KR20030054077A - Method to coat ceramic powder with TiO2 and Method to improve wettability of B4C-Al composite material - Google Patents

Abstract

PURPOSE: A method for coating titanium oxide(TiO2) on ceramic powder homogeneously by a sol-gel process is provided. Also, a method for improving wettability of ceramic-metal composites is provided by thermal treating TiO2- coated boron carbide(B4C)-aluminum powder at low temperature. CONSTITUTION: The TiO2-coated ceramic powder is prepared by the following steps of: dispersing ceramic powder into alcohol; adding 0.001-0.1M(based on the total solution) titanium tetraisopropoxide; adding a mixed solution of alcohol and water, having a concentration 3-6times higher than titanium tetraisopropoxide for coating titanium hydroxide on ceramic powder; and calcining. Also, the wettability of boron carbide-metal(Al) composites is improved by thermal treating TiO2-coated B4C powder at 900-1200deg.C under vacuum, resulting in formation of a titanium boride(TiB2) coating layer on the surface of B4C powder.

Description

Method for coating ceramic powder with TiO2 and Method to improve wettability of B4C-Al composite material}

The present invention relates to a titanium oxide coating method on a ceramic powder and a method for improving the wettability of a boron carbide-aluminum composite material using the same, and more particularly, to titanium oxide (TiO ₂ ) on a ceramic powder using a sol-gel method. The present invention relates to a method of coating and a method of improving the wettability of a ceramic-metal composite material by heat treating a titanium oxide coated boron carbide (B ₄ C) powder prepared by the method to form a titanium boride layer.

Ceramic-metal composite materials have recently been in the spotlight as a material exhibiting a new property combining the hardness of the ceramic and the toughness of the metal. Wetness is an important issue in the manufacture of such ceramic-metal composites. In the manufacture of ceramic-metal composite materials, if the wettability of the system is excellent, the different phases can be strongly bonded at the contact surface, and the liquid phase can be well arranged in the required position, and the manufacturing process is also economical. to be. On the other hand, if the wetness is not good, it is necessary to apply pressure during the process, in which case it is often not satisfactory to make the composite material containing many ceramic phases compact, and the interface of the two phases tends to be fragile. Therefore, it is very necessary to improve the wettability as much as possible in the manufacture of the ceramic-metal composite material, but in many systems, satisfactory wettability is not obtained, which is a problem.

Wetting is also a problem in the production of a boron carbide (B ₄ C) -aluminum (Al) composite material. Boron carbide has very high hardness, excellent neutron absorption ability, abrasion resistance, fire resistance, and thermoelectricity, and is light, so that it can be used in various applications. In particular, the boron carbide-aluminum composite material may be used as a high toughness neutron absorber, a bulletproof material, a light structural material having hardness and toughness, and a computer hard disk component.

For the production of boron carbide-aluminum composites, infiltration is used instead of the general powder metallurgy for densification of the composites. However, the preparation of boron carbide-aluminum composites by this method requires temperature conditions significantly higher than the melting point of the metal in order to achieve redness. Under high temperature conditions, various unwanted reaction products, such as aluminum carbide (Al ₄ C ₃ ), which have a very bad effect on physical properties, are generated and change the physical properties in an undesirable direction. In particular, in the case of neutron absorbent material, which is one of the most important applications of boron carbide, the content of boron carbide should be high in order to obtain sufficient absorbing capacity, and also provide toughness and fast thermal conductivity to prevent the diffusion of cracks caused by helium accumulation. In order for the aluminum content to be as high as possible, it is necessary to suppress all reactions that lower the content of boron carbide and aluminum.

Of course, depending on the use, it is possible to economically obtain the required properties by producing a suitable reactant, but in the use of maintaining the original phase, such as a neutron absorber, such a by-product generation phenomenon is a big problem. Therefore, there is a demand for a technology capable of reducing the driving force of the chemical reaction by reducing the driving force of the chemical reaction by performing the densification process at a low temperature while obtaining the necessary wettability.

The present invention is to solve the problems of the prior art as described above, an object of the present invention is to provide a method for uniformly coating titanium oxide on fine ceramic powder using the sol-gel method.

Still another object of the present invention is to provide an economical method of improving the wettability by forming a titanium boride coating layer by heat treating a titanium oxide-coated boron carbide-aluminum powder for a short time at low temperature.

1 is an electron micrograph of a boron carbide powder having an average particle diameter of about 30 μm used in one embodiment of the present invention;

2 is an electron micrograph of the boron carbide powder coated with titanium hydroxide on the surface,

3 is an electron micrograph of a titanium boride (TiB ₂ ) coating layer formed by heat treating titanium oxide coated on boron carbide powder,

4 is an X-ray diffraction analysis showing that the coating layer formed on the boron carbide powder according to the present invention is titanium boride,

FIG. 5 is a photograph comparing the time-dependent aspects of infiltration of aluminum at 1000 ° C. with respect to a molded article of a boron carbide powder (right) and an uncoated boron carbide powder (left) on which a titanium boride coating layer is formed according to the present invention. ,

FIG. 6 shows the results of X-ray diffraction analysis of specimens in which aluminum was infiltrated to the boron carbide powder without coating.

7 is an X-ray diffraction analysis of a specimen in which aluminum was infiltrated with boron carbide powder having a titanium boride coating layer formed thereon for 40 minutes according to the present invention.

8 is a graph showing the toughness and hardness according to the titanium boride content in the ceramic powder.

In order to achieve the above object, the titanium oxide coating method on the ceramic powder using the sol-gel method according to the present invention, after dispersing and stirring the ceramic powder in alcohol, the titanium tetraisoproposide of the total solution (A) applying titanium hydroxide to the ceramic powder by adding hydrochloric acid at a concentration of 0.001M to 0.1M and adding distilled water mixed with alcohol at a concentration of 3 to 6 times the titanium tetraisopropoxide concentration; And (b) obtaining a titanium oxide coating layer by sintering the ceramic powder coated with titanium hydroxide of step (a).

In the titanium oxide coating method according to the present invention, the step (a) is characterized in that the titanium tetraisopropoxide is added in a ratio of 0.0010 mol to 0.015 mol per 1g of ceramic powder.

In the method for improving the wettability of the boron carbide-metal composite material according to the present invention, the titanium oxide-coated boron carbide powder prepared by the titanium oxide coating method is subjected to heat treatment at a temperature of 900 ° C. to 1200 ° C. under vacuum conditions. It is characterized by forming a titanium boride coating layer excellent in the core on the surface of the boron carbide powder.

In the method for improving the wettability of the boron carbide-metal composite according to the present invention, the metal is characterized in that aluminum or an alloy thereof.

In order to improve the wettability in the manufacture of ceramic-metal composites, a material layer having excellent wettability at the interface needs to exist. It is known that the coating of titanium-based compounds such as titanium boride, titanium carbide (TiC) and titanium nitride (TiN) through chemical vapor deposition is effective when the metal is aluminum, but it is difficult to uniformly coat the material when the ceramic is in powder form. Very difficult.

In the present invention, in the preparation of the boron carbide-aluminum composite material, the boron carbide powder was first coated with titanium oxide, and then the boron carbide powder coated with titanium oxide was heated to form a titanium boride coating layer.

Titanium oxide has traditionally been used as a white pigment and is a material that has been greatly attracting attention as the applicability to photocatalytic effects is known recently. The technique of coating titanium oxide on the surface of other materials has been studied, but the technique of uniformly coating the surface of the powder has not been advanced yet.

In the present invention, the titanium oxide is uniformly coated on the fine ceramic powder using the sol-gel method. In the present invention, the particle diameter of the fine ceramic powder is in the range of 10 nm to 200 μm. Specifically, the titanium oxide layer by condensation polymerization is coated by applying and heating titanium hydroxide by the sol-gel method. At this time, titanium hydroxide causes nucleation and particle growth. In other words, the titanium hydroxide can be produced by growing through heterogeneous nucleation only on the surface of the powder to obtain the effect of coating.

The sol-gel method is a method of solidifying a sol into a gel by carrying out a hydrolysis and polycondensation reaction of a compound in a solution by using an organic or inorganic compound of a metal as a solution, and heating the gel to prepare an oxide solid. At this time, since water and alkoxide cannot be mixed, a solvent in which two substances can be dissolved simultaneously, such as alcohol, is utilized. Thus, when a homogenizing agent such as alcohol is present, the hydrolysis reaction is facilitated due to the miscibility of water and alkoxides. As the polycondensation bonds increase, each molecule crosslinks, aggregates into a sol, and a gel forms when the sol particles are linked to each other in an aggregate or network. During drying, volatiles (water, alcohol, etc.) in the gel are removed and the gel shrinks.

Hereinafter, the configuration and the effects of the present invention will be described in more detail with reference to Examples. The following examples illustrate the content of the invention, but the content of the invention is not limited thereto.

<Example 1: Titanium boride coating layer formed on the boron carbide powder>

Titanium tetraisopropoxide (TTIP) was used in anhydrous ethanol as a precursor for titanium oxide coating. As the boron carbide, a powder having an average particle diameter of 30 μm was used. 1 is an electron micrograph of a boron carbide powder having a particle diameter of 30 μm used in the present embodiment. The boron carbide powder was dispersed in anhydrous ethanol, sufficiently stirred and TTIP was added, and distilled water mixed with ethanol was also added to cause hydrolysis.

As a result of exploring suitable conditions in which the titanium hydroxide causes heterogeneous nucleation but does not produce discrete particles with homogeneous nucleation and does not introduce too small an amount, the TTIP in the total solution is 0.001M to 0.1M, preferably Is 0.033M, distilled water is 3 to 6 times the concentration, and the ratio is adjusted so that the TTIP per 0.00g of boron carbide into 0.0010 mol to 0.015 mol, and while stirring slowly for about 20 hours to maintain a suitable thickness by heterogeneous nucleation It was observed that titanium hydroxide was applied to the boron carbide powder. This reaction is summarized as in the following formula (1).

Ti [OCH (CH ₃ ) ₂ ] ₄ + 4H ₂ O = Ti (OH) ₄ + 4C ₃ H ₇ OH

2 is an electron micrograph of the boron carbide powder coated with titanium hydroxide by the above method. When the boron carbide powder coated with titanium hydroxide is heated, a coating of titanium oxide is obtained, and the reaction is represented by the following Chemical Formula 2.

Ti (OH) ₄ = TiO ₂ + 2H ₂ O

When the titanium hydroxide-coated powder is heated to a higher temperature, the produced titanium oxide reacts with boron carbide to turn into titanium boride. That is, reactions such as the following Chemical Formula 3 occur.

B ₄ C + 2TiO ₂ + 3C = 2TiB ₂ + 4CO

In the present embodiment, the titanium oxide coated powder was dried and then heat treated at 900 to 1200 ° C. while maintaining a vacuum (herein, 10 ⁻⁴ torr) in a graphite crucible to obtain a boron carbide powder having a titanium boride coating layer.

3 is a high magnification electron micrograph of the boron carbide powder in which the titanium boride coating layer is formed according to the present embodiment, and FIG. 4 is an X-ray diffraction analysis to confirm that the coating layer material is titanium boride.

As described above, the present invention uses a sol-gel method to uniformly coat titanium oxide on the surface of the boron carbide powder, and then heat-treat it to chemically change it to titanium boride. Although the thick coating layer may crack during the drying process, the titanium boride coating layer covers most of the surface of the boron carbide powder, which can significantly change the surface properties.

<Example 2>

Boron carbide powder having a titanium boride coating layer was prepared in the same manner as in Example 1 using a powder having an average particle diameter of boron carbide.

The spherical titanium oxide particles generated by uniform nucleation were not found even for the powder having a small particle diameter, and the titanium boride was confirmed by X-ray diffraction analysis, indicating that the titanium oxide was coated.

Example 3: Aluminum Infiltration

Infiltration method was used for densification of ceramic-metal composites. 0.33 g of ceramic powder was uniaxially pressurized to form a molded product, and the porosity thereof was about 38%. On top of this was placed aluminum to fill the pores and heated in vacuum to infiltrate. At this time, in the case where the titanium boride coating layer was formed, the infiltration proceeded quickly even at 1000 ° C. lower than the general infiltration temperature irrespective of the powder particle size.

5 is a photograph of the infiltration behavior at 1000 ℃ for the powder having a small particle diameter. As shown in FIG. 5, when the titanium boride coating layer was formed, the wetness was rapidly decreased and infiltration proceeded smoothly, but when the coating was not performed, the wetness was gradually decreased over a long time, and thus, the titanium boride coating layer was formed. The infiltration of the liquid phase did not start until the end of the infiltration. As a result, the time required for small powders decreased from about 120 to 35 minutes, and for large powders from about 25 to less than 10 minutes. When the infiltration rate is improved in this manner, it is possible to greatly suppress the progress of unwanted chemical reactions.

FIG. 6 is an X-ray diffraction analysis result when the powder is infiltrated at 1200 ° C. without coating, and FIG. 7 shows a case where a titanium boride is formed on the powder and a short time process is performed at a low temperature of 1000 ° C. FIG. X-ray diffraction analysis results. As shown in FIG. 7, the amount of the overall reaction product was reduced, and a large amount of aluminum metal remained, and in particular, no production of Al ₄ C ₃ , which had a fatal effect on physical properties, was found.

8 is a graph showing the toughness and hardness according to the titanium boride content in the ceramic powder measured by the indentation (indentation). As shown in FIG. 8, the physical properties of the case where the titanium boride is infiltrated at a temperature of 1200 ° C. without a coating (content = 0) and the titanium boride coating layer is formed and infiltrated at 1000 ° C. significantly contrast. That is, when the titanium boride coating layer is formed, it can be seen that toughness is greatly increased instead of decreasing hardness as the reaction product decreases.

As described above, the present invention forms a titanium boride coating layer having excellent wettability on the surface of the ceramic powder in order to improve the wettability of the boron carbide-aluminum composite material. In addition, in the present invention, in order to form a titanium boride coating layer, the titanium hydroxide was first applied to the surface of the boron carbide powder by sol-gel method and then sintered to coat the titanium oxide layer. At this time, the coating of titanium oxide utilizes the property that the hydrolysis product generated during the sol-gel process causes non-uniform nucleation on the surface of the powder.

In summary, the present invention forms a titanium boride coating layer on the surface of the boron carbide powder by coating and thermally treating the titanium oxide by the sol-gel method, thereby suppressing unnecessary chemical reactions by completing the process at a lower temperature than the conventional method. As a result, while maintaining a large number of initial phases, it was possible to produce a composite material having high toughness and satisfying the conditions required by a neutron absorber.

As described above, the titanium oxide coating method on the surface of the ceramic powder using the sol-gel method of the present invention is uniform on the surface of the fine ceramic powder using the principle that the precursor of titanium oxide causes uneven nucleation on the surface of the powder. One titanium oxide coating was made possible. Titanium oxide-coated ceramic powder prepared by the present invention can be used critically in many applications requiring the photocatalytic effect of titanium oxide.

The method for improving the wettability of the boron carbide-metal (aluminum, etc.) composite material according to the present invention is economical by reducing the process temperature and time by forming a titanium boride coating layer having excellent wettability on ceramic powder.

Since the method for improving the wettability according to the present invention suppresses various chemical reactions in a reactive system, the final manufactured boron carbide-aluminum composite material retains much of its initial phase while increasing toughness to satisfy the necessary properties as a neutron absorber. Can be.

Claims (4)

After dispersing and stirring the ceramic powder in alcohol, titanium tetraisopropoxide was added at a concentration of 0.001 M to 0.1 M of the total solution, and distilled water mixed with alcohol at a concentration of 3 to 6 times the concentration of the titanium tetraisopropoxide was added. (A) applying titanium hydroxide to the ceramic powder by hydrolysis by addition; And And (b) obtaining a titanium oxide coating layer by sintering the ceramic powder coated with titanium hydroxide in the step (a). The method of claim 1, The step (a) is a titanium oxide coating method on the ceramic powder using the sol-gel method, characterized in that the addition of titanium tetraisopropoxide in a ratio of 0.0010 mol to 0.015 mol per 1g of ceramic powder. The method of claim 1, wherein the titanium oxide coated boron carbide powder prepared by the titanium oxide coating method is heat-treated under vacuum conditions at a temperature of 900 ° C to 1200 ° C to form a titanium boride coating layer having excellent wettability on the surface of the boron carbide powder. A method of improving the wettability of a boron carbide-metal composite material. The method of claim 3, The metal is a method of improving the wettability of the boron carbide-metal composite, characterized in that the aluminum or an alloy thereof.