COMPACT DEVICE AND PROCESS FOR THE PRODUCTION OF NANOPARTICLES IN SUSPENSION

Abstract

The invention shows a device for producing nanoparticles, the device having a pulsed laser with a scanning device for guiding the beam of the laser over a target that is fixed in a flow-through chamber. The flow-through chamber is reversibly connected to a supply line for carrier fluid, so that the flow-through chamber is exchangeable e.g. for a further flow-through chamber having a different target and/or a different dimensioning.

Claims

1. A device for the production of nanoparticles, comprising a pulsed laser, a scanning device to guide a beam of the laser, a flow-through chamber having a target support wall, a radiation-transparent wall opposite the target support wall, a supply line connected to at least one reservoir for carrier fluid and connected to the flow-through chamber, a controlled conveying device arranged in the supply line and configured to control a flow velocity of carrier fluid within the flow-through chamber in a range of 1 to 10 mm/s, wherein the laser has a maximum power of 5 W and is configured to emit pulses having a pulse energy of 0.01 to 10 mJ and a pulse duration of 0.5 to 10 ns with a repetition rate of 500 to 5000 Hz and a fluence of 0.1 to 10 J/cm.sup.2.

2. The device according to claim 1, wherein the laser is configured to emit pulses having a pulse energy of 10 to 1000 μJ and a pulse duration of 0.5 to 1 ns with a repetition rate of 500 to 5000 Hz and a fluence of 0.1 to 10 J/cm.sup.2.

3. The device according to claim 1, wherein a distance of the radiation-transparent wall section from a target supported by the target support wall is at maximum 5 mm.

4. The device according to claim 1, wherein the scanning device is configured to guide the laser beam at a speed of 0.1 to 10 m/s over a target supported by the target support wall.

5. The device according to claim 1, the conveying device comprising one or both of a controlled valve and a controlled pump.

6. The device according to claim 1, wherein the flow-through chamber is arranged with its cross-section at an angle of at maximum 30° to the horizontal.

7. The device according to claim 1, wherein the supply line is connected to an inlet of the flow-through chamber and the inlet is arranged below the flow-through chamber.

8. The device according to claim 1, comprising one or both of a radiation sensor and a temperature sensor configured to sense a target on the target support wall from outside the flow-through chamber and to transmit a signal for switching off the laser when radiation or a temperature above a predetermined value is recorded.

9. The device according to claim 1, wherein the flow-through chamber is reversibly connectable to the supply line and the flow-through chamber is contained in an insert which is reversibly fixable in a socket of a housing, wherein one or both of the scanning device and the laser are arranged in the housing.

10. The device according to claim 9, comprising a switch in the housing that changes its switching position upon fixation of the insert in the socket and enables power supply for the laser only upon fixation of the insert in the socket.

11. The device according to claim 9, wherein the housing is light-proof against radiation of the laser.

12. The device according to claim 1, comprising at least two reservoirs for carrier liquid connected to the supply line by a switchable multi-port valve.

13. The device according to claim 1, comprising a drain line connected to an outlet of the flow-through chamber, a turbidity sensor configured to record the turbidity in the drain line and connected to a control unit for the laser, the control unit being configured to switch off the laser after recording measurement values for presence of turbidity for a predetermined total duration.

14. The device according to claim 13, wherein the insert comprises a coding, a reading unit for reading out the coding is attached to the socket, and the reading unit is configured to send a specific control signal depending on the coding read out to the control unit.

15. The device according to claim 14, wherein the specific control signal is asserted for a predetermined maximum duration of operation of the laser.

16. The device according to claim 1, comprising one or both of a telescope arranged in a beam path of the laser before the scanning unit and a focusing unit arranged in the beam path after the scanning unit.

17. The device according to claim 1, comprising a sound sensor in contact with an inner volume and configured to record duration and amplitude for predetermined frequencies and to send a control signal for switching off the laser when one or both of a predetermined total duration and a predetermined amplitude are senses.

18. The device according to claim 1, comprising a controlled shutter arranged in a beam path of the laser.

19. A process for producing nanoparticles suspended in a carrier liquid, comprising irradiating a target with laser radiation which is guided over the target that is mounted in a flow-through chamber which has a radiation-transparent wall section opposite the target while the carrier liquid flows through the flow-through chamber, the carrier liquid being supplied from a reservoir through a supply line in which a controlled conveying device is arranged, wherein the conveying device controls the flow of the carrier liquid to a flow velocity of 1 to 10 mm/s through the flow-through chamber, and wherein the laser provides a maximum power of 5 W and emits pulses with a pulse energy of 0.01 to 10 mJ and a pulse duration of 0.5 to 10 ns with a repetition rate of 500 to 5000 Hz and a fluence of 0.1 to 10 J/cm.sup.2.

20. The process according to claim 19, wherein the laser emits pulses with a pulse energy of 10 to 1000 μJ and a pulse duration of 0.5 to 1 ns with a repetition rate of 500 to 5000 Hz and a fluence of 0.1 to 10 J/cm.sup.2.

21. The process according to claim 19, wherein a laser beam of the laser is guided at a speed of 0.1 to 10 m/s over the target in a controlled pattern by a scanning device.

22. The process according to claim 19, wherein one or both of a radiation sensor and a temperature sensor monitors the target from outside the flow-through chamber and recording one or both of radiation and a temperature above a predetermined value transmits a signal to switch off the laser.

23. The process according to claim 19, wherein the flow-through chamber is contained in an insert releasably fixed in a socket of the housing, and the flow-through chamber is releasably connected to the supply line, and the flow-through chamber is aligned to the scanning device and the laser.

24. The process according to claim 23, wherein the fixing of the insert in the socket influences the switching position of a switch and the switch establishes a power supply for the laser only in its switching position in which the insert is fixed in the socket.

25. The process according to claim 24, wherein a sound sensor in contact with the inner volume of the flow-through chamber records their duration and amplitude or predetermined frequencies and upon reaching a predetermined total duration and/or upon recording a predetermined amplitude sends a control signal for switching off the laser.

26. The process according to claim 25, wherein a drain line is connected to an outlet of the flow-through chamber and a turbidity sensor records turbidity in the drain line and, after recording readings for the presence of turbidity for a predetermined total duration, sends a signal for shutting down the laser.

27. The process according to claim 23, wherein the insert has a coding for the material and/or for the size of the target and/or for control signals for a control unit of the laser and/or for the conveying device, a reading unit for reading out the coding is attached to the socket, and the reading unit reads out the coding and sends a control signal dependent thereon to the control unit of the laser and/or to the control unit of the conveying device.

Description

[0038] The invention is now described in more detail with reference to the figures, which schematically show in

[0039] FIG. 1 a device according to the invention,

[0040] FIGS. 2 and 3 flow-through chambers having an optical sensor,

[0041] FIG. 4 a flow-through chamber having an acoustic sensor,

[0042] FIG. 5 a flow-through chamber having a turbidity sensor,

[0043] FIG. 6 a flow-through chamber having a temperature sensor, and in

[0044] FIGS. 7 and 8 embodiments of a switch at the insert.

[0045] FIG. 1 shows an overview of a device according to the invention having a pulsed laser 1, the beam of which by means of a scanning device 2 can be directed onto a target 3 and guided over the target 3. In the beam path between the laser 1 and the scanning device 2, a telescope 4 is arranged, as is preferred, which expands the laser beam to the scanning device. The target 3 is attached to a wall 5 of a flow-through chamber 6, which opposite the target 3 has a wall section 7 that is transparent to the laser beam. This radiation-transparent wall section 7 can be made of plastic or glass. As preferred, the flow-through chamber 6 is arranged with its cross-section approximately horizontally and its inlet 8 is located below the target 3, so that a carrier liquid flows through the flow-through chamber 6 from bottom to top and gas bubbles are discharged. The carrier fluid is guided from a reservoir 9 to the inlet of the flow-through chamber 6 via a supply line 10, in which a conveying device 11 is arranged, and exits from an outlet 12 arranged opposite the inlet 8, to which outlet 12 a drain line 13 is connected which discharges into a collecting vessel 17. The laser 1, the scanning device 2 for guiding its beam, the flow-through chamber 6, the conveying device 11 in the supply line 10, and sensors 14 are, as is preferred, arranged in a common housing which has no supply line for cooled cooling medium. The laser 1 can be cooled exclusively by cooling elements around which ambient air can flow, optionally reinforced by a fan.

[0046] The conveying device 11, which generally preferably comprises a flow meter, in the embodiment shown here is formed by a pump and a controlled valve 15, which is arranged in the supply line 10. Alternatively, the conveying device can be formed by pressurized gas being applied to the reservoir 9 for carrier liquid, e.g. from a pressurized gas cylinder, and in that a controlled valve 15 is arranged in the supply line 10.

[0047] A sensor 14, which is arranged at the flow-through chamber 6 and which in particular is directed to the wall 5 opposite the wall section 7 which is transparent to the laser radiation, is connected to a control unit 16 which is set up to control, depending on a signal from the sensor 14, the laser 1, the conveying device 11, and/or the scanning device 2.

[0048] FIG. 2 shows a flow-through chamber 6 in cross-section along the direction of flow of the carrier fluid, in which laser radiation passing through the radiation-transparent wall section 7 hits the target 3, or resp. in the absence of the target 3 passes through the wall 5 of the flow-through chamber 6 on which the target 3 was arranged and subsequently hits a sensor 14 formed as a radiation sensor. Between the flow-through chamber and the radiation sensor, a scattering disk 18, e.g. a frosted glass disk, is arranged which scatters laser radiation passing through the wall 5 of the flow-through chamber 6 onto the radiation sensor 14.

[0049] FIG. 3 shows, as an alternative to a scattering disk 18, the arrangement of the radiation sensor 14 at a sufficiently large distance from the flow-through chamber 6 so that laser radiation passing through can hit the sensor 14.

[0050] FIG. 4 shows a sensor 14 embodied as a sound sensor, which may be mounted at a distance from the flow-through chamber 6, e.g. on a housing. It has shown that the ablation of material from the target 3 during laser irradiation leads to characteristic vibrations, and the impingement of the laser beam directly onto the wall 5 of the flow-through chamber 6, in front of which the target 3 had been arranged, leads to changes in the vibrations.

[0051] FIG. 5 shows a setup for a turbidity sensor arranged as sensor 14 at the flow-through chamber 6, the signal of which sensor 14 is a measure for the concentration of nanoparticles produced. The turbidity sensor 14 may be formed by a light emitting diode and a photodiode arranged opposite at the flow-through chamber. In the embodiment of the sensor 14 as a turbidity sensor, preferably also the wall 5 that is opposite to the wall section that is transparent to the laser beam is transparent to the laser beam, e.g. this wall may be formed by an identical wall section 7 transparent to laser radiation.

[0052] FIG. 6, as sensor 14, shows a temperature sensor that is thermally coupled to the wall 5 of the flow-through chamber 6 to which the target 3 is attached, e.g. by means of a metal plate connecting the temperature sensor to the flow-through chamber 6. It has shown that upon irradiation of the target 3 by a laser, a significant increase of temperature can be measured after about 3 to 5 s on the outer surface of that wall 5 of the flow-through chamber 6 to which the target 3 is attached, so that the signal from a temperature sensor generates a signal for the impingement of the laser beam onto the target 3, and this signal can be passed to the control unit 16 of the laser 1, e.g. as a control signal.

[0053] FIG. 7 shows a section of an insert in which a flow-through chamber 6 may be arranged and which upon positioning in a socket 19 on the housing actuates a pressure switch 20. This switch 20 can e.g. switch-on the power supply to the laser 1 when the insert is correctly positioned in the socket 19, and/or generate a signal for the control unit 16 of the conveying device 11.

[0054] FIG. 8 shows an alternative switch 20 in which upon positioning the insert containing the flow-through chamber 6 in the socket on the housing, a conductor 21 on the insert closes an open current conductor 22 in order to generate a signal for the presence of the insert and/or to switch-on a line to the power supply.

[0055] The following table shows the result of a comparison of the production of gold nanoparticles by irradiating a gold target in water with different lasers, each of which produced a fluence of up to 20 J/cm.sup.2. The laser that was used according to the invention was a diode-pumped microchip laser having an average maximum power of 0.15 W, for comparison a laser with about 10 W (medium class) and a laser with 500 W (high power class).

TABLE-US-00001 according to the medium high power invention class class pulse duration (ps) 1000 5000 3 mean wattage (W) 0.15 5 500 M.sup.2 <1.4 <1.5 <1.2 wavelength (nm) 1064 1064 1030 repetition rate (kHz) 1.2 15 5000 pulse energy (μJ) 130 330 100 Maximum of absorbed 2.5 6.7 0.3 fluence pulse distance (μm) 8300 670 97 productivity (μg/s) 1.8 10.3 1660.7 efficiency of 43.1 7.1 12.4 production (mg/Wh)

[0056] This comparative test makes it clear that the energy-specific efficiency is highest for the laser used in the process according to the invention, although this has the lowest power. The laser used in the process according to the invention shows an efficiency that is better by a factor of 6 than the medium-class laser and an efficiency that is better by a factor of 3.5 than the high power class laser. A further advantage of the process and device according to the invention results from the lower energy consumption for the laser and the lower costs for the laser.

LIST OF REFERENCE SIGNS

[0057] 1 laser [0058] 2 scanning device [0059] 3 target [0060] 4 telescope [0061] 5 wall [0062] 6 flow-through chamber [0063] 7 wall section transparent to laser radiation [0064] 8 inlet [0065] 9 reservoir [0066] 10 supply line [0067] 11 conveying device [0068] 12 outlet [0069] 13 drain line [0070] 14 sensor [0071] 15 valve [0072] 16 control unit [0073] 17 collection vessel [0074] 18 scattering disk [0075] 19 socket on housing [0076] 20 switch [0077] 21 conductor [0078] 22 open conductor