WO2019078729A2

WO2019078729A2 - Method for producing an icing protected arrangement and icing protected arrangement

Info

Publication number: WO2019078729A2
Application number: PCT/NO2018/050249
Authority: WO
Inventors: Bodil HOLST; Naureen AKTHAR
Original assignee: Bergen Teknologioverforing As
Priority date: 2017-10-20
Filing date: 2018-10-19
Publication date: 2019-04-25
Also published as: WO2019078729A3

Abstract

An Icing protected arrangement (10), comprising a substrate(11)coated by an anti- icing coating (12), is capable to at least reduce the need for additional deicing provisions like heating or spraying with deicing solutions, if said anti-icing coating (12) comprising a fluorinated graphene layer (15).

Description

Method for producing an icing protected arrangement and icing protected arrangement

D e s c r i p t i o n :

The invention relates to a method for producing an icing protected arrangement. Furthermore, the invention relates to an icing protected arrangement, comprising a substrate coated by an anti-icing coating. During winter or in harsh environments icing of surfaces can be a problem. Sensors, surveillance cameras, windows or other critical surfaces must be free of ice for proper operation. This requires for example heating, manual cleaning or chemical cleaning, which is power consuming and thus to be avoided. Furthermore, the wings or rotors and/or some other critical parts i.e. rudder, elevators, stabilizers, propeller, swatch plates etc. of aircrafts have to be de-iced during flight or prior to the take-off in winter or in harsh environments. For that reason the aircraft is sprayed with a special de-icing solution and/or heated. This is time consuming and expensive.

The problem to be solved is to provide a method for producing an icing protected arrangement and such an icing protected arrangement which is capable to at least reduce the need for additional de-icing provisions like heating or spraying with de-icing solutions or manual cleaning.

The problem is solved by a method as mentioned above comprising the steps forming graphene coating on a substrate

fluorinating said graphene coating in a one side fluorination with a saturation of 20 % to 50 %.

Furthermore, the problem is solved by an icing protected arrangement as mentioned above with its anti-icing coating comprising a one side fluorinated graphene layer with a saturation of 20 % to 50 %.

Fluorinated graphene shows good anti-icing properties. Using this icing protected arrangement keeps the windows of sensors or surveillance cameras or other windows or critical surfaces free of ice, even in hash or arctic environment for example for environmental monitoring or in the oil and gas industry. Further, by using this icing protected arrangement there is no or at least a reduced need of de-icing of aircrafts during flight or before take-off. Preferably, said graphene coating or said anti-icing coating is comprising one or more layers, preferably monolayers. This results in a good coverage of the surface to be kept free of ice. In a preferable embodiment of the method said graphene coating is formed by mechanical cleavage, epitaxial growth, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), unzipping of carbon nanotubes, carbon nanotube slicing, arc discharge, thermal graphitization of silicon carbide, growth from polymerized self-assembled monolayers followed by thermal treatment, growth from the thermal decomposition of chemisorbed fullerene molecules, intercalation of graphite, spraying, dip coating, spin coating, spray coating, spray drying, layer- by- layer self-assembly, painting or using polydimethylsiloxane (PDMS) stamps. This results in easy and proper formation of said graphene coating.

It is further to be preferred if the method comprises the step of forming an intermediate layer, preferably between said substrate and said graphene coating, more preferably the intermediate layer forms a catalyst layer and/or an adhesion layer and/or is made of metals such as Cu, Ni, Fe, Pt, Ru, Ir, Co, Au, oxides such as CuO_x, SiO_x, Co_yO_x, Al_yO_x, composite material or graphene. Most preferably the intermediate layer is removed with an etchant, preferably 1 M solution of ferric chloride in water Concerning the arrangement it is to be preferred that said anti-icing coating comprising an intermediate layer, preferably from ruthenium or graphene. The intermediate layer can give a more accurate connection between the substrate and the coating.

For smooth surfaces where the optical properties needs to be preserved such as sapphire surfaces, quartz surfaces or various glass surfaces, the graphene is placed directly on the surface without an intermediate layer or the intermediate layer used for growing the graphene layer is removed before or after fluorination, preferably removed before fluorination step.

In another preferred embodiment the method comprises the steps forming the graphene coating (14, 15) on a growth substrate, preferably the intermediate layer, transferring the graphene coating (14, 15), preferably as graphene sheets, from said growth substrate to said substrate (11), curing of liquid polydimethylsiloxane (PDMS) on graphene followed by fast release of graphene from substrate though wet-etching- assisted mechanical peeling. This yields good results for large scale production. Another advantage results from the step of producing a heating element from said graphene coating or that intermediate layer. Accordingly, it is of advantage, if said anti- icing coating comprising a heating element from graphene, preferably from one or more graphene layers. In case of remaining moisture or ice on the surface this results in an easy and direct heating, which is highly transparent.

In yet another preferred embodiment of the method according to the invention said fluorination comprising at least one of the following fluorination methods Exposure to fluorine gas, preferably at high temperatures, more preferred with fluorine gas diluted in noble gas, most preferred in Xenon

XeF2 etching, preferably by gas exposure

F-based plasma, preferably using SF6, CF₄ or Ar/F2

Hydrothermal and photochemical synthesis,

Exfoliation of graphite fluoride or fluorinated graphite, preferably sonochemical exfoliation, more preferably liquid phase exfoliation assisted by ultrasonication, using most preferably ethanol, isopropanol, acetonitrile, ionic liquids, surfactants as intercalating agents or thermal exfoliation

In literature fully fluorinated graphene is referred to as fluorographene, carbon monofluoride of graphene, graphene fluoride or perfluorographene [Small 2010, 6, No. 24, 2877-2884]. This is a stoichiometric derivative of graphene with a fluorine atom attached to each carbon and is two-dimensional (2D), merely, a 2D counterpart of graphite fluoride. This is a 2D insulator with a wide optical bandgap of 3eV [Small 2010, 6, No. 24, 2877-2884].

For partially fluorinated graphene (CF_X with 0<x<1), a certain amount of carbon atoms are bonded to fluorine atoms with bonding character varying from ionic to semi-ionic to covalent. Control of the C-F bonding character and the mole ratio of fluorine to carbon is important for tuning the electrical conductivity in fluorinated graphene and can be achieved through optimizing the fluorination conditions including pressure, temperature, the species of fluorination agents and treatment time with fluorination agent [Adv. Sci. 2016, 3, 1500413]. Using XeF2 gas at room temperature as fluorinating agent, it is shown that fluorine coverage saturates at 25% for one-side fluorination and 100% for double-side fluorination [Nano Lett. 2010, 10, 3001-3005].

It is further of advantage, if the method according to the invention comprises a one side fluorination of the graphene coating with a surface saturation of 25 % to 50 %, preferably with a saturation of 25 %, more preferably one carbon atom per every two primitive graphene unit cells in the graphene coating surface is fluorinated. For the arrangement according to the invention said anti-icing coating comprises a one side fluorinated graphene coating with a saturation of 20% to 50%. Preferably said anti-icing coating comprises a one side fluorinated graphene coating with a saturation of 25 % to 50 %, more preferably with a saturation of 25 %, most preferably one carbon atom per every two primitive graphene unit cells in the graphene coating surface is fluorinated. This yields proper anti-icing properties with little influence of the fluorination to the bulk as well as the sticking of the coating to the substrate.

Another advantage of the invention is achieved, if the method comprises the step of producing an anti-icing coating on the surface of an aircraft, preferably on a wing or rotors and/or some other critical parts i.e. rudder, elevators, stabilizers, propeller, swatch plates etc. of the aircraft. Accordingly, it is to be preferred that said substrate of the arrangement is an aircraft, preferably a wing or rotors and/or some other critical parts i.e. rudder, elevators, stabilizers, propeller, swatch plates etc. of an aircraft. In that case de-icing during flight or prior to take-off can be avoided.

Yet, another advantage is achieved, if the method according to invention comprises the step of producing an anti-icing coating on a optically transparent surface, a lens or a window, preferably on an sapphire substrate, lens or window. It is in the same way to be preferred, if said substrate of said arrangement is a window, preferably a sapphire window.

Hereinafter characteristics of the invention will be described with reference to the attached figures. The figures show:

Fig. 1 a schematically view of an icing protected arrangement according to the invention,

Fig. 2 a number of images with a cross-sectional view of water droplets resting on different arrangements, and at different temperatures,

Fig. 3 a table (Tab. 1), representing the onset of freezing and the delay of freezing for the water droplets resting on the different arrangements from Fig. 2,

Fig. 4 a diagram showing the variation of the static contact angle as a function of the arrangement surface temperature, by applying water droplets on different arrangements,

Fig. 5 a diagram showing the contact angle hysteresis data, in accordance to Fig. 4, and

Fig. 6 a schematically view similar to Fig. 1 of another embodiment of an icing protected arrangement according to the invention.

Fig. 1 shows a schematically view of an icing protected arrangement 10 according to the invention. In this embodiment, the icing protected arrangement 10 comprises a substrate 1 1 covered by a coating 12. An intermediate layer 13 is arranged between the substrate 1 1 and the coating 12.

In the shown embodiment the substrate 1 1 is a window 1 1 , in detail it is a sapphire window 1 1. In principal it can be any other substrate to be protected against icing as for example a part of an aircraft, as a wing of an aircraft. The intermediate layer 13 of the embodiment is a ruthenium layer 13. The intermediate layer 13 can be made of other material as for example graphene. It can be omitted as well.

The coating 12 of the shown embodiment is an anti-icing coating 12, comprising a graphene layer 14 adjacent to the intermediate layer 13 and opposite to the substrate. In this embodiment, the anti-icing coating 12 comprises several layers graphene as graphene layer 14. A monolayer of graphene or more than one layer of graphene can be intended. In particular, the graphene layer 14 is fluorinated, thus forming a fluorinated graphene CxF layer 15.

The shown anti-icing coating 12 is hydrophobic. In particular, the anti-icing coating 12 has icephobic properties.

Fig. 2 shows a number of images with a cross-sectional view of water droplets, resting on different substrates, and at different temperatures. In the shown embodiment, the substrates are sapphire samples. In particular, the sapphire samples are designed as sapphire windows. With reference to Fig. 2, twelve images are shown, grouped into four lines and three columns: The first line shows water droplets, resting on sapphire windows without any surface treatment; the second line shows water droplets, resting on sapphire windows providing a graphene coating; and the third and fourth line shows water droplets, resting on sapphire windows providing a fluorinated graphene coating, with two different fluorine contents. Thereby, the third line shows a sapphire window providing a graphene coating, which is fluorinated for 30 seconds and the fourth line shows a sapphire window providing a graphene coating, which is fluorinated for 1200 seconds. The left, middle and right columns represent the water droplets resting on the sapphire windows at room temperature (left), at a temperature where freezing begins (middle) and at a temperature after freezing (right), respectively.

Fig. 3 shows Tab. 1 , representing the onset of freezing and the delay of freezing for water droplets resting on different substrates. According to Fig. 1 these substrates represent sapphire windows without any surface treatment or with varying coating. The onset of freezing was identified as a change in the optical appearance of the droplet. The onset of freezing was shifted towards lower temperatures for water droplets, resting on sapphire windows providing a graphene coating. The onset of freezing was lowered further for water droplets, resting on sapphire windows providing a fluorinated graphene layer. The displayed water droplets have a volume of 4 μΙ_, each. Fig. 4 shows the variation of the static contact angle as a function of the substrate surface temperature, by applying water droplets on different substrates. The substrates used for this study are designed as sapphire windows. The sapphire windows are provided (1) without any surface treatment, (2) with a graphene coating and (3) with a fluorinated graphene coating. Measurements were done in ambient air with about 50 % relative humidity at 23° C. The used water droplets have a volume of 4 μΙ_, each. Static contact angles measurements were done by placing the sapphire windows on a cooling stage. Water droplets were dispensed on the surface of the sapphire window. Afterwards, the temperature was lowered from room temperature to the desired low temperature. All low temperature measurements were performed in dry nitrogen (N2) atmosphere to avoid water condensation at temperatures below zero degrees.

Advancing (ACA) and receding (RCA) contact angles were determined by dispensing the water droplets on the surface of the sapphire window and tilting the sample stage.

A slight decrease of the static contact angle was observed only for samples using sapphire windows providing the highest graphene fluorination. However, this decrease is not as significant as observed for super-hydrophobic surfaces where condensation and frost formation below 0° C facilitates wetting of the surface.

Fig. 5 shows contact angle hysteresis data, in accordance to Fig. 4. The contact angle hysteresis data were calculated as difference between advancing and receding contact angles at corresponding tilting angles of sample. A 4μΙ_ water droplet was deposited at the surface of the substrate, which is designed as sapphire windows, at 0° tilt. Measurements were done in ambient air with about 50 % relative humidity at 23° C. The hysteresis was observed to reduce for water droplets, resting on sapphire windows providing a graphene coating. The hysteresis was observed to reduce further for water droplets, resting on sapphire windows providing a fluorinated graphene layer. Moreover, a delay in freezing (time taken by the water droplet to freeze after the surface reached the desired temperature) was observed for samples using a sapphire window providing a graphene coating with a maximum delay time of 90 minutes for samples using a sapphire window providing a graphene coating with higher fluorine content, when measured at -15°C.

Example

Producing of graphene and fluorinating graphene:

Graphene is produced using various methods such as mechanical cleavage, epitaxial growth, chemical vapor deposition (CVD), carbon nanotube slicing and intercalation of graphite. Fluorination is the process in which a Fluoride ion bonds to a sp2 orbital of graphene that is only bonded to one carbon atom of the graphene substrate. Bond character can vary from ionic to semi-ionic to covalent. It is different from the approach in which graphene sheet/ribbons are functionalized with fluorocarbon alkyl chains. Usually, in this case, alkyl chains covalently bond to the edges only. However, in case of fluorination, fluoride ions are distributed over the whole sheet and the functionalisation consists of fluor only without any alkyl or other chain.

Graphene coated sapphire windows were fluorinated using the Xactix® XeF2 etching system. The XeF2 gas exposure times were 30 seconds and 1200 seconds, using a temperature of approximately 30° C. The XeF2 treatment is shown to fluorinate graphene without etching. For one-sided fluorination, the fluorine content was observed (Nano Lett. 2010, 10, 3001-3005) to saturate at 25 % coverage or C₄F, which corresponds to one atom per every two primitive graphene unit cells in graphene.

Fluorination of graphene can be achieved through number of techniques including exposure to fluorine gas (F2) at high temperatures and F-based plasma. Exfoliation of graphite fluoride has also been used to get fluorinated graphene sheets. Sapphire windows were characterized using a DataPhysics OCA 20 instrument (DataPhysics GmbH, Germany). The system is equipped with a high speed CCD camera, a computer programmable droplet-dispensing unit, a Peltier cooling stage and an electronic tilt table. The electronic tilt table can tilt the sample stage up to 90°. Data were analyzed utilizing the SCA 20 software.

Applying of graphene on substrates:

Graphene was deposited through chemical vapor deposition (CVD) method on sapphire windows. The sapphire windows used for the examples of Fig. 1 to 5 have an Ru(0001) intermediate layer 13. Firstly Ru(0001) was deposited followed by graphene via CVD. It is also possible to place the graphene directly on the substrates or to use an intermediate layer which can be removed after deposition.

Fig. 6 shows a schematically view similar to Fig. 1 of another embodiment of an icing protected arrangement 16 according to the invention. The icing protected arrangement 16 is similar to the icing protected arrangement 10. Similar elements have the same reference numerals.

In contrast to the icing protected arrangement 10 of Fig. 1 the icing protected arrangement 16 does not comprise the intermediate layer 13. An anti-icing coating 17 similar to the anti-icing coating 12 is directly arranged on the substrate. Thus, the graphene layer 14 is directly attached to the substrate 11 with the fluorinated graphene layer 15 on top.

Methods for synthesizing fluorinated graphene:

1. Fluorination of pre-synthesized graphene

1.1. Graphene prodcution methods

Liquid phase or mechanical exfoliation of bulk graphite, epitaxial growth, chemical vapour deposition (CVD) and plasma enhanced chemical vapor deposition (PECVD), unzipping of carbon nanotubes arc discharge [J. Phys. Chem. C 1 13.1 1 (2009): 4257-4259], thermal graphitization of silicon carbide [Nat. Mater 8.3 (2009): 203], growth from polymerized self-assembled monolayers followed by thermal treatment [Adv. Mater. 25.30 (2013): 4146-4151 ], growth from the thermal decomposition of chemisorbed fullerene molecules [Surf. sci. 437.1 (1999): 249- 260]

1.2. Fluorination

Direct gas fluorination (such as F2 and XeF2), plasma fluorination (such as SF6, CF₄, Ar/F₂), hydrothermal and photochemical synthesis. [Adv. Sci. 2016, 3, 1500413]

2. Exfoliation of graphite fluoride or fluorinated graphite.

Sonochemical exfoliation (liquid phase exfoliation assisted by ultrasonication, ethanol, isopropanol, acetonitrile, ionic liquids, surfactants etc. are used as intercalating agents) and thermal exfoliation [Adv. Sci. 2016, 3, 1500413]

3. Deposition of (fluorinated) graphene

3.1. CVD method (for small substrates)

Graphene is grown directly on the surfaces using CVD method or with an intermediate metal layer (metals such as Cu, Ni, Fe, Pt, Ru, Ir, Co, Au, oxides such as CuO_x, SiO_x, CoyOx, AlyOx, composite materials). The intermediate layer may be removed prior to fluorination step. For the work presented here, Xactix® XeF2 etching system was used for fluorination. Other methods as described above could also be employed.

3.2. Large scale production

(a) Large area graphene sheets can be grown on metal surfaces and fluorinated in post process. Metal layer can be removed with an etchant (for example 1 M solution of ferric chloride in water for Cu and Ni) and the graphene sheet or fluorinated graphene sheet can be placed directly on the target surface using polydimethylsiloxane (PDMS) stamps [Nanotechnology 27 (2016) 365705]. Transfer of graphene sheet from growth substrate to target surface involve curing of liquid PDMS on graphene followed by fast release of graphene from substrate though wet-etching-assisted mechanical peeling. (b) Exfoliated graphene sheets are coated on any surface using methods such as dip coating, spin coating, spray coating, spray drying, layer-by layer self- assembly. Fluorination is done afterwards to get fluorinated graphene coating. This coating is transferred to target substrate using PDMS stamps

[Nanotechnology 27 (2016) 365705]. An intermediate adhesion layer may also be used to ensure good adhesion of coating to the target surface.

(c) Exfoliated fluorinated graphene micro/nano sheets can be deposited to target surface using methods such as dip coating, spin coating, spray coating, spray drying, layer-by layer self-assembly. An intermediate adhesion layer may also be used to ensure good adhesion of coating to the target surface.

R e f e r e n c e N u m e r a l s :

10 arrangement

11 substrate

12 coating

13 intermediate layer

14 graphene layer

15 fluorinated graphene layer

16 arrangement

17 coating

Claims

C l a i m s :

Method for producing an icing protected arrangement (10, 16) comprising the steps

forming graphene coating (14, 15) on a substrate (1 1)

fluorinating said graphene coating (15) in a one side fluorination with a saturation of 20 % to 50 %.

Method according to claim 1 , characterized in that said graphene coating (14, 15) is comprising one or more layers, preferably monolayers.

Method according to claim 1 or 2, characterized in that said graphene coating (14, 15) is formed by mechanical cleavage, epitaxial growth, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), unzipping of carbon nanotubes, carbon nanotube slicing, arc discharge, thermal graphitization of silicon carbide, growth from polymerized self-assembled monolayers followed by thermal treatment, growth from the thermal decomposition of chemisorbed fullerene molecules, intercalation of graphite, spraying, dip coating, spin coating, spray coating, spray drying, layer-by-layer self-assembly, painting or using polydimethylsiloxane (PDMS) stamps.

Method according to one of the preceding claims, characterized in the step of forming an intermediate layer (13), preferably between said substrate (1 1) and said graphene coating (14, 15), more preferably the intermediate layer (13) forms a catalyst layer and/or an adhesion layer and/or is made of metals such as Cu, Ni, Fe, Pt, Ru, Ir, Co, Au, oxides such as CuO_x, SiO_x, Co_yO_x, Al_yO_x, composite materials or graphene, most preferably the intermediate layer is removed with an etchant, preferably 1 M solution of ferric chloride in water.

Method according to one of the preceding claims, characterized in the steps forming the graphene coating (14, 15) on a growth substrate, preferably the intermediate layer, transferring the graphene coating (14, 15), preferably as graphene sheets, from said growth substrate to said substrate (1 1) through curing of liquid PDMS on graphene followed by fast release of graphene from substrate though wet-etching-assisted mechanical peeling.

Method according to one of the preceding claims, characterized in the step of producing a heating element from said graphene coating (14) or that intermediate layer (13).

Method according to one of the preceding claims, characterized in that said fluorination comprising at least one of the following fluorination methods Exposure to fluorine gas, preferably at high temperatures, more preferred with fluorine gas diluted in noble gas, most preferred in Xenon

XeF2 etching, preferably by gas exposure

F-based plasma, preferably using SF6, CF₄ or Ar/F2

Hydrothermal and photochemical synthesis,

Method according to one of the preceding claims, characterized in that a one side fluorination of the graphene coating (15) with a saturation of 25 % to 50 %, preferably with a saturation of 25 %, more preferably one carbon atom per every two primitive graphene unit cells in the graphene coating (15) surface is fluorinated.

Method according to one of the preceding claims, characterized in producing an anti-icing coating on the surface of an aircraft, preferably on a wing or rotor and/or some other critical parts i.e. rudder, elevators, stabilizers, propeller, swatch plates etc. of the aircraft.

Method according to one of the preceding claims, characterized in producing an anti-icing coating (12, 17) on a optically transparent surface, a lens or a window, preferably on an sapphire substrate, lens or window (11).

Icing protected arrangement, preferably produced according to one of the preceding claims, comprising a substrate (1 1) coated by an anti-icing coating (12, 17), characterized in said anti-icing coating (12, 17) comprising a one side fluorinated graphene coating (15) with a saturation of 20 % to 50 %.

Arrangement according to claim 1 1 , characterized in that said anti-icing coating (12, 17) comprising one or more layers, preferably monolayers.

Arrangement according to claim 1 1 or 12, characterized in that said anti-icing coating (12, 17) comprising an intermediate layer (13), preferably forming a catalyst layer and/or an adhesion layer and/or is made of metals such as Cu, Ni, Fe, Pt, Ru, Ir, Co, Au, oxides such as CuO_x, SiO_x, Co_yO_x, Al_yO_x, composite materials or graphene.

14. Arrangement according to one of the claims 11 to 13, characterized in that said anti-icing coating (12, 17) comprising a heating element from graphene, preferably from one or more graphene layers. Arrangement according to one of the claims 11 to 14, characterized in that said anti-icing coating (12, 17) comprising a one side fluorinated graphene coating (15) with a saturation of 25 % to 50 %, more preferably with a saturation of 25 %, most preferably one carbon atom per every two primitive graphene unit cells in the graphene coating surface is fluorinated.

Arrangement according to one of the claims 11 to 15, characterized in that said substrate is an aircraft, preferably a wing or rotor and/or some other critical parts i.e. rudder, elevators, stabilizers, propeller, swatch plates etc. of an aircraft.

Arrangement according to one of the claims 11 to 15, characterized in that said substrate is an optically transparent surface, a lens or a window, preferably on an sapphire substrate, lens or window (1 1).