WO2018085988A1

WO2018085988A1 - A method of providing a graphene coating on a carbon steel substrate

Info

Publication number: WO2018085988A1
Application number: PCT/CN2016/105059
Authority: WO
Inventors: Haiyong Cai; Chunyang DUAN; Lene Hviid; Li QIAO; Yu Wang
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company; Institute of Process Engineering, Chinese Academy of Science
Priority date: 2016-11-08
Filing date: 2016-11-08
Publication date: 2018-05-17

Abstract

A method of providing a graphene coating on a carbon steel substrate, at least comprising the steps of (a) providing a carbon steel substrate; (b) heating the carbon steel substrate as provided in step (a) in an oxygen-free chamber in the presence of a carbon source to a temperature above 800℃, thereby obtaining a heated carbon steel substrate; (c) decreasing the surface temperature of the heated carbon steel substrate as obtained in step (b) to lower than 700℃ at a cooling rate of at least 1℃/s, thereby obtaining a cooled graphene-coated carbon steel substrate. The graphene coating reduced the corrosion rate by 54.8%, which confirm the good anti-corrosion ability of the as-grown graphene coating.

Description

A METHOD OF PROVIDING A GRAPHENE COATING ON A CARBON STEEL SUBSTRATE

The present invention relates to a method of providing a graphene coating on a carbon steel substrate.

Various methods of providing a graphene coating on a metal substrate are known in the art.

As an example, US20130251998 discloses a steel sheet coated with graphene and a method for manufacturing the same. The method for manufacturing the graphene-coated sheet according to US20130251998 comprises the steps of: washing a surface of a steel sheet in a vacuum container with inert gas ions； and forming a graphene layer on the steel sheet by heating the washed steel sheet and injecting hydrocarbon into the vacuum container to dissociatively absorb the hydrocarbon onto the steel sheet.

Furthermore, US20150118411 discloses a method of producing a graphene coating on a stainless steel surface, the method comprising the steps of electrochemically polishing of the stainless steel surface, and heating the polished stainless steel surface in contact with a carbon precursor.

A problem of the above known and other methods is that under certain circumstances no graphene coating is formed on the metal substrate, in particular if the metal substrate is low in Ni content, such as carbon steel comprising less than 5.0 wt. ％Ni.

It is an object of the present invention to overcome or minimize the above problem.

It is a further object of the present invention to provide a method of providing a graphene coating on a carbon steel substrate, in particular on a carbon steel substrate that is low in Ni content (such as carbon steel comprising less than 5.0 wt. ％Ni) .

One or more of the above or other objects can be achieved by providing a method of providing a graphene coating on a carbon steel substrate, the method at least comprising the steps of:

(a) providing a carbon steel substrate；

(b) heating the carbon steel substrate as provided in step (a) in an oxygen-free chamber in the presence of a carbon source to a temperature above 800℃, thereby obtaining a heated carbon steel substrate；

(c) decreasing the surface temperature of the heated carbon steel substrate as obtained in step (b) to lower than 700℃ at a cooling rate of at least 1℃/s, thereby obtaining a cooled graphene-coated carbon steel substrate.

It has surprisingly been found according to the present invention that no proper graphene coating was formed on the carbon steel substrate (in particular when low or free in Ni content； without wanting to be bound to any specific theory it is believed that the presence of Ni helps in the growing of a graphene coating on a metal substrate) , unless the surface temperature of the heated carbon steel substrate was decreased relatively quickly.

In step (a) of the method according to the present invention, a carbon steel substrate is provided. The person skilled in the art will readily understand that the carbon steel substrate is not particularly limited. Preferably, the carbon steel substrate provided in step (a) comprises at least 0.1 wt. ％carbon (C) , preferably at least 0.5 wt. ％. Typically, the carbon steel substrate comprises at most 2.5 wt. ％carbon (C) , preferably less than 2.2 wt. ％, more preferably less than 2.11 wt. ％. Further it is preferred that the carbon steel substrate provided in step (a) comprises at most 9.0 wt. ％Ni, preferably less than 5.0 wt. ％, more preferably less than 1.0 wt. ％, even more preferably less than 0.5 wt. ％or even less than 0.1 wt. ％ (or even Ni-free) . Also, the carbon steel substrate typically contains at least 90 wt. ％Fe. Other components of the carbon steel may e.g. be Si, Cu, Mn, P, which are typically present as trace components.

It is preferred according to the present invention that commonly used carbon steel grades are used, such as X60 and X70. Hence, typically, the carbon steel substrate as used according to the present invention has a yield strength of at least 50 KSI (kilopounds per square inch) and includes steel grades such as X60 and X70.

Usually, before the heating in step (b) , the carbon steel substrate is washed (e.g. using dichloromethane to remove protection oil) and polished (e.g. to remove any rust spots) . As the person skilled in the art is familiar with how to do this, this is not discussed here in detail.

In step (b) , the carbon steel substrate as provided in step (a) is heated in an oxygen-free chamber in the presence of a carbon source to a temperature above 800℃, thereby obtaining a heated carbon steel substrate. As will be further discussed below, the surface temperature of the heated carbon steel substrate is subsequently decreased in step (c) thereby obtaining a graphene coating on the carbon steel substrate.

As the person skilled in the art is generally familiar with the process of forming a graphene coating on a metal substrate, this is not discussed here in detail.

Preferably the carbon steel substrate as provided in step (a) is subjected in step (b) to Chemical Vapour Deposition (CVD) , preferably continuous CVD. Although the growing of the graphene coating in the method according to the present invention is preferably by means of CVD, other coating methods may in principle be used. Usually, the graphene coating comprises 1-20 graphene layers, preferably 1-10 graphene layers. The coating method may be a continuous or a batch process. In case the coating process is a continuous CVD process, the movement rate is typically from 0.1-2.0 m/min, preferably below 0.5 m/min, more preferably below 0.3 m/min.

According to the present invention, with the term ‘oxygen-free’ is meant a concentration of less than 0.1 vol. ％O₂, preferably less than 0.05 vol. ％O₂, and preferably no O₂ at all.

Preferably, the heating in step (b) is to above 850℃, more preferably above 900℃. Typically, the heating in step (b) is to below 1400℃, preferably below 1200℃, more preferably below 1000℃.

Further, it is preferred that the heating in step (b) is performed at a pressure of from 10 to 1000 Pa, preferably above 20 Pa, and preferably below 500 Pa, more preferably below 100 Pa.

Also, it is preferred that the heating in step (b) is performed in the presence of H₂ (hydrogen) . Preferably, the heating in step (b) is performed at an H₂ flow rate of from 1 to 500 sccm (Standard Cubic Centimeter per Minute) , preferably above 10 sccm, more preferably above 20 sccm and preferably below 200 sccm, more preferably below 100 sccm, even more preferably below 50 sccm. In order to obtain absence of oxygen, the reaction zone is typically purged with an inert gas such nitrogen or argon.

The person skilled in the art will readily understand that the presence of the carbon source during the heating of the carbon steel substrate in the oxygen-free chamber of step (b) can be obtained in various ways. Preferably the presence of the carbon source is obtained by injecting the carbon source (rather than pre-coating the substrate or the like) , in particular as a gas. Furthermore, it is preferred that the carbon source is selected from C1-C8 alkanes and olefins, preferably C1-C6 alkanes and olefins, more preferably C1-C6 alkanes. Typically, the flow rate of the carbon source is typically from 0.001 to 500 sccm, preferably above 1 sccm, more preferably above 2 sccm and preferably below 50 sccm, more preferably below 25 sccm [cf. Ex. 1: 20 sccm] .

Preferably, the heating in step (b) a temperature above 800℃ is done for a period of between 3 and 400 minutes, preferably above 5 minutes and preferably below 50 minutes, more preferably below 25 minutes.

If desired, an intermediate ( ‘buffer’ ) coating layer is applied on the carbon steel substrate before allowing to grow the graphene coating in step (b) . Suitable methods of applying a buffer layer include CVD, electroplating, chemical plating, sputtering, thermal evaporating, etc. Typically, the buffer layer has a thickness of 0.1-10 μm and usually contains Ni, Cu, Si, etc. Of course, two or more buffer layers may be present. However, preferably, the carbon steel substrate contains no buffer layer (as a result of which the graphene is coated directly onto the carbon steel substrate) .

In step (c) , the surface temperature of the heated carbon steel substrate as obtained in step (b) is decreased to lower than 700℃ at a cooling rate of at least 1℃/s, thereby obtaining a cooled graphene-coated carbon steel substrate.

As already mentioned above, it has surprisingly been found according to the present invention that no proper graphene coating was formed on the carbon steel substrate, unless the surface temperature of the heated carbon steel substrate was decreased relatively quickly by active cooling. In this respect it is noted that a normal temperature decrease (i.e. when no active cooling is applied) is significantly less than 1℃/s. In this respect it is noted that US20150118411 refers (e.g. in claim 20 and paragraph [0032] ) to “quickly cooling the stainless steel surface” (after heating thereof) ； however, paragraph [0073] clearly indicates that “…Herein, “quickly cooled” does not mean quenching of the surface. Quickly cooling rather refers to cooling rates such as those obtained by turning off the heat source and continuing circulating said atmosphere. ” . Hence, US20150118411 does not make use of active cooling as used in the present invention； it is estimated that the cooling according to US20150118411 will be in the order of magnitude of 5℃/m (～0.08℃/s) , i.e. significantly less than 1℃/saccording to the present invention.

The person skilled in the art will readily understand that further cooling to ambient temperature may take place, but this does not have to occur at the fast temperature decreasing speed (and using active cooling) as indicated in step (c) . However, preferably, the heated carbon steel substrate as obtained in step (b) is cooled to below 600℃, more preferably to below 500℃, even more preferably to below 400℃, yet even more preferably to below 300℃ or even below 250℃, at the cooling rate of at least 1℃/s. Furthermore it is preferred that the cooling rate (either to 600℃, 500℃, 400℃, 300℃ or 250℃, or even below that) is at least 2℃/s, preferably at least 5℃/s, more preferably at least 8℃/s.

The person skilled in the art will readily understand that the relatively fast decrease in temperature (by active cooling) may be achieved in various ways, such as by using fans, additional cooling in CVD device, etc. Also, if desired, the temperature decrease of the surface temperature may be monitored, e.g. using a conventional thermal sensor such as a thermal couple.

Typically, after cooling down, the cooled graphene-coated carbon steel substrate will be subjected to characterization and evaluation. For this purpose, conventional methods such as Raman spectrum, NSS (neutral salt spray； e.g. according to ISO 9227: 2012) , Raman mapping, optical microscope, SEM (Scanning Electron Microscope) and XRD and electrochemistry may be used.

Hereinafter the invention will be further illustrated by the following non-limiting examples.

Examples

Example 1

X60 carbon steel (Ni-free) was cut into small pieces (1.5 x 2 cm²) , cleaned by washing in dichloromethane and polished to remove rust. Then the cleaned carbon steel substrate pieces were put in an apparatus as shown in Figure 1. As can be seen, the apparatus (generally referred to with reference number 1) comprises a chamber 2 (defined by a quartz tube) , a movable heating zone 3, an air cooling system 4 (external to the chamber 2) , the (cleaned) carbon steel substrates 5, a temperature sensor (not shown) for determining the surface temperature of the substrates 5, a container 6 for liquid carbon source (i.c. hexane) , a mechanical vacuum pump 7 and a gas flow meter 8 for controlling the composition of the carrier gas.

Argon gas was first injected into the chamber 2 to remove the O₂ in the chamber 2. Then the pressure in the chamber was reduced to low pressure (10 Pa) using the pump 7. Then, whilst introducing Ar/H₂ at a rate of 200 sccm/100 sccm, the carbon steel substrates were heated to 980℃ at a heating rate of 10℃/min.

After reaching the target temperature of 980℃, hexane vapour (stored in the container 6 as hexane liquid) was introduced as a carbon source at a flow rate of 20 sccm, due to the low pressure in the heating chamber 2. The hexane injection was 7 min and the pressure in the chamber 2 was maintained at 50 Pa. Then the temperature of the chamber was rapidly reduced to 800℃ at a rate of 5℃/sby moving the movable heating zone 3 to the distal end of the chamber 3 and by applying active cooling using the air cooling system 4. This active cooling at a rate of 5℃/swas continued until the surface temperature (as measured using a thermal couple； commercially available from Shanghai Jvj ing Precision Instrument Manufacturing Co.Ltd. (Shanghai, China) ) of the carbon steel substrates 5 reached a temperature of 680℃. Subsequently, the carbon steel substrates 5 were allowed to cool down further in the chamber 2, whilst the air cooling system 4 was turned off.

The graphene coating on the carbon steel substrates 5 was examined using XRD and Raman tests. A carbon peak at 26.46° confirmed the growth of graphene on the carbon steel substrates 5. Raman spectra and Raman mapping methods were used to evaluate the quality of the as-grown graphene. The characteristic peaks of graphene were clearly present in the Raman spectra with sharp G peak and 2D peaks and a very low D peak； this demonstrated the low defects in and high crystallization of the as-grown multi-layer graphene coating.

Comparative Example 1

The procedure of Example 1 was repeated, except for that no active cooling was applied, i.e. the air cooling system 4 was not used. It was confirmed by the Raman spectra that no graphene had grown on the surface of the carbon steel substrates.

Anti-corrosion performance

The anti-corrosion performance of the graphene-coated carbon steel substrates of Example 1 were evaluated by an NSS (Neutral Salt Spray) test and an electrochemical test, and compared with carbon steel substrates without graphene coating.

-NSS test

The carbon steel substrates were subjected, in accordance with ISO 9227: 2012, to a NSS solution of 5 wt. ％NaCl, with pH of 6.5-7.2 adjusted by HCl. SEM (Scanning Electron Microscope) images were taken after exposing the samples for 1h in an NSS chamber.

It was found that the bare (non-coated) carbon steel samples started to be corroded seriously, as time passed by, with corrosion pits spreading all across the surface of the carbon steel plates. The graphene-coated substrates had corroded less severe than the bare carbon steel samples and the area of pits were comparably small.

-Electrochemical test

The corrosion rates of the carbon steel samples with and without graphene coating were calculated by corrosion current as obtained from Tafel-plots in an electrochemical test. In the electrochemical test, a 3-electrode cell was used which used the carbon steel samples as the work electrode and a saturated calomel (SCE) as the reference electrode and a platinum sheet as counter electrode. The exposed area of the working electrode was 1x1 cm² and a (CHI 660D) electrochemical workstation was used to provide the required potential. All tests were carried out in a 5 wt. ％NaCl solution. Before obtaining the Tafel-plots and electrochemical impedance spectroscopy (EIS) spectra, the work electrodes were scanned for open circuit potential during 2 min to make the surface stable.

The results of the electrochemical test showed that the corrosion rates of the graphene-coated and bare carbon steel samples were and 1.82 mil/year and 0.83 mil/year, respectively.

Therefore, the graphene coating reduced the corrosion rate by 54.8％, which confirmed the good anti-corrosion ability of the as-grown graphene coating.

Discussion

As can be seen from the Examples, the present invention surprisingly provides a method for providing a graphene coating on a Ni-free carbon steel substrate. It has surprisingly been found according to the present invention that active cooling helped in obtaining a graphene-coated carbon steel substrate having desirable anti-corrosion properties.

The person skilled in the art will readily understand that many modifications may be made without departing from the scope of the invention.

Claims

A method of providing a graphene coating on a carbon steel substrate, the method at least comprising the steps of:

(a) providing a carbon steel substrate；

(b) heating the carbon steel substrate as provided in step (a) in an oxygen-free chamber in the presence of a carbon source to a temperature above 800℃, thereby obtaining a heated carbon steel substrate；

(c) decreasing the surface temperature of the heated carbon steel substrate as obtained in step (b) to lower than 700℃ at a cooling rate of at least 1℃/s, thereby obtaining a cooled graphene-coated carbon steel substrate.
The method according to claim 1, wherein the carbon steel substrate provided in step (a) comprises at least 0.1 wt.％ carbon.
The method according to claim 1 or 2, wherein the carbon steel substrate provided in step (a) comprises at most 9.0 wt.％ Ni, preferably less than 5.0 wt.％, more preferably less than 1.0 wt.％, even more preferably less than 0.5 wt.％.
The method according to any one of the preceding claims, wherein the carbon steel substrate as provided in step (a) is subj ected in step (b) to Chemical Vapour Deposition (CVD) , preferably continuous CVD.
The method according to any one of the preceding claims, wherein the heating in step (b) is to above 850℃.
The method according to any one of the preceding claims, wherein the heating in step (b) is performed at a pressure of from 10 to 1000 Pa, preferably above 20 Pa, and preferably below 500 Pa, more preferably below 100 Pa.
The method according to any one of the preceding claims, wherein the heating in step (b) is performed in the presence of H₂ (hydrogen) .
The method according to claim 7, wherein the heating in step (b) is performed at an H₂ flow rate of from 1 to 500 sccm (Standard Cubic Centimeter per Minute) , preferably above 10 sccm, more preferably above 20 sccm and preferably below 200 sccm, more preferably below 100 sccm, even more preferably below 50 sccm.
The method according to any one of the preceding claims, wherein the carbon source is selected from C1-C8 alkanes and olefins, preferably C1-C6 alkanes and olefins, more preferably C1-C6 alkanes.
The method according to any one of the preceding claims, wherein the heating in step (b) a temperature above 800℃ is done for a period of 3-400 minutes, preferably above 5 minutes and preferably below 50 minutes, more preferably below 25 minutes.
The method according to any one of the preceding claims, wherein an intermediate (‘buffer’) coating layer is applied on the carbon steel substrate before allowing to grow the graphene coating in step (b) .