The invention relates to the technology of carbon nanomaterials, specifically to the technology for producing modified carbon nanotubes.
Carbon nanotubes (CNTs) tend to form agglomerates, making them difficult to distribute in different media. Even if CNTs are uniformly distributed in some medium, for example, by intense ultrasound, after a short time they spontaneously form agglomerates. To obtain stable CNT dispersions, various methods of modifying CNTs are used, which are carried out by attaching certain functional groups to the surface of the CNT, ensuring the compatibility of the CNT with the environment, using surfactants, and shortening too long CNTs using various methods.
In the description of this invention, the term “modification” means a change in the nature of the CNT surface and the geometric parameters of individual nanotubes. A special case of modification is the functionalization of CNTs, which consists of grafting certain functional groups onto the CNT surface.
There is a known method for modifying CNTs, which involves the oxidation of CNTs under the influence of various liquid or gaseous oxidizing agents (nitric acid in the form of liquid or vapor, hydrogen peroxide, solutions of ammonium persulfate at different pH, ozone, nitrogen dioxide and others). There are many publications on this method. However, since the essence of the various methods of oxidation of carbon nanotubes is the same, namely the oxidation of the surface of carbon nanotubes with the formation of surface hydroxyl and carboxyl groups, this gives reason to consider the various methods described as variants of one method. A typical example is the publication of Datsyuk V., Kalyva M., Papagelis K., Parthenios J., Tasis D., Siokou A., Kallitsis I., Galiotis C. Chemical oxidation of multiwalled carbon nanotubes //Carbon, 2008, vol.46, p.833-840, which describes several options (using nitric acid, hydrogen peroxide and ammonium persulfate).
The common essential features of the considered method and the claimed invention is the treatment of carbon nanotubes with an oxidizing agent solution.
The considered method is characterized by insufficient efficiency for splitting CNT agglomerates and achieving good dispersibility of oxidized CNTs in water and polar organic solvents. As a rule, carbon nanotubes oxidized by known methods are well dispersed in water and polar organic solvents (under the influence of ultrasound) only at a very low concentration of nanotubes in the liquid (usually on the order of 0.001-0.05% by weight). When the threshold concentration is exceeded, nanotubes gather into large agglomerates (flakes), which precipitate.
In a number of works, for example, Wang Y., Deng W., Liu X., Wang X. Electrochemical hydrogen storage properties of ball-milled multi-wall carbon nanotubes //International journal of hydrogen energy, 2009, vol.34, p. 1437-1443; Lee J., Jeong T., Heo J., Park S.-H., Lee D., Park J.-B., Han H., Kwon Y., Kovalev I., Yoon S.M., Choi J.-Y ., Jin Y., Kirn J.M., An K.H., Lee Y.H., Yu S. Short carbon nanotubes produced by cryogenic crushing //Carbon, 2006, vol.44, p.2984-2989; Konya Z., Zhu J., Niesz K., Mehn D., Kiricsi I. End morphology of ball milled carbon nanotubes //Carbon, 2004, vol.42, p.2001-2008, describes a method for modifying CNTs by shortening them, which is achieved by prolonged mechanical processing of CNTs in liquids or frozen matrices. Shortened CNTs have better dispersibility in liquids and better electrochemical properties.
The common essential features of the considered and proposed methods are the mechanical processing of CNTs dispersed in any medium.
The disadvantage of the considered method is that it does not ensure the functionalization of CNTs with polar groups, as a result of which CNTs treated in this way are still not well dispersed in polar media.
The closest to the claimed invention is the method described in the work of Chiang Y.-C., Lin W.-H., Chang Y.-C. The influence of treatment duration on multi-walled carbon nanotubes functionalized by H2SO4/HNO3 oxidation //Applied Surface Science, 2011, vol.257, p.2401-2410 (prototype). According to this method, modification of CNTs is achieved by their deep oxidation during prolonged boiling in an aqueous solution containing sulfuric and nitric acids. In this case, first, polar functional groups (in particular, carboxyl groups) are grafted onto the CNT surface, and with a sufficiently long treatment time, shortening of the nanotubes is achieved. At the same time, a decrease in the thickness of the nanotubes was also observed due to the complete oxidation of the surface carbon layers to carbon dioxide. Variants of this method are described in other sources, for example in the mentioned article by Datsyuk V., Kalyva M. et al., as well as Ziegler K.J., Gu Z., Peng H., Flor E.L., Hauge R.H., Smalley R.E. Controlled oxidative cutting of single-walled carbon nanotubes //Journal of American Chemical Society, 2005, vol.127, issue 5, p.1541-1547. Published sources indicate that shortened oxidized carbon nanotubes have an increased ability to disperse in water and polar organic solvents.
A common essential feature of the proposed method and the prototype method is the treatment of CNTs with an aqueous solution of an oxidizing agent. The inventive method and the prototype method also coincide in the achieved result, namely, the grafting of polar functional groups to the surface of CNTs is achieved simultaneously with the shortening of long CNTs.
The disadvantages of the prototype method are the need to use a large excess of acids, which increases the cost of the process and creates environmental problems during waste disposal, as well as the oxidation of part of the carbon nanotubes to carbon dioxide, which reduces the yield of the final product (modified carbon nanotubes) and makes it more expensive. In addition, this method is difficult to scale. In laboratory conditions, glass instruments can be used, but for pilot production, stainless steel equipment is preferable. Boiling nanotubes in acid solutions creates the problem of equipment corrosion resistance.
The basis of the claimed invention is the task of eliminating the disadvantages of the known method by selecting the oxidizing reagent and oxidation conditions.
The problem is solved by the fact that according to the method of modifying carbon nanotubes, which includes treating carbon nanotubes with an aqueous solution of an oxidizing agent, the treatment of carbon nanotubes with an aqueous solution of an oxidizing agent is carried out simultaneously with mechanical treatment, and a solution of persulfate or hypochlorite at a pH of more than 10 is used as an oxidizing agent.
Mechanical processing is carried out using a bead mill.
The oxidizing agent is taken in an amount equivalent to 0.1 to 1 g atom of active oxygen per 1 g carbon atom of nanotubes.
Excess hypochlorite in the reaction mixture at a pH greater than 10 is removed by adding hydrogen peroxide.
Carrying out the treatment of carbon nanotubes with an aqueous solution of an oxidizing agent simultaneously with mechanical treatment and the use of a persulfate or hypochlorite solution as an oxidizing agent at a pH of more than 10 eliminates the need to use a large excess of acids, which increases the cost of the process and creates environmental problems during waste disposal, as well as the loss of the finished product due to oxidation of part of the carbon of nanotubes to carbon dioxide.
For mechanical processing, devices known in the art can be used, such as a bead mill, a vibration mill, a ball mill and other similar devices. In fact, a bead mill is one of the most convenient devices for solving the task.
Ammonium persulfate, sodium persulfate, potassium persulfate, sodium hypochlorite, potassium hypochlorite can be used as oxidizing agents. The most effectively claimed method is carried out when treating carbon nanotubes with an oxidizing agent solution at a pH of more than 10. At a lower pH, corrosion of equipment and inappropriate decomposition of the oxidizing agent with the release of chlorine (from hypochlorite) or oxygen (from persulfate) are possible. The required pH value can be set by adding known substances that have an alkaline reaction to the solution, for example, ammonia, sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, and other alkaline substances that do not react with the oxidizing agent under processing conditions. In this case, one should take into account the known data that hypochlorite reacts with ammonia. Therefore, ammonia cannot be used in a hypochlorite system. When using persulfate to establish an alkaline pH, all of the listed substances can be used.
To implement the proposed method, the optimal amount of oxidizing agent is equivalent to 0.1 to 1 g atom of active oxygen per 1 g carbon atom of nanotubes. When the amount of oxidizing agent is less than the specified lower limit, the resulting modified carbon nanotubes are less well dispersed in water and polar organic solvents. Exceeding the amount of oxidizer above the specified upper limit is impractical, because, although it accelerates the oxidation process of nanotubes, it does not improve the beneficial effect.
To implement the proposed method, the following starting materials and equipment were used:
Carbon nanotubes of the Taunit and Taunit-M brands produced by NanoTechCenter LLC, Tambov.
Ammonium persulfate, analytical grade.
Sodium hypochlorite according to GOST 11086-76 in the form of an aqueous solution containing 190 g/l active chlorine and 12 g/l free sodium hydroxide.
Aqueous ammonia 25% analytical grade.
Anhydrous sodium carbonate, analytical grade.
Distilled water.
Dimethylacetamide, analytical grade.
Ethyl alcohol 96%.
Horizontal bead mill MShPM-1/0.05-VK-04 produced by NPO DISPOD. Zirconium dioxide balls with a diameter of 1.6 mm were used as grinding media.
Ultrasonic installation IL-10.
1460 ml of distilled water was poured into a 4-liter stainless steel container and 228.4 g of ammonium persulfate was dissolved, after which 460 ml of 25% ammonia was added. 1099 g of aqueous paste of Taunit-M carbon nanotubes (purified of mineral impurities by treatment with hydrochloric acid), containing 5.46% dry matter, were added to this solution and thoroughly mixed until a homogeneous suspension was formed. The resulting suspension was loaded into a bead mill with zirconium dioxide beads with a diameter of 1.6 mm and processed for 7 hours. Then the treated suspension was unloaded, filtered from the beads, acidified with hydrochloric acid to an acidic reaction, filtered through a filter made of non-woven polypropylene material and washed with water until the wash water was neutral. The washed sediment was sucked off in a vacuum and packaged in a sealed plastic container. The mass content of dry matter (nanotubes) in the resulting paste was 8.52% (the rest was water). The resulting product was dried in an oven at 80°C to constant weight.
To test solubility (dispersibility), a sample of CNTM-1 was dispersed in water or organic solvents using ultrasound treatment. Experiments have shown that CNT-1 are highly soluble in water, preferably at basic pH (created by the addition of ammonia or organic bases). The addition of a base promotes the formation of a stable solution (dispersion) of modified nanotubes, since it leads to the ionization of surface carboxyl groups and the appearance of a negative charge on the nanotubes.
Thus, a stable aqueous solution was obtained (as can be seen from the transparency of the solution and the absence of flakes) containing 0.5% CNTM-1 in the presence of 0.5% triethanolamine as a pH regulator. The solubility limit of CNTM-1 in this system is approximately 1%; when this concentration is exceeded, gel inclusions appear.
In dimethylacetamide (without foreign additives), stable transparent solutions of CNTM-1 with mass concentrations of 1 and 2% were obtained by ultrasonic treatment. In this case, dimethylacetamide, which itself is a weak base, effectively dissolves CNTM-1 without the addition of extraneous pH regulators. The 1% solution was indefinitely stable during storage, but after a few days the 2% solution began to show signs of thixotropy, but without the formation of agglomerates.
Pour 2.7 liters of distilled water into a 4-liter stainless steel container, add 397.5 g of anhydrous sodium carbonate and stir until completely dissolved. After dissolving the sodium carbonate, sodium hypochlorite solution (0.280 l) was poured in and the mixture was thoroughly mixed. Then, gradually, with stirring, 60 g of crude Taunit-M (containing about 3% by weight of catalyst impurities, predominantly magnesium oxide) was added and stirred until a homogeneous suspension. This suspension was loaded into a bead mill with 1.6 mm diameter zirconia beads and processed for 7 hours. Then the treated suspension was unloaded, filtered from the beads, acidified with hydrochloric acid to an acidic reaction and kept for 3 days at room temperature to completely dissolve catalyst residues and possible impurities of iron compounds (from the body and fingers of the bead mill). Thus, the nanotubes were simultaneously acid-cleaned from catalyst impurities. The resulting acidic suspension was filtered through a filter made of non-woven polypropylene material and washed with water until the wash water was neutral. The washed sediment was sucked off in a vacuum and packaged in a sealed plastic container. The mass content of dry matter (nanotubes) in the resulting paste was 7.33% (the rest was water). The resulting product was dried in an oven at 80°C to constant weight.
If the amount of hypochlorite in the reaction mixture with nanotubes is excessive, this accelerates the oxidation of the surface of the nanotubes, but creates an environmental problem because when the mixture is acidified, unreacted hypochlorite releases chlorine, according to the reaction equation:
2NaOCl+2НCl→2NaCl+Н 2 O+Сl 2
In order to neutralize excess hypochlorite, hydrogen peroxide is added to the reaction mixture at a pH greater than 10. As we have established, the following reaction occurs:
NaOCl+H 2 O 2 →NaCl+H 2 O+O 2
As a result, harmless products are formed.
To test solubility (dispersibility), a sample of CNTM-1 was dispersed in water or organic solvents using ultrasound treatment. Experiments have shown that CNTM-1 are highly soluble in water, preferably at basic pH (created by the addition of ammonia or triethanolamine). The addition of a base promotes the formation of a stable solution (dispersion) of modified nanotubes, since it leads to the ionization of surface carboxyl groups and the appearance of a negative charge on the nanotubes.
Thus, a stable aqueous solution was obtained (as can be seen from the transparency of the solution and the absence of flakes) containing 0.5% CNTM-1 in the presence of 0.5% triethanolamine as a pH regulator. The solubility limit of CNTM-1 in this system is approximately 1%; when this concentration is exceeded, gel inclusions appear.
In dimethylacetamide (without foreign additives), stable transparent solutions of CNTM-1 with mass concentrations of 1 and 2% were obtained by ultrasonic treatment. In this case, dimethylacetamide, which itself is a base, effectively dissolves CNTM-1 without the addition of extraneous pH regulators; the 1% solution was indefinitely stable during storage, while the 2% solution began to show signs of thixotropy after a few days, but without the formation agglomerates.
For comparison, the solubility was studied (under the influence of ultrasound under the same conditions) in the same solvents of Taunit-M carbon nanotubes, oxidized according to the procedure given in the prototype method, with a mixture of nitric and sulfuric acids without mechanical treatment. Experiments have shown that CNTs oxidized with excess nitric acid without mechanical treatment have the same solubility as those obtained according to the claimed invention. However, the proposed method is easy to scale, there are no problems with the corrosion resistance of equipment and environmental problems with waste neutralization. The process of mechanochemical treatment according to the claimed method occurs at room temperature. The prototype method requires the use of such a large excess of nitric and sulfuric acids that scaling it and ensuring environmental safety is very problematic.
The data presented confirm the effectiveness of the proposed method for producing modified CNTs. In this case, aggressive acid solutions are not used, as in the prototype method, and the loss of carbon from nanotubes due to oxidation to carbon dioxide (carbonate in an alkaline solution) is practically absent.
Thus, the proposed method makes it possible to obtain modified carbon nanotubes that have good dispersibility in water and polar organic solvents, can be easily scaled up, and ensures environmentally friendly production.
1. A method for modifying carbon nanotubes, including treating carbon nanotubes with an aqueous solution of an oxidizing agent, characterized in that the treatment of carbon nanotubes with an aqueous solution of an oxidizing agent is carried out simultaneously with mechanical treatment, and a solution of persulfate or hypochlorite is used as an oxidizing agent at pH more than 10, and the oxidizing agent is taken in an amount , equivalent to 0.1 to 1 g-atom of active oxygen per 1 g-atom of carbon nanotubes.
2. The method according to claim 1, characterized in that mechanical processing is carried out using a bead mill.
3. The method according to claim 1, characterized in that excess hypochlorite in the reaction mixture at a pH greater than 10 is removed by adding hydrogen peroxide.
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Schemes of the structure of various modifications of carbon
a: diamond, b: graphite, c: lonsdaleite
d: fullerene - buckyball C 60, e: fullerene C 540, f: fullerene C 70
g: amorphous carbon, h: carbon nanotube
More details: Allotropy of carbon
Crystalline carbon
- diamond
- Graphene
- graphite
- Carbin
- lonsdaleite
- Nanodiamond
- Fullerenes
- Fullerite
- Carbon fiber
- Carbon nanofibers
- Carbon nanotubes
Amorphous carbon
- Activated carbon
- Charcoal
- Fossil coal: anthracite, etc.
- Coal coke, petroleum coke, etc.
- Glassy carbon
- Carbon black
- Carbon nanofoam
In practice, usually, the amorphous forms listed above are chemical compounds with a high carbon content, rather than the pure allotropic form of carbon.
Cluster forms
- Astralens
- Dicarbon
- Carbon nanocones
Structure
The electron orbitals of a carbon atom can have different geometries, based on the degree of hybridization of its electron orbitals. There are three basic geometries of the carbon atom.
- tetrahedral, formed by mixing one s- and three p-electrons (sp 3 hybridization). The carbon atom is located in the center of the tetrahedron, connected by four equivalent -bonds to carbon or other atoms at the vertices of the tetrahedron. The carbon allotropic modifications diamond and lonsdaleite correspond to this geometry of the carbon atom. Carbon exhibits such hybridization, for example, in methane and other hydrocarbons.
- trigonal, formed by mixing one s- and two p-electron orbitals (sp 2 hybridization). The carbon atom has three equivalent -bonds located in the same plane at an angle of 120° to each other. The p-orbital, which is not involved in hybridization and is located perpendicular to the -bond plane, is used to form -bonds with other atoms. This carbon geometry is characteristic of graphite, phenol, etc.
- digonal, formed by mixing one s- and one p-electrons (sp-hybridization). In addition, two electron clouds are elongated along the same direction and look like asymmetrical dumbbells. The other two p electrons make -bonds. Carbon with such an atomic geometry forms a special allotropic modification - Carbyne.
In 2010, University of Nottingham researchers Stephen Liddle and colleagues obtained a compound (monomeric dilithio methandium) in which four carbon atom bonds are in the same plane. The possibility of "flat carbon" had previously been predicted for the substance by Paul von Schleyer, but it was not synthesized.
Graphite and diamond
The main and well-studied allotropic modifications of carbon are diamond and graphite. Under normal conditions, only graphite is thermodynamically stable, while diamond and other forms are metastable. At atmospheric pressure and temperatures above 1200 K, diamond begins to transform into graphite; above 2100 K, the transformation takes place in seconds. H 0 transition - 1.898 kJ/mol. At normal pressure, carbon sublimates at 3,780 K. Liquid carbon exists only at a certain external pressure. Triple points: graphite-liquid-vapor T = 4130 K, R= 10.7 MPa. The direct transition of graphite to diamond occurs at 3000 K and a pressure of 11-12 GPa.
At pressures above 60 GPa, the formation of a very dense modification C III (density 15-20% higher than the density of diamond), which has metallic conductivity, is assumed. At high pressures and relatively low temperatures (approx. 1,200 K), a hexagonal modification of carbon with a wurtzite-type crystal lattice - lonsdaleite (a = 0.252 nm, c = 0.412 nm, space group) is formed from highly oriented graphite P6 3 /mmc), density 3.51 g/cm, that is, the same as that of diamond. Lonsdaleite is also found in meteorites.
Ultradisperse diamonds (nanodiamonds)
In the 1980s In the USSR, it was found that under conditions of dynamic loading of carbon-containing materials, diamond-like structures, called ultrafine diamonds (UDD), can form. Today, the term “nanodiamonds” is increasingly used. The particle size in such materials is a few nanometers. The conditions for the formation of UDD can be realized during the detonation of explosives with a significant negative oxygen balance, for example, mixtures of TNT with hexogen. Such conditions can also be realized during impacts of celestial bodies on the surface of the Earth in the presence of carbon-containing materials (organic matter, peat, coal, etc.). Thus, in the fall zone of the Tunguska meteorite, UDAs were discovered in the forest floor.
Carbin
The crystalline modification of carbon of the hexagonal system with a chain structure of molecules is called Carbyne. The chains have either a polyene structure (-CC-) or a polycumulene structure (=C=C=). Several forms of carbyne are known, differing in the number of atoms in the unit cell, cell sizes and density (2.68-3.30 g/cm). Carbyne occurs in nature in the form of the mineral chaoite (white veins and inclusions in graphite) and is obtained artificially - by oxidative dehydropolycondensation of acetylene, by the action of laser radiation on graphite, from hydrocarbons or CCl 4 in low-temperature plasma.
Carbin is a fine-crystalline black powder (density 1.9-2 g/cm) and has semiconductor properties. Obtained under artificial conditions from long chains of carbon atoms laid parallel to each other.
Carbyne is a linear polymer of carbon. In the carbyne molecule, the carbon atoms are connected in chains alternately either by triple and single bonds (polyene structure) or permanently by double bonds (polycumulene structure). This substance was first obtained by Soviet chemists V.V. Korshak, A.M. Sladkov, V.I. Kasatochkin and Yu.P. Kudryavtsev in the early 60s. at the Institute of Organoelement Compounds of the USSR Academy of Sciences. Carbyne has semiconducting properties, and its conductivity increases greatly when exposed to light. The first practical application is based on this property - in photocells.
Fullerenes and Carbon Nanotubes
Carbon is also known in the form of cluster particles C 60, C 70, C 80, C 90, C 100 and the like (Fullerenes), and in addition graphenes, nanotubes and complex structures - astralenes.
Amorphous carbon (structure)
The structure of amorphous carbon is based on the disordered structure of single-crystalline (always contains impurities) graphite. These are coke, brown and black coals, carbon black, soot, activated carbon.
Graphene
More details: Graphene
Graphene is a two-dimensional allotropic modification of carbon, formed by a layer of carbon atoms one atom thick, connected through sp bonds into a hexagonal two-dimensional crystal lattice.
Powdered carbon materials (graphites, carbons, carbon blacks, CNTs, graphenes) are widely used as functional fillers for various materials, and the electrical properties of composites with carbon fillers are determined by the structure and properties of carbon, as well as the technology for their production. CNTs are a powder material made from framework structures of the allotropic form of carbon in the form of hollow multi-walled CNTs with an outer diameter of 10–100 nm (Fig. 1). As is known, the electrical resistivity (ρ, Ohm∙m) of CNTs depends on the method of their synthesis and purification and can range from 5∙10-8 to 0.008 Ohm∙m, which is less than
at graphite.
When producing conductive composites, highly conductive materials (metal powders, carbon black, graphite, carbon and metal fibers) are added to the dielectric. This allows you to vary the electrical conductivity and dielectric characteristics of polymer composites.
This study was carried out to determine the possibility of changing the electrical resistivity of CNTs through their modification. This will expand the use of such tubes as a filler for polymer composites with planned electrical conductivity. The work used samples of CNT powders produced by ALIT-ISM (Zhitomir, Kyiv) and CNT powders subjected to chemical modification. To compare the electrical characteristics of carbon materials, we used samples of CNT "Taunit" (Tambov), synthesized according to TU 2166-001-02069289-2007, CNT LLC "TMSpetsmash" (Kyiv), manufactured according to TU U 24.1-03291669-009:2009, crucible graphite . CNTs produced by ALIT-ISM and Taunit are synthesized by the CVD method on a NiO/MgO catalyst, and CNTs by TMSpetsmash LLC are synthesized on a FeO/NiO catalyst (Fig. 2). In the study, under the same conditions and using the same developed methods, the electrical characteristics of samples of carbon materials were determined. The electrical resistivity of the samples was calculated by determining the current-voltage characteristics of a sample of dry powder pressed at a pressure of 50 kG (Table 1).
Modification of CNTs (No. 1–4) showed the possibility of changing the electrophysical characteristics of CNTs using physical and chemical influences (see Table 1). In particular, the electrical resistivity of the original sample was reduced by 1.5 times (No. 1); and for samples No. 2–4 – increase by 1.5–3 times.
At the same time, the total amount of impurities (the share in the form of non-combustible residue) decreased from
2.21 (original CNTs) to 1.8% for
sample No. 1 and up to 0.5% for No. 3. The specific magnetic susceptibility of samples No. 2–4 decreased from 127∙10-8 to 3.9∙10-8 m3/kg. The specific surface area of all samples increased by almost 40%. Among the modified CNTs, the minimum electrical resistivity (574∙10-6 Ohm∙m) was recorded in sample No. 1, which is close to the resistance of crucible graphite (33∙10-6 Ohm∙m). In terms of specific resistance, CNT samples from Taunit and TMSpetsmash LLC are comparable to samples No. 2, 3, and the specific magnetic susceptibility of these samples is an order of magnitude higher than that of modified CNT samples (ALIT-ISM).
It has been established that the electrical resistivity of CNTs can be varied from 6∙10-4 to
12∙10-4 Ohm∙m. Specifications have been developed for the use of modified CNTs in the manufacture of composite and polycrystalline materials, coatings, fillers, suspensions, pastes and other similar materials
TU U 24.1-05417377-231:2011 "Nanopowders of multi-walled CNTs of the MWCNT-A grades",
MUN-V (MWCNT-B), MUN-S (MWCNT-S)"
(Table 2).
When modified CNT powders are introduced into the polyethylene base of composites as a filler, the electrical conductivity of the polymer composite increases with an increase in their electrical conductivity. Thus, as a result of targeted modification of CNTs, the possibility of varying their characteristics, in particular, electrical resistivity, opens up.
Literature
1. Tkachev A.G., Zolotukhin I.V. Equipment and methods for the synthesis of solid-state nanostructures. – M.: Mashinostroenie-1, 2007.
2. Bogatyreva G.P., Marinich M.A., Bazaliy G.A., Ilnitskaya G.D., Kozina G.K., Frolova L.A. Study of the influence of chemical treatment on the physicochemical properties of carbon nanotubes. Sat. scientific tr. "Fullerenes and nanostructures in condensed matter." / Ed.
P.A. Vityaz. – Minsk: State Scientific Institution “Institute of Heat and Mass Transfer”
exchange them A.V. Lykova" NAS of Belarus, 2011, pp. 141–146.
3. Novak D.S., Berezenko N.M., Shostak T.S., Pakharenko V.O., Bogatyreva G.P., Oleynik N.A., Bazaliy G.A. Electrically conductive nanocomposites based on polyethylene. Sat. scientific tr. "Rock cutting and metalworking tools - equipment and technology for their manufacture and use." – Kyiv: ISM
them. V.N.Bakulya NAS of Ukraine, 2011, issue 14, pp.394–398.
Powdered carbon materials (graphite, coals, soot, CNTs, graphene) are widely used as functional fillers of different materials, and the electrical properties of composites with carbon fillers are determined by the structure and properties of carbon and by the production technology. The CNTs are a powder material of frame structures of allotropic form of carbon in the form of hollow multiwalled CNTs with an outside diameter of 10 to 100 nm (Fig.1a,b). It is known that the electrical resistivity (ρ, Ohm∙m) of CNTs depends on the method of their synthesis and purification and can range from 5∙10-8 to 0.008 Ohm∙m, which is by order lower than that of graphite .
Fig.1. a) – CNTs powder, b) – a fragment of CNTs (Power Electronic Microscopy)
At manufacture of conductive composites high conductive materials (metal powders, technical carbon, graphite, carbon and metal fibers) are added to dielectrics. This allows to vary the conductivity and dielectric properties of polymer composites.
The present investigation was conducted to determine the possibility of changing the specific electrical resistance of CNTs through their modification. This will expand the use of such tubes as a filler of polymer composites with planned electrical conductivity. The investigation used samples of initial powders of CNTs made by ALIT-ISM (Zhytomyr, Kiev) and CNTs powders which were subject to various chemical modifications. To compare the electrophysical characteristics of carbon materials CNTs samples "Taunit" (Tambov, Russia) synthesized under 2166-001-02069289-2007, LLC "TMSpetsmash" (Kiev), made under 24.1-03291669-009:2009, crucible graphite, CNTs made by ALIT-ISM and "Taunit" are synthesized with CVD- method on NiO/MgO catalyst and CNTs made by LLC "TMSpetsmash" – on the FeO/NiO catalyst were used (Fig. 2).
Fig.2 a – CNT (ALIT-ISM), b – CNT "TMSpetsmash" (PEM-images).
Investigations under the same conditions using with the same methods developed in the ISM determined the electrical physical characteristics of the samples of carbon materials were determined. The specific electrical resistance of the samples was calculated by determining the current-voltage characteristic of dry powder element pressed under pressure of 50 kg. (Table 1).
The modification of CNTs (No.1-4) has shown the possibility to change the electrical properties of them porpusfully with the help of physical and chemical effects. In particular, specific electrical resistivity of the initial sample was reduced 1.5 times (No.1) and for No. 2 – 4 it was increased 1.5-3 times.
In this case the total amount of impurities (their shere in the form of non-combustible residue) was decreased from 2.21% (initial CNTs) to 1.8% for No.1 and to 0.5% for No.3. Magnetic susceptibility of samples No.2 – 4 was decreased by order. The specific surface area of all samples was increased almost by 40%. Among the modified CNTs minimum specific electrical resistance (574∙10-6 Ohm∙m) is fixed for the sample No.1 which is close to such resistance of crucible graphite (337∙10-6 Ohm∙m). By specific resistance the samples of CNTs "Taunit" and "TMSpetsmash" can be compared with that of samples No.2 and No.3, and the magnetic susceptibility of these samples is by order higher than that of the modified CNTs samples ("Alit -ISM").
Thus, the possibility of modifying CNTs to vary the specific electrical resistivity value of CNTs in the range 6∙10-4÷12∙10-4Ohm∙m was stated. There have been developed specifications 24.1-05417377-231:2011 "Nanopowders of multiwalled CNTs of grades MWCNTs-A, MWCNTs-B, MWCNTs-C (Table 2) for modified CNTs for production of composite and polycrystalline materials, coatings, fillers, suspensions , pastes and other similar materials.
At introduction into the polyethylene base of composites as a filler of modified powders of CNTs of new grades with increasing electrical conductivity of CNTs electrical conductivity of the polymer composite increases. Thus, as a result of the directed modification of CNTs there are new opportunities to vary of their characteristics, in particular, the value of electric resistivity.
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