JPH0760100A - Radiant adiabatic pressure medium for high temperature and ultra-high pressure - Google Patents

Abstract

PURPOSE:To enhance the excellent article yield of diamond, to conserve power consumption and to extend the life of a cylinder by enhancing heat insulating effect without damaging the flowability of a pressure medium. CONSTITUTION:A radiant adiabatic pressure medium contains 0.1-25wt.% of sodium chloride or a pressure medium containing sodium chloride and a heat insulating material whose heat conductivity is lower than that of sodium chloride and a radiant adiabatic absorbent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation adiabatic pressure medium for high temperature and ultra high pressure used in the production of diamond, cubic boron nitride and the like.

[0002]

2. Description of the Related Art The most common pressure medium for producing diamond and cubic boron nitride is sodium chloride (Japanese Patent Publication No. 43-28690). Since sodium chloride has low shear strength, it has fluidity even when cold-compressed, and a uniform pressure distribution can be obtained even when the system temperature is low. Therefore, sodium chloride is particularly preferable as a pressure medium. However, the heat insulating effect at high temperature can hardly be expected. For the purpose of improving this, an attempt has been made to add a heat insulating ceramic having a low thermal conductivity to sodium chloride to have a heat insulating effect (Japanese Patent Publication No. 63-1).
9207). However, this method only reduces the heat conduction, and the heat insulation effect greatly depends on the compounding ratio,
If an attempt is made to obtain a sufficient heat insulating effect, the workability is lowered and there is a practical problem.

[0003]

DISCLOSURE OF THE INVENTION The present invention further improves the heat insulating property of the pressure medium and makes the temperature distribution of the system uniform, without impairing the excellent properties of sodium chloride as a pressure medium, especially the fluidity. The object of the present invention is to improve the yield of non-defective products such as diamond, reduce the power consumption, and extend the life of the mold member for synthesizing diamond or for high temperature and ultra high pressure.

[Means for Solving the Problems]

The present invention relates to a radiant adiabatic pressure medium for high temperature ultrahigh pressure containing a pressure medium containing sodium chloride or sodium chloride and a heat insulating material having a thermal conductivity lower than that of sodium chloride, and a radiation adiabatic absorber of 0.1 to 25% by weight. . The pressure medium used in the present invention is sodium chloride alone or a combination of sodium chloride and a heat insulating material having a lower thermal conductivity than sodium chloride.

Insulating materials having a lower thermal conductivity than sodium chloride include alkali metal halides other than sodium chloride, such as potassium bromide, as well as ceramics, zirconia (ZrO ₂ ) and fosterite (Mg ₂ SiO ₄ ). It is illustrated.

The thermal conductivity of sodium chloride is about 0.10 W.
・ Cm ^-1 · K ^-1 (specific gravity: 2.16), which has a thermal conductivity lower than that of sodium chloride and is generally used, has a thermal conductivity of about 0.02 (ZrO ₂ ). To 0.06 (KB
r) Since it is K · cm ⁻¹ · K ⁻¹ , the more the amount of these components is blended, the more the heat insulation of the pressure medium is improved, but the fluidity (hydrostatic pressure) is decreased or the volume is decreased due to the phase transition. Since such phenomena occur, the amount is naturally limited. Generally, the compounding amount may be determined based on the desired properties, but in the case of an alkali metal halide such as potassium bromide, the moldability is good, but at low pressure (about 18,000 atm), the volume is Since large-scale presses for industrial production such as belt type and cubic type, which have a limited stroke, have a limit of 50% by weight at most, because they cause phase transfer accompanied by reduction. Further, ceramics, zirconia, fosterite, etc. have too high a shear strength, and therefore a large amount of the compound markedly impairs the fluidity. Therefore, the amount used is at most 10% by weight.

In the present invention, the pressure medium is mixed with a radiation adiabatic absorber to absorb the radiant heat and insulate it. Sodium chloride itself has essentially no radiation adiabatic effect because it becomes transparent and colorless under melting at high temperature and high pressure during diamond synthesis. In the present invention, an attempt is made to perform heat insulation by absorbing this radiant heat, which has been completely ignored in the past. The radiation adiabatic absorber blended in the pressure medium is black and can be easily formed into a uniform dispersion in the pressure medium, especially sodium chloride, and does not segregate or separate when the pressure medium, especially sodium chloride is melted (melt It has to have a small difference in specific gravity and good wettability), must not decompose at high temperature and ultra high pressure, and must not react with the pressure medium. As those satisfying these characteristics, carbon-based ones such as artificial graphite, natural graphite, carbon black, amorphous carbon, charcoal tar and pitch are particularly preferable. Particularly, the carbon-based radiation adiabatic absorber is preferable because it exhibits excellent fluidity.

The amount of these radiation adiabatic absorbers to be blended is preferably 0.1% by weight to 25% by weight, and more preferably 0.3% by weight to 5% by weight, based on the total amount of the radiation adiabatic pressure medium for high temperature and high pressure. The radiation adiabatic absorption effect is clearly observed from 0.1% by weight (for example, FIG. 2), and becomes substantially constant at 0.3% by weight or more. 25
If it is more than 10% by weight, moldability is adversely affected and conductivity is generated. Speaking of moldability, natural graphite and carbon black are excellent, and natural graphite and artificial graphite are particularly excellent in thermal stability.

The particle size of the radiation adiabatic absorber to be blended is not particularly limited, but artificial graphite is preferably # 100 or less from the viewpoint of dispersibility. The particle size is not so important because natural graphite and carbon black easily crush and flow during molding. A normally available grade product may be appropriately used.

The radiation adiabatic pressure medium for high temperature ultra high pressure of the present invention uniformly mixes predetermined raw materials, puts it in a molding die having a predetermined shape, and pressurizes it at 1,000 kgf / cm ^{2 to} 3,000 kgf / cm ^2.
Compress at room temperature. This condition is a guideline and is not fixed, and may be appropriately determined depending on the mold material, the formability of the pressure medium, and the like. Usually, it is molded into a shape such as a cylinder or a pellet.

The present invention will be described below with reference to examples. Examples 1 and 2 and Comparative Examples 1 and 2 The formulations of the radiation adiabatic pressure medium for high temperature ultrahigh pressure are shown below. Formulation 1 (Comparative Example 1) Sodium chloride alone Formulation 2 (Comparative Example 2) Parts by weight Sodium chloride 90 Potassium bromide 10 Formulation 3 (Example 1) Parts by weight Sodium chloride 99 Artificial graphite (# 400) 1 Formulation 4 (Example 2) Parts by weight Sodium chloride 89 Potassium bromide 10 Artificial black smoke (# 400) 1

A uniform mixture of the above formulation is placed in a molding die of a predetermined shape, compressed at a pressure of 2,000 kgf / cm ² at room temperature, and radiated adiabatic pressure medium for cylindrical high temperature ultrahigh pressure (outer circumference 40 mm, inner circumference 34 mm, A height of 40 mm) was obtained.

The material for diamond production in the radiant heat insulating pressure medium (5) for cylindrical high temperature ultra high pressure according to the present invention obtained above.
As (6), artificial graphite and Ni-Fe alloy catalyst (diameter 34 m
m, thickness 0.5 mm) were alternately laminated vertically in 40 layers. Insert the radiant adiabatic pressure medium for high temperature ultra high pressure into the cylinder (3) with the gasket (4) of the diamond manufacturing machine shown in FIG.
The electrode plates (11, 12) are sandwiched between the energizing rings (7, 8) and the heat insulating materials (9, 10) above and below, and an ultrahigh pressure of about 50,000 atm is applied by the anvils (1, 2). Then, it was energized and heated to about 1500 ° C for about 15 minutes. Pressure is a fixed point substance in advance
A calibration curve of the electric resistance change of (Bi, Tl, Ba) and its corresponding hydraulic pressure was prepared, and the control was performed based on this curve. The reaction temperature was measured by inserting a Pt-PtRh 13% thermocouple in the center of the raw material.

The above operation was repeated to produce diamond, and the yield of good diamond and the life of the mold were examined.
Good quality criteria for diamond is unreacted graphite with automorphic crystals (having a hexa-octahedral shape) surrounded by flat low index planes,
It is a bright and transparent yellow crystal containing little catalyst. The results are shown in Table 1.

[0015]

[Table 1]

The input power required to raise the reaction temperature to 1500 ° C. was measured for Comparative Examples 1 and 2, and for Example 1 and 2, the input power when the amount of radiation adiabatic absorber was increased. Was measured. In Example 2, the amount of potassium bromide was kept constant at 10 parts by weight, and the amount of sodium chloride was reduced by the increased amount of artificial graphite. The results are shown in Figure 2. In the figure, (13), (14), (15)
And (16) are Comparative Examples 1 and 2 and Example 1, respectively.
Results corresponding to and are shown.

[0017]

EFFECTS OF THE INVENTION By using the radiation adiabatic pressure medium for high temperature and ultrahigh pressure of the present invention, the adiabatic effect can be improved without impairing the fluidity of the pressure medium, so that the yield of good diamond products is improved and the power consumption is reduced. Saves money and extends cylinder life.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a diamond manufacturing apparatus.

FIG. 2 is a diagram showing the relationship between the blending amount and power consumption when the radiation adiabatic pressure medium for high temperature and ultrahigh pressure of the present invention is used.

[Explanation of symbols]

1, 2: Anvil, 3: Cylinder, 4: Gasket, 5: Pressure medium, 6: Diamond manufacturing material,
7, 8: energizing ring, 9, 10: heat insulating material, 11, 1
2: electrode plate, 13: comparative example 1, 14: comparative example 2, 1
5: Example 1, 16: Example 2

Claims (4)

[Claims] 1. A radiation adiabatic pressure medium for high temperature ultrahigh pressure, comprising a pressure medium containing sodium chloride or sodium chloride and a heat insulating material having a lower thermal conductivity than sodium chloride, and a radiation adiabatic absorber of 0.1 to 25% by weight. 2. The radiation adiabatic absorber is artificial graphite, natural graphite,
The radiant adiabatic pressure medium for high temperature ultra high pressure according to claim 1, which is selected from amorphous carbon, charcoal, tar and pitch. 3. The particle size of the radiation adiabatic absorber is # 10- # 40.
The radiant adiabatic pressure medium for high temperature ultrahigh pressure according to claim 1, which is 0. 4. The radiant heat insulating pressure medium for high temperature ultrahigh pressure according to claim 1, wherein the heat insulating material having a lower thermal conductivity than sodium chloride is selected from alkali metal halides other than sodium chloride, ceramics, zirconia and forsterite.