JP3837486B2 - Synthesis method of hexagonal diamond powder. - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for synthesizing hexagonal diamond powder that utilizes effective shear stress even under pressure and temperature conditions that are conventionally considered to be a stable region of cubic diamond thermodynamically. The present invention relates to a method of synthesizing hexagonal diamond powder by a so-called impact pressing method in which cubic diamond is instantaneously converted to hexagonal diamond using a conventionally known impact compression method by collision of a high-speed object.
[0002]
[Prior art]
Conventionally, two methods for synthesizing hexagonal diamond have been known. One is a method in which graphite with good crystallinity is compressed at a high pressure of 10 GPa or more at room temperature and heated at a temperature of about 1000 ° C. The other is a method in which graphite with good crystallinity is mixed with a large amount of metal such as copper powder, and this mixture is subjected to an impact compression treatment of about 50 GPa.
[0003]
[Problems to be solved by the invention]
Thus, in the prior art, graphite is used as a starting material. This is based on the idea that the graphite layer is shrunk by pressure to form a new bond. As a result, hexagonal diamond was inevitable coexisting with cubic diamond.
[0004]
[Means for Solving the Problems]
The present inventor has noted that it is derived from the difference in the lamination structure differences simply their respective crystal structure result of extensive studies to solve the above problems, the cubic diamond and hexagonal diamond and transition between the laminated structure of their respective are closely energetically, the transition in the effect of the shear stress that can be realized by uniaxial compression, such as impact compression is based on a new concept called would be accelerated, By selecting cubic diamond as the starting material and utilizing the effect of shear stress, the impact compression treatment is applied to cubic diamond at an appropriate collision speed even within its thermodynamic stability region. As a result, it has been found that it can be converted into hexagonal diamond in a high yield.
[0005]
That is, the present invention provides a cubic diamond powder in the thermodynamic stability region of cubic diamond by colliding a high-speed object with cubic diamond powder at an impact pressure of 30 GPa or more generated by instantaneous uniaxial pressurization by a shock wave. A hexagonal crystal characterized by transforming cubic diamond powder into hexagonal diamond powder by deforming it by generating shear stress and promoting transition between the laminated structures of cubic diamond and hexagonal diamond. This is a method for synthesizing diamond powder . Et al of the present invention, the target average particle size of 10 microns or less on the surface of the copper powder pressed compact secure the cubic diamond particles having an average particle size of 30-50 microns, accelerates the projectile by pulsed laser The method of synthesizing the above hexagonal diamond powder, characterized in that it is made to collide with a target.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, since the material conversion by utilizing the effect of the shear stress to deform the powder generated by the impact compression of the powder by the collision of the powder fast an object, sample the initial state in the practice and impact It is necessary to select environmental conditions. Selecting the starting material and the shape and material of the flying object, which is a high-speed object, are important for the initial sample state, and the impact speed, impact pressure, the inclination and flatness of the projectile at the time of the collision are important as the impact environment. It is.
[0007]
The starting cubic diamond powder may be a commercially available one synthesized by a high-temperature high-pressure method or the like, and is preferably a homogeneous one having good crystallinity. The particle diameter depends on the size of the flying object, but if the diameter of the flying object is about mm to several tens of centimeters, about 10% or less is desirable. This is because the generation of effective shear stress is weakened when the particle is about the diameter of the flying object, that is, a single crystal sample.
[0008]
The shape of the flying object may be a disk shape, a rectangle or a square. The material such as aluminum, stainless steel, copper, etc. that can be easily chemically removed after collision, and that does not react with diamond powder during impact compression is preferable. The impact speed of the flying object affects the generation of impact pressure. In impact compression by collision, the pressure is calculated from the collision speed, so the necessary speed is known once the material of the flying object is determined.
[0009]
The impact environment condition requires an impact pressure of 30 GPa or more. If it falls below 30 GPa, the generated shear stress is not sufficient, and the deformation of the diamond powder due to the shear stress is too small, so conversion to hexagonal diamond hardly occurs.
[0010]
The impact treatment method used in the synthesis method of the present invention may be a collision speed in the range of about 1.5 km or more of the collision speed of the flying object accelerated by an explosive, a single-stage gunpowder, a laser or an electron beam, etc. Acceleration methods according to the prior art can be used.
[0011]
As for the upper limit of the pressure, considering that the diamond melts at 600 GPa, and referring to the current technical level, the upper limit is about 300 to 500 GPa. In this 30-500 GPa impact compression state, cubic diamond is thermodynamically stable. However, cubic diamond can be converted to hexagonal diamond in a compressed state where shear stress exists. This shows that the energy difference between the two is slight, and that conversion is possible when a deviation of the lamination of the cubic diamond laminated structure occurs due to deformation due to shear stress.
[0012]
The shape, material, collision speed, and surface roughness of the collision surface are important for the shear stress generated during the high-speed collision of the flying object. In more detail, the diamond profile also affects the magnitude of the shear stress experienced by the particles. The shape of the collision surface at the time of collision of the flying object depends on which acceleration method is used, for example, when accelerating with a laser or electron beam, it collides with a shape depending on the spatial distribution of the intensity of the laser or electron beam It will be.
[0013]
Since the Gaussian distribution is usually used, the shape of the flying object is a bowl shape with a sharp center. The shape of the bowl is desirable for effective generation of shear stress. Flying plates accelerated by explosives and single-stage gunpowder guns have a normal inclination, and the degree of the inclination affects the generation of shear stress. The generation of these shear stresses is ultimately determined by the relative relationship between the diamond particle shape and the flying object shape. In other words, it is determined by what type of projectile collides with what type of particles.
[0014]
Regarding the diamond particle fixing method, it is necessary to embed diamond particles in a metal fine powder molded body in order to increase pressure sufficiently at the time of impact compression and to be effective against deformation of diamond particles due to shear stress. is there. As this metal, copper powder that does not react with diamond, has a large impact impedance, is easy to be pressure-molded, and is easily removed by chemical treatment or the like is desirable. The particle size of the copper powder is preferably at least 10 microns or less, smaller than the diamond particles.
[0015]
【Example】
Example 1
An embodiment will be described with reference to FIG. Cubic diamond particles 1 (average particle size 30 to 50 microns) are fixed to the surface of a copper powder pressure-molded body 2 having an average particle size of 10 microns to obtain a target 3. On the other hand, in order to accelerate the flying object with the pulse laser 4 at high speed, a laser beam with a pulse width of 10 nanoseconds of a YAG fundamental wave was focused on a 10 micron thick aluminum foil 5 to a beam diameter of 1.5 mm.
[0016]
The impact pressure was calculated by the impedance match method from the velocity immediately before the impact of the flying object. The impact velocity was calculated based on the experimental results of investigating the relationship between laser pulse energy and velocity in advance. In this example, an aluminum foil 5 having a thickness of 10 microns was made to collide with the target 3 at a speed of 4.8 Km / sec, and an impact treatment of about 80 GPa was performed on the cubic diamond particles 1 .
[0017]
The recovered sample was identified by micro-Raman spectroscopy after removing the flying aluminum with hydrochloric acid. The obtained results are shown in FIG. 1 is the starting cubic diamond. The symbol C corresponds to 1332 cm ^-1 for cubic diamond. 2 is a product after impact treatment, in addition to the C peak, a new peak corresponding to hexagonal diamond coexists. 3 is a product in the same sample and shows a peak of only hexagonal diamond. As shown in FIG. 2, depending on the location, a peak of 100% hexagonal diamond was observed, and it was revealed that the peak was locally converted to hexagonal diamond with a high conversion rate of almost 100% .
[0018]
【The invention's effect】
As described above in detail, the method of the present invention makes it possible to synthesize hexagonal diamond powder from cubic diamond powder at a high conversion rate by a single impact treatment.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory diagram of a method of Example 1. FIG.
FIG. 2 is a graph showing the results of Raman spectroscopic measurement of the impact recovery sample obtained in Example 1.

Claims (2)

By causing a high-speed object to collide with cubic diamond powder at an impact pressure of 30 GPa or more generated by instantaneous uniaxial pressurization by shock waves , shear stress is generated in cubic diamond powder within the thermodynamic stability region of cubic diamond. A method for synthesizing hexagonal diamond powder, characterized in that it transforms cubic diamond powder into hexagonal diamond powder by promoting transition between the laminated structures of cubic diamond and hexagonal diamond. . A cubic diamond particle having an average particle size of 30 to 50 microns is fixed on the surface of a copper powder pressure molded body having an average particle size of 10 microns or less to be a target, and the flying object is accelerated by a pulse laser to collide with the target. The method for synthesizing hexagonal diamond powder according to claim 1 .

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