rus
Issue #1/2023
T. V. Gordeychuk, M. V. Kazachek
Calcium Ionization During Sonoluminescence from CaCl2 Aqueous Solution
Calcium Ionization During Sonoluminescence from CaCl2 Aqueous Solution
DOI: 10.22184/1993-7296.FRos.2023.17.1.72.76
The weak lines of CaII at 393 and 397 nm were observed upon 20 kHz insonification of 2M CaCl2 aqueous solution in the multibubble sonoluminescence spectrum. The rough estimation of Ca ionization degree having made by comparison with the solar spectrum that indicates the significant thermodynamic nonequilibrium of processes in a cavitation bubble.
The weak lines of CaII at 393 and 397 nm were observed upon 20 kHz insonification of 2M CaCl2 aqueous solution in the multibubble sonoluminescence spectrum. The rough estimation of Ca ionization degree having made by comparison with the solar spectrum that indicates the significant thermodynamic nonequilibrium of processes in a cavitation bubble.
Теги: cacl2 aqueous solution ca ionization sonoluminescence водный раствор cacl2 ионизация сa сонолюминесценция
Calcium Ionization During Sonoluminescence From CaCl2 Aqueous Solution
T. V. Gordeychuk, M. V. Kazachek
Iljichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia
The weak lines of CaII at 393 and 397 nm were observed upon 20 kHz insonification of 2M CaCl2 aqueous solution in the multibubble sonoluminescence spectrum. The rough estimation of Ca ionization degree having made by comparison with the solar spectrum that indicates the significant thermodynamic nonequilibrium of processes in a cavitation bubble.
Keywords: sonoluminescence, CaCl2 aqueous solution, Ca ionization
Received: December 02, 2022
Accepted: December 25, 2022
The ultrasonic wave transmission through the liquids is accompanied by a number of nonlinear acoustic phenomena, the most important of which is cavitation, namely the bubble formation, its growth, and explosive collapse. The property of cavitation bubbles to concentrate the ultrasound energy leads to the occurrence of localized, short-lived hot spots in the liquid with the extremely high temperature and density of the substance, subject to the high-speed almost adiabatic compression [1]. Sonoluminescence (SL) that is the weak glow of liquids in a wide range from the UV to IR spectra is a consequence of such extreme conditions. The spectral measurements demonstrate that the conditions in cavitation bubbles are thermodynamically nonequilibrium. The emission spectra of stable SL of a single bubble in asulfuric acid aqueous solution have shown the vibrationally hot SO with Tv = 2 100 K that is also rotationally cold with Tr = 290 K [2]. The same phenomenon has been observed for NH in the case of multibubble SL in an aqueous solution of ammonia [3]. The nonequilibrium sigs have also been found for the ionization process in the case of sonoluminescence in the mode of a consistently pulsating single bubble [4, 5]. In [5], under conditions providing a highly efficient collapse (sulfuric acid with a low content of inert gases), the highly excited ionic states of gases with the energies up to 37 eV (Ar+) have been registered, while the experimental temperature assessment based on the Ar line mutual intensity under such conditions has not exceeded 16 000 K [3].
During the multi-bubble SL of aqueous solutions, the estimated cavitation temperatures are lower being at the level of 2 500–4 000 K [6, 7]. Nevertheless, we observe the Ca ionic lines in the multibubble SL spectra of CaCl2 aqueous solution that has allowed us to make a rough estimate of the substance ionization degree under our experimental conditions.
Experiment
The detailed description of the experimental method and setup for measuring SL spectra has been provided multiple times [8]. Ultrasonic oscillations were excited in a temperature-controlled steel flow-type cell [9] using a Sonics VC750 generator with the frequency of 20 kHz. The released power at the level of 18 W was determined based on the generator parameters. The solution temperature was maintained at 10±1 °C. The solutions were prepared using CaCl2 (Neva-reaktiv, 95%) and distilled water. The solution was saturated with argon for 2 hours before and throughout the experiment. The spectra were recorded using an MDR‑23 monochromator (grating: 1 200 lines / mm, the highest energy concentration area: 500 nm), FEU‑100 photodetector (color sensitivity area: 200–800 mm). The measurement control and data processing were performed by a computer. To obtain the solar spectrum, the entrance slit of the monochromator was illuminated by the scattered sky light. Spectral correction for the PMT sensitivity and reflection of the diffraction grating was performed using the calibrated lamps OP‑33–0.3 and DDS‑30.
Results
In the spectrum of 2 M CaCl2 aqueous solution, under certain conditions, probably favorable for the metal luminescence processes (this issue requires a separate study), we have observed weak lines of the CaII ion at 393 and 397 nm (Fig. 1). We have found the only mention of Ca ionic lines in the multibubble SL spectrum of CaCl2 aqueous solution in the classical paper [10], but at a high ultrasonic frequency (500 kHz). The authors did not observe these lines at an ultrasonic frequency of 16 kHz that was attributed to their low brightness during SL and their proximity to the SL continuum maximum. Moreover, we have recorded these lines only at the concentrations of ~2 M (saturation concentration is about ~5 M). Figure 1 shows the SL spectrum fragment of a 2 M CaCl2 solution, measured with a resolution of 0.6 nm, and the solar (sky) emission spectrum measured with a resolution of 0.3 nm using the same spectrometer. The SL spectrum in Fig. 1 is normalized to a wavelength of 423 nm. For illustrative purposes, the solar spectrum is modified according to the formula J = log(J0 / 2) + 1.5, where J, J0 are the calculated and measured intensity, respectively. The solar spectrum demonstrates the intense CaII lines and a weak CaI line. According to [11], the reduced width (brightness) of lines in the solar spectrum is 342 for CaI at 422.7 nm, 4874 for CaII at 393.4 nm, and 3 435 for CaII at 396.8 nm. Apparently, the radiation conditions in the case of the Sun are significantly different from SL: in particular, the photosphere pressure is ~0.1 atm, while in a compressing bubble it reaches hundreds of atm. The lines in the SL spectrum are redshifted and broadened in relation to the solar ones due to the high density of the radiating medium during SL. It should be noted that the ionic line excitation energy (3.15 and 3.12 eV) is comparable with the value for CaI at 423 nm (2.93 eV).
The observation of ionic lines in the SL spectra confirms availability of a low-temperature plasma in the bubbles. The Ca ionization degree in the bubbles (fraction of ions) Xb can be roughly estimated by comparing the brightness of atomic and ionic lines in the SL and solar spectra (Fig. 1). We have not found exact data for Ca. It was noted in the paper [12] that Ca in the solar chromosphere is represented “mostly” (the author’s expression) in the ionized form. Since we observe an atomic line in the solar spectrum, this is obviously not 100% ionization. We can also assume that if we consider the ionization degree for hydrogen in the solar photosphere as 10–4, as well as the ionization energies of the Ca (6.1 eV) and H (13.6 eV) atoms, then it is obvious that the Ca ionization degree in the Xs photosphere will be many times greater. Let Xs = 30%. The expression Xb / Xs = (Ibi / Ibn) / (Isi / Isn) ≈ 1 / 200, where I is the spectral line brightness, the indices b, s, i, n refer to the bubbles, the Sun, ions, and neutral atoms, respectively, provides a rough estimate leading to Xb = 0.15%.
Previously, we determined the metal emission temperature during SL as ~3 300 [6] while applying the Ornstein method and using two atomic Mn emission lines in the SL spectrum of MnCl2 aqueous solution under the similar experimental conditions. This result is in line with that obtained for an aqueous solution of benzene for the Swan molecular bands [7]. In this case, we filled the experimental spectrum of a 2M CaCl2 aqueous solution with the black body spectrum according to the Planck formula (Fig. 2). The SL spectrum was adjusted for the color sensitivity of the PMT – grating system. The thick line in Fig. 2 determines the SL spectrum fragment used for the approximation. The fragment includes a continuum and does not contain any spectral lines. The temperature and the intensity scale served as the fitting parameters for the mean-square deviation minimization method. The best congruence was obtained for T = 6 350 K that emphasized the difference in the emission mechanisms of the continuum and atomic lines.
The cavitation temperature estimates provide very low values to admit the thermal nature of ionization during SL. The presented results once again prove the thermodynamic non-equilibrium and the extraordinary nature of processes in the bubble.
The works were performed as a part of the state assignment, registration number: АААА-А20-120021990003-3.
Contribution of authors
T. V. Gordeychuk – setting of the task, discussion of the results, writing of the article; M. V. Kazachek – design and conduction of the experiment, discussion of the results, writing of the article.
authors
M. V. Kazachek, Cand. of Sc.(in Chemistry), position: senior scientist, Iljichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia. Area of interest: spectroscopy, physical chemistry.
ORCID: 0000-0001-9320-1124
T. V. Gordeychuk, Cand. of Sc.(Phys. & Math.), position: senior scientist, Iljichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia. Area of interest: spectroscopy, physical acoustics.
ORCID: 0000-0001-8425-4080
T. V. Gordeychuk, M. V. Kazachek
Iljichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia
The weak lines of CaII at 393 and 397 nm were observed upon 20 kHz insonification of 2M CaCl2 aqueous solution in the multibubble sonoluminescence spectrum. The rough estimation of Ca ionization degree having made by comparison with the solar spectrum that indicates the significant thermodynamic nonequilibrium of processes in a cavitation bubble.
Keywords: sonoluminescence, CaCl2 aqueous solution, Ca ionization
Received: December 02, 2022
Accepted: December 25, 2022
The ultrasonic wave transmission through the liquids is accompanied by a number of nonlinear acoustic phenomena, the most important of which is cavitation, namely the bubble formation, its growth, and explosive collapse. The property of cavitation bubbles to concentrate the ultrasound energy leads to the occurrence of localized, short-lived hot spots in the liquid with the extremely high temperature and density of the substance, subject to the high-speed almost adiabatic compression [1]. Sonoluminescence (SL) that is the weak glow of liquids in a wide range from the UV to IR spectra is a consequence of such extreme conditions. The spectral measurements demonstrate that the conditions in cavitation bubbles are thermodynamically nonequilibrium. The emission spectra of stable SL of a single bubble in asulfuric acid aqueous solution have shown the vibrationally hot SO with Tv = 2 100 K that is also rotationally cold with Tr = 290 K [2]. The same phenomenon has been observed for NH in the case of multibubble SL in an aqueous solution of ammonia [3]. The nonequilibrium sigs have also been found for the ionization process in the case of sonoluminescence in the mode of a consistently pulsating single bubble [4, 5]. In [5], under conditions providing a highly efficient collapse (sulfuric acid with a low content of inert gases), the highly excited ionic states of gases with the energies up to 37 eV (Ar+) have been registered, while the experimental temperature assessment based on the Ar line mutual intensity under such conditions has not exceeded 16 000 K [3].
During the multi-bubble SL of aqueous solutions, the estimated cavitation temperatures are lower being at the level of 2 500–4 000 K [6, 7]. Nevertheless, we observe the Ca ionic lines in the multibubble SL spectra of CaCl2 aqueous solution that has allowed us to make a rough estimate of the substance ionization degree under our experimental conditions.
Experiment
The detailed description of the experimental method and setup for measuring SL spectra has been provided multiple times [8]. Ultrasonic oscillations were excited in a temperature-controlled steel flow-type cell [9] using a Sonics VC750 generator with the frequency of 20 kHz. The released power at the level of 18 W was determined based on the generator parameters. The solution temperature was maintained at 10±1 °C. The solutions were prepared using CaCl2 (Neva-reaktiv, 95%) and distilled water. The solution was saturated with argon for 2 hours before and throughout the experiment. The spectra were recorded using an MDR‑23 monochromator (grating: 1 200 lines / mm, the highest energy concentration area: 500 nm), FEU‑100 photodetector (color sensitivity area: 200–800 mm). The measurement control and data processing were performed by a computer. To obtain the solar spectrum, the entrance slit of the monochromator was illuminated by the scattered sky light. Spectral correction for the PMT sensitivity and reflection of the diffraction grating was performed using the calibrated lamps OP‑33–0.3 and DDS‑30.
Results
In the spectrum of 2 M CaCl2 aqueous solution, under certain conditions, probably favorable for the metal luminescence processes (this issue requires a separate study), we have observed weak lines of the CaII ion at 393 and 397 nm (Fig. 1). We have found the only mention of Ca ionic lines in the multibubble SL spectrum of CaCl2 aqueous solution in the classical paper [10], but at a high ultrasonic frequency (500 kHz). The authors did not observe these lines at an ultrasonic frequency of 16 kHz that was attributed to their low brightness during SL and their proximity to the SL continuum maximum. Moreover, we have recorded these lines only at the concentrations of ~2 M (saturation concentration is about ~5 M). Figure 1 shows the SL spectrum fragment of a 2 M CaCl2 solution, measured with a resolution of 0.6 nm, and the solar (sky) emission spectrum measured with a resolution of 0.3 nm using the same spectrometer. The SL spectrum in Fig. 1 is normalized to a wavelength of 423 nm. For illustrative purposes, the solar spectrum is modified according to the formula J = log(J0 / 2) + 1.5, where J, J0 are the calculated and measured intensity, respectively. The solar spectrum demonstrates the intense CaII lines and a weak CaI line. According to [11], the reduced width (brightness) of lines in the solar spectrum is 342 for CaI at 422.7 nm, 4874 for CaII at 393.4 nm, and 3 435 for CaII at 396.8 nm. Apparently, the radiation conditions in the case of the Sun are significantly different from SL: in particular, the photosphere pressure is ~0.1 atm, while in a compressing bubble it reaches hundreds of atm. The lines in the SL spectrum are redshifted and broadened in relation to the solar ones due to the high density of the radiating medium during SL. It should be noted that the ionic line excitation energy (3.15 and 3.12 eV) is comparable with the value for CaI at 423 nm (2.93 eV).
The observation of ionic lines in the SL spectra confirms availability of a low-temperature plasma in the bubbles. The Ca ionization degree in the bubbles (fraction of ions) Xb can be roughly estimated by comparing the brightness of atomic and ionic lines in the SL and solar spectra (Fig. 1). We have not found exact data for Ca. It was noted in the paper [12] that Ca in the solar chromosphere is represented “mostly” (the author’s expression) in the ionized form. Since we observe an atomic line in the solar spectrum, this is obviously not 100% ionization. We can also assume that if we consider the ionization degree for hydrogen in the solar photosphere as 10–4, as well as the ionization energies of the Ca (6.1 eV) and H (13.6 eV) atoms, then it is obvious that the Ca ionization degree in the Xs photosphere will be many times greater. Let Xs = 30%. The expression Xb / Xs = (Ibi / Ibn) / (Isi / Isn) ≈ 1 / 200, where I is the spectral line brightness, the indices b, s, i, n refer to the bubbles, the Sun, ions, and neutral atoms, respectively, provides a rough estimate leading to Xb = 0.15%.
Previously, we determined the metal emission temperature during SL as ~3 300 [6] while applying the Ornstein method and using two atomic Mn emission lines in the SL spectrum of MnCl2 aqueous solution under the similar experimental conditions. This result is in line with that obtained for an aqueous solution of benzene for the Swan molecular bands [7]. In this case, we filled the experimental spectrum of a 2M CaCl2 aqueous solution with the black body spectrum according to the Planck formula (Fig. 2). The SL spectrum was adjusted for the color sensitivity of the PMT – grating system. The thick line in Fig. 2 determines the SL spectrum fragment used for the approximation. The fragment includes a continuum and does not contain any spectral lines. The temperature and the intensity scale served as the fitting parameters for the mean-square deviation minimization method. The best congruence was obtained for T = 6 350 K that emphasized the difference in the emission mechanisms of the continuum and atomic lines.
The cavitation temperature estimates provide very low values to admit the thermal nature of ionization during SL. The presented results once again prove the thermodynamic non-equilibrium and the extraordinary nature of processes in the bubble.
The works were performed as a part of the state assignment, registration number: АААА-А20-120021990003-3.
Contribution of authors
T. V. Gordeychuk – setting of the task, discussion of the results, writing of the article; M. V. Kazachek – design and conduction of the experiment, discussion of the results, writing of the article.
authors
M. V. Kazachek, Cand. of Sc.(in Chemistry), position: senior scientist, Iljichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia. Area of interest: spectroscopy, physical chemistry.
ORCID: 0000-0001-9320-1124
T. V. Gordeychuk, Cand. of Sc.(Phys. & Math.), position: senior scientist, Iljichev Pacific Oceanological Institute of the Far Eastern Branch of the Russian Academy of Sciences, Vladivostok, Russia. Area of interest: spectroscopy, physical acoustics.
ORCID: 0000-0001-8425-4080
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