SHEAR MILLING APPARATUS AND METHOD

PRIORITY CROSS-OVER

[001] The present applications claims priority from Australian Provisional Patent application No. 2022901735 filed on 23 June 2022, the contents of which should be understood to be incorporated into this specification by this reference.

TECHNICAL FIELD

[002] The present invention generally relates to a new shear milling apparatus which utilises one or more bearings to comminute, mill and/or shear a feed material. The new shear milling apparatus can be used as a scalable production method of two- dimensional materials such as, but not limited to, boron nitride nanosheet (BNNS) or White Graphene, graphene, MXenes, g-CsN4, black phosphorus, molybdenum disulphide (M0S2), tungsten disulphide (WS2), and other transition metal dichalcogenides (TMDs) and it will be convenient to hereinafter disclose the invention in relation to that exemplary application. However, it should be appreciated that the shear milling apparatus can be applied to a variety of other feed materials for a variety of milling and/or comminution applications.

BACKGROUND OF THE INVENTION

[003] The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.

[004] There is currently a world-wide interest in two-dimensional (2D) materials including boron nitride nanosheet (BNNS), graphene, molybdenum disulphide (M0S2), tungsten disulphide (WS2) and other transition metal dichalcogenides (TMDs) because of their attractive mechanical, thermal and electronic properties which make them promising candidates for various applications. These 2D materials exhibit superior mechanical, electrical, optical, magnetic, chemical, and/or thermal properties than their bulk counterparts, leading to exciting opportunities for new multifunctional devices and a wide range of potential applications in electronic, optics, catalysis, sensing, energy storage and conversion.

[005] Graphene is the most studied 2D material. It has sp ² hybridization forming a honeycomb in-plane structure with covalently bonded carbon atoms (a state C-C bond) with unpaired electrons forming TT bonds. The covalent in-plane structure and atomic thickness gift graphene extremely high electrical and thermal conductivities, 98% optical transparency, and unprecedented strength and stiffness. Although graphene is brittle, its elastic modulus can reach 1 TPa, and its fracture strength can be as high as 130 GPa with an ultimate strain of 25%. Resultantly, graphene is a desirable filler in composites to dramatically improve the mechanical, electrical, and thermal properties.

[006] Boron nitride nanosheet (BNNS) or “White Graphene” has a similar honeycomb structure as graphene but consists of boron and nitrogen atoms instead of carbon. It is electrically insulating and mostly transparent to visible light. BNNS has high thermal conductivity (-750 W/mK) and excellent mechanical properties (Young’s modulus of 0.87 TPa and fracture strength of 70.5 GPa). This material is more chemically inert and thermally stable than carbon graphene. For example, BNNS starts to oxidise at 800 °~C in air; while carbon graphene oxidizes at 350 °C under otherwise similar conditions. BNNS has a wide range of applications, such as heat sink, reinforcement filaments for metals, ceramics, polymers, and anti-corrosion coatings. However, it is more difficult to produce BNNS compared to graphene due to its high chemical and thermal stability as well as the presence of additional ionic interactions between layers.

[007] TMD nanosheets are another group of 2D materials. These dichalcogenide nanosheets (MX2) consist of a transition metal M (W, Mo, V, or the like) and a chalcogenide X (S, Se, Te, or the like). Their structure is more complex than that of graphene and BNNS, as their monolayer is multi-atom thick, i.e. normally with two layers of chalcogenides covalently bonded with a layer of metal atoms in between, though their interlayer interaction is mostly presented by weak van der Waals forces. These materials have a wide range of bandgaps from 0 to 2.5 eV, where indirect-direct bandgap transition could occur during thickness reduction to the atomic level. TMD nanosheets have high carrier mobilities at room temperature and a range of valence band splitting which governs the unique electronic, spin, and valley physics. Although most of TMDs have a 2H staking phase, tungsten ditelluride (WTe2) has a 1 T’ phase, leading to huge positive magnetoresistance at low temperatures. The mechanical properties of 2D TMDs are lower than graphene and White Graphene but still comparable to or even higher than those of conventional metal and ceramic materials. The Young’s modulus of these materials is in the range of 150 to 370 GPa with the fracture strength of 5 to 50 GPa.

[008] Various methods have been proposed to produce 2D materials, and each has its advantages and disadvantages:

[009] Mechanical exfoliation by tape is normally used to produce one-atom-thin and defect-free 2D materials with the highest possible quality needed for fundamental studies, but the yield is extremely low.

[010] Chemical vapor deposition (CVD) could also produce relatively high-quality 2D materials with controlled thickness and lateral size up to meters. However, CVD methods are expensive and therefore not suitable for most industrial applications. Chemical exfoliation methods such as oxidation and chemical intercalation could produce 2D materials at lower costs and larger scales. However, the quality of the products is inferior, and the methods can only be applied to specific materials. For example, graphite can be easily chemically oxidized or intercalated and then exfoliated to graphene, but there is no effective method to oxide or intercalate hexagonal BN crystals.

[011] Mechanical exfoliation by ultrasonication, impact, or shear forces has been shown to be an effective method to exfoliate layered crystals to 2D materials, including graphene, BN nanosheet (White Graphene), M0S2 and other TMD nanosheets. The mechanical methods include liquid sonication, ball mill, shear mixer, microfluidisation, show good potential for large-scale production.

[012] Based on the above, there is scope to develop new and/or improved mechanical exfoliation production technique that can be used to form two-dimensional materials such as (but not limited to), boron nitride nanosheet (BNNS), graphene, MXenes, g-CsN4, black phosphorus, molybdenum disulphide (M0S2), tungsten disulphide (WS2) and transition metal dichalcogenides (TMDs). SUMMARY OF THE INVENTION

[013] The present invention provides a new shear milling apparatus and associated shear milling method that can be used to produce two-dimensional materials such as (but not limited to) graphene, boron nitride nanosheet (BNNS), MXenes, g-CsN4, black phosphorus, molybdenum disulphide (M0S2), tungsten disulphide (WS2) and other transition metal dichalcogenides (TMDs). The present invention is intended to be a scalable production method for producing high-quality two-dimensional materials or nanosheets with high yields.

[014] A first aspect of the present invention provides a shear milling apparatus comprising: at least one bearing mill that includes at least one bearing configured to impart shear forces on a precursor material contained in a milling liquid that flows through the at least one bearing.

[015] The inventors have found that a bearing provides an effective mechanical exfoliation device. In exemplary applications, the bearing can be used as a mechanical exfoliation device for producing two-dimensional materials or nanosheets from a nanosheet producing precursor material contained in a liquid (typically as a mixture or dispersion). In this bearing milling process, at least one bearing can be used to generate shear forces on the nanosheet producing precursor material thereby exfoliating a two-dimensional material from that precursor material. Whilst not wishing to be limited to any one theory, the operating principle of the new bearing mill arrangement is that running bearings create mostly shear forces or loads on layered material precursors, that can mechanically exfoliate them to 2D materials. Due to the dominant shear loads, the damage to the in-plane structure of the 2D material product is low. This advantageously produces a consistent and low defect (preferably defect- free) 2D material product.

[016] Each bearing mill typically comprises at least one bearing comprising a rotatable element and a house within a bearing enclosure. Each rotatable element is configured to rotatably move within the bearing enclosure, with the outer surface of the rotatable element being spaced apart from an inner surface of the bearing enclosure by a milling gap. The configuration of the rotatable element and bearing enclosure depends on the configuration of the bearing. As discussed below a variety of bearings can be used in the bearing mill of the present invention. As an example, for plain bearings, particularly simple plain bearings, the rotatable element comprises an inner shaft/journal that rotates within a cylindrical bearing housing. Here the milling gap is formed by a gap between the opposing surfaces of the inner shaft/journal and the cylindrical bearing housing. A plain bearing may include one or more bushings, that is inserted into the cylindrical bearing housing to provide a bearing surface for rotary applications. Here, the milling gap is formed by a gap between the opposing surfaces of the inner shaft/journal and the bushing. For a two-piece plain bearing, the rotatable element comprises an inner shell or bush attached to a shaft/journal that rotates relative to an outer shell or bush which is located within a cylindrical bearing housing forming the bearing enclosure. Here the milling gap is formed by a gap between the opposing surfaces of the outer shell/ bush and inner shell/ bush. For a ball bearing, the rotatable element comprises the plurality of ball bearings housed between two bearing rings (an outer ring (or race) and an inner ring (or race)) which forms the bearing enclosure. Here the milling gap is formed by a gap between the opposing surfaces of the ball bearings and each of the outer ring and inner ring.

[017] The particular milling gap of a bearing influences a number of operational and production factors of the apparatus. For example, tuning the milling gap in each bearing can also provide control over the precursor flow rate through the bearing. The size of the milling gap can also influence the size, particle distribution and quality of the formed nanosheets. The size of the milling gap is also dependent on the particular bearing configuration used in the apparatus. In embodiments, the milling gap can be from 0.005 mm to 3 mm, preferably 0.005 mm to 0.5 mm, and more preferably from 0.005 mm to 0.1 mm, depending on the bearing type and size. In embodiments, the milling gap can be tailored to the specific bearing mill configuration and the desired degree of exfoliation of the nanosheet producing precursor.

[018] The geometry and materials of the bearings can be varied for different impact forces and exfoliation requirements. A variety of bearing types and configurations can be used in the bearing mill of the present invention. The bearing can comprise at least one of: a ball bearing; a roller bearing; or a plain bearing. It should be appreciated that a ball bearing may comprise a deep-groove ball bearing, self-aligning ball bearing, angular contact ball bearing, thrust ball bearing, or the like. It should also be appreciated that a roller bearing may comprise a tapered roller bearing, spherical roller bearing, cylindrical roller bearing, needle roller bearing, or the like. Additionally, it should be appreciated that a plain bearing may comprise a simple plain bearing, a spherical plain bearing, a two-part plain bearing or the like.

[019] Advantageously, the inventors have found that a spherical plain bearing provides advantageous milling production yield and quality. A number of different types of bearings were tested by the inventors to produce 2D materials such as White Graphene, including deep groove ball bearings, cylindrical roller bearings, needle roller bearings, and spherical plain bearings. Of these bearing configurations, spherical plain bearings gave the best results in terms of production yield and quality of White Graphene. Whilst not wishing to be limited to any one theory, the Inventors consider that these favourable results can be attributed to the bearings of spherical plain type having: a larger continuous shear surface compared to other bearing types of the same size; a small gap between the outer and inner rings; less impact force from rotating objects in these bearing; and no empty gaps, so no opportunity for material to pass through the bearing without interaction with a bearing surface. Thus, in many embodiments of the present invention, the bearing preferably comprises a spherical plain bearing, and more preferably a radial spherical plain bearing. In some embodiments, the plain bearing comprises a two-part plain bearing, preferably a two- part spherical plain bearing.

[020] It should be appreciated that a spherical plain bearing comprises two sliding shells enclosed between an outer housing and inner rotating shaft/ journal. The inner shell includes a curved typically convex-shaped annulus which is fixed to the rotating shaft/ journal. The inner shell is contained within a spherical outer shell, which includes a cooperating curved typically concave surface which allows the bearing to pivot/rotate in order to match the orientation of the shaft/ journal.

[021 ] Other advantages of the present invention over existing 2D material production methods, which are: low cost of the production device, i.e. bearings; the smaller size of the bearing device, which can contain several bearings; a continuous processing capacity; simple maintenance of the bearing device (replacement is straightforward).

[022] The bearings of each bearing mill can be formed from any suitable material. In embodiments, the bearings comprise at least one of metal, ceramic or a polymer. However, in most cases the bearings will be formed from a metal, for example iron, an iron alloy, such as a steel, or an alloy steel such as a stainless steel or hardened carbon chromium steel, or a copper alloy. For spherical plain bearings, in embodiments, the inner/outer rings of a spherical plain bearings are made of hardened carbon chromium steel, hardened stainless steel, or copper alloy or the like.

[023] The apparatus may also include a motor to drive rotation of the at least one bearing relative to the bearing enclosure. The motor is preferably configured with suitable torque and may have controllable rotation speed. The motor rotates the bearing relative to the bearing enclosure, causing the surfaces of the bearing to contact the nanosheet producing precursor flowing through the bearing. The forces from that impact, and associated impacts of material in the milling gap impart shear forces on a precursor material contained in a milling liquid that flows through the at least one bearing. The motor can drive rotation at any desired rotational speed. In embodiments, the bearing rotates relative to the bearing enclosure at a speed of from 50 rpm to 5000 rpm, preferably from 100 to 4000 rpm, more preferably from 500 to 3000 rpm. In some embodiments, the bearing rotates relative to bearing enclosure at a speed of from 500 rpm to 4000 rpm, preferably from 1000 to 4000 rpm, more preferably from 1000 to 3000 rpm.

[024] The overall bearing mill can have any suitable configuration. In embodiments, the at least one bearing is enclosed in a housing which includes a drive shaft which is driven to rotation the bearing relative to the bearing enclosure. The bearing enclosure can be located between a stationary section of the bearing mill (for example a section of the housing) and a rotating shaft, rotation of the shaft being driven by the motor. At least a section of the bearing enclosure or the rotating element of the bearing is preferably circumferentially attached to the rotating shaft or to a body attached to the rotating shaft, preferably a disc, cone, or cylinder. [025] In many embodiments, the apparatus includes a feed housing fluidly connected to the at least one bearing configured to hold a fluid reservoir of the precursor material contained in a milling liquid and feed that fluid to the bearing. The at least one bearing is preferably located proximate to or at a base of the feed housing. The feed housing is configured so that the milling liquid containing the precursor material can only flow through the running bearing for the desired length of time. The apparatus is typically operated at room temperature or lower temperatures. The feed housing may also include at least one mixing device, preferably a mechanical mixer. The mixing device is used to keep the precursor material homogeneously dispersed in the liquid without settling.

[026] The apparatus typically also includes a product housing fluidly connected to the bearing configured to receive fluid that has passed through the bearing. The product housing is typically sized to receive a certain volume of the product, before that product exits the bearing mill at an outlet for further treatment (for example ultrasonication, separation processes or the like). The apparatus may also include a pressure differential device configured to create a reduced pressure across the bearing from the feed housing to the product housing. The reduced pressure can be created by a number of means, for example increasing the pressure in the feed housing relative to the product housing, or reducing the pressure in the product housing relative to the feed housing. In embodiments, the pressure differential device comprises a vacuum pump configured to reduce the pressure in the product housing relative to the pressure in the feed housing. That vacuum pump is preferably fluidly attached to the product housing. The reduced pressure improves the flow rate or passing rate of the precursor for all types of bearings. It also affects the size of the milling gap (the distance between the outer surface of the bearing and the inner surface of the bearing enclosure surfaces) in bearings, such as spherical plain bearings, which affects the exfoliation efficiency.

[027] The bearing mill can include a single bearing, a plurality of bearings or multiple bearings, arranged in series or parallel relative to the feed precursor material and milling liquid and the feed housing that includes a reservoir of the precursor material in the milling liquid. Embodiments of the apparatus can therefore further include at least two bearings located between the feed housing and product housing. The two or more bearings can be arranged in parallel between the feed housing and product housing, with each bearing having a direct fluid connection to the feed housing and product housing, or in series, with two or more bearings being located in a common fluid connection or conduit between the feed housing and product housing. In some embodiments, the at least two bearings fluidly connected in series, preferably located in a common fluid conduit through which the precursor material contained in a milling liquid is configured to flow. Series connection of two or more bearings provides higher production yield on the precursor as the material passes through successive bearings, milling that precursor in successive bearing milling processes. Similarly, a parallel arrangement can produce higher production as this increases production throughout with more precursor being processed through multiple parallel arranged bearings.

[028] The shear milling apparatus of the present invention can be configured to produce nanosheets from a nanosheet producing precursor. For this application, the milling mixture comprises the nanosheet producing precursor material in a milling liquid. That mixture may be a solid-liquid mixture of the nanosheet producing precursor material in the milling liquid, or may be a solid dispersion of the nanosheet producing precursor material within the milling liquid. The milling liquid can comprise any suitable liquid in which the nanosheet producing precursor material can be mixed and/or dispersed. In embodiments, the milling liquid comprises at least one of water, an organic solvent, an alcohol, an oil, or a combination thereof. In some embodiments, the milling liquid comprises at least one of water, ethanol, isopropyl alcohol, methanol, palm oil, linseed oil, o-dichlorobenzene (o-DCB), N-methyl-1 ,2-pyrrolidone (NMP), DMF (N,N-Dimethylformamide), organic amine-based solvents (DMPA, DMAPMA, BAEMA, MAEMA), or a mixture thereof. In particular embodiments, the milling liquid comprises a mixture of water and ethanol, preferably a 1 :1 mixture of water and ethanol. It should be appreciated that the milling liquid could include any number of additives such as weak acids, surfactants, emulsifiers or the like, for example trimesic acid or 1 -butyl-3-methylimidazolium hexafluorophosphate.

[029] The nanosheet producing precursor material can be mixed or dispersed within the milling liquid at any suitable concentration. In embodiments, the concentration of the nanosheet producing precursor material within the milling liquid is between 0.001 g/ml to 0.5 g/ml, preferably from 0.05 g/ml to 0.3 g/ml, preferably from 0.05 g/ml to 0.1 g/m I . In some embodiments, the concentration of the nanosheet producing precursor material within the milling liquid is between 0.01 g/ml to 0.05 g/ml.

[030] The apparatus of the present invention can be used to mill a variety of precursor materials. The nanosheet producing precursor can comprise any suitable starting material. In exemplary embodiments, the nanosheet producing precursor material comprises a bulk layered material such as at least one of hexagonal boron nitride (hBN), graphite, graphene oxide, molybdenum disulphide (M0S2), tungsten disulphide (WS2), transition metal dichalcogenides (TMDs), MXenes, g-CsIXU, or black phosphorus crystals. The apparatus is used to produce a substantially two- dimensional product material, for example substantially two-dimensional nanosheets. Based on the above precursor material, the two-dimensional nanosheets therefore preferably comprises at least one of boron nitride nanosheet (BNNS), graphene, graphene oxide, molybdenum disulphide (M0S2), tungsten disulphide (WS2), transition metal dichalcogenides (TMDs), MXenes, g-CsIXk, or black phosphorus. It should be appreciated that the process is also applicable to produce others van der Waals/layered 2D materials, with controllable lateral sizes and thicknesses. Furthermore, as can be appreciated, the nanosheet producing precursor material and the produced two-dimensional nanosheets are similar materials.

[031] The milling mixture is fed into the bearing mill process and at least one bearing mill thereof at any suitable flow rate. It should be appreciated that the feed rate will depend on the configuration, scale and number of bearing mills in the bearing milling process. In embodiments, the milling mixture is fed into each bearing mill of the bearing milling process with a flow rate of 0.05 to 4 m ³ /h, preferably 0.1 to 2 m ³ /h, and more preferably 0.1 to 1 m ³ /h. The milling mixture can be fed into the bearing milling process (and each bearing mill thereof) by a variety of methods, for example gravity feed, pumped or other liquid feeding or flow process.

[032] The nanosheet producing precursor material can be provided with any suitable dimensions. In some embodiments, the nanosheet producing precursor material comprises layered crystals with each crystal having an average diameter of 1 pm to 50 pm, preferably 10 pm to 50 pm and a thickness of 500 nm to 2 pm, preferably 1 pm to 2 pm. [033] The formed two-dimensional material product can be tailored to have any suitable size and/or dimensions. In embodiments, the formed substantially two- dimensional nanosheets have an average lateral size from 100 nm to 7 pm, preferably 500 nm to 5 pm, more preferably 1 pm to 3 pm.

[034] Once the substantially two-dimensional nanosheet product has been exfoliated from the nanosheet producing precursor material, that product is preferably separated from the milling mixture - i.e. the remaining nanosheet producing precursor material and milling liquid. This can involve a variety of separation stages to both (i) separate the produced nanosheet from the nanosheet producing precursor material; and also (ii) separate the nanosheet producing precursor material from the milling liquid. Suitable separation techniques include filtration, centrifugation, floatation or the like. In some embodiments, the apparatus further comprises at least one separation stage for separating the produced nanosheet material from the milling liquid and the remaining nanosheet producing precursor. In preferred forms, the separation stage includes at least one centrifugation step. In some embodiments, the separation stage includes two or more consecutive centrifugation steps.

[035] A second aspect of the present invention provides a method of shear milling a precursor material, comprising: feeding a milling mixture comprising a precursor material in a milling liquid through at least one bearing configured to impart shear forces on the precursor flowing through the at least one bearing, thereby comminuting, shearing and/or exfoliating a product material from the precursor material.

[036] As outlined above for the first aspect, the inventors have found that a bearing can be used to as an effective mechanical exfoliation device. It should be appreciated that this second aspect of the present invention can be performed using an apparatus according to the first aspect of the present invention. It should therefore be understood that the disclosure of the present invention in relation to the first aspect of the present invention equally applies to similar features of this second aspect of the present invention. [037] As outlined for the first aspect, any suitable milling liquid can be used. In embodiments, the milling liquid comprises at least one of water, an organic solvent, an alcohol, an oil, or a combination thereof. Examples of suitable milling liquids include water, isopropyl alcohol, methanol, palm oil, linseed oil, o-dichlorobenzene (o-DCB), N-methyl-1 ,2-pyrrolidone (NMP), DMF (N,N-Dimethylformamide), organic amine- based solvents (DMPA, DMAPMA, BAEMA, MAEMA), or a mixture of one or more thereof. It should be appreciated that in some embodiments the milling liquid may include at least one additive selected from weak acids, surfactants, emulsifiers or the like.

[038] The precursor material is included in the milling liquid as a mixture or dispersion of particles therein. The amount of precursor material depends on the desired properties of that mixture or dispersion and the composition of that precursor material. For some embodiments, the concentration of the precursor material within the milling liquid is between 0.001 g/ml to 0.5 g/ml, preferably from 0.05 g/ml to 0.3 g/ml, more preferably from 0.05 g/ml to 0.1 g/ml. However, it should be appreciated that other concentration ranges may also be appliable and used in the process and apparatus of the present invention.

[039] The process of the present invention can be used to mill a variety of precursor materials. In exemplary embodiments, the method is used to exfoliate a substantially two-dimensional product material such as nanosheets from a nanosheet producing precursor material contained in a liquid precursor containing (a mixture or dispersion). In such embodiments, the precursor material comprises a nanosheet producing precursor contained in a milling liquid, and the bearing is configured to exfoliate at least one nanosheet from the nanosheet producing precursor. Again, any suitable nanosheet producing precursor material can be used. In embodiments, the nanosheet producing precursor material comprises a bulk layered material such as at least one of at least one of hexagonal boron nitride (hBN), graphite, graphene oxide, molybdenum disulphide (M0S2), tungsten disulphide (WS2), transition metal dichalcogenides (TMDs), MXenes, g-CsIXk, or black phosphorus crystals. The substantially two-dimensional product material preferably comprises a substantially two-dimensional nanosheets. Based on the above nanosheet producing precursor material, that substantially two-dimensional product material may comprise at least one of boron nitride nanosheet (BNNS), graphene, graphene oxide, molybdenum disulphide (M0S2), tungsten disulphide (WS2), transition metal dichalcogenides (TMDs), MXenes, g-CsN4, or black phosphorus. Again, as can be appreciated, the nanosheet producing precursor material and the produced two-dimensional material (nanosheets) are similar materials.

[040] The precursor material may settle out of the milling liquid prior to being fed through the at least one bearing. To assist in maintaining an even mixture/ dispersion of the precursor material in the milling liquid, the method may further comprise the step of mixing the milling mixture in a fluid reservoir which is fluidly connected to the at least one bearing prior to feeding said milling mixture through the at least one bearing. Here the milling liquid can be fed into a fluid reservoir and mixed, preferably using a mechanical mixer to keep the precursor material homogeneously dispersed in the liquid without settling.

[041] Similarly, fluid flow (feed) through the at least one bearing can be assisted by creating a pressure differential, typically a reduction in pressure, across the at least one bearing from the fluid reservoir through the bearing to an outlet or product side of the bearing. In embodiments, the at least one bearing includes a feed side in which fluid is fed into the bearing and a product side, include fluid egresses the bearing, and the method further comprising creating a reduced pressure across the bearing from the feed side to the product side. The reduced pressure can be created by a number of means, for example increasing the pressure on the feed side relative to the product side, or reducing the pressure on the product side relative to the feed side. In embodiments, the reduced pressure is created using a vacuum pump operating on the product side of the at least one bearing.

[042] The liquid passing rate or flow rate through the bearing is normally controlled by the type of bearing, the viscosity of the liquid, the concentration of the layered material in the liquid, the speed of the bearing, and adjustable pressure. In embodiments, the milling mixture flows through each bearing with a flow rate of 0.05 to 4 m ³ /h, preferably 0.1 to 2 m ³ /h, and more preferably 0.1 to 1 m ³ /h. [043] The at least one bearing generally comprises a rotatable element and a housed within a bearing enclosure, each rotatable element configured to rotatably move within the bearing enclosure, the outer surface of the rotatable element being spaced apart from an inner surface of the bearing enclosure by a milling gap.

[044] As taught for the first aspect of the present invention, the quality and dimensions of the product can be controlled by control and selection of suitable bearing rotation speed, precursor feeding rate, and selected bearing design including factors such as bearing configuration and gap size. In embodiments, the milling gap can be tailored to the specific bearing mill configuration and the desired degree of exfoliation of the nanosheet producing precursor. In embodiments, the milling gap is from 0.005 mm to 3 mm, preferably 0.005 mm to 0.5 mm, and more preferably from 0.005 mm to 0.1 mm.

[045] Again, the geometry and materials of the bearings can be varied for different impact forces and exfoliation requirements. As taught in the first aspect, a variety of bearing configurations can be used in the bearing mill including at least one of: a ball bearing; a roller bearing; or a plain bearing. One advantageous bearing configuration that can be used in the present invention is a spherical plain bearing. In embodiments, the bearing comprises a spherical plain bearing, preferably a radial spherical plain bearing. The plain bearing preferably comprises a two-part plain bearing, preferably a two-part spherical plain bearing.

[046] The at least one bearing is typically included in a bearing mill. That bearing mill may include a single bearing, a plurality of bearings or multiple bearings. In embodiments, the process (and bearing mill used therein) can include at least two bearings. Again, the two or more bearings can be arranged in parallel between the feed housing and product housing, with each bearing having a direct fluid connection to the feed housing and product housing, or in series, with two or more bearings being located in a common fluid connection or conduit between the feed housing and product housing.

[047] The efficiency of the exfoliation process and the size and thickness of the comminuted or exfoliated product can be tuned by changing bearing type, chemical composition and viscosity of the liquid, concentration of precursor material in the liquid, flow rate through the bearing, the bearing rotational speed, pressure, and temperature.

[048] The produced nanosheets can be produced with a variety of dimensions depending on the bearing configuration and process conditions in producing the nanosheets. In embodiments, the nanosheets are produced with an average lateral size from 100 nm to 7 pm, preferably 500 nm to 5 pm, more preferably 1 pm to 3 pm. In embodiments, the nanosheets have a thickness of at least 0.5 nm, preferably between 1 nm and 50 nm, more preferably between 1 nm and 20 nm . In embodiments, the nanosheet producing precursor material comprises layered crystals with each crystal having an average diameter of 1 pm to 50 pm and a thickness of 500 nm to 2 pm.

[049] The nanosheet product can be subjected to one or more post treatment processes. For example, some embodiments further include the step of subjecting the nanosheet product to at least one post treatment ultrasonication process. This post treatment process facilitates the exfoliation to atomically thin nanosheets.

[050] The product is also typically subjected to one or more separation processes to extract the nanosheet product from the milling liquid and remaining nanosheet producing precursor. The method therefore preferably further comprises separating the produced nanosheet material from the milling mixture using at least one separation stage. In some embodiments, the separation stage includes at least one centrifugation step. In embodiments, the separation stage includes two or more consecutive centrifugation steps.

[051] The method of the present invention is typically configured to produce a high production yield. The production yield depends on the scale/ size of the bearing milling equipment and overall processing capacity. However, in embodiments the production flow rate can be up to or greater than 4000 L/h.

[052] A third aspect of the present invention provides nanosheets produced according to the method of the second aspect of the present invention. In embodiments, have an average lateral size from 100 nm to 7 pm, preferably 500 nm to 5 pm, more preferably 1 pm to 3 pm. In embodiments, the substantially two- dimensional nanosheets have a thickness of at least 0.5 nm, preferably between 1 nm and 50 nm, more preferably between 1 nm and 20 nm.

[053] The advantages of this bearing mill production method of the present invention include:

• a continuous processing capacity,

• potentially fully automated process,

• high flow rate, for example 4000 L/h,

• High yield,

• high-quality products,

• repeatable, controllable product size and quality,

• low production cost,

• low maintenance,

• accessible components; and

• scalability to large product yields.

BRIEF DESCRIPTION OF THE DRAWINGS

[054] The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein:

[055] Figure 1A provides a schematic representation of a first embodiment of a bearing mill which embodies the bearing device concept of the present invention.

[056] Figure 1 B provides an expanded view of a bearing from the bearing mill apparatus illustrated in Figure 1.

[057] Figure 2A provides a schematic representation of the operating section of a bearing mill that includes a spherical plain bearing device for 2D material production according to a second embodiment of the present invention.

[058] Figure 2B provides a schematic representation of a spherical plain bearing that is used in the bearing mill illustrated in Figure 2A, which includes cut out section X of its outer shell to illustrate the details of the inner shell. [059] Figure 3 provides SEM images of BN nanosheet (White Graphene) produced by a shear milling apparatus similar to the apparatus shown in Figure 1 A that includes: A) deep-groove ball bearing, B) a cylindrical roller bearing, and C) a needle roller bearing.

[060] Figure 4 provides SEM images of a) hexagonal BN precursors and b) BN nanosheet (White Graphene) produced by a shear milling apparatus including a spherical plain bearing similar to the apparatus shown in Figure 2A.

DETAILED DESCRIPTION

[061] The present invention provides a new shear milling apparatus and an associated scalable shear milling method using that new shear milling apparatus which can be used to produce high-quality two-dimensional materials or nanosheets preferably with high product yields, and that can be configured to produce a nanosheet product. The apparatus and method of the present invention can be used to exfoliate bulk layered materials with different chemical compositions and physical properties to 2D materials or nanosheets. In particular, this apparatus and method is intended to be applicable to the production of a large variety of two-dimensional materials or nanosheets, including but not limited to: boron nitride nanosheet (BNNS), graphene, MXenes, g-CsN4, black phosphorus, molybdenum disulphide (M0S2), tungsten disulphide (WS2), and transition metal dichalcogenides (TMDs) nanosheets.

[062] The present invention uses at least one bearing to mechanically exfoliate a precursor material to comminute, shear and/or exfoliate a product material from the precursor material. As noted previously, the working principle of the present invention is that a liquid precursor containing a mixture or dispersion of bulk layered materials, such as graphite, hexagonal boron nitride, molybdenum disulfide crystals passes through a running bearing, and the shear forces created between the rotating bearing and the bearing enclosure exfoliate them to 2D materials or nanosheets. Running bearings create mostly shear forces or loads on layered material precursors, which can mechanically exfoliate them to 2D materials. Due to the dominant shear loads, the damage to the in-plane structure is low. [063] It should be appreciated that upper, lower, between and the like refer to the orientations of features shown in the illustrated Figures. Those terms are not intended to be limitations on the possible orientations and configuration of the apparatus of the present invention, but rather are only intended to convey the relative locations of the sections and features of the apparatus for the embodiments illustrated in the Figures.

[064] An example of a first embodiment of the shear milling apparatus 100 is shown in Figures 1A and 1 B. Figure 1 A provides a schematic representation of a first embodiment of the present invention which embodies the general concept of the shear milling device of the present invention. Figure 1 B provides an enlarged view of one bearing of the apparatus 100 shown in Figure 1A that is used for milling a precursor material.

[065] As shown in Figure 1A, the illustrated shear milling apparatus 100 includes a housing 110 that includes an upper feed housing 112 which includes a fluid reservoir 114, bearing mill 116, and lower product housing 118 (as orientated in Figure 1A). The bearing mill 116 is located between the feed housing 112 and product housing 118 and forms a fluid connection between these two sections.

[066] The bearing mill 116 illustrated in Figures 1A and 1 B includes a bearing 117 comprising a plurality of ball or roller bearings 120 housed between two bearing rings (or races) - an outer ring and an inner ring (or race)) which forms the bearing enclosure 125. A milling gap G (Figure 1 B) is formed by a gap (spaced apart distance) between the opposing surfaces of the ball bearings 120 and each of the outer ring 122 and inner ring 124. The outer ring 122 is fixed to the base of the feed housing 1 12. The inner ring 124 is circumferentially attached to a rotating shaft 128. As best shown in Figure 1A, the rotating shaft comprises a drive shaft 130 and a conical section 132 which extends to a base section 134 around which the outer ring 122 of the bearing 117 is attached. The drive shaft 130 is connected to a drive motor 131 which drives rotation of the rotating shaft 128, and thereby drives rotation of the inner ring 124 relative to the outer ring 122 of the bearing 117, thereby moving the ball or roller bearings 120 housed therebetween. The drive motor 131 has suitable torque and controllable rotation speed. [067] The feed housing 112 comprises a tank configured to hold a fluid reservoir 114 of a feed liquid 115 comprising a precursor material contained in a milling liquid (of which compositional details are explained previously in this specification). The bearing 117 is located at a base of the feed housing 112, therefore enabling, in operation, for the feed liquid 115 to flow from the bottom of the fluid reservoir and through the running bearing for a desired length of time. The feed housing 112 also includes a mixing device 140, in the illustrated embodiment a mechanical mixer including rotor 142. The mixing device 140 is used to keep the precursor material homogeneously dispersed in the milling liquid without settling.

[068] The product housing 118 is located underneath the feed housing 112 and is fluidly connected to the bearing 117 located above (as orientated in Figure 1A). As illustrated in Figure 1A, the product housing 118 includes a funnel section 152 configured to collect and direct the product fluid mixture 160 into product tank 154 configured to receive and contain the product fluid mixture 160 that has passed through the bearing. The product tank 154 is typically sized to receive a certain volume of the product, before that product exits the apparatus 100 at an outlet 162 for further treatment (for example ultrasonication, separation processes or the like).

[069] The product housing 118 also includes a vacuum port 166 which is fluidly connected to a vacuum pump (not illustrated) configured to reduce the pressure in the product housing 118 relative to the pressure in the feed housing 112. The reduced pressure improves the flow rate or passing rate of the precursor through the bearing mill 117.

[070] In operation, the drive motor 131 is operated to drive rotation of the rotating shaft 132, this in turn drives movement of the ball bearings 120 in the bearing 117. The vacuum pump (not illustrated) is operated to reduce the pressure in the product housing 118 relative to the pressure in the feed housing 112, thereby enhancing fluid flow through the running bearing 117. The feed liquid 115 flows from the bottom of the fluid reservoir 114 and through the running bearing 117 and through to the product housing 118 in the direction shown by arrows F and FB in Figure 1 B. The product liquid mixture is directed into the product tank 154 via conical section 132 in the direction shown by arrows FB in Figure 1 A. As the feed liquid 115 passes through the running bearing 1 17, the precursor material contained in the milling liquid undergoes mechanical exfoliation, through shearing forces produced on the precursor material in the milling gap G between the ball bearing 120 and the opposing surfaces of the outer ring 122 and inner ring 124 of the bearing 117. Here, the bearing 117 can generate shear forces on the precursor material thereby exfoliating a material from that precursor material.

[071] Whilst the apparatus in Figure 1 A and 1 B illustrate the bearing mill 1 16 section of the apparatus 100 using a ball bearing type bearing, it should be appreciated that the particular type of bearing could have a variety of different bearing configurations. For example, the bearing can be a ball bearing (deep-groove ball bearing, self-aligning ball bearing, angular contact ball bearing, thrust ball bearing, etc.), or roller bearing (tapered roller bearing, spherical roller bearing, cylindrical roller bearing, needle roller bearing, etc.), or plain bearing (simple plain bearing, spherical plain bearing, two-part plain bearing etc.).

[072] A second embodiment of a shear milling apparatus 200 according to the present invention is illustrated in Figures 2A and 2B. Figure 2A shows the central section of the apparatus, only showing parts of the feed housing 212 and product housing 218. The apparatus 200 follows the same general configuration as the apparatus illustrated in Figure 1A but includes a spherical plain bearing 217 rather than ball or roller bearings in the bearing mill 216. Accordingly, like features in Figure 2A have been assigned the same reference numeral as used in Figure 1A plus 100.

[073] Like the previous embodiment, the illustrated shear milling apparatus 200 includes a housing 210 that includes an upper feed housing 212 which includes a fluid reservoir 214, bearing mill 216, and lower product housing 218 (as orientated in Figure 3A). The bearing mill 216 is located between the feed housing 212 and product housing 218 and forms a fluid connection between these two sections.

[074] The bearing mill 216 illustrated in Figures 2A and 2B comprises a two-piece spherical plain bearing 217. Here the plain bearing 217 comprises a rotatable element in the form of an inner shell or bush 224 attached to a rotating shaft 232 that rotates relative to an outer shell or bush 222 which is attached to the base of the feed housing 212. As best seen in cut-out section X of Figure 2B, the inner shell 224 includes a curved typically convex shaped annulus which is fixed to the rotating shaft 232. The inner shell 224 is contained within a spherically curved outer shell 222, which includes a cooperating curved surface (typically concave). Here the milling gap G is formed by a gap between the opposing surfaces of the outer shell 222 and inner shell 224 (see Figure 2A). This gap G through which precursor solution passes from the feed housing 212 to the product housing 218 is where exfoliation of the precursor material occurs. It should be understood that plain bearings operate on the principle of sliding friction and employ no rolling elements.

[075] The outer ring 222 is fixed to the base of the feed housing 212. The inner ring 224 is circumferentially attached to the rotating shaft 228. As best shown in Figure 2A, the rotating shaft comprises a drive shaft 230 and a cylindrical section 232 around which the outer ring 222 of the bearing 217 is attached. Similar to the configuration illustrated in Figure 1 A, the drive shaft 230 is connected to a drive motor (not illustrated but in a similar position in this apparatus 200 to drive motor 131 of the apparatus 100 in Figure 1 ) which drives rotation of the rotating shaft 228, and thereby drives rotation of the inner ring 224 relative to the outer ring 222 of the bearing 217. Again, the drive motor (not illustrated) has suitable torque and controllable rotation speed.

[076] The feed housing 212 and product housing 214 have a similar configuration as described in relation to the embodiment illustrated in Figure 1 A. The product housing 218 again includes a vacuum port 266 which is fluidly connected to a vacuum pump (not illustrated) configured to reduce the pressure in the product housing 218 relative to the pressure in the feed housing 212 to improves the flow rate or passing rate of the precursor through the bearing mill 217. For this embodiment, the reduced pressure can also affect the size of the milling gap G in spherical plain bearings 217, which affects the exfoliation efficiency.

[077] In operation, the drive motor (not illustrated) is operated to drive rotation of the rotating shaft 232, this in turn drives relative movement between the inner ring 224 and the outer ring 222. The vacuum pump (not illustrated) is operated to reduce the pressure in the product housing 218 relative to the pressure in the feed housing 212, thereby enhancing fluid flow through the running bearing 217. The feed liquid 215 flows from the bottom of the fluid reservoir 214 and through the running bearing 217 and through to the product housing 218 and product tank 254. As the feed liquid 215 passes through the running bearing 217, the precursor material contained in the milling liquid undergoes mechanical exfoliation, through shearing forces produced on the precursor material in the milling gap G between the sliding and opposing surfaces of the outer ring 222 and inner ring 224 of the bearing 217.

[078] The speed of the running bearing 117, 217 can be adjusted to suit the particular material undergoing shear milling. Typical rotational speeds driven by the drive motor 131 and 231 is from 50 rpm to 5000 rpm. The liquid passing rate or flow rate is normally controlled by the type of bearing, the viscosity of the liquid, the concentration of the layered material in the liquid, the speed of the bearing, and adjustable pressure.

[079] The product passing through the bearing 117, 217 can be post-treated, such as by ultrasonication to facilitate the exfoliation to atomically thin nanosheets.

[080] Whilst a single bearing 117, 217 is illustrated in Figures 1A and 2A, other embodiments of the bearing mill 116, 216 (not illustrated) can include a two or more bearings arranged in series or parallel relative to the feed housing 112, 212 and the product housing 118, 218 as noted above. The two or more bearings 1 17, 217 can be arranged in parallel between the feed housing 112, 212 and product housing 118, 218, with each bearing 117, 217 having a direct fluid connection to the feed housing 112, 212 and product housing 118, 218, or in series, with two or more bearings 117, 217 being located in a common fluid connection or conduit (not illustrated) between the feed housing 112, 212 and product housing 118, 218. It should be appreciated that two or more bearings connected in series (for example stacked on top of each other) increases the time the precursor material is in contact with shear forces from a bearing. This produces higher production yield of nanosheets from the precursor material.

[081] Furthermore, by selecting the optimised parameters and suitable bearings, the bearing mill device can produce high-quality 2D nanosheets, such as graphene, graphene oxide, boron nitride nanosheets or White Graphene, TDMs, MXenes, g- C3N4, black phosphorus, and others van der Waals/layered 2D materials, with controllable lateral sizes and thicknesses. The particle size produced by bearing milling can be controlled by the following factors: a. Shape, configuration and distribution of the bearings 1 17, 217; b. Physical properties of the feed nanosheet producing precursor material; c. Milling gap G between the bearing and bearing enclosure; d. Precursor material feed rate; e. Fluid flow rate through the bearing mill 116, 216; and f. Rotational speed of the bearing.

[082] The milling gap G is one factor used to determine particle size. In the illustrated bearing mill (Figures 1A and 2A), the milling gap G can be between 0.005 mm to 3 mm. Tuning the milling gap G allows the control over the precursor flow rate through the bearing 117, 217 and the resultant degree of exfoliation of the feed precursor material.

[083] The bearings 117 and 217 can be formed from any suitable material. In many embodiments, these items are formed from a suitable metal, such as iron, an iron alloy such as steel or an alloy steel such as a stainless steel or hardened carbon chromium steel, or a copper alloy.

[084] The shear milling apparatus 100, 200 illustrated in Figures 1A and 2A can be used to produce a variety of two-dimensional materials or nanosheets, including but not limited to: boron nitride nanosheet (BNNS), graphene, MXenes, g-CsISU, black phosphorus, molybdenum disulphide (M0S2), tungsten disulphide (WS2)and transition metal dichalcogenides (TMDs) nanosheets. Take the production of BNNS as an example.

[085] Production of BNNS begins by adding hexagonal boron nitride particles (for example 1 to 50 pm in size) at desired concentrations in a liquid solution (for example water, ethanol, etc.) with optional chemical additives (for example weak acids, surfactants, etc. as previously discussed in this specification). The feed liquid 115, 215 comprises a solid-liquid mixture/ dispersion of the nanosheet producing precursor material in the milling liquid, or may be a solid dispersion of the nanosheet producing precursor material within the milling liquid as previously discussed. The milling liquid to disperse the bulk layered material could be water, organic solvents, oils, other liquids, or a mixture of thereof. The concentration of the layered materials or crystals is normally 0.001 g/ml to 0.1 g/ml, but may also vary in the ranges previously discussed. The precursor can be gravity fed or pumped with a flow rate of 50 L/h to 4000 L/h.

[086] The liquid containing the hexagonal BN particles is loaded into the feed housing 112, 212 with a mechanical mixer 140 to keep the hexagonal BN particles homogeneously dispersed in the liquid without settling. The mixed liquid is ducted into the feed housing 112, 212, at the bottom of which the bearing 117, 217 is fitted. Rotation of the bearing 117, 217 is driven by drive motor 131 , 231 as described above. The liquid containing hexagonal BN particles flow from the feed housing 112, 212 through the running bearing for 117, 217 for a desired length of time at room temperature or low temperatures.

[087] The efficiency of the exfoliation process and the size and thickness of the BN nanosheet or White Graphene product can be tuned by changing bearing type, chemical composition and viscosity of the liquid, concentration of hexagonal BN precursor in the liquid, passing/flow.

[088] The main advantages of the bearing mill method for 2D material production are:

1 . large scale and continuous production;

2. potentially fully automated process

3. high quality of the product;

4. fully controllable exfoliation effectiveness and efficiency

5. easy scalability, with high yield.

The process of the present invention has a strong potential to produce mass quantities of 2D materials.

[089] Finally, it should be noted that BN nanosheet (White Graphene) is more difficult to produce due to its high chemical and thermal stability as well as the presence of additional interlayer ionic interactions. Therefore, many production methods that successfully produced graphene cannot be used to produce BN nanosheet or White Graphene. The described bearing milling apparatus and method of the present invention is able to exfoliate a range of layered materials with van der Waals interlayer interactions at high efficiency to produce different 2D materials or nanosheets of relatively high quality at low cost and high yield. This method is especially suitable for industrial scale-up due to its straightforward design, continuous process, accessible key components, inexpensive setups, high flexibility, and high yield.

EXAMPLES

[090] It is to be understood that whilst the examples are limited to bearing milling of hexagonal boron nitride (h-BN) to produce BNNS or White Graphene, the described method is equally applicable to other similar two-dimensional materials such as graphene, and molybdenum disulphide (M0S2). h-BN has used been used in the examples for demonstration purposes only.

Example 1 : Bearing Comparative Tests

[091] Bearing mills including deep groove ball bearings, cylindrical roller bearings, needle roller bearings, and spherical plain bearings were tested to compare the milling performance of each bearing configuration.

Experimental

[092] The setup for the bearing mill devices was based on the apparatus 100 illustrated in Figure 1A, fitted in three trial runs respectively with A) a deep-groove ball bearing; B) a cylindrical roller bearing; and C) a needle roller bearing. For all tests, water + ethanol in ratio 1 :1 was used as the precursor base liquid; the particle size of hexagonal BN precursor was about 20 pm; the concentration of hexagonal BN in liquid was 10 to 100 mg/mL; and the running speed of the selected bearing was 100 to 2000 rpm.

Results

[093] Figures 3(A) to 3(C) provides SEM images of BN nanosheet (White Graphene) produced by these tests, using 3A) the deep-groove ball bearing, 3B) the cylindrical roller bearing, and 3C) the needle roller bearing. The results of these tests showed that the ball bearings showed the least exfoliating efficiency (yield) for all hBN concentrations and bearing running speed (Figure 3A). The quality of exfoliation improved using cylindrical roller bearings (Figure 3B) and needle roller bearings (Figure 3C) where the latter showed better results. [094] As will be shown in the next example, the best result among all bearing types used in the comparative tests was shown by spherical plain bearings (Figure 4B).

Example 2: Spherical Plain Bearing Device

[095] A bearing mill including a spherical bearing as illustrated in Figure 2 was used to mill a hexagonal BN precursor to produce of BN nanosheets (White Graphene).

Experimental

[096] The setup for the spherical bearing device is shown in Figure 2. In this specific case of spherical plain bearing, water and ethanol mixer was used as the liquid; the particle size of hexagonal BN precursor was about 20 pm; the concentration of hexagonal BN in liquid was 10 to 100 mg/mL; the running speed of the bearing was 100 to 2000 rpm. To facilitate the passing of precursor through the spherical plain bearing, a vacuum pump connected to the product housing creates the negative pressure which significantly increases the flow rate. The product passing through the bearing was collected, bath ultrasonicated for 0.5 hour, and then further processed for the separation of BN nanosheet from unexfoliated hexagonal BN precursor in the liquid, by centrifuge or filtration.

Results

[097] The experiments found that just after one passing cycle through the spherical plain bearing, a large percentage of BN nanosheet could be obtained at a high passing rate of 5 to 20 L/min (with a vacuum pump). The lateral sizes of the BN nanosheet product from the spherical plain bearing can be in the range of 300 nm to 5 pm with thickness down to a few atomic layers as shown in the SEM images of Figure 4.

[098] Furthermore, the best result among all bearing types used when comparing all of the test runs was shown by spherical plain bearings (Figure 4B). As shown by the comparative results, among the different types of bearings that were tested, including deep groove ball bearings, cylindrical roller bearings, needle roller bearings, and spherical plain bearings; the spherical plain bearings gave the best results in terms of production yield and quality of White Graphene, though the ball and roller types of bearings had higher flow rates due to the differences in contact surface and structural features. In this sense, this result can be attributed to the difference in effective contact(shear) area of moving elements of the bearings: for the ball bearings it is the smallest, and then it increases for roller bearings, reaching its maximum for spherical plain bearings.

[099] It is thought that the better results from the spherical plain bearing are related to the difference in contact surface which is higher for the spherical plain bearing and to the better controllable contact load. The material of the bearing and the contact surfaces also have great impacts on the quality of the product and exfoliation efficiency. The best results in terms of quality and yield were obtained using bearings made of steel, but the plastic, glass, and ceramic can be used for products required high purity and mild contact load. Carbon steel and stainless steel bearings of the same type showed similar results, where carbon steel versions in general are more efficient, but stainless steel bearings do not lead to contamination.

[100] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[101] Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.