APPARATUS AND METHOD FOR BULK PRODUCTION OF ATOMICALLY THIN 2-DIMENSIONAL MATERIALS INCLUDING GRAPHENE

Abstract

An apparatus for production of Graphene and similar atomic scale laminar materials by the delamination of a bulk laminar material, such as graphite; comprising: a pump for pumping a fluid being a suspension of solid particles of the bulk laminar material, at a pressure of greater than 1 MPa, along a fluid conduit and against; an impact head having an impact face substantially perpendicular to the trajectory of incoming fluid to form a narrow variable gap. Variation is mediated by pneumatic pressure directly or indirectly in opposition to the force applied to the impact head along the principle axis by, in use, the pressure applied by the fluid. This provides a self-unblocking delamination apparatus maintaining high product quality and consistency. Relatively small variation in gap size being sufficient to avoid blockage, such as occurs by aggregation of large particles or groups of particles in the high shear gap used for delamination.

Claims

1. An apparatus for the production of Graphene and similar atomic scale laminar materials by the delamination of a bulk laminar material; the apparatus comprising: a main pump (112), suitable for pumping a fluid, the fluid being a suspension of solid particles of the bulk laminar material, at a pressure of greater than 1M Pa, in a first direction and along a principle axis towards and in fluid communication with; core components (10), the core components comprising: a fluid conduit (12) defining a principal axis along which the fluid is pumpable and suitable for conveying said fluid, wherein the fluid conduit is arranged to direct fluid at said pressure from that conduit against; an impact head (16) having an impact face (28) perpendicular or substantially perpendicular to said principal axis and so produce a resultant first force in the first direction; the impact head and the conduit being arranged so that a variable, preferably annular, gap (20) results between an end (24) of the conduit proximate to the impact head and the impact head wherein the gap forms a continuous region surrounding the end of the conduit and being substantially coplanar with the impact head; and wherein, the apparatus is configured to bias the impact head in a second direction in direct opposition to the fluid in the first direction and to do so with a second force and the impact head (16) of the apparatus is configured so as to be movable along the principal axis relative to the proximal end (24) of the conduit so as to vary the gap (20) and wherein that movement is a result of the magnitude of first force in opposition to the second force, the second force being the result of a pneumatic pressure directly or indirectly in opposition to the first force exerted on the impact head along the principle axis.

2. The apparatus of claim 1, wherein the impact head comprises at least one of: alumina, silicon nitride, tungsten carbide, silicon carbide, boron nitride, graphite and diamond.

3. The apparatus of claim 1, wherein the impact head comprises a combination of carbon materials.

4. The apparatus of claim 3, wherein the impact head comprises a combination of graphite and diamond materials.

5. The apparatus of claim 1, wherein the impact head comprises a diamond material and is cooled to a temperature of less than 50° C.

6. The apparatus of claim 1, wherein the impact head comprises a diamond material and is cooled to a temperature of less than 10° C.

7. The apparatus of claim 1, further comprising a pressure drop valve downstream of the impact head so as to, in use, maintain a secondary backpressure after the impact head.

8. The apparatus of claim 1, wherein the impact head of the apparatus is freely rotatable about the principal axis.

9. The apparatus of claim 1, wherein the impact head of the apparatus is configured to be rotatable about the principal axis as constrained by a mechanism.

10. The apparatus of claim 1, further comprising a cooler in fluid communication with said fluid conduit and said main pump, such that the suspension to be processed will pass through the cooler and out to the main pump before passing through the core components, the cooler being configured to reduce the temperature of said fluid.

11. The apparatus of claim 10, further comprising a second, lower-pressure, pump in fluid communication with an inlet to the cooler and the outlet of the cooler being in fluid communication with the main pump such that the suspension is first drawn into the second pump, passes through the cooler and out to the main pump before passing through the core components.

12. The apparatus of claim 1 wherein the main pump has a reciprocating action configured to inducing a pressure fluctuation in fluid and hence in the magnitude of the first force.

13. The apparatus of claim 1 wherein the pneumatic pressure is indirectly in opposition to the first force and exerts the second force to the impact head by means of a mechanical linkage giving a mechanical advantage.

14. A method for exfoliation of laminar materials to produce atomic scale laminar materials by the delamination of bulk material; the method comprises the steps of: providing the apparatus described in claim 1; and passing through the apparatus a suspension of laminar material in a liquid at a pressure of greater than 1 MPa.

15. The method of claim 14, wherein the fluid that exits the core components is recycled back to the inlet of the main pump optionally via a cooler or a second pump.

16. The method of claim 14, wherein the temperature of the fluid is maintained in the range 30° C. to 80° C.

17. The method of claim 14, where the particles are in the size range 3 μm to 50 μm.

18. The method of claim 14, wherein the laminar material loading in the liquid phase is in the range up to 500 grams per litre (g/l).

19. A method comprising: utilizing the apparatus of claim 1 for the production of graphene and similar atomic scale laminar materials by the delamination of a bulk laminar material.

20. A method comprising: utilizing the apparatus of claim 1 for the production of graphene and similar atomic scale laminar materials wherein the solid particles are particles of graphite, hexagonal boron nitride or molybdenum disulphide.

Description

SPECIFIC DESCRIPTION

[0071] The apparatus of the present invention will now be illustrated by means of the following figures in which:

[0072] FIG. 1 shows a schematic view of the fluid path through the apparatus of the present invention and illustrates core components;

[0073] FIG. 2 shows a schematic view in cross-section of a first arrangement of core components of the apparatus of the present invention;

[0074] FIG. 3 shows a schematic view in cross-section of a second arrangement of core components of the apparatus of the present invention;

[0075] FIG. 4 shows a schematic view in cross-section of a second arrangement of core components of the apparatus of the present invention;

[0076] FIG. 5 shows a schematic view of a system or apparatus of the present invention comprising the core components in conjunction with auxiliary components to provide an optimal processing system for performing the method of the present invention.

[0077] FIG. 6 shows an impact head having suffered damage by use over prolonged use and which was constrained from rotation.

[0078] FIG. 7 shows an impact head having suffered minimal wear from use over prolonged use and which was not constrained from rotation.

[0079] The diagrams provide the following features: [0080] 10 assembly of core components; [0081] 12 fluid conduit/volume; [0082] 14 entrance to fluid conduit at a point distal from the impact head; [0083] 16 impact head assembly; [0084] 18 optional facing (impact face) of impact head assembly; [0085] 20 annulus/annular gap; [0086] 202 frusto conical annulus/frusto conical annular gap; [0087] 204 outer annulus/outer annular gap; [0088] 22 support structure: [0089] 24 exit of fluid conduit proximal to the impact head/proximal end of the conduit; [0090] 242 proximal end of the conduit, alternative form; [0091] 26 impact head surround; [0092] 28 face of the impact head; [0093] 32 conduit/pipe; (lower line FIG. 5). [0094] 100 system or (extended) apparatus of the present invention; [0095] 110 starting material vessel; [0096] 112 high pressure pump; [0097] 114 valve; [0098] 124 pressure drop valve; [0099] 116 finished product vessel; [0100] 118 chiller/cooler.

[0101] Referring to FIGS. 1 to 4. In use the apparatus of the present invention has fluid pumped from a pump 112 through a conduit 32 and 12 in the form of a pipe which terminates as part of the core assembly 10. The core assembly 10 has a proximal end 24 of the pipe 12/32 in which fluid in the volume of the conduit 12 exits the conduit under pressure so as to impact upon impact head 16; which can have a face of a hardened material 18. When the fluid impacts upon the face of the impact head it then travels through annulus 20 defined between the face 28 of the impact head and the proximal end of the conduit 24 before exiting the core components, such as to be recirculated or to recover it as finished product. In the particular figure a further impact head surround 26 is provided so as to extend the region in which the fluid is constrained before exiting the core components in use. The impact head 16 of the apparatus is configured so as to be movable relative to the proximal end of the conduit 24 and thus defines an annular gap 20.

[0102] As indicated by the arrow in FIG. 1 the impact head 16 is movable towards the proximal end of the conduit 24 by a mechanism, such as a screw adjustment, for carrying out gross changes in position of the impact head and hence the resulting gap which in operation is maintained in the range between 500 μm and 1 μm. The apparatus of the present invention provides a pneumatic pressure in the same direction as the arrow, however, the movement of the head is restricted so as to maintain a minimum gap, such as by use of an end stop. In use of the apparatus, as shown in FIG. 2 the impact head 16 with optional impact face 18 is capable of adjusting its position as indicated by the double-headed arrow. In use, this adjustment is governed, by the pressure exerted by incoming suspension of bulk material which is being delaminated at the entrance to fluid conduit at a point 14 distal from the impact head, (termed a backpressure) as opposed by pressure exerted from the pneumatic pressure. Hence, as the backpressure increases the impact head will move away from the proximal end of the conduit 24 so as to increase the annular gap 20 and so clear any blockage. Similarly, once the blockage has cleared then the backpressure will, for a given incoming liquid pressure decrease as the hindrance to flow of the liquid through the device is reduced and the impact head will again move, this time so as to reduce the gap. The maximum retreat of the impact head due to backpressure may be limited by an end stop and, as mentioned the maximum advance of the impact head will also be limited by an end stop. The preferred allowable variation in movement of the impact head by means of the above mechanism, such as mediated by a pneumatic link is preferably in the range 1 to 100 μm so the blockages are cleared, with 1 to 10 μm being sufficient to stop blockage build up in many instances.

[0103] In FIG. 3 the proximal end of the conduit 242 has an internally bevelled face such that in use fluid being transferred from the volume of the conduit 12 through the core components accelerates in the annulus (which is now frusto conical) until a pinch point is arrived at giving maximal shear.

[0104] In FIG. 4 the proximal end of the conduit 24 does not abut the impact head surround and provides an outer annulus region 204 in which turbulent flow may occur for improved processing. The outer annulus region 204 is presented in FIG. 3 in conjunction with the internally bevelled face but FIG. 3 may be provided without region 204.

[0105] Referring to FIG. 5 a processing system of the present invention comprises core components 10 as previously described. The system is configured so that raw material is provided in vessel 110 and is pumped through high pressure pump 112 into the conduit 12/32 into the core components 10 and in particular the impact head 16 before exiting to optional pressure drop valve 124 so as to provide backpressure to the core components for improved processing. The system is further configured so that fluid then passes through directional control valve 114 either as finished product to product vessel 116 or is recirculated through chiller 118 before entering high pressure pump 112 for optional recirculation.

EXPERIMENTAL

[0106] An apparatus of the present invention comprising a 3 kw impeller pre-pump at 400 kPa output feeds a 30 kW multiple piston main pump pumping a graphite suspension of average particle size 20 μm and 100 g/l of graphite solid particles at a pressure of 60 MPa (+/−1 MPa) and a flow rate of 1200 l/hr along a fluid conduit having a principal axis a cylindrical impact head having an end impact face perpendicular to said principal axis. The cylinder is 15 mm diameter and 25 mm long and set in corresponding bore of a housing (itself a 20 cm long cylinder), the bore accommodating 10 to 15 mm of the cylindrical impact head (from first end stop to second end stop). The gap is set at 5 μm in the fully extended first end stop position. The suspension is initially at a temperature of 20° C. and is maintained at a temperature of 30° C. by cooling before recirculating back into the apparatus. The recirculation loop having a hold-up of 500 litres. The base of the cylindrical impact head (the face remote from the impact face) is supported by the housing and biased outward (by the pneumatic force) at the first end stop. The biasing force is set as 10% above the, in operation (i.e. in use) biasing force in the first direction from the pumped fluid. The impact head is located in the housing with a clearance fit according to ISO 286-2 H7. The machine was run for 15 minutes. The foregoing is runs 1 and 4. The experiment was repeated with fresh suspension and the impact head mechanically immobilised against the first end stop with the 5 μm gap. This is runs 2 and 3. The pneumatic pressure (the second pressure giving rise to the second force) is not directly applied to the impact head but is applied by means of a mechanical linkage giving an approximately 100:1 mechanical advantage due to an approximately 25:1 surface area increase (over the π(15/2).sup.2 mm.sup.2 due to the fluid) and a mechanical leverage for the remainder.

Results

[0107]

TABLE-US-00001 Result Movement of head Run 1 Clean run, no blockage Pressure fluctuations indicative of head movement between 0 to +10 μm. Run 2 Blockage evidenced by 50% increase in Head unmoved when backpressure after 6 minutes. inspected on dismantling. Run 3 Run 2 unblocked and continued Head unmoved when blockage evidenced by 50% increase in inspected on backpressure after 7 minutes dismantling. Run 4 Clean run, no blockage - repeat of run 1 Pressure fluctuations after adhesive removed and parts indicative of head polished. movement between 0 to +10 μm.

[0108] It is thought that the head movement serves to stop blockages building up by breaking up and dislodging the material before significant back-pressure is created. The blockage was also indirectly evidenced by seeing the residue on the apparatus when taken apart. Whilst blockage could be avoided by using a finer starting material this would require a pre-processing run to reduce the feedstock size and turn a continuous process into a less efficient batch process. A larger gap could also be used by this would give rise to a much longer processing time as the equipment would be run in two stages of gap size. The degree of impact head movement is inferred from the pressure changes. The product of Runs 1 and 4 comprised graphene. The fluctuations suggest an oscillation of the impact head, that oscillation is in the order of the pumping frequency of the pistons of the main pump. This suggests a cooperative effect of the piston pump and the head movement. There is no reason to believe that the invention would not work with an unmodulated fluid supply but the modulation suggests a co-operative effect of the two features.

[0109] The present invention provides an apparatus more resistant to blockage when used with a suspended solid capable of delamination.

[0110] Mechanical advantage is the ratio of the force produced by a machine to the force applied to it, used in assessing the performance of a machine. Preferred mechanical advantage if from 50:1 to 200:1 as this allows the use of conventional pneumatic pressure equipment, such as at around 0.5 Mpa overpressure. Pressures herein are pressures above atmospheric pressure. Temperatures herein are 20° C. unless stated otherwise.

[0111] Preferred embodiments of the invention are: [0112] 1 An apparatus for the production of graphene and similar atomic scale laminar materials by the delamination of a bulk laminar material, such as graphite; the apparatus comprising: [0113] a main pump (112) suitable for pumping a fluid, the fluid being a suspension of solid particles of the bulk laminar material, at a pressure of greater than 1 MPa, towards and in fluid communication with; [0114] core components (10), the core components comprising: [0115] a fluid conduit (12) having a principal axis suitable for conveying said fluid, wherein the fluid conduit is arranged to direct fluid at said pressure from that conduit against; [0116] an impact head (16) having an impact face perpendicular or substantially perpendicular to said principal axis; the impact head and the conduit being arranged so that a variable, preferably annular, gap (20) of between 500 μm and 1 μm results between an end of the conduit proximate to the impact head and the impact head wherein the gap forms a continuous region surrounding the end of the conduit and being substantially coplanar with the impact head; and [0117] an impact head surround (26) which extends the region in which the fluid is constrained before exiting the core components wherein, [0118] the impact head (16) of the apparatus is configured so as to be movable along the principal axis relative to the proximal end of the conduit (24) so as to vary the gap (20) and wherein [0119] that variation is mediated by means of a pneumatic pressure directly or indirectly in opposition to force applied to the impact head along the principle axis by, in use, the pressure applied by the pumped fluid. [0120] 2 The apparatus of embodiment 1, further comprising a pressure drop valve (124) downstream of the impact head so as to, in use, maintain a secondary backpressure after the impact head. [0121] 3 The apparatus of embodiment 1 wherein the arrangement between the impact head face and the principal axis is 1° or less from perpendicular. [0122] 4 The apparatus of any preceding embodiment wherein the impact head (16) of the apparatus is freely rotatable about the principal axis. [0123] 5 The apparatus of any of embodiments 1 to 4 wherein the impact head (16) of the apparatus is configured to be rotatable about the principal axis as constrained by a mechanism. [0124] 6 The apparatus of any preceding embodiment wherein the proximal end of the conduit (242) has an internally bevelled face such that the annular gap is frusto conical, whereby in use fluid being transferred from the volume of the conduit (12) through the core components accelerates in until a minimum width of the annular gap is arrived at for giving maximal shear. [0125] 7 The apparatus of embodiment 6 wherein the width of the annular gap is between 500 μm and 200 μm at its widest point, and between 200 μm and 1 μm at its narrowest point. [0126] 8 The apparatus of any preceding embodiment wherein the proximal end of the conduit (24) does not abut the impact head surround and provides an outer annulus region (204). [0127] 9 The apparatus of any preceding embodiment further comprising a cooler (118) in fluid communication with said fluid conduit and said main pump, such that the suspension to be processed will pass through the cooler and out to the main pump before passing through the core components (10), the cooler being configured to reduce the temperature of said fluid. [0128] 10 The apparatus of Embodiment 9, further comprising a second, lower-pressure, pump in fluid communication with an inlet to the cooler and the outlet of the cooler being in fluid communication with the main pump such that the suspension is first drawn into the second pump, passes through the cooler and out to the main pump before passing through the core components (10). [0129] 11 The apparatus of any preceding embodiment, wherein the impact face (18) of the impact head (16) comprises material selected from the group tungsten carbide, zirconia, silicon nitride, alumina silicon carbide, boron nitride and diamond. [0130] 12 The apparatus of any preceding embodiment, wherein the impact face (18) of the impact head (16) comprises diamond. [0131] 13 A method for exfoliation of laminar materials to produce atomic scale laminar materials by the delamination of bulk material; the method comprises the steps of: providing the apparatus described in Embodiment 1 and; passing through the apparatus a suspension of laminar material in a liquid at a pressure of greater than 1 MPa. [0132] 14 The apparatus or method of any preceding embodiment, wherein the fluid that exits the core components is recycled back to the inlet of the main pump optionally via the cooler of embodiment 9 and/or the second pump of embodiment 10. [0133] 15 The apparatus or method of any preceding embodiment, wherein the temperature of the fluid is maintained in the range 30° C. to 80° C. [0134] 16 The method or apparatus of any preceding embodiment wherein the fluid is impacted upon the impact head at a pressure in the range 10 MPa to 150 MPa. [0135] 17 The method or apparatus of any preceding embodiment wherein the fluid is impacted upon the impact head at a pressure in the range 50 MPa to 70 MPa. [0136] 18 The method or apparatus of any preceding embodiment wherein the fluid is impacted upon the impact head at a flow rate of greater than 1000 I/hr. [0137] 19 The method or apparatus of any preceding embodiment where the particles are in the size range 3 μm to 50 μm. [0138] 20 The method or apparatus of any preceding embodiment wherein the laminar material loading in the liquid phase is in the range up to 500 grams per litre (g/l). [0139] 21 The use of the apparatus of any of embodiments 1 to 12 for the production of graphene and similar atomic scale laminar materials by the delamination of a bulk laminar material. [0140] 22 The use of the apparatus of any of embodiments 1 to 12 for the production of graphene and similar atomic scale laminar materials wherein the solid particles are particles of graphite, hexagonal boron nitride or molybdenum disulphide. [0141] 23 The use of the apparatus of any of embodiments 1 to 12 for the production of graphene from an aqueous suspension of graphite.