JP2849606B2 - Gas phase impregnation method and its apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to producing a dense body having excellent mechanical properties by depositing a matrix component in a void of a porous molded body by a gas phase method. The present invention relates to a phase impregnation method and an apparatus for producing the same.

(Prior art) In recent years, as high-strength materials or high-temperature materials, ceramics such as non-oxide ceramics such as silicon nitride, silicon carbide, and sialon or oxide ceramics such as aluminum oxide and zirconium oxide have been used instead of conventional metal materials. Has attracted attention, and various types of research and development have been conducted.
Silicon nitride, silicon carbide and the like are being applied to high temperature mechanical parts such as gas turbine parts and diesel engines due to their excellent mechanical properties and high temperature properties.

However, the above-mentioned ceramics are all known as brittle materials, and are not reliable because they are destroyed by small defects, which hinders their application to structural materials that require high strength. That is the current situation.

To solve such problems, research and development of so-called fiber-reinforced ceramics, which add toughness to the ceramics itself by mixing whiskers, carbon fibers, and other inorganic fibrous substances into the ceramics, have been actively conducted. I have.

Specific examples of the fiber-reinforced ceramic include a ceramic powder obtained by adding an inorganic fibrous substance to a ceramic powder and firing the same, a ceramic obtained by depositing a specific ceramic on the surface of a reinforcing fiber by a chemical vapor deposition method (CVD method), or A so-called chemical vapor impregnation method (Chemical Vapor Infiltr) in which a specific ceramic is deposited as a matrix component in a void portion of a molded body composed of reinforcing fibers by a vapor phase method (CVD method).
ation) are known.

Among them, those obtained by the gas phase impregnation method are particularly noted as being capable of obtaining a material having extremely excellent toughness as compared with others, for example, Am. Ceram.Soc.Bull., 6
5 [2] 345-50, 1986, proposed by Davad P. Stenton et al.

Thus, this conventional method is shown in FIG. The apparatus used here is basically a porous molded body 21, a holder 22 for holding the porous molded body 21, a gas inlet 23 for introducing a matrix forming gas, a heater 24 and the above. It comprises a water cooling jacket 25 for cooling one side of the support means. According to this device, a high-temperature region is formed by the heating means 24, and the porous molded body 21 is arranged together with the holder 22 in this high-temperature region. When a matrix-forming gas is introduced into the porous molded body 21 through the gas inlet 23, matrix components are precipitated in voids inside the molded body. However, when the compact exists in the complete heat equalizing region, the compact precipitates on the surface of the compact 21 before the inside of the compact, and the matrix cannot be deposited inside the compact 21. So, with this method,
The gas inlet side of the molded body 21 is cooled by a water cooling jacket 25 to a low temperature to form a temperature gradient inside the molded body 21, and a matrix is gradually deposited from a lower portion of the molded body 21 to form a molded body. The matrix is deposited on the entire 21.

(Problems to be Solved by the Invention) However, a water cooling jacket 25 for cooling one side of the molded body 21 to form a temperature gradient inside the molded body 21
In the method using cooling means such as the above, there is a limit in the configuration of the apparatus itself, and even when considering cooling one side uniformly, it is only possible to obtain a compact molded article having a simple shape such as a disk or a flat plate. It could not be applied, and it was almost difficult to produce a product having a complicated shape or a large shape. In addition, when the matrix is deposited on a large molded body when the temperature in the furnace is soaked, there is a problem that the precipitation on the surface portion occurs preferentially, so that it cannot be deposited inside the molded body. there were.

(Means for Solving the Problems) The present invention has been made by repeatedly studying the above problems,
By forming a temperature gradient in the furnace and the molded body by controlling the heating means, a region where matrix components can be precipitated and a region where matrix is not precipitated are formed in the furnace, and the porous molded body is moved from the non-precipitated region to the precipitation region. The molded body is supported so as to be able to move to an arbitrary position in between, and the matrix component can be precipitated in the voids of the molded body while moving the molded body to the precipitation area, thereby eliminating the need for any cooling means. We have found that matrix components can be uniformly deposited on the inside and on the surface of large-sized and complex-shaped molded products.

That is, in the gas phase impregnation method of the present invention, a porous molded body is placed in a reaction furnace, and a matrix forming gas is passed through the molded body, and at the same time, the molded body is heated by heating the molded body. In a gas phase impregnation method of depositing a matrix component in a void, a matrix component deposition region and a matrix component non-precipitation region are formed in the furnace, and the molding is performed while moving the compact from the non-precipitation region to the deposition region. The present invention is characterized in that a matrix component is precipitated in a void of a body.

Further, the gas phase impregnation apparatus of the present invention comprises a porous molded body, a means for holding the molded body, and a gas introduction for introducing a matrix forming gas into a void of the molded body. Means for introducing a gas into the molded article, and simultaneously heating the molded article to a predetermined temperature by the heating means to precipitate a matrix component in the voids of the molded article. In, while controlling the heating means so that a matrix component precipitation region and a matrix component non-precipitation region are formed in a specific region in the reaction furnace, the molded body is the matrix non-precipitation region and the matrix precipitation region The holding means is movable so that it can be moved between the holding means.

(Example) Hereinafter, an example of a manufacturing method and a manufacturing apparatus of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 is a schematic diagram of a gas-phase impregnation apparatus according to the present invention. According to FIG. 1, a porous molded body 1 is placed in a reaction furnace A.
Are supported by the holder 2.

The holder 2 itself is formed of a cylindrical body made of a heat-resistant substance such as graphite, and the molded body 1 is supported at an upper portion of the cylindrical body. A gas introduction pipe 3 for introducing a matrix forming gas from outside the reaction furnace is introduced inside the holder 2, and the inside of the holder 2 is substantially sealed from the outside by a seal 4. Further, the holder 2 is connected to a table 5 installed outside the reactor 1 and driven up and down by a motor (not shown).
The holder 2 and the molded body 1 are also configured to be able to move up and down in the reaction furnace by moving the table 5 up and down.

On the other hand, heaters 6a, 6b, and 6c that can independently control the temperature of each part of the furnace are installed on the outer peripheral portion of the inside of the reaction furnace A.

According to this apparatus, the matrix forming gas is introduced into the holder 2 from the gas introduction pipe 3 and then appropriately reacted by heating with a heater while passing through the inside of the porous formed body 1 to precipitate a matrix component. 2 and finally exhausted from an exhaust port 7 provided at the bottom of the furnace.

Next, a method of impregnating a porous matrix with a predetermined matrix component in the gas phase using the above-described apparatus will be described.

First, the temperature of each heater 6 in the above-described apparatus is controlled as follows. According to the present invention, when the respective set temperatures of the heaters 6a, 6b, and 6c are ta, tb, and tc, it is important to control the relationship such that ta> tb ≧ tc. Has the temperature distribution shown in FIG. In FIG. 2, the vertical axis indicates the distance in the length direction of the furnace, and the horizontal axis indicates the temperature at the center of the furnace at each position. At this time, the temperature ta is set so that ta ≧ T with respect to the minimum temperature T at which a matrix component is precipitated from the matrix forming gas by a gas phase reaction.
Thereby, a matrix component precipitation region B is formed near the high temperature side from the intersection of the temperature distribution curve and the temperature T in FIG. 2, and a matrix component non-precipitation region is formed on the low temperature side from the intersection.

Next, FIGS. 3a, 3b, and 3c illustrate a process for precipitating a matrix component in voids in the porous molded body.

First, in the initial step, as shown in FIG. 3a, the table 5 is raised with respect to the matrix component precipitation region B, and the porous molded body 1 supported by the holder 2 is subjected to matrix component analysis from the matrix component non-precipitation region. The porous body 1 is moved to the discharge region B, and is positioned so that the upper portion of the porous molded body 1 reaches the matrix component precipitation region B. At this time, based on the temperature gradient in the furnace, a temperature gradient is formed in the porous molded body 1 in which the gas-side discharge side is higher in temperature than the gas introduction side. When the gas for matrix generation is supplied from the gas introduction pipe, the gas for matrix generation does not react on the low-temperature gas introduction side when passing through the porous molded body having a temperature gradient, and reaches the matrix component precipitation region B. The matrix precipitates in the voids inside the compact above the compact that satisfies the matrix precipitation conditions. Specifically, when the molded body is composed of a fibrous substance, the matrix component is first deposited on the surface of the fibrous body, and the amount of the deposited matrix component is increased to fill all voids of the molded body. Further, the deposited matrix itself becomes a heat transfer medium, and the matrix deposition region moves from the gas discharge side to the gas introduction side.
At this time, if the compact has a small shape, the matrix can be deposited over the entire compact by precipitation of the chain matrix, but heat transfer is limited to a large compact. Therefore, the matrix cannot be deposited to the entire formed body.

Therefore, according to the present invention, as shown in FIG.
Moves to the gas introduction side of the molded body 1, whereby the matrix can be further deposited.

After appropriately raising this table 5, finally the second c
As shown in the figure, the matrix can be deposited on the entire inside of the molded body by locating the matrix precipitation region at the lowermost part of the molded body 1.

The movement of the matrix generation region by the movement of the table 5 can be performed intermittently or continuously according to the deposition rate of the matrix component and the size of the compact.

According to the above-described apparatus and method, as the porous molded body, carbon, a two-dimensional woven fabric made of carbonaceous fibers such as SiC, a laminate of woven fabric, a three-dimensional woven fabric or SiC whisker, Si ₃ N ₄ whisker, Al ₂ A molded body made of ceramic whiskers such as O ₃ whiskers can be adopted, and as a matrix component to be filled in the voids of the porous molded body, silicon carbide, pyrolytic carbon, silicon nitride, sialon, alumina, or the like is applied. You.

Among them, in particular, a porous body made of silicon carbide fiber is impregnated with silicon carbide in a gas phase, whereby a structure having high-temperature strength and high toughness can be produced.

Further, as the fibers constituting the porous molded body, those having an average diameter (short diameter) of 1 to 30 μm are suitable, and those obtained by plain weaving or three-dimensional weaving are suitable. Trichloromethylsilane, silicon tetrachloride, methane, and aluminum trichloride are used as a reaction gas for depositing the matrix, and these gases are supplied by being mixed with a carrier gas such as hydrogen.

The deposition temperature at the time of matrix formation varies depending on the type of matrix to be deposited, but when depositing carbon silicon, it is preferably from 900 ° C to 950 ° C. In this range, β-SiC is deposited and the deposition rate is This is because the control is slow and easy.
At 1150 ° C, high-purity SiC is not generated due to the precipitation of two phases of β-SiC and Si, and at 1200 ° C to 1300 ° C, β-SiC precipitates. Is not sufficiently formed.

Further, the pressure in the reaction furnace is greatly related to the deposition rate of the matrix, and the higher the concentration, the faster the deposition rate. According to this gas phase impregnation method, when the matrix is deposited on the porous molded body, if the speed is too high, a sufficient matrix cannot be formed. Preferably, the pressure is 100 Torr or less. The gas concentration is also a major factor in determining the deposition rate. In particular, it is desirable to mix the above-mentioned predetermined gas in the gas at a ratio of 0.4 to 10% by volume.

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

Example The size of the porous molded body was 100 × 100 × 5 mm,
A carbon fiber long fiber plain weave was prepared. This compact was set on the holder 2 in the vapor-phase impregnation apparatus shown in FIG.

Then, the temperature of the heaters 6a, 6b, 6c is set to 1200 ° C., respectively.
950 ° C and 750 ° C were set. After confirming that the temperature in the furnace was in a uniform temperature state and measuring the temperature distribution in the furnace, the temperature difference between the highest temperature and the lowest temperature was 450 ° C. It was confirmed that the temperature gradient in the molded body was 220 ° C. at the maximum.

Next, the compact 1 is adjusted to the position shown in FIG. 3a with respect to the matrix component precipitation formation region B in the furnace, and contains CH ₃ SiCl ₃ gas at a rate of 1% by volume as a matrix forming gas.
Introducing H ₂ gas into the furnace. At this time, when introducing the reaction gas, the pressure is increased and the inside of the cylindrical holder 2 is 760 Torr and the atmosphere outside the holder 2 is 25 Torr at the boundary of the molded body 1.
And a pressure gradient was formed.

In this state, the reaction is started, and β
A matrix consisting of -SiC was deposited. Following this, the table 5 was gradually and gradually raised to the position shown in FIG. 3b, and finally the compact 1 was controlled to the position shown in FIG. 3c.

As a result, matrix molding was able to be deposited on the entire molded body.

The obtained molded body had a theoretical density ratio of 85%, and as a result of measuring the fracture toughness by the SENB method, it was 21 MPa · m ^1/2 .

Note that the fracture toughness of the conventional SiC monolithic material is about 5 MPa · m ^1/2 .

(Effects of the Invention) As described above in detail, according to the present invention, a matrix generation region is set in a specific region in a furnace, and a porous formed body is supported so as to be vertically movable with respect to this region. By adjusting the position between the porous compact and the matrix generation area according to the size of the compact, the cooling of large compacts and complex compacts can be performed without the need for any cooling means. Can uniformly deposit matrix components on the inside and on the surface. As a result, the production of various structural materials and the like by vapor phase impregnation can be put to practical use, and the field of use can be greatly expanded.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a gas phase impregnation apparatus of the present invention, FIG. 2 is a view showing a temperature distribution in a furnace, and FIGS. 3a to 3c are steps for explaining a gas phase impregnation method of the present invention. FIG. 4 is a schematic view for explaining a conventional gas phase impregnation apparatus. A: Gas phase impregnating device B: Matrix component deposition region 1: Porous molded body 2: Holder 3: Gas inlet 5: Movable table 6a to 6c: Heater

Claims (6)

(57) [Claims] 1. A porous molded body is placed in a reaction furnace, and a matrix forming gas is passed through the molded body. At the same time, the molded body is heated to precipitate matrix components in voids in the molded body. In the gas phase impregnation method, a matrix component precipitation region and a matrix component non-precipitation region are formed in the furnace, and the molded body is moved from the non-precipitation region to the precipitation region while moving into the void of the molded body. A gas phase impregnation method comprising precipitating a matrix component. 2. The gas-phase impregnation method according to claim 1, wherein the porous molded body is made of carbonaceous fiber. 3. The gas phase impregnation method according to claim 1, wherein said matrix component comprises silicon carbide. 4. A method according to claim 1, further comprising the steps of: providing a porous molded body in the reaction furnace; holding means for holding the molded body; gas introducing means for introducing a matrix forming gas into a gap of the molded body; A gas-phase impregnating apparatus, which comprises introducing a gas into the molded body and simultaneously heating the molded body to a predetermined temperature by the heating means to precipitate a matrix component in voids in the molded body; Along with controlling the heating means so that a matrix component precipitation region and a matrix component non-precipitation region are formed in a specific region, the molded body can be moved between the matrix non-precipitation region and the matrix precipitation region. A gas phase impregnation apparatus wherein the holding means is movable. 5. The gas-phase impregnating apparatus according to claim 4, wherein said porous formed body is made of carbonaceous fiber. 6. The gas-phase impregnating apparatus according to claim 4, wherein said matrix component is made of silicon carbide.