APPARATUS

Abstract

A reactor for forming fully coated particles having a solid core, the reactor comprises a reactor vessel which is configured to receive particles, and a gas phase coating mechanism that is configured to selectively introduce pulses of gas phase materials that form a coating on the particles. The reactor also includes a sieve (16) that is located within the reactor vessel, and a forcing means that is configured to force the particles through the sieve (16) in use. The sieve is configured to deagglomerate any particle aggregates formed in the reactor vessel upon forcing of the particles by the forcing means through the sieve.

Claims

1. A reactor for forming a plurality of fully coated particles having solid cores, the reactor comprising: a reactor vessel configured to receive particles in the form of microparticles comprising a biologically active agent; a gas phase coating mechanism configured to selectively introduce pulses of gas phase materials that form a coating on the particles; at least one sieve located within the reactor vessel; and a forcing means configured to force the particles through the sieve in use, wherein the sieve is configured to deagglomerate any particle aggregates formed in the reactor vessel upon forcing of the particles by the forcing means through the sieve.

2. The reactor according to claim 1, wherein the forcing means comprises shaking, tapping, oscillating, tumbling, horizontal rotation, periodic displacement of the sieve, centrifugal force, sonic vibration, ultrasonic vibration, vacuum, air column, pressure gradient, gas flow, brushing, gravitational or a combination thereof.

3. The reactor according to claim 1, wherein the forcing means is integrated with the reactor vessel and is or includes ultrasonic vibration such that the vessel and sieve act as a sonic sifter.

4. The reactor according to claim 1, wherein the forcing means comprises a forcing aid to aid in forcing the particles through the sieve in use.

5. The reactor according to claim 1, wherein the ratio of the size of particles to the sieve mesh size is about 1:2.

6. The reactor according to claim 1, further comprising a plurality of sieves located within the reactor vessel, each sieve having progressively finer meshes in the direction of forceable movement of the particles.

7. The reactor according to claim 1, wherein the reactor vessel comprises more than one reactor chamber, the sieve being located between each neighbouring reactor chamber, the gas phase coating mechanism being configured to selectively introduce one or more pulses of gas phase material to the particles in one or each reactor chamber.

8. The reactor according to claim 7, further comprising a particle position changing means configured to action movement of the particles from one physical space in the reactor to another to permit subsequent forcing of the particles through the sieve.

9. The reactor according to claim 8, wherein the particle position changing means is a movement member configured to physically move each of the reactor chambers so as to switch places of the reactor chambers.

10. The reactor according to claim 9, wherein the movement member is configured to rotate the reactor chambers along a single axis to switch places of the reactor chambers.

11. The reactor according to claim 9, wherein the movement member is configured to switch places of the reactor chambers without rotation of the reactor chambers.

12. The reactor according to claim 9, wherein each reactor chamber includes a sieve located on an intermediate surface, the intermediate surface being located between neighbouring reactor chambers upon switching of their places so that a sieve is located between the reactor chambers at any given time.

13. The reactor according to claim 8 wherein the particle position changing means is a particle transport mechanism configured to transport the particles between each of the reactor chambers.

14. The reactor according to claim 8, wherein the particle position changing means includes a movement member configured to physically move each of the reactor chambers so as to switch places of the reactor chambers and a particle transport mechanism configured to transport the particles between each of the reactor chambers.

15. The reactor according to claim 7, further comprising a stop means positioned relative to each sieve to selectively prevent passing of the particles through the sieve into a neighbouring reactor chamber.

16.-17. (canceled)

18. The reactor according to claim 1, wherein the gas phase coating mechanism incorporates one of the following gas phase coating techniques: atomic layer deposition (ALD), atomic layer epitaxy (ALE), molecular layer deposition (MLD), molecular layer epitaxy (MLE), chemical vapor deposition (CVD), atomic layer CVD, molecular layer CVD, physical vapor deposition (PVD), sputtering PVD, reactive sputtering PVD, evaporation PVD, binary reaction sequence chemistry.

19. A method of forming fully coated particles comprising the steps of: i) providing a plurality of particles in the form of microparticles comprising a biologically active agent into a gas phase coating reactor; ii) subjecting those particles to pulses of gas phase materials by a gas phase coating technique so as to coat the particles; iii) forcing the coated particles through a sieve within the reactor to deagglomerate any particle aggregates formed during step ii); and iv) repeating steps ii) and iii) to form particles with a solid core, the solid core being fully enclosed by the coating formed by the gas phase coating technique.

20. The method according to claim 19, wherein step ii) includes subjecting the particles to pulses of gas phase materials by a gas phase coating technique so as to perform at least one ALD cycle and step iii) includes forcing the particles through the sieve after the at least one ALD cycle performed in step ii).

21. The reactor according to claim 1, wherein the gas phase coating mechanism is configured to introduce pulses of gas phase materials to perform at least one ALD cycle between the forcing means forcing the particles through the sieve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0131] Preferred embodiments of the invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings in which:

[0132] FIGS. 1a and 1b show schematic views of a reactor according to a first embodiment of the invention;

[0133] FIG. 2 shows a schematic view of a reactor according to a second embodiment of the invention;

[0134] FIG. 3a shows a schematic view of a reactor according to a third embodiment of the invention;

[0135] FIG. 3b shows the reactor of FIG. 3a as the chambers are switching places;

[0136] FIG. 4 shows a schematic view of a reactor according to a fourth embodiment of the invention;

[0137] FIGS. 5a to 5d show schematic views of a reactor according to a fifth embodiment of the invention;

[0138] FIG. 6 shows a schematic view of a reactor according to a sixth embodiment of the invention; and

[0139] FIG. 7 shows a schematic view of a reactor according to a seventh embodiment of the invention.

DETAILED DESCRIPTION

[0140] A reactor according to a first embodiment of the invention is shown in FIG. 1a and is designated generally by reference numeral 10.

[0141] The reactor 10 includes a reactor vessel 12 which has first and second reactor chambers 14a, 14b. In the embodiment shown, the first and second reactor chambers 14a, 14b are positioned as “upper” and “lower” chambers relative to the reactor 10. However, it is appreciated that the orientation of the first and second reactor chambers 14a, 14b may mean that they cannot be designated with such relative terms.

[0142] The reactor 10 is able to receive particles, e.g. via an inlet (not shown) into the first (i.e. upper) reactor chamber 14a. As previously stated in the application, the particles are preferably nanoparticles or, more preferably, microparticles. In the examples given below, the particles are typically in powder form.

[0143] The reactor 10 also includes a sieve 16 which is located inside the reactor vessel 12 between the first and second reactor chambers 14a, 14b. More specifically, in this embodiment, the sieve 16 is located on an intermediate surface 18 between the first and second reactor chambers 14a, 14b. The intermediate surface 18 being the surface which divides the first and second reactor chambers 14a, 14b.

[0144] As shown in FIG. 1b the reactor vessel 12 may include first and second shutters 15a, 15b located immediately above and below the sieve 16. The shutters can be controlled between an open position and a closed position so as to selectively act as a physical barrier (or stop) to the particles moving between the reactor chambers 14a, 14b and vice versa.

[0145] In other embodiments of the invention, instead of shutters being used to stop the particles moving between the reactor chambers 14a, 14b, a pressured air flow may instead be used to keep the particles in a desired reactor chamber 14a, 14b.

[0146] The reactor 10 further includes a forcing means 19 which is configured to force the particles through the sieve 16. In this embodiment, it is intended that the forcing means 19 is a generator which causes physical vibration of the reactor vessel 12 via a mechanical pulse. The forcing means 19 can also be located in the intermediate space 18.

[0147] Other suitable forcing means 19 may be used. For example, a sonic or ultrasonic generator may be used to produce high-frequency vibrations which are transmitted to the reactor vessel 12 and/or the sieve 16 itself. Alternatively, or in addition, a vertical air jet may be applied to the bottom of the sieve 16 surface and at the same time a vacuum acts in the opposite direction to the air jet so that the air jet deagglomerates the particles while the vacuum pulls the deagglomerated particles down through the sieve 16. Alternatively, or in addition, the reactor vessel 12 or reactor chambers 14a, 14b may be subjected to fast rotation so as to provide centrifugal force to the particles as they contact the sieve 16, thus causing deagglomeration. The forcing means 19 may instead be the shaking movement caused by tumbling/rotating of the first and second reactor chambers 14a, 14b. Alternatively, the forcing means may be a vibration that are introduced to the reactor chambers 14a, 14b by “punches” or “tapping” imparted on the chambers 14a, 14b and/or the sieve 16 by, e.g. a solenoid, (or other means of physically “punching” or “tapping” the chambers 14a, 14b and/or sieve 16). Alternatively, the forcing means 19 may be caused by oscillating the chambers 14a, 14b and/or the sieve 16. The forcing means 19 may instead be a pressure gradient force applied to the sieve 16 surface. Alternatively, the forcing means 19 may be the force applied due to horizontal rotation, e.g. of the sieve 16 and/or the chambers 14a, 14b. The forcing means 19 may instead be the force applied from periodic displacement/motion of the sieve 16.

[0148] Any suitable combination of one or more of the forcing means discussed above may be used. Exemplary combinations (which are non-limiting) include: oscillating and tapping, rotating and tapping, ultrasonic vibration and sonic vibration, sonic vibration and tapping, ultrasonic vibration and tapping, horizontal rotation and period displacement. The combination may be chosen to achieve the desired deagglomeration and/or to combine different functionalities of the forcing means. For example, ultrasonic vibration may be chosen to help clean the sieve 16 which may be combined with another forcing means to move the particles through the sieve 16.

[0149] Although not shown in the figures, the forcing means 19 may include a forcing aid. The forcing aid may be any one or a combination of the following: [0150] Brush cleaning with one or more brushes which brush over the sieve 16 to help break up particle aggregates, the brush(es) may sweep along the sieve surface 16 in a circular motion via an arm; [0151] Bouncing ball cleaning with a plurality of balls, e.g. hard 2 mm balls, that are bounced on the sieve surface to help break up particle aggregates; [0152] Air jet cleaning with a fan to blow air or gas into a central cavity and then out of j et arms which are aimed towards the sieve, the air jet may reach speeds of up to 120 m/s [0153] Use of a scraper, spatula or paddle in a similar manner to that described above in relation to brush cleaning, with the scraper/spatula/paddle typically being made from rubber.

[0154] The reactor 10 also includes a gas phase coating mechanism which is configured to introduce pulses of gas phase materials into one or both of the reactor chambers 14a, 14b so as to form a coating on the particles.

[0155] In the embodiment shown, the gas phase coating mechanism incorporates an atomic layer deposition (ALD) technique, although other related techniques may instead be used.

[0156] The general ALD technique is described in the introductory part of the application. The reaction chamber of an ALD process is under vacuum, typically 1 to 20 mbar for thermal ALD, although lower or higher pressures can be used. The temperature in the vacuum chamber is also well controlled and may typically be in the range of 20-300° C., although lower or higher temperatures can be used.

[0157] It can be typical to have some dislocation of the substrate in the ALD reaction chamber, for example rotating or tumbling or shaking of the chamber so as to keep the substrate

[0158] 20 moving during the process. However, the substrate, particularly particles (e.g. powder), is not forced through a sieve nor deagglomerated by such dislocation techniques. Instead, the particles are simply moved around in the reaction chamber.

[0159] With reference to the reactor 10 of the first embodiment of the invention, the gas phase coating mechanism applies ALD technique according to the following steps: [0160] a) Pulse 1: Introducing a first precursor in a gaseous state into the reactor chamber 14a, 14b which contains the particles to be coated. The precursor is adsorbed onto the surface of the particles to form an adsorbed (e.g. chemisorbed) layer of precursor molecule on all surfaces exposed to the gas. For example, the first precursor may be H2O in a gaseous state. The water terminates the surface with hydroxy (—OH) groups. [0161] b) Pulse 2: Introducing chemically inert rinse gas (e.g. N2 or Ar) to the reactor chamber 14a, 14b to rinse the reactor chamber 14a, 14b of excess of the first precursor. The excess also includes ligands from the precursor that detach from the precursor molecule when it adsorbs to the surface. All that remains on the particles is a monolayer of the first precursor. [0162] c) Pulse 3: Introducing a second precursor in a gaseous state into the reactor chamber 14a, 14b which contains the particles to be coated. The precursor reacts with the adsorbed first precursor to form a new substance (i.e. a new layer of a different chemical composition than before) which coats the particles. For example, the new substance that is formed on the particles may be aluminium oxide (Al.sub.2O.sub.3). [0163] d) Pulse 4: Introducing a chemically inert rinse gas (e.g. N2 or Ar) to the reactor chamber 14a, 14b to rinse the reactor chamber 14a, 14b of excess of the second precursor and ligands from the precursor that detach from the precursor molecule when it adsorbs to the surface and any by-products from the reaction between the first and second precursors. All that remains on the particles is essentially a monolayer of the reaction product, e.g. Al.sub.2O.sub.3.

[0164] The four pulses described above represent a so-called “ALD cycle”, which can be repeated several times as an “ALD set”. For example, an ALD set may consist of 10, 25 or 100 cycles.

[0165] An ALD pulse can in consist of many pulses, e.g. a pulse may be repeated 2-1000 times with purging or evacuation in between. A set of repeating ALD pulses are referred to as multipulses.

[0166] The skilled person would readily understand the components required to carry out such an ALD technique, as well as the interface of such components with the reactor vessel 12, and so such components are not discussed here.

[0167] In the first embodiment, an ALD cycle is performed in the first (upper) reactor chamber 14a, and so the appropriate ALD gases, i.e. precursor and rinse gases, would be introduced as pulses through an upper inlet 21 and out through an upper outlet 21′ at the first reactor chamber 14a. Alternatively the appropriate precursor and rinse gases can instead be introduced as pulses through an upper inlet 23 and out through a lower outlet 23′ at the second (lower) reactor chamber 14b.

[0168] The forcing means 19 is configured to force the particles through the sieve 16 in use, and the sieve 16 is configured to deagglomerate any particle aggregates formed in the reactor vessel 12. The ratio of the size of particles to the sieve mesh size may be 1:2. For example, for particle sizes in the region of 10 μm, a 20 μm sieve mesh could be used. The ratio of the size of particles to the sieve mesh size may be 1:4. For example, for particle sizes in the region of 5 μm, a 20 μm sieve mesh could also be used.

[0169] The sieve 16 may take any suitable form. For example, the sieve 16 may have a sieve mesh that is made from threads or wires, e.g. it may be a woven wire sieve 16. The sieve 16 may instead be in the form of a perforated plate sieve, a microplate sieve, a grid sieve or a diamond sieve.

[0170] The reactor 10 further includes a particle position changing means 22, in the form of a movement member 24. The movement member 24 has an axle 26 secured to the reactor vessel 12 which is rotated so as to rotate the whole reactor vessel 12 along the axis of the axle 26 (i.e. the horizontal axis in the example shown). Rotation of the reactor vessel 12 results in the first and second reactor chambers 14a, 14b switching places with one another. In other words, the reactor chamber 14a, 14b which was the upper chamber becomes the lower chamber and vice versa. In this way, the particles are moved from one physical space in the reactor 10, e.g. the space of the lower chamber before rotation, to another physical space in the reactor 10, e.g. to the space of the upper chamber after rotation.

[0171] The reactor 10 may further include anti-static electricity prevention equipment. Such equipment may be included within the reactor 10 at suitable locations, such as within the reactor chambers 14a, 14b, so as to remove static energy from the particles and/or parts of the reactor 10.

[0172] In use, particles, in this case a powder, are introduced to the first (upper) reactor chamber 14a. The ALD process coats the particles using one ALD cycle. The ALD gases are introduced to the upper chamber 14a through the upper inlet 21 and extracted through the upper outlet 21′. The ALD gases can also be extracted from the lower outlet 23′ in the second (lower) reactor chamber 14b. The particles are forced through the sieve 16 by the vibration caused by the generator of the forcing means 19, so that the particles are forced into the second (lower) reactor chamber 14b.

[0173] The reactor vessel 12 can also include first and second shutters 15a, 15b located immediately above and below the sieve 16, as shown in FIG. 1b. The shutters 15a, 15b can be controlled between an open position and a closed position so as to selectively act as a physical barrier (or stop) to the particles moving between the reactor chambers 14a, 14b.

[0174] In use, the shutters 15a, 15b are in a closed position during the ALD process and are opened prior to forcing the particles through the sieve 16. Particles that have aggregated together during the ALD process are deagglomerated by the forceable sieving. These particles will have pinholes of uncoated surface area such that the core (what was the original particle) may be exposed.

[0175] In both of the examples shown in FIGS. 1a and 1b, the movement member 24 then rotates the reactor vessel 12 along the movement member axle 26 so that the reactor chambers 14a, 14b switch places. The second reactor chamber 14b, which was the lower chamber, that contains the coated particles is now located as the upper chamber in the reactor 10. The ALD process is then repeated. These steps may be repeated any number of times to achieve fully coated particles. The steps may also be repeated a further number of times to achieve the desired thickness of coating.

[0176] In other embodiments of the invention, an ALD set (i.e. several ALD cycles) may be performed to the particles in the reactor chamber 14a, 14b before rotation of the reactor chambers 14a, 14b is carried out. Thus, the particles are forced through the sieve (and therefore deagglomeration is performed) after every ALD set.

[0177] In further embodiments, a single pulse is performed to the particles in the reactor chamber 14a, 14b before rotation of the reactor chambers 14a, 14b is carried out. Thus, the particles are forced through the sieve (and therefore deagglomeration is performed) after each pulse.

[0178] In any event, the fully coated particles with the desired coating thickness are finally removed from the reactor vessel 12 by an outlet (not shown) or by disassembling the reactor 12.

[0179] It may be necessary (depending upon how the particles are initially provided) to wash and/or clean them to remove impurities that may derive from their production, and then dry them before carrying out the steps outlined above. Drying may be carried out by way of numerous techniques known to those skilled in the art, including evaporation, spray-drying, vacuum drying, freeze drying, fluidized bed drying, microwave drying, IR radiation, drum drying, etc. If dried, the particles may then be deagglomerated by grinding, screening, milling and/or dry sonication. Alternatively, the particles may be treated to remove any volatile materials that may be absorbed onto its surface, e.g. by exposing the particle to vacuum and/or elevated temperature.

[0180] Surfaces of the particles may be chemically activated prior to applying the first inorganic coating, e.g. by treatment with hydrogen peroxide, ozone, free radical-containing reactants or by applying a plasma treatment, in order to create free oxygen radicals at the surface of the particle. This in turn may produce favorable adsorption/nucleation sites on the particles for the ALD precursors.

[0181] In ALD, coatings may be applied at process temperatures from about 0° C. to about 800° C., or from about 40° C. to about 200° C., e.g. from about 40° C. to about 150°, such as from about 30° C. to about 100° C. The optimal process temperature depends on the reactivity of the precursors and/or the substances (including biologically-active agents) that are employed in the particles and/or melting point and/or vapor pressure of the particle substance(s).

[0182] In most instances, the first of the consecutive reactions will involve some functional group or free electron pairs or radicals at the surface to be coated, such as a hydroxy group (—OH) or a primary or secondary amino group (—NH.sub.2 or —NHR where R e.g. is an aliphatic group, such as an alkyl group). The individual reactions are advantageously carried out separately and under conditions such that all excess reagents and reaction products are essentially removed before conducting the subsequent reaction.

[0183] A reactor according to a second embodiment of the invention is shown in FIG. 2 and is designated generally by reference numeral 50.

[0184] The reactor 50 of the second embodiment of the invention is similar to the reactor 10 of the first embodiment of the invention, and like features share the same reference numerals.

[0185] The reactor 50 of the second embodiment differs from the reactor 10 of the first embodiment in that the forcing means 52 is integrated with the reactor vessel 12 such that the vessel 12 and sieve 16 act as a sonic sifter. In particular, the top of the first (upper) reactor chamber 14a and the bottom of the second (lower) reactor chamber 14b is fabricated from a polymeric material, preferably an elastomer, to form a polymer membrane 54. Moreover, the sieve 16 is also fabricated from a polymeric material, preferably an elastomer. Sound waves or ultrasonic sound waves are applied to the reactor vessel 12 via a generator (not shown) such that the whole vessel 12 acts as a sonic sifter with the sound travelling through the polymer membranes 54 and polymer sieve 16.

[0186] Operation of the reactor 50 of the second embodiment is the same as the reactor 10 of the first embodiment, but with the mechanical pulse being replaced with the sonic sifter as outlined above.

[0187] A reactor according to a third embodiment of the invention is shown in FIGS. 3a and 3b and is designated generally by reference numeral 60.

[0188] The reactor 60 of the third embodiment of the invention is similar to the reactor 10 of the first embodiment of the invention, and like features share the same reference numerals.

[0189] The reactor 60 of the third embodiment differs from the reactor 10 of the first embodiment in that each of the first and second reactor chambers 14a, 14b has a sieving surface 62 which is made from a sieve mesh. The sieving surface 62 is located towards the bottom end of each first and second reactor chamber 14a, 14b.

[0190] Moreover, each of the first and second reactor chambers 14a, 14b has a shutter surface 64 both at the top and bottom surfaces of the chambers 14a, 14b, so that when the reactor chambers 14a, 14b are switched places with one another (as described in more detail below), there is always a shutter surface 64 of each chamber 14a, 14b located between the chambers 14a, 14b.

[0191] The movement member (not shown in FIG. 3a or 3b) is configured to switch places of the first and second chambers 14a, 14b without rotation. For example, the movement member may remove each of the chambers 14a, 14b out of line with one another and insert them back into line with one another in the opposite order, as indicated by FIG. 3b. The movement member in such an embodiment may do this simultaneously or sequentially.

[0192] In contrast to the first embodiment reactor 10 in which the reactor chambers 14a, 14b form a single, integrated unit, the first and second reactor chambers 14a, 14b of the second embodiment reactor 60 are individual, discrete chambers (as shown in FIG. 3b).

[0193] Operation of the reactor 60 of the third embodiment is the same as the reactor 10 of the first embodiment, but with the movement member switching places of the first and second reactor chambers 14a, 14b without rotation. Moreover, the shutter surfaces 64 of each chamber 14a, 14b that are positioned between the two chambers 14a, 14b are controlled to be in an opened position when the particles are being forced through the sieve 62, and are controlled to be in a closed position when the reactor chambers 14a, 14b are being switched places.

[0194] A reactor according to a fourth embodiment of the invention is shown in FIG. 4 and is designated generally by reference numeral 70.

[0195] The reactor 70 of the fourth embodiment of the invention is similar to the reactor 10 of the first embodiment of the invention, and like features share the same reference numerals.

[0196] The reactor 70 of the fourth embodiment differs from the reactor 10 of the first embodiment in that the first and second chambers 14a, 14b each include respective first and second secondary sieves 27a, 27b. The mesh size of each secondary sieve 27a, 27b may be smaller than the size of the particles being introduced into the reactor 12.

[0197] The ALD process (a pulse, cycle or set) is performed in the second (lower) chamber 14b. The particles are placed on the second (lower) secondary sieve 27b and ALD gases are introduced through the lower inlet 23 and extracted through the lower outlet 23′ or through the upper outlet 21′ in the same way as in the first embodiment.

[0198] The reactor 70 can then be rotated to switch places of the reactor chambers 14a, 14b (or otherwise switched places without rotation, as described in relation to the third embodiment), and the ALD process is repeated. The particles are forced through the second (lower) secondary sieve 27b by a forcing means (not shown) either before or after the reactor 70 is rotated, depending on the nature of rotation of the reactor 70. The particles are then also forced through the sieve 16, which lies between the reactor chambers 14a, 14b by a forcing means so that the particles are moved from one chamber to the other 14a, 14b (as described in the previous embodiments).

[0199] This process is repeated until fully coated particles with a desired coating thickness are achieved.

[0200] Any suitable forcing means as previously described could be used for forcing of the particles through the secondary sieves 27a, 27b.

[0201] In other embodiments of the invention, the particle position changing means is a particle transport mechanism which is configured to transport the particles from the second (lower) chamber 14b to the first (upper) chamber 14a after ALD has been carried out in the second (lower) chamber 14b. In this way, the reactor chambers 14a, 14b themselves do not need to be moved (rotated or otherwise).

[0202] A reactor according to a fifth embodiment of the invention is shown in FIGS. 5a to 5d and is designated generally by reference numeral 80.

[0203] The reactor 80 of the fifth embodiment of the invention is similar to the reactor 10 of the first embodiment of the invention, and like features share the same reference numerals.

[0204] The reactor 80 of the fifth embodiment differs from the reactor 10 of the first embodiment in that it includes a selective gas flow means 82 to form a particle bed flow 84 in each reactor chamber 14a, 14b in turn.

[0205] In particular, the gas flow means 82 provides a flow of gas at a high pressure from the second (lower) reactor chamber 14b to the first (upper) reactor chamber 14a, which forms a “flowing” particle bed 84, as would be found on a flushbed, in the first (upper) reactor chamber 14a. In other words, the gas flow means 82 keeps the floating particles 84 in the first (upper) reactor chamber 14a, as shown in FIG. 5a.

[0206] An ALD set, cycle or pulse can be performed in the first (upper) reactor chamber 14a while the particles are being held in place by the gas flow means 82.

[0207] The gas flow means 82 switches to provide a flow of gas at high pressure from the first (upper) reactor chamber 14a to the second (lower) reactor chamber 14b. The gas flow means 82 are thereafter switched off and the particle bed 84 is therefore pushed through the sieve 16, which deagglomerates any aggregate particles formed during the ALD process. This step is shown in FIG. 5b.

[0208] The particles being forced through the sieve 16 by the gas flow may be aided by vibrations to the reactor vessel 12 (e.g. physical, sonic, ultrasonic). As mentioned previously, a forcing aid may also be used, such as balls, brushes, paddles etc.

[0209] The flowing particle bed 84 is now in the second (lower) chamber, as shown in FIG. 5c. As indicated in FIG. 5c, the reactor chambers 14a, 14b are then rotated, in the same manner as described above in relation to the first embodiment of the invention, so that the reactor chambers 14a, 14b switch places.

[0210] The flowing particle bed 84 is still in the second chamber 14b, but the second reactor chamber 14b is now the upper chamber, as shown in FIG. 5d.

[0211] The ALD process is repeated in the second (now upper) reactor chamber 14b, and the gas flow means 82 is again switched to force the particles through the sieve 16. The ALD and forced sieving steps are repeated to form fully coated particles with a desired coating thickness.

[0212] As with the reactor 10 of the first embodiment, the first and second reactor chambers 14a, 14b may instead be switched places by means other than rotation.

[0213] Moreover, in other embodiments of the invention, after the flowing particle bed 84 has been forced through the sieve 16 from the first (upper) reactor chamber 14a to the second (lower) reactor chamber 14b (i.e. after the step shown in FIG. 5b), the ALD process (i.e. an ALD set, cycle or pulse) may be performed in the second (lower) reactor chamber 14b. The gas flow means 82 may then force the flowing particle bed 84 back through the sieve 16 from the second (lower) reactor chamber 14b to the first (upper) reactor chamber 14a. the ALD process (e.g. an ALD set, cycle or pulse) may then be carried out in the first (upper) reactor chamber 14a. This process is repeated as desired. In this way, no movement of the reactor chambers 14a, 14b is needed. Moreover, the forcing means (i.e. the gas flow means 82) is the particle position changing means (i.e. a particle transport mechanism) in such an embodiment.

[0214] A reactor according to a sixth embodiment of the invention is shown in FIG. 6 and is designated generally by reference numeral 90.

[0215] The reactor 90 of the sixth embodiment of the invention is similar to the reactor 10 of the first embodiment of the invention, and like features share the same reference numerals.

[0216] The reactor 90 of the sixth embodiment differs from the reactor 10 of the first embodiment in that it includes two sieves 92a, 92b within the reactor vessel 12. The sieves 92a, 92b are spaced from one another to form three associated reactor chambers 14a, 14b, 14c.

[0217] The sieves 92a, 92b each have a finer mesh in the direction of forceable movement 94 of the particles. In this embodiment, the upper sieve 92a has a finer sieve mesh than the lower sieve 92b since the particles are forced from the bottom of the reactor vessel 12 upwards.

[0218] In the latter regard, the reactor 90 includes a gas flow means 96 which provides high pressure gas flow from the bottom of the reactor vessel 12 so as to force the particles upwards through the lower and upper sieves 92b, 92a in turn.

[0219] In other embodiments of the invention, there may be more than two sieves 92a, 92b, each having a finer mesh in the direction of forceable movement 94 of the particles.

[0220] As shown, the gas phase coating mechanism, i.e. via an inlet 21 and outlet 21′, is configured to perform an ALD process in the uppermost chamber 14a. The gas phase coating mechanism may perform an ALD set, cycle or pulse in the uppermost chamber 14a. After which time, a particle position changing means 22, in the form of a particle transport mechanism 98, transports the particles from the uppermost chamber 14a to the lowermost chamber 14c. The gas flow means 96 then forces the particles again up through the sieves 92a, 92b. This deagglomeration is carried out after each ALD set, cycle or pulse.

[0221] This process is repeated until the particles are fully enclosed in the coating and the coating has a desired thickness.

[0222] A reactor according to a seventh embodiment of the invention is shown in FIG. 7 and is designated generally by reference numeral 100.

[0223] The reactor 100 of the seventh embodiment of the invention is similar to the reactor 10 of the first embodiment of the invention, and like features share the same reference numerals.

[0224] The reactor 100 of the seventh embodiment differs from the reactor 10 of the first embodiment in that it includes a plurality of reactor chambers 102a, 102b, 102c . . . 102l stacked together in a tower configuration. In this embodiment there are 12 reactor chambers 102a-102l with a sieve 16 positioned between each neighboring chamber 102a-102l.

[0225] In this embodiment, each reactor chamber 102a-102l performs an ALD pulse, and the particles are forced through each sieve 16 in turn after each pulse. Thus, deagglomeration is carried out between each pulse of an ALD cycle.

[0226] The particles are forced through each sieve 16 by the forcing means (not shown) which may be any suitable form as already described in this application.

[0227] As a further explanation, the gas phase coating mechanism, i.e. via the inlet 21 and outlet 21′, at the first reactor chamber 102a introduces the first precursor (e.g. H.sub.2O in gaseous form), i.e. pulse 1. The forcing means, e.g. a sonic sifter, forces the partially coated particles through the neighboring sieve 16 and into the second reactor chamber 102b. The gas phase coating mechanism, i.e. via the inlet 23 and outlet 23′, at the second reactor chamber 102b introduces the rinse gas (e.g. N2) to rinse the reaction chamber and particles from excess of the first precursor, i.e. pulse 2. The forcing means again forces the partially coated particles through the next neighboring sieve 16 and into the third reactor chamber 102c. The gas phase coating mechanism 21, 21′ at the third reactor chamber 102c introduces the second precursor, i.e. pulse 3. The forcing means once again forces the coated particles through the neighboring sieve 16 and into the fourth reactor chamber 102d. The gas phase coating mechanism 23, 23′ at the fourth reactor chamber 102d introduces the rinse gas (e.g. N2) to rinse the reactor chamber and particles of excess of the second precursor and any by-products from the reaction between the first and second precursors.

[0228] If this number of pulses, i.e. one ALD cycle, is sufficient to fully coat the particles (which is a possibility since deagglomeration is taking place every pulse) and the desired coating thickness has been reached, then the reactor 100 would include only 4 reactor chambers 102a, 102b, 102c, 102d and the fully coated particles would be removed from the fourth reactor chamber 102d. If, however, further cycles are required, then the reactor 100 would include the required further reactor chambers 102e, 102f . . . 102l (as shown in FIG. 7) and the alternating gas pulse and deagglomeration steps would be repeated.

[0229] As indicated, any number of reactor chambers 102a-102l can be added to the reactor 100 so that the alternating ALD pulse and deagglomeration process can be repeated a desired number of times. Theoretically, there could be hundreds of reactor chambers 102a-102l.

[0230] The particles are fed into the reactor 100 at an inlet 104 at the first reactor chamber 102a, and the fully coated particles exit the reactor 100 at an outlet 106 at the last reactor chamber 1021. In this way, new particles can be continuously fed into the reactor 100 at the inlet 104 while a previous batch of particles are still making their way through the reactor 100. The feed rate can be adjusted in relation to the product output at the outlet 106.

[0231] In other embodiments of the invention, each reactor chamber 102a-102k may perform more than one ALD pulse. For example, each reactor chamber 102a-102l may perform an ALD cycle (e.g. four pulses), so that deagglomeration is carried out between each ALD cycle. Alternatively, each reactor chamber 102 may perform an ALD set (e.g. 25 cycles) so that deagglomeration is carried out between each ALD set. In such embodiments, the reactor 100 may include a particle position changing means (either in the form of a movement member or a particle transport mechanism) which is configured to action movement of the particles from one reactor chamber 102 to another, thus allowing the ALD and deagglomeration process to be repeated.

[0232] For example, the reactor 100 may include four reactor chambers 102a, 102b, 102c, 102d, each of which is configured to carry out an ALD pulse with deagglomeration in between each pulse. After the four pulses have been completed (i.e. one ALD cycle), the whole reactor vessel 12 may be rotated by a movement member (in a similar manner to that described in relation to the first embodiment of the invention) so that the particles that were in the lowermost chamber are then in the uppermost chamber. The ALD pulse and deagglomeration process can then be repeated any number of times.