RU2570440C2 - Method for obtaining graphite-based thermally expandable compounds - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in manufacturing electrochemical elements, supercapacitors, adsorbents, vacuum and space lubricants, fireproof coatings. Graphite-containing powder material 4 with graphite content not less than 93 wt %, for instance, natural flake graphite, is placed in vacuumed by forevacuum pump 9 closed volume 1 on mirror of iodine heptafluoride liquid phase 5 or above it. Ratio of weight of graphite-containing powder material 4 to iodine heptafluoride weight 5 is from 1:2.21 to 1:5.02. Processing is carried out at 16÷25°C. Composition of obtained compounds corresponds to empirical formula C_xFJ_0,14·yJF₇, wherein x=1÷6, y=0÷0.05.

EFFECT: method is simple, safe and makes it possible to extend nomenclature of obtained products.

18 cl, 5 dwg, 5 ex

Description

Technical field

The invention relates to the field of production of graphite compounds with a layered structure capable of thermal expansion with the formation of new forms of expanded graphite. The resulting materials have many actual and potential applications in various fields of science and technology, such as electrochemical cells, supercapacitors, adsorbents, vacuum and space lubricants, fire retardant coatings and much more.

State of the art

Expanded graphite, also called thermally expanded (TEG) or thermally split graphite [A. Celzard, J.F. Marêché, G. Furdin. Modeling of exfoliated graphite. // Progress in Materials Science. - 2005. Vol.50. Is.1. P.93-179], is a fine powdery fluffy carbon materials obtained by rapid heating of intercalated graphite compounds [M.S. Dresselhaus, G. Dresselhaus. Intercalation compounds of graphite. // Advances in Physics. - 2002. Vol. 51. No.1, P.1-186]. When heating intercalated graphite compounds, the intercalate pressure in the interlayer space increases rapidly, which leads to delamination of the graphite matrix. As a result, a porous defective carbon structure is formed, consisting of layered graphite domains.

Known methods for producing thermally expanded compounds of graphite, which consist in the preliminary preparation of layered intercalated compounds of oxidized graphite by processing powder of natural flake graphite with concentrated nitric and glacial acetic acids [SU 1614350, IPC 6 C01B 31/04. Priority from 05/19/89. Publ. 02.20.95] (analogue), concentrated nitric acid, acetic acid and organic compounds [SU 1476785, IPC 6 C01B 31/04. Priority from 07/02/86. Publ. 02.20.95] (analogue).

The disadvantage of analogues is that the expansion of intercalated compounds of oxidized graphite requires high-speed heating (thermal shock) to a temperature of 950 ÷ 1250 ° C. Only in this case, pairs of acids formed in the interlayer space create high pressure in the graphite matrix, which causes the separation of carbon layers (graphenes), which is visually recorded as a multiple increase in the size of graphite flakes. The coefficient of expansion (increase in volume) of graphite powder does not exceed 100 ÷ 150.

The proposed methods are characterized by the presence of a large number of stages and a large time duration during implementation.

Known methods for producing an expanded form of graphite, differing from previous analogues in that intercalated compounds of fluorinated graphite (ISFG), in particular diocarbon fluoride, are used as starting material [RU 2144497, IPC C01B 31/04. Priority from 03/31/1998. Publ. 01/20/2000; RU 2223219, IPC C01B 31/04. Priority from 11.28.2001. Publ. 02/10/2004]. Receive ISFG low-temperature (up to 100 ° C) gas-phase fluorination of natural flake graphite strong fluoroxidant - fluorine halogen ClF ₃ (or ClF ₅ ).

In such parameters as the increase in volume and surface area, the expanded forms of graphite obtained from ISFG significantly exceed the known forms of TWG from intercalated compounds of oxidized graphite. Thus, the expansion coefficient of ISFG during shock thermal heating (up to 600 ÷ 700 ° C) reaches 300 ÷ 500.

The disadvantages of the well-known proposals for the production of ISFG are that the strong fluoroxidants ClF ₃ and CF ₅ used in low-temperature synthesis are extremely dangerous chemicals. The process of gas-phase fluorination and intercalation of graphite lasts for tens of hours, since the product of the fluorination reaction of chlorofluoride monofluoride (ClF) prevents the access of new portions of fluoroxidant to the graphite layer. Proposals for obtaining ISFG by analogue methods remained at the level of laboratory research.

Patents are also known for the production of ISFG through the contact of graphite powder with the liquid phase of fluorohalides.

So, in the method for producing ISFG described in the patent [RU 2404918, IPC C01B 31/00. Priority from 02/18/2009. Publ. November 27, 2010] (analogue), the graphite powder is treated first with the liquid phase of chlorine trifluoride, and then the split carbon material is re-fluorinated with gaseous chlorine trifluoride at room temperature. The analogue method is absolutely not acceptable for industrial practice due to the tendency of liquid ClF ₃ to ignite and explode.

In the patent [RU 2404121, IPC C01B 31/04. Priority of July 31, 2007. Publ. November 20, 2010] (analogue), a thermally expanding graphite-based compound is prepared by contacting a graphite-containing powder material with the liquid phase of iodine heptafluoride (JF ₇ ). Of the known halide fluoroxides, JF _{7 is the} least dangerous. Reacts with atmospheric moisture and organic compounds without popping or exploding. At a slight pressure (111 kPa) and a temperature above 6.4 ° C, JF ₇ passes from a solid state to a colorless liquid. In the liquid phase, JF ₇ fluorinates all known carbon-containing compounds, including graphite.

Hereinafter, the term "graphite-containing powder material" refers to the powder (grains) of natural or artificial graphite in a mixture with mineral impurities. The proportion of impurities in some commercial varieties of natural fine crystalline graphites can reach 25 wt.%.

However, iodine heptafluoride is a heavy liquid, the density of liquid JF ₇ is 2.7 g / cm ³ at 20 ° C, which is significantly more than the specific gravity of all known graphite-containing powder materials from natural flake graphites (from 1.9 to 2.6 g / cm ³ ), which are usually used to obtain intercalated graphites. For this reason, flake graphite powder does not mix with the liquid and the contact of the liquid phase mirror JF ₇ occurs only with a thin layer of graphite-containing powder material. Thus, the analogue method, as described in the patent, is suitable for the preparation of small batches of thermally expandable compounds based on graphite.

Closest to the proposed solution can be attributed a method of obtaining a thermally expandable compound based on graphite [RU 2419586, IPC C01B 31/04. Priority from 12/18/2009. Publ. 05/27/2011] (prototype), which includes the treatment of graphite-containing powder material with the gas phase of iodine heptafluoride in a closed volume at a pressure of 78 ÷ 240 kPa. Processing is carried out at a temperature of 18 ÷ 40 ° C. The resulting iodine pentafluoride (JF ₅ ) does not inhibit the progress of a chemical reaction, since it is removed from the reaction zone due to the formation of a liquid phase and its subsequent draining to the bottom of a closed volume - a technological reactor. The equilibrium vapor pressure of JF ₅ over the liquid phase is approximately 20 times less than the equilibrium pressure of JF ₇ and the pressure in the closed volume does not increase during the processing of graphite.

Hereinafter, a closed volume is understood to mean an internal isolated technological volume of an apparatus or a group of apparatuses, which makes it possible to contact graphite-containing powder material with the gas phase of iodine heptafluoride at the same pressure in technological volumes.

The prototype method has the following disadvantages. At low pressures of the gas phase of iodine heptafluoride in a closed volume (below atmospheric), the intercalation of graphite-containing powder material is extremely slow. At elevated pressures (above atmospheric), the intercalation rate is significantly accelerated, and the method becomes quite suitable for industrial use. However, in the latter case, under a high pressure of such a chemically active reagent and a strong fluoroxidizer like JF ₇ , a significant part of the technological scheme is constantly found: a cylinder with iodine heptafluoride, pipelines, a technological reactor, measuring equipment, etc. Such operating conditions of technological equipment reduce the industrial safety of the process and require tight control.

The tasks solved by the invention

The present invention is directed to:

- improving the industrial safety of the method of producing thermally expanding compounds based on graphite in industrial sales;

- expansion of the range of products obtained having different chemical composition of thermally expanding graphite compounds.

SUMMARY OF THE INVENTION

The above objectives are achieved by a technical solution, the essence of which is that in a method for producing thermally expanding compounds based on graphite, which includes treating a graphite-containing powder material with a gas phase of iodine heptafluoride in a closed volume, the treatment is carried out with a ratio of the mass of graphite-containing powder material to the mass of iodine heptafluoride from 1 : 2.21 to 1: 5.02.

The tasks listed above are achieved by additional technical solutions, consisting in the fact that iodine heptafluoride in a closed volume is in the liquid phase. In this case, the graphite-containing powder material in a closed volume can be located both on the mirror of the liquid phase of iodine heptafluoride and above the liquid phase of iodine heptafluoride. As a graphite-containing powder material, it is desirable to use various grades of natural flake graphite. In addition, it is preferable to use a graphite-containing powder material with a graphite content of at least 93 wt.% And iodine heptafluoride with a basic substance content of at least 95 wt.%, However, there may be other values. The ratio of the value of the closed volume to the mass of graphite-containing powder material, as a rule, should be in the range of 0.011 ÷ 0.134 m ³ / kg, although it may go beyond these limits. In addition, to obtain the necessary proportions of a graphite-containing powder material with iodine heptafluoride, it is desirable to freeze the latter in a closed volume, and then heat to a temperature preferably in the range of 16 ÷ 25 ° C, but there may be other temperatures differing by several degrees to a greater or lesser extent side. It is best to freeze iodine heptafluoride into a closed volume with graphite-containing powder material at a temperature of (-196) ° C and in batches, however, it is only desirable that the temperature of the process reactor is less than 0 ° C. It is advisable to conduct subsequent heating of the enclosed volume with graphite-containing powder material and iodine heptafluoride due to natural heat exchange with the environment of the process room, although there may be various options for its organization. The compositions of thermally expandable compounds based on graphite, which are expedient to obtain, should correspond to the empirical formula C _x FJ _0.14 · yJF ₇ , where x = 1 ÷ 6, y = 0 ÷ 0.05, but they can also differ depending on what graphite powder material was used. After obtaining thermally expanding compounds based on graphite, it is desirable to treat with gaseous carbon dioxide, this can be done directly in a closed volume or processed outside a closed volume after unloading the product from the process reactor. In the latter case, the preferred option is the placement of thermally expandable compounds based on graphite above the surface of solid carbon dioxide. It is also possible to hold the obtained thermally expanding compounds based on graphite before unloading under dynamic vacuum at a pressure in a closed volume of not more than 200 Pa. However, the magnitude of the residual pressure is not fundamental here and is determined by the available vacuum equipment.

The main distinguishing feature of the proposed method is the treatment of graphite-containing powder material with iodine heptafluoride with a ratio of the mass of graphite-containing powder material to the mass of iodine heptafluoride from 1: 2.21 to 1: 5.02. This feature is new and significant, as it eliminates the inherent prototype disadvantages.

Firstly, significantly reduced consumption of iodine heptafluoride, since it is almost completely consumed only ISFG formation, the above mass ratio of the reagents allow to obtain a definite composition thermally expanding graphite-based compounds within the empirical formula C _x FJ _0,14 · yJF ₇ where x = 1 ÷ 6, y = 0 ÷ 0.05. The heating of the ISFG powder above 130 ° C (including without thermal shock) is accompanied by the production of thermally expanded graphite in the form of a fluffy material.

Beyond the lower limit of the claimed range, compositions with x> 6 and y = 0 are formed, which are subject to thermal expansion at a temperature of more than 500 ° C with a low coefficient of expansion. Beyond the upper limit of the declared range (at x = 1 and y> 0.05), compounds are formed, the thermal expansion of which releases toxic gases, in particular hydrogen fluoride, and the compounds themselves have a chemical composition that is unstable in time.

Most of the known methods for producing ISFG (see analogues) began with natural flake graphite as a starting material. In this proposal, the type of graphite-containing powder material is not limited to one brand of natural flake graphite. Materials from the group of coarse-grained and finely crystalline natural graphites, artificial graphites, highly oriented pyrolytic graphite, and also combinations thereof can be selected. These materials have different dispersion, bulk density, surface area, etc. From all of them it is possible to obtain thermally expanding compounds. However, in the proposed method, it is preferable to use various grades of coarse and fine crystalline natural flake graphite.

Secondly, as shown by special studies of the authors, the fluoroxidant in this case is almost completely incorporated into the layered lattice of graphite, forming limiting stoichiometric compounds corresponding to the mass ratio with graphite, and the residual pressure of the gas phase of iodine heptafluoride in a closed volume in this case is extremely small and not exceeds atmospheric pressure. Thus, the stated goals are simultaneously achieved - industrial safety of the process and expansion of the range of products obtained in the form of thermally expanding compounds based on graphite of various chemical composition.

From the point of view of minimizing the technological dimensions of the apparatus used, it is advisable that the iodine heptafluoride is initially in a closed volume in the liquid phase. Regarding the location of the graphite-containing powder material, this may be a single volume in a process reactor or a process volume in an adjacent apparatus.

The maximum pressure under which a graphite-containing powder material can temporarily be in a closed volume is determined by the equilibrium pressure of the iodine heptafluoride gas phase above the liquid - from 146 kPa at 16 ° C to 198 kPa at 25 ° C. Closed-space heating from (-196) ° C (with solid JF ₇ ) to a process room temperature of 16 ÷ 25 ° C, due to natural heat exchange with the environment, does not require the use of an additional source of external heating, therefore achieving equilibrium pressure JF ₇ over the liquid phase will be gradual and smooth.

The liquid phase of iodine heptafluoride in a closed volume quickly disappears due to the intensive introduction of JF ₇ into the interlayer space of graphite with the formation of an intercalated compound in the form of a fluorographic graphite containing iodine fluoride heteroatoms, and at the final stage of the process, the pressure in the closed volume will be determined only by the gas phase of the fluoroxidizer.

The claimed temperature range for processing graphite-containing powder material provides comfortable (lower limit) and safe (upper limit) conditions for the implementation of the method.

A layer of graphite-containing powder material can be located directly on the liquid mirror of the iodine heptafluoride, or a sample of graphite-containing powder material can be located above the mirror of the liquid phase, for example, in a perforated basket. The option of finding the liquid phase of iodine heptafluoride in an adjacent technological apparatus within the same closed volume with a weighed portion of graphite-containing powder material was discussed above.

For more rapid introduction of iodine heptafluoride into the interlayer space of graphite, it is necessary to maintain the presence of the liquid phase of iodine heptafluoride in a closed volume for as long as possible. This can be achieved if the ratio of the value of the closed volume to the mass of graphite-containing powder material is in the range of 0.011 ÷ 0.134 m ³ / kg. The lower limit of the interval determines the minimum required volume for the gas phase of iodine heptafluoride. Upper - the maximum dimensions of the closed volume, ensuring the long-term presence of the liquid phase of iodine heptafluoride together with graphite-containing powder material.

Iodine heptafluoride reacts with mineral impurities contained in graphite-containing powder material, forming various fluorides, some of which may be volatile, for example, SiF ₄ . Iodine heptafluoride itself may also contain impurities in the form of hydrogen fluoride (HF) and iodine oxypentafluoride (JOF ₅ ). With a significant amount, they can create undesirable additional pressure in a confined space and, in principle, the amount of these impurities should be limited. For this reason, to implement the method, it is proposed to use low-ash brands of natural graphites with a basic substance content of at least 93 wt.% And JF _{7 with a} purity of at least 95 wt.%.

Obtaining the required ratio of the mass of graphite-containing powder material to the mass of iodine heptafluoride from 1: 2.21 to 1: 5.02 is proposed to be carried out by portioned filling and desublimation of JF ₇ in a closed volume, creating any ratio of reagents. In principle, iodine heptafluoride can be frozen at a temperature below (+4.8) ° C (desublimation temperature JF ₇ ), in particular at a sublimation temperature of carbon dioxide (-78.9) ° C, but the best option is the boiling point of liquid nitrogen ( -196) ° C, at which the residual pressure of iodine heptafluoride above the crystals is zero.

An enclosed volume with solid iodine heptafluoride and graphite-containing powder material is heated by natural heat exchange with the environment of the process room. In principle, to accelerate the heating, forced blowing of the enclosed volume shell by the air of the technological room is possible. The use of an external heat source is undesirable, as this can cause a sharp increase in vapor pressure JF ₇ .

The obtained ISFG powders are desirable for passivation before contact with moist air. This can be done by holding the powders under dynamic vacuum at a preferred pressure in a closed volume of not more than 200 Pa, which removes traces of the resulting low-volatility iodine pentafluoride (JF ₅ ). In another embodiment, passivation can be carried out by treating the ISPH powders with gaseous carbon dioxide both directly in a closed volume after receiving them and outside the closed volume. In the latter case, it is optimal to place a perforated basket with ISFG above the surface of “dry ice” (crystals of solid carbon dioxide).

Passivation of ISFG with carbon dioxide CO ₂ proceeds according to the mechanism:

The resulting elemental iodine can be removed by vacuum distillation.

Brief Description of the Drawings

Figure 1 shows a diagram of a plant for the synthesis through gas phase intercalated compounds of fluorinated graphite, capable of thermal expansion. Here: 1 - closed volume (technological reactor); 2 - cylinder with JF ₇ ; 3 - capacity for collecting excess JF ₇ from the technological reactor 1; 4 - a hinge of graphite; 5 - liquid (solid) phase JF ₇ ; 6, 7 - Dewar vessel; 8 - liquid nitrogen; 9 - fore-vacuum pump; 10 - column with a chemical absorber; 11 - micromanometer; 12 - pressure gauge; 13 - valve for cutting off the reactor 1 from the technological scheme of the installation; 14 - valve for filling the reactor 1 with dry nitrogen or carbon dioxide.

Figure 2-5 shows, respectively, micrographs of natural flake graphite powder, ISFG powder and particles of thermally expanded graphite from different precursors.

The following examples serve to ensure the best practice of the present invention and should not be construed as limiting the scope of the invention.

Example 1. A sample 4 weighing 38.52 grams of natural flake graphite grade GT-1 (crucible graphite in accordance with GOST 4596-75) with an ash content of not more than 7.0 wt.%, Having an average particle size of 200 ÷ 300 microns and a bulk density of 0, 45 g / cm ³ (see figure 2), previously dried at 200 ° C, is placed in a nickel reactor 1 with a volume of 4.0 × l0 ^-3 m ³ (see figure 1). The ratio of the value of the closed volume to the mass of graphite-containing powder material is 0.106 m ³ / kg (the calculation took into account the internal volume of the valve in the reactor, equal to 8 × 10 ^-6 m ³ ). The reactor 1 and the vessel 3 with a volume of 0.20 dm ^{3 are} pumped out by a foreline pump 9 to a residual pressure of 13.3 Pa. Pressure control in the technological scheme is carried out by a micromanometer 11. Stand for checking the vacuum density. Reactor 1 is cooled by pouring liquid nitrogen 8 into a Dewar 6. 85.1 grams of iodine heptafluoride are transferred from cylinder 2 to reactor 1, where at a temperature of (-196) ° C it goes into solid state. Use iodine heptafluoride with a basic substance content of at least 95 wt.%. Filling is controlled by the readings of pressure gauge 12. The ratio of the mass of graphite-containing powder material to the mass of iodine heptafluoride 1: 2.21. The reactor 1 is cut off from the process circuit by valve 13 and, after removing the Dewar 6, is left to warm to a temperature of the process room of 18 ° C. At a temperature of 6.4 ° C, the pressure in reactor 1 exceeds 111 kPa, JF ₇ crystals melt and flow from the walls to the bottom of the reactor in the form of a liquid. A portion of graphite begins to float on the mirror of the liquid phase of iodine heptafluoride.

After 4 hours, valve 13 is opened. The absolute pressure in the technological volume of the reactor, according to the pressure gauge 12, is only 91 kPa. Thus, iodine heptafluoride was used almost completely. The remnants of JF ₇ from the reactor 1 and the technological lines of the installation are frozen in a tank 3, previously freezing it with liquid nitrogen 8, poured into the Dewar 7.

Capacity 3 is cut off from the technological scheme and reactor 1.

The reactor 1 and the installation paths are evacuated with a foreline pump 9 to a residual pressure of not more than 200 Pa, usually 67 Pa (the pressure in the system is monitored by a micronometer 11), with neutralization of the evacuated gases in a column with a chemical absorber 10. The reactor 1 with the ISFG 4 sample is kept under dynamic vacuum for 0.5 hours, then through the valve 14 is filled with dry nitrogen to atmospheric pressure and disconnected from the technological scheme.

After unloading, a black powder is obtained, weighing 80.71 grams, having a bulk density of 0.45 g / cm ³ . According to the weight analysis, the composition of the obtained substance can be characterized by the empirical formula C ₆ FJ _0.14 . The obtained ISFH powder is thermally stable to a temperature of 350 ° C.

ISFG powder is poured into a thin-walled crucible made of monel, closed with a metal mesh and placed in a muffle furnace previously heated to a temperature of 450 ° C. After the crucible is heated, the ISFG is thermally decomposed with the formation of a downy material from expanded graphite particles with a length in the range of 3–5 mm (see Fig. 4).

The coefficient of expansion of the synthesized ISFG is ~ 170. The density by volume of expanded graphite corresponds to about 0.25 dm ³ / g. The output of graphite in an expanded form is 0.82.

Example 2. A portion 4 of natural flake graphite grade GSM-2 (special low-ash graphite according to GOST 18191-78, ash content less than 0.5 wt.%) Having an average particle size of 100 ÷ 300 microns and bulk density of 0.45 g / cm ³ , weighing 20.0 grams are placed in a perforated basket in the middle part of the Nickel reactor 7 with a volume of 2.5 × 10 ^-3 m ³ . The ratio of the value of the closed volume to the mass of graphite-containing powder material is 0.125 m ³ / kg.

The installation for operation is prepared according to example 1. The frozen reactor 1 is filled with 87.8 grams of iodine heptafluoride. The ratio of the mass of graphite-containing powder material to the mass of iodine heptafluoride in reactor 1 was 1: 4.39. The reactor 1 is thawed by removing the Dewar 6, while at a room temperature of 25 ° C JF ₇ goes into the liquid phase state. A portion of graphite is located above the liquid phase of iodine heptafluoride. Graphite is kept under the influence of the gas phase at room temperature for 8 hours.

The absolute pressure in the technological volume of reactor 1 after opening valve 13 according to the pressure gauge 12 is only 98 kPa. Thus, iodine heptafluoride was used almost completely.

83.9 grams of ISPH powder is unloaded from the reactor 1 from white to light brown in color (see FIG. 3), having a bulk density of 0.40 g / cm ³ . According to the results of the weight analysis, the composition of the obtained substance can be characterized by the empirical formula CFJ _0.14 · 0.03JF ₇ .

ISFG powder is placed in an oven heated to 150 ° C. Get downy material from expanded graphite particles with a length in the range of 7 ÷ 12 mm (see figure 5).

The coefficient of swelling of the synthesized ISFG is ~ 500. The density by volume of expanded graphite corresponds to approximately 1.0 dm ³ / g. The output of graphite in an expanded form is 0.75.

Example 3. A portion 4 of natural flake graphite grade GSM-1 (special low-ash graphite according to GOST 18191-78, ash content less than 0.1 wt.%) Having an average particle size of 200 ÷ 300 microns and bulk density of 0.45 g / cm ³ (cm Fig. 2), weighing 30.0 grams, is treated with iodine heptafluoride in the installation of Fig. 1 according to the conditions of Example 2. The ratio of the closed volume to the mass of graphite-containing powder material is 0.084 m ³ / kg.

The frozen reactor 1 is filled with 150.7 grams of iodine heptafluoride, obtaining the ratio of the mass of graphite-containing powder material to the mass of iodine heptafluoride 1: 5.02. Reactor 1 is thawed by removing the Dewar 6. Iodine heptafluoride at a process room temperature of 16 ° C goes into the liquid phase state. A portion of graphite is located over the liquid phase of iodine heptafluoride for 10 hours.

The absolute pressure in the technological volume of reactor 1 after opening valve 13 according to the pressure gauge 12 is only 57 kPa. Thus, iodine heptafluoride was used almost completely during the reaction. The remains of JF ₇ from the reactor 1 and the technological lines of the installation are frozen into a tank 4. The reactor 1 is pumped out to a pressure of 0.133 kPa and carbon dioxide is injected through valve 14 to a pressure of 6.6 kPa. Withstand 0.5 hours.

From reactor 1, 158.4 grams of ISFH powder of white-brown-black color is discharged. The blackening of the ISFG powder indicates the formation of elemental iodine crystals according to reactions (1) and (2). According to the results of the weight analysis, the composition of the obtained substance can be characterized by the empirical formula CFJ _0.14 · 0.05JF ₇ .

ISFG powder is placed in an oven heated to 150 ° C. Get downy material from expanded graphite particles with a length in the range of 7 ÷ 12 mm (see figure 5).

The coefficient of swelling of the synthesized ISFG is ~ 600. The density by volume of expanded graphite is approximately 1.2 dm ³ / g. The output of graphite in an expanded form is 0.7.

Example 4. A portion 4 of natural flake graphite brand GAK-3 (battery graphite in accordance with GOST 17022-81, ash content not more than 2.0 wt.%) Weighing 30.0 grams, having an average particle size of 60 ÷ 100 microns and bulk density 0, 40 g / cm ³ , treated with iodine heptafluoride in the installation (see figure 1) according to the conditions of example 1. The ratio of the value of the closed volume to the mass of graphite-containing powder material is 0.084 m ³ / kg

106.8 grams of JF _{7 are} introduced into reactor 1. The ratio of the mass of graphite-containing powder material to the mass of iodine heptafluoride is 1: 3.56. Reactor 1 is thawed by removing the Dewar 6. Iodine heptafluoride at a room temperature of 20 ° C becomes liquid-phase. Stand for 7 hours.

The absolute pressure in the technological volume of the reactor 1 after opening the valve 13 according to the pressure gauge 12 is 53 kPa. Thus, iodine heptafluoride was used almost completely during the reaction. The remains of JF ₇ from the reactor 1 and the technological lines of the installation are frozen in a tank 3. The reactor 1 is pumped out to a pressure of 0.133 kPa and dry nitrogen is introduced through valve 14 to atmospheric pressure.

White-brown ISFH powder weighing 96.2 g is discharged from reactor 1 into a nickel boat, which is placed over crystals of solid carbon dioxide. After exposure for 2 hours, the powder becomes brown-black. According to the results of the weight analysis, the composition of the obtained substance can be characterized by the empirical formula C _1.5 FJ _0.14 .

ISFG powder is placed in an oven heated to 200 ° C. A fluffy material is obtained from expanded graphite particles with a length in the range of 7 ÷ 12 mm.

The coefficient of swelling of the synthesized ISFG is ~ 500. The density by volume of expanded graphite corresponds to approximately 1.0 dm ³ / g. The output of graphite in an expanded form is 0.75.

Example 5. The experiment was carried out according to the conditions of example 1. Used the reactor 1 with a volume of 0.4 × l0 ^-3 m ³ . A portion of 4 natural flake graphite grade GT-1 - 35.0 grams. The ratio of the value of the closed volume to the mass of graphite-containing powder material was 0.011 m ³ / kg

The ratio of the mass of graphite-containing powder material to the mass of iodine heptafluoride is 1: 3.80 (lump 132.8 grams of JF ₇ ).

The absolute pressure in the technological volume of reactor 1 after opening valve 13 according to the pressure gauge 12 rose only to 88 kPa.

After unloading, a light brown powder weighing 148.21 grams was obtained. According to the weight analysis, the composition of the obtained substance can be characterized by the empirical formula CFJ _0.14 .

ISFG powder is placed in an oven heated to 150 ° C. Get downy material from expanded graphite particles with a length in the range of 7 ÷ 12 mm (see figure 5).

In conclusion, we note that at present, the proposed method for the synthesis of a thermally expanding graphite-based compound with the introduction of iodine heptafluoride into the graphite matrix has many advantages over its known analogues, since it is simple and technologically safe, does not require complex equipment, the synthesis is carried out in a relatively short time (4 ÷ 8 hours versus 24 ÷ 30 hours in known methods) at a temperature of 16 ÷ 25 ° C. Excess reagents are reused. The synthesis of iodine heptafluoride is a mastered process that is not particularly difficult. The resulting compounds are resistant to prolonged exposure to water and moist air and can be stored for several years. Since the need for thermally expanding compounds based on graphite is great in various fields of science and technology, the great practical importance of the proposed method is very obvious.

Claims (18)

1. A method of producing thermally expandable compounds based on graphite, comprising treating a graphite-containing powder material with a gas phase of iodine heptafluoride in a closed volume, characterized in that the treatment is carried out with a ratio of the mass of graphite-containing powder material to the mass of iodine heptafluoride from 1: 2.21 to 1: 5, 02. 2. The method according to claim 1, characterized in that the iodine heptafluoride in a closed volume is in the liquid phase. 3. The method according to claim 2, characterized in that the graphite-containing powder material in a closed volume is placed on the mirror of the liquid phase of iodine heptafluoride. 4. The method according to claim 2, characterized in that the graphite-containing powder material in a closed volume is located above the liquid phase of iodine heptafluoride. 5. The method according to claim 1, characterized in that natural flake graphite is used as the graphite-containing powder material. 6. The method according to claim 1 or 5, characterized in that they use graphite-containing powder material with a graphite content of at least 93 wt.%. 7. The method according to claim 1 or 2, characterized in that iodine heptafluoride is used with a basic substance content of at least 95 wt.%. 8. The method according to any one of claims 1, 3 or 4, characterized in that the ratio of the value of the closed volume to the mass of graphite-containing powder material is in the range of 0.011 ÷ 0.134 m ³ / kg. 9. The method according to claim 1 or 2, characterized in that iodine heptafluoride in the required proportion is frozen in a closed volume with graphite-containing powder material, and then heated to a temperature of 16 ÷ 25 ° C. 10. The method according to claim 9, characterized in that the freezing of iodine heptafluoride into a closed volume with graphite-containing powder material is carried out at a temperature of (-196) ° C. 11. The method according to claim 10, characterized in that the freezing of iodine heptafluoride into a closed volume with graphite-containing powder material is carried out portionwise. 12. The method according to claim 9, characterized in that the heating of the closed volume with graphite-containing powder material and iodine heptafluoride is carried out due to natural heat exchange with the environment of the process room. 13. The method according to claim 1, characterized in that the composition of thermally expandable compounds based on graphite corresponds to the empirical formula C _x FJ _0.14 · yJF ₇ , where x = 1 ÷ 6, y = 0 ÷ 0.05. 14. The method according to claim 1 or 13, characterized in that the obtained thermally expandable compounds based on graphite are treated with gaseous carbon dioxide. 15. The method according to 14, characterized in that the thermally expandable compounds based on graphite are treated with carbon dioxide directly in a closed volume after receiving them. 16. The method according to 14, characterized in that the thermally expanding compounds based on graphite are treated with carbon dioxide outside a closed volume. 17. The method according to clause 16, characterized in that the thermally expandable compounds based on graphite are placed over the surface of solid carbon dioxide. 18. The method according to any one of claims 1, 13 or 15, characterized in that the obtained thermally expanding compounds based on graphite are subjected to exposure under dynamic vacuum at a pressure in a closed volume of not more than 200 Pa.

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