JPH0558786A - Method for synthesizing diamond - Google Patents

Abstract

PURPOSE:To remove nitrogen which makes diamond crystals yellowish from a solvent by adding Al, Ti or Zr to the solvent when seed diamond crystals are put in a region in which diamond is stably grown by a temp. difference method in the case of diamond synthesis with the seed crystals as nuclei by diffusing carbon from a carbon source fed through the solvent and to inhibit the intrusion of carbide and nitride into diamond crystals, since the deterioration of the quality of synthesized diamond due to the intrusion is occurred in the case when Ti or Zr is added. CONSTITUTION:An element forming nitride and carbide at the same time is added as a nitrogen getter to a solvent. The element has lower viscosity than the solvent. Nitride and carbide formed before the growth of diamond crystals are allowed to float or settle.

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, pp. 1838-1843, a series of reports on laboratory diamonds is made. Among them, as described in the right column of page 1841, lines 5 to 3, it was stated that an experimental report was made that aluminum was an important getter for nitrogen in the growth of diamond single crystals. However, the diamond produced by the laboratory exhibits a yellow color because it contains nitrogen, but by using aluminum as a getter, it is possible to synthesize the yellow diamond in a colorless manner, and US Patent No. 4034066.
Nos. 3, 5 and 7 of the specification in which "Method and high-pressure reactor for quality control of diamond growth by seed diamond" of the specification is the title of the invention, 3 wt% and 5 wt% of Al is added to the Fe solvent. Show that it is possible to synthesize gem grade semi-colorless or colorless diamond.

As described above, in the conventional quasi-colorless or colorless diamond synthesis, Fe is used as a getter of nitrogen.
Almost all of them were added with Al, and large diamond was successfully synthesized on the seed crystal by the temperature difference method. The method of synthesizing diamond by the temperature difference method is disclosed in the above-mentioned US Pat. No. 4034066 and the drawings.

Examples of the use of nitrogen getters other than Al include Ti, Zr in Fe, Ni, Co,
It has been reported that diamond is synthesized by adding it to a metal or alloy solvent such as Mn or Cr.

However, the combination that produced colorless diamond was Fe-Zr, (Fe-Ni) alloy-Zr,
(Ni-Mn) alloy-Zr, which cannot use other combinations as the solvent, cannot be made. Of the above combinations (1) to (4), the only one that has no absorption in the wavelength range of 500 nm or less is the combination of Fe and Zr. 500 nm
The absorption occurring in the following wavelength range suggests that the nitrogen atom has not been completely removed.

[0006]

[Problems to be Solved by the Invention] As described above,
In the conventional method, a method of mainly adding Al to a solvent and removing nitrogen was 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 addition amount of Al and the inclusion (solvent metal content, inclusion amount) in the crystal The relationship is shown in FIG. 2, but has the following problems. Increasing the amount of addition of Al decreases the nitrogen concentration in the crystal but increases the inclusion. To synthesize a good-quality single crystal with few inclusions, it is necessary to reduce the growth rate. If nitrogen is removed too much, the crystals will turn blue due to the slight amount of boron (B) remaining in the solvent. On the other hand, like Ti and Zr, it also has a gettering function for nitrogen,
At the same time, if an element that also forms a carbide is added, the formed carbide is taken into the crystal, and it is not possible to obtain a good quality one.

[0007]

In order to solve the above problems, the present invention uses the following method. As a nitrogen getter, the solvent is Ti, Zr, Hf, V, Nb, Ta.
One selected from the above or a composite of two or more selected is used. These elements easily form borides and have an effect of removing blue color. In order to prevent the carbide from being incorporated into the crystal,
Carbide formed by adding low-viscosity elements such as Al, Sn, In, Ga, Ag, Cu, Cs, Pb, Sb, and Zn, and increasing the speed of precipitation (precipitation) of the carbide is incorporated into the crystal. Before being exposed, it is floated above the solvent or precipitated below.

[0008]

(1) Action of using Ti, Zr, Hf, V, Nb, and Ta as a nitrogen getter The above elements or a combination of these elements forms a stable nitride and acts as a nitrogen getter. At that time, assuming that the above element is A, nitrogen is removed by reacting according to the following chemical reaction formula.

[0009]

[Chemical 1]

Fe, Co, Ni, Mn and Cr are used as a solvent for synthesizing ordinary diamond. 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 and is small in the Ni solvent,
Large in Fe solvent. Therefore, when synthesized in Fe solvent, nitrogen is easily removed, but carbon diffusion rate is slow in the solvent,
Since insufficient carbon supply is likely to occur, high-quality crystals cannot be obtained if the growth rate is high. The solvent with a high carbon diffusion rate is Co
Is. Therefore, it is preferable to use an alloy solvent of Fe and Co. In addition, in the above solvent metal, usually a small amount of boron (number
ppm) is included. In the crystal, the solvent concentration is about 1
Boron of about / 10 is taken in and the concentration becomes about 0.1 to 0.6 ppm. If the nitrogen getter removes too much nitrogen,
Nitrogen, which has been electrically neutralized with boron in the solvent, is not contained in the crystal, and becomes transparent to bluish. The elements of Ti, Zr, Hf, V, Nb, and Ta are easy to form borides, and can reduce the blue color as a boron getter.

(2) Effect of adding low-viscosity metal element such as Al and Sn Ti, Zr, Hf, V, Nb, and Ta are effective in removing nitrogen in the solvent because they form stable nitrides. Acts as a good getter. However, at the same time, it reacts with the carbon dissolved in the solvent to form a large amount of carbide. The carbides and nitrides are caught in the crystal and deteriorate the quality of the crystal. Further, these carbides and nitrides serve as nuclei, and the solvent metal is likely to be contained in the crystal. Therefore, it is an important problem to remove carbides and nitrides before crystal growth. Since the getter element, carbon, and nitrogen are uniformly dispersed in the formed carbide or nitride, minute carbide or 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 from the solvent. In order to float or precipitate the carbides and nitrides in a short time so as not to float in the solvent during crystal growth, it is effective to reduce the viscosity of the solvent. Generally, the sedimentation (or floating) rate of colloidal spherical micromaterials is expressed by the following equation.

[0012]

[Equation 1]

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

Regarding the method and apparatus for synthesizing a diamond single crystal by the temperature difference method using seed diamond,
Although shown in the above-mentioned US Pat. No. 4034066 and the drawings, an outline thereof will be explained in carrying out the present invention. As shown in FIG. 3, a graphite tube heater 2 is provided inside a pyrophyllite cylinder 3, a pyrophyllite 1 is provided inside the pyrophyllite cylinder 3, a seed diamond 5 is placed inside the pyrophyllite cylinder 1, and a solvent metal 6 is placed on the seed diamond 5. Further, a carbon source 7 is arranged, and plugs 4 and 8 are filled at the top and bottom of the stack. The plugs 4, 8 and the pyrophyllite cylinder 3 are of the same standard and are pressure transmitting members. Although not shown, a die made of a cemented metal and upper and lower punches corresponding to the holes of the die are used to pressurize the reaction container placed in the hole of the die, and the heater 2
Is energized to heat the inside of the reaction vessel and pressurize with a punch to synthesize diamond. By heating, the carbon source dissolves in the metal solvent, and the temperature difference (20 to 30 ° C.) causes crystal growth on the seed crystal.

[0015]

[Example 1] Diamond stable region (5.4 GPa, 1320
The temperature difference method was used to grow 0.6-0.8 carat diamonds over 60 hours on seed diamond crystals. As a synthetic solvent, Fe-Co to which Ti and Al were added was used. The results are shown in Table 1. The nitrogen concentration in the crystal was determined by ESR (electron spin resonance), and the amount of solvent entrained 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 Ti is 0.5 wt% or more, but the amount of solvent entrainment increases and the value for decorative use is lost. The increase in Al drastically reduces the amount of solvent entrainment, and good quality crystals can be obtained. However, the addition of 5 wt% Al increases the amount of solvent entrainment. Further, even if Al is added, if 10 wt% of Ti is added, the amount of solvent entrainment increases, and good quality crystals cannot be obtained. As described above, the addition ranges of Al and Ti that can obtain good color and good quality crystals are in the range of 0.5≤Al≤3 (wt%) and 0.5≤Ti≤7 (wt%). In addition, Sn, In, Ag, Cu, Cs, Pb, Sb, Zn are Al
Similar results can be obtained by adding instead of.

[0018]

Example 2 Using the temperature difference method, in the stable region of diamond (5.3 GPa, 1300 ° C.), 140
8-10 carat IIa diamonds were grown over time. A 3 mm single crystal was used as the seed diamond crystal. As the solvent, an alloy ingot was prepared in advance and powdered and mixed with carbon powder. The composition of the alloy is Fe-Co-Ni with Zr, Hf, V, as a nitrogen getter.
Sn, I is added as a substance to reduce the viscosity by selectively adding Ti.
We used n, Ga and Zn selected and added. The resulting single crystal was processed into a disk shape and subjected to ultraviolet-visible and infrared spectroscopic analysis. In addition, a carbide and a nitride in the crystal were examined by a transmission microscope. It was determined by spectroscopic analysis and a microscope whether it could be used as a window material. The results are shown in Table 2.

[0019]

[Table 2]

As can be seen from Table 2, carbonitrides (mainly carbides) are formed only by adding the getter material, are caught in the crystal, and cannot be used as a window material. However, S
By adding n, In, Ga, 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 it can be supplied at a low cost. Became. It is effective to use the diamond synthesized by the method of the present invention for ornaments and infrared optical parts.

[Brief description of drawings]

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

FIG. 2 shows the content of solvent metal in crystals in the conventional method and
The relation of the added amount of Al is shown.

FIG. 3 shows an outline of the inside of a reaction vessel for carrying out the present invention.

[Explanation of symbols]

 1 Pyrophyllite 2 Heater 3 Pyrophyllite Cylinder 4,8 Plug 5 Kinds of diamond crystals 6 Solvent metal 7 Carbon source

Claims (4)

[Claims] 1. A crystal is obtained by using a temperature difference method in a stable region of diamond to add an element that simultaneously forms a nitride and a carbide in a solvent as a nitrogen getter, and further adding an element having a lower viscosity than the solvent. A method for synthesizing type IIa diamond, characterized in that a nitride and a carbide are floated upward or precipitated downward before growing. 2. As a nitrogen getter, 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. An element having a low viscosity is Al, Sn, In, G.
The method for synthesizing diamond according to claim 1, wherein a, Cu, Cs, Pb, and Zn are added. 4. A nitrogen getter is added in an amount of 0.
The method for synthesizing diamond according to claim 1, wherein the addition amount of the element having a viscosity of 5 or more and 7 or less and a low viscosity is 0.5 to 3 in weight%.