JPS5917751B2 - Manufacturing method of silicon nitride abrasive grains - Google Patents

Description

Detailed Description of the Invention 5 The present invention relates to a method for producing silicon nitride abrasive grains, and more specifically, the present invention relates to a method for producing silicon nitride abrasive grains, and more specifically, crushing silicon nitride precipitates deposited and grown on a substrate by vapor phase decomposition deposition or chemical vapor deposition. The present invention relates to a method for producing high-purity, high-density silicon nitride abrasive grains adjusted to a desired grain size.

'0 Conventionally, silicon nitride (Si3N4) generally exhibits excellent heat resistance, thermal shock resistance, and corrosion resistance, and also has excellent properties such as high hardness and high strength, but these properties vary depending on the manufacturing method. make a difference.

Various methods are known for its production.

For example, a reaction sintering method in which silicon powder or a mixed powder of silicon and silicon nitride is molded and then heated and nitrided in a nitrogen stream, or a sintering accelerator such as MgO is added to silicon nitride powder and heated under pressure. Hot press method for sintering, vapor phase decomposition deposition method or chemical vapor deposition method for thermally decomposing silicon halide or silicon hydride vapor and compound vapor containing ammonia gas or nitrogen in an inert gas or hydrogen stream. method (CVD method)
and so on. Silicon nitride produced by the reaction sintering method has a low density of 70 to 80% of the theoretical value (3.1841/d), so
It has a low compressive strength of 25 degrees and hardness, and is brittle. Silicon nitride produced by hot pressing has a density of 97 to 100% of the theoretical value, a compressive strength of 100 kg/cwl, and a hardness (load of 10
Microbits hardness at 0y, MVH) 3500kg
/m71L, but since this is a mixture of α- and β-30 silicon nitrides and also contains 1 wt % or more of Mg as a sintering accelerator, the strength and hardness decrease at high temperatures of 1000° C. or higher. Also, due to the added impurities, the oxidation resistance is low, and when kept in air at 1250°C for 2 hours, O,
This results in a weight change of 1Tn9/Cd of 35%. Regarding the synthesis of Si3N4 by CVD method, there are US patents etc. that use SiF4 and NH3 as raw materials, but the hardness is 2850 kg.
/1 and extremely low deposition rate of 0.4mm/Hr
It is impractical because it is slow.

In the present invention, Si3N4 with extremely high purity, high density, and high hardness is precipitated on a base material by the G1 method, and this is crushed to obtain abrasive grains.

The production of silicon nitride used in the present invention is described in detail by one of the present applicants in Japanese Patent Application Laid-Open No. 52-96999.

Here, the method for producing silicon nitride disclosed in JP-A-52-96999 is to combine a nitrogen deposition source gas and a silicon deposition source gas onto a substrate heated within a temperature range of 1000 to 1900°C using a tube. The periphery of the nitrogen deposition source gas flow rate sprayed onto the substrate is surrounded by the silicon deposition source gas, and a gas phase decomposition reaction of both gases occurs on or near the substrate, essentially forming fine crystals. by producing a crystalline or oriented crystalline silicon nitride and depositing it on the substrate;
This is a method of manufacturing silicon nitride. According to this manufacturing method,
There is no need to add a densification accelerator (Si or MgO, etc.) which is absolutely necessary when using the reactive sintering method, hot pressing method, etc. Therefore, the silicon nitride of the present invention has extremely high purity, has high density and high compressive strength at room temperature and high temperature as described above, and has extremely excellent mechanical properties at room temperature and high temperature. One of the reasons why the silicon nitride of the present invention has excellent properties is thought to be that no densification promoter is added. Conventional high-density sintered silicon nitride molded bodies can only be obtained by adding 1 to 10 wt% of a sintering accelerator such as MgO or Si and performing hot pressing or reaction sintering.
The presence of these impurities causes deterioration of mechanical properties at high temperatures. The thermal expansion coefficient of the oriented crystalline silicon nitride of the present invention is 2.2 x 10-6/°C, and the thermal expansion coefficient is 1200°C.
~Withstands more than 700 to 1800 heating and quenching cycles at room temperature, compared to about 600 for conventional reaction sintered Si3N4
It can be seen that the oriented crystalline silicon nitride of the present invention has extremely excellent thermal shock resistance, compared to about 250 times for sintered SiC.

The thermal expansion coefficient of the fine-grained crystalline silicon nitride according to the present invention is 2.7.
×10-6/°C, and can endure heating and quenching cycles from 1200°C to room temperature 700 to 2000 times or more. Furthermore, the thermal expansion coefficient of the amorphous silicon nitride of the present invention is 2.92X10-6/
It is ℃. The oriented crystalline, fine-grained crystalline, and amorphous silicon nitride of the present invention all show a weight change of 0.05η/Cd or less even when heated in air at 1250°C for 2 hours, and the weight change is 0.05η/Cd or less compared to hot-pressed sintered silicon nitride. It can be seen that the oxidation resistance is extremely excellent compared to 1W19/Cd and 5η/Cd of reactive sintered silicon nitride.

Also, both are Na. K. Li. Al. Good corrosion resistance against molten metals such as Fe.

The oriented crystalline and fine-grained crystalline silicon nitride of the present invention have a room temperature electrical resistance of 1014 to 1015 Ω. The electrical resistance is 10 to 100 times greater than that of reactive sintered silicon nitride, and it has high electrical insulation properties.

The hardness, which is the most significant feature of the silicon nitride of the present invention, will be explained below.

It is said that the hardness of the oriented crystalline silicon nitride of the present invention is much higher than that of the known crystalline silicon nitride manufactured from NH3 by vapor phase decomposition deposition as shown in Fig. 4, which has M285Okg/Md at 100y load. It has characteristics.

The reason why the oriented crystalline silicon nitride of the present invention has extremely superior hardness compared to the known crystalline silicon nitride is that the known silicon nitride has an α-type crystal structure, according to research by the present inventors. , (001) plane orientation, whereas that of the present invention has the same α-type crystal structure, but (HkO), (H
The silicon nitride of the present invention has an orientation of one or more planes consisting of one or more of the (001) plane and the (001) plane, and the oriented plane of the silicon nitride of the present invention essentially has a higher degree of carbide than the (001) plane. It is considered that this is because it has.

That is, as a result of measuring the hardness of each crystal plane of an α-type silicon nitride single crystal, as shown in Table 1 below, the hardness of the (001) plane was the lowest;
O), (HOk), and (11k1) planes are respectively the above-mentioned (0
01) far higher than the plane 71)), 3550-3650
kg/MIL. The hardness listed in Table 1 above is the hardness measured for each crystal plane of the α-type silicon nitride single crystal, but the hardness of the oriented crystalline silicon nitride of the present invention is the hardness of the single crystal ( HlcO), (HOk)
, (Hkl) surface, which is higher than the hardness of each surface.
As an example of this is shown by the curve PO in FIG. 6, it reaches 3800 kg/Md at a load of 1007. The hardness of fine-grained crystalline silicon nitride is 10, as shown by curve FG in Figure 6.
MVH4OOOO~5000kg/Mdll5 at 07 load
MVH is 35OO~4300kg/MIL under O7 load, and the hardness of fine-grained crystalline silicon nitride manufactured by the conventionally known hot pressing method is MVH approximately 350 under 100f load.
01<g/M7l, and the hardness of crystalline silicon nitride manufactured by conventionally known vapor phase decomposition deposition is MVH285Okg/7 at a load of 1007! Compared to Td, it has much higher hardness than diamond. It has an ultra-high hardness that is second only to cubic BN.

Note that the particle size of silicon nitride obtained by the present invention has a particle size range similar to that of conventional abrasive grains.

Hereinafter, the present invention will be explained in detail based on Examples. Example 1
A substrate 2 made of graphite was prepared, the surface of which was provided with irregularities α or serrated protrusions and a waveform as shown in FIG.

Next, the graphite substrate was fixed in a device as shown in FIG. 2 using a water-cooled conductive gripping rod 3. The pressure inside the furnace was previously reduced to 10 −3 mmHg, and the substrate was electrically heated to 500° C. or higher to degas it. Then, the substrate 2 was heated to 1350°C.
Inner tube 4 was heated with 60CC/Tlin of ammonia gas.
Then, hydrogen gas saturated with silicon tetrachloride at 20° C. was introduced from the outer tube 5 at 700 CC/772.

After 30 minutes had elapsed after the furnace pressure was maintained at 50 Hg, the substrate was maintained at 1400°C for 4 hours, and then the furnace pressure was increased to 40 Hg.
mmHg and the inflow of both gases was stopped, the load output was gradually reduced by an automatic control device, and the substrate was slowly cooled to room temperature in 1.5 hours, and then the substrate was taken out. The generated Si3N4 is crystalline and has a precipitation rate of about 1 mm/Hr.
Thickness 4~5mT! A layer of L was deposited on the graphite substrate 2. Density is 99-100% of theoretical density, hardness (MV
H, load 1007) 3200-3800kg/m! Reached L. The graphite substrate on which the Si3N4 layer was deposited was taken out, and the graphite substrate was removed.
Separation of 3N4 from the graphite substrate can alternatively be carried out, for example, by immersing it in a concentrated sulfuric acid + concentrated nitric acid (3:7 to 5:5) solution, or by placing it in Br vapor or Br liquid to make it C+Br, and then converting it to C+Br in a vacuum. Separation is possible even when heated to 100°C. In order to remove graphite more completely, the graphite attached to the plate crystals must be polished away, the crystal + graphite powder must be fired in an oxidizing atmosphere to burn off the carbonaceous matter, or the graphite must be mixed. Methods such as powder flotation can be used. Next, the aforementioned Si3N4
When the precipitated graphite substrate (with serrations) is placed in a known press and pressurized to about 1 t/Cd, the precipitated Si3N4 The layer was fractured from the growth cone.
Sieve by conventional method and adjust particle size to desired abrasive particle size 15
I got number 0. Next, grindstones were made using these abrasive grains and tested for grinding performance, etc. Grinding Test 1 A vitrified grindstone for internal grinding was manufactured using Si3N4 abrasive grains.

It was ground under the following conditions and its characteristics were evaluated. A vitrified borazone whetstone and a general vitrified whetstone were simultaneously evaluated as test control whetstones.

As a result, it was found that the Si3N4 whetstone had slightly inferior performance compared to the Borazon whetstone, but was significantly superior when compared to general whetstones.

Example 2 A mesh woven fabric 10 made of carbon fiber as shown in FIG. 3 was held as a graphite substrate 2 in the CVD apparatus shown in FIG. 2, and Si3N4 was deposited under the same conditions as in Example 1. However, the generation of Si3N4 on carbon fiber fabric is approximately 1
Starting from 100℃, crystalline Si3N4 becomes more than 1300℃
was generated and left to cool at 1400° C. for 4 hours, taken out from the apparatus, crushed by a conventional crushing method, carbon fibers were removed by flotation, and only Si3N4 was collected and the particle size was adjusted.

(Particle size 150: approximately 95% or more of theoretical density; hardness 100
7 load MVH33OO~3800kg/M77l) Grinding wheels using these abrasive grains were made and their grinding performance etc. were tested. Grinding Test 2 A resinoid grindstone for surface grinding was manufactured using Si3N4 abrasive grains.

It was ground under the following conditions and its characteristics were evaluated.

A resinoid borazone grindstone was evaluated as a 4θ test control grindstone.

As a result, the Si3N4 grinding wheel is the same as the Borazon grinding wheel;
It was found that it has the following grinding properties.

Example 3 Using the same apparatus as in Example 1, fine-grained crystalline silicon nitride was produced.

The manufacturing conditions are as follows. Substrate temperature: 1500°C, ammonia gas flow rate: 60cc/Mml hydrogen gas flow rate: 7
Vapor pressure of 00cc/Mml silicon tetrachloride: 180mmHg
, Gas pressure in the container: 10 degrees Hgl Deposition time: 4 hours. As a result, white-gray fine-grained crystalline silicon nitride with a thickness of 2.4 mm was obtained on the surface of the substrate 2. The sedimentation speed at this time is 0.6m
It was m/Hr. The characteristics of this fine-grained crystalline silicon nitride were as follows. Crystal structure: Crystalline α type, Crystal orientation:
(110), (210), plane, crystal grain size: 10μ or less,
Density: 3.1847/d, S/N: 0.73, Hardness: 4
500-5000kg/MTl (load 1007), 15
No oxidation was observed at 00℃, compressive strength: 200k9/
MdO Note that when the obtained silicon nitride was treated and tested in the same manner as in Example 1, good results were obtained as in the other examples.

The properties of the silicon nitride abrasive grains obtained by the production method of the present invention are as follows.

Thermal expansion coefficient (25.

~1000°C) is 2.9×'10-6.

Particle size follows JISR-6001 and R-6002.

The particle shape of crushed Si3N4 is shown in FIG.

This abrasive grain can be used not only for steel and stainless steel, but also for CO-Cr.
- It was confirmed that it is most effective for grinding and polishing non-metals such as W alloy, sapphire, yellow jade, and quartz.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view illustrating the shape of the substrate used in the present invention, where a is an uneven surface type, b1 to B6 are a sawtooth surface type,
Figure 2 is an example of a CVD apparatus used in the present invention, Figure 3 is an example of a carbon woven fabric for vapor phase precipitation of Si3N4, Figure 4 is an X-ray diffraction diagram of Si3N4, and Figure 5 is a is an optical micrograph of a Si3N4 crystal with a diameter of approximately 0.2 mm (corresponding to No. 70 abrasive grain) with fine powder attached to the surface of the Si3N4 crystal particle, b is a scanning image of the grain surface of the Si3N4 crystal after ultrasonic cleaning The electron micrograph and FIG. 6 are diagrams comparing the hardness of silicon nitride of the present invention with the hardness of other materials. 2: Substrate, 4: Ammonia gas supply pipe, 5: Hydrogen gas supply pipe.

Claims (1)

[Claims] 1. Nitrogen deposition source gas and silicon deposition source gas are each sprayed onto a substrate heated within a temperature range of 1000 to 1900° C. using a combination tube, and nitrogen deposition is sprayed onto the substrate. surrounding the source gas flow rate with a silicon deposition source gas, causing a gas phase decomposition reaction of both gases to occur on or near the substrate to produce essentially fine-grained or oriented crystalline silicon nitride; Silicon nitride polishing, characterized in that the precipitated layer deposited on a substrate and consisting of fine-grained crystalline or blended crystalline silicon nitride is crushed and subjected to grain size adjustment after or without removal from the substrate. Manufacturing method of abrasive grains. 2 The substrate has an uneven, serrated or corrugated surface (1) graphite, (2) alumina, magnesia,
Oxides such as zirconia and titania, (3) nitrides such as silicon nitride, aluminum nitride and boron nitride, (4)
) is a member selected from carbides such as silicon carbide, tungsten carbide, and titanium carbide.
Manufacturing method described in section. 3. The manufacturing method according to claim 1, wherein the substrate is a mesh woven fabric made of carbon fiber.