WO2013001170A1

WO2013001170A1 - Surface treatment device and method

Info

Publication number: WO2013001170A1
Application number: PCT/FI2012/050690
Authority: WO
Inventors: Markku Rajala
Original assignee: Beneq Oy
Priority date: 2011-06-30
Filing date: 2012-06-29
Publication date: 2013-01-03
Also published as: FI20115683A0

Abstract

A surface treatment device that comprises a burner and an impaction chamber that encloses the flame of the burner. Temperatures in the impaction chamber are controlled such that the temperature of the flow of particles at the elongated outlet opening is lower than 70 % of a bulk melting point of the particles. The impaction chamber is further dimensioned to reduce the cross-sectional dimension of the flow towards an elongated outlet opening of the impaction chamber. Probability of the desired surface treatment processes to take place increases and better spatial distribution of particles in the treated areas is achieved.

Description

SURFACE TREATMENT DEVICE AND METHOD

FIELD OF THE INVENTION

The present invention relates to a surface treatment device and method according to preambles of the independent claims. BACKGROUND ART

Surface treatment refers here to a layering process where a surface layer of a substrate is modified by allowing particles to diffuse in the substrate matrix, or where particles are deposited on the surface such that a surface layer is produced on the substrate. Particles used for this kind of surface treat- ment are typically very small, the mean particle diameter ranging from 10 to 100 nm. Particles of this size are typically generated in a particle synthesis process where precursor chemicals are exposed to a thermal reactor. In the intense heat of the thermal reactor they undergo specific thermochemical and -physical reactions that lead to development of desired particles.

In industrial applications, the particle synthesis process typically incorporates a source element that ejects a combination of precursor substances for surface treatment particles, and a thermal reactor that transforms the combination of precursor substances to a directed particle flow. Very often the thermal reactor is a turbulent hydrogen-oxygen flame into which the nozzle outlet channels from one or more nozzles feed materials, either mixed together or through separate outlets.

In industrial applications, the use of flame-based surface treatment processes is still challenged by problems with uniformity and efficiency. The ratio of particles impacted or diffused on the surface is often quite low and a large amount of precursor substances end up being blown away as exhaust gases from the process. Furthermore, especially treatment of larger surfaces, like glass sheets or conveyed float glass, is difficult because a flame is essentially a point source. Treatment of larger areas requires configurations where the point source moves over the areas to be treated, or configurations combin- ing a number of point sources. Results achieved with such configurations are often unsatisfactory, the distribution of deposited particles is not uniform and particles are not efficiently deposited on or in the treated surface.

SUMMARY An object of the present invention is thus to provide a method and an apparatus for implementing the method so as to overcome, or at least alleviate at least one of the above problems. The object of the invention is achieved by a surface treatment device and a surface treatment method, which are characterized by what is stated in the respective independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on generating particles in a temperature- controlled impaction chamber. In the confinement of the impaction chamber the particles efficiently mix into a spatially homogenous flow and the limited temperature ensures that an advantageous particle composition for efficient deposition is achieved. The flow of particles is directed towards a treated surface through an elongated outlet opening, but before release they are accelerated by reducing the cross-sectional dimension of the flow towards the outlet opening.

Due to the proposed configuration, the probability of the desired surface treatment processes to take place increases, so the yield from the precursor components improves and less precursor substances remain to be cleaned from the process atmosphere. Also a more even spatial distribution of particles in the treated areas is achieved. Advantages of the invention are discussed further and in more detail in the following description of its embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments will be described in greater detail with reference to accompanying drawings, in which

Figure 1A shows a side view of an embodiment of a surface treatment device;

Figure 1 B shows a front view of an embodiment of a surface treatment device;

Figure 2 illustrates an embodiment with secondary nozzles; Figure 3 illustrates a surface treatment device comprising a flow guide;

Figure 4 illustrates a side view of a surface treatment device in operation;

Figure 5 illustrates stages of an embodiment of a surface treatment method. DETAILED DESCRIPTION OF SOME EMBODIMENTS

The following embodiments are exemplary. Although the specification may refer to "an", "one", or "some" embodiment(s), this does not neces- sarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may be combined to provide further embodiments.

In the following, features of the invention will be described with a simple example of a device architecture in which various embodiments of the invention may be implemented. Only elements relevant for illustrating the embodiments are described in detail. Various implementations of surface treatment methods and devices comprise elements that are generally known to a person skilled in the art and may not be specifically described herein.

A surface treatment device refers here to an apparatus that generates particles applicable for a particular type of surface treatment and directs them towards a surface to be treated. Figure 1A shows a side view and Figure 1 B shows a front view of an embodiment of a surface treatment device according the invention. The surface treatment device comprises a burner 100 and an impaction chamber 150. The burner 100 represents here means for generating particles in a flame-based particle synthesis process. In the process a flame is fed with precursor chemicals in a liquid, vaporous or gaseous form. In the intense heat of the flame, the precursors undergo thermochemical and - physical reactions, ultimately leading to synthesis of particulate matter that flows out of the flame and may be deposited on or in the surface to be treated. The particles produced in the flame-based surface treatment procedure principally exhibit a mean particle diameter ranging from 10 to 100 nm, depending on the precursor composition and process parameters.

The burner 100 comprises, or is connected to a source unit 102 that provides reservoirs of various substances necessary for the generation of the particles. The reservoirs may be implemented, for example, as storage containers, or as a feed connection from a remote material supply system. The reservoirs comprise a precursor source 104 that provides one or more precursors of the particles. One or more of the precursors may be in liquid form. Before inputting a precursor substance into the heat of the burner 100, liquid mix- tures comprising the precursor substances are advantageously atomized into droplets. A droplet refers here to a very small sized drop, the diameter of a droplet being of the order of tens of micrometers or less. For atomizing, the burner may comprise a nozzle 106, for example a two-fluid atomizer where gas is used to break up a liquid feed from the precursor source 104 into droplets. The liquid droplets and the atomizing gas form an aerosol that sprays out of the nozzle 106 into the impaction chamber 150. Other well-known methods of atomization, like a vibrating ultra-sound plate, may naturally be applied without deviating from the scope of protection.

The reservoirs comprise also a source 108 for burning substances. Burning substances refer here to a mixture of one or more combustible fluids that may be ignited to burn in an exothermic process in the impaction chamber 150. Combustible fluids typically comprise combustible gases, like hydrogen, methane, propane or butane.

The reservoirs may comprise further a source 1 10 for burn control substances. Burn control substances refer here to fluids that effect on a burning process, typically in relation to their relative proportion in the space where burning takes place. Burn control substances often comprise an oxygen carrying gas, for example air, oxygen, or ozone. Burn control substances may also comprise one or more inert gases, like nitrogen or carbon dioxide.

The liquid droplets, burning substances and burn control substances from their respective reservoirs 104, 108, 1 10 may be input via their respective feeds into the nozzle 106 and sprayed into the impaction chamber 150. The nozzle 106 efficiently mixes the substances and forms a homogeneous combustible aerosol of defined composition. Accordingly, when the aerosol exits the nozzle and enters the impaction chamber, it can be ignited to form a flame 1 12. It is noted that Figures 1A and 1 B only illustrate functional elements necessary for describing the present embodiment. The functional elements may be implemented in various ways. For example, a combustible gas may be partially fed as an atomizing gas of the two-fluid atomizer such that inlets 104 and 108 wholly or partially merge in physical implementation.

The impaction chamber 150 is connected to the burner 100 in such a manner that it encloses the flame 1 12 of the burner 100. In the present embodiment the impaction chamber 150 comprises a casing 152 that confines the flame 1 12 into an impermeable burning space 154. Impermeable in this con- text means that the burning space 154 within the casing 152 is detached from the ambient environment around the casing 152 such that fluids (gas and/or liquids) do not substantially enter or exit the burning space 154 through the casing 152. However, heat may be conducted to the burning space through the casing 152.

The flame 1 12 provides a thermal reactor, i.e. a local distribution of heat such that objects traversing locations of that distribution are exposed to the heat accordingly. Substances flowing out in the aerosol from the nozzle 106 are exposed to the intense heat of the flame. However, according to the invention, the device comprises a control mechanism 156 for controlling temperature distribution within the impaction chamber such that the temperature of the aerosol flow exiting the impaction chamber is lower than 70% of a bulk melting point of the particles generated in the flame. Bulk melting point of particles refers here to a temperature in which a material in bulk changes phase from solid to liquid. For example, bulk melting point of S1O2 is 1700 degrees Celsius, and bulk melting point of T1O2 is 1640 degrees Celsius.

Within this predefined temperature range, the conventional evaporation, reaction, condensation, nucleation and coagulation processes for synthesis of particle types of flame-based deposition reactors dominate and primary particles and/or particle agglomerates are formed. However, particles applied in flame-based deposition reactors typically need temperatures above this temperature range to sinter. Controlling temperatures in the defined way results in that coalescence does not yet effectively take place in the impaction chamber 150. This leads to a particle size distribution that is favourable for many effective deposition processes. Effects of particle size distribution will be discussed later in more detail.

In addition, it is understood that the casing 152 is continuously exposed to intense heat of burning and easily begins to deteriorate. In order to achieve uniform particle flow from the impaction chamber, the structure in the outlet of the casing should, however, be robust and maintain its dimensions also in continued use. The casing may be made of conventional refractory ma- terials, like metals or ceramics, and the temperatures at the casing 152 of the impaction chamber 150 should thus to be kept below a rated operating temperature of these materials. The term rated operating temperature refers here to a material property of the casing and indicates a design value for operating temperatures of the material. This value is typically given by the manufacturer of the material or the casing and in practise corresponds to a maximum temperature in which the casing may be continuously and industrially applied. It is appreciated that the configuration of the burner 100 and the chamber 150 are advantageously defined such that both the requirements of the particle generation and requirements of the robustness are taken into consideration. In many implementations the rated operating temperature of refrac- tory materials applied in flame-based deposition reactors is well above the predefined temperature range such that from the point of view of the spatial configuration of the casing, temperatures could be even higher than 70% of a bulk melting point of the particles generated in the flame. Examples of such casing materials comprise AI2O3 and Zr0₂ that provide high rated operating temperatures such that limiting the particle generation to the predefined temperature range at the same time ensures that rated operating temperature of the casing materials are not exceeded. On the other hand, there may be configurations where even the exiting temperature 70% level of the bulk melting point of the particles generated in the flame exceeds the rated operating tem- perature of the material used in the impaction chamber. This means that in industrial use, the dimensions of the impaction chamber would quickly deteriorate by melting and other deformations. Even this type of configurations may, however, be implemented by allowing temperatures in and around the flame to reach the higher values and arranging additional cooling to regions immediate to the walls of the casing such that rated operating temperatures of the casing materials are not continuously exceeded during use. Due to this, the dimensions of the casing remain consistently predictable and the form of the casing can used to effectively control flows within and out of the casing.

Due to the material properties of the combustible gases, without ad- ditional measures, temperatures of flames applied in flame-based particle synthesis processes would easily exceed the predefined temperature range. For example, the adiabatic flame temperature of hydrogen-air flame is of the order of 2100 degrees Celsius. In the embodiment of Figures 1A and 1 B, the required control mechanism is illustrated by means of a controller 156 included in the surface treatment device. The controller 156 of Figure 1 shows an operational unit that interconnects one or more sensors 158 that monitor the burning conditions within the impaction chamber 150, one or more flow control elements 160, 162, 164 for controlling the input flows from reservoirs 104, 108, 1 10 and a control logic 166 that adjusts the input flows in response to signals received from the sensor 158. Flow control elements 160, 162, 164 may be implemented as control valves or in various other ways, well known to a person skilled in the art.

The sensors 158 advantageously comprise a thermosensor by means of which the controller 156 may during operation monitor the prevailing temperature at certain measurement point within the burning space 154 or at the casing 152 of the impaction chamber 150. If the temperature rises above a predefined control temperature threshold, it may trigger a control operation in one or more of the flow control elements 160, 162, 164. The measurement point may be positioned to a point where the aerosol flows out of the chamber. In some configurations, control of the temperature may be based on temperatures of the flame, so the measurement point may be positioned to some other point at or within the casing, as long as it facilitates control of the temperatures within the impaction chamber such that the temperature of the aerosol flow at the point where the aerosol flows out of the chamber remains lower than 70% of a bulk melting point of the particles generated in the flame. It is noted that the configuration shown in Figure 1 is exemplary; the controller 156 may be implemented in various other ways, well known to a person skilled in the art. For example, control operations and logic of the automatic controller 156 may be implemented manually by the operator of the surface treatment device.

In order to control temperatures within the impaction chamber 150, the controller 156 may, for example, change the composition of the burning substances or burn control substances or adjust the amount of substances from feeds 108, 1 10. For example, reduction in the amount of available oxygen within the confined burning space 154 effectively slows the burning process, and thereby decreases the temperature within the impaction chamber. By decreasing the flow rate from feed 1 10, or reducing the proportion of oxygen in the flow from feed 1 10, the burning slows down, and temperatures within the burning space remain well in the predefined temperature range.

The flame 1 12 generates an aerosol flow 170 that carries the gen- erated particles through the impaction chamber. In the confined burning space this aerosol flow progresses according to characteristics of the flame and the form of the casing 152. The impaction chamber comprises an outlet opening 171 through which the aerosol flow 170 eventually runs out. The outlet opening 171 and the impaction chamber 150 are advantageously dimensioned to effi- ciently mix the composition of particles and spread them into a broad homogenous aerosol flow that has an elongated cross-sectional form. This means that the aerosol flow can then be used to treat simultaneously a broad planar surface. The elongated cross-sectional form of the outgoing aerosol flow is a result of an elongated form of the outlet opening 171 . Elongated in this context means that if the outlet opening extends to a length D1 in one direction and to a breadth D2 in the traverse direction, the breadth D2 is less than one fifth of the length D1 of the opening (D2<0,2^*D1 ). In the embodiment of Figures 1A and 1 B, the elongated outlet opening 171 is an elongate rectangle, but other elongate forms may be applied, as well.

For efficient mixing of the particles in the impaction chamber, the area A1 =D1 ^*D2 of the opening is advantageously much smaller than the cross-sectional area of the impaction chamber. In the configuration of Figures 1A and 1 B, the casing 152 has a rectangular cross-section in the direction of the flame, with constant width D1 , height D3 and breadth that varies between values D4 and D2. More specifically, the casing is tapered such that its rectan- gular shape at the height of the nozzle corresponds to width D1 and breadth D4. After a defined distance L1 from the nozzle, the breadth begins to decrease in relation to increase of the distance from the nozzle. When the distance from the nozzle is D3, the breadth reaches a value D2, i.e. the breadth of the opening 171 . It has been detected that good surface treatment results are achieved when reduction of the dimension is at least five to one. For example, in the above case of the rectangular casing 152, the area of the opening is A1 =D1 ^*D2 and the cross-section of the impaction chamber at the defined distance L1 is A2= D1 ^*D4. The relation of dimensions A1 , A2 is preferably A2>5^*A1 , more preferably A2>10^*A1 .

On the other hand, decrease in temperatures within the impaction chamber reduces the velocity of the outgoing particles. The reduction of dimension of the impaction chamber in the direction of the flow at the same time reduces the dimension of the aerosol flow and causes acceleration of the particles at the opening. Critical velocity for a particular particle deposition may thus be reached by appropriate adjustment of flame composition and dimensioning of the casing.

It is well known that when a flow progresses around an obstacle, small particles with will follow streamlines of the flow, but large particles tend to continue straightforwardly, regardless of what the gas flow does. A curvilinear motion of an aerosol flow may be characterized by a dimensionless number called the Stokes number S. When S » 1 , particles tend to continue moving in a straight line when the flow turns. On the other hand, S « 1 , particles tend to follow the flow streamlines and make the turn. Particles in a flow may thus move differently, depending on their size. Impaction is an advantageous mechanism for collection of particles in the system, and it is typically more ef- fective for larger particles. Larger particles, due to their higher inertia, deviate easily from the gas stream, and impact on the obstacle. Stokes number considers both flow velocity and particle dimensions and can be used to classify the potential whether the particle will be impacted. The impaction efficiency is a function of the Stokes number, and it increases as S increases. As a practical approach, many industrially applied impactors can be assumed to be ideal and their efficiency curves characterized by a single number Stk₅₀. Stk₅₀ is the Stokes number that gives 50% impaction efficiency, and has been calculated for a diameter of a particle that has a 50% probability of being separated from the flow.

Typically the critical velocity for deposition of particles with mean particle diameter below 100 nm is very high. In the configuration of Figures 1A and 1 B, due to the controlled temperature range, the particles do not easily sinter but substantially remain as primary particles or as loose aggregates. Also the reduced dimensioning increases the particle concentration in the area of the outlet opening 171 , which further favours particle agglomeration. Formed particle aggregates act as large particles, i.e. impact effectively to a substrate opposite the outlet opening 171 . After impaction they are, however, easily disintegrated and dissolved into the substrate. The proposed configuration thus leads to very effective impaction. In implementations, the combination of the constitution of the flame and the dimensioning of the casing may be configured to provide a flow where Stokes number S for a selected particle aggregate size is greater than Stk₅₀. Good surface treatment results may be achieved with configurations where the selected particle aggregate size is about one micrometer (mean particle diameter).

On the other hand, when particle concentration in the flow is sufficiently low, the particles will essentially not agglomerate and the particle deposition is based on deposition of non-agglomerated particles. In such cases good surface treatment results may be achieved with configurations where the mean particle diameter is set to be approximately 100 nm. Particles which are essentially smaller than this size are difficult to impact on the surface and they carry little mass for dissolution into the substrate. Deposition of particles to the substrate typically improves when the substrate or the substrate surface is heated, as long as the temperature of the substrate does not exceed the temperature of the aerosol flow. Deposition achieved with the surface treatment device is thus further intensified when the surface of the substrate is heated by convection with the higher-temperature aerosol flow that comes out from the impaction chamber. In the configuration of Figures 1A and 1 B, the temperature of the exiting aerosol flow may thus effectively range from 40 to 70 percent of the bulk melting point of the particles. In these temperatures the effect from heating the surface is typically applicable and an appropriate particle agglomeration state for effective impaction may be maintained.

Figure 2 illustrates a further embodiment where the configuration is complemented with at least one secondary nozzle for providing a quenching gas flow to the impaction chamber. Each secondary nozzle 200 is advantageously mounted such that the direction of a jet 202 of gas flow from the nozzle 200 is directed towards the flame 1 12, and positioned between the flame and the casing of the impaction chamber. The configuration of Figure 2 comprises two secondary nozzles 200, 201 positioned to the same top wall of the casing where the primary nozzle 100 resides and directed in both sides towards the flame 1 12 of the primary nozzle 100. The gas flows from the secondary nozzles enhance the mixing of the gases in the impaction chamber and thereby improve homogeneity of the outgoing aerosol flow. In addition, the gas flow cools regions around the flame, reduces the possibility of sintering and thereby improves the possibility to achieve a desired particle agglomerate size for optimal impaction efficiency. The quenching flow may also protect walls of the impaction chamber from the heat of the flame. The quenching flow may be arranged as a separate element of the device or be integrated to the system via the shared source unit 102 and control unit 156. One or more gas flow el- ements may be connected to the device to direct a jet of gas externally towards the casing of the impaction chamber. The intention of such external gas flow is to externally cool the casing of the impaction chamber and thereby further improve durability of the designed dimensions in the configuration.

Figure 3 illustrates a further embodiment applying a similar design, but the device is further enhanced by means of a flow guide 320 attached to the opening 310 in the casing 300. The flow guide 320 moves with the casing 300 and comprises a planar structure 322 that that extends outwards from the opening 310 substantially perpendicular to the direction of the flow 324 that runs out of the opening 310. In operation the flow guide typically moves in parallel to the surface of a planar substrate 330. During operation, the space be- tween the substrate surface and the planar structure 322 thus forms a flow channel for particles that do not impact on the surface but remain in the gas flow. In the flow channel the particles traversing in the flow channel remain in the vicinity of the surface of the substrate, which increases the probability that they deposit on the substrate by diffusion. The form of the flow guide may be further optimized such that length L2 of the planar structure corresponds to a zone of the flame where deposition by diffusion optimally takes place. The temperature of the flow of particles traversing on the surface of the substrate decreases, and at some distance from the opening 310 adverse surface effects begin to prevail. L2 is advantageously arranged to be shorter than this distance.

The block chart of figure 4 illustrates a side view of a surface treatment device that during its operation applies the configuration disclosed in Figures 1A and 1 B, 2 or 3. The surface treatment device comprises conveying means 40 adapted to linearly transfer planar objects, like glass sheets, in a defined direction 41 . In Figure 4 the conveying means are shown as a roller conveyor with a plurality of successive rollers rotating in one direction. During operation, a planar object 42 positioned on the rotating rollers thus moves in the defined direction. It is noted that type of conveyor is not, as such, relevant for the invention. The roller conveyor is used here as an example of a variety of possible means that allow linear transfer of planar objects in a defined direction. For example, in case the planar object is a continuum of float glass, the conveying means include a hot metal bath that floats the treated glass material.

The surface treatment device of Figure 4 comprises one or more flow units 44 that apply the configuration shown earlier. The flow units 44 are arranged into a row. Impaction chambers of the flow units may be separated with side walls of the respective casings or they may be combined into an extended impaction chamber that encloses flames of all burners of the flow units in the row. Particles generated in the flames flow out of an elongated outlet opening 45 that is in the opposite side the casing and extends to the width of passing planar objects. The elongated outlet opening 45 is advantageously a continuum of elongated outlet openings of the flow units. As disclosed above, temperatures in or at the extended impaction chamber are controlled such that temperature of the aerosol flow coming out of the impaction chamber is lower than 70% of a bulk melting point of the particles generated in the flames. Fur- thermore, dimensions of the flow are adjusted with the form of the casings of the flow units such that critical velocity for a particular particle deposition is reached.

The conveying means and the flow units are mutually positioned so that during use the flow of agglomerated particles is directed towards planar objects travelling on the conveying means. The hot aerosol flow 46 from the elongated outlet opening heats the surface of a conveyed planar object and particles in the flame are impacted on the surface. The configuration of the embodiment allows quick and effective coating for planar objects. A considerably larger portion of generated particles is deposited on the passing objects, and the surface treatment procedure thus significantly improved.

Embodiments of the invention comprise also a surface treatment method implemented in an apparatus disclosed in Figures 1A to 4. Figure 5 illustrates stages of the method, but additional information on the stages may also be referred from description of Figures 1A to 4. The procedure of Figure 5 begins in the state where the surface treatment device is in operative condition. The surface treatment device comprises an impaction chamber ICH dimensioned such that it may enclose a flame (stage 50). Substances carrying one or more precursors of the defined particles and burning substances are input into the impaction chamber where they are exposed to the heat of the flame (stage 51 ). An aerosol flow of hot gas and particles is formed. In order to achieve an advantageous particle composition in the flow, temperatures TICH within the impaction chamber are controlled (stage 52) such that the temperature of the aerosol flow exiting the impaction chamber is lower than 70% of a bulk melting point T_pd of the particles. In order to accelerate the particles to an optimal velocity for impaction, the dimension D_Fi_ of the flow in the direction of the flow is reduced (stage 53). The particles are output (stage 54) through an elongated outlet opening that is dimensioned to have a smaller cross-section in the direction of the flow than the cross-section of the impaction chamber.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The in- vention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A surface treatment device, comprising

a burner for exposing precursors of particles to a flame, characterized by

an impaction chamber connected to the burner and configured to enclose the flame of the burner;

the impaction chamber comprising an elongated outlet opening configured to output a flow of particles generated in the flame from the impaction chamber, the impaction chamber being dimensioned to reduce the cross- sectional dimension of the flow towards the elongated outlet opening;

a control mechanism configured to control temperatures in the impaction chamber to allow agglomeration of the generated particles such that the temperature of the flow of particles at the elongated outlet opening is lower than 70% of a bulk melting point of the particles.

2. A surface treatment device according to claim ^characterized in that the impaction chamber has a defined cross-sectional shape that tapers towards the direction of the outlet opening.

3. A surface treatment device according to claim 2, characterize d in that the impaction chamber has a defined cross-sectional shape that extends to a distance from the burner, and the area of the cross-section of the impaction chamber in the distance from the burner is at least five times the area of the elongated outlet opening.

4. A surface treatment device according to claim 2, characterize d in that the impaction chamber has a defined cross-sectional shape that extends to a distance from the burner, and the area of the cross-section of the impaction chamber in the distance from the burner is at least ten times the area of the elongated outlet opening.

5. A surface treatment device according to claim 2 or 3, character i z e d in that the impaction chamber has a constant rectangular cross- sectional shape that extends to a distance from the burner.

6. A surface treatment device according to any of claims 1 to 5, characterized in that constitution of the flame and the dimensioning of the casing are configured to provide a flow where the Stokes number for particles with mean diameter of one micrometer at the elongated outlet opening is greater or equal to Stk₅o-

7. A surface treatment device according to any of claims 1 to 5, characterized in that constitution of the flame and the dimensioning of the casing are configured to provide a flow where the Stokes number for particles with mean diameter of 100 nm at the elongated outlet opening is greater or equal to Stk₅o

8. A surface treatment device according to any of claims 1 to 6, characterized in that the temperature of the flow of particles at the elongated outlet opening is above 40 percent of the bulk melting point of the particles.

9. A surface treatment device according to any of claims 1 to 7, characterized by comprising a flow guide attached to the elongated outlet opening and extending outwards from the outlet opening in a direction substantially perpendicular to the direction of the flow.

10. A surface treatment device according to any of claims 1 to 8, characterized by conveying means adapted to linearly transfer planar objects in a defined direction past the elongated outlet opening, the defined direction being transverse to the direction of the flow.

11. A surface treatment device according to claim 9, characterized in that the surface treatment device comprises two or more burners, arranged into a row.

12. A surface treatment device according to claim 10, characterized in that the flow from each burner is confined into an individual impaction chamber.

13. A surface treatment device according to claim 10, characterized in that the flows from the burners are combined into an extended impaction chamber.

14. A surface treatment method, comprising

generating a flow of particles by exposing precursors of the particles to a flame enclosed into an impaction chamber,

outputting the flow from the impaction chamber through an elongate outlet opening,

controlling temperatures in the impaction chamber to allow agglomeration of the generated particles and such that the temperature of the flow of particles at the elongated outlet opening is lower than 70% of a bulk melting point of the particles;

reducing the cross-sectional dimension of the flow when it progresses towards the elongated outlet opening.