Improvements to apparatus and a method for applying a coating onto items

Abstract

An apparatus for applying a coating comprises means for depositing one or more materials, a cup 1 and vibration means for vibrating the cup and items to be coated held therein. The apparatus is suitab

Description

The invention to which this application relates is to the provision of apparatus and a method for the application of a coating formed of one or a plurality of layers, onto items, and particularly small items such as powder particles, and to do so in a manner which allows the coating to be applied to substantially all of the external surface of the item and to be repeatedly achieved for all items in a group of the items in a batch process so as to provide relatively uniform coating of the items and allow the reliable usage and performance of the coated items thereafter. In particular, although not necessarily exclusively, the invention relates to the application of the coating material using magnetron sputtering apparatus and techniques. The use of magnetron sputtering technology in general is known and has been used commercially successfully in many different industries to create coatings formed of one or a plurality of layers. The coatings are typically referred to as high-performance PVD (Physical Vapour Deposition) coatings and are produced by the magnetron sputtering technique. However, the coatings which are applied using the conventional apparatus and method are typically applied onto a relatively planer surface or onto articles which have a relatively simple geometry. This is due largely to the fact that the coating material is applied by being sputtered along a “line of sight” between the source or target of the coating material and the surface of the item onto the material is to be applied. As a result, the use of magnetron sputtering techniques to apply coatings uniformly on a three-dimensional item and / or an item with relatively complex shapes, is difficult as only the surface of the item which faces the source or target of the coating material is properly coated at a given instant of time. These challenges are further increased when attempts are made to perform magnetron sputtering deposition on the surfaces of small items such as powder particles due to the difficulty to reliably present all of the surfaces of the relatively small size particles to the “line of sight” of the sputtering source in a given period of time and thereby ensure that all of the surface of each particle has the coating applied thereto at the end of the coating process. This has meant that, conventionally, while powder particles are regarded as being important materials in many manufacturing and industrial fields, for example 111 polymer, ceramic and powder metallurgy, the use of magnetron sputtering techniques to apply what are required to be high-quality coatings thereto, has been limited. Examples of conventional techniques include powder materials which are used as a catalyst support in catalytic chemical industries and in relation to which there have been attempts to adapt the use of magnetron sputtering apparatus in order to enhance the coatings which can be achieved on this type of particle. Known methods and apparatus, include the use of rotating drums, a tilted cup or a vibrating cup. The rotating drum form of apparatus is conventionally the most popular for magnetron sputtering due to the ease of setting up and scalability for relatively high-volume production. Known uses, such as for example as disclosed in H Poelman et al, Poelman, H.; Eufinger, K.; Depla, D.; Poelman, D.; De Gryse, R.; Seis, B. F.; Marin, G. B. Magnetron Sputter Deposition for Catalyst Synthesis. \ppl. Catal. Gen. 2007, 325 (2), 213-219. https: / / doi.Org / 10.1016 / j.apcata.2007.02.028, preform consecutive sputter deposition in a rotating drum to synthesise two different layer support combinations in the form of vanadia / silica and vanadia / titania / silica. The resultant catalyst shows well-dispersed material, irrespective of the underlying support and the sputtered deposited vanadia / titania catalysts show a very high selectivity and low conversion and so yielding a turnover frequency comparable to classical catalysts. In the document by A. Taguchi et al Taguchi, A.; Inoue, M.; Hiromi, C.; Tanizawa, M.; Kitami, T.; Abe, T. Study of the Surface Morphology of Platinum Thin Films on Powdery Substrates Prepared by the Barrel Sputtering System. Vacuum 2008, 83 (3), 575—578. https: / / doi.Org / 10.1016 / j.vacuum.2008.04.023 Pt nanoparticles are deposited and applied to a powdery S1O2 substrate by a rotating drum sputtering system and it was found that the Pt nanoparticles grow m size with an increase in the duration of sputter deposition and the growth of the Pt film on powdery substrates starts tn a two-dimensional mode then followed by an island mode. The use of a tilted cup apparatus for DC magnetron sputtering apparatus is disclosed in the document in the name of G.M. Veith Veith, G.; Lupini, A.; Pennycook, S.; Ownby, G.; Dudney, N. Nanoparticles of Gold on -A1O Produced by De Magnetron Sputtering. J. Catal. 2005, 231 (1), 151—158. http.S.:ZZdot-org / 10. t016 / i.jcat.2004.12.008. in which the apparatus is used to deposit gold nanoparticles on gamma alumina powder. Also, as disclosed in the documents, Hell, J.; Horkel, M.; Neubauer, E.; Eisenmenger-Sittner, C. Construction and Characterization of a Sputter Deposition System for Coating Granular Materials. Vacuum 2009, 84 (4), 453—457. https: / / doi.org / 10.1016 / j.vacuum.2009.09.007; Schmid, G.; Eisenmenger-Sittner, C.; Hell, J.; Horkel, M.; Keding, M.; Mahr, H. Optimization of a Container Design for Depositing Uniform Metal Coatings on Glass Microspheres by Magnetron Sputtering. Surf. Coat. Technol. 2010, 205 (7), 1929—1936. https: / / dGi.org / l0.1016 / i.surfcoat.2010-08.076; Schmid, G. H. S.; Eisenmenger-Sittner, C. A Method for Uniformly Coating Powdery Substrates by Magnetron Sputtering. Surf. Coat. Technol. 2013, 236, 353—360. https: / / doi.org / 10.1016 / i.surfcoat.2013.10.012 and Eder, A.; Schmid, G. H. S.; Mahr, H.; Eisenmenger-Sittner, C. Aspects of Thin Film Deposition on Granulates by Physical Vapor Deposition. Eur. Phys. J. D 2016, 70 (11), 247. https: / / doi.org / 10.1140 / epjd / e2016-70435-7 , the research group of C. Eisenmanger-Sittner at Vienna University of Technology has systematically improved the tilted cup design by adding a concussion mechanism such as blades, fins, springs and / or spanning rods in order to increase the coating uniformities on the powder particle surfaces. They have also deposited various metals, including Cu, Al, Ti, Pt and Mo, on the surfaces of diamond particles and hollow glass microspheres (HGM). It has been shown that the concussion mechanism enables the breaking apart of powder clusters that form during the deposition and results in coatings being applied which are of greater uniformity. Typically, the rotating drum and tilted cup mechanisms are driven by a rotary motor. It is found that the rotating drum approach performs well in terms of full usage of sputtered atoms and scalabilities. However, the coating uniformity becomes a concern if the tumbling movement is too gentle, or, if the powder particles are tumbled more energetically, the magnetron target can be contaminated by those powder materials that have gained enough energy to transfer to the target surface. Also, the loss of powder can be substantial if the agitation is too harsh. The drawbacks of the tilted cup apparatus include that the powder cup has a larger movement range and, if the magnetron is relatively small, the cup can move out of the main atom flux area i.e. where the coating material is present, which wastes materials. Furthermore, the loss of powder particles is considerable during the coating process, which can take many hours of deposition, as the powder movement in the cup can sometimes become too vigorous. Furthermore, in order to achieve an efficient and uniform coating on powder surfaces, any form of agitation device faces the same engineering challenges in that the majority of sputtered atoms need to be used, the powder amount should be variable and the powder lost during agitation must be small, the strength of agitation should be tuneable and the electrical charging of the powder should be suppressed, and it is found that, in practice, this cannot be reliably achieved. Furthermore, existing forms of apparatus which incorporate vibration provided by the provision of a membrane, an ultrasonic source or a piezoelectric crystal, cannot provide a satisfactory solution to allow the agitation of a wide range of powder particles of different sizes. The aim of the present invention is therefore to provide apparatus which has the ability to allow the more efficient, uniform and reliable application of a coating material onto an item surface and, in particular, an item in the form of a powder particle and more preferably, the application of the coating materials onto a plurality of the items simultaneously. In a first aspect of the invention, there is provided apparatus for applying a coating formed by one or more materials onto an outer surface of one or a plurality of items, said apparatus including sputter deposition means to sputter deposit said one or more materials from one or more magnetron targets, a holding means in the form of a cup in which the said items are held, said cup located in the path of the said one or more sputtered materials, means to cause a vibration effect on the said cup and, in turn, said items, during the application of the coating onto said outer surface of the one or plurality of said items, said cup located on a cup holder which, in turn, is mounted on a mounting means to allow the vibration effect to pass to the cup and, in turn, said one or more items and wherein the mounting means includes one or more pillars located in respective channels formed in the cup holder. In one embodiment, the materials are applied to form coatings simultaneously on said plurality of items located in the cup. In one embodiment, the said items are powder particles and onto the surfaces of which it is desired that the coating is applied to cover all, or substantially, all of the surface of each of the powder particles when located in the said cup and for the coatings to be substantially uniform on each particle and to be formed of substantially the same material on each of the particles. In one embodiment, the said cup has an opening, typically at the top when the cup is in position, sidewalls, and a base which define a cavity in which the items are held and the said items are accessible to the deposited coating material through said opening. Typically the cup and cup holder are provided in a fixed relationship during the application of the coating materials for the formation of the coating. Typically, the respective dimensions of the said pillars and channels are such as to provide a gap or tolerance which allows vibrational movement of the cup holder, and hence cup, with respect to the mounting apparatus within a given range of vibration. Typically, the cup and cup holder are able to move in vertical and horizontal directions within a predetermined range of movement. Typically therefore the difference in dimensions between each pillar and the respective channel in which the same is located, determine the maximum vibration amplitude of the cup. In one embodiment, the means for creating the vibration effect vibration, is a vibration motor which, in one embodiment, can be tuned to provide a desired frequency of vibration so as to take into account the form of the items which are to be coated at that time of use and / or the type of coating which is to be applied. In one embodiment, the bombardment energy of the coating material when sputtered onto the item surface is selectively adjustable by tuning a negative voltage which is applied to the cup. In one embodiment, the tuning is possible within a range of -20V to -500V. In one embodiment, the level of bombardment energy allows the control of the creation of an interlayer formed between the surface of the powder particle and the coating materials which are subsequently deposited. In one embodiment, the cup is made of a conductive material and the cup holder is made from an insulating material so as to electrically isolate the cup from the mounting means. In one embodiment, the coating, which is applied to items in the form of powder particles, includes a layer of carbon or comprises a layer of carbon. In one embodiment, the powder particles to which the coating is applied is substantially spherical and may have a diameter of less than 10 microns. In one embodiment, the magnetron deposition apparatus operates in a closed field configuration within which the said cup is located. In one embodiment, the said items are provided as particles formed of carbon or silicon oxide. In one embodiment the coated particles are subsequently used in batteries or power cells. Thus, in accordance with the invention, there is provided apparatus for the application of a coating material onto items which allows improvements in the provision of relatively high controllability of the coating process, a relatively high reproducibility in the coating process and the ability to perform near surface treatments so that the bulk properties are not changed. Furthermore, a one-step processing procedure is provided which is environmentally friendly as no harmful by-products are used or created, and allows nonequilibrium processing whilst, at the same time, allowing the application, simultaneously, of substantially uniform coatings to a plurality of the said particles. In a further aspect of the invention there is provided a method of coating the outer surface of a plurality of items substantially simultaneously, said method including the steps of providing a cup having a cavity in which the said plurality of items are placed, locating said cup in the path of one or more materials which are sputter deposited using at least one magnetron and control means therefore, to form the said coating, operating means to cause a vibration effect on the said cup and, in turn, said items, during the sputter deposition of the said one or more materials onto the said items wherein said cup is located on a cup holder which, in turn, is mounted on a mounting means to allow the vibration effect to pass to the cup and, in turn, said one or more items and wherein the mounting means includes one or more pillars located in respective channels formed in the cup holder. Typically the level of the vibration effect can be controlled to be within a vibration range. Typically the step of operating said at least one magnetron and control means therefor allows the sputtering of said one or more materials from one or more targets of said materials which are to form the coating under the influence of said at least one magnetron. In one embodiment batches of said items are placed into the cup at a time and coated. In one embodiment the mounting means include the plurality of pillars and a plate. Typically relative movement occurs between the cup holder and the mounting means when vibration is applied. In accordance with the invention there is provided a powder particle with a coating applied thereto using the apparatus and / or method as herein described. Specific embodiments of the invention are now described with reference to the accompanying drawings wherein: Figure 1 illustrates the structure of the apparatus in accordance with one embodiment of the invention; Figure 2 illustrates a cross-sectional view of the apparatus of Figure 1; Figure 3 illustrates a TEM image of PD / Ti nanoparticles on a gamma-alumina powder formed in accordance with one example of the invention; and Figure 4 shows an SEM image of carbon coated glass microspheres created in accordance with another example of the invention. Figure 1 illustrates apparatus in accordance with one embodiment of the invention. The apparatus includes a cup 1, including a cavity in which items, in this embodiment in the form of the powder particles wdiich are to be coated, are loaded and the cup is located with, and held in place by, a cup holder 3. The cup holder 3 is located on mounting means including a support plate 4, without any screw fixation, so that the cup holder and powder cup can move freely with respect to the mounting means in both horizontal and vertical directions within a predetermined range of movement. The mounting means also includes four pillars 2 fixed to the support plate 4 and which pass through channels 7 formed in the cup holder 3 and these limit the extent to which the cup holder can move laterally. The support stand 5 supports the weight of the holding means in the form of the cup holder. In this embodiment, a vacuum compatible vibration motor 6 is attached to the bottom of the cup holder 3, to generate a required vibrating movement of the cup holder and cup with respect to the mounting means. The pillars 2 control the extent of vibration of the cup, as the outer diameter of each pillar is slightly smaller than the inner diameter of the channel 7 on the cup holder into which the pillar passes, and so the difference in diameters determines the maximum possible vibration amplitude of the cup. In one embodiment, the diameter of the pillar channels on the cup holder is set at 12 mm and the pillar diameter is 11 mm so that the vibration amp Etude is 1 mm. For another set of pillars, if the diameter is 10 mm, then the vibration amp Etude is 2 mm. In this example, it is envisaged that the smaUest pillar diameter that could be used without losing mechanical strength, is 6 mm, thus providing a maximum ampEtude of 6 mm for the cup vibration. Thus it will be appreciated that the use of different sets of pillars can provide different vibration ampEtude settings for the same apparatus. Alternatively, different cup holders with different channel sizes can be used with a set of pillars to alter the vibration ampEtude. The bigger the vibration ampEtude, the more vigorous the particles held in the cup can be agitated. Depending on the particle’s size, shape and density, different levels of vibration amplitude may be needed to achieve an optimised agitation for the powder to have a uniform coating deposition. In practice, for a particular type of particle, a series of experiments can be performed to find the best amplitude that should be used. The motor 6 used to provide the vibration may be a brushless vacuum compatible vibration motor can be used so as to provide an extended life-time operation. Also, the motor controller has the abihty to allow vibration frequency tuning, such as from 5 Hz to 500 Hz. In addition to ampEtude control, frequency tuning is an important factor for powder agitation control. A higher frequency tends to give a more intense agitation for the powders. Depending on the mounting orientation of the vibration motor, the cup 1 typically experiences a combination of movements hi both horizontal direction and vertical direction, which are restricted by the four pillars 2 and channels 7, resulting in a relatively complex form of cup movement which is beneficial for an effective agitation of the items and to ensure that the coating which is formed is substantially uniform. The cup 1 can be made of stainless steel or another suitable conductive material, so that it is durable and allows a negative voltage to be applied on the same, which provides a kinetic energy for the sputtered ions and argon ions to bombard the particle surface along the line of sight from the sputtering apparatus as indicated by arrow 8. The bombardment energy is adjustable by tuning the negative voltage value from -20 V to -500 V. In one embodiment the ion bombardment on the particle items surface is initially performed in order to create and deposit a desired interlayer between the particle surface and the subsequent coating applied thereto. In the case of catalyst application, the bombardment will influence the interactions between subsequently deposited metallic atoms and the oxide particle supports, which could determine the activity of the catalysts produced in this way. Moreover, a lot of electrons can escape from the plasma sputtering area close to the magnetron target surface and arrive at the powder particles in the cup. As most of the powder particle materials have very poor electrical conductivity, these electrons can accumulate on the particles, and cause so-called ‘charge-up’ issues. Once the powders particles are charged up, they repel each other and stick to the cup wall, and then it becomes very difficult to agitate them, because of the much stronger electrostatic force. To resolve this issue, a pulse of positive voltage can be applied to the cup, to reduce the “charge-up” effect. Thus, in the powder particle coating process, the voltage applied on the cup consists of alternative of negative pulse with long duration and positive pulse with relatively short duration. The cup holder 3 is made of insulating material, which electrically isolates the cup 1 from the mounting means including the support plate (both are grounded to earth). In one embodiment, PTFE (Teflon) is chosen for its high insulation resistance and reasonably good vacuum compatibility to a base pressure of 2 x In' mbar. Alternative materials such as PIT’K or Kapton can also be chosen. The choice of ceramic materials is discouraged in this case, because the cup holder collides with the, typically metal, pillars up to hundreds of times per second. A relatively brittle ceramic material would quickly develop cracks after vibration starts. The collisions between cup holder (PTFE) and pillars (stainless steel) are cushioned mostly by the soft plastic PTFE of the cup holder, which avoids a high wearing rate. Examples of the apparatus and method are now provided with reference to Figures 3 and 4 Example 1, Pd / TI alloy nanoparticles were deposited on the surface of gammaalumina powder (HP14-150, Sasol) using the vibrating cup device described above. The TEM image in Fig. 3 shows the uniform distribution of Pd / Ti nanoparticles coated on the surface of alumina. The catalytical performance of this novel material has been investigated, and it was found that the favourable combinations of efficiency and selectivity for Pd / Ti binary metal clusters in both liquid and gas phase hydrogenation experiments, when compared with catalysts prepared via conventional chemical routes. Example 2, thin carbon layer was deposited on the surface of glass microspheres (SiOz), which have an average diameter of ~4 pm. For the magnetron sputtering, a DC power of 100 W was applied on the 2-inch circular magnetron, which is mounted 5 cm above the vibrating cup device. The vibration amplitude of the powder cup was chosen at 1 mm, and the vibration frequency was set at 90 Hz. In this trial run, there was no bias voltage applied on the cup; instead, it was grounded to the earth. Two grams of glass microspheres were loaded in the cup, and after 30 hours deposition, a thin uniform carbon layer with a thickness of ~300 nm was coated on the surface of microspheres, as shown in Fig. 4.

Claims

1 .Apparatus for applying a coating formed by one or more materials onto an outer surface of one or a plurality of items, said apparatus including sputter deposition means to sputter deposit said one or more materials from one or more magnetron targets, a holding means in the form of a cup in which the said items are held, said cup located in the path of the said one or more sputtered materials, means to cause a vibration effect on the said cup and, in turn, said items, during the application of the coating onto said outer surface of the one or plurality of said items, said cup located on a cup holder which, in turn, is mounted on a mounting means to allow the vibration effect to pass to the cup and, in turn, said one or more items and wherein the mounting means includes one or more pillars located in respective channels formed in the cup holder.2.Apparatus according to claim 1 wherein said one or more materials are applied to form the coatings simultaneously on said items located in the cup.d.Apparatus according to claim 1 wherein the items are powder particles.

4. Apparatus according to claim 1 wherein the said cup has an opening, sidewalls, and a base which define a cavity and said deposited material passes through said opening to form the coatings on said items held in said cavity.

5. Apparatus according to claim 1 wherein the cup is made of a conductive material and the cup holder is made from an insulating material so as to electrically isolate the cup from the mounting means.

6. Apparatus according to claims 1 or 5 wherein the cup and cup holder are provided in a fixed relationship during the formation of the coating.

7. Apparatus according to claim 1 wherein the respective dimensions of the pillars and channels are selected so as to allow vibrational movement of the cup holder with respect to the mounting means within a predetermined range.8 Apparatus according to claim 7 wherein the cup and cup holder are movable in both a vertical and horizontal direction within a given predetermined range of movement.9 Apparatus according to any of claims 1,7 or 8 wherein the difference in dimensions between each pillar and the respective channel in which the same is located, determine the vibration amplitude range of the cup.

10. Apparatus according to any of the preceding claims wherein the means for inducing vibration, is a vibration motor.

11. Apparatus according to claim 10 wherein the said motor is selectively tuned to provide a predetermined range of frequency of vibration so as to take into account the form of the items which are to be coated at that time of use and / or the type of coating which is to be applied.

12. Apparatus according to any of the preceding claims wherein the magnetrons are operated in a closed field configuration and within which the said cup is located13. Apparatus according to any of the preceding claims wherein the bombardment energy of the said one or more materials is selectively adjustable by tuning means used to provide a negative voltage which is applied to the cup.14 Apparatus according to claim 13 wherein the tuning is to provide a voltage within the range of -20V to -500V.15 Apparatus according to claims 13 or 14 wherein the level of bombardment energy allows the control of an interlayer between the surface of the said items and the coating materials which are subsequently deposited to form the coating.16 Apparatus according to any of the preceding claims wherein the coating which is applied includes a layer of carbon.17 Apparatus according to any of the preceding claims wherein the items to which the coating is applied are substantially spherical and have a diameter of less than 10 microns.18 Apparatus according to any of the preceding claims wherein said items are formed of carbon or silicon oxide and provided for use in power cells.19 A method of coating the outer surface of a plurality of items substantially simultaneously, said method including the steps of providing a cup having a cavity in which the said plurality of items are placed, locating said cup in the path of one or more materials which are sputter deposited using at least one magnetron and control means therefore, to form the said coating, operating means to cause a vibration effect on the said cup and, in turn, said items, during the sputter deposition of the said one or more materials onto the said items wherein said cup is located on a cup holder which, in turn, is mounted on a mounting means to allow the vibration effect to pass to the cup and, in turn, said one or more items and wherein the mounting means includes one or more pillars located in respective channels formed in the cup holder.

20. A method according to claim 19 wherein the coating is applied to cover substantially all of the surface of each of the items and to form substantially the same and uniform coatings on each item.o

Images