JPH01131066A - Boron nitride based compact calcined under ordinary pressure - Google Patents

Abstract

PURPOSE:To obtain a boron nitride based compact calcined under ordinary pressure containing BN, Al2O3 and high-silicate glass at a specific ratio, having a relative density of specific value or above and improved shape restriction and productivity as well as high density and strength and good abrasion resistance, thermal shock resistance and corrosion resistance. CONSTITUTION:The aimed boron nitride based compact calcined under ordinary pressure consists of 70-15wt.% BN, 5-75wt.% Al2O and 10-80wt.% high-silicate glass and has >=55% relative density. The above-mentioned high-silicate glass means boron silicate glass existing in the state where the surface of silica particle is coated with a film of boron oxide and is obtained e.g., by the following method: Borate or boron oxide is added at an amount of about 2-10wt.% as B2O3 to SiO2 existing in the ultrafine particle state and the blend is calcined at about 800-1300 deg.C to afford a calcined compact, which is then pulverized and repeatedly calcined at the above- mentioned temperature and pulverized. The above-mentioned boron nitride compact calcined under ordinary pressure is obtained e.g., by blending each raw material at a prescribed ratio, pulverizing the blend under non-oxidizing atmosphere and then molding the powder and calcining the resultant compact.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a pressureless sintered boron nitride molded body.

<Prior Art> Boron nitride (BN) has excellent properties such as electrical insulation, thermal conductivity, corrosion resistance, thermal shock resistance, and lubricity, and is one of the few ceramics that can be easily machined. For this reason, it is widely used in various metal melting containers that require the above-mentioned properties, electrical insulation materials, high-temperature heat transfer materials, and the like.

Since BN is difficult to sinter, BN sintered bodies are generally produced by a hot press (pressure sintering) method. Since this method is carried out at 1500 to 2300° C. and under a pressure exceeding 100 kg/cffl, there are problems in that large-sized products cannot be obtained and it is not suitable for manufacturing complex-shaped products. Moreover, the BN molded bodies currently on the market are expensive because they are first hot-pressed into a cylindrical shape and then machined into the final product shape.

Various pressureless sintering methods have been attempted to solve the above problems, but so far no BN sintered body capable of exhibiting the characteristics of BN has been obtained. For example, JP-A-6
No. 1-132563 attempts to perform sintering by rubber press molding under high pressure and inserting the obtained preform into a graphite mold to restrict free expansion.
In addition to low strength, there are problems in that production efficiency is poor and large-sized products cannot be obtained. Therefore, it is desired to provide a pressureless sintered BN molded body that has the inherent excellent properties of BN, such as electrical insulation, thermal conductivity, corrosion resistance, and thermal shock resistance, and can be manufactured easily and efficiently at low cost. Ta.

<Problems to be Solved by the Invention> The present invention improves the shape constraints and productivity of BN sintered bodies, and provides high density, high strength, and wear resistance, thermal shock resistance, and corrosion resistance that were previously unobtainable. The object is to provide a good pressureless sintered BN molded body.

<Means for Solving the Problems> That is, the present invention provides a method for solving problems in which BN70 to 15% by weight, AN20
It is an atmospheric pressure sintered BN-based molded body having a relative density of 55% or more and consisting of 35 to 75 weight percent high silicate glass and 10 to 80 weight percent high silicate glass.

The present invention will be explained in detail below.

Since it has excellent plastic deformability during preforming, it is easy to obtain a high-density preform.

The AA 203 powder may be a commercially available product, but preferably has a purity of 99.0% or more and an average particle size of 1 μm or less.

A 7!20. The particle size is preferably equal to or finer than that of BN powder because the density and strength of the sintered body are improved.

Next, high silicate glass as used in the present invention means borosilicate glass in which the surface of silica particles is coated with a film of boron oxide. This material is, for example, 5in2 in an ultra-fine state.
The sintered body obtained by adding 2 to 10% by weight of boric acid or boron oxide as 8203 and firing at a temperature range of about 800 to 1300°C is crushed, then fired again at the above temperature range, and crushed. can be obtained by repeating the operation. It exhibits particularly superior water resistance than when ordinary borosilicate glass is included as a component,
As a result, a sintered body with excellent electrical properties and thermal shock resistance is obtained.

The pressureless sintered BN-based compact of the present invention comprises the above BN powder, A
7!203 powder and specially synthesized high silicate glass are mixed to make the final product composition, and the mixture is mixed with 5 tol.
1203 powder and high silicate glass are mixed into the BN powder obtained by pulverizing it until the specific surface area is more than twice that of the obtained one, or A mixture of BN, AN 203, and high silicate glass is pulverized by breaking, shearing, grinding, etc. until the specific surface area becomes more than twice the original size, then molded at a pressure of 2 ton/c♂ or more, and then fired. It can be manufactured by a method.

The molding equipment includes a mold molding machine, a cold isostatic press molding machine (C
A conventional molding machine such as IP) can be used. The molding pressure when using highly crystalline hexagonal BN powder or amorphous BN powder as is is 5 ton/cn! More preferably, it is 7 ton/cJ or more.

At a molding pressure of 5 ton/cJ without grooves, the relative density is 55%.
It becomes difficult to obtain the above pressureless sintered BN-based compact.

On the other hand, when using finely pulverized BN powder or fine powder obtained by mixing and pulverizing obtained raw materials, the molding pressure is 2 tons.
/cut or more, the same effect as above can be obtained. As a crushing device at this time, a conventional crusher such as a ball mill, a vibrating ball mill, an attritor, a Raikai machine, etc. can be used. The pulverization is performed until the specific surface area of the powder becomes at least twice, preferably at least 10 times, the specific surface area of the original powder. If the pulverization is less than twice, it becomes difficult to obtain a pressureless sintered BN-based compact having a relative density of 55% or more.

If pulverization is carried out in an oxidizing atmosphere, boron oxide will be generated, and if the sintered body is sintered, free boron oxide will be present in the sintered body, which will only lead to a decrease in moisture resistance and thermal conductivity. Otherwise, a crank will occur in the sintered body. In this case, by performing a treatment to remove the generated boron oxide, it can be used as a raw material for obtaining the product of the present invention. A method for removing boron oxides is treatment with alcohols such as methanol, ethanol, and glycerin. Specifically, this involves heating a slurry containing alcohol, or washing and filtering with alcohol. If the pulverization is performed in a non-oxidizing atmosphere such as N2 or Ar where boron oxides are not produced, the above-mentioned measures to remove boron oxides are not necessarily required.

When pulverized by the method described above, a pressureless sintered BN-based molded body having a relative density of 55% or more can be obtained without high-pressure molding. This is considered to be because newly formed particle surfaces appeared at the same time as the crystal lattice misalignment and partial amorphization progressed, resulting in a powder activated by a so-called mechanochemical effect. In order to obtain a high-strength pressureless sintered BN-based compact, it is desirable to increase the compacting pressure to make the preform density as high as possible.

Firing is performed in a non-oxidizing atmosphere at 1200-1800°C. When the firing temperature is less than 1200°C, BN grains and B
H grain and i20. Since the high silicate glass is difficult to bond directly, a high-strength pressureless sintered BN-based molded body cannot be obtained. on the other hand,
A7 when it exceeds 1800℃! , 03, high silicate glass causes thermal decomposition and evaporation and loses its original function as an additive.

A non-oxidizing atmosphere at 1,400 to 1,600° C. is preferable, in which a particularly high-strength pressureless sintered BN-based molded body can be obtained.

As the non-oxidizing atmosphere, an inert atmosphere such as He, Ar, N2, etc. is suitable. As the firing device, a Tammann furnace, a resistance heating furnace, a high frequency furnace, etc. are used.

The pressureless sintered BN-based molded body of the present invention produced as described above has a BH of 70 to 15% weight I! 2035~
75% by weight and 10-80% by weight of high silicate glass. If Al2O2 exceeds 75% by weight, the BN content will be relatively reduced and the BH properties will not be exhibited. On the other hand, A
7! , B2O produced by oxidation when 03 becomes 5% by weight
The ability to fix 3 becomes small, and a high-strength sintered body cannot be obtained. When the content of high silicate glass exceeds 80% by weight, the excellent properties of BN such as thermal conductivity and electrical insulation properties are significantly reduced.

In particular, as the temperature at which the molded product is used increases, this tendency becomes even more severe. Note that high silicate glass can be identified by X-rays. Moreover, the sintered body density of the pressureless sintered BN-based molded body of the present invention produced as described above is 55% or more in terms of relative density. If the relative density is less than 55%, it has many pores and is not dense, so bending strength, thermal shock resistance, abrasion resistance, and corrosion resistance do not improve, making it unsuitable for applications such as break rings and continuous casting nozzles.

<Examples> The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these.

Commercially available BN powder (hexagonal crystal, purity 99.0%, specific surface area 6)
n'f/g) to 60 parts by weight of Aβ203 powder (99% purity)
, specific surface area 8 m/g), 20 parts by weight of high silicate glass (10% high purity B2O3 was added to 90% dry process white carbon commercially available as Aerosil, and 11 parts by weight was added in air.
The material obtained by heating at 00° C. for 2 hours was ground in a ball mill to make it myself. Average particle diameter 3μm, specific surface area 8n (/g
) After adding 20 parts by weight, the mixture was mixed in a vibrating ball mill to obtain a mixed powder for molding. Next, add this mixed powder to 5tol/c.
The preform obtained by cold isostatic pressing at a pressure of J was embedded in a graphite container containing the BN powder and fired in a high frequency furnace at 1600° C. for 60 minutes in an N2 atmosphere. The measurement results of the relative density, bending strength, and Shore hardness of the obtained sintered body are shown in the table.

Using the mixed powder for molding obtained in Example 1, the molding pressure was 7 to
n/cn! It was carried out in the same manner as in Example 1 except for the following.

Daisenen↓ 50 parts by weight of BN powder, 40 parts by weight of NzO + 40 parts by weight, and 10 parts by weight of high silicate glass were added and mixed to obtain a mixed powder for molding, and this mixed powder was used at a firing temperature of 1400°C. Except for this, the same method as in Example 1 was used.

Boric acid and melamine were mixed at a weight ratio of 1:1 and heat treated at 1200°C for 14 hours in an ammonia gas stream to obtain BN powder with a BN purity of 90% and a specific surface area of 50 m/g. As a result of X-ray diffraction of this powder, it was found that it was amorphous BN. 40 parts by weight of this powder, 340 parts by weight of A#zO, and 20 parts by weight of high silicate glass were added and mixed to obtain a mixed powder for molding. Using this mixed powder, the molding pressure was 7 tons.
The same method as in Example 1 was carried out except that /cJ and the firing temperature were 1400°C.

Implementation Flaming The BN powder used in Example 1 was heated with a Raikai machine to a specific surface area of 6.
0n? After pulverizing in the air until the powder was pulverized to 1.2 g, the powder was washed with methanol and dried to obtain fine BN powder.

The specific surface area was measured by the BET method. To 50 parts by weight of this powder, 25 parts by weight of AN20325 and 25 parts by weight of high silicate glass were added and mixed in a ball mill to obtain a mixed powder for molding. Next, the mixed powder was filled into a mold and the amount was 2 tons/cnT.
Uniaxial pressure molding was carried out at a pressure of . It was carried out in the same manner as in Example 1 except that this preform was used.

Example ■ Add A A 203 to 40 parts by weight of the BN fine powder obtained in Example 5.
20 parts by weight and 40 parts by weight of high silicate glass were added and mixed to obtain a mixed powder for molding. The same method as in Example 1 was carried out except that this mixed powder was used and the firing temperature was 1400°C.

Example 1 The BN powder used in Example 1 was pulverized with an attritor under an N2 atmosphere until the specific surface area became 70 m/g to obtain BNi powder. It was carried out in the same manner as in Example 5 except that this powder was used.

Example 1 A 12203 was added to 40 parts by weight of the BN powder used in Example 1.
After adding 30 parts by weight and 30 parts by weight of high silicate glass,
After pulverizing in the air using a Raikai machine until the specific surface area became 60 rrr/g, the mixture was washed with methanol and dried to obtain a mixed powder for molding.

The same method as in Example 5 was carried out except that this mixed powder was used.

Main Example The same method as in Example 1 was carried out except that the powder for molding obtained in Example 8 was used.

After adding 20°60 parts by weight of AN and 20 parts by weight of high silicate glass to 20 parts by weight of the BN powder used in Example 1,
N2 until the specific surface area becomes 70n (/g) with an attritor.
It was pulverized in an atmosphere to obtain a mixed powder for molding. The same method as in Example 5 was carried out except that this mixed powder was used.

Aj2.0°2 was added to 20 parts by weight of the BN powder used in Example 1.
After adding 0 parts by weight and 60 parts by weight of high silicate glass, N2 was added with an attritor until the specific surface area became 70%/g.
It was pulverized in an atmosphere to obtain a mixed powder for molding.

The same method as in Example 5 was carried out except that this mixed powder was used.

Comparative Coal Soil The same method as in Example 1 was carried out except that the BN powder used in Example 1 was used as it was as a powder for molding.

Using the mixed powder for molding obtained in Example 3, the molding pressure was set to 2.
It was carried out in the same manner as in Example 1 except that ton/c+J was used.

Roasting ■1 Add Al1203 to 40 parts by weight of the BN powder used in Example 1.
After adding 40 parts by weight of high silicate glass and 20 parts by weight of high silicate glass, they were mixed in a ball mill to obtain a mixed powder for molding. The same method as in Example 5 was carried out except that this mixed powder was used.

50 parts by weight of AA and 40 parts by weight of high silicate glass were added to 10 parts by weight of the BN powder used in Example 1, and then mixed in a ball mill to obtain a mixed powder for molding. The same method as in Example 1 was carried out except that this mixed powder was used.

In addition, each physical property measurement of the BN sintered compact described in the table was performed by the following method.

+11 Relative density; After determining the volume using the sintered body method and determining the density from its weight, calculate relative density (%) - density (g
/c+J)/theoretical density (g/cd)X100O formula.

(2) Room temperature bending strength, measured in accordance with JIS R1601.

(3) Shore hardness, measured in accordance with JIS Z 2246.

(4) Thermal shock resistance; 15nx 45n+X from sintered body
When a sample of 5 cranes was cut out, and the cycle of rapidly heating it to 1500°C, holding it for 10 minutes, and rapidly cooling it was repeated, the number of cycles at which cranking occurred (effects of the invention) The pressureless sintered BN-based molded body of the present invention is as follows: It has high density, high strength, and is not subject to shape restrictions.

Patent applicant Denki Kagaku Kogyo Co., Ltd.

Claims (1)

[Claims] 1. A pressureless sintered boron nitride-based molded body comprising 70 to 15% by weight of BN, 35 to 75% by weight of Al_2O_, and 10 to 80% by weight of high silicate glass, and having a relative density of 55% or more.