JP2754260B2 - Polycrystalline diamond grains and method for producing the same - Google Patents

Description

The present invention relates to polycrystalline diamond grains and a method for producing the same. More specifically, the present invention relates to a polycrystalline diamond grain having a new structure different from that of a conventional synthetic natural diamond, and a method for producing the same. The diamond grains of the present invention are large grains and have properties such as wear resistance, corrosion resistance, high thermal conductivity, and high specific elasticity, and are used for carbide tool materials, abrasive materials, abrasive materials, sliding materials, corrosion-resistant materials, and cutting edges. It is useful for members and the like.

<Conventional Technology> As a method for synthesizing diamond, an ultra-high pressure method has been practically used for a long time, and a gas phase method has been further developed in recent years. The inventors of the present application invented the combustion flame method as an improvement of the gas phase method, and
35th Federated Lectures on Applied Physics (Preprints of the Second Lecture Volume 434)
Page 299-T-1) and Japanese Patent Application No. 63-71758.
As an application. The diamonds produced in these synthetic methods are based on the crystal forms of natural ores whose crystal forms are generally known, ie, octahedral, dodecahedral, and hexahedral crystals.

<Problems to be Solved by the Invention> A large-diameter diamond produced by a conventional ultrahigh-pressure method has a low growth rate, and the production equipment is enormous and expensive.
Further, in the gas phase method including the combustion flame method, diamond is usually obtained as a thin film, and in a granular state, the number of crystals is suppressed, and diamond is obtained only at a low speed.

It is thought that with the increase in demand for diamond, large grains are desired, and if a structure having a structure different from the conventional concept is developed, the range of demand will be further widened. The present inventors have conducted studies in consideration of these points and completed the present invention.

<Means for Solving the Problems> The present invention for achieving the object, the crystal is a polycrystalline diamond grains having a structure in which the skeleton crosses each other,
A combustion flame method in which a combustion flame of a mixed gas of acetylene and oxygen strikes a substrate for diamond deposition to deposit diamond on the substrate, and a first step of forming a nucleus on the substrate And a second step of growing the formed diamond nuclei, and a method for producing polycrystalline diamond in which the mixing ratio of oxygen and acetylene is changed between the two steps.

 The present invention will be described in more detail.

The polycrystalline diamond grains of the present invention have a structure in which the skeletons cross each other.

In other words, it also has a butterfly-shaped crystal face and has many cleavage faces. It is considered that the octahedral crystal mainly composed of (111) planes and the dodecahedral crystal mainly having (110) planes, which are almost twin crystals, are gathered together.

Next, the specific shape of the polycrystalline diamond grains of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view of a basic form in which skeletons intersect. Second
The figure is an elevation view of a basic pyramid-shaped polyhedron.

FIG. 3 is a plan view showing a case where the intersecting skeletons are vertically related.

FIG. 4 is a plan view showing a case where the skeletons cross obliquely.

FIG. 5 is a plan view when the length of the cross skeleton is short, and FIG. 6 is a plan view when the cross is oblique and in a vertical relationship.
FIG. 7 is a plan view showing an example in which the crossing position is shifted and the length of the cross skeleton is short.

 FIG. 8 shows a plan view of a multiple deposition type.

The basic form shown in FIGS. 1 and 2 has a structure in which crystals extend in four directions from the center, which is regarded as a nucleation point, while bending, and skeletons cross each other. That is, a crystal structure in which exactly two butterflies overlap is generated. 3 to 8
Various variations illustrated in the figures also occur.

Next, a method for producing the polycrystalline diamond grains of the present invention will be described. That is, the present invention is basically a combustion flame method in which acetylene which is a raw material gas for depositing carbon containing carbon is burned so as to have an incomplete combustion region. In this combustion process, nuclei are selectively grown. It is characterized in that a step and a step of growing the nuclei are provided, and the mixing ratio of oxygen and acetylene in both steps is changed. In particular, when the latter condition is not appropriate, the crystal is a normal spinel-like octahedron, garnet-like dodecahedron, or a combination of cubic tetrahedral basic crystals (6 + 8) -hedron, ( 12 + 6) face, (12+)
8) A single crystal such as a facet, a (12 + 8 + 6) facet, or a confetti-like crystal having a large number of pyramidal projections or a mirror ball-like polycrystal having a square or rectangular surface on its surface grows.

 Next, the present invention will be described.

As the substrate, W, WC, Mo, Si, TiC, TiN, cermet, or the like can be used. The substrate cleaned by ultrasonic waves is set on a support table whose temperature can be adjusted by water cooling, and a reducing flame of a mixed gas of acetylene and oxygen is blown from the burner to the substrate. In this case, the substrate temperature in the first nucleation stage is slightly higher than the normal diamond formation condition, that is, 900 to 1000 ° C.
The growth nucleus is selectively grown during the nucleation process while maintaining the temperature at ℃. Usually, at 900 ° C or outside, 10 ⁵ to 10 ⁶ / mm ² nuclei are generated on the substrate, but since these widths ultimately limit the number of crystal nuclei to 10 ² / mm ² or less, Intentionally suppresses the growth of crystal nuclei. The present invention is characterized in that a step of forming the nucleus and a step of growing the nucleus under different burning conditions are provided.
Next, the conditions will be described.

Synthesis conditions O ₂ / C ₂ H ₂ is preferably in the range of 0.83 to 0.86 in the nucleation step and 0.88 to 0.92 in the nucleus growth step.

When the reaction is carried out under such conditions, the following results are obtained in each step.

That is, a fine single crystal is formed as a nucleus in the first stage,
By performing rapid growth in the second stage, nuclei are selected and the selected nuclei are grown. A specific nucleus grows at a growth rate of 100 μ / hr or more while suppressing the growth of surrounding crystal nuclei. Crystal grows.

<Example 1> A 0.5 t × 20 × 20 (mm) molybdenum plate was subjected to ultrasonic cleaning in an ethanol solution and set on a sample support.

Keep the crater distance between the substrate and the burner at 7 mm, ignite a mixed gas of acetylene 5.0 / min and oxygen 4.25 / min from the burner port in the air, keep the substrate in the feather, and keep the substrate temperature at 1000 ° C. The temperature of the support of the substrate is adjusted by the cooling water.

Five minutes later, the inside of the feather on the substrate turns pale white, and the generation of fine crystal nuclei is confirmed. Immediately increase the oxygen flow to 4.5 / min. After 10 minutes, a considerable number of small grains start to form from within the pale white region. Eventually, after 20 minutes, mutually independent grains will compete for shoulders and grow. The substrate is rotated little by little and kept for 30 minutes while emitting the feather uniformly to the crystal.

After completion of the reaction, the substrate was gradually cooled, the precipitate was observed with a scanning electron microscope, and further examined by X-ray diffraction and Raman spectroscopy. As a result, it was confirmed that large butterfly-shaped lumps having a particle size of 300 to 500 μm occupied the majority, and block-shaped lumps of 100 to 200 μm were formed around the large diameter. Scanning electron micrographs at 400 times and 200 times of two representative examples of the grains are shown in FIGS.

<Comparative Example 1> An experiment was started under the same conditions as in Example 1, and the production was performed for 30 minutes while maintaining the flow rates of acetylene 5.0 / min and oxygen 4.25 / min without changing the oxygen flow rate. It was examined with a stereo microscope. At the center of the precipitation, polycrystalline mirror-balls with a square or rectangular surface on the surface of several tens of microns or confetti-like grains with pyramidal protrusions are laminated at the center, and DLC (diamond-like carbon) is surrounded by the periphery. In addition, round particles of ic (eye carbon) overlap and deposit on the outer periphery to form a film. That is, a structure in which the skeleton of the present invention crossed was not obtained. In each case, the precipitate at the center was confirmed to be diamond by X-ray diffraction and Raman spectroscopy.

<Comparative Example 2> A substrate was treated in the same manner as in Example 1, and the distance between the substrate and the crater was 7 m.
m and set on a sample support.

Generation was performed for 35 minutes while maintaining a flow rate of acetylene of 5.0 / min and oxygen of 4.5 / min. After the reaction was completed, the precipitate was observed with a stereoscopic microscope.

At the center of the precipitation where the substrate temperature was increased, a large lump of graphite was raised, and no diamond was found. It was found that monohedral grains, which had grown only on the (100) plane, were slightly precipitated in the periphery.

<Effect of the Invention> The diamond particles of the present invention have a remarkably larger particle size than ordinary crystal particles of several microns to several tens of microns obtained by a conventional vapor phase method, and have features that are not found in natural or other artificial diamonds. have. Moreover, since large diamonds can be easily obtained, they can be used in fields where conventional artificial diamonds are used, that is, for (petroleum) drill bits, stone processing grindstones, and various cutting tools. Further, since it has many cleaved surfaces, an effect of anchoring to the matrix is expected, and a highly durable tool with high spontaneous cutting performance in the cutting process can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view of a basic form of a polycrystalline diamond grain of the present invention, FIG. 2 is a vertical view of a pyramidal polyhedron of a basic form of a polycrystalline diamond grain of the present invention, FIG. 3, FIG. 6 and 7 are plan views showing various examples of intersecting skeletons of the basic form in FIG. 1, FIG. 8 is a plan view showing an example in which the structure is a multi-stack type, FIG. 9 and FIG. The figure shows 400 × and 200 × scanning electron micrographs of two typical examples of the polycrystalline diamond of the present invention produced according to Example 1.

Claims (2)

(57) [Claims] 1. Polycrystalline diamond grains having a structure in which the crystal skeletons cross each other. 2. A first step in which acetylene is burned so as to have an incomplete combustion region to form a nucleus on a substrate when diamond is synthesized by a combustion flame method, and the formed diamond nucleus is grown. is a second step is provided to the first step and changing the mixed gas composition for combustion flame of the second step, and mixed gas combustion flame in the first step O ₂ / C ₂ H ₂ is from 0.80 to 0.87, the gas mixture for two-step combustion flame O ₂ / C ₂ H ₂ is the preparation of polycrystalline diamond grains in the range of 0.85 to 0.98.