JP3205970B2 - Diamond synthesis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing a high-purity (IIa type) diamond single crystal used for decoration and optical parts.

[0002]

[Prior Art] The Journal of Physical Chemistry, V
ol. 75, No. 12, 1971, pages 1838-1843, a series of reports on laboratory diamonds. Among them, as described in the right column of page 1841, from the lower right column, the fifth to third lines, it was described that an experimental report that aluminum was an important getter for nitrogen in growing a diamond single crystal was made. In the laboratory, diamond produced by research laboratories exhibits a yellow color due to nitrogen content, but the use of aluminum as a getter makes it possible to synthesize a yellow diamond in a colorless manner.
No. 3, "Method of Quality Control of Diamond Growth by Seed Diamond and High-Pressure Reaction Vessel", to Examples 6, 7, and 8 of the specification entitled "Addition of 3 wt% and 5 wt% of Al to Fe solvent." Shows that a gem-grade semi-colorless or colorless diamond can be synthesized.

[0003] As described above, in the conventional synthesis of semi-colorless or colorless diamond, Fe is used as a getter for nitrogen.
Almost all of them have been added, and large diamonds have been successfully synthesized on seed crystals by the temperature difference method. The method of synthesizing diamond by the temperature difference method is disclosed in the above-mentioned U.S. Pat. No. 4,340,066 and the drawings.

[0004] As an example of using a nitrogen getter other than Al, an inorganic material research institute report No. 39 discloses that Ti and Zr are replaced with Fe, Ni, Co,
It has been reported that diamond is synthesized by being added to a metal or alloy solvent such as Mn or Cr.

[0005] However, the combinations that have produced colorless diamonds are Fe-Zr, (Fe-Ni) alloy-Zr,
(Ni-Mn) alloy-Zr, which cannot be obtained by using another combination as a solvent. Of the above combinations, those having no absorption in the wavelength region of 500 nm or less are only the combinations of Fe-Zr. 500nm
The occurrence of absorption in the following wavelength ranges suggests that the nitrogen atoms have not been completely removed.

[0006]

SUMMARY OF THE INVENTION As already mentioned,
In the conventional method, a method of mainly adding Al to a solvent and removing nitrogen is used. In this case, the relationship between the amount of Al added to the solvent and the nitrogen concentration (nitrogen content) in the crystal is shown in FIG. 1, and the relationship between the amount of Al added and the inclusion (solvent metal content, entrainment amount) in the crystal. The relationship is shown in FIG. 2, but has the following problems. Increasing the amount of Al decreases the nitrogen concentration in the crystal, but increases the inclusion. In order to synthesize a high-quality single crystal with little inclusion, it is necessary to reduce the growth rate. If the nitrogen is removed too much, the crystals are colored blue by the boron (B) remaining slightly in the solvent. On the other hand, like Ti and Zr, there is a getter action of nitrogen,
At the same time, when an element that also forms a carbide is added, the formed carbide is taken into the crystal, and there is a disadvantage that a high-quality one cannot be obtained.

[0007]

In order to solve the above problems, the present invention employs the following method. As a nitrogen getter, Ti, Zr, Hf, V, Nb, Ta
One or more selected compounds are used. These elements easily form borides and have an effect of removing blue. In order not to incorporate carbide into the crystal,
A low-viscosity element such as Al, Sn, In, Ga, Ag, Cu, Cs, Pb, Sb, and Zn is added to increase the floating (precipitation) speed of the carbide, and the carbide formed is taken into the crystal. Float above the solvent or settle below.

[0008]

[Function] (1) Function of using Ti, Zr, Hf, V, Nb, and Ta as a nitrogen getter The above-mentioned element or a compound of these elements forms a stable nitride and functions as a nitrogen getter. At this time, assuming that the above element is A, it reacts according to the following chemical reaction formula to remove nitrogen.

[0009]

Embedded image

As a solvent for synthesizing ordinary diamond, Fe, Co, Ni, Mn, and Cr are used. The higher the reaction constant of the above reaction formula, the greater the effect of removing nitrogen. The reaction constant K depends on the solvent element, is small in the Ni solvent,
Large in Fe solvent. Therefore, nitrogen is easily removed when synthesized with Fe solvent, but the diffusion rate of carbon is slow in the same solvent,
Since a shortage of carbon is likely to occur, high-quality crystals cannot be obtained if the growth rate is high. Solvent with high carbon diffusion rate is Co
It is. Therefore, it is preferable to use an alloy solvent of Fe and Co. The solvent metal usually contains a small amount of boron (number
ppm). In the crystal, a solvent concentration of about 1
About / 10 of boron is taken in, resulting in a concentration of about 0.1 to 0.6 ppm. If the nitrogen getter's nitrogen removal action is too great,
Nitrogen, which has been electrically neutralized with boron in the solvent, is not contained in the crystal and becomes bluish instead of transparent. The elements Ti, Zr, Hf, V, Nb, and Ta are also easy to form borides, and can reduce blue as a boron getter.

(2) Effect of adding low-viscosity metal elements such as Al and Sn Ti, Zr, Hf, V, Nb and Ta form stable nitrides and are effective in removing nitrogen from the solvent. Act as a getter. However, at the same time, it reacts with the carbon dissolved in the solvent to produce a large amount of carbide. The carbides and nitrides are caught in the crystal and lower the quality of the crystal. In addition, these carbides and nitrides serve as nuclei, and the solvent metal is likely to be contained in the crystal. Therefore, it is important to remove carbides and nitrides before crystal growth. Since the getter element, carbon, and nitrogen are uniformly dispersed in the formed carbide and nitride, minute carbide and nitride can be formed. These minute carbides and nitrides do not float or precipitate in a short time even if there is a difference in specific gravity with the solvent. It is effective to lower the viscosity of the solvent in order to float or precipitate the carbides and nitrides in a short time so that the carbides and nitrides do not float in the solvent during crystal growth. Generally, the sedimentation (or floating) speed of a colloidal spherical microparticle is represented by the following equation.

[0012]

(Equation 1)

Therefore, the sedimentation (or floating) speed of the solvent theoretically decreases in inverse proportion to the viscosity of the solvent. Therefore, to increase the sedimentation (or floating) speed, it is effective to lower the viscosity of the solvent. In addition, Al, In, Ga, and the like are elements that easily form nitride at the same time. Therefore, nitrogen can be removed by adding these elements. in this case,
Rather than adding metals such as Al, In, and Ga alone, Ti, Zr, Hf
The amount of the solvent entangled in the crystal is reduced by the addition of the above. For example, when Al is solely added as a getter, 2
Crystals of good quality up to wt% are obtained, and when these crystals are brilliant cut, the clarity of inclusions can be evaluated as VS or SI. When Al and Ti are added at the same time, even if 3 wt% of Al is added, the same result as above is obtained.
It is presumed that a nitride composed of three elements such as the above is formed.

A method and an apparatus for synthesizing a diamond single crystal by a temperature difference method using seed diamond are described below.
Although shown in the above-mentioned U.S. Patent Specification No. 4034066 and the drawings, the outline of the present invention will be described. As shown in FIG. 3, a graphite tube heater 2 is provided inside a pyrophyllite cylinder 3, a pyrophyllite 1 is provided inside the same, a seed diamond 5 is disposed inside the pyrophilite 1, and a solvent metal 6 is disposed thereon. Further, a carbon source 7 is provided, and the upper and lower portions of the laminate are filled with plugs 4 and 8, respectively. The plugs 4 and 8 and the pyrophyllite cylinder 3 are of the same standard and are pressure transmitting members. Although not shown, a die made of cemented carbide, and a predetermined pressure placed in the reaction vessel placed in the hole of the die by using upper and lower punches corresponding to the hole of the die so that the heater 2
To heat the reaction vessel and pressurize it with a punch to synthesize diamond. Upon heating, the carbon source dissolves in the metal solvent, and crystal growth occurs on the seed crystal due to the temperature difference (20 to 30 ° C.).

[0015]

Example 1 Diamond stable region (5.4 GPa, 1320
C.) and 0.6 to 0.8 carats of diamond were grown on seed diamond crystals over 60 hours using the temperature difference method. As a synthesis solvent, one obtained by adding Ti and Al to Fe-Co was used. Table 1 shows the results. The nitrogen concentration in the crystal was determined by ESR (electron spin resonance), and the amount of solvent involved in the crystal was measured by a magnetic balance.

[0016]

[Table 1]

As shown in Table 1, when only Ti is added, the color becomes H color or more when the content of Ti is 0.5 wt% or more, but the amount of solvent involved increases, and the value of decorative use is lost. Due to the increase in Al, the amount of solvent involved is drastically reduced, and high-quality crystals can be obtained. However, when 5 wt% of Al is added, the amount of solvent involved increases. Even when Al is added, if 10 wt% of Ti is added, the amount of solvent involved increases, and good crystals cannot be obtained. As described above, the range of addition of Al and Ti from which a good color and high quality crystals can be obtained is in the range of 0.5 ≦ Al ≦ 3 (wt%) and 0.5 ≦ Ti ≦ 7 (wt%). Further, Sn, In, Ag, Cu, Cs, Pb, Sb, and Zn are converted to Al.
Similar results can be obtained by adding instead of.

[0018]

[Example 2] Using a temperature difference method, in the stable region of diamond (5.3 GPa, 1300 ° C), 140
Over time, 8-10 carats of IIa diamond were grown. A 3 mm single crystal was used as the seed diamond crystal. As the solvent, an ingot of an alloy was prepared in advance, and a mixture of a powder and carbon powder was used. The composition of the alloy was as follows: Zr, Hf, V,
Select and add Ti, Sn, I as a substance to reduce viscosity
A material obtained by selecting and adding n, Ga, and Zn was used. The resulting single crystal was processed into a disk shape and subjected to ultraviolet-visible and infrared spectroscopy. In addition, carbides and nitrides in the crystals were examined with a transmission microscope. It was determined by spectroscopic analysis and a microscope whether or not it could be used as a window material. Table 2 shows the results.

[0019]

[Table 2]

As can be seen from Table 2, only by adding the getter material, carbonitrides (mainly carbides) are formed and are caught in the crystal and cannot be used as window materials. But S
By adding n, In, Ga, and Zn, these carbides and nitrides float or precipitate in a short time and are not contained in the crystal.
It is considered that good quality crystals can be obtained.

[0021]

As described above, according to the present invention, a colorless and transparent diamond single crystal with less entrainment of a metal solvent can be easily synthesized as compared with the conventional method, and can be supplied at a low cost. Became. It is effective to use the diamond synthesized by the method of the present invention for decorative articles and infrared optical parts.

[Brief description of the drawings]

FIG. 1 shows the relationship between the nitrogen content in a crystal and the amount of Al added to a nitrogen getter in a conventional method.

FIG. 2 shows the content of a solvent metal in a crystal according to a conventional method.
The relationship between the amounts of Al added is shown.

FIG. 3 shows a schematic view of the inside of a reaction vessel for carrying out the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pyrophyllite 2 Heater 3 Pyrophyllite cylinder 4,8 Plug 5 seed diamond crystal 6 Solvent metal 7 Carbon source

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-96712 (JP, A) JP-A-48-81793 (JP, A) JP-A-50-10795 (JP, A) 7639 (JP, B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 3/06 C01B 31/06

Claims (4)

(57) [Claims] 1. A method comprising: adding an element which simultaneously forms nitride and carbide in a solvent as a nitrogen getter in a stable region of diamond using a temperature difference method as a nitrogen getter; A method of synthesizing a type IIa diamond, wherein nitrides and carbides are floated upward or precipitated downwardly before GaN grows. 2. Nitrogen getters such as Ti, Zr, Hf, V,
Consisting of one or more elements selected from Nb and Ta,
The method for synthesizing diamond according to claim 1, wherein boron remaining in the solvent is removed. 3. As an element having a low viscosity, Al, Sn, In, G
2. The method according to claim 1, wherein a, Cu, Cs, Pb, and Zn are added. 4. The amount of nitrogen getter added is 0.1% by weight.
2. The method for synthesizing diamond according to claim 1, wherein the addition amount of the element having a low viscosity of 5 or more and 7 or less and 0.5 to 3 in weight%.