Method of purifying synthetic diamond powders polluted with carbon-containing impurities

FIELD: carbon materials.

SUBSTANCE: invention relates to electrochemistry of carbon materials, namely to removing carbon-containing impurities from diamond powders. Method comprises electrochemical treatment of diamond powder in sulfuric acid electrolyte, more specifically in sulfuric acid solution of manganese sulfate while electrochemical treatment is effected at concentration of manganese in electrolyte 15-30 g/L, solids/liquids ratio 1:(3-5), anodic current density 0.10-0.20 A/cm2. and temperature 125 to 170°C for 2 to 7 h. Degree of purification reaches 99.8%.

EFFECT: increased degree of removing residual graphite under relatively low temperature preventing oxidation of diamond.

1 tbl, 7 ex

 

The invention relates to electrochemistry of carbon materials, in particular to a method of purification of synthetic diamond powders from carbonaceous impurities, and can be used at the enterprises of the diamond tool in the production of synthetic diamonds.

Synthetic diamond powders are widely used in the manufacture of abrasive tools and pastes, medical instrument, electronic and other industries.

The diamond synthesis is carried out on graphite at high temperatures and pressures in the presence of a catalyst based on a metal alloy, in particular an alloy Ni-Mn. While 40-50% of the graphite is converted to diamond. The final and most difficult stage in the process of getting diamonds is their purification from metal catalysts and supercriticalities graphite.

Methods of extraction of diamonds from fusion products in a well-lit review [V.A. Mukhanov Improved methods of extraction of diamonds from a variety of diamond-containing materials. Superhard materials. 2003, №4, p.16-26.; Vereshchagin A.L., Larionov I.S. Cleaning diamonds. / Polzunov almanac, No. 3, 1999); Isaev R.N. Methods of extraction of diamonds from various materials and methods for their purification. Superhard materials, 1989, No. 2, pp.30-34; Putyatin A.A., St. Nicholas IV, Kalashnikov AA Chemical methods of extraction is possible diamond from the fusion products. Superhard materials, 1982, No. 2, p.20-28]. Product synthesis after crushing and grinding in the beginning is subjected to chemical processing, mineral acids and their mixtures for the removal of metal components. Then obtained from almaghribia product the main part of the graphite is removed mechanically, in particular gravity methods. At the final stage of purification to remove residual graphite diamond powder treated in an oxidizing atmosphere by various chemical methods. In a review of the literature deals with the oxidation of graphite in a gaseous environment (dry process), in alkaline melts, solutions and suspensions (wet process).

In the dry process, a powder mixture of diamond and graphite subjected to heat treatment at 500 to 600°in an atmosphere of air. Graphite has a higher oxidation rate than the diamond. With the aim of reducing the temperature and increasing the selectivity of the oxidation of graphite propose the use of different catalysts (oxides of lead, zinc, vanadium, copper, magnesium, ammonium nitrate, etc.). Dry methods do not allow to achieve a complete removal of graphite at one stage, and you need to repeat the process to get the diamond without admixture of graphite, which leads to increasing loss of the diamond. In these methods, the yield of diamond is not PR is more than 90%.

The oxidation of graphite in molten alkali in the presence of nitrates or carbonates of alkali metals is carried out in the temperature range of 500-550°C. Then cooled mass is leached with water, clarified part of the solution is drained, and the residue is treated with hydrochloric acid. After the dissolution of impurities, the solution is drained and the diamond powder is washed with water. In addition to the large consumption of reagents, firstly, is not provided clear diamonds from graphite and, secondly, there is a partial burnout of diamonds due to the increased aggressiveness of alkaline melts at high temperatures. These drawbacks severely limit the application of these techniques in the selection of diamonds from the fusion products.

A widespread method of liquid-phase oxidation of graphite with a mixture of acids with different oxidants. The most commonly used mixture of sulfuric acid with chromic anhydride or potassium bichromate [see, for example, Putyatin A.A., St. Nicholas IV, Kalashnikov AA Chemical methods of extraction of diamonds from the fusion products. Superhard materials, 1982, No. 2, p.20-28]. The oxidation of graphite in the mixture takes place in the temperature range of 150-190°C. the Main advantage of the process is in principle possible cleaning of diamonds without losses due to the low reaction temperature. Its disadvantages are : high twoswitch costs chromic anhydride and sulfuric acid (for cleaning 100 g of diamond powder, contains about 3-4% of graphite, consumption CrO3and H2SO4is 40-50 and 400-500 g, respectively), the toxicity of the oxidant and the probability of formation of insoluble in solutions of acids and alkali oxide of trivalent chromium in the case of raising the temperature of the mixture above the 200°C. the Combination of these negative factors is one of the major limiting reasons for the expansion of production of synthetic diamond powder.

The disadvantages of liquid-phase oxidation of graphite can be eliminated when using for cleaning diamond electrochemical methods. The use of anodic processes will reduce the concentration of the reagent-oxidant in the electrolyte and organize a closed loop cleaning of diamonds from graphite with full regeneration of the working solution (electrolyte).

In the work [Drozdovich V.B. have been, smoked I.I. Study of chemical and electrochemical decomposition of the metal-carbon class of diamond synthesis. Powder metallurgy (Republican interdepartmental collection of scientific works - Belarus), issue 21, 1998, p.34-37] there remains the possibility of electrochemical oxidation of carbon-containing impurities in the products of diamond synthesis in a sulfuric acid electrolyte containing ions of the three - and hexavalent chromium. Studied the kinetic features of the electrochemical behaviour of the reaction Spa is offering the synthesis of diamonds in chromium sulfate electrolyte and optimized the composition of the redox system on the basis of Cr 6+/Cr3+when the boiling temperature of the solution. At work there are no technological parameters and other process parameters on the electrochemical oxidation of graphite.

The closest technical solution is the process of electrochemical purification of synthetic diamond micron from carbonaceous impurities [see, for example, Chernik A.A., hot IM ABOUT the possibility of electrochemical purification micron diamond from carbon-containing impurities. Journal of applied chemistry, 1997, t 4 str-601]. In the work of the kinetics of electrochemical (anodic) oxidation of carbon-containing mixture with ultradispersed diamonds in sulfuric acid solution chromic anhydride - CrO3in the temperature range of 20-80°and the optimal process parameters. It is shown that it is expedient to conduct the oxidation at an anode current density of 0.25 A/cm2. The disadvantage of this process is that it cannot be used for deep cleaning of diamond powders from carbonaceous impurities, so as oxidation of graphite decreases its content in the charge, she (anode material) becomes non-conductive, and the electrochemical process is completely terminated. Another important disadvantage of this process is the very low rate of oxidation of the graphite in the investigated temperature region. Known to intensive oxidation of graphite ions Cr 6+in sulfuric acid occurs in the temperature range of 150-190°C.

The proposed method allows you to virtually eliminate these drawbacks and to carry out deep cleaning of diamond powder from residual graphite. This is achieved by the use of electrochemical machining of diamond powder in sulfuric acid electrolyte, which is used as a solution of manganese sulfate in sulfuric acid.

Determinants of electrochemical cleaning of diamond powder from residual graphite are manganese concentration (reagent-oxidant in the electrolyte component of 15-20 g/l, the ratio of the weight of the diamond powder to the volume of sulfuric acid of the electrolyte - T:W=1:3÷5, the anode current density (ithe anode.) - 0,10-0,20 A/cm2temperature 125-170°and the duration of the process (τ) - 2-7 hours.

When the electrochemical machining of diamond powder in mn containing sulfuric acid electrolyte occurs at the anode of the electrochemical oxidation of ions of Mn2+to Mn3+reaction

2MnSO4+H2SO4-2e→Mn2(SO4)3+H2O,

and the resulting ions Mn3+in the electrolyte interact with the graphite particles with the formation of gaseous compounds of co and CO2and ions of Mn2+according to the following reactions:

Mn2(SO4)3+H2O+C→2nSO 4+H2SO4+CO,

2Mn2(SO4)3+2H2O+C→4MnSO4+2H2SO4+CO2.

The recovered manganese in contact with the anode is again oxidized to the trivalent state, in other words, the oxidizing reagent is a compound of manganese, not consumed, and plays the role of catalyst. The process continues until complete oxidation of graphite in diamond powder.

Thus, in contrast to the process in the proposed method, the oxidation of graphite is not on the anode in electrochemical mechanism, and the volume of the electrolyte on the chemical mechanism. Electrochemical process helps to regenerate and maintain a certain concentration of oxidant (ions Mn3+in sulfuric acid solution, more precisely maintaining the oxidation potential of the system.

After complete oxidation of graphite diamond powder with the electrolyte is discharged, separated from the sulfuric acid electrolyte by decantation or by filtration, washed with distilled water, and dried in a quality product shipped to the consumer. The mother liquor and wash water are combined and after finishing up the required amount in the form of a working electrolyte return in the electrochemical process for the purification of a new portion of the diamond powder of carbonaceous impurities. The result is an environmentally friendly waste-free replacement of the mentioned loop solution and the reagent-oxidant.

In the proposed method, an electrochemical process in a sulfuric acid electrolyte is carried out in the temperature range of 110-190°S, more preferably 125-170°C. the process Temperature is regulated by the concentration of sulfuric acid in the electrolyte, which can range from 50%to 80%. On the other hand, the sulfuric acid concentration strongly influences the solubility of manganese in the electrolyte. Thus, with increasing concentration of H2SO4the solubility of manganese is reduced and the excess of it is precipitated in the form MnSO4. For achieving high performance in the oxidation of graphite manganese concentration in the electrolyte is maintained at a level of 10-25 g/l, preferably 15-20 g/l decrease in the concentration of manganese adversely affects the oxidation of graphite. At temperatures below 125°slows down the speed of the chemical stage of the process - oxidation of graphite ions Mn3+and at high temperatures (above 170°) in which you want to use the electrolyte at a concentration of H2SO4above 75%, significantly decreases the solubility of MnSO4and, accordingly, the concentration of manganese ions in the electrolyte, which results in a decrease in the oxidative capacity of the system. In addition, at higher concentrations of sulfuric acid decreases the conductivity of the electrolyte that Negele is compulsory for the electrochemical process. Therefore, a more favorable process temperature is in the field of 125-170°C.

Electrochemical processing of diamond powder in sulfuric acid electrolyte lead at T:W=1:2÷10, more preferably at T:W=1:3÷5. When values of T:W=1:2 and below becomes difficult maintaining the oxidation potential of the system at a sufficient level due to the small volume of electrolyte with low specific conductivity and number in it reagent-oxidant. And at higher relations T:W increase the size of the equipment and decreases the specific productivity, more precisely the efficiency of the process.

The electrochemical process is carried out at an anode current density of i=0.05 to 0.25 a/cm2more preferably 0,10-0,20 A/cm2. From the values of anodic current density strongly depends on the duration of the electrochemical cleaning process of the diamond powder from residual graphite. At low values of current density, the system experiences a deficit in ions of Mn3+that slows down the oxidation of graphite and as a result increases the duration of the process, and at higher values of current density, along with the oxidation of manganese ions, increases the release of oxygen. This increases the energy consumption. When the optimal parameters, the duration of the process varies in the interval for the Le 2-7 PM Reducing the duration of the process does not provide a complete cleaning of the diamond powder from graphite. In the proposed method, due to the low process temperature oxidation of the diamond does not occur, and it is completely extracted into a marketable product.

The main results achieved in the electrochemical purification of synthetic diamond powder from residual graphite by the proposed method are shown in table. The graphite content in the diamond powder used in the experiments amounted to 3.41%, and the volume of electrolyte - V=300 ml

The following examples illustrate the possibilities of the proposed method (these examples in the table in bold; indices 1-7 at room experience denote respectively the number of examples).

Example 1. 60 g of diamond powder was subjected to electrochemical treatment in 300 ml of sulfuric acid electrolyte (T:W=1:5) at a temperature of 130°C for 5 hours, the Process was conducted at an anode current density of ithe anode.=0,10 A/cm2. The electrolyte composition: 20 g/l Mn 60%H2SO4. After the process is finished, the diamond powder was separated from the electrolyte by filtration through a glass filter, washed with hot distilled water, dried at 105-110°With, then after cooling, weighed on an analytical balance. The content of residual graphite in the final product was determined by the weight loss of the nave is key. The degree of purification of the diamond powder from graphite (or the degree of removal of graphite) was calculated by the difference of the content of graphite in the original sample and in the final product. In this case, the degree of purification was 99.8%.

Example 2. A portion of the diamond powder was taken in a quantity of 100 g of an electrolytic treatment in a sulfuric acid electrolyte was carried out at T:W=1:3, and the anode current density of ithe anode.=0,20 A/cm2in conditions similar to that shown in example 1. Was achieved for 99.5%degree of removal of graphite.

Example 3. Electrochemical processing of diamond powder were carried out in conditions similar to that shown in example 2, however, the process temperature was lowered to 125°and the duration increased to 7 o'clock the degree of removal of graphite from the diamond powder has reached 97,9%.

Example 4. Processing 100 g of diamond powder was carried out in an electrolyte containing 70% H2SO4at a temperature of 150°C for 4 hours. Other process parameters (concentration of reagent-oxidant, T:W, anodic current density) similar to that shown in example 2. The results of the analysis was achieved 100%oxidation of graphite.

Example 5. In contrast to example 4, the temperature of the electrochemical processing of diamond powder is raised to 160°and the duration reduced to 3 p.m oxidation of graphite was 976%.

Example 6. Electrochemical cleaning of the powder was carried out at 170°and an anode current density of 0.15 A/cm2in the electrolyte containing 75% H2SO4and 15 g/l Mn. The number of sample, T:W and the duration of the experiment as in example 5. The graphite content in the final product decreased to 0.03%. The degree of purification of the powder reached 99.2%.

Example 7. The experiment was carried out in conditions similar to that shown in example 6, however, the anodic current density was increased to 0.2 a/cm2and the duration of the process was reduced to 2 hours While the degree of purification of the diamond powder from graphite 98.9%.

The main advantages of the proposed method lies in the fact that the technological process of cleaning synthetic diamond powder from carbon-containing impurities is in the closed solution of the loop. Thanks to the combination of chemical oxidation of graphite ions Mn3+with the formation of gaseous products (CO and CO2) and electrochemical regeneration of the oxidant by anodic oxidation of ions of Mn2+to Mn3+in sulfuric acid electrolyte, is almost completely eliminated (if not to take into account the compensation of minor losses from wash waters) flow rate of sulfuric acid and reagent-oxidant. Implementation of the proposed method will allow you to remove the existing ecological damage to the environment and C is acetelyne to increase production of synthetic diamond powder.

The results of the experiments electrochemical cleaning of diamond powder of residual graphite is shown in the table.

1:3
Table
The results of the experiments electrochemical cleaning of diamond powder from residual graphite (graphite content in the diamond powder is 3.41%, Velectrolyte=300 ml)
№ p/pThe composition of the electrolyteT:Wt °Cithe anode., A/cm2τ, hThe graphite content after treatment, %The degree of removal of graphite, %
WithMn, g/l
1251:101000,0533,377,1
2251:101100,0531,9542,6
3251:101100,0551,3261,2
4251:10110/td> 0,05100,6082,5
550201:101200,0531,1865,3
650201:101250,0530,3689,3
760201:101300,0530,1099,7
860201:51300,0531,0170,3
960201:51300,1040,1994,5
10160201:51300,1050,0199,8
1160201:31300,1050,9173,4
1260201:31300,1550,4487,1
13260201300,2050,0299,5
1460201:21300,1550,8176,2
1560201:1,51300,205of 1.3460,7
1660201:31250,2050,3390,3
17360201:31250,2070,0797,9
1860201:31250,2550,2193,9
1970201:31500,1540,4487,2
20470201:31500,2040,00100,0
21570201:31600,2030,0897,6
226/sup> 75151:31700,1530,0399,2
23775151:31700,2020,04the 98.9
2475151:31700,201,50,3689,4
2575151:31700,201,00,3673,9
2680101:31900,2020,2891,2
2780101:32000,2020,3190,8

The method of purification of synthetic diamond powders from carbonaceous impurities, including electrochemical processing of diamond powder in sulfuric acid electrolyte, characterized in that the electrolyte used is a solution of manganese sulfate in sulfuric acid, and electrochemical processing in the electrolyte is carried out at concentrations of manganese in the electrolyte 15-20 g/l, the ratio of T:W=1:3-5, anode density that is and 0,10-0,20 A/cm 2and temperature 125-170°C for 2-7 hours



 

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2 cl, 2 dwg

FIELD: methods and devices used for production of diamonds.

SUBSTANCE: the invention is pertaining to methods and devices for production of diamonds and may be used in materials technology. Assemble a mold. Ignite a thermit grain and heat up the powdered graphite. After that they initiate explosion of a charge. The explosion energy sets in motion a striker, which is directly caulking the powder graphite in the capsule. After that disassemble the mold, extract the produced diamond. The invention allows to miniaturize the sizes of the charge and the mold, to simplify the production process and to use such a mold multiply.

EFFECT: the invention allows to miniaturize the charge and the mold sizes, to simplify the process of diamonds production and to use such a mold multiply.

2 dwg

FIELD: production of the jewelry quality diamonds from the natural low-grade undecoratively colored diamonds.

SUBSTANCE: the invention is pertaining to production of the diamonds of the jewelry quality from the natural low grade undecoratively colored so-called "brown" diamonds, especially from the diamonds of IIa type and IaA/B type, in which nitrogen forms predominantly B-center for improvement of heir color. The invention provides for realization of the rough faceting and molding of the undecoratively colored natural diamond for giving it the streamline form to avoid its breakup in the press of the high-pressure and heating (HP/HT press). The indicated undecoratively colored natural diamond is put in the pressure transferring medium, which then is compacted into the tablet. Then the tablet is put in the HP/HT squeezer under the high pressure and temperature kept in the field of stability of the blacklead or the field of stability of the diamond of the phase diagram of carbon for the time duration sufficient for improvement of the color of the diamond. After the operation is terminated extract the diamond from the squeezer. The method ensures production of the colorless and decoratively colored diamonds.

EFFECT: the invention ensures production of the colorless and decoratively colored diamonds.

25 cl, 6 ex, 2 dwg

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