JPS6340771A - Normal pressure high density composite sintered body of cubic boron nitride and manufacture - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to an atmospheric pressure high-density composite sintered body of hexagonal boron nitride (hereinafter referred to as "boron nitride"), a metal nitride, and a metal oxide, and a method for manufacturing the same. Regarding.

The high-density composite sintered body of boron nitride obtained here has heat resistance,
Its performance is demonstrated in fields where thermal shock resistance, lubricity, or corrosion resistance are required.

BACKGROUND OF THE INVENTION Boron nitride is a ceramic material with many excellent properties, including excellent thermal, chemical, and electrical properties, lubricity, and ease of machining. That is, it is thermally stable up to approximately 3000 t:' in an inert atmosphere, has extremely high thermal conductivity and high thermal shock resistance, and has chemical stability such as being difficult to wet with molten metal and not reacting. It has excellent properties and has a wide range of uses as a heat-resistant and corrosion-resistant material.

In addition, it has excellent lubricity in addition to thermal stability, making it a valuable material as a high-humidity lubricant.

Furthermore, it has an extremely high electrical resistance and does not change much even at high temperatures, making it an electrically insulating material that can be used over a wide temperature range.

However, although boron nitride has excellent thermal and chemical properties, it is difficult to burn and requires high temperature and mechanical high pressure treatment to produce a sintered body. A method of heating and sintering at a temperature around 2 DOOC using a high-frequency induction heating furnace while pressurizing with Alkaline earth metal borates in the body, such as Mda0・B2O3,0cLO・
Several percent of B2O3, SrO, B2O3, etc. as a binder
It is mixed with 10% from

Problems to be Solved by the Invention As mentioned above, the production of conventional sintered bodies requires high temperature and mechanical high pressure treatment, which makes it difficult to improve productivity.
In addition, because high mechanical pressure is required, only molded objects with simple shapes can be manufactured, and various shapes can be produced from simple molded objects. Making it takes time and effort in post-processing, and there is also a large amount of material loss.

The loss of expensive materials leads to a significant increase in the cost of producing sintered bodies.

In addition, manufacturing a large sintered body requires increasing the size of the sintering furnace and graphite die, and it is technically not easy to manufacture a large graphite die material in particular.

Furthermore, since the sintered body contains alkaline earth metal borates, there are the following problems. For example, even with boron nitride, which is stable up to around 3000 tons in an inert atmosphere, in a sintered body containing a large amount of binder phase such as alkaline earth metal borate, the binder phase will blow out from a temperature of more than 100 degrees At present, the temperature at which the boron nitride can be used is severely limited because it reacts with other materials, pollutes the surrounding area due to volatilization of the binder phase, and cracks occur in the boron nitride sintered body itself.

Therefore, there is a strong demand for the development of a boron nitride composite sintered body that can be fired at normal pressure and does not have the above-mentioned drawbacks due to the inclusion of alkaline earth metal borates.

Means to solve the problem: The need for mechanical high-pressure treatment during sintering severely limits the shape of the compact, so pressureless sintering makes it possible to produce a composite sintered body for practical use. and 0CL
As a result of various studies on ways to minimize the use of OO5, etc., we found that by using a specific boron nitride, compounding it with metal oxides and metal nitrides, and increasing the density of the green compact, we succeeded in atmospheric pressure sintering. The present invention was completed based on the discovery that a sintered body with sufficient density and strength could be obtained using the following method.

That is, the present invention contains hexagonal boron nitride, at least one of metal nitrides and metal oxides, and has a bulk density of 70% of the theoretical density.
The above atmospheric pressure high density composite sintered body of hexagonal boron nitride and the highly packed hexagonal boron nitride powder having a vibration method bulk density of at least 0.5 y-/d are combined with a metal powder capable of forming nitrides. The above-mentioned high-density composite sintering method is characterized in that at least one metal oxide or at least one metal oxide is mixed and the former is sintered in a non-oxidizing nitrogenous atmosphere, and the latter is sintered under normal pressure in an inert atmosphere. This invention relates to a method for producing a solid.

The details of the invention will be explained below.

Boron nitride powder is generally heated in ammonia gas with boric acid anhydride or borax, or mixed with a nitrogen-containing organic compound that generates ammonia gas and heated, and the resulting boron nitride ff1F is heated again at high temperature in a nitrogen atmosphere. The product is heated to increase crystallinity.

The commercially available boron nitride powder thus obtained usually has a crystal size exceeding 1 .mu.m, and the crystal growth is insufficient, and the vibration method bulk density is 0.1 to 0.6%/cIIt.

The vibration method bulk density is the filling density obtained by placing a 4001 sample into a graduated cylinder, and measuring the volume after vibrating filling for 180 seconds using a vibrating SS type DE-2 manufactured by Tsukiyama Scientific Instruments.

Using such boron nitride powder, boron nitride composite sintered body 2
When I produced the product, the density of the raw compact did not increase during the molding stage, and when I tried to forcefully increase the density by applying high pressure, cracks occurred in the compact during the molding or firing stage, and a satisfactory sintered body could not be obtained.Q We believed that in order to increase the density of a sintered body, it was first necessary to increase the density of the green compact, and as a result of various studies, we created a highly filling boron nitride that was obtained by increasing the crystal size and adjusting the particle size distribution. It has been discovered that a molded body with high green density can be easily obtained by using powder as a raw material, and that a sintered body with high density can be obtained by firing this at normal pressure.

One method for obtaining highly packed boron nitride powder is to first heat boron nitride in the presence of a specific substance to grow crystals. For example, if commercially available boron nitride powder is made into briquettes by adding fluoride to it and heated to 1700C or higher in a nitrogen atmosphere, the crystal size will be several 1 Dμ.

Next, this? Pulverize with a pulverizer such as a roll mill or a ball mill to obtain particles with a particle size ranging from 100 to several microns and an average diameter of 10 to several microns.
By adjusting the particle size to 20μ, the bulk density of the oscillation method is at least 0.5 P/d, and if the average particle size is 60 to 40μ in the particle size range of 200 to several μ, the bulk density is 0.85'.
/7 or more. As mentioned above, the filling property of powder is determined by the crystal size, particle size, distribution thereof, etc., and the above-mentioned processing method is an example of obtaining a powder with high filling property. For example, by adjusting the particle size of processing waste from a boron nitride hot press molded body, it is possible to obtain a powder with a desired filling property.

Next, we will discuss a method for manufacturing a normal-pressure high-density composite sintered body of boron nitride.

When manufacturing a composite sintered body of metal nitride and boron nitride, for example, silicon,
After mixing and forming metal powder that can produce nitrides such as aluminum and titanium, nitrogen or nitrogen? The metal powder is fired in a non-oxidizing atmosphere containing nitrogen, and the metal powder is bonded with nitride produced by reacting with nitrogen. The metal powder used here is 100μ
It is as fine as the following, preferably about 40 μm or less.

The mixing ratio of metal powder to boron nitride is determined by the use of the sintered body to be manufactured, and the ratio of metal powder should be lowered for applications that make the best use of the properties of boron nitride, especially lubricity, corrosion resistance, and thermal conductivity. Therefore, for applications where strength is required, the proportion of metal powder can be increased to strengthen the bond.Practically speaking, it is preferable that boron nitride be 60 to 85% by weight of the mixed powder. .

The premixing of boron nitride and metal powder may be done either dry or wet. Organic binder and dispersion medium in mixed powder? After addition and kneading, the mixture is once dried to form granules, and then molded into a predetermined shape by molding, rubber pressing, or a combination thereof.

In order to increase the molding density It is preferable to pressurize at 1000 kp/7 or more.

Of course, as long as the green density can be sufficiently increased, the method is not limited to the pressure molding method, and any method such as slip casting or extrusion can be used.

After removing the organic binder, the resulting green body is fired in nitrogen or a nitrogen-containing atmosphere to react with the metal powder and form a sintered body. In this case, normal pressure firing may be used.

It is necessary to select the firing temperature and atmosphere depending on the metal to be mixed. For example, in the case of silicon, nitrogen or ammonia or a combination thereof must be selected in the atmosphere.
The temperature is raised to 1400 to 1500 C at a rate of 100 C/hr and fired for 2 to 10 hours.

The rate of temperature increase is determined by the blending ratio of 31 and the size of the molded body, and although the blending ratio of Si is high and the size of the molded body is large, the rate of temperature rise needs to be slow.

In this manufacturing method, it is important to mix the metals, shape them, and then nitride them. Even if the metals are mixed and sintered after being nitrided in advance, the density will not increase and high strength will not be obtained.

Next, a method for manufacturing a composite sintered body of metal oxide and boron nitride will be described. In this case, the above-mentioned highly filled boron nitride powder is mixed with an oxide such as a mono-oxide such as silica, alumina, or zirconia, or a composite m-oxide powder such as murai and spinel, or a combination thereof. After molding, it is fired in nitrogen, a non-oxidizing atmosphere containing nitrogen, an inert atmosphere, or a combination thereof to bond boron nitride with an oxide to form a sintered body. In this case as well, normal pressure firing may be used.

The purity of the oxide used here does not matter, but it is preferable that the squid grain size be as fine as possible, and an oxide powder is selected that has properties that allow sufficient bonding even at a firing temperature of about 1600C. Specifically, it is necessary to use powder P with an average particle diameter of several microns to submicrons. In the case of oxides, it is not possible to mix and form metals and then oxidize them. The reason for this is that boron nitride itself is oxidized.

The reason for choosing oxide powder 3, which can be sintered at a firing humidity of about 16ooC, is that if the firing temperature is low, a special furnace is required for sintering, and the energy cost is also high. This is because if the temperature is increased, the boron nitride composite sintered body becomes bulky and the density may be lowered.

The blending ratio of oxide powder to boron nitride is determined by the use of the sintered body to be manufactured. Lubricity, which is a characteristic of boron nitride,
For applications that take advantage of corrosion resistance and thermal conductivity as much as possible, the ratio of oxide powder should be lowered, and for applications that require strength, the ratio of oxide powder can be increased to strengthen the bond. . Practically speaking, it is preferable that boron nitride accounts for 70 to 95% by weight of the mixed powder.

The conditions of the method for mixing and molding boron nitride and oxide powder are almost the same as in the case of the metal nitride bonded boron nitride sintered body described above.

As mentioned above, the normal pressure high density composite sintered body of hexagonal boron nitride obtained by the method of the present invention has a bulk density of 70% of the theoretical density.
As described above, the sintered body satisfies the conditions normally required for practical use.

The theoretical density of the above-mentioned composite is determined as follows. That is, when the composite is composed of A and B, the true specific gravity of A is α, the true specific gravity of B is b, and A in the rL3 sintered body
The theoretical density of the composite is α+(1-n)h.

This theoretical density and relative density have the following relationship.

Effect In the present invention, the vibration method bulk density is at least o, sy
By using highly filled outer hexagonal boron nitride, which is 'Crd, high-pressure firing is not required as in the past, and high-density and high-strength boron nitride composite sintered bodies can be produced by normal pressure firing! I
IS! It became possible to send For this purpose, it is possible to form a complex shaped molded body without post-processing, and there is no loss due to post-processing. Furthermore, the sintering furnace and graphite die do not need to be particularly large, and the practical effect is very large. Calcium carbonate, magnesium carbonate,
Barium carbonate and calcium fluoride were added and mixed. This was pressure-molded with p/d Te in K1000, placed in a graphite crucible, inserted into a high frequency heating furnace, and heated with 2CI while flowing nitrogen gas.
It was baked for 2 hours at I:lot::. After cooling, the molded product taken out from the furnace was ground in an alumina ball mill and sieved through a 40-mesh sieve. The particle size of the obtained boron nitride powder was 200 μm or less, the average particle size was 38 μm, and the vibration method bulk density was 0.89 P/cr/L.

40% by weight of silicon powder with an S1 content of 98% by weight or more and an average particle size of 2μ was mixed with 60% by weight of the highly filled boron nitride powder obtained in this way, and the mixture was processed in an alumina ball mill for 1 hour. Mixed. An organic binder and an organic solvent were added to this mixed powder, and the mixture was further kneaded in a ball mill for 1 hour.

The obtained slurry was dried to form granules. Next, this was once preformed with a mold at 300kp/cr/l, and then 2000kp/cIf using a rubber press.
Molded with. Insert the molded body into an electrically heated closed furnace and heat it with nitrogen gas. 150 at a rate of 50C per hour at normal pressure while flowing.
The temperature was raised to 0C and held for 5 hours, then cooled in the furnace and taken out.

The density of the obtained sintered body was 2.15547 d (relative density 78%). Test piece cut out from the sintered body (3
The 6-point bending strength of X4X35+n) is 450 to 490 k
g/Crd.

Ratio Soft Example 1 A boron nitride composite sintered body was produced in the same manner as in Example 1, except that commercially available boron nitride powder having a vibration method density of 0°27 fi'/cI/l was used. The density of the obtained sintered body was 1.81/m (relative density: 65%). Example 1
The three-point bending strength of the test piece obtained in the same manner as 235/
It was Cr11.

Examples 2 to 6 Sintered bodies were produced in the same manner as in Example 1 using the same highly filled boron nitride powder and silicon powder as in Example 1 but with different blending ratios. Table 1 shows the density and strength of the obtained sintered body.

Table 1 Example 7 60% by weight of the same highly filled boron nitride powder as in Example 1 was mixed with 40% by weight of aluminum powder having an average particle size of 5 μm, and the mixture was molded and fired in the same manner as in Example 1.

The density of the obtained sintered body was 2.07 P/m (relative density 75%). A test piece cut out from the sintered body (3X
The three-point bending strength of the 4X35 fight is 562, f! /crI
Met.

Example 8 Highly filled boron nitride powder obtained in the same manner as in Example 1.
5% by weight of high-purity mullite powder with an average particle diameter of 0°2μ was mixed in a ball mill for 1 hour, and then
Add an organic binder aqueous solution and further mill in a ball mill.
Kneaded for hours.

The resulting slurry was dried and made into granules. Next, this was once preformed using a mold at 300kf/7, and then molded using a rubber press at 2000kf/Cd. The molded body was inserted into an electrically heated closed furnace, and the temperature was raised to 1500 tr at a rate of 15 DC per hour under normal pressure while flowing nitrogen gas, held for 5 hours, cooled in the furnace, and taken out.

The density of the obtained sintered body was 1.875'/d (relative density 8
1%]. A test piece cut out from the sintered body (3X
4 x 35 yr) 3-point bending strength is 178ks
+/m.

Claims (4)

[Claims] (1) An atmospheric pressure high-density composite sintered body of hexagonal boron nitride containing at least one of a metal nitride and a metal oxide, and having a bulk density of 70% or more of the theoretical density. (2) At least one of metal oxides and metal nitrides contains 60%
% or less by weight of hexagonal boron nitride as claimed in claim 1. (3) Bulk density by vibration method is at least 0.5 g/cm^3
A conventional method for producing hexagonal boron nitride, which is characterized in that a highly packed hexagonal boron nitride powder is mixed with at least one metal powder capable of forming nitrides, and the mixture is sintered at normal pressure in a non-oxidizing nitrogen atmosphere. A method for producing a compressed high-density composite sintered body. (4) Bulk density by vibration method is at least 0.5 g/cm^3
Atmospheric pressure high-density composite sintering of hexagonal boron nitride characterized by mixing at least one kind of metal oxide powder with highly packed hexagonal boron nitride powder and sintering the mixture at normal pressure in an inert atmosphere. Method for producing solids.