Method of change of diamond color at high temperature and high pressure

FIELD: treatment of diamonds.

SUBSTANCE: proposed method of change of diamond color includes the following stages: (i) forming reaction mass at presence of diamond in pressure-transmitting medium fully surrounds the diamond; (ii) subjecting the reaction mass to action of high temperature and pressure during required period of time; proposed diamond is brown diamond, type IIa; its color is changed from brown to colorless by subjecting the reaction mass to action of temperature of from 2200°C to 2600°C at pressure of 7.6 Gpa to 9 Gpa.

EFFECT: possibility of keeping diamond intact during treatment.

46 cl, 4 dwg, 1 ex

 

Background of invention

This invention relates to a method of changing the color of the diamond.

Diamonds usually are divided into four main types: Ia, Ib, IIa and IIb. These types usually differ in the infrared and ultraviolet spectra. The diamonds are type Ia and Ib contain nitrogen in a combination of different forms. Diamond type Ib contains single substitutional nitrogen atoms or centers. Diamond type Ia contains a combination of different structures of the nitrogen atoms. Diamonds of type IIa have a nitrogen content of less than a few parts per million and can be characterized as diamonds, which do not exhibit essentially no absorption in the range 1332-400 cm-1irradiated by infrared radiation. The diamond is type IIa may have a brown color, due, as I believe, structural deformation within the crystal lattice of the diamond.

In U.S. patent 4124690 described method of converting nitrogen type Ib nitrogen to type Ia in diamond type Ib by high-temperature annealing under pressure, which prevents graphitization. The result of this processing is to reduce the yellow color of the diamond type Ib.

The invention

In accordance with the present invention, a method for changing the color of a diamond, comprising the stage of:

(i) creating a reaction mixture by providing diamond in re the non pressure environment, which completely surrounds the diamond; and

(ii) impact on the reaction mass to high temperature and pressure for a suitable period of time,

characterized in that a diamond is a brown diamond type IIa, and its color change from brown to colorless by treatment of the reaction mass temperature in the range from 2200 to 2600°at a pressure of from 7.6 to 9 GPA.

The period of time during which the diamond is exposed to conditions of stage (ii), will generally be the longer than used below the temperature of the above interval. The duration of heat treatment, as a rule, does not exceed 5 hours. The preferred conditions for stage (ii) are a temperature in the range from 2500 to 2550°supported during the period of time up to 90 minutes. Examples of suitable conditions for stage (ii) are the following:

2500°during the period of 1 hour;

2300°C for a time period of 5 hours.

The reaction mass may also be subjected to two-stage heat treatment in stage (ii). In the first stage, the reaction mass is subjected to temperatures in the range from 1900 to 2300°under pressure from 6.9 to 8.5 GPA for a suitable period of time, and then, in the second stage, is exposed to higher the temperature, in the above interval. In the first phase diamond color changes to pink or lighter brown, and the second stage diamond color changes from pink or lighter brown to colorless. In this embodiment of the invention, the heat treatment at the first stage will usually continue for a period of time in the interval from 10 minutes to 10 hours, preferably from 20 minutes to 4 hours. The preferred temperature is in the range from 2100 to 2300°and the preferred pressure is from 7.4 to 8.5 GPA. At the end of the first phase of the diamond is preferably examined to determine its color. The heat treatment at the second stage is preferably carried out within a period of up to 90 minutes, usually about 1 hour. You can use over extended periods of time up to 5 hours, but, as a rule, they are undesirable because of the high temperatures used in this step. In the second stage, the preferred temperature is from 2500 to 2550°and the preferred pressure is between 8.4 to 8.6 GPA.

Description of embodiments

In accordance with the present invention a brown crystal diamond type IIa, which, as a rule, is a natural diamond is annealed under pressure, which prevents significant g is oficialy, to modify the structural deformation, which causes staining in brown color, and thus reduce brown color and to obtain a colorless diamond. Two-step annealing process in the above stage (ii) allows changing colors orderly manner, limiting the potential damage of a diamond.

A typical absorption spectrum of the diamond type IIa in the infrared region is shown in figure 1. However, not all diamonds are type IIa suitable for color change due to processing at high temperature and high pressure according to the present invention. Diamonds should have a brown color, which can vary from dark to light brown, including, for example, pinkish-brown. Those diamonds are type IIa, which is most suitable for the present invention are the nitrogen concentration less than 2 ppm, preferably less than 0.2 parts per million, have colors ranging from brown to pinkish-brown and have a typical absorption spectrum in the ultraviolet and visible region, shown in figure 2 in the form of lines (a), which shows a monotonically increasing absorption or monotonically increasing absorption with wide bands with centers at wavelengths of about 390 and 550 nm, as shown in figure 2 as line (b).

Color changing crystal diamond type IIa can be quantitative is estimated by changes in the absorption spectrum of the crystal, obtained before and after annealing. Absorption spectra of the crystal get at room temperature using a spectrometer in the usual way, which allows to obtain the absorption spectrum of the crystal in the UV and visible region. After annealing the crystal again obtain spectra at room temperature.

The handling of such diamonds in accordance with the method according to this invention leads to the reduction or elimination as a monotonically increasing absorption, and the absorption bands at wavelengths of 390 and 550 nm, which results in virtually colorless diamond. If you use the two-step heat treatment, the first step will be a reduction in the intensity monotonically increasing absorption and the formation or the intensity of the broad absorption bands at wavelengths of 390 and 550 nm.

In the method according to this invention, the reaction mass is generated by the availability of diamond in a pressure-transmitting medium, which completely surrounds the diamond. Preferably, the reaction mass is generated by sealing a pressure-transmitting medium around the diamond before placing the diamond in the reaction zone of the plant for treatment at a high temperature and high pressure and prior to exposure to the reaction mass to conditions of stage (ii). Transmitting the pressure of the environment represents Narodnoy (homogeneous) environment, which completely surrounds the diamond or each of the diamond and which is applied over the entire surface of a diamond or of each of the diamonds. Transmitting the pressure medium is preferably a homogeneous transmitting pressure environment, which provides a uniform distribution of pressure, which is applied over the entire surface of the processed diamond. Examples of suitable media are those that have low shear strength, such as metal salts, for example, halide salts of metals. Transmitting the pressure medium may be a salt of an alkali metal or a salt of the noble metal. Examples of suitable halide salts of metals are potassium bromide, sodium chloride, potassium chloride, cesium chloride, cesium bromide, copper chloride and copper bromide.

It was found that such environments provide the desired uniform distribution of pressure, which ensures that any graphitization that can occur on the surface of the diamond will remain minimal. A special advantage of the use of halide metal salt as a pressure-transmitting medium is that diamonds can be easily extracted after processing by dissolving medium in hot water.

The method according to the invention can be used for processing a single diamond or sets discre is different (disparate) diamonds. If handle multiple diamonds at the same time, each diamond must be separated from adjacent diamonds a pressure-transmitting medium. The maximum volume of the diamond, which can be subjected to processing is limited only by the capacity of the used setup for processing at high pressure and high temperature.

To implement the method according to the invention it is possible to use the typical installation for processing at high temperature and high pressure. In the patent literature discloses various designs reaction vessels, which provide indirect or direct heating of the reaction mass, they are suitable for the implementation of the annealing process of the present invention. These reaction vessels are typically composed of many fitted to each other cylindrical elements and end caps or discs for holding the reaction mass in the Central cylinder. In a reaction vessel with indirect heating one of the cylindrical elements made of graphite, which is heated by passing an electric current through it, and which thereby heats the reaction mass. In a reaction vessel with a direct heating of the reaction mass is conductive, the result eliminates the need for using a cylinder of electrically conductive graphite, while electricity is such a current is passed directly through the reaction mass to heat it.

The invention is illustrated using the following example.

Was used natural brown diamond type IIa with the absorption spectrum in the ultraviolet and visible regions before processing, shown in figure 3 as line (a). Many of these diamonds was placed in transmitting the pressure medium in the reaction vessel of this type, as illustrated in figure 4, where the crystals 10 diamonds placed in transmitting the pressure medium 12 so that the crystals were isolated (discrete) and were separated from each other in a pressure-transmitting medium. Diamonds, preferably evenly distributed in the environment. Transmitting a pressure medium, preferably, represents an environment with low resistance to shear of the type indicated above. Containing diamonds Wednesday 12 is placed in the container 14 made of graphite, pyrophyllite, magnesium oxide or zirconium oxide and completely surrounded vzaimopodchinennym metal caps 16, 18, which form a metal enclosure around the container 14. The metal may be molybdenum, tantalum or steel. The housing can be pressed against the container to eliminate air pockets. The container is loaded in the housing is then placed into the reaction zone of a typical installation for processing at high temperature and high pressure. The contents of the capsule was to be settled by the temperature of 2250° C and a pressure of 7.8 GPA, but these conditions were maintained for a time period of 4 hours. After that, the contents of the capsules were subjected to temperatures 2550°C and maintained at this temperature for 1 hour under a pressure of 8.6 GPA. The capsule was removed from the plant and allowed to cool. Case and graphite container was removed and the diamonds were extracted from the environment. Absorption spectrum of the diamond in the ultraviolet and visible regions after processing is shown in figure 3 as line (b). The spectrum shows a significant decrease in the absorption, and the diamond can be considered colorless.

1. How to change the color of the diamond, which includes stage

(i) creating a reaction mixture by ensuring the presence of diamond in a pressure-transmitting medium, which completely surrounds the diamond; and

(ii) impact on the reaction mass to high temperature and pressure for a suitable period of time, characterized in that a diamond is a brown diamond type IIa, and its color change from brown to colorless by treatment of the reaction mass temperature in the range from 2200 to 2600°at a pressure of from 7.6 to 9 GPA.

2. The method according to claim 1, characterized in that a diamond is a natural diamond.

3. The method according to claim 1 or 2, characterized in that the diamond has a concentration of nitrogen is less than 2 parts per mi is Lyon has brown to pinkish-brown and has an absorption spectrum in the ultraviolet and visible region, which shows a monotonically increasing absorption or monotonically increasing absorption with wide bands with centers at wavelengths of about 390 and 550 nm.

4. The method according to claim 3, characterized in that the nitrogen concentration is less than 0.2 parts per million.

5. The method according to any of the preceding paragraphs, characterized in that the diamond after exposure stage (ii) is characterized by the reduction or the actual removal as monotonically increasing absorption, and the absorption bands at wavelengths of 390 and 550 nm.

6. The method according to any of the preceding items, wherein the temperature in stage (ii) is in the range from 2500 to 2550°C.

7. The method according to any of the preceding paragraphs, characterized in that period of time during which the diamond is exposed to conditions of stage (ii), does not exceed 5 hours

8. The method according to any of the preceding paragraphs, characterized in that period of time during which the diamond is exposed to conditions of stage (ii), does not exceed 90 minutes

9. The method according to any of the preceding paragraphs, characterized in that the reaction mass at stage (ii) is subjected to two-stage heat treatment, while in the second stage, the reaction is th mass is exposed to higher temperatures, than at the first stage, within the interval specified in claim 1 of the formula.

10. The method according to claim 9, characterized in that at the end of the first phase of the diamond is examined to determine its color.

11. The method according to claim 9 or 10, characterized in that the period of heat treatment at the second stage is much shorter than in the first phase.

12. The method according to any of PP-11, characterized in that in the first phase diamond color change to pink or lighter brown, and the second phase diamond color change from pink or lighter brown to colorless.

13. The method according to any of PP-12, characterized in that the reaction mass at stage (ii) is subjected to the first stage to temperatures in the range from 1900 to 2300°C.

14. The method according to any of PP-12, characterized in that the reaction mass at stage (ii) is subjected to the first stage to temperatures in the range from 2100 to 2300°C.

15. The method according to any of PP-12, characterized in that the reaction mass at stage (ii) is subjected to the first stage to temperatures not exceeding 2300°C.

16. The method according to any of PP-15, characterized in that the reaction mass at stage (ii) is subjected to the first stage pressure from 6.9 to 8.5 GPA.

17. The method according to any of PP-15, characterized in that the reaction mass at stage (ii) is subjected to the first stage pressure from 7.4 to 8.5 GPA./p>

18. The method according to any of PP-15, characterized in that the reaction mass at stage (ii) is subjected to the first stage pressure not exceeding 8.5 HPa.

19. The method according to any of PP-18, characterized in that the period of heat treatment at the first stage is from 10 minutes to 10 hours

20. The method according to any of PP-18, characterized in that the period of heat treatment at the first stage is from 20 min to 4 hours

21. The method according to any of PP-20, characterized in that the heat treatment temperature in the second stage ranges from 2500 to 2550°C.

22. The method according to any of PP-20, characterized in that the reaction mass at stage (ii) is subjected to the second stage pressure between 8.4 to 8.6 GPA.

23. The method according to any of PP-22, characterized in that the period of heat treatment at the second stage does not exceed 5 hours

24. The method according to any of PP-22, characterized in that the period of heat treatment at the second stage does not exceed 90 minutes

25. The method according to any of PP-22, characterized in that the period of heat treatment at the second stage is approximately 1 hour

26. The method according to any of the preceding paragraphs, characterized in that the set of diamonds are placed in transmitting pressure environment, with each diamond is separated from the adjacent diamond a pressure-transmitting medium.

27. The method according to any of the preceding paragraphs, characterized in that predostavlenie environment is a homogeneous environment, which completely surrounds the diamond or each of the diamond and which is applied over the entire surface of a diamond or of each of the diamonds.

28. The method according to any of the preceding paragraphs, characterized in that the reaction mass is generated by sealing a pressure-transmitting medium around the diamond before placing the diamond in the reaction zone of the plant for treatment at a high temperature and high pressure and influence on the reaction mass to conditions of stage (ii).

29. The method according to any of the preceding items, wherein transmitting pressure environment to a low shear strength.

30. The method according to any of the preceding items, wherein transmitting the pressure medium is soluble in water.

31. The method according to any of the preceding items, wherein transmitting the pressure medium is a salt of the metal.

32. The method according to p, wherein transmitting the pressure medium is a halide salt of the metal.

33. The method according to p, characterized in that the halide is a chloride or bromide.

34. The method according to p or 32, wherein transmitting the pressure medium is a salt of an alkali metal.

35. The method according to p or 32, wherein transmitting the pressure medium is a salt of a noble metal.

36. The way is about p or 32, wherein transmitting the pressure medium is a salt of potassium.

37. The method according to p or 32, wherein transmitting the pressure medium is a sodium salt.

38. The method according to p or 32, wherein transmitting the pressure medium is a salt of cesium.

39. The method according to p or 32, wherein transmitting the pressure medium is a salt of copper.

40. The method according to any one of claims 1 to 28, wherein transmitting the pressure medium is a bromide of potassium.

41. The method according to any one of claims 1 to 28, wherein transmitting the pressure medium is sodium chloride.

42. The method according to any one of claims 1 to 28, wherein transmitting the pressure medium is potassium chloride.

43. The method according to any one of claims 1 to 28, wherein transmitting the pressure medium is a caesium chloride.

44. The method according to any one of claims 1 to 28, wherein transmitting the pressure medium is a bromide cesium.

45. The method according to any one of claims 1 to 28, wherein transmitting the pressure medium is a chloride of copper.

46. The method according to any one of claims 1 to 28, wherein transmitting the pressure medium is a copper bromide.



 

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