JPH05155671A - Silicon nitride structural body - Google Patents

Abstract

PURPOSE:To obtain a silicon nitride structural body having largely improved heat insulating property while maintaining high temp. strength of the whole structural body by constituting both of a dense structural body and a porous structural body of silicon nitride, and making these members into one body. CONSTITUTION:The dense structural body is obtd. by sintering powder or a granular material of silicon nitride in a frame of specified shape at high temp. The porous structural body having 10-70% relative density is obtd. by entangling fibrous silicon nitride (e.g. alpha-silicon nitride whisker) having 0.05-10mum fiber diameter and 0.01-10mm length so as to obtain 90-30% porosity, compounding and mixing a binder (e.g. aluminum oxide) by <=30wt.% to the fibrous silicon nitride, filtering by sucking according to the specified shape, and then sintering. To make the dense structural body and the porous structural body in one body, a cup-like base 1 is formed by using the dense structural body, the porous structural body 2 is fitted to the inside of the base and covered with a plate 3 comprising the dense structural body, and then the base 1 and plate 3 are joined with an adhesive 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride type structure, and more particularly to a silicon nitride type structure excellent in high temperature strength and heat insulation.

[0002]

2. Description of the Related Art Conventionally, much research has been conducted on manufacturing automobile engines and the like from ceramics. In this case, the type of ceramic is changed depending on the engine part so that the excellent characteristics of various ceramics can be fully exhibited. For example, in parts such as pistons, cylinder liners, exhaust valves, turbochargers, etc. that require thermal shock resistance in addition to high temperature strength, silicon nitride ceramics are used, and exhaust manifolds, port liners, etc. Cordureite and aluminum titanate are used in parts that require thermal insulation in addition to thermal shock resistance.

[0003]

In the case of the ceramic engine as described above, it is necessary to improve the heat insulating properties of the piston and the cylinder liner in order to improve the heat insulating property in terms of cooling efficiency. However, the silicon nitride sintered body that made up these pistons has a high thermal conductivity, and since the conventional piston was made of an integral sintered body of silicon nitride, the heat transfer was good and the heat insulation was good. It was not enough in terms of sex. On the other hand, other cordierite, ceramics such as aluminum titanate,
Although it is superior to silicon nitride in terms of heat insulation, it has a problem in mechanical strength at high temperatures and cannot be used for pistons and the like.

Therefore, a technical object of the present invention is to provide a ceramic structure having excellent heat insulating properties and high temperature mechanical strength that can withstand use at high temperatures such as an automobile engine.

[0005]

In order to solve the above technical problems, the present invention provides a silicon nitride structure having a dense structure,
A silicon nitride-based structure integrated with a porous silicon nitride structure having a relative density of 10 to 70% is used as a means.

The dense silicon nitride structure is the same as that which has been conventionally used for a piston of a ceramic engine or the like. For example, a silicon nitride powder or granules are contained in a frame having a predetermined shape. Obtained by sintering at high temperature.

On the other hand, the porous structure having a relative density of 10 to 70% is composed of the same silicon nitride as the dense structure. Therefore, both have the same coefficient of thermal expansion. In this way, the two have the same thermal expansion coefficient because the porous structure is sandwiched between the two upper and lower dense structures and the upper and lower dense structures are joined to each other, such as mullite. For ceramics whose ratio is higher than that of silicon nitride, the porous structure expands more during the temperature rising process during bonding, damaging the dense structure, and adjusting the position during bonding temperature rising. This is because, in the case of being present, cracks may be generated in the porous structure during cooling, or a gap may be formed between the porous structure and the dense structure. On the other hand, when a cordierite material or aluminum titanate having a smaller coefficient of thermal expansion than the dense structure is used as the porous structure, the expansion of the dense structure is higher than that of the porous structure when used at high temperature. This is because a large gap is created between the two. When used in a state where a gap is formed, when an external force is applied to the dense structure, the force is not sufficiently transmitted to the porous structure, which causes damage to the dense structure, which is not preferable. In this respect, when silicon nitride is used as the porous structure, the coefficient of thermal expansion is equal to that of the dense structure, and it is stable up to 1800 ° C. in a nitrogen gas atmosphere. There are few restrictions. In this respect, the cordierite material is 130
There is a problem that in a non-oxidizing atmosphere at 0 ° C. or higher, it reacts and dissolves with the silicon nitride material, and aluminum titanate undergoes reductive decomposition at 1000 ° C. or higher.

The porous structure of the present invention has a relative density in the range of 10 to 70%. This is because if it is less than 10%, sufficient strength cannot be obtained and it becomes poor in practicality as a heat insulating material, and if it is more than 70%, sufficient heat insulating performance cannot be obtained. Therefore, it is preferable that the silicon nitride constituting the same is needle-like or fibrous, unlike the dense structure. This is because when a large number of these needle-like or fibrous strips are entwined with each other and joined to form a predetermined shape,
This is because it is easy to create many pores inside the porous structure to enhance the heat insulating effect, and it is possible to keep the mechanical strength of the obtained porous structure high while maintaining a high mechanical strength as compared with the granular or powdery silicon nitride material. This is because it becomes possible to increase the density.
In the present invention, in order to adjust the relative density within the range of 10 to 70%, it is desirable to set the porosity of the porous structure within the range of 90 to 30%.

The needle-like or fibrous silicon nitride as described above preferably has a wire diameter of about 0.05 to 10 μm and a length of about 0.01 to 10 mm. And, as its kind, for example, α-silicon nitride whiskers, β-
Silicon nitride whiskers, silicon nitride fibers, etc. can be preferably used. Further, in the present invention, it is desirable to use a binder in order to increase the strength of the porous structure. The binder is preferably composed of silicon oxide and at least one selected from aluminum oxide, calcium oxide and rare earth oxide, but may be at least silicon oxide. When making a porous structure, these binders are mixed in a predetermined amount with silicon nitride whiskers or silicon nitride fibers in advance before molding the porous structure, and after mixing well, the mixture is adjusted to a predetermined shape. After suction filtration, it is sintered. By doing so, the binder reacts with the silicon nitride whiskers and fibers to form an oxynitride, and this oxynitride helps the whiskers to bond with each other, or the fibers to secure a predetermined strength. Become. Further, the added aluminum and oxygen atoms form a solid solution in the silicon nitride, which reduces the thermal conductivity of the silicon nitride. When the α-silicon nitride whiskers and β-silicon nitride whiskers are compared, α-silicon nitride whiskers are preferable in terms of heat insulation, but in this case, when forming the porous structure. It is necessary to set the sintering temperature to 1600 ° C or lower. In addition, it is not preferable to add the binder in an amount of 30 wt% or more because a difference in coefficient of thermal expansion with that of silicon nitride occurs.

Next, a method of integrating the dense structure and the porous structure will be described. In the first method, as shown in FIG. 1, the cup-shaped base 1 is formed of a dense structure,
The porous structure 2 is fitted into the inside, and further covered with a plate 3 made of a dense structure, and the base 1 and the plate 3 are made of a bonding agent 4 made of, for example, CaO—SiO ₂ —Si ₃ N ₄ glass. The porous structure 2 is sealed in the dense structure by bonding. In the second method, as shown in FIG. 2, a base 1 composed of a dense structure and a porous structure 2 are directly bonded with a bonding agent 5 composed of, for example, CaO—SiO ₂ —Si ₃ N ₄ glass. Is. In the third method, as shown in FIG. 3, the porous structure 2 protruding from the upper surface of the cup is fitted into the cup-shaped base 1 and the porous structure 2 is hot-pressed to form the base structure 1. It is to be embedded in. The first to third methods may be combined with each other. For example, the base 1 and the porous structure 2 may be joined by the first method, or the second and third methods may be performed. The porous structure 2 may be enclosed in the dense structure using the plate 3 in the method.

[0011]

According to the above-mentioned means, since the porous structure and the dense structure are integrally formed, heat transfer between the porous structure itself and between the porous structure and the dense structure is poor, and As a result, a silicon nitride structure having a large heat insulating effect is obtained. In addition, since the porous structure has the same coefficient of thermal expansion as the dense structure, the porous structure or the dense structure may be cracked due to the difference in thermal expansion between the two at the time of joining and use at high temperature, or between the two. There are no gaps.

[0012]

【Example】

Example 1 80 wt% β-silicon nitride whiskers and 20 wt% silica gel were sufficiently mixed, shaped into a predetermined shape, and fired to obtain a heat insulating material having a porosity of 70%. This heat insulating material has a bending strength of 5 kg / mm ² , a compressive strength of 5 kg / mm ² , and a thermal conductivity of 2 w / mk.
Had the characteristics of. Next, a piston head 6 for an engine as shown in FIG. 4 was produced using the above heat insulating material. The piston head 6 is mounted on the lower flange 7 by fitting a base member 9 as a dense structure into a ring member 8 as a dense structure having a lower flange 7 and placing the base member 9 on the upper surface of the base member 9 in a porous manner. The heat insulating material 10 as a quality structure was placed. Thereafter, the ring member 8 and the base member 9 and the base member 9 and the heat insulating material 10 are bonded to each other with a bonding agent 11 made of CaO—SiO ₂ —Si ₃ N ₄ based glass, and the ring member 8 and The base member 9 and the heat insulating material 10 were fixed. Next, a bonding agent 12 made of CaO—SiO ₂ —Si ₃ N ₄ glass is applied to the entire upper surface of the ring member 8 to be slightly thicker than the height of the heat insulating material 10, and then a plate having a dense structure is formed on the heat insulating material 10. The member 13 was placed, and a predetermined pressure was applied to the plate member 13 under heating to join the peripheral portion of the plate member 13 to the upper surface of the ring member 8. In this case, by applying pressure to the upper surface of the plate member 13 under heating, the bonding agent 12 gradually softens, and the plate member 1
3 gradually falls, but it stops coming down by hitting the heat insulating material 10 evenly, the plate member 13 and the ring member 8 are joined, and the heat insulating material 10 is enclosed inside the dense structure. Becomes

Piston head 6 having such a structure
In the above, no fracture deformation of the ring member 8 and the plate member 13 was observed during the bonding heating, and the heat insulating material 10
There was no problem such as a gap between the plate member 13 and the plate member 13. Further, a load of 5 tons was applied from above the plate member 13 and a repeated fatigue test was conducted.
There were no problems such as peeling damage of the heat insulating material 10 and damage of the plate member 13.

COMPARATIVE EXAMPLE 1 A mullite material was used to produce a heat insulating material made of the same porous material as described above, and a piston head having the same structure as shown in FIG. Each of the ring member, the base member and the plate member was made of the same silicon nitride as the above. Then, when the ring member and the plate member were joined using the same joining agent as described above, the ring member was broken by the thermal expansion of the mullite material.

[0015]

As described above, according to the silicon nitride-based structure of the present invention, both the dense structure and the porous structure are made of silicon nitride, and these are integrated structures. Therefore, while maintaining the high temperature strength of the entire structure, the heat insulating property is significantly improved. As a result, when this silicon nitride-based structure is applied to, for example, a piston of a ceramic engine of an automobile, heat generation in the piston can be suppressed and the cooling efficiency of the entire engine can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view in which a porous structure is enclosed inside a dense structure to form an integrated structure.

FIG. 2 is a cross-sectional view in which a porous structure is joined to a dense structure to form an integrated structure.

FIG. 3 is a cross-sectional view in which a porous structure is embedded in a dense structure to form an integrated structure.

FIG. 4 is a sectional view of a piston head.

[Explanation of symbols]

 1 Base (dense structure) 2 Porous structure 3 Plate (dense structure)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mabuchi Makoto 585 Tomimachi, Funabashi, Chiba Prefecture Sumitomo Cement Corporation Central Research Institute (72) Inventor Hiroshi Suzuki 585 Tomimachi, Funabashi, Chiba Sumitomo Cement Co., Ltd. Central research institute

Claims (3)

[Claims] 1. A silicon nitride-based structure characterized by integrally forming a dense silicon nitride structure and a porous silicon nitride structure having a relative density of 10 to 70%. .. 2. The silicon nitride structure having a porous structure is an aggregate of silicon nitride fine particles formed in a needle shape or a fiber shape, which are bonded by a binder. Silicon nitride-based structure. 3. The binder is composed of at least one selected from aluminum oxide, calcium oxide and rare earth oxides and silicon oxide, and the binder is contained in an amount of 30 wt% or less. The described silicon nitride-based structure.