JP2012530036A - Direct low temperature growth method of carbon nanotube (CNT) and fiber (CNF) on steel strip - Google Patents

Abstract

  The present invention relates to a method for direct low temperature growth of carbon nanotubes and carbon nanofibers on a steel strip and a substrate obtained by the method.

Description

  Carbon nanotubes and carbon nanofibers (hereinafter abbreviated as CNT / CNF) have a small cylindrical structure with a diameter on the order of several nanometers and an aspect ratio of 10 to 1000. CNT / CNF has a honeycomb-shaped hexagonal pattern in which each carbon atom is combined with three adjacent carbon atoms. Moreover, CNT / CNF can function as a conductor, for example, a metal, or a semiconductor according to their structure, and the application field of these CNT / CNF is expected to be wide. CNT / CNF has more attractive properties such as low density, high strength, high toughness, high flexibility, high surface area and excellent electrical conductivity. Unfortunately, the production of CNT / CNF is not so easy.

  Discharges using hydrocarbons, laser deposition, and chemical vapor deposition are widely used to synthesize CNT / CNF on a large scale. In particular, the discharge technique grows CNT / CNF by arc discharge using a carbon electrode. In the laser deposition method, CNT / CNF is synthesized by irradiating graphite with laser light. However, these two methods are unsuitable for controlling the diameter and length of CNT / CNF and the structure of the carbonaceous material. Therefore, it is difficult to obtain an excellent crystalline structure when synthesizing CNT / CNF. In addition, since a large amount of amorphous carbon mass is produced at the same time, further complicated purification is required after the synthesis of CNT / CNF, which complicates the production method. Another disadvantage of these methods is that it is impossible to synthesize CNT / CNF over a relatively large area. Therefore, these methods cannot be applied to various apparatuses. The method of synthesizing CNT / CNF by plasma CVD is not attractive because CNT / CNF can be damaged by plasma impact and it is difficult to synthesize CNT / CNF on a relatively large substrate.

  The object of the present invention is to provide a simple method of growing CNT / CNF on a steel substrate.

  It is an object of the present invention to provide a method for producing a corrosion resistant coating on a steel substrate.

  It is also an object of the present invention to provide a method for producing an adhesive coating of carbon nanotubes and / or nanofibers on a steel substrate.

According to the first aspect, at least one of these objectives is the adhesion of carbon nanotubes and / or carbon nanofibers (CNT / CNF) on one or both surfaces of a carbon steel or low alloy steel strip substrate. A method for direct low temperature growth of a coating,
-Prepare a steel substrate, optionally with a metallic coating,
-CNT / CNF is grown on the surface of the substrate by a thermal chemical vapor deposition (CVD) process at a temperature of 500-750 ° C, preferably 600-750 ° C, using a carbon source gas comprising hydrogen Let
-No catalyst is added to catalyze the growth of the CNT / CNF, the growth of the CNT / CNF being caused by iron, nickel and / or chromium present in the substrate and / or the metallic coating This is achieved by providing a method comprising the step of catalyzing by:

  The inventors have found that by using a carbon-containing source gas, such as an olefin gas or low molecular weight oil, a layer of CNT / CNF can be grown on the steel substrate by CVD at low temperatures. . Catalyst, eg iron, nanoparticles were found at the tip and / or bottom of the CNT / CNF. CNT / CNF had a diameter of 30-120 nm depending on the reaction conditions. It was proved that the adhesion of these CNT / CNF to the steel substrate was very strong. A layer thickness of 1-60 μm could be achieved. CNT / CNF exhibits bi-directional growth as well as tip growth. The steel used as the substrate is: Carbon steel or 2. Preferably, it is a low alloy steel containing 7% or less non-ferrous element, preferably 4% or less non-ferrous element. In the SAE method, category 1. And 2. Steels are shown in four-digit numbers, the first digit indicates the main alloying element, the second digit indicates the secondary alloying element, and the last two digits indicate the amount of carbon in 1/100% by weight It shows with. For example, 1060 steel is a plain carbon steel containing 0.60 wt% C. The steel substrate is not stainless steel. In the SAE display, the stainless steel grade is specified as a three-digit number, optionally followed by one or more letters. The substrate is preferably prepared in the form of a band, a plate (sheet) or a foil. The substrate is cleaned and / or the oxide removed before depositing the CNT / CNF coating.

  In one embodiment of the invention, iron coming from a steel substrate catalyzes the growth of CNT / CNF. Surprisingly, this process of forming a CNT / CNF layer on a steel substrate formed a CNT / CNF layer without the addition of iron as a catalyst. However, even in this case, it was concluded that iron nanoparticles were also confirmed at the tip and / or bottom of the CNT / CNF by an electron microscope, and that the catalytic effect was obtained by the iron particles originating from the steel substrate. It was.

In one embodiment of the present invention, the carbon-containing source gas comprises one or more of acetylene, ethylene, methane, carbon monoxide, carbon dioxide, or low molecular weight fatty oil. It has been found that by using these carbon-containing sources, a good layer of CNT / CNF is formed on the substrate. In a preferred embodiment, the carbon source gas consists of hydrogen, carbon monoxide and carbon dioxide, preferably in a volume ratio of about 30:60:10. Experiments 44 to 65 vol% CO: 26-5 vol% _CO 2: a mixture of 30 vol% _{H 2} was found to provide excellent results and the growth rate. With this mixture, good results were obtained even when the hydrogen content was changed to 25-35% while maintaining the ratio of CO to CO _{2 at} a ratio of about 2: 1 to 8: 1. Thus, surprising results were obtained by adding carbon dioxide to the CO: H ₂ mixture.

  In one embodiment of the invention, CNT / CNF is grown on the substrate surface at a temperature of 600-750 ° C. Due to the catalytic effect of iron, the processing temperature can be kept low. The range of 600 to 750 ° C. was considered a good temperature range, and a good layer of CNT / CNF was formed with good reliability and economically. A more preferable temperature range is 600 to 700 ° C. A more preferred maximum temperature is 695 ° C.

  In one embodiment of the invention, the steel substrate is high strength steel (HSS), modified HSS, boron containing steel, super HSS or composite phase steel, preferably 0.01-1% C, 0.15. ~ 2% Mn, 0.005-2% Si, 0.01-1.5% Al, 10-200 ppm N, up to 0.015% P, up to 0.15% S, as desired Contains one or more of 0.01-0.1% Nb, 0.002-0.15% Ti, 0.02-0.2% V, 10-60 ppm B, and the balance iron and inevitable impurities It becomes.

  In a preferred embodiment of the invention, the steel substrate is provided with a nickel, nickel-chromium or chromium plating layer or zinc alloy layer before growing CNT / CNF on one or both surfaces of the substrate.

  In a preferred embodiment of the present invention, there is provided a method for forming a corrosion resistant coating on a steel strip substrate by in situ forming a layer of CNT / CNF on the substrate according to the present invention, the CNT / CNF comprising: A method is provided for applying a polymer coating to a layer. In a preferred embodiment, the polymer coating is a poly-imide (PI) based coating. The thickness of the CNT / CNF with the polymer layer may be 1 μm to 60 μm, giving a heat resistance of 300 to 550 ° C. with a loss of 0.2 to 0.5% by weight.

By applying the polymer coating to the CNT / CNF adhesive coating, the properties of the CNT / CNF layer are retained. The polymer coating further protects the CNT / CNF coated substrate from corrosion. Poly-imide-based coatings have been found to have thermal stability, good chemical resistance, excellent mechanical properties and insulating properties. However, there is a problem with the adhesion of these polymers to the steel substrate. As described above, a layer of CNT / CNF is first applied on a steel substrate, and subsequently, a poly-imide coating is applied to the CNT / CNF layer, whereby adhesion of PI to the CNT / CNF layer and CNT / CNF Since the adhesion of the CNF layer to the steel substrate is excellent, the adhesion of the poly-imide coating to the steel substrate is much improved. The CNT / CNF on the surface of the steel creates a large interfacial surface area in the poly-imide based coating or any other polymer coating to be adhered. The similarity between CNT / CNF and the polymer increases its wettability and compatibility, so that microcrack formation and its propagation are suppressed. Tests have shown that excellent CNT / CNF-PI coated steel substrates and CNT / CNF-polymer coated steel substrates are formed. This product, CNT / CNF is a polymer, such as poly - imide coatings are good alternative for the composite material are dispersed in a. It is well known that it is difficult to disperse CNT / CNF in a polymer, and it is difficult for CNT / CNF to coagulate which leads to poor dispersion. The addition of a polymer layer, such as a poly-imide coating, over CNT / CNF has the advantage that CNT / CNF can no longer be detached from that layer. Thereby, possible health problems associated with free CNT / CNF are prevented. It should be noted that poly-imide based coatings are a preferred embodiment of the present invention. However, it should also be noted that other polymers that can withstand the conditions of manufacture and use, such as polyolefins such as polyethylene, can be used.

  In one embodiment of the invention, the poly-imide-based coating is applied over the CNT / CNF layer, preferably by roll coating and / or spraying, followed by imidization. To form.

  In one embodiment of the present invention, the poly-imide coating is coated on the CNT / CNF layer by adding Mn, Ag, Si, Ti, Al and / or Mg during synthesis of PAA, followed by imidization. To form.

In one embodiment of the present invention, a poly-imide based coating is made from a poly-ether imide, the poly-imide based coating is applied over a CNT / CNF layer, followed by a liquid polyether amic (PEA) solution, It is formed by imidization. In one embodiment of the invention, CNT / CNF is subsequently treated with a suitable compound, such as MgO or CaO, to form a catalyst support for storing CO ₂ in the form of a carbonaceous compound, or a photocatalyst, Treatment with, for example, titania, or an organic photoinitiator to form a catalytic conversion agent and convert carbon dioxide to a carboxylic acid, such as formic acid (HCOOH), and / or an alcohol, such as ethanol (C ₂ H ₅ OH), A method of forming a coating is provided. Treat the steel surface with CNT / CNF treated in this way and convert it into, for example, a tubular form, or deposit CNT / CNF on carbon steel or low alloy steel tubes and make them suitable compounds as described above Alternatively, treatment with a photocatalyst provides a highly effective and economical catalyst for reducing the carbon traces of any method that generates carbon dioxide.

  In one embodiment of the present invention, the above manufacturing method includes a step of preparing a coil of a cold-rolled steel strip, a step of subjecting the coil to continuous annealing, a step of recrystallizing the cold-rolled coil as desired, Reducing, deoxygenating and / or cleaning the surface of the steel, forming a layer of CNT / CNF on the steel at a temperature of 600-750 ° C., cooling the steel, and optionally, Applying a poly-imide coating to the coated steel. By this manufacturing method, it is possible to make use of the economic efficiency obtained by the scale of the continuous manufacturing method. Cold rolled strip coils provide relatively inexpensive substrates, and these substrates can be coated with a CNT / CNF adhesive coating in a continuous fashion. This greatly reduces the cost of such coated substrates. Reducing the surface means removing oxides from the steel surface in a reducing atmosphere.

  In one embodiment, the method for producing CNT / CNF further comprises removing CNT / CNF from the surface of the steel substrate, for example by mechanical grinding, and collecting the CNT / CNF. By this simple and inexpensive CNT / CNF manufacturing method, a large amount of CNT / CNF that can be used for electrical and mechanical applications is supplied at low cost.

  In one embodiment of the present manufacturing method, the steel substrate provided with the CNT / CNF layer as described above is used in a corrosive environment, for solar cell use, for fuel cell use, for hydrogen storage, as a catalyst carrier, and for radar capture. Use in coatings or as interfacial conductive layers or antimicrobial products.

  In a preferred embodiment of the present invention, a polymer coating, such as a poly-imide coating, is applied to a steel substrate having a CNT / CNF layer as described above, for use in corrosive environments, for solar cell applications, and for fuel cells. Use in hydrogen storage, as a catalyst support, as a radar capture coating, or as an interfacial conductive layer or antimicrobial product. Of course, in coatings that act as radar capture coatings, the polymer coating that is optionally used needs to be transparent to the radar radiation in question.

  In a preferred embodiment of the invention, the steel substrate provided with a CNT / CNF layer according to the invention is used for the production of electrode parts of batteries, for example Li-based batteries and / or alkaline batteries, or for flexible back contact type electrodes. Used in the production of photovoltaic substrates. The thickness of the CNT / CNF provided with the polymer layer may be 0.5 μm to 60 μm, and gives heat resistance of 300 to 500 ° C. with a loss of 0.2 to 0.5% by weight. As an example, the Li battery consists of a thin layer of electrode material, an electrolyte and a current collector because the diffusion rate of Li through the electrode material is low. These layers are rolled up to obtain sufficient material. In a conventional Li battery, these layers comprise a copper layer, both sides of which are coated with a carbon layer. A plated steel substrate, such as a Ni—Cr plated steel substrate, is used, coated on both sides with a CNT / CNF coating layer and optionally coated with a polymer layer, such as a PI layer. Thus, this expensive copper substrate can be replaced by a substrate with a cheaper CNT / CNF coating. The substrate is an excellent alternative to expensive copper layers because of the excellent adhesion of the coating to the plated layer, such as the Ni-Cr layer, and, if desired, the corrosion protection of the layer supplemented with the polymer layer. Very suitable. Since this electrode does not require a binder, the weight of the battery is also reduced.

  In a preferred embodiment of the invention, the CNT / CNF powder removed from the substrate, for example by grinding, is used for the production of water-dispersed nanocoolants or fluids for heat exchangers or for the production of nanocomposite coatings. By using these powders in formulating water-dispersed nanocoolant fluids for heat exchangers, the heat exchangers are cooled more efficiently than water.

  The invention will now be further illustrated by the following non-limiting examples and drawings.

1 shows a general reaction scheme for CNT / CNF formation. FIG. 2 is an SEM image showing CNF formation on the steel surface in the presence of ethylene gas according to the reaction scheme of FIG. FIG. 2 is a TEM image showing CNF formation in the presence of ethylene gas according to the reaction scheme of FIG. The formation of the PI coating is shown schematically. The results of the kinetic potential test of various samples, namely uncoated steel metal, CNT / CNF coated steel, and CNT / CNF coated steel with a PI-based coating are shown. The battery and its constituent layers are shown. The TEM photograph of CNT formation on the steel surface is shown. Figure 3 schematically shows a combination of CNT / CNF (3) and polymer layer (2) on a steel substrate (1) for fuel cell applications.

Example: A chemical composition having the following range (min-max) was applied to a steel substrate.

Synthesis was carried out by chemical vapor deposition on cold rolled CNT / CNF steel using ethylene as a carbon-containing source as follows. High purity gases H ₂ (99.999%, INDUGAS), N ₂ (99.999%, INDUGAS), and ethylene (99.95%, PRAXAIR) were used. Cold rolled samples (3 cm x 3 cm) were mounted on a quartz plate placed in a glass tube with an inlet and outlet for the gas mixture. The glass tube was heated to the required temperature in a furnace. The sample was first reduced with H ₂ / N ₂ at a total flow rate of 100 ml / min. CNT / CNF was then synthesized using a gas mixture containing C ₂ H ₄ / N ₂ at the same flow rate of 100 ml / min.
The sample was cooled to room temperature in N _2. The amount of carbon formed on the steel substrate was determined by measuring the weight gain caused by the formation of CNT / CNF. The carbon nanotube-coated sample was purged with pressurized air and the mechanical loss was calculated. Morphological features were examined by scanning electron microscope (SEM) LEO 1550 FEG-SEM equipped with an in-lens detector.

The reaction scheme of FIG. 1 shows that acetylene (C ₂ H ₂ ) or carbon monoxide, optionally carbon dioxide, and hydrogen can be used instead of ethylene. An SEM image of the CNF coated sample is shown in FIG. This image clearly shows the uniform distribution and growth of CNF. The image also shows the CNF tip growth and the iron nanoparticles on the tip.

  The polyimide coating was produced as follows. PAA acid was prepared according to the scheme of FIG. 4, then applied onto a CNT / CNF coated steel substrate, placed in a furnace at a different temperature of 250-350 ° C., and then the sample was allowed to cool to room temperature. Subsequently, it was tested in various ways.

  A plurality of steel substrates provided with a carbon nanotube layer were subjected to poly-imide coating. These samples were exposed to a simulated salt water environment according to ASTM B117 and evaluated for wet adhesion and corrosion behavior. Potential differential mechanical measurements were performed in a simulated saline environment. These results indicate that the performance of the CNT / CNF with the poly-imide coating is far superior to the uncoated CNT / CNF layer (1000 hours in SST).

Table 3 outlines various processing conditions for growing CNT / CNF on low carbon steel substrates. The growth rate is expressed as a ratio to the mass of CNT / CNF formed per unit time and per surface.
The potential differential mechanical measurement was performed in a 3.5% NaCl solution at a scanning speed of 1.67 mV / s and a potential range of −0.5 mV to 1.5 mV (see FIG. 5). A significant current density drop was measured from 2-3 × 10 ⁻² A / cm ² in the case of uncoated steel to 1-2 × 10 ⁻⁷ A / cm ² in the case of polymer coated CNT. It was. There is clear evidence that the electrochemical reaction at the large passivating zone (-0.225 V to +1.032 V) and the coated surface was cathodically controlled. In the absence of a polymer layer on the CNT / CNF coating, FIG. 5 shows that the current density of the CNT / CNF coated substrate is already one grade lower than the uncoated steel sheet. Carbon nanotube-PI coated samples were found to exhibit significant passivity and reduced current density, which is a measure of low corrosion rate. On the other hand, the performance of uncoated steel is one grade worse than CNT / CNF coated steel. It should also be noted that a CNT / CNF layer in which CNT / CNF has been treated or filled with a corrosion inhibitor gives the layer a self-healing behavior.

Additional tests conducted at 600 ° C. using a carbon source gas comprising 60% CO, 10% CO ₂ and 30% H ₂ showed a growth rate of 1.00 mg / min.

A Ni—Cr plated steel substrate with a CNT / CNF coating layer on both sides was used for a Li battery according to FIG. The capacity was found to be as high as 1500 mAh / g using a 0.1 C charge rate. In both the low potential range 1 V to 5 mV and the large potential range 3 V to 5 mV, the electrode maintains approximately the same capacity in cycle testing. When comparing these results with commercially available carbon-based anodes, these capacities are very good. In FIG. 6, L represents a liquid electrolyte, C represents a can wall, S represents a separator, and A represents a metal layer (for example, aluminum) covered with Li _{1 + x} Mn ₂ O ₄ on both sides. F is a carbon steel or low alloy steel substrate with a CNT / CNF layer on both sides and optionally a polymer layer such as a PI coating.

  The corrosion resistance of the steel with CNT / CNF and PI coating was compared with the corrosion resistance of the same steel without the CNT / CNF layer. The PI coating peels after 5 days in the accelerated corrosion test. On the other hand, in the CNT / CNF interface layer, the coating lasted longer than 30 days.

  FIG. 8 schematically shows a combination of CNT / CNF (3) and polymer layer (2) on a steel substrate (1) for fuel cell applications. The main components of the PEM fuel cell structure are the bipolar plate and membrane electrode assembly (MEA). The MEA comprises a proton exchange membrane, a gas diffusion layer (GDL) and a catalyst layer. The main requirements for a bipolar plate are low cost, ease of manufacture and good electrical and mechanical properties. Bipolar plates are important functions in so-called stacking structures in fuel cells, such as carrying current away from each cell, distributing fuel and oxidant homogeneously in individual cells, separating individual cells, To achieve sufficient water management. By the method of the present invention, a bipolar plate can be produced by growing CNT / CNF on a steel substrate. CNTs were grown on cold rolling and a thin polymer coating, in this case polyether-imide, was applied using a roll coater and cured at 250 ° C. for 2 minutes. The coating thickness was 8 μm. Next, the substrate was subjected to a contact resistance test and a potential differential mechanical test. By further adding a polyetherimide layer, corrosion resistance is obtained, CNT / CNF provides good conductivity, and the properties of the CNT / CNF-PEI combination meet US Department of Energy (DOE) standards.

Claims (15)

A method of directly low temperature growing a carbon nanotube and / or carbon nanofiber (CNT / CNF) adhesion coating on one or both surfaces of a carbon steel or low alloy steel strip substrate,
-Prepare a steel substrate, optionally with a metallic coating,
-CNT / CNF is grown on the surface of the substrate by a thermal chemical vapor deposition (CVD) process using a carbon source gas comprising hydrogen at a temperature of 500-750 ° C, preferably 600-750 ° C. Let
-No catalyst is added to catalyze the growth of the CNT / CNF, the growth of the CNT / CNF being caused by iron, nickel and / or chromium present in the substrate and / or the metallic coating Comprising the step of catalyzing by.   The method of claim 1, wherein the carbon source gas comprises one or more of acetylene, ethylene, methane, carbon monoxide, carbon dioxide, or low molecular weight fatty oil.   3. A method according to claim 1 or 2, wherein the carbon source gas consists of hydrogen, carbon monoxide and carbon dioxide, preferably in a ratio of about 30:60:10.   The steel substrate is high strength steel (HSS), improved HSS, super HSS or composite phase steel, preferably 0.01 to 1% C, 0.15 to 2% Mn, 0.005 to 2 % Si, 0.01-1.5% Al, 10-200 ppm N, up to 0.015% P, up to 0.15% S, optionally 0.01-0.1% Nb, One or more of 0.002-0.15% Ti, 0.02-0.2% V, 10-60 ppm B, and the balance iron and inevitable impurities. The method according to one item.   Any of the preceding claims, wherein the steel substrate comprises nickel, nickel-chromium or a chromium plating layer or a zinc alloy layer before growing CNT / CNF on one or both surfaces of the substrate. The method according to one item.   A method of forming a coating on a steel substrate by forming a CNT / CNF layer on the substrate according to any one of claims 1 to 5, wherein the CNT / CNF layer is formed. Applying a polymer coating, such as a poly-imide-based coating. The poly-imide coating is on the CNT / CNF layer,
By applying a layer of polyamic acid (PAA), followed by imidization, and / or by adding Mn, Ag, Si, Ti, Al and / or Mg in the synthesis of PAA, followed by imide And / or by applying a liquid polyetherimide (PEI) solution, preferably by roll coating and / or spraying, and / or by producing the poly-imide from a poly-etherimide. The manufacturing method of the poly-imide type | system | group coating | cover of Claim 6 manufactured. Suitable compounds followed the CNT / CNF, such as MgO or CaO, in processes, the CO ₂ to form a catalyst support for saving in the form of a carbonaceous compound, or a photocatalyst, for example, titania or organic photoinitiators To convert the carbon dioxide into a carboxylic acid, such as formic acid (HCOOH), and / or an alcohol, such as ethanol (C ₂ H ₅ OH). The coating manufacturing method as described in any one of Claims.   A step of preparing a coil of cold-rolled steel in a continuous production method, a step of subjecting the coil to continuous annealing, a step of recrystallizing the cold-rolled coil as desired, a step of reducing the surface of the steel, Forming a layer of CNT / CNF on the steel at a temperature of 600 to 750 ° C., cooling the steel, and optionally applying a poly-imide coating to the coated steel, The method according to claim 1.   A method for producing a CNT / CNF powder by producing a coating according to any one of claims 1 to 5, wherein the CNT / CNF is mechanically ground, for example ground, from the surface of the steel substrate. And collecting the CNT / CNF.   9. Any of claims 1-8 for use in solar cells, for fuel cells, for hydrogen storage, as a catalyst support, for radar capture coatings, or as an interfacial conductive layer, or as an antimicrobial product. A steel substrate provided with the CNT / CNF layer according to claim 1.   Polymers for use in corrosive environments, for solar cell applications, for fuel cell applications, for hydrogen storage, as catalyst supports, for radar capture coatings, or as interfacial conductive layers, or as antibacterial products The steel base material which gave the layer of CNT / CNF as described in any one of Claims 1-8 with which coating | coated was given.   Use of the steel substrate according to claim 5 for producing electrode parts of batteries, for example Li-based batteries and / or alkaline batteries.   Use of the steel substrate / foil according to claim 5 for producing a photovoltaic substrate for a flexible back contact electrode.   Use of the powder according to claim 10 in the manufacture of water-dispersed nanocoolants or fluids for heat exchangers or in the manufacture of nanocomposite coatings.