

It has been proved that the aluminum precursor is well coated on the graphite surface. Evidence for the coating of the aluminum precursor can be observed by microstructure and elemental analysis. The surface modification of graphite improves the coating efficiency of the aluminum precursor on the graphite surface. In the case of no surface modification, the mass gain is 1.5% and the surface modification is 1.9%.

On the other hand, graphite whose surface was not reformed started to react with oxygen in a combustion test at 700 ° C and completely reacted at 900 ° C.

However, aluminum coated graphite showed good conditions at 700 ℃ in the combustion test, and the reaction started at 900 ℃. The aluminum coated graphite was maintained up to 1000 DEG C even if the color changed to white.

This result means that the coating layer uniformly and continuously coating the graphite surface to retard the oxidation of the graphite.

In addition, aluminum coated graphite is detected up to 900 ° C, and alumina and graphite coexist at 1000 ° C.

Finally, the aluminum-coated graphite was completely converted to alumina at 1200 ° C. As a result, the high antioxidative properties of aluminum-coated graphite are achieved by surface-modified graphite and in this study aluminum-coated graphite can enhance the antioxidant properties of the MgO-C refractory.

Claims (8)

A modification step (S100) of acid-treating the surface of graphite particles contained in the magnesia-carbon refractory; And
Coating a surface of the modified graphite particle with an aluminum precursor (S200); Lt; / RTI >
The coating step (S200)
A first step 21 in which the graphite particle subjected to the reforming step (S100) and the mixture stirred for Al (NO _{3) 3} solution (S210);
(S220) filtering and drying the mixed and agitated graphite particles; And
(S230) of pre-heating the dried smoking particles to a specific temperature; Characterized in that the magnesium-carbon refractory comprises graphite.
The method according to claim 1,
The reforming step (S100) comprises eleventh step (S110) of injecting the graphite particles into a mixture of sulfuric acid and nitric acid at a ratio of 3: 1 (volume ratio) to increase the antioxidative properties of the graphite contained in the magnesia- Way.
3. The method of claim 2,
A twelfth step (S120) of performing ultrasonic treatment of the mixture in which the graphite particles are charged for 3 hours and stirring for 24 hours after the 11th step (S110)
A thirteenth step S130 of washing the agitated graphite particles with distilled water,
And a step (S140) of drying the washed graphite particles. The method for enhancing the antioxidative activity of graphite contained in a magnesia-carbon refractory material by surface modification.
The method of claim 3,
In the thirteenth step S130, the graphite particles are washed with distilled water until the pH of the graphite particles reaches 7,
The method for enhancing the antioxidative activity of graphite contained in the magnesia-carbon refractory material by surface modification in which the washed graphite particles are filtered and dried at 80 ° C for 48 hours in the 14th step (S140).
delete delete The method according to claim 1,
In step 21, the graphite particles mixed in the Al (NO ₃ ) ₃ solution are stirred at room temperature for 1 hour,
The twenty-second step (S220) is performed at 80 DEG C for one hour,
The method for enhancing the antioxidative activity of graphite contained in the magnesia-carbon refractory material by surface reforming at a temperature of 300 DEG C for 1 hour in a hydrogen atmosphere in the step S230.
A magnesia-carbon refractory produced by the method according to claim 1.

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