rus
Issue #8/2021
T. V. Gordeychuk, M. V. Kazachek
Bright Sonoluminescence of Metals from High Concentrated Aqueous CaCl2 and NaCl Solutions
Bright Sonoluminescence of Metals from High Concentrated Aqueous CaCl2 and NaCl Solutions
DOI: 10.22184/1993-7296.FRos.2021.15.8.666.673
Bright multibubble sonoluminescence was observed in high concentrated aqueous solutions of CaCl2 and NaCl under argon. The emission was visible to the naked eye. The photos of the luminous cavitation cloud of CaCl2 solutions presented for the first time. The observations and spectra show that the radiation of both the continuum of the emission and the Ca lines occurs in streamers away from an ultrasonic horn.
Bright multibubble sonoluminescence was observed in high concentrated aqueous solutions of CaCl2 and NaCl under argon. The emission was visible to the naked eye. The photos of the luminous cavitation cloud of CaCl2 solutions presented for the first time. The observations and spectra show that the radiation of both the continuum of the emission and the Ca lines occurs in streamers away from an ultrasonic horn.
Bright Sonoluminescence of Metals from High Concentrated Aqueous CaCl2 and NaCl Solutions
T. V. Gordeychuk, M. V. Kazachek
V. I. Il’ichev Pacific oceanological institute FEB RAS, Vladivostok, Russia
Bright multibubble sonoluminescence was observed in high concentrated aqueous solutions of CaCl2 and NaCl under argon. The emission was visible to the naked eye. The photos of the luminous cavitation cloud of CaCl2 solutions presented for the first time. The observations and spectra show that the radiation of both the continuum of the emission and the Ca lines occurs in streamers away from an ultrasonic horn.
Keywords: sonoluminescence, photo, spectra, CaCl2, NaCl
The article was received: 20.10.2021
The article was accepted: 15.11.2021
Multibubble sonoluminescence (SL) is a weak luminescence of liquids, which can be observed with the naked eye only under experimental conditions that provide a high intensity of cavitation collapse of non-linearly pulsating bubbles in the ultrasonic field. Such conditions are observed, for example, in liquids with low saturated vapor pressure (concentrated acids), when saturated with gases with low thermal conductivity (Xe), at low solution temperature and higher hydrostatic pressure. Several papers have photos published showing the luminous cavitation cloud in similar solutions containing Na ions supported by optical spectra [1–5]. At low frequencies of 20–30 kHz, the structure of the luminescent cloud has the form of a flame with a blue glow near the surface of the ultrasonic horn. At the flame tail, thin dynamic threads are observed – streamers – with an orange glow. Parallel measurement of optical spectra confirms the spatial separation of luminous zones. Namely, the blue glow gives a continuum of SL formed by high-energy processes in “hot” bubbles prone to effective spherical collapse in an area where there is a high sound energy density. Orange streamers occur in an area with a low energy density, where conditions that are suitable for the Na radiation excitation are formed. In particular, it is believed that the microturbulence of the liquid and the surface instability of such “cold” bubbles contributes to the ingress of metal into the bubble. At frequencies of 100–500 kHz, a layered structure of the colored radiance of SL is observed, corresponding to the location of standing waves in the ultrasonic in the cell. Streamers can also be observed at the edges of the layers, away from the acoustic axis. In this case, the sonoluminescence spectra usually contain both a continuum and a Na line.
We have not found photos of the luminous area in solutions containing Ca ions in the literature. Nevertheless, we observed bright SL in concentrated aqueous CaCl2 solutions. Ca has an electronic structure that differs from that of Na and has a different energy spectrum. It may have other excitation mechanisms, although for Na they are still only conjectural. Indeed, we observe a different structure of the luminous cloud. Such observations are informative for further understanding of the nature of metal SL.
Experiment
A detailed description of the methodology and experimental setup for measuring SL spectra has been provided repeatedly [6–7]. Ultrasonic vibrations were excited in a thermostatically controlled flow-through type steel cell (Fig. 1) by means of a Sonics VC750 generator, the frequency was 20 kHz, with the output power in watts determined by the generator readings.
The temperature of the solution was kept constant and equal to 10 ± 2 °C using a Julabo F12 thermostat. To produce solutions, high-grade reagents and distilled water were used. The solution was saturated with argon for 2 hours before and throughout the experiment. The spectra were recorded using the MDR‑23 monochromator (1 200 grooves / mm grid, 2.9 nm instrumental bandwidth) and the FEU‑100 photomultiplier. Measurement control and data processing were carried out by a computer. No spectral correction procedure was performed.
Photos and optical spectra were obtained for two cases: (1) in the near ultrasonic field, which is the distance between the ultrasonic horn (item 4, Fig.1) and the cell window (item 5, Fig.1), L = 17 mm; (2) in the far ultrasonic field, L = 100 mm. In order to shield the light radiation near the ultrasonic horn, a shutter (item 7, Fig.1), made of brass tape about 0.1 mm thick, transparent for ultrasound, was placed in the middle of the ultrasonic cell. To average the angular motion of the bubbles and obtain smoother spectra, a frosted quartz glass (item 8, Fig. 1) was placed between the cell window and the slit of the scanning monochromator.
Observations of SL
from NaCl Aqueous Solution
With the molar concentration of NaCl being 3M and above, SL was observed in the near ultrasound field with the naked eye (Fig. 2). The orange spot is the Na radiation zone at the flame tail. The positioning of the shooting provides an opportunity to estimate the spatial location of the spot (approximately 5 mm from the window). Near the ultrasonic horn, a bluish glow of the continuum was observed (not visible in the photo).
Figure 3 shows photos and the optical SL spectrum of the 2M NaCl solution taken in the far ultrasound field. A very faint blue glow can be seen in the volume of the cell and near the ultrasonic horn, as well as moving orange streamers can be seen in the center of the cell closer to the quartz window.
Observations of SL from CaCl2 Aqueous Solution
All observations of calcium SL were performed in the far ultrasound field. With the molar concentration of CaCl2 being 3M and above, SL was observed with the naked eye. The structure of the luminous cloud differed from the case of Na and had the form of fast-moving polyline streamers of luminous bubbles. They could be located along (Fig. 4) or across (Fig. 5) the axis of the cell. Streamers looked like arcs and jets of jumping dots. The color of the streamers was blue, which matched the emission of the continuum. From time to time, bright red dots appeared at the ends of the jets, which matched the emission of Ca (Fig. 6). The flow rate of the sample cell did not affect the long-term stability of the sonoluminescence pattern as a whole.
Spectroscopy of SL
from the Aqueous CaCl2 Solution
The SL spectrum from the aqueous CaCl2 solution contains a fairly smooth continuum and a 310 nm OH radical band (are characteristic of all aqueous solutions), as well as atomic and molecular emission bands (Fig. 7). The 338 and 385 nm bands are not defined [8–9]. The 423 nm peak is a CaI atomic line CaI (4s2 1S – 4s4p 1P). The 554 and 618 nm bands belong to the molecular CaOH (, ). They are known in analytical spectroscopy and are used to analyze the calcium content in samples. The results show that in the SL spectra, the lines of Ca and CaOH are either not observed, or are observed together. For example, they appear in the SL spectra when the temperature of the solution decreases (Fig. 7). In this case, glowing red dots are visible in the luminous area, since the red band of 618 nm makes the predominant contribution to the emission. The effect of the temperature of the solution for SL is described in many papers [6, 10–12]. The temperature rise increases the pressure of saturated vapors, which leads to a decrease in the efficiency of the concentration of the energy of bubble collapse and, as a consequence, to a decrease in the brightness of SL. The brightness of the lines in relation to the continuum changes due to a decrease in the role of the mechanisms that generate lines.
Use of Frosted Glass
The SL spectra obtained by scanning are often noisy due to rapid changes in brightness and the rapid movement of luminous bubbles across the aperture. This problem is not present when photographing or recording spectra with a CCD matrix. The use of frosted quartz glass in front of the spectrometer slit makes it possible to average the angular movement of bubbles. It has emerged that the total illumination they emit is quite constant. This made it possible to obtain smooth SL spectra from rapidly changing streamers (Fig. 8).
Using the Shutter When Measuring Spectra
The optical shutter was placed inside the ultrasonic cell approximately in the middle between the ultrasonic horn and the quartz window. The shutter practically did not affect any pattern of SL of CaCl2. This can be seen by the location and color of the bubbles from the comparison of photos without the shutter (Fig. 5) and with the shutter (Fig. 6). The focus in Figure 5 shows that the streamers are located approximately 50 mm deep, in Figure 6 – from 10 to 50 mm deep, and in Figure 4 – along the entire length of the cell. Consequently, it can be concluded that both the continuum and the Ca lines are emitted in the volume of the liquid but not near the ultrasonic transducer. When SL of NaCl solutions occurred, the pattern of separation of the blue glow at the ultrasonic horn and the orange streamers was typical. The spectral composition of SL of CaCl2 solutions does not change when the shutter is inserted (Fig. 9). This also indicates that both the continuum and the Ca radiation are formed in mobile streamers away from the ultrasonic transducer. Figure 9 shows the SL spectrum at increased power and pulsating ultrasound mode (1 sec / 1 sec) (blue line). This mode lowers the brightness of the continuum, while there are no red bubbles or Ca lines in the spectrum observed. A similar spectrum without Ca lines corresponds to Fig. 4 and Fig. 5. It should be noted that the appearance of Ca emission when SL occurs is sensitive to the changes in experimental modes (static pressure, ultrasonic power, solution temperature, concentration and others, for example, periodic activation of ultrasound).
Conclusion
An abundant spatial structure of the sonoluminescence of aqueous CaCl2 solutions was observed. It was found that the radiation of both continuum and calcium originated from streamers remote from the ultrasonic horn, whereas in the case of NaCl, continuum radiation was observed near the ultrasonic horn, and sodium in the streamers. In the case of CaCl2, the radiation near the ultrasonic horn is negligible. Calcium radiation, 423 nm atomic lines, and molecular 554 and 618 nm CaOH lines can be observed not along the entire length of the streamers, but only at their ends far from the ultrasonic horn, where compact regions of several bright dancing red bubbles are formed.
The work was carried out within the framework of the state task, with its registration number: AAAAA-A20–120021990003–3.
Contribution of the authors
T. V. Gordeychuk – statement of the problem, discussion of the results, writing an article;
M. V. Kazachek – statement of the experiment, discussion of the results, writing an article.
About the authors
M. V. Kazachek, Candidate of Chemical Sciences, e-mail: mihail@poi.dvo.ru,
Senior Researcher, V. I. Ilyichev Pacific Oceanological Institute, FEB RAS, Vladivostok, Russia.
ORCID: 0000-0001-9320-1124
Αrea of interest: spectroscopy, physical chemistry.
T. V. Gordeychuk, Candidate of Physical and Mathematical Sciences,
e-mail: tanya@poi.dvo.ru, Senior Researcher, V. I. Ilyichev Pacific Oceanological Institute, FEB RAS, Vladivostok, Russia.
ORCID: 0000-0001-8425-4080
Αrea of interest: spectroscopy, physical acoustics.
T. V. Gordeychuk, M. V. Kazachek
V. I. Il’ichev Pacific oceanological institute FEB RAS, Vladivostok, Russia
Bright multibubble sonoluminescence was observed in high concentrated aqueous solutions of CaCl2 and NaCl under argon. The emission was visible to the naked eye. The photos of the luminous cavitation cloud of CaCl2 solutions presented for the first time. The observations and spectra show that the radiation of both the continuum of the emission and the Ca lines occurs in streamers away from an ultrasonic horn.
Keywords: sonoluminescence, photo, spectra, CaCl2, NaCl
The article was received: 20.10.2021
The article was accepted: 15.11.2021
Multibubble sonoluminescence (SL) is a weak luminescence of liquids, which can be observed with the naked eye only under experimental conditions that provide a high intensity of cavitation collapse of non-linearly pulsating bubbles in the ultrasonic field. Such conditions are observed, for example, in liquids with low saturated vapor pressure (concentrated acids), when saturated with gases with low thermal conductivity (Xe), at low solution temperature and higher hydrostatic pressure. Several papers have photos published showing the luminous cavitation cloud in similar solutions containing Na ions supported by optical spectra [1–5]. At low frequencies of 20–30 kHz, the structure of the luminescent cloud has the form of a flame with a blue glow near the surface of the ultrasonic horn. At the flame tail, thin dynamic threads are observed – streamers – with an orange glow. Parallel measurement of optical spectra confirms the spatial separation of luminous zones. Namely, the blue glow gives a continuum of SL formed by high-energy processes in “hot” bubbles prone to effective spherical collapse in an area where there is a high sound energy density. Orange streamers occur in an area with a low energy density, where conditions that are suitable for the Na radiation excitation are formed. In particular, it is believed that the microturbulence of the liquid and the surface instability of such “cold” bubbles contributes to the ingress of metal into the bubble. At frequencies of 100–500 kHz, a layered structure of the colored radiance of SL is observed, corresponding to the location of standing waves in the ultrasonic in the cell. Streamers can also be observed at the edges of the layers, away from the acoustic axis. In this case, the sonoluminescence spectra usually contain both a continuum and a Na line.
We have not found photos of the luminous area in solutions containing Ca ions in the literature. Nevertheless, we observed bright SL in concentrated aqueous CaCl2 solutions. Ca has an electronic structure that differs from that of Na and has a different energy spectrum. It may have other excitation mechanisms, although for Na they are still only conjectural. Indeed, we observe a different structure of the luminous cloud. Such observations are informative for further understanding of the nature of metal SL.
Experiment
A detailed description of the methodology and experimental setup for measuring SL spectra has been provided repeatedly [6–7]. Ultrasonic vibrations were excited in a thermostatically controlled flow-through type steel cell (Fig. 1) by means of a Sonics VC750 generator, the frequency was 20 kHz, with the output power in watts determined by the generator readings.
The temperature of the solution was kept constant and equal to 10 ± 2 °C using a Julabo F12 thermostat. To produce solutions, high-grade reagents and distilled water were used. The solution was saturated with argon for 2 hours before and throughout the experiment. The spectra were recorded using the MDR‑23 monochromator (1 200 grooves / mm grid, 2.9 nm instrumental bandwidth) and the FEU‑100 photomultiplier. Measurement control and data processing were carried out by a computer. No spectral correction procedure was performed.
Photos and optical spectra were obtained for two cases: (1) in the near ultrasonic field, which is the distance between the ultrasonic horn (item 4, Fig.1) and the cell window (item 5, Fig.1), L = 17 mm; (2) in the far ultrasonic field, L = 100 mm. In order to shield the light radiation near the ultrasonic horn, a shutter (item 7, Fig.1), made of brass tape about 0.1 mm thick, transparent for ultrasound, was placed in the middle of the ultrasonic cell. To average the angular motion of the bubbles and obtain smoother spectra, a frosted quartz glass (item 8, Fig. 1) was placed between the cell window and the slit of the scanning monochromator.
Observations of SL
from NaCl Aqueous Solution
With the molar concentration of NaCl being 3M and above, SL was observed in the near ultrasound field with the naked eye (Fig. 2). The orange spot is the Na radiation zone at the flame tail. The positioning of the shooting provides an opportunity to estimate the spatial location of the spot (approximately 5 mm from the window). Near the ultrasonic horn, a bluish glow of the continuum was observed (not visible in the photo).
Figure 3 shows photos and the optical SL spectrum of the 2M NaCl solution taken in the far ultrasound field. A very faint blue glow can be seen in the volume of the cell and near the ultrasonic horn, as well as moving orange streamers can be seen in the center of the cell closer to the quartz window.
Observations of SL from CaCl2 Aqueous Solution
All observations of calcium SL were performed in the far ultrasound field. With the molar concentration of CaCl2 being 3M and above, SL was observed with the naked eye. The structure of the luminous cloud differed from the case of Na and had the form of fast-moving polyline streamers of luminous bubbles. They could be located along (Fig. 4) or across (Fig. 5) the axis of the cell. Streamers looked like arcs and jets of jumping dots. The color of the streamers was blue, which matched the emission of the continuum. From time to time, bright red dots appeared at the ends of the jets, which matched the emission of Ca (Fig. 6). The flow rate of the sample cell did not affect the long-term stability of the sonoluminescence pattern as a whole.
Spectroscopy of SL
from the Aqueous CaCl2 Solution
The SL spectrum from the aqueous CaCl2 solution contains a fairly smooth continuum and a 310 nm OH radical band (are characteristic of all aqueous solutions), as well as atomic and molecular emission bands (Fig. 7). The 338 and 385 nm bands are not defined [8–9]. The 423 nm peak is a CaI atomic line CaI (4s2 1S – 4s4p 1P). The 554 and 618 nm bands belong to the molecular CaOH (, ). They are known in analytical spectroscopy and are used to analyze the calcium content in samples. The results show that in the SL spectra, the lines of Ca and CaOH are either not observed, or are observed together. For example, they appear in the SL spectra when the temperature of the solution decreases (Fig. 7). In this case, glowing red dots are visible in the luminous area, since the red band of 618 nm makes the predominant contribution to the emission. The effect of the temperature of the solution for SL is described in many papers [6, 10–12]. The temperature rise increases the pressure of saturated vapors, which leads to a decrease in the efficiency of the concentration of the energy of bubble collapse and, as a consequence, to a decrease in the brightness of SL. The brightness of the lines in relation to the continuum changes due to a decrease in the role of the mechanisms that generate lines.
Use of Frosted Glass
The SL spectra obtained by scanning are often noisy due to rapid changes in brightness and the rapid movement of luminous bubbles across the aperture. This problem is not present when photographing or recording spectra with a CCD matrix. The use of frosted quartz glass in front of the spectrometer slit makes it possible to average the angular movement of bubbles. It has emerged that the total illumination they emit is quite constant. This made it possible to obtain smooth SL spectra from rapidly changing streamers (Fig. 8).
Using the Shutter When Measuring Spectra
The optical shutter was placed inside the ultrasonic cell approximately in the middle between the ultrasonic horn and the quartz window. The shutter practically did not affect any pattern of SL of CaCl2. This can be seen by the location and color of the bubbles from the comparison of photos without the shutter (Fig. 5) and with the shutter (Fig. 6). The focus in Figure 5 shows that the streamers are located approximately 50 mm deep, in Figure 6 – from 10 to 50 mm deep, and in Figure 4 – along the entire length of the cell. Consequently, it can be concluded that both the continuum and the Ca lines are emitted in the volume of the liquid but not near the ultrasonic transducer. When SL of NaCl solutions occurred, the pattern of separation of the blue glow at the ultrasonic horn and the orange streamers was typical. The spectral composition of SL of CaCl2 solutions does not change when the shutter is inserted (Fig. 9). This also indicates that both the continuum and the Ca radiation are formed in mobile streamers away from the ultrasonic transducer. Figure 9 shows the SL spectrum at increased power and pulsating ultrasound mode (1 sec / 1 sec) (blue line). This mode lowers the brightness of the continuum, while there are no red bubbles or Ca lines in the spectrum observed. A similar spectrum without Ca lines corresponds to Fig. 4 and Fig. 5. It should be noted that the appearance of Ca emission when SL occurs is sensitive to the changes in experimental modes (static pressure, ultrasonic power, solution temperature, concentration and others, for example, periodic activation of ultrasound).
Conclusion
An abundant spatial structure of the sonoluminescence of aqueous CaCl2 solutions was observed. It was found that the radiation of both continuum and calcium originated from streamers remote from the ultrasonic horn, whereas in the case of NaCl, continuum radiation was observed near the ultrasonic horn, and sodium in the streamers. In the case of CaCl2, the radiation near the ultrasonic horn is negligible. Calcium radiation, 423 nm atomic lines, and molecular 554 and 618 nm CaOH lines can be observed not along the entire length of the streamers, but only at their ends far from the ultrasonic horn, where compact regions of several bright dancing red bubbles are formed.
The work was carried out within the framework of the state task, with its registration number: AAAAA-A20–120021990003–3.
Contribution of the authors
T. V. Gordeychuk – statement of the problem, discussion of the results, writing an article;
M. V. Kazachek – statement of the experiment, discussion of the results, writing an article.
About the authors
M. V. Kazachek, Candidate of Chemical Sciences, e-mail: mihail@poi.dvo.ru,
Senior Researcher, V. I. Ilyichev Pacific Oceanological Institute, FEB RAS, Vladivostok, Russia.
ORCID: 0000-0001-9320-1124
Αrea of interest: spectroscopy, physical chemistry.
T. V. Gordeychuk, Candidate of Physical and Mathematical Sciences,
e-mail: tanya@poi.dvo.ru, Senior Researcher, V. I. Ilyichev Pacific Oceanological Institute, FEB RAS, Vladivostok, Russia.
ORCID: 0000-0001-8425-4080
Αrea of interest: spectroscopy, physical acoustics.
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