JPH03112896A - Polycrystal diamond grain and its production - Google Patents

Abstract

PURPOSE:To obtain a polycrystal having a structure of mutually crossed crystal skeletons by changing the ratio of O2 to C2H2 of a combustion mixed gas on forming nuclei on a substrate and growing the nuclei in synthesizing diamond according to incomplete combustion of the C2H2. CONSTITUTION:C2H2 is incompletely burned to synthesize diamond. In the process, a mixed gas of O2 and C2H2 at 0.8-0.87 ratio (O2/C2H2) is used to form nuclei on a substrate. A mixed gas at 0.85-0.98 ratio (O2/C2H2) is then used to grow the above-mentioned formed nuclei. Thereby, polycrystal diamond grains having a structure of mutually crossed crystal skeletons are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to polycrystalline diamond grains and a method for producing the same. More specifically, the present invention relates to polycrystalline diamond grains having a new structure different from that of conventional synthetic natural diamonds and a method for producing the same. The diamond grains of the present invention are large grains and have wear resistance, corrosion resistance, high thermal conductivity,
It has properties such as high specific elasticity, and is useful for carbide tool materials, abrasive materials, grinding materials, sliding materials, corrosion-resistant materials, cutting edge members, etc.

<Prior art> Ultra-high pressure methods have been put into practical use as diamond synthesis methods for a long time, and gas phase methods have 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 announced it at the 35th Applied Physics Joint Conference (Presentation Proceedings, Volume 2, 434, p. 299-T-1),
And it has been filed as Japanese Patent Application No. 1983-71758. The crystal forms of diamonds produced by these synthetic methods are based on the commonly known crystal forms of natural rough stones, ie, octahedral crystals, dodecahedral crystals, and hexahedral crystals.

<Problems to be Solved by the Invention> Large diamonds produced by the conventional ultra-high pressure method have a slow 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 in the form of a thin film, and in the form of granules, the number of crystals is suppressed and can only be obtained at low speed.

As the demand for diamonds increases, larger diamonds are desired, and if diamonds with a structure different from the conventional concept are developed, it is thought that the range of demand will further expand.The inventors of the present invention took these points into consideration, conducted repeated research, and completed the present invention.

Means for Solving the Problems> To achieve the above object, the present invention uses polycrystalline diamond grains whose crystal skeletons intersect with each other and a combustion flame of a mixed gas of acetylene and oxygen for diamond precipitation. A combustion flame diamond synthesis method in which diamond is precipitated on the base material by colliding with the base material, the method comprising a first step of forming a nucleus on the base material, and a second step of growing the formed diamond nucleus. The present invention also relates to a method for producing polycrystalline diamond in which the mixing ratio of oxygen and acetylene is changed between both steps.

The present invention will be explained in more detail.

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

In other words, it has bisphenoidal crystal faces and multiple cleavage planes.It is generally twinned, and has an octahedral crystal mainly composed of (111) planes, which is unique to diamond. It is considered that a part of a dodecahedral crystal having 110) faces is gathered together.

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

FIG. 1 is a plan view of the basic shape in which the skeletons intersect. FIG. 2 is an elevational view of the basic pyramidal polyhedron.

FIG. 3 is a plan view showing a case where the intersecting skeletons are in a vertical relationship.

FIG. 4 is a plan view showing a case where the skeletons intersect diagonally.

Fig. 5 is a plan view when the length of the chiasm skeleton is short, Fig. 6 is a plan view when the chiasm is diagonal and in a vertical relationship, and Fig. 7 is a plan view when the cross position is shifted and the chiasm skeleton is A plan view of an example in which the length of is short is shown.

Furthermore, FIG. 8 shows a plan view of the multiple stack type.

The basic shape shown in FIGS. 1 and 2 has a structure in which the crystals bend and extend in all directions from the center, which is considered to be the nucleation point, and the skeletons intersect with each other. In other words, a crystal structure similar to two butterflies superimposed on each other is created. Various modifications illustrated in FIGS. 3 to 8 also occur.

Next, a method for producing polycrystalline diamond grains according to 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 diamond precipitation containing carbon, is combusted so as to have an incomplete combustion region, but in this combustion process, nuclei are selectively grown. process and then
The method is characterized in that it includes a step of growing the resulting nuclei, and that the mixing ratio of oxygen and acetylene in both steps is changed. And especially when the latter condition is unsuitable, the crystal is a combination of the basic crystals of the usual spinel-like octahedron, or garnet-like dodecahedron, or cubic tetrahedron (6+8)-hedron, ( 12+6) face piece, (12+
8) Single crystals such as hedrons and (12+8+6) hedrons, or polycrystals in the shape of spinous twigs having a large number of pyramidal protrusions or mirror balls having square or rectangular surfaces on the surface grow.

Next, the present invention will be explained.

W, WC, Mo, SL, TiC as substrates.

TiN, cermet, etc. can be used. The ultrasonically cleaned substrate is set on a support stand whose temperature can be controlled by water cooling, and a reducing flame of a mixed gas of acetylene and oxygen is blown onto the substrate from a burner. In this case, the substrate temperature is maintained at a temperature slightly higher than normal diamond formation conditions at the initial stage of nucleation, ie, 900° to 1000° C., to selectively grow growth nuclei during the nucleation process. Normally, at temperatures around 900°C, 106 to 10'/+++m" nuclei are generated on the substrate, but in order to limit the number of crystal nuclei to a width of 1027 mm or less, the number of crystal nuclei is intentionally Inhibits nuclear growth. The present invention is characterized in that it includes a step of forming this nucleus and a step of growing it with different combustion conditions. Next, the conditions will be described.

Synthesis conditions (setting time) (Ozvol/CtHzvol) (C
zH! cc/c is -S) (02"c/CIl+",
S) [Nucleation 15-15 minutes 0.80-0.87 1
00-70 85-60 [Crystal growth 17-10 minutes 0
．． 85~0.98 100~7090~63 and 0
□/C2H2 is 0.83 to 0.86 in the nucleation process,
In the nuclear growth step, it is preferably in the range of 0.88 to 0.92.

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

(Number of nuclei generated) (Growth rate) (Crystal form)
That is, in the first step, a fine single crystal is formed as a nucleus, and in the second step, by rapid growth, selection of the nucleus and growth of the selected nucleus are performed, and a specific nucleus grows at a rate of 100μ/hr or more. It uses its speed to suppress the growth of surrounding crystal nuclei while growing itself into a gigantic crystal.

<Example 1> A molybdenum plate of 0.5 t×20×20 (mm) is ultrasonically cleaned in an ethanol solution and set on a sample support stand.

Keeping the distance between the substrate and the burner at 7 mm, acetylene 5.0 ffi/min s oxygen 4.2
A mixed gas of 51/min was ignited in the atmosphere, the substrate was kept in the feather, and the temperature of the substrate support was adjusted using cooling water so that the substrate temperature was maintained at 1000°C.

After 5 minutes, the inside of the feather on the substrate changed color to pale white, and the generation of fine crystal nuclei was confirmed. Immediately increase the oxygen flow rate slightly to 4.5 ffi/min. After 10 minutes, a considerable number of small particles begin to form within the pale white area.

Eventually, after 20 minutes, independent grains will grow competing with each other. The substrate is rotated little by little to uniformly radiate feathers onto the crystals, and the substrate is held for 30 minutes.

After the reaction was completed, the substrate was slowly cooled, and the precipitate was observed using a scanning electron microscope (5) and further examined by X-ray diffraction and Raman spectroscopy.

As a result, it was confirmed that diamond-shaped large lumps with a grain size of 300 to 500 μm occupied the majority, and block-shaped diamond grains with a diameter of 100 to 200 μm were generated around them.

Scanning electron micrographs of representative two sides of the grain at 400x and 200x are shown in Figures 9-10.

<Comparative Example 1> An experiment was started under the same conditions as in Example 1, and the oxygen flow rate was unchanged, with acetylene at 5.0 j/win and oxygen at 4.0 j/win. z5
j/I! Generation was carried out for 30 minutes while maintaining the flow rate of lin, and after the reaction was completed, the precipitate was examined using a stereomicroscope. At the center of the precipitation, mirror ball-shaped polycrystals with square or rectangular faces on the surface of several tens of microns and confetti-shaped grains with pyramidal protrusions are piled up in the center, and DLC (diamond-like carbon) is deposited in the periphery. can be seen, and IC (
Round grains of iCarbon) are deposited on top of each other to form a film. That is, a structure in which the skeletons of the present invention were crossed could not be obtained. In each case, the precipitate at the center was confirmed to be diamond by X-ray diffraction and Raman spectroscopy.

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

Acetylene 5. Of/min, oxygen 4.5ffi/m
Generation was carried out for 35 minutes while maintaining the flow rate of in. After the reaction was completed, the precipitate was observed using a stereomicroscope.

At the center of the precipitation, where the substrate temperature had risen, a large mass of graphite swelled up, and no diamonds were found. In the periphery (1
A small amount of monohedral grains, in which only the 00) plane grew, was observed to be precipitated.

<Effects of the Invention> The diamond particles of the present invention have a significantly larger particle size than the crystal grains normally obtained from a few microns to several tens of microns obtained by conventional vapor phase methods, and have a shape that is not found in natural or other man-made diamonds. have. However, since large diamonds can be easily obtained, it is suitable for fields where conventional artificial diamonds are used.
That is, it can be used for (oil) drilling bits, stone processing grindstones, and various cutting tools. In addition, since it has many cleavage planes, it is expected to have an anchoring effect to the matrix, and it is possible to create a tool that has high spontaneity in the cutting process and is sharp and durable.

[Brief explanation of drawings]

Fig. 1 is a plan view of the basic shape of polycrystalline diamond grains of the present invention, Fig. 2 is an elevational view of a pyramidal polyhedron of the basic form of polycrystalline diamond grains of the present invention, Figs. 3, 4, and 5. , Figures 6 and 7 are plan views showing various examples of intersecting skeletons of the basic form shown in Figure 1, Figure 8 is a plan view showing examples whose structure is of the multi-layered type, Figures 9 and 7 are Figure 10 shows two representative polycrystalline diamonds of the present invention produced according to Example 1, 400x and 200x.
A scanning electron micrograph of magnification is shown.

Claims (2)

[Claims] (1) Polycrystalline diamond grains have a structure in which the crystal skeletons intersect with each other. (2) When synthesizing diamond by the combustion flame method by burning acetylene so that it has an incomplete combustion region, the first step is to form a nucleus on the base material, and the second step is to grow the formed diamond nucleus. The mixture gas composition for combustion flame in the first step and the second step is changed, and the mixed gas for combustion flame in the first step has O_2/C_2H_2 of 0.8.
0 to 0.87, the mixed gas for the combustion flame in the second step is O_2/
A method for producing polycrystalline diamond grains in which C_2H_2 is in the range of 0.85 to 0.98.