GB2175709A - Controlling flow of particles - Google Patents

Abstract

An apparatus for controlling a flow of fine particles comprises a plurality of convergent-divergent nozzles 1 in the flow path of said fine particles. The particles impinge on a target 6 in a vacuum chamber 4. The particles may be ionised. <IMAGE>

Description

SPECIFICATION Apparatus for controlling flow of fine particles BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an apparatus for controlling a flow of fine particles, employed for transportation or blowing of fine particles and adaptable to film forming, formation of composite material, doping etc. with fine particles, or a field of fine particle formation.

In the present specification, "fine particles" include atoms, molecules, ultra-fine particles and general fine particles. "Ultra-fine particles" mean those generally smaller than 0.5 ,um, obtained for example by evaporation in gas, plasma evaporation, chemical vapor reaction, colloidal precipitation in a liquid or pyrolysis of liquid spray. "General fine particles" mean fine particles obtained by ordinary methods such as mechanical crushing, crystallization or precipitation. "A beam" means a flow with a substantially constant cross section along the flow direction independently of the geometry of said cross section.

Description of the Related Art In general, fine particles are dispersed and suspended in a carrier gas and are transported by the flow of said carrier gas.

Conventionally, the control of flow of fine particles in the transportation thereof has merely been achieved by defining the entire flow of fine particles flowing together with a carrier gas by means of a pipe or a casing, utilizing the pressure difference between the upstream and downstream sides. Consequently the flow of fine particles is inevitably dispersed over the entire pipe or casing defining the flow path, though there is certain distribution in the flow.

In case of defining the entire flow path of fine particles with a pipe or a casing and of transporting the fine particles with carrier gas along said flow path by means of the pressure difference between the upstream and downstream sides, a gas flow-out at the downstream side for generating said pressure difference not only induces the flow-out of fine particles but also is unable to achieve a very high transport velocity. Also the fine particles inevitably contact the walls of the pipe or casing defining the flow path over the entire course of transportation.

Therefore, in case of iransporting active fine particles to a desired site, there may result a loss in activity by the time elapsed in said transportation or by contact with the walls of the pipe or casing. Also the defining of the entire flow path of fine particles with a pipe or casing may result, for example by the formation of a dead space in the flow, in a lowered trapping rate of the fine particles and a lowered utilization efficiency of the carrier gas for fine particle transportation, and it is disadvantageous for transportation of a large quantity of fine particles.

On the other hand, in case of blowing the fine particles to a substrate, they are generally ejected with carrier gas from a nozzle. The nozzle employed in such fine particle blowing is a straight or convergent nozzle, and the cross section of the flow of fine particles immediately after the ejection is constricted according to the area of the nozzle outlet. However the flow is at the same time diffused at the nozzle outlet, so that said constriction is only temporary and the flow velocity does not exceed acoustic velocity.

That is to say, the conventional straight or covergent nozzle generates a diffused flow in which the fine particles show a large distribution in density. Therefore, in case of blowing fine particles onto a substrate, it is difficult to achieve uniform blowing, to control the area in which such uniform blowing is obtained, and to perform blowing over a broad area.

The United States Patent No. 4,200,264 discloses an apparatus for producing metallic Mg or Ca by carbon reduction method.

In said apparatus, a reduction reaction is caused by heating an oxide of Mg or Ca with carbon in a reaction chamber, and the resulting gaseous mixture is introduced into a divergent nozzle to cause adiabatic expansion for cooling thereby obtaining fine particles of Mg or Ca.

The divergent nozzle in said apparatus achieves instantaneous cooling of the mixture of Mg (or Ca) and CO to prevent the reverse reaction therebetween, utilizing a fact that said nozzle rapidly cools the passing gaps by adiabatic expansion, and is utilized for separating Mg (or Ca) and CO.

In this case, said divergent nozzle functions under a condition of underexpansion.

In other words, the divergent nozzle in the aforementioned apparatus is utilized as means for preventing reverse reaction of the products, Mg (or Ca) and CO, and separating said products before they are introduced into condensers, but is not utilized as reaction control means for maintaining the products as an easily processable beam flow. That is to say, the use of a divergent nozzle for rapid cooling to a temperature suitable for preventing a reaction, or for accelerating the products to a desired velocity is irrelevant to the state of flow of the gas that has passed the nozzle.

In case the pressure in the throat of the divergent nozzle is below the critical pressure, the gas flow from the divergent nozzle is decelerated, diffused after ejection and does not reach the acoustic velocity. On the other hand, if the pressure in said throat is equal to or higher than the critical pressure, the ejecting velocity from the nozzle can be supersonic but the state of flow after ejection is determined by whether the pressure Pj of the gas flow at the ejection approximately coincides with the pressure P in the downstream side of the divergent nozzle. A state of Pj=P is called an optimum expansion, while a state of pj > P is called underexpansion, and a state of Pj < P is called overexpansion.In case of the optimum expansion, the gas passing through the divergent nozzle flows along the internal wall at the outlet of said nozzle and is ejected as a flow having a uniform distribution of speed in the cross-sectional direction. On the other hand, in case of underexpansion or overexpansion, the flow is decelerated and is diffused.

However, the divergent nozzle in the aforementioned apparatus is employed, as explained above, in a mode irrelevant to the formation of flow under optimum expansion, so that the flow ejected from the divergent nozzle is inevitably diffused. Once such diffused flow is generated, the products in finely powdered state are diffused in the entire capturing chamber, and a part of such products contacts the walls thereof, thus causing deposition thereon or losing activity.

These phenomena lead to various drawbacks such as a loss in production yield and contamination of the reaction products with unreacted substances. Further, the reaction products transported in a diffused flow are difficult to capture and results also in a lowered yield. Besides, certain raw materials or reaction products require activation by plasma or laser beam irradiation after passing the nozzle, but such activation is difficult to achieve in a diffused flow, so that a general-purpose reaction apparatus is difficult to obtain.

SUMMARY OF THE INVENTION The present invention is to overcome the above-explained problems.

More specifically, an object of the present invention is to provide a flow control apparatus for generating a plurality of flows of fine particles with a substantially constant cross section (i.e. as beams) and with minimum diffusion.

Another object of the present invention is to provide a flow control apparatus enabling efficient trapping of a large quantity of fine particles of a limited life, for example active fine particles, without loss in activity thereof.

According to the present invention, there is provided an apparatus for controlling a flow of fine particles, comprising a plurality of convergent-divergent nozzles in a flow path.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view showing the basic principle of the present invention; Figure 2 is a schematic view of a film-forming apparatus with ultra-fine particles embodying the present invention; Figures 3A to 3C are views showing embodiments of gas exciting means; Figures 4A to 4D are views showing different shapes of the convergent-divergent nozzle; Figures 5A and 5B are views of different examples of a skimmer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Convergent-divergent nozzles 1 employed in the present invention have an aperture cross section which, as shown in Fig. 1, is gradually reduced from an inlet la to an intermediate throat 2 and is then gradually enlarged toward an outlet 1 b. For the convenience of explanation, in Fig. 1, the inlet and outlet of the convergent-divergent nozzle 1 are respectively connected to a closed upstream chamber 3 and a closed downstream chamber 4. However, the inlet and outlet of the convergent-divergent nozzle 1 of the present invention may be connected to closed or open systems as long as the fine particles are caused to pass together with carrier gas by a pressure difference therebetween.Further, although the apparatus in Fig. 1 are furnished exemplarily with three convergent-divergent nozzles, the number thereof may be two or four or more.

In the present invention, a pressure difference between the upstream chamber 3 and the downstream chamber 4 is generated, as shown in Fig. 1, by supplying the upstream chamber 3 with carrier gas in which the fine particles are dispersed in a suspension state, and evacuating the downstream chamber 4 with a vacuum pump 5, whereby the supplied carrier gas containing the fine particles flows from the upstream chamber 3 to the downstream chamber 4 through the plural convergent-divergent nozzles 1.

The respective convergent-divergent nozzles 1 perform functions not only of ejecting the fine particles together with carrier gas according to the pressure difference between the upstream and downstream sides, but also of rendering the ejected flow of carrier gas and fine particles uniform. Such a plurality of uniform flows of fine particles can be utilized for blowing the fine particles uniformly onto a wide area of a substrate 6.

The respective convergent-divergent nozzles 1 are capable of accelerating the flow of fine particles ejected with the carrier gas, by suitable selection of a pressure ratio P/PO of the pressure P in the downstream chamber 4 to the pressure P0 in the upstream chamber, and a ratio A/A of the aperture cross-sectional area A of the outlet 1 b to that A of the throat 2. If said ratio P/PO of the pressures in the upstream and downstream chambers 3, 4 is above the critical ratio of pressure, the flow velocity at the outlets of the nozzles 1 becomes subsonic or less, and the fine particles and the carrier gas are ejected at a reduced velocity.On the other hand, if said pressure ratio P/PO is below the critical ratio of pressure, said flow velocity at the outlets becomes supersonic, so that the fine particles and the carrier gas are ejected at an supersonic velocity.

If the flows of the fine particles are assumed to compressive one-dimensional flows with adiabatic expansion, the Mach number M that can be reached by the flow is determined by the pressure P0 of the upstream chamber and the pressure P of the downstream chamber, according to a following formula:

wherein u is the velocity of the fine particle flow, a is the local acoustic velocity at this point, and y is the ratio of specific hearts of said fluid; and M exceeds 1 when the ratio P/PO is below the critical ratio of pressure.

The acoustic velocity a can be determined by a formula:

wherein T is the local temperature and R is gas constant. Also there stands a following relation among the aperture cross sections A and A respectively of the outlet 1b and throat 2, and the Mach number M:

The flow reaches a state of optimum expansion flow in case the mach number M determined by the equation (1) as a function of the pressure ratio P/PO of the unstream chamber 2 and the downstream chamber 3 coincides with the Mach number determined by the equation (2) as a function of the aperture area A of the outlet 1b and the aperture area A of the throat 2.It is therefore possible to regulate the velocity of the flows of fine particles ejected from the nozzles 1, by selecting the aperture ratio A/A* according to the Mach number M determined by the equation (1) from the pressure ratio P/PO of the upstream and downstream chambers, or by regulating said ratio P/PO according to the value of M determined by the equation (2) from the aperture ratio A/A*. The velocity u of the flow of fine particles can be determined by a following equation (3):

Optimum expansion flows ejected from the outlets 1 b of the nozzles 1 flow along the inner walls of the outlets 1 b with a substantially uniform velocity distribution in the cross section and are formed as beams.The beam formation minimizes the diffusion and allows to maintain the fine particles, ejected from the nozzles 1, in a spatially independent state from the walls of the downstream chamber 3, thus preventing undesirable effects caused by contact with the walls.

The loss in yield caused by diffusion can also be prevented if the flows are captured in the beam state by a substrate 4. Furthermore the activation of the powdered raw materials or reaction products with plasma or laser beam irradiation can be more effectively achieved by effecting such energy supply onto the flows in a beam state. For obtaining optimum expansion flows, pressure sensors are provided at or around the outlets of the nozzles and the downstream chamber respectively, and P0 at the upstream portion and P at the downstream portion are controlled so that the pressure arround the outlets and in the downstream chamber detected by the sensors may be approximately equal to each other.

The state of flows of the fine particles can be maintained at a state determined by the aperture area ratio A/A*, if the pressure ratio P/PO of the upstream chamber 3 and the downstream chamber 4 is maintained constant. Accordingly the vacuum pump 5 for evacuating the downstream side or the downstream chamber 4 has to be able to maintain said chamber at a constant pressure independently of the inflow of the fine particles through the convergent divergent nozzles 1, if the upstream chamber 3 is maintained at a constant pressure.

The mass that can be evacuated by a vacuum pump generally depends on the capacity of said pump. However, if the flow rate through the nozzles is selected smaller than the evacuation rate of the pump, the pressure in the downstream chamber 4 can be maintained constant by regulating the flow rate through the pump substantially equal to the flow rate through the nozzles, for example with a valve. Particularly by selecting the cross-sectional area of the throat 2 of the convergent divergent nozzles 1 in such a manner that the flow rate through said nozzles 1 becomes equal to the effective evacuation rate of the pump, the flow of the fine particles is subjected to optimum expansion at the nozzle outlets 1 b without the regulation of flow velocity by the valve or the like, and a maximum flow velocity within the performance of the pump can be stably obtained.

The flow rate through the nozzles and the flow rate of evacuation are represented by mass flow rate, respectively.

The nozzle flow rate in through a convergent-divergent nozzle 1 is determined by the following equation (4):

and is determined by the aperture cross-sectional area A of a throat 2 if the pressure P and temperature To of the upstream chamber 3 are constant.

Incidentally, in an ejection with a pressure ratio P/PO above the critical ratio, the ejected carrier gas and fine particles form a uniform diffusing flow, so that the fine particles can be blown uniformly over a relatively wide area.

On the other hand, the carrier gas and fine particles, if ejected in the form of highspeed flows, constitute beams, substantially maintaining the cross section immediately after the ejection.

Consequently the fine particles, transported by carrier gas, also constitute a plurality of beams which are transported at a highspeed in the downstream chamber 4, with minimum diffusion and spatially without interference with the walls of the downstream chamber 4, so that the evacuation of the fine particles by the pump 5 can be easily prevented.

It is therefore rendered possible to capture active fine particles on the substrate 6 in the downstream chamber 4 in satisfactory active state, by generating said active fine particles in the upstream chamber 3 and transporting said particles through the nozzles 1, or by generating said active fine particles in or immediately after the nozzles 1 and transporting the particles, in the form of a plurality of spatially independent supersonic beams. It is therefore possible to capture a large quantity of fine particles in a properly active state. Also the region of capture can be easily controlled over a wide area, i.e. the sum of respective beam areas, since the fine particles are blown onto the substrate 6 in the form of a plurality of beams with a cross section substantially constant along the flow.

Fig. 2 schematically shows an embodiment in which the present invention is applied to an apparatus for film formation with ultra-fine particles, wherein illustrated are these convergentdivergent nozzles 1; an upstream chamber 3; a first downstream chamber 4a; and a second downstream chamber 4b.

The upstream chamber 3 and the first downstream chamber 4a are constructed as an integral unit, and, to said first downstream chamber 4a, there are detachably connected a skimmer 7, a gate valve 8 and a second downstream chamber 4b in similar unit structures, through flanges of a common diameter, which will hereinafter be referred to as common flanges. The upstream chamber 3, first downstream chamber 4a and second downstream chamber 4b are maintained at successively higher degrees of vacuum by a vacuum system to be explained later.

To the upstream chamber 3 there is connected, by a common flange, a gas exciting means 9 which generates active ultra-fine particles by plasma and sends said particles to the confronting three convergent-divergent nozzles 1, together with carrier gas such as hydrogen, helium, argon or nitrogen. The upstream chamber 3 may be provided with an anti-adhesion treatment on the inner walls thereof, in order to prevent the adhesion of thus generated ultra-fine particles onto said inner walls. Due to the pressure difference between the upstream chamber 3 and the first downstream chamber 4a caused by the higher degree of vacuum in the latter, the generated ultra-fine particles flow, together with said carrier gas, through the respective nozzles 1 to the first downstream chamber 4a.

As shown in Fig. 3A, the gas exciting means 9 comprises a rod-shaped first electrode 9a and a tubular second electrode 9b. While the carrier gas and the raw material gas are supplied into the second electrode 9b, and electric discharge is induced between both electrodes. Also in the gas exciting means 9, as shown in Fig. 3B, the second electrode 9b may incorporate a first electrode 9a with plural pores whereby the carrier gas and the raw material gas are supplied through the first electrode 9a to the space between both the electrodes.

Also as shown in Fig. 3C, a semi-circular first electrode 9a and a second electrode 9b of a similar structure may be assembled through insulators 9c composed for example of quartz or ceramics, and thereby the carrier gas and the raw material gas be supplied into the thus formed pipe.

The respective convergent-divergent nozzles 1 are mounted, by a common flange, on a lateral end of the first downstream chamber 4a directed toward the upstream chamber 3 so as to protrude in the upstream chamber 3, with the inlets 1a opened in the upstream chamber 3 and the outlets 1 b opened in said first downstream chamber 4a. Those nozzles 1 may also be mounted so as to protrude in the first downstream chamber 4a, or to protrude partly in the upstream chamber 4a and partly in the first downstream chamber 4b. The protruding direction of the nozzles 1 is determined according to the size, quantity and nature of the ultra-fine particles to be transported.

As explained before, the cross section of the convergent-divergent nozzles 1 is gradually reduced from the inlet 1a to the throat 2, and is then gradually expanded to the outlet 1b, and preferably the differential coefficient of the stream line at the channel changes continuously and reaches zero at the throat 2, thereby minimizing the formation of flow boundary layers in the nozzles 1. In the present invention, the stream line at the channel in the nozzles 1 means the curve of the internal wall on a cross-section along the direction of flow. In this manner it is rendered possible to make the effective cross sectional area of the flow in the nozzle 1 close to the designed value and to fully exploit the performance of the nozzle 1.As shown in a magnified view in Fig. 4A, the internal periphery in the vicinity of the outlet 1b is preferably substantially parallel to the central axis in order to facilitate the formation of a parallel flow, since the direction of flow of the ejected carrier gas and fine particles is affected, to a certain extent, by the direction of the internal periphery in the vicinity of the outlet 1b. However, if the angle a of the internal wall from the throat 2 to the outlet 1 b with respect to the central axis is selected smaller than 7 , preferably 5 or less as shown in Fig. 4B, it is possible to prevent the peelingoff phenomenon and to maintain a substantially uniform state in the ejected carrier gas and ultrafine particles.Consequently, in such a case, the above-mentioned parallel internal peripheral wall can be dispensed with, and the manufacture of the nozzle 1 can be facilitated by the elimination of said parallel wall portion. Also a slit-shaped ejection of the carrier gas and ultra-fine particles can be obtained by employing a rectangular nozzle 1 as shown in Fig. 4C.

The above-mentioned peeling-off phenomenon means a formation of an enlarged boundary layer between the internal wall of the nozzle 1 and the passing fluid, caused for example by a projection on said internal wall, giving rise to an uneven flow, and such phenomenon tends to occur more frequently in the flow of a higher velocity. In order to prevent such peeling-off phenomenon, the aforementioned angle a is preferably selected smaller when the internal wall of the nozzle 1 is finished less precisely. The internal wall of the nozzle 1 should be finished with a precision indicated by three, preferably four, inverted triangle marks as defined in the JIS B 0601.Since the peeling-off phenomenon in the divergent portion of the nozzle 1 significantly affects the flow of carrier gas and ultra-fine particles thereafter, the emphasis on the surface finishing should be given to said divergent portion, in order to facilitate the fabrication of the nozzle 1. Also for preventing said peeling-off phenomenon, it is necessary to form the throat portion 2 with a smooth curve and to avoid the presence of an infinitely large differential coefficient in the change rate of the cross-sectional area.

However, the formation of a boundary layer caused by said peeling-off phenomenon is unavoidable, since it is practically impossible to finish the internal wall of the nozzle 1 as a completely mirror surface. Formation of such boundary layer in the downstream side of the throat 2, corresponds to a reduction in the ratio A/A*, thus not giving the desired flow velocity. For this reason, the effective cross-sectional area of the outlet is equal to the cross sectional area of the outlet minus the total area of said boundary layer at the outlet, is preferably at least equal to 90% of said cross-sectional area of the outlet.

Thus, the thickness of said boundary layer should not exceed ca. 0.5 mm for an outlet of 20 mm9, or ca. 0.05 mm for an exit of 2 mm9. Since said thickness cannot be made less than a certain lower limit, the diameter of the outlet 1 b, in case of a circular outlet, should be at least 1 mm, and the gap of the outlet 1b, in case of a rectangular outlet, should be at least ca. 1mm.

The upper limit depends for example on the capacity of the vacuum pump 5b at the downstream side. Also the streamline of the flow should coincide with the curve of the internal wall of the nozzle 1 as far as possible, since otherwise the aforementioned boundary layer becomes thicker.

In addition to the forms shown in Figs. 4A, 4B and 4C, the convergent-divergent nozzle 1 may be provided with plural throats 2, 2' as shown in Fig. 4D. In such case the flow accelerated on passing the first throat 2 is decelerated in a diameter decreasing portion, and again accelerated at the second throat 2'. In such structure the temperature of the flow rises and falls repeatedly, corresponding to the change in velocity in the nozzle 1, by the mutual conversion of the thermal energy and the kinetic energy as will be explained later, and there can therefore be formed an interesting reaction field. The number of throats is not limited to two but can be increased to three or more.

Examples of the material of the convergent-divergent nozzle 1 include metals such as iron and stainless steel, plastics such as acrylic resin, polyvinyl chloride, polyethylene, polystyrene and polypropylene, ceramic materials, quartz, glass etc. Said material can be selected in consideration of absence of reaction with the ultra-fine particles to be generated, ease of mechanical working, gas emission in the vacuum system. Also the internal wall of the nozzle 1 may be plated or coated with a material that prevents adhesion of or reaction with the ultra-fine particles. An example of such material is polyfluoroethylene coating.

The length of the covergent-divergent nozzle 1 can be arbitrarily decided, in consideration, for example, of the length of the apparatus. On the other hand, the thermal energy is converted into kinetic energy while the carrier gas and fine particles pass the respective nozzles. Particularly in case of a supersonic ejection, the thermal energy is significantly reduced to reach a supercooled state. Thus, if the carrier gas contains condensable components, it is also possible to form the ultra-fine particles by condensing said components by such super-cooling. Such method allows to obtain uniform ultra-fine particles, due to the formation of uniform nuclei. Also in such case, the respective convergent-divergent nozzles 1 should preferably be longer for achieving sufficient condensation. On the other hand, such condensation increases the thermal energy and reduces the kinetic energy.Consequently, in order to maintain high-speed ejection, the respective nozzles 1 should preferably be shorter.

By passing the flow of carrier gas, containing ultra-fine particles through the aforementioned convergent-divergent nozzles 1, with an appropriate selection of the pressure ratio P/PO of the upstream chamber 3 and the downstream chamber 4 and of an aperture area ratio A/A" of the throat 2 and the outlet 1b, said flow is formed as a beam, flowing at a highspeed from the first downstream chamber 4a to the second downstream chamber 4b.

The skimmer 7 is a variable aperture which can be externally regulated to stepwise vary the area of the aperture between the first downstream chamber 4a and the second downstream chamber 4b, in order to maintain a higher degree of vacuum in the second downstream chamber 4b than in the first 4a. More specifically, said skimmer is composed, as shown in Fig. 5A, of two adjusting plates 11, 11' which are respectively provided with notches 10, 10' and which are slidably positioned in such a manner that said notches 10, 10' mutually oppose. Said adjusting plates 11, 11' can be moved externally, and the notches 10, 10' cooperate each other to define an aperture which allows the beam to pass and still is capable of maintaining a sufficient degree of vacuum in the second downstream chamber.Also the shape of the notches 10, 10' of the skimmer 7 and of the adjusting plates 11, 11' is not limited to the foregoing Vshape shown in Fig. 5A but may be semi-circular or otherwise.

For example, there may be employed a diaphragm mechanism similar to that employed in a camera, as shown in Fig. 5B, and such mechanism enables delicate pressure control.

The gate valve 8 is provided with a damshaped valve member 13 opened or closed by a handle 12, and is fully opened when the beam flows. By closing said gate valve 8, it is rendered possible to exchange the unit of the second downstream chamber 4b while maintaining the upstream chamber 3 and the first downstream chamber 4a in vacuum state. In case the ultrafine particles are easily oxidizable metal particles, it is rendered possible to replace the unit without danger of rapid oxidation by employing a ball valve or the like as said gate valve 8 and replacing the second downstream chamber 4b together with said ball valve.

In the second downstream chamber 4b, there is provided a substrate 6 for capturing the ultrafine particles, transported in the form of a beam, as a film. Said substrate is mounted on a substrate holder 16 at an end of a sliding shaft 15 which is mounted in the second downstream chamber 4b through a common flange and is moved by a cylinder 14. In front of the substrate 6 there is provided a shutter 17 for intercepting the beam when required. Also the substrate holder 16 is capable of heating or cooling the substrate 6 to an optimum condition for capturing the ultrafine particles.

On the top and bottom walls of the upstream chamber 3 and the second downstream chamber 4b, glass windows 18 are mounted by common flanges as illustrated for enabling observation of the interior. Though not illustrated, similar glass windows are mounted by common flanges on the side walls of the upstream chamber 3, first downstream chamber 4a and second downstream chamber 4b. These glass windows, when removed, may be utilized for mounting various measuring instruments or a load lock chamber through the common flanges.

In the following there will be explained a vacuum system to be employed in the present embodiment.

The upstream chamber 3 is connected to a main valve 20a through a pressure regulating valve 19. The first downstream chamber 4a is directly connected to the main valve 20a, which is in turn connected to a vacuum pump 5a. The second downstream chamber 4b is connected to a main valve 20b which is connected to a vacuum valve 5b. Rough pumps 21a, 21b are respectively connected to the upstream side of the main valves 20a, 20b through preliminary vacuum valves 22a, 22b, and are also connected to the vacuum pumps 5a, 5b through auxiliary valves 23a, 23b. Said rough pumps 21a, 21b are used for preliminary evacuation of the upstream chamber 3, first downstream chamber 4a and second downstream chamber 4b. Leak/purge valves 24a-24h are provided for the chambers 3, 4a, 4b and pumps 5a, 5b, 21a, 21b.

At first the preliminary vacuum valves 22a, 22b and the pressure regulating valve 19 are opened to effect preliminary evacuation of the upstream chamber 3 and first and second downstream chambers 4a, 4b by means of the rough pumps 21a, 21b. Then the preliminary vacuum valves 22a, 22b are closed and the auxiliary valves 23a, 23b and the main valves 20a, 20b are opened to sufficiently evacuate the upstream chamber 3 and the first and second downstream chambers 4a, 4b by the vacuum pumps 5a, 5b. In this state the opening of the pressure regulating valve 19 is controlled to achieve a higher degree of vacuum in the first downstream chamber 4a than in the upstream chamber 3, then the carrier gas and the raw material gas are supplied and the skimmer 7 is regulated to achieve a still higher-degree of vacuum in the second downstream chamber 4b than in the first downstream chamber 4a.Said regulation can also be achieved by the main valve 20b. Further control is made in such a manner that each of the chambers 3, 4a, 4b is maintained at a constant degree of vacuum throughout the generation of ultra-fine particles and the film formation by beam ejection. Said control can be achieved either manually or automatically by detecting the pressures in the chambers 3, 4a, 4b and accordingly driving the pressure regulating valve 19, main valves 20a, 20b and skimmer 7.

Also if the carrier gas and the fine particles supplied to the upstream chamber 3 are immediately transported to the downstream side through the nozzle 1, the evacuation during the transportation can be made only in the first and second downstream chambers 4a, 4b.

The upstream chamber 3 and the first downstream chamber 4a may be provided with separate vacuum pumps for the above-mentioned vacuum control. However, if a single vacuum pump 5a is employed, as explained above, for evacuation in the direction of beam flow to control the degrees of vacuum in the upstream chamber 3 and the first downstream chamber 4a, the pressure difference therebetween can be maintained constant even when the vacuum pump 5a has certain pulsation. It is therefore made easier to maintain a constant flow state, which is easily affected by a change in the pressure difference.

The suction by the vacuum pumps 5a, 5b is preferably from upside, particularly in the first and second downstream chambers 4a, 4b, since such suction from upside will prevent, to a certain extent, the descent of beam by gravity.

The above-explained apparatus of the present embodiment can also be subjected to following modifications.

Firstly, the convergent-divergent nozzle 1 may be inclined vertically or horizontally, or may be so constructed as to perform a scanning motion over a certain range to form a film over a lager area. Such inclination or scanning motion is advantageous when combined with the rectangular nozzle shown in Fig. 4C.

It is also possible to form the nozzle 1 with an insulator such as quartz and to supply a microwave thereto, thereby generating active ultra-fine particles therein, or to form the nozzle with a translucent material and to irradiate the flow with light of various wavelength such as ultraviolet light, infrared light or laser light. Also the respective convergent-divergent nozzles may be arranged not only in parallel but also inclined with one another so that plural beams may be focused to one point on the substrate 6. Particularly, the connection of plural nozzles 1 with independent upstream chambers 3 enables to simultaneously generate beams of different fine particles, thereby realizing lamination or mixed capture of different fine particles, or even generation of new fine particles through collisions of crossing beams.

The substrate 6 may be rendered vertically or horizontally movable, or rotatably supported, in order to receive the beam over a wider area. Also the substrate may be unwound and advanced from a roll to receive the beam, thereby subjecting a web-shaped substrate to the treatment with fine particles. Furthermore the treatment with the fine particles may be applied to a rotating drum-shaped substrate 6.

The above-explained embodiment consists of the upstream chamber 3, first downstream chamber 4a and second downstream chamber 4b, but it is also possible to eliminate the second downstream chamber 4b or to connect additional downstream chamber or chambers to the second downstream chamber. The first downstream chamber 4a may be operated under an open system if the upstream chamber 3 is pressurized, or, the upstream chamber 3 may be operated under an open system if the first downstream chamber 4a is reduced in pressure. It is also possible to pressurize the upstream chamber 3 as in an autoclave and to depressurize the first and ensuing downstream chambers.

In this embodiment it is also possible to provide shutter means 25 for opening or closing the flow parts of the respective convergent-divergent nozzles thereby temporarily storing the fine particles in the upstream chamber 3 and pulsating the respective ejections from the nozzles by intermittent opening and closing of said shutter means.

Said shutter means can be positioned in front of, behind or in the nozzles, but is preferably positioned in front of the nozzles for fully exploiting the characteristics thereof. Said shutter means can be composed for example of ball valves or a butterfly valves, but are most preferably of solenoid valves because of the quick response.

Said shutter means may also be opened and closed in synchronization with the energy supply by the laser beam or irradiation of light of various wavelengths in the throat 2 of the nozzle 1 or in the downstream side thereof, thereby significantly reducing the load of vacuum system, avoiding unnecessary ejection to achieve effective utilization of the raw materials, and obtaining pulsating flows of the fine particles. Also, for a given vacuum system, the above-mentioned intermittent openings facilitates to achieve a higher degree of vacuum in the downstream side.

In the foregoing explanation the active ultra-fine particles are generated in the upstream chamber 3, but they can also be generated elsewhere and supplied to said chamber together with the carrier gas.

For example, a reservoir for temporarily storing the ultra-fine particles may be provided above the upstream chamber 3. The particles are supplied, through nozzles formed at the end of said reservoir, to the vicinity of the entrance of the convergent-divergent nozzles 1. The inner walls of the upstream chamber 3 may be subjected to a suitable treatment for preventing the deposition of the fine particles. Because the first downstream chamber 4a is in a higher degree of vacuum compared with the upstream chamber 3, the ultra-fine particles supplied from the reservoir immediately flows, together with the carrier gas, to the first downstream chamber 4a through the convergent-divergent nozzles 1.

It is furthermore possible to employ plural nozzles 1 in series and to regulate the pressure ratio between the upstream side and downstream side of each nozzle, in order to maintain a constant beam speed, and to employ spherical chamber to prevent the formation of dead spaces.

In an application of the apparatus of the present invention, the interior of the upstream chamber 3 may be maintained at the atmospheric pressure or higher. If the upstream side is maintained at the atmospheric pressure, the downstream side can be maintained at a lower pressure, and, if the upstream chamber is maintained at a pressure higher than atmospheric pressure, the downstream side can be maintained at the atmospheric pressure or can be pressurized or depressyrized in a range not exceeding the pressure of said upstream chamber.

It is therefore possible to obtain a solid reaction product, which is formed in a pressurized liquid phase in the upstream side, without exposure to the atmosphere. Also such reaction product can be condensed in a larger amount under a higher pressure in the downstream side, and can therefore be formed in a high concentration.

According to the present invention, fine particles can be transported as uniformly dispersed plural supersonic beams. Thus high-speed transportation of a large quantity of fine particles at one time can be achieved in a spatially independent state, and it becomes easier to prevent the loss of fine particles entrained by the discharge in the downstream side. It is also rendered possible to securely transport the active fine particles of a large quantity to the capturing position in the active state, and to exactly control the wide area of capture as the sum of plural beam capturing areas by the control of plural beams. It is also expected to obtain a new field of reaction, realized by the presence of beams, i.e. concentrated ultra-high speed parallel streams, and by the conversion of thermal energy into kinetic energy upon beam formation, to maintain the fine particle in frozen state.Furthermore, utilizing the abovementioned frozen state, the flow control apparatus of the present invention is capable of defining a microscopic state of the molecules in the fluid to handle a transition from a state to another. More specifically, there is opened a possibility of a novel gaseous chemical reaction in which the molecule is defined even as to the energy level thereof and is given an energy corresponding to said energy level. There is provided a new field of energy transfer, which can be easily utilized for obtaining intermolecular compounds formed with relatively weak intermolecular forces such as hydrogen bond or van der Waals force. Furthermore, the intermittent irradiation with a light beam is effective also in combination with a process of fine particle generation from a raw material gas by means of excitation with a pulsed laser. Such intermittent irradiation is also effective in case of a light source in which the intensity of the short wavelength range is significantly higher by pulsed drive, such as a mercury lamp.

The ejection may be interrupted when not needed, for example during the movement of the substrate, thus enabling effective utilization of the raw materials or enabling formation of certain patterns.

Furthermore, the gas exciting means employed in the present invention is capable of effective formation of fine particles, since it can uniformly mix the gasses in a pipe and can apply an electric discharge without external diffusion of the gasses.

Claims (16)

1. An apparatus for controlling a flow of fine particles, comprising a plurality of convergentdivergent nozzles in the flow path of said fine particles.

2. An apparatus according to Claim 1, wherein each said nozzle is operated under an optimum expansion condition.

3. An apparatus according to Claim 1, wherein the differential coefficient of the streamline at the channel inside each said nozzle varies continuously and is equal to zero at a throat portion of said nozzle.

4. An apparatus according to Claim 1, further comprising, at the upstream side of said nozzles, a reservoir for storing the fine particles for supply into the flow path.

5. An apparatus according to Claim 1, further comprising a shutter means for said nozzles.

6. An apparatus according to Claim 1, further comprising, at the downstream side of said nozzles, a skimmer having a variable aperture function.

7. An apparatus for controlling a flow of fine particles, comprising a plurality of convergentdivergent nozzles in the flow path in which a gas exciting means is provided at the upstream side thereof.

8. An apparatus according to Claim 7, wherein each said nozzle is operated under an optimum expansion condition.

9. An apparatus according to Claim 7, wherein the differential coefficient of the streamline at the channel inside each said nozzle varies continuously and is equal to zero at the throat portion of the nozzle.

10. An apparatus according to Claim 7, further comprising a shutter means for said nozzles.

11. An apparatus according to Claim 7, further comprising, at the downstream side of said nozzles, a skimmer having a variable aperture function.

12. An apparatus according to Claim 7, further comprising a fine-particle capturing means at the downstream side of said nozzles.

13. An apparatus according to Claim 7, wherein said gas exciting means comprises a tubular second electrode and a rod-shaped first electrode positioned at the center of said second electrode.

14. An apparatus according to Claim 7, wherein said gas exciting means comprises first and second electrodes of a semi-circular cross section, which are mutually linked through insulators to form a pipe.

15. An apparatus according to Claim 1, further comprising a fine-particle capturing means at the downstream side of said nozzles.

16. Apparatus for controlling flow of fine particles substantially as herein described with reference to the accompanying drawings.