JP3175170B2 - Method for producing TiC sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fine ceramics, and more particularly to a TiC sintered body having excellent corrosion resistance and electrical conductivity, and a method for producing the same.

[0002]

2. Description of the Related Art In general, there are oxide-based and non-oxide-based fine ceramics. Oxide-based materials have been developed relatively early and are widely used in various fields today. On the other hand, non-oxide systems have a shorter history than oxide systems, and their development has been pursued with the automotive industry, nuclear power, and space development. This non-oxide system is nitride,
These are carbides, borides, silicides, or mixtures thereof, and each has its own properties.However, in particular, TiC of carbides is not only excellent in mechanical properties, but also because of its excellent chemical and electrical properties. At times, ceramics have been attracting attention.

[0003] When ceramics are used for machinery, it is necessary to densify them to as close to theoretical density as possible in the sintering process in order to obtain high strength. In some cases, it is preferable that the ceramic is porous so as to have a large surface area. Since porous TiC has corrosion resistance and high conductivity, it is most suitable as an electrode material for a high-temperature fuel cell.

[0004] In the production of ceramic products, the raw ceramic powder is molded and then sintered. Usually, in order to improve the diffusion of the ceramic powder during the sintering and to accelerate the sintering rate at a low temperature, a ceramic powder is added. Pressing or sintering aids may be used. In particular, since TiC is difficult to sinter, it is indispensable to apply pressure or to use a sintering aid during sintering. HIP, hot press and the like have been used for pressurization. Metal powders such as Fe, Ni, and Co were usually added as sintering aids.

[0005]

However, if a sintering aid is used in the production of a TiC sintered body, the sintering itself can be easily carried out. Not only deteriorates the corrosion resistance of the TiC sintered body, but also decreases the porosity by flowing between the pores, and the properties of the pores such as the porosity and the pore diameter are controlled by the raw material components or the composition. Was difficult. Therefore, the use of a sintering aid has not been favorable for the production of materials requiring porosity, corrosion resistance, high conductivity and specific porosity conditions, such as electrode materials for high temperature fuel cells.

The present invention solves the above-mentioned problems in the prior art and provides a porous TiC sintered body having a sufficient level of characteristics required for an electrode of a high-temperature fuel cell, for example, and a method for producing the same. The purpose is to do so.

[0007]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies, and as a result, focused on the combustion reaction method, which has been conventionally used as a method for synthesizing carbides, nitrides, borides and the like. By utilizing the combustion reaction method used for sintering TiC and, if necessary, incorporating at least part of the TiC powder in the green compact in advance, it is possible to adjust properties such as strength and porosity. And came to the present invention.

[0008] Here, the combustion reaction method means that when a certain amount of energy is added to a mixture of a metal Ti powder and a carbon powder, the reaction is started, and the heat of the reaction causes the reaction to proceed in a chain, so that the desired carbide is produced. , Nitrides, borides and the like are synthesized efficiently. In the present invention, this combustion reaction method is used for sintering TiC, and is referred to as "combustion sintering method" in this specification.

The gist of the present invention is that a mixture of a metal Ti powder and a carbon powder is compacted, a mixture of the Ti powder and the carbon powder is filled around the obtained compact, and the latter is compacted. This is a method for producing a porous TiC sintered body, characterized in that the mixture is ignited by a combustion sintering method by a combustion sintering method without sintering agent under non-pressure. From another aspect, the present invention provides a method of compacting a mixture of a metal Ti powder and a carbon powder, at least partially containing TiC powder, and forming a titanium compact around the obtained compact.
A method for producing a porous TiC sintered body, characterized in that a mixture of powder and carbon powder is filled, and the latter mixture is ignited to be sintered under non-pressure without a sintering aid by a combustion sintering method. It is. According to a more specific aspect of the present invention, in the TiC sintered body, TiC generated by a combustion reaction is generated first.
TiC or TiC added from the beginning is sintered or bonded in a porous state.

Here, the “combustion sintering method” is broadly defined as
When sintering a green compact (also referred to as a molding mixture), this is a sintering method that is performed under the non-pressurized state without a sintering aid and using the combustion reaction method described above. The thermal energy required for sintering is
The heat of powder combustion of C may be used. Alternatively, in some cases, only the combustion heat of the Ti and C powders contained in the green compact may be used, and only ignition energy may be supplied from the outside.

Specific examples of the combustion sintering method according to the present invention include, for example, the following embodiments, but are not limited thereto, and all embodiments are based on the same principle. The inclusion in the present invention will be fully understood from the above description. However,
In any case, no sintering aid is used, and sintering proceeds under no pressure.

(1) A mixture in which Ti powder and carbon powder are mixed in a molar ratio of 80:20 to 35:65: A A mixture obtained by compression-molding the mixture A: B 5 to 50% of the total filling amount A raw material comprising the molding mixture B and the remaining mixture A is charged into a reaction vessel, and these are heated and ignited in a vacuum or an inert atmosphere to cause a combustion reaction, thereby obtaining a porous TiC sintered body. (2) Mixture in which Ti powder and carbon powder are mixed at a molar ratio of 80:20 to 35:65: A Molding mixture in which the mixture A is compression-molded: B The mixture A and the TiC powder are in a weight ratio of 100: 0 to Mixture mixed at 60:40 ... C (excluding the case of 100: 0) The raw material consisting of the molding mixture B consisting of 5 to 50% of the total filling amount and the remaining mixture C is filled in a reaction vessel, Is heated and ignited in a vacuum or an inert atmosphere to cause a combustion reaction to obtain a porous TiC sintered body.

(3) A mixture of Ti powder and carbon powder in a molar ratio of 80:20 to 35:65: A The mixture A and the TiC powder are mixed in a weight ratio of 100: 0 to 5:95, In addition, a compression-molded molding mixture B (except for the case of 100: 0) A raw material composed of a molding mixture B consisting of 5 to 50% of the total filling amount and the remaining mixture A is filled in a reaction vessel, and these are mixed. A porous TiC sintered body is obtained by heating and igniting in a vacuum or an inert atmosphere to cause a combustion reaction. (4) A mixture in which Ti powder and carbon powder are mixed at a molar ratio of 80:20 to 35:65: A The mixture A and the TiC powder are mixed at a weight ratio of 100: 0 to 5:95, and are compression-molded. Molded mixture: B (except for 100: 0) Mixture of the mixture A and TiC powder in a weight ratio of 100: 0 to 60:40: C (except for 100: 0) A raw material comprising a molding mixture B comprising 5 to 50% of the filling amount and a residual mixture C is filled in a reaction vessel, and these are heated and ignited in a vacuum or an inert atmosphere to cause a combustion reaction, whereby the porosity is increased. To obtain a TiC sintered body.

[0014]

Next, a TiC sintered body of the present invention and a method for producing the same will be described.

FIG. 1 is a schematic explanatory view of the manufacturing method of the present invention. In the illustrated example, in addition to the Ti + carbon powder contained in the green compact, a mixture of the Ti + carbon powder is filled around the green compact, and the combustion heat of this mixture is also used for sintering the green compact. Is done. In the figure, a molded mixture B, which is a green compact, is placed in a porous carbon crucible 1, which is a reaction vessel, and the periphery thereof is filled with a mixture C, which is a mixture of Ti + carbon powder. By igniting the mixture C, the green compact is fired and sintered instantaneously. In the illustrated example, the mixture C is further formed into a pellet at the top of the packed bed and then placed. And carbon heater 2
Ignite by.

The present invention is characterized in that a sintering aid usually used for sintering a hardly sinterable raw material is not used. Also,
The method differs from the above-mentioned method of sintering reaction products (borides, nitrides, etc.) as they are by reacting them under pressure, which is partially observed in the combustion reaction method.

That is, in the present invention, a self-reaction sintering method is used, in which the constituent elements of a hardly sinterable substance (raw material) are added and reacted to combine the raw materials themselves. Therefore, in the present invention, a sintered body of TiC can be obtained without having to continuously apply energy (heat) from the outside.

As the reaction of the mixture of the Ti powder and the carbon powder proceeds, the heat of reaction increases. First, the metal Ti is melted, the raw material powders are attracted to each other, and at the same time, the C is introduced into the molten Ti.
Melts into TiC, and this TiC
C or TiC added from the beginning is combined and sintered. That is, it is considered that metal Ti plays a role as a commonly used sintering aid. Further, the obtained sintered body has such a shape that the gap around the raw material is filled with TiC generated by the reaction. Since the porous sintered body thus obtained does not contain a sintering aid that generates a liquid phase at a low temperature, there is an advantage that the characteristics of the raw material can be utilized 100%.

According to a preferred embodiment of the present invention, by changing the amount of the TiC powder in the mixture B and the mixture C,
The characteristics of the TiC sintered body can be easily changed. The characteristics of the obtained sintered body depend on the composition of the raw material. Metal Ti
The reaction of the mixture of the powder and the carbon powder is rapid, and the tendency of the mixture to expand due to heat generation is extremely large. Therefore, the higher the mixing ratio of the TiC powder in the green compact, the higher the density of the resulting sintered body is obtained.However, when the weight ratio of the TiC powder in the green compact exceeds 95, If the weight ratio of the raw material mixture exceeds 40, the metal Ti
The amounts of the powder and the carbon powder are reduced, and there is a possibility that reaction heat is not generated sufficiently to enable sintering. In order to sufficiently perform sintering by reaction heat, the mixture C preferably accounts for 50% by weight or more of the filling in the reaction vessel, and if it exceeds 95%, it is not economical.

[0020]

EXAMPLE A porous carbon crucible 1 was filled with a predetermined amount and shape of a green compact B and a predetermined amount of a mixture C or A, which were compression-molded with a hydraulic press, at the respective composition ratios shown in Table 1. The mixture C or A in the form of a pellet is placed on the plate.
Then, these are ignited in a vacuum or an inert atmosphere (Ar, He, vacuum, etc.) to the pellet mixture C or A by the carbon heater 2 and the Ti powder is burned and reacted in a crucible as a reaction vessel at 2500 ° C. By obtaining the above high temperature, the green compact B is sintered to obtain a TiC sintered body. Each characteristic of the obtained TiC sintered body was measured. The results are also shown in Table 1. In the table, the conventional example is a case in which TiC powder is sintered using Fe powder as a sintering agent.

Next, as the mixture A, a mixture having a molar ratio of Ti: carbon powder of 1: 1 was used, and a green compact was obtained by mixing the mixture with the TiC powder in an amount of 0 to 80% by weight. The same operation as above was repeated to perform combustion sintering,
C A sintered body was manufactured. The bending strength, bulk density, apparent density, porosity, and pore volume of the obtained sintered body were measured. These results are summarized in Table 2, FIG. 2 and FIG. However, in FIGS. 2 and 3, the amount of TiC is shown in mol%.

[0022]

[Table 1]

[0023]

[Table 2] Amount of TiC added (% by weight) Flexural strength (MPa) 0 70 30 85 60 100 80 125 As can be seen from these results, TiC in the green compact was
It can be seen that a reasonable TiC sintered body can be obtained even when the powder blending ratio is zero, but as the TiC blending amount increases, the bending strength improves, and the bulk density and apparent density tend to increase slightly. Can be seen.

[0024]

Since the TiC sintered body of the present invention does not contain a sintering agent, it has a high porosity, is excellent in corrosion resistance and electric conductivity, and is suitable for a high temperature fuel cell material or a filter. I have. Further, the method for producing a TiC sintered body of the present invention can obtain a high temperature without applying a large amount of external energy, so that not only fuel can be saved, but also sintering of hardly sinterable TiC can be achieved. Strong sintering can be performed without an agent, and a porous sintered body can be obtained, which has an unprecedented excellent effect, and is extremely useful in industry.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for producing a TiC sintered body of the present invention.

FIG. 2 is a graph collectively showing the results of Examples of the present invention.

FIG. 3 is a graph collectively showing the results of the examples of the present invention.

[Explanation of symbols]

 1: crucible 2: carbon heater B: molding mixture (compacted green body) C (A): mixture

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsuyuki Oyanagi 1-5 Yokoya, Seta-Oe-cho, Otsu, Shiga Prefecture Inside Ryukoku University (72) Inventor Takeshi Ken Sakuma 1 Matsuyama-cho, Moka-shi, Tochigi Sensen Metal Industry Co., Ltd. In-house (56) References JP-A-63-190778 (JP, A) JP-A-63-277578 (JP, A) JP-A-60-246271 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C04B 35 / 56,35 / 64,38 / 00

Claims (2)

(57) [Claims] 1. A mixture of a metal Ti powder and a carbon powder is compacted, a mixture of the Ti powder and the carbon powder is filled around the obtained compact, and the latter mixture is ignited for combustion. A method for producing a porous TiC sintered body, characterized by sintering under no pressure by a sintering method without a sintering aid. 2. A compact of a mixture of a metal Ti powder and a carbon powder blended with at least a part of a TiC powder is compacted, and a mixture of the Ti powder and the carbon powder is filled around the obtained compact. A method for producing a porous TiC sintered body, characterized in that the latter mixture is ignited by a combustion sintering method without sintering by igniting the mixture under non-pressure.