JPH0798702B2 - Method for manufacturing ceramic structure - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a ceramic structure having excellent heat insulating properties.

(Prior Art) Conventionally, silicon nitride ceramics have been widely used in various industrial fields because of their excellent high-temperature strength, heat resistance, impact resistance, and the like. When this silicon nitride ceramic is applied as a component exposed to high temperature such as an engine component for a vehicle such as an automobile, a particularly excellent heat insulating property is required.

Therefore, as a means for further improving the heat insulating properties of the ceramic, for example, by forming a porous layer in the ceramic,
It is also conceivable to use a ceramic and another member such as a metal together to form an air layer between them, or to coat the surface of the ceramic with a heat insulating material.

On the other hand, as disclosed in, for example, Japanese Unexamined Patent Publication No. 59-6303, a silicon nitride ceramic surface is irradiated with, for example, a CO ₂ laser beam to generate silicon, and then neutralized with argon gas or the like. By heating above the melting point of silicon in an atmosphere to melt the silicon generated on the ceramic surface, a surface layer of silicon and an impregnated layer are formed on the surface of the ceramic, which results in oxidation resistance and airtightness of the ceramic. It is known to try to improve.

(Problems to be Solved by the Invention) However, in the case where the above-mentioned conventional porous layer is formed, the strength is lowered, and it is difficult to employ it, for example, in an engine part or the like. Further, in the case where an air layer is formed between the metal member and the like, there is a problem in the sealing property, and the contact area between the two becomes small due to the presence of the air layer, and the holding strength of the metal member, etc. is reduced. Therefore, the use as a structural material is limited. Further, the heat-insulating material coated has a problem that the heat-insulating material peels off due to the low adhesive strength of the heat-insulating material to the ceramic, and the peeling phenomenon is remarkable especially in the case of a ceramic structure having a recess. Therefore, the shape of the ceramic structure and the layer thickness of the heat insulating material are limited, which is not practical.

On the other hand, a ceramic surface layer and an impregnated layer formed on the surface of the ceramic as in the above publication can improve the oxidation resistance and airtightness of the ceramic as described above, but are expected to be improved in heat insulation. Can not.

The present invention has been made in view of such a point, and the purpose thereof is to adopt an irradiation means using a laser beam as described above, and by performing irradiation of this laser beam in a specific atmosphere, An object of the present invention is to efficiently manufacture a ceramic structure having a further excellent heat insulating property by forming a layer having a low thermal conductivity on the surface of a silicon nitride ceramic base material.

(Means for Solving the Problems) In order to achieve the above object, the solution means of the present invention is to irradiate a surface of a silicon nitride ceramic base material with a laser beam in an oxidizing atmosphere to thereby make the surface of the ceramic base material. A compound compound layer of the above-mentioned sintering aid and silicon oxide is formed on the surface of the ceramic base material by producing silicon oxide and reacting the silicon oxide with the sintering aid in the ceramic base material. And

(Operation) According to the manufacturing method of the present invention having the above structure, when the surface of the silicon nitride ceramic base material is irradiated with the laser beam in the oxidizing atmosphere, silicon oxide is generated on the surface of the ceramic base material, and the oxidation is performed. When silicon reacts with the sintering aid in the ceramic base material, a composite compound layer of the sintering aid and silicon oxide is formed on the surface of the ceramic base material. This composite compound layer has a characteristic that the thermal conductivity thereof is lower than that of the ceramic base material, whereby a ceramic structure having a further excellent heat insulating property can be obtained. Moreover, since the composite compound layer having a low thermal conductivity is formed only by irradiating the laser beam in the oxidizing atmosphere without heating at a high temperature for a long time, the ceramic structure can be efficiently obtained.

(Example) Hereinafter, the manufacturing method of the ceramic structure which concerns on this invention is demonstrated based on drawing.

According to the method of the present invention, the surface of a silicon nitride (Si ₃ N ₄ ) based ceramic base material is irradiated with a laser beam such as a CO ₂ laser beam in an oxidizing atmosphere so that the surface of the silicon base material (Si ₃ N ₄ ) is exposed.
O ₂ ) is produced and the silicon oxide (SiO ₂ ) is reacted with the sintering aid in the ceramic base material, whereby the sintering aid and silicon oxide (Si-O ₂ ) are formed on the surface of the ceramic base material. ) And a composite compound layer are formed.

The oxidizing atmosphere is, for example, in the air, but oxygen may be used together as an assist gas.

As the sintering aid, yttrium oxide (Y ₂ O ₃ ), magnesium oxide (MgO), zirconium oxide (ZrO ₂ ),
An oxide-based sintering aid such as aluminum oxide (Al ₂ O ₃ ) is used.

The composite compound layer is, for example, a layer of MgO.SiO ₂ when the sintering aid is magnesium oxide (MgO),
When the sintering aid is yttrium oxide (Y ₂ O ₃₎ of Y ₂
It is a layer of O ₃ · SiO ₂ and the sintering aid is zirconium oxide (Zr
O ₂ ), it is a layer of ZrO ₂ · SiO ₂ , and when the sintering aid is aluminum oxide (Al ₂ O ₃ ), Al ₂ O ₃ · SiO ₂
Layers. The composite compound forming these layers has a characteristic that the thermal conductivity is lower than that of the above silicon nitride (Si ₃ N ₄ ), and for example, the thermal conductivity of silicon nitride (Si ₃ N ₄ ) is about
0.04 cal / cm · sec · ° C, while the above MgO / SiO ₂
0.006cal / cm ・ sec ・ ℃, 2MgO ・ SiO ₂ 0.008cal / cm ・ sec
・ ℃, ZrO ₂・ SiO ₂ is 0.012cal / cm ・ sec ・ ℃, Al ₂ O ₃・ SiO
₂ is 0.01 cal / cm · sec · ° C.

Thus the layer made of silicon nitride (Si ₃ N ₄₎ system such as the above complex compound on the surface of the ceramic matrix is formed, the silicon nitride in an oxidizing atmosphere (Si ₃ N ₄₎ type of ceramic matrix When the surface is irradiated with a laser beam, the Si
Part of the ₃ N ₄ particles sublime to form free silicon (Si) particles, and the Si particles easily become silicon oxide (SiO ₂ ). On the other hand, magnesium oxide (MgO), which is the oxide-based sintering aid in the grain boundary of Si ₃ N ₄ particles, is activated by the laser beam irradiation and is in a slightly molten state. Silicon oxide (SiO ₂ ) and magnesium oxide (MgO), etc. which have been converted to each other are chemically bonded to each other, and thus M
It seems to form a complex compound such as gO / SiO ₂ .

Next, the method for producing a ceramic structure in which a layer made of the complex compound such as MgO.SiO ₂ is formed on the surface of a silicon nitride (Si ₃ N ₄ ) ceramic base material will be described in more detail.

First, silicon nitride (Si ₃ N ₄ ) powder containing 91% α-type Si ₃ N _{4 and} having an average particle size of 0.7 μm was added to yttrium oxide (Y
₂ O ₃ ) and magnesium oxide (MgO) having an average particle size of 0.8 μm are mixed so that the composition ratio is Si ₃ N ₄ : Y ₂ O ₃ : MgO = 90: 5: 5 in weight%. Then, after mixing and pulverizing this mixture, it is sintered by hot pressing under the conditions of a sintering temperature of 1600 ° C., a sintering time of 1 hour and a pressing pressure of 200 kg · f / cm ² , and a density of 3.24 kg / cm ² . A dense sintered body was obtained.

Next, this sintered body was processed into a size of 30 × 30 × 10 mm to form a sample 1 (shown in FIG. 1), and a CO ₂ laser beam was emitted to the surface of the sample 1 in the atmosphere at 2.0 Kw, Processing speed 1000 mm / mi
n, focal length 127 mm, defocus amount + 50 mm, and at the same time, oxygen as an assist gas is ejected at a pressure of 1.5 kg / cm
² , the ejection rate was 50 / min, and the surface of the sample 1 was machined to have a width of 30 mm and a machining depth of 500 μm.

After that, as shown in FIG.
Was adhered to the aluminum alloy plate-shaped member 2 processed to the same size as the sample 1 without any gaps, and then the thermocouples 3 and 3 were attached to the central portions of the sample 1 and the plate-shaped member 2, respectively.
Moreover, a heater 4 with an output of 80 W was further attached to the sample 1 side, and the whole thereof was covered with a heat insulating material (not shown) to prevent the heat of the heater 4 from being dissipated. And. It was examined how the heat of the heater 4 was transferred to the aluminum alloy plate-shaped member 2 while the heater 4 was kept constant at 400 ° C. for a predetermined time by the control of the power controller 5. In FIG. 1, 6 is an AD converter for converting the electromotive force of the thermocouples 3, 3 into an electric signal, and 7 is a microcomputer for measuring the temperature change based on the electric signal of the AD converter 6.

The data at that time are shown in FIG. 2 together with the data of another sample not irradiated with the CO ₂ laser beam as a comparative example. In the figure, those marked with Δ are the surface temperature of the sample 1 according to this example, those marked with □ are the surface temperatures of the sample according to the comparative example, and those marked with ○ are the heater 4 Surface temperatures are shown respectively. Then, as is clear from this data, when the heater 4 is kept at 400 ° C. for 20 minutes after the heating is started, the temperature rise degree of the present embodiment is lower than that of the comparative example, and the present embodiment It can be seen that the example has better insulation properties.

This means that when the surface of the sample 1, that is, the surface of the silicon nitride (Si ₃ N ₄ ) ceramic base material is irradiated with a laser beam in an oxidizing atmosphere, some of the Si ₃ N ₄ particles in the irradiated part sublime and become free. Silicon (Si) particles are formed, and while these Si particles easily become silicon oxide (SiO ₂ ), magnesium oxide (MgO), which is the above oxide-based sintering aid at the grain boundary of Si ₃ N ₄ particles, etc. Are activated by the irradiation of the laser beam and are in a molten state to some extent, and the activated silicon oxide (SiO ₂ ) and magnesium oxide (MgO) are chemically bonded to each other, and the thermal conductivity of Low MgO ・ SiO ₂ , 2MgO ・ SiO ₂ ,, Y ₂ O ₃・ S
This is probably due to the formation of complex compounds such as iO ₂ . And, for example, the thermal conductivity of MgO.SiO ₂ is 0.0
At 06 cal / cm ・ sec ・ ° C, about 0.04 cal / cm ・ sec ・ ° C of Si ₃ N ₄
It is as low as about 1/7 of that of the above. Therefore, even if about 50% of MgO / SiO ₂ is generated in the processing depth of 500 μm, it will have a thermal resistance equivalent to about 2 mm of Si ₃ N ₄ based ceramic. As shown in the figure, it can be expected to improve the heat insulation property by about 10%.

Further, the above-described manufacturing method is a simple means of irradiating a CO ₂ laser beam, so that, for example, as compared with the case where a composite compound layer made of MgO / SiO ₂ or the like is formed by heating and reacting at a high temperature for a long time, Silicon nitride (Si
It is possible to efficiently manufacture ₃ N ₄ ) -based ceramic structures.

In addition, although oxygen is used as the assist gas in the above embodiment, the present invention is not limited to this, and it is also possible to use, for example, the atmosphere.

(Effects of the Invention) As described above, according to the manufacturing method of the present invention, a sintering aid can be formed by a simple method of irradiating the surface of a silicon nitride ceramic base material with a laser beam in an oxidizing atmosphere. It is possible to efficiently manufacture a ceramic structure having excellent heat insulating properties, which has a layer having a low thermal conductivity which is a composite compound with silicon oxide.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a measuring device for explaining the procedure for measuring the heat conduction characteristics of a ceramic structure, and FIG. 2 is data showing the heat conduction characteristics of the ceramic structures in the present example and comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-55-109286 (JP, A) JP-A-62-30679 (JP, A) JP-A-62-252388 (JP, A)

Claims (1)

[Claims] 1. A surface of a silicon nitride ceramic base material is irradiated with a laser beam in an oxidizing atmosphere to generate silicon oxide on the surface of the ceramic base material and a sintering aid in the silicon oxide and the ceramic base material. A method of manufacturing a ceramic structure, comprising forming a composite compound layer of the above-mentioned sintering aid and silicon oxide on the surface of a ceramic base material by reacting with.