BE1031682A1 - UNIFORM COATING OF A HOLLOW OBJECT AND METHOD FOR SAME - Google Patents

Abstract

The current invention relates to a method of DPV coating an internal surface of a hollow object, wherein the internal surface of the hollow object defines an internal volume, the method comprising the steps of: providing a cylindrical electrode having a radial external surface, said cylindrical electrode comprising a target material, wherein said radial external surface comprises said target material, within the internal volume of the hollow object, preferably coaxially positioned for uniform coating, wherein said cylindrical electrode and said internal surface of the hollow object are separated by an average distance De,s of at least 0.5 mm and at most 20 mm; and generating an electric field between the cylindrical electrode and the internal surface of the hollow object, wherein a product of a working pressure and the average distance De,s is between 0.01 Torr.cm and 10 Torr.cm.

Description

1 | BE2023/5468

UNIFORM COATING OF A HOLLOW OBJECT AND METHOD FOR

THIS ONE

FIELD OF THE INVENTION

The present invention relates to a method of DPV coating an internal surface of a hollow object, particularly a hollow tube, using a cylindrical electrode.

In a second aspect, the present invention also relates to a hollow object having an internal surface comprising a DPV coating.

STATE OF THE ART

Hollow objects, such as pipes, casings, and valves, are often exposed to extreme conditions, including high temperatures, mechanical stress, and exposure to chemicals. To extend the service life of these objects and improve their surface properties, coatings are commonly applied to their internal surfaces. However, coating the internal surfaces of hollow objects can be challenging due to factors such as accessibility, geometry.

Various techniques have been developed for coating surfaces with different materials. A commonly used method for coating components is physical vapor deposition (PVD), which involves depositing thin films of materials on various surfaces. PVD processes, such as sputtering,

Cathodic arc evaporation, thermal evaporation or electron beam evaporation, are often performed in vacuum chambers, where substrates or workpieces are placed on a substrate holder and exposed to a coating source. However, applying DPV coatings to the internal surfaces of hollow objects can be difficult since these processes rely on line-of-sight and are not suitable for depositing coatings inside deep cavities.

An example is known in WO2022261684A1 and describes an apparatus and method for coating or modifying the inner surface of a hollow article using a plasma source having an elongated shape. The plasma source includes a cathode and a thermionic electron emission source target, connected in an electrically conductive manner. The apparatus also has a masking element that partially covers the outer surface of the cathode and

2 BE2023/5468 of the target to prevent plasma formation in the masked area during operation. The target has a plasma formation area that is not covered by the masking element. Also provided are a target, apparatus arrangement, method and hollow article.

LUS8110043B2 describes an apparatus and method for applying coatings to interior surfaces of components, such as pipes or tubes, using a vacuum chamber and a source of evaporant. Primary carrier gas streams divert the flow of evaporated vapor from a region distal and external to the substrate into the interior cavity, coating at least a portion of the interior of the longitudinal section of the substrate. The method involves using an energy beam and primary carrier gas streams to direct the vapor flow to the interior surfaces for coating.

Despite advances in DPV techniques, none of the existing methods fully meet the industry’s requirements in terms of robustness, process temperature, versatility, coating properties and workpiece dimensions. In addition, health and environmental risks associated with some of the existing techniques may limit their suitability for certain applications.

The present invention aims to solve at least some of the problems and disadvantages mentioned above. The purpose of the invention is to provide a method that eliminates these disadvantages. The present invention targets the solution of at least one of the disadvantages mentioned above.

SUMMARY OF THE INVENTION

The present invention and embodiments thereof serve to provide a solution to one or more of the above-mentioned disadvantages. To this end, the present invention provides a method of DPV coating an internal surface of a hollow object according to claim 1. Preferred embodiments of the method are shown in any one of claims 2 to 12.

The present invention introduces a method of uniformly coating the interior surface of hollow objects, specifically small diameter tubes, using a

DPV. This method offers distinct advantages over other coating techniques. One advantage of this method is the ability to achieve a uniform coating thickness across the entire internal surface of the object.

3 BE2023/5468 hollow. By isotropically spraying the target material in a radially homogeneous manner, the coating has a consistent thickness and quality, ensuring reliable and consistent performance in various applications. In addition, this method allows for precise control of the coating thickness. By carefully selecting the working pressure and the distance between the electrode and the internal surface, the coating thickness can be accurately controlled, making it ideal for applications where precise coating thickness is crucial.

Another important advantage is that this method is particularly well suited for coating small diameter tubes. Coating small diameter tubes using conventional methods can be tricky, but this method overcomes these limitations, making it highly advantageous for small diameter tubing applications.

Furthermore, this method is suitable for coating long hollow objects. This makes it suitable for coating continuous lengths of tubing or other long hollow objects, enabling efficient and continuous operation in various industrial applications. In addition, the method offers versatility in material selection, as it enables the use of a variety of target materials. This allows for customization of coatings with specific characteristics, such as low friction, high hardness, and resistance to mechanical, thermal, and chemical stresses, making it adaptable to various applications.

In addition, the method can accommodate multiple sub-electrodes within the cylindrical electrode, enabling the deposition of multilayer coatings. This capability provides additional versatility in the development of coatings with complex compositions or properties, expanding its potential applications.

Finally, the method can be combined with additional pretreatment steps to further improve the coating properties. This flexibility allows for additional customization and optimization of coating properties for specific applications, making it a versatile and adaptable coating method.

The method thus makes it possible to obtain the deposition of coatings with a controlled thickness, excellent adhesion, and specific characteristics, such as a

4 BE2023/5468 low friction, high hardness, resistance to mechanical and thermal stresses, and resistance to chemical stresses.

In a second aspect, the present invention relates to a hollow object having an internal surface comprising a DPV coating according to claim 13. A preferred embodiment of the method is shown in claim 14.

Having a hollow object with an internal surface that is coated with a physical vapor deposition (PVD) coating can provide several important benefits in a variety of applications. One of the key benefits is the improved performance that PVD coatings provide. These coatings are known for their exceptional mechanical and physical properties, including high hardness, low friction, wear resistance, and corrosion resistance. When applied to the internal surface of a hollow object, PVD coatings can significantly improve its performance and durability. This is particularly beneficial in industries such as automotive, aerospace, and energy, where components often face harsh conditions such as high temperatures, abrasive wear, or exposure to chemicals. The PVD coating acts as a protective barrier, extending the life of the component and ensuring its optimal performance.

DPV coating can be precisely engineered to meet specific performance requirements, such as optimizing friction properties or improving wear resistance, without altering the external dimensions or shape of the object. This allows for greater freedom in designing complex shapes or lightweight structures, which can be advantageous in industries where weight reduction and performance optimization are critical factors. Compatibility with different materials makes DPV-coated hollow objects versatile and adaptable to various applications in different industries. In addition, the precise coating thickness achieved by the DPV coating process ensures consistent and uniform coating quality, resulting in reliable performance and functionality in various applications.

In a third aspect the present invention relates to a use according to claim 15. The use as described herein provides an advantageous effect in terms of improved gas permeation barrier, solvent-free corrosion protection, surface energy modification, and erosion resistance in various applications.

FIGURES

The following description of the figures of specific embodiments of the invention 5 is merely illustrative in nature and is not intended to limit the present teachings, their application or their uses. Throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

Figure 1 shows a schematic representation of a cross-sectional view of a hollow object with its internal surface visible, highlighting the coaxial positioning of a cylindrical electrode according to one embodiment of the invention.

Figure 2 shows a schematic representation of a longitudinal section of a reaction chamber with a hollow object to be coated, where the cylindrical electrode is positioned coaxially inside the hollow object according to one embodiment of the present invention.

Figure 3 shows a schematic representation of a longitudinal section of a reaction chamber, a hollow object and a cylindrical electrode positioned coaxially with a single type of target material, wherein the cylindrical electrode is shorter than the hollow object according to one embodiment of the invention.

Figure 4 shows a schematic representation of a longitudinal section of a reaction chamber illustrating a cylindrical electrode with three sub-electrodes positioned coaxially with a hollow object according to one embodiment of the invention.

Figure 5 shows a schematic representation of a longitudinal section of a coated hollow object having multiple layers of different coating materials forming a multi-coated structure on its internal surface according to one embodiment of the invention.

Figure 6 shows an example of a longitudinal section of a surface of a hollow object coated according to one embodiment of the invention.

6 BE2023/5468

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method of DPV coating an internal surface of a hollow object, in particular a hollow tube, using a cylindrical electrode.

Unless otherwise indicated, all terms used in the disclosure of the invention, including technical and scientific terms, have the meanings generally recognized by those skilled in the art to which this invention pertains. Definitions of terms are included for convenience to better appreciate the teaching of the present invention. “A,” “an,” “the” and “the” as used herein denote both the singular and the plural, unless the context clearly indicates otherwise. For example, “a compartment” denotes one or more compartments. "About" as used herein in reference to a measurable value such as a parameter, quantity, time duration and the like, is intended to encompass variations of +/-20% or less, preferably +/-10% or less, more preferably +/-5% or less, even more preferably +/-1% or less, and even more preferably +/-0.1% or less from and relative to the specified value, to the extent that such variations are appropriate to the disclosed invention. However, it is understood that the value to which the modifier "about" refers is itself also specifically disclosed. “Comprise,” “comprising,” and “comprises” and “composed of,” as used herein, are synonymous with “include,” “including,” “includes,” or “contain,” “containing,” “contains,” and are inclusive or open terms that — specify the presence of the following, e.g., a component, and do not exclude or preclude the presence of additional uncited components, features, elements, members, steps known in the art or disclosed herein.

Furthermore, the terms first, second, third and the like in the description and claims are used to distinguish between similar elements and not necessarily to describe a sequential or chronological order, unless otherwise specified. It is understood that the terms so used are interchangeable in appropriate circumstances and that embodiments of the invention described herein may operate in sequences other than those described or illustrated herein.

7 BE2023/5468

The citation of numerical ranges by bounds includes all numbers and fractions subsumed within that range, as well as the bounds cited.

The term “% by weight” or “percent by weight,” herein and throughout the specification, unless otherwise defined, refers to the relative weight of the respective component based on the overall weight of the formulation.

While the terms "one or more" or "at least one", such as one or more or at least one member(s) of a group of members, are clear per se, by way of further exemplification, the term encompasses inter alia a reference to any one of said members, or to any two or more of said members, such as, e.g., any number > 3, > 4, > 5, > 6 or > 7 etc. of said members, and up to all of said members.

Unless otherwise defined, all terms used in the disclosure of the invention, including technical and scientific terms, have the meanings generally recognized by those skilled in the art to which this disclosure pertains. Definitions of terms used in the description are included for convenience in understanding the teaching of this disclosure. The terms or definitions used herein are provided solely to facilitate understanding of the disclosure.

Reference throughout this specification to “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the occurrence of the phrase “in an embodiment” at various locations throughout this specification does not necessarily always refer to the same embodiment, but may. Additionally, the particular feature, structure, or characteristic may be combined in any suitable manner, as would be apparent to those skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other feature elements included in other embodiments, combinations of feature elements from different embodiments are intended to be within the scope of the invention, and to form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments may be used in any combination.

8 BE2023/5468

In a first aspect, the invention provides a method of DPV coating an internal surface of a hollow object, wherein the internal surface of the hollow object defines an internal volume.

According to the invention, the term "hollow object" refers to any object that includes an internal surface. Non-limiting examples of hollow objects are tubes, pipes, hollow shafts, or the like.

According to the invention, the term "internal surface" refers to a surface of an opening that extends into the hollow object. Non-limiting examples of internal surfaces are the internal surfaces of boreholes, or surfaces extending along the internal diameter surfaces of pipes, tubes, hollow shafts, or the like.

According to the invention, the term "DPV" refers to a process used to deposit thin films of material onto a surface. In a DPV process, a material is first evaporated from a solid source, typically using a high-energy source. This creates a vapor of the material, which then condenses on a substrate, forming a thin film. The process takes place in a vacuum chamber, which is important because the absence of air and other gases prevents contamination of the film and ensures that the material can be deposited uniformly.

In this context, the type of DPV technique is called sputtering. In sputtering, atoms are ejected from a target material by bombarding it with high-energy ions or plasma. The ejected atoms then condense on the substrate and form a thin-film coating.

In a preferred embodiment of the invention, the method comprises providing a cylindrical electrode having a radial outer surface, said cylindrical electrode comprising a target material, wherein said radial outer surface comprises said target material, within the internal volume of the hollow object. This allows for isotropic sputtering, meaning that the target material is sputtered in a radially homogeneous manner such that all areas of the inner surface are covered by the target material. This leads to a more uniform and constant coating thickness on the inner surface of the hollow object. In a further preferred embodiment of the invention, the cylindrical electrode is positioned coaxially for uniform coating.

In this context, “coaxially positioned” means that the cylindrical electrode is placed in the center of the hollow object to be coated, such that the longitudinal axis of the electrode is aligned with the longitudinal axis of the object. This ensures that the coating is deposited uniformly and evenly on the internal surface.

9 BE2023/5468 entire hollow part. In other words, the distance between the inner surface and the cylindrical electrode is substantially uniform at each position. The coaxial positioning of the cylindrical electrode ensures that the distance between the inner surface of the hollow object and the electrode is substantially uniform at each position. This means that the coating is deposited consistently at the same distance from the inner surface throughout the entire interior of the hollow object, resulting in a uniform and constant coating thickness.

In a further preferred embodiment, the cylindrical electrode and the inner surface of the hollow object are separated by an average distance Des of at least 0.5 mm, more preferably at least 1.5 mm, more preferably at least 2.0 mm, more preferably at least 2.5 mm, more preferably at least 3.0 mm, more preferably at least 3.5 mm, more preferably at least 4.0 mm, more preferably at least 4.5 mm, more preferably at least 5 mm, more preferably at least 5.5 mm, more preferably at least 6.0 mm, more preferably at least 6.5 mm, more preferably at least 7.0 mm, more preferably at least 7.5 mm, more preferably at least 8.0 mm, more preferably at least 8.5 mm, more preferably at least 9.0 mm, more preferably at least 10.0 mm.

In a further preferred embodiment, the cylindrical electrode and the inner surface of the hollow object are separated by an average distance Des of at most 25.0 mm, more preferably at most 20.0 mm, more preferably at most 19.5 mm, more preferably at most 19.0 mm, more preferably at most 18.5 mm, more preferably at most 18.0 mm, more preferably at most 17.5 mm, more preferably at most 17.0 mm, more preferably at most 16.5 mm, more preferably at most 16.0 mm, more preferably at most 15.5 mm, more preferably at most 15.0 mm, more preferably at most 14.5 mm, more preferably at most 14.0 mm, more preferably at most 15.5 mm. more preferably not more than 13.5 mm, more preferably not more than 13.0 mm, more preferably not more than 12.5 mm, more preferably not more than 12.0 mm, more preferably not more than 11.5 mm, more preferably not more than 11.0 mm, more preferably not more than 10.5 mm.

10 BE2023/5468

According to the invention, the term "average distance", denoted by Des, represents the typical space between the cylindrical electrode and the inner surface of the hollow object. It is important to note that the term "average distance" implies that there may be slight variations or fluctuations in the actual separation or space between the electrode and the inner surface, but the average or typical value must fall within the specified range.

The distance between the cylindrical electrode and the inner surface of the hollow object can be precisely controlled, which allows fine adjustment of the coating process parameters such as deposition rate, voltage and current, leading to improved coating quality and reproducibility. By placing the cylindrical electrode at the center of the hollow object, the maximum possible distance between the inner surface and the cylindrical electrode can be achieved, without the cylindrical electrode coming into contact with the inner surface. This allows for an efficient and effective coating process, since the coating can be deposited—evenly across the entire inner surface of the hollow object without any area being missed. Such positioning of the cylindrical electrode ensures that the coating is deposited uniformly and evenly over the entire inner surface of the hollow object. This helps to achieve a consistent thickness of the deposited coating throughout the interior of the hollow object, resulting in a uniform and high-quality coating. The uniform coating achieved by such positioning of the cylindrical electrode helps to improve the overall coating quality. It minimizes the risk of uneven coating thickness, uneven coverage, or omitted spots, which can result in poor coating quality and reduced performance of the coated object. It is further understood that the maximum possible distance depends on the internal diameter of the hollow object.

In a preferred embodiment of the invention, the shape of the cylindrical electrode can be adapted to the diameter and size of the inner surface of the hollow object to be treated. For insertion into the hollow object, the outer diameter of the cylindrical electrode must be smaller than the inner diameter of the hollow object to be treated. The length of the cylindrical electrode can be as long as necessary for the inner surface to be treated completely.

In a preferred embodiment of the invention, the cylindrical electrode and the hollow object are configured to move relative to each other, to enable tube coating or continuous operation, wherein the movement is parallel to maintain coaxial positioning of the cylindrical electrode within the internal volume of the hollow object.

11 BE2023/5468

In a preferred embodiment of the invention, the target material forms a continuous and uniform radial outer surface of the cylindrical electrode. This means that the cylindrical electrode used for coating has a continuous and uniform radial outer surface that is made of the same material as the target material.

In other words, the entire outer surface of the cylindrical electrode is made of the same material that is to be deposited on the surface of the hollow object being coated. This helps ensure that the coating material is deposited evenly and uniformly on the surface of the object, resulting in a high-quality coating.

In a preferred embodiment of the invention, the cylindrical electrode comprises a plurality of sub-electrodes arranged in series to achieve a multi-layer coating, wherein each sub-electrode comprises the target material. The target material of at least two of the plurality of sub-electrodes may be the same or may be different. The sub-electrodes may be sequentially activated and deactivated to deposit different layers of material on the internal surface of the hollow part.

In a preferred embodiment of the invention, the target materials of the cylindrical electrode and/or sub-electrodes are selected from a group consisting of a metal, a metal alloy, a ceramic material and combinations thereof. Alternatively or additionally, the metal is chromium. Alternatively or additionally, the target material comprises a ceramic material. More preferably, the target may comprise one or more materials/elements selected from a group consisting of: aluminum, boron, carbon, chromium, cobalt, copper, gold, holmium, iron, lanthanum, lithium, magnesium, manganese, molybdenum, nickel, silicon, silver, tin, titanium, vanadium, ytterbium, yttrium, zinc, zirconium, hafnium, tantalum, alloys thereof. These target materials enable customization of coating properties based on the specific requirements of the hollow object being coated. The specified target materials are known for their desirable properties, such as high thermal and electrical conductivity, excellent corrosion resistance, good mechanical strength, and other functional characteristics. Coating the inner surface of the hollow object with these materials can impart these properties to the coated object, improving its overall performance and durability. The coating process can be optimized for different applications, such as automotive, aerospace, electronics, energy, medical, and others.

12 BE2023/5468

In a preferred embodiment of the invention, the hollow object to be coated is provided, i.e. arranged or positioned or placed, in a reaction chamber.

The hollow object may be provided in a vertical position relative to the surface of the Earth, in a horizontal position, or at a position inclined at an angle between 0° and 180° relative to the surface of the Earth.

In a preferred embodiment of the invention, once the cylindrical electrode is arranged coaxially with the hollow object, the reaction chamber is closed and evacuated to reduce the working pressure inside the chamber until a predetermined value is reached. This allows any contaminants, such as moisture, to be removed from the reaction chamber.

In a further preferred embodiment, a gas is passed through the reaction chamber. As a result, the gas is supplied into the internal volume of the hollow object comprising the cylindrical electrode. The working pressure is chosen such that the product of the working pressure and the average distance De,s is between 0.01 Torr.cm and 10 Torr.cm, more preferably between 0.02 Torr.cm and 9 Torr.cm, more preferably between 0.03 Torr.cm and 8 Torr.cm, more preferably between 0.04 Torr.cm and 7 Torr.cm, more preferably between 0.05 Torr.cm and 6 Torr.cm, more preferably between 0.06 Torr.cm and 5 Torr.cm, more preferably between 0.07 Torr.cm and 4 Torr.cm, Torr.cm and 3 Torr.cm, more preferably between 0.09 Torr.cm and 2 Torr.cm, more preferably between 0.1 Torr.cm and 1 Torr.cm, more preferably between 0.2 Torr.cm and 2 Torr.cm, more preferably between 0.3 Torr.cm and 3 Torr.cm, more preferably between 0.4 Torr.cm and 4 Torr.cm, more preferably between 0.5 Torr.cm and 5 Torr.cm, more preferably between 0.6 Torr.cm and 6 Torr.cm, more preferably between 0.7 Torr.cm and 8 Torr.cm, more preferably between 0.8 Torr.cm and 1 Torr.cm, more preferably between 0.9 Torr.cm and 2 Torr.cm, more preferably between 0.10 Torr.cm and 2 Torr.cm, more preferably between 0.11 Torr.cm and 2 Torr.cm, more preferably between 0.12 Torr.cm and 2 Torr.cm, more preferably between 0.13 Torr.cm and 2 Torr.cm, more preferably between 0.14 Torr.cm and 2 Torr.cm, more preferably between 0.15 Torr.cm and 2 Torr.cm, more preferably between 0.16 Torr.cm and 2 Torr.cm, more preferably between 0.17 more preferably between 10° > Torr.cm and 45 Torr.cm, more preferably between 10% Torr.cm and 40 Torr.cm, more preferably between 103 Torr.cm and 35 Torr.cm, more preferably between 0.01 Torr.cm and 30 Torr.cm, more preferably between 0.1 Torr.cm and 25 Torr.cm, more preferably between 1 Torr.cm and 20 Torr.cm. This is one of the key parameters since it affects many of the plasma characteristics and this is only possible because the distance between the electrodes is small, due to the limited diameter of the hollow object to be coated. The reason for specifying this working pressure range is that it has been determined to be optimal for the coating process. Within this range, the electric field generated between the cylindrical electrode (cathode) and the internal surface of the hollow object (anode) is sufficient to facilitate the coating process and ensure uniform deposition of the coating material.

The working pressure range is carefully selected to create a suitable environment for the coating process, achieving a

13 BE2023/5468 efficient ionization of the target material, ion transport, and deposition on the inner surface of the hollow object. This range has been found to be effective in achieving the desired coating quality, thickness, and uniformity for the specific application of the invention. The specified working pressure range may also be influenced by other factors such as the properties of the target material, the type of coating process being used, the geometry and size of the hollow object, and other process parameters. Therefore, it is important to carefully control and maintain the working pressure within the specified range to optimize the coating process and achieve the desired coating results.

According to the invention, the term "working pressure" refers to the local absolute pressure where the plasma is formed. The working pressure is measured near or at the target surface. It thus represents the absolute pressure at or near the target surface where the plasma is formed. The working pressure refers to the equilibrium pressure that is achieved by injecting a gas and pumping simultaneously into a plasma system. It is typically expressed as a product of pressure and distance, which provides a more accurate description of the type of plasma regime that is present. In cases where a gas mixture is injected, the working pressure is the sum of the pressures of the individual injected gases. When no gas is injected, the resulting pressure is called the base pressure, which is significantly lower, approximately one million times, compared to the working pressure.

In a preferred embodiment of the invention, the gas provided in the internal volume may comprise a single gas or a mixture of two or more gases. Preferably, the gas comprises an inert gas, a reactive gas or a combination thereof. More preferably, the inert gas is selected from a group comprising helium, neon, argon, krypton. More preferably the reactive gas is selected from a group comprising nitrogen, oxygen, methane, ammonia, acetylene or a fluorinated gas.

In a further preferred embodiment of the invention, the method further comprises generating an electric field between the cylindrical electrode and the inner surface of the hollow object, with the cylindrical electrode serving as a cathode and the hollow object serving as an anode. The electric field applied to the electrode is used to activate the gas into a plasma gas and to extract at least a portion of the target material from the cathode, which is then deposited on the inner surface of the hollow part or tube.

14 BE2023/5468

When an electric field is applied to a cylindrical electrode, it activates or discharges the gas surrounding it, converting it into a plasma gas or a plasma discharge, i.e., the electric field ignites a plasma comprising the activated gas.

This plasma gas, also called activated gas, is then used to extract at least a portion of the target material from the cathode, particularly through the interaction of ions in the plasma gas with the cathode. The extracted target material is then deposited onto the inner surface of the hollow object, known as the anode, resulting in the creation of a treated hollow object. More specifically, for the formation of a coating. This method of deposition is commonly known as sputtering. Therefore, the cylindrical electrode functions as a plasma source in this specific method. The use of a cylindrical electrode in this process results in isotropic sputtering, where the target material is uniformly sprayed in a radially homogeneous manner, ensuring that all areas of the inner surface of the hollow object are evenly coated with the target material.

In a preferred embodiment of the invention, the gas discharge occurs in the Townsend regime. The Townsend regime is a concept in plasma physics that refers to a specific range of electric field strengths in which a plasma discharge occurs. In the Townsend regime, the electric field is — strong enough to ionize gas particles, creating a plasma, but not strong enough to cause significant electron multiplication by secondary electron emission. In the Townsend regime, the electric field strength is typically moderate, allowing for a stable, self-sustaining plasma discharge. Plasma behavior in the Townsend regime is — characterized by a linear relationship between the electric field and the ionization rate, known as the Townsend discharge law. This regime is commonly observed in many practical plasma applications, such as in the gas discharges used in fluorescent lights, plasma displays, and certain types of plasma processing techniques. Understanding the Townsend Regime

Townsend is important for controlling and optimizing plasma processes in various technological applications. This results in a homogeneous discharge of a large radius, and contributes to the homogeneity and uniformity of the coating obtained.

In a preferred embodiment of the invention, the type of electric field applied to the cylindrical electrode for the plasma gas activation and spraying process can vary. Both AC (alternating current) and DC (direct current) can potentially be used for this purpose, as long as the electric field is

15 BE2023/5468 applied for a period of time long enough to form a layer of target material on the internal surface.

In some cases, a DC power supply is commonly used for sputtering, where a constant voltage or current is applied to the electrode to generate the plasma gas and facilitate the extraction and deposition of target material.

CC spraying is known for its simplicity and ease of control, making it a popular choice for many applications. On the other hand, a power supply

DC can also be used for sputtering, where the polarity of the electric field alternates periodically. AC sputtering includes techniques such as RF sputtering and HiPIMS (high-power pulsed magnetron sputtering). These methods offer specific advantages in certain situations. AC sputtering is known to provide certain advantages in certain situations, such as improved uniformity of the deposited coating and reduced arcing. The choice between AC and DC power for sputtering depends on a variety of factors, including the specific material being deposited, the desired coating properties, and the equipment setup.

In a preferred embodiment of the invention, a power density applied to the cathode is preferably between 0.01 W/cm? and 50 W/cm?, preferably between 0.01 W/cm? and 40 W/cm?, preferably between 0.05 W/cm? and 30 W/cm?, preferably between 0.1 W/cm2 and 35 W/cm?2, preferably between 0.03 W/cm2 and 25 W/cm?, preferably between 0.01 W/cm2 and 5 W/cm?, preferably between 0.05 W/cm2 and 2 W/cm?, preferably between 0.1 W/cm? and 2 W/cm2, preferably between 0.1 W/cm2 and 8 W/cm?, preferably between 0.1 W/cm? and 25 W/cm2, preferably between 0.2 W/cm? and 5 W/cm2, preferably between 0.5 W/cm2 and 10 W/cm?, preferably between 0.5 W/cm? and 15 W/cm?, preferably between 1 W/cm? and 10 W/cm?, preferably between 1 W/cm? and 20 W/cm?, preferably between 0.05 W/cm? and 25 W/cm?, preferably between 0.2 W/cm? and 10 W/cm?, preferably between 0.2 W/cm2 and 15 W/cm2, preferably between 0.01 W/cm? and 20 W/cm?, preferably between 0.05 W/cm? and 10 W/cm2. Power density refers to the amount of power applied per unit area of the cathode surface. The proposed densities may result in increased ion bombardment energy, which may affect coating properties such as coating adhesion, microstructure, and thickness control.

Higher power densities can also lead to higher deposition rates, which can affect the efficiency and productivity of the overall process.

16 BE2023/5468

In a preferred embodiment of the invention, an average current density applied to the cathode is preferably between 0.001 A/cm2 and 10 A/cm?, preferably between 0.002 A/cm? and 9 A/cm?, preferably between 0.003 A/cm? and 8 A/cm?, preferably between 0.004 A/cm2 and 7 A/cm?, preferably between 0.005 A/cm2 and 6 A/cm?, preferably between 0.001 A/cm2 and 0.5 A/cm?, preferably between 0.001 A/cm? and 1 A/cm?, preferably between 0.001 A/cm2 and 5 A/cm2, preferably between 0.001 A/cm2 and 10 A/cm?, preferably between 0.005 A/cm2 and 0.5 A/cm?, preferably between 0.005 A/cm2 and 1 A/cm?, preferably between 0.005 A/cm2 and 5 A/cm?, preferably between 0.01 A/cm2 and 0.5 A/cm?, preferably between 0.01 A/cm2 and 1 A/cm2, preferably between 0.01 A/cm? and 5 A/cm?, preferably between 0.01 A/cm? and 10 A/cm2. The average current density refers to the amount of electric current passing through the cathode per unit area. The average current density affects the ionization of the process gas and the generation of plasma, which in turn influences the ion bombardment energy and the resulting coating characteristics. For very thin films, low currents such as 0.001 A/cm2 can be particularly useful. Higher average current densities can result in higher plasma densities and increased ion bombardment energy, which can affect coating properties such as — coating adhesion, density, and microstructure.

Optimizing power density and average current density within preferred ranges can help achieve desired results in the coating process. However, the specific effects of power density and average current density on the coating process depend on various factors—such as the material being processed, electrode configuration, process gas, and other process parameters. Therefore, careful consideration and adjustment of these parameters based on the requirements and process conditions of the specific coating is necessary to achieve the desired coating properties and performance.

In a preferred embodiment of the invention, the method comprises a step of pretreating the inner surface of the hollow object prior to depositing the target material on the inner surface, i.e., prior to coating the inner surface. Preferably, the pretreatment is performed prior to placing the hollow object in the reaction chamber. Ideally, the pretreatment is accomplished in the same reaction chamber as that used for the coating deposition process, providing convenience and efficiency. For the pretreatment, a coating-assisted approach

17 BE2023/5468 plasma is preferred. This pretreatment may be accomplished exclusively or primarily within the reaction chamber itself. The plasma-assisted pretreatment occurs after reaching the predetermined working pressure value but before introducing the gas used to extract the target material from the electrode. This sequence ensures optimal timing of the pretreatment step in relation to the overall process. It is important to note that the specifics of the pretreatment may vary. The pretreatment may be performed at the same pressure as the sputtering process or at a different pressure. Similarly, the pretreatment may use the same gas as the sputtering process or a different gas. However, in the pretreatment step, the polarity is reversed to ensure that it is the hollow object itself that undergoes the “sputtering” process, effectively cleaning and preparing its internal surface.

In a preferred embodiment of the invention, the pretreatment comprises a cleaning and/or etching step, for example ultrasonic cleaning or sandblasting. According to the present disclosure, the term "cleaning" refers to the process of removing contaminants, in particular organic contaminants, from a surface. In other words, "cleaning" refers to the basic removal of contaminants. On the other hand, in the context of the present invention, "etching" refers to a process that involves both the removal of contaminants and the attachment of specific functional groups to the inner surface of a hollow object. These functional groups are intended to improve the adhesion of a target material coating to the surface. In other words, "etching" encompasses a more comprehensive process that not only removes contaminants but also modifies the surface by adding functional groups that facilitate the bonding of a coating material.

In a further preferred embodiment of the invention, the pretreatment comprises an etching step. Preferably, the plasma etching is performed in the reaction chamber when the predetermined working pressure is reached and before the gas passes through the reaction chamber. Plasma etching—comprises passing an etching gas through the reaction chamber, thereby providing the etching gas into the internal volume of the hollow object. Then, a second electric field is applied to the hollow object, with the cylindrical electrode serving as an anode and the hollow object serving as a cathode. The second electric field advantageously activates the etching gas, thereby obtaining an etching plasma. The ions of the etching plasma dissociate organic contaminants at the surface of the internal surface of the hollow object, resulting in the extraction of volatile components by the etching gas. The ions of the etching plasma

18 BE2023/5468 also attach to the inner surface, thereby providing the inner surface with functional groups.

In a further preferred embodiment of the invention, the etching gas is selected from a group consisting of argon, helium, nitrogen, oxygen, methane, ethylene, nitrogen dioxide, nitrous oxide or fluorine.

In a second aspect, the invention provides a hollow object having an internal surface comprising a DPV coating.

In a particularly preferred embodiment, the hollow object has an internal diameter of less than 5 cm, the coating has a thickness between 0.01 µm and 50 µm, and a relative deviation in the thickness of the coating is at most 20%.

In a preferred embodiment of the invention, a ratio of a length of the hollow object to its inner diameter is at least 10, preferably at least 15, more preferably at least 20, more preferably at least 25, more preferably at least 30, more preferably at least 40, more preferably at least 45, more preferably at least 50, more preferably at least 50, more preferably at least 60, more preferably at least 70, more preferably at least 80, more preferably at least 90, more preferably at least 100.

In a preferred embodiment of the invention, a ratio of a length of the hollow object to its inner diameter is at most 10,000, more preferably at most 5,000, more preferably at most 4,500, more preferably at most 4,000, more preferably at most 3,500, more preferably at most 3,000, more preferably at most 2,500, more preferably at most 2,000, more preferably at most 1,500, more preferably at most 1,000, more preferably at most 500, more preferably at most 400, more preferably at most 300, more preferably at most 200.

Most preferably, the ratio of the length of the hollow object to its internal diameter is in a range between 10 and 2,000, preferably between 15 and 1,500, more preferably between 20 and 1,000, more preferably between 25 and 500, more preferably between 30 and 400,

19 BE2023/5468 more preferably between 40 and 300, more preferably between 50 and 200.

Preferably, the inner diameter of the hollow object is at least 0.1 mm, preferably at least 0.5 mm, more preferably at least 1.0 mm, more preferably at least 2.0 mm, more preferably at least 3.0 mm, more preferably at least 4.0 mm, more preferably at least 5.0 mm, more preferably at least 6.0 mm, more preferably at least 7.0 mm, more preferably at least 8.0 mm, more preferably at least 9.0 mm, more preferably at least 10.0 mm, more preferably at least 15.0 mm, more preferably at least 20.0 mm, more preferably at least 25.0 mm.

Preferably, the inner diameter of the hollow object is at most 50.0 mm, preferably at most 49.0 mm, more preferably at most 48.0 mm, more preferably at most 47.0 mm, more preferably at most 46.0 mm, more preferably at most 45.0 mm, more preferably at most 44.0 mm, more preferably at most 43.0 mm, more preferably at most 42.0 mm, more preferably at most 41.0 mm, more preferably at most 40.0 mm, more preferably at most 39.0 mm, more preferably at most 38.0 mm, more preferably at most 37.0 mm, more preferably at most 36.0 mm, more preferably at most 35.0 mm, more preferably at most 34.0 mm, more preferably at most 33.0 mm, more preferably at most 32.0 mm, more preferably at most 31.0 mm, more preferably at most 30.0 mm.

In a further preferred embodiment of the invention, the hollow object has the shape of a hollow tube or a cylinder. In other words, the inner surface of the hollow object defines an internal volume. The hollow object is for example made of steel and steel-based alloys.

In one embodiment of the invention, the coating formed is a tribological coating. Tribological coatings are used in applications that are exposed to severe contact forces under which normal thin film coatings would fracture and lose their adhesion, thereby losing their protective function. These coatings are designed to have

20 BE2023/5468 low coefficients of friction, high hardness, and increased durability to resist wear caused by various forms such as bond welding, shearing, abrasion, high-velocity particle impact, erosion, corrosion, and chemical interaction induced by high temperatures. Examples of applications that benefit from tribological coatings include metal cutting tools, surfaces operating at high temperatures, optical surfaces exposed to high-velocity impacts, and surfaces exposed to contact abrasion and corrosive liquids.

Tribological coatings find applications in a wide range of industries, including machining, medical implants, military air and marine vehicles, commercial decorative metals, and polymer surfaces. An example of tribological coatings in commercial use is the adaptation of military technology for supersonic aircraft, where coatings such as diamond-like carbon (DLC), germanium carbide (Gec), boron nitride (BN), and others are used to protect optical windows from erosion by sand, dust, and rain. These coatings also find use in thermal infrared (IR) imaging windows for high-end automobiles and environmental protection in military operations in harsh environments.

Multilayer coatings are often used for tribological applications, as they offer improved performance compared to single-layer coatings. Typically, tribological coatings have a thickness ranging from 5 to 30 um, and multilayer coatings consist of alternating layers of hard and softer materials to reduce internal stresses and increase durability. Our method allows for the convenient development of multilayer coatings by simply switching the gas used. Examples of highly attractive material pairs for tribological coatings include Ti/TiC,

Ti/TiN, TiAI/TiAIN, Cr/CrN, and Ta/TaN. In addition, materials such as nitrides, carbides, and diamond-like carbon (DLC) are excellent candidates for tribological coatings due to their wear-resistant properties, which cannot be achieved by electrodeposition methods.

In one embodiment of the invention, the formed coating is for — enabling gas permeation. Gas permeation is a multifaceted process involving absorption, dissociation, diffusion,

21 BE2023/5468 recombination and desorption of gas molecules, similar to the phenomenon of material outgassing. The coating is specifically designed to facilitate the controlled movement of gas molecules through its structure, while maintaining its integrity and performance characteristics. This gas permeation capability of the coating makes it suitable for applications where controlled gas transport or barrier properties are desired, such as in gas separation, packaging, or other specialized environments. For gas permeation barriers, a dense coating is typically required, which can be achieved by sputtering. The materials considered for gas permeation barriers are mainly nitrides, as for tribological applications. However, the thickness of the coating is typically thinner, around 1 um. Some of the most promising materials for hydrogen permeation barriers are TiN, TiAIN, SiN and SiC. For other gases, oxides such as AI203 or SiO2 can also be included as coating materials.

In one embodiment of the invention, the coating formed is intended to provide corrosion resistance. This coating can be applied to pipes or other components that are in contact with corrosive fluids, providing a protective barrier to prevent corrosion and extend the life of the material. The coating is typically composed of oxides or nitrides, with thicknesses ranging from 1 to 10 µm. Commonly used materials for corrosion resistant coatings include SiO2, Al203,

ZrO2, ZrSiO4, TiN and TiAIN. These materials are chosen for their excellent corrosion resistance properties, which can prevent or reduce the =— degradation of the underlying material due to chemical reactions with corrosive fluids. This corrosion resistant coating can find applications in various industries where protection against corrosive environments is critical, such as oil and gas, chemical processing, marine and automotive.

In one embodiment of the invention, the formed coating is intended to function as a catalyst. This coating can be applied to tubes within or after a chemical reactor, where it can promote or accelerate specific chemical reactions. The choice of catalyst material will depend on the desired reaction and operating conditions, but generally, metallic coatings, particularly noble metals such as Pt, Pd, Au or their oxides, are commonly used for catalysis.

22 BE2023/5468

Unlike gas permeation or corrosion resistant coatings, catalytic coatings are typically much thinner, often in the nanoscale, to maximize the surface area available for catalytic activity. The coating is designed to provide high catalytic activity and selectivity, while maintaining stability and durability under the operating conditions of the chemical reaction. The properties of the catalyst coating, such as its composition, morphology, and thickness, can be tailored based on the specific requirements of the targeted chemical reaction. Coating tubular objects with catalysts can significantly improve the efficiency and performance of chemical processes in industries such as petrochemicals, pharmaceuticals, and environmental applications. The use of catalyst coatings can achieve higher conversion rates, lower reaction temperatures, reduced energy consumption, and improved product selectivity, making them useful for a variety of catalytic applications in different industries.

In one embodiment of the invention, the formed coating is intended to be conductive. This conductive coating can be applied to the interior of a tube, and it can serve a variety of purposes depending on the specific application. For example, copper (Cu) and silver (Ag) are commonly used as conductive coating materials when transparency is not a requirement. These coatings can provide electrical conductivity, making them suitable for applications where an electrical current must flow through the coated surface, such as in electronic devices, sensors, or wiring. In some cases, transparency may be desired, such as in glass tubes or other transparent substrates. In such scenarios, indium tin oxide (ITO) can be used as the coating material. ITO is a transparent conductive material that can be deposited as a thin coating, allowing light to pass through while maintaining its conductive properties. This makes it suitable for applications where both electrical conductivity and transparency are required, such as in touch screens, displays or optical sensors. The thickness and composition of the conductive coating can be optimized based on the specific requirements of the application, including factors such as electrical conductivity, transparency, adhesion and durability. Conductive coatings can provide enhanced functionality and performance at a

23 BE2023/5468 wide range of applications, making them useful in various industries including electronics, optics, automotive and aerospace.

In a third aspect, the invention provides a use of a method according to the first aspect of the invention, and for obtaining a hollow object having an internal surface comprising a coating according to the second aspect of the invention.

In one embodiment of the invention, the coating is used as a gas permeation barrier, which is particularly crucial in the context of the development of hydrogen-based technologies. An important application is the coating of the inner surface of hollow objects used for hydrogen delivery to prevent embrittlement of the hollow object. This is considered a significant challenge in hydrogen transportation and storage, and the development of effective gas permeation barriers is very important. The gas permeation barrier coating can be designed to have an optimized thickness, composition, and adhesion to meet the specific requirements of the application. It can provide reliable protection against gas permeation, minimizing the risk of embrittlement or other adverse effects on the pipe or substrate material, and ensuring the integrity and performance of the coated component. This gas permeation barrier application has potential uses in various industries, including hydrogen fuel cells, energy storage, and gas distribution systems, among others.

In one embodiment of the invention, the coating serves as a highly effective solution for corrosion resistance. Unlike traditional wet coating options, this innovative method offers the advantage of being solvent-free, making it particularly suitable for developing anti-corrosion coatings inside hollow objects. Corrosion resistance is a critical requirement in various industries where for example pipelines are used to transport fluids or gases. The traditional approach of using wet coatings, which involve the use of solvents, can have environmental and safety implications, as solvents can release harmful fumes and contribute to air pollution. In addition, solvent-based coatings can require additional drying time and curing processes, leading to longer production cycles and increased costs. However, when used as a corrosion-resistant coating, the need for solvents is eliminated, making it an environmentally friendly option that minimizes the

24 BE2023/5468 emissions and reduces the risk of health hazards. In addition, the absence of solvents allows for faster drying and curing, enabling more efficient production processes and shorter lead times. The solvent-free anti-corrosion coating can be applied to the internal surfaces of hollow objects, such as pipes. The coating acts as a barrier, preventing corrosive substances from coming into contact with the pipe surface, thereby significantly reducing the risk of corrosion and extending the service life of the pipes. In fact, it can even improve the protective properties of the coating, as it eliminates potential solvent-related problems, such as uneven coverage or poor adhesion.

In one embodiment of the invention, the coating serves as a highly efficient solution for surface energy modifications. This innovative method can be applied to various applications where the objective is to improve the sliding ability of fluids on pipe walls, such as in injectors or in the food sector. Coatings with highly hydrophilic or hydrophobic properties can be advantageously deposited using this method. Surface energy modifications are crucial in many sectors where the interaction between fluids and surfaces plays an important role. For example, in injectors, coatings with specific surface properties can optimize fluid flow, improving their performance and efficiency. Similarly, in the food sector, coatings with suitable surface energy characteristics can improve the processing and handling of food products, ensuring easy and efficient operations. Highly hydrophilic coatings can be deposited to promote the wetting of fluids on pipe walls, reducing friction and improving fluid flow. On the other hand, highly hydrophobic coatings can be applied to repel fluids, minimizing adhesion, and reducing fouling or buildup on pipe walls. In addition, the coating can be customized to exhibit other desired surface energy properties, such as oleophobic, amphiphilic, or superhydrophobic, depending on the requirements of specific applications. This versatility in surface energy modifications makes the coating highly adaptable to a wide range of industrial applications where fluid interactions with surfaces are critical. In addition, the coating can be uniformly applied to the interior surfaces of hollow objects, such as pipes, ensuring consistent and long-lasting surface energy modifications. The precise deposition process allows

25 BE2023/5468 to obtain controlled and uniform coverage, allowing reliable and efficient performance of the coating over time.

In one embodiment of the invention, the coating serves as a highly effective solution for erosion resistance. It can be used to protect surfaces from erosion caused by solid particle impact, which can occur in various industrial applications, such as in aircraft diffusers. Erosion is a significant concern in many industries where surfaces are subjected to high velocity impacts from solid particles, resulting in progressive wear and damage over time. For example, in aircraft diffusers, which direct air into the combustion chamber through many narrow gas inlets arranged around a circular frame, erosion caused by dust particles in the air can result in an increase in the diameter of the gas inlets, leading to potential damage to the aircraft engine. The erosion resistant coating provides a robust protective layer that effectively resists erosion from solid particle impacts. The coating composition is designed to resist high velocity impacts and prevent wear, reducing

Potential damage and extending the life of critical components.

In addition, the precise deposition process allows for uniform coating coverage on surfaces, ensuring complete erosion protection across the entire surface. The coating adheres firmly to the substrate, maintaining its erosion-resistant properties even under harsh conditions. In addition to aircraft diffusers, this erosion-resistant coating can also find applications in other industries where surfaces are exposed to solid particle impacts, such as in gas turbines, pumps, and other high-velocity flow systems. By providing reliable erosion protection, the coating can help reduce high maintenance, repair, and replacement costs of damaged components, resulting in increased operational efficiency and reduced downtime.

The invention is further described by the following non-limiting examples which further illustrate the invention, and are not intended to limit the scope of the invention, nor should they be construed as such.

DESCRIPTION OF FIGURES AND EXAMPLES

With the aim of better illustrating the properties of the invention, the following presents, by way of example and without limiting in any way other applications

26 BE2023/5468 potential, a description of a number of preferred applications of the method for examining the condition of grout used in a mechanical connection based on the invention.

The following numbering refers to: 1. Hollow object 2. Inner surface of the hollow object 3. Cylindrical electrode 4. Reaction chamber 5. Target material A 6. Target material B 7. Target material C 8. Sub-electrode A 9. Sub-electrode B 10. Sub-electrode C 11. Coating 1 12. Coating 2 13. Coating 3

In most cases, the target materials A 5, B 6 and C 7 used for the coating process correspond to the same materials as the cylindrical electrode 3.

This means that a wire of the respective target material is used, and different materials are welded together to form a wire with multiple targets. The use of a wire made of different target materials allows for efficient and convenient deposition of various coatings. By controlling the relative motion between the cylindrical electrode 3 and the hollow object 1, it becomes possible to deposit layers of different materials on the inner surface. This technique allows for the creation of multilayer coatings having distinct properties and compositions. It should be noted that this approach contributes to the versatility and flexibility of the coating process. It allows for the deposition of coatings having varying material compositions, leading to improved functionality and performance of the coated hollow object 1.

It is further important to clarify that in some cases, the hollow object 1 may also function as a reaction chamber. In some configurations, such as those shown in Figures 2-4, a separate reaction chamber exists along the hollow object 1. This dedicated reaction chamber is designed to facilitate the coating process by providing controlled conditions for the deposition of the target material on the internal surface of the hollow object 2.

27 BE2023/5468

The cylindrical electrode 3 and the target materials are positioned within this reaction chamber, and the coating process occurs within this confined space. However, there are situations where the hollow object 1 itself can act as the reaction chamber. In such cases, the coating process takes place directly within the internal volume of the hollow object 1, eliminating the need for a separate reaction chamber. This can simplify installation and potentially provide benefits in terms of efficiency and coating quality.

In Figure 1, the hollow object 1 is shown with its inner surface 2 visible. In addition, a cylindrical electrode 3, functioning as a cathode, is positioned coaxially with respect to the hollow object 1, which serves as an anode. The cylindrical electrode 3 and the inner surface of the hollow object 2 are separated by an average distance designated by Des. This representation emphasizes the precise coaxial alignment of the cylindrical electrode 3 relative to the hollow object 1, as a notable aspect of the invention.

Figure 2 shows a longitudinal section of a reaction chamber 4, showing an embodiment of the present invention in which a hollow object 1 to be coated is inserted. In particular, the hollow object 1 comprises a cylindrical electrode 3 which functions as a cathode, while the inner surface of the hollow object 2 serves as an anode. The cylindrical electrode 3 acts as a cathode on which the electric field is applied to ignite a plasma for deposition of the target material thereof on the inner surface of the hollow object 2 is provided.

The cylindrical electrode 3 is positioned coaxially inside the hollow object 1. The cylindrical electrode 3 has a single type of target material regularly distributed on the entire outer surface of the electrode.

The cylindrical electrode 3 has a length which is equal to the length of the hollow tube.

This allows the cylindrical electrode 3 to be fixed or attached to retaining means within the reaction chamber 4 so that the cylindrical electrode 3 remains in place. The cathode allows the generation of plasma along the entire length of the hollow object 1, resulting in the simultaneous coating of the entire internal surface of the hollow object 2. Although a horizontal installation is shown, the installation, i.e., the positioning of the hollow object 1 and the cylindrical electrode 3 in the reaction chamber 4, may also be vertical or at any other angle.

28 BE2023/5468

Figure 3 shows a longitudinal section of a reaction chamber 4 and a hollow object 1 having an internal surface 2 to be treated defining an internal volume. Furthermore this figure shows a cylindrical electrode 3, functioning as a cathode, and it is used to generate an electric field which ignites a plasma for the deposition of the target material 5 on the internal surface of the hollow object 2. The cylindrical electrode 3 is positioned coaxially with the hollow object 1 and is coated with a single type of target material 5 which is distributed regularly on its entire external surface.

The length of the cylindrical electrode 3 is typically designed to match or exceed the length of the hollow tube being coated. For open tubes, the cylindrical electrode 3 is at least of equal length to ensure complete coverage. In fact, it is common practice for the electrode to be longer than the tube itself to ensure uniform coating over the entire length.

However, Figure 3 shows a specific scenario representing a shorter cylindrical electrode 3. This arrangement is specifically employed for semi-open tubes where the target material cannot pass through the restricted opening. It is important to note that this particular case is an exception, and that in all other situations, the cylindrical electrode 3 is the same length as or greater than the hollow tube to facilitate a complete and uniform coating process.

It is worth mentioning that the following information regarding relative motion is not applicable when using a single target, as in our case. However, it is relevant for multiple target setups, as shown in Figure 4. To achieve uniform coating on the inner surface of the hollow object 2, the cylindrical electrode 3 and the hollow object 1 are arranged to move relative to each other while maintaining their coaxial position.

This relative motion may involve the cylindrical electrode 3 moving alone, or the hollow object 1 moving alone, or the cylindrical electrode 3 and the hollow object 1 both moving simultaneously.

During the deposition process, the cylindrical electrode 3 can advantageously move along the central axis of the hollow object 1. If both the cylindrical electrode 3 and the hollow object 1 are moved, they can move in the same direction at different speeds, or in opposite directions at the same speed or at different speeds. This makes it possible to achieve the creation of areas having varying plasma discharge densities on the inner surface of the hollow object 2.

Specifically, the highest plasma density is generated at the

29 BE2023/5468 portion of the inner surface 2 which is closest to, or at the minimum distance from, the electrode. On the other hand, areas of lower plasma density are created at portions of the inner surface 2 which are further away from the electrode.

In Figure 3, it should be noted that the configuration shown is specifically designed for coating the internal part of a semi-open tube, such as a clarinet, where access to the interior is limited. In this particular scenario, the cylindrical electrode 3 shown is shorter than the hollow object 1 to accommodate the shape of the tube. However, it is important to emphasize that for any other coating application, where the hollow object 1 is fully accessible, the cylindrical electrode 3 must be at least as long as the length of the object to ensure uniform and efficient coating over its entire surface.

This consideration ensures optimal coating deposition and maintains consistency across different coating processes.

Figure 4 illustrates a longitudinal section of a reaction chamber 4 and a hollow object 1 to be coated. A hollow object 1 has an internal surface 2 that requires treatment, and it encompasses an internal volume. A cylindrical electrode 3, serving as a cathode where an electric field is applied to generate a plasma for deposition of the target material 5, is positioned coaxially with the hollow object 1, aligned with its central axis. — The cylindrical electrode 3 is composed of three sub-electrodes 8, 9, 10 that are arranged in series, providing advantages, in particular for achieving specific coating designs and optimizing efficiency. One advantage is the ability to create a chemical composition exhibiting a gradient within the hollow object 1 when the targets and the hollow object 1 remain stationary relative to each other. This means that different sections of the hollow object 1 can be coated with different materials, resulting in a composition exhibiting a gradient. This gradient can improve the properties and performance of the material.

Another advantage is the ability to design multilayer coatings of different materials, such as A, B and C, as shown in Figure 5. This is achieved when the targets and the hollow object 1 move relative to each other during the coating process. The sub-electrodes, working in series, facilitate the controlled deposition of each layer of material, allowing the creation of complex coatings with the desired properties.

By using the multi-component electrode configuration, the coating process becomes more efficient, saving time comparatively

30 BE2023/5468 to the realization of three separate deposition steps with different electrodes. In addition, the risk of misalignment or positioning errors is reduced since the number of operations is reduced to a minimum.

In this figure, the sub-electrodes 8, 9, 10 comprise a different target material (target material A 5, target material B 6, target material C 7), allowing the deposition of multilayer coatings having variable compositions along the internal surface of the hollow object 2. It should be noted that they can also comprise the same target material.

It should further be emphasized that while Figure 4 illustrates a cylindrical electrode 3 which is of equal length to that of the hollow object 1, the cylindrical electrode 3 may also have a shorter or longer length than the hollow object 1. When the cylindrical electrode 3 is longer than the hollow object 1, it allows the use of sub-electrodes 8, 9, 10 having different target materials.

This configuration facilitates the deposition of coatings having varying compositions along the length of the hollow object 1. Additionally, it is important to note that longer wires of a single material are commonly used to ensure uniform coating, even at the edges of the hollow object 1. This approach helps maintain the consistency and quality of the deposited coatings. Furthermore, having the centering piece positioned outside the hollow object 1, as shown in the accompanying drawing, allows the plasma to remain undisturbed, contributing to the effectiveness and efficiency of the coating process.

In addition, the average distance De, between the cylindrical electrode 3 and the inner surface of the hollow object 2 is remarkably visible in FIG. 1 to 4, since it is a crucial parameter in the coating process according to the embodiment of the present invention. This emphasizes the importance of the precise alignment and separation of the cylindrical electrode 3 and the inner surface of the hollow object 2 for the coating process.

In Figure 5, a detailed diagram of a coated hollow object 1 is shown in longitudinal section. The inner surface of the hollow object 2 has been coated with multiple layers of different coating materials, identified as layers 11, 12 and 13. These layers form a multiple coating structure on the inner surface of the hollow object 2.

Figure 6 shows a longitudinal section of a coated hollow object 1, showing one embodiment of the invention. The coated object is a hollow tube or cylinder,

31 BE2023/5468 and the section through the tube reveals its inner surface, which has been coated with a single target material 5. The coating 11 on the inner surface of the hollow object 2 appears as a uniform and continuous layer, covering the entire inner surface of the hollow object 1.

The present invention will now be exemplified with reference to the following example.

The present invention is in no way limited to the example given or to the embodiments shown in the figures.

Example 1: a coated hollow object.

The coated hollow object, as shown in Figure 6, is a small diameter tube with an internal diameter of 2 mm and a length of 50 mm. The objective of the coating process was to deposit a titanium nitride (TiN) coating on the internal surface, which is a common tribological coating known for its high hardness and wear resistance properties.

To achieve the desired coating, a physical vapor deposition (PVD) technique called sputtering was employed. The setup involved a cylindrical electrode, acting as a cathode, positioned inside the tube in a coaxial manner to ensure uniform thickness distribution. In this case, a titanium (Ti) target material was used. To promote the formation of the TiN coating, pure nitrogen gas was injected into the chamber during the sputtering process. The interaction of the nitrogen plasma with the sputtered Ti atoms resulted in the desired TiN coating on the inner surface of the tube.

The tube was configured as the anode, and an electric field was applied to the cylindrical electrode, acting as the cathode.

A working pressure of 5 Torr was maintained in the reaction chamber, and the power was set to 200 W with a frequency of 250 KHz. The pulse duration was set to 1600 ns, ensuring efficient sputtering of the target material onto the inner surface of the tube.

After the coating process was completed, the coated object was evaluated to determine the quality and homogeneity of the coating. Cross sections of the coated tube were prepared using standard metallographic techniques. The cross sections were then observed using scanning electron microscopy (SEM) to assess coating thickness, morphology, and adhesion to the substrate. SEM images showed a uniform and dense coating with a thickness of approximately 1 µm,

32 BE2023/5468 adhering well to the entire internal surface of the tube. The coating exhibited a smooth and homogeneous morphology, indicating a high quality coating.

Additionally, optical microscopy (OM) was also used to observe the coated object for any visible defects, such as cracks or voids. The images

MO showed a visually uniform and defect-free coating, confirming the high quality and uniformity of the coating obtained with the given parameters.

Overall, the coated object obtained with the parameters of 5 Torr working pressure, 200 W power, 250 KHz frequency, and 1600 ns pulse duration exhibited a uniform, dense, and high-quality coating on the entire inner surface of the small-diameter tube, as evaluated by SEM and MO observations.

The present invention is in no way limited to the embodiments described in the examples and/or shown in the figures. On the contrary, the methods according to the present invention can be carried out in many different ways without departing from the scope of the invention.

Claims (14)

33 BE2023/5468 CLAIMS 1. A method of DPV coating an internal surface of a hollow object, wherein the internal surface of the hollow object defines an internal volume, the method comprising the steps of: a. providing a cylindrical electrode having a radial outer surface, said cylindrical electrode comprising a target material, wherein said radial outer surface comprises said target material, within the internal volume of the hollow object, preferably coaxially positioned for uniform coating, wherein said cylindrical electrode and said inner surface of the hollow object are separated by an average distance De, of at least 0.5 mm and at most 20 mm; and b. generating an electric field between the cylindrical electrode and the inner surface of the hollow object, with the cylindrical electrode serving as a cathode and the hollow object serving as an anode, wherein a product of a working pressure and the average distance Des is between 0.01 Torr.cm and 10 Torr.cm. 2. Method according to claim 1, characterized in that the target material forms a continuous and uniform radial external surface of the cylindrical electrode. 3. Method according to claim 1 or 2, characterized in that the cylindrical electrode and the hollow object are configured to move relative to each other, to allow obtaining the coating of tubes or a continuous operation, in which the movement is parallel to maintain the coaxial positioning of the cylindrical electrode inside the internal volume of the hollow object. 4. A method according to any one of the preceding claims 1 to 3, characterized in that, wherein the cylindrical electrode comprises a plurality of sub-electrodes arranged in series to achieve a multi-layer coating, wherein each sub-electrode comprises the target material, preferably the target material of at least two of the plurality of sub-electrodes is different. 5. Method according to claim 4, characterized in that the sub-electrodes can be sequentially activated and deactivated for 34 BE2023/5468 deposit different layers of material on the internal surface of the hollow part. 6. Method according to any one of the preceding claims 1 to 5, characterized in that the target material is chosen from a list consisting of: a metal, a metal alloy, a ceramic material, and combinations thereof. 7. Method according to any one of the preceding claims 1 to 6, characterized in that a power density applied to the cathode is between 0.01 W/cm? and 50 W/cm2. 8. Method according to any one of the preceding claims 1 to 7, characterized in that an average current density applied to the cathode is between 0.001 A/cm? and 10 A/cm2. 9. A method according to any one of the preceding claims 1 to 8, characterized in that a gas, provided in the internal volume, comprises an inert gas, a reactive gas or a combination thereof; wherein the inert gas is selected from a group comprising helium, neon, argon, krypton; wherein the reactive gas is selected from a group comprising nitrogen, oxygen, methane, ammonia or acetylene. 10. Method according to any one of the preceding claims 1 to 9, characterized in that the method comprises a step of pre-treatment of the internal surface of the hollow object before the deposition of the target material on the internal surface, in which the pre-treatment of the internal surface of the hollow object comprises a step of cleaning and/or etching, preferably plasma etching. 11. A method according to claim 10, characterized in that the plasma etching comprises the steps of: - passing an etching gas through the reaction chamber, thereby providing the etching gas into the internal volume of the hollow object; and - applying a second electric field to the hollow object, with the cylindrical electrode serving as an anode and the hollow object serving as a cathode, to activate the etching gas and generate an etching plasma. 35 BE2023/5468 12. Method according to claim 11, characterized in that the etching gas is chosen from a group comprising argon, helium, nitrogen, oxygen, methane, ethylene, nitrogen dioxide or nitrous oxide. 13. Hollow object having an internal surface comprising a DPV coating, characterized in that said hollow object has an internal diameter of less than 5 cm, the coating has a thickness between 0.01 um and 50 um, and a relative deviation of the thickness of the coating is at most 20%. 14. A hollow object having an internal surface comprising a coating according to claim 13, characterized in that a ratio of a length of the hollow object to its internal diameter is at least 10. 15. Use of a method according to at least one of the preceding claims 1 to 12, for obtaining a hollow object having an internal surface comprising a coating according to one of the preceding claims 13 to 14.