Estimation of Sonoluminescence Temperature with the Ornstein Method
The temperature of Mn emission was determined with the Ornstein method using two atomic emission lines in the sonoluminescence spectrum of aqueous MnCl2 solution. The calculated temperature is about 3300K and consistent with the temperature estimated earlier using Swan molecular bands for aqueous solution of benzene (Didenko Y. T., McNamara III W.B., Suslick K. S., J. Am. Chem. Soc., 1999, V. 121, P. 5817).
of Sonoluminescence Temperature
with the Ornstein Method
M. V. Kazachek 1, T. V. Gordeychuk 1, A. S. Pochinok 1
V. I. Iljichev Pacific oceanological institute FEB RAS,
The temperature of Mn emission was determined with the Ornstein method using two atomic emission lines in the sonoluminescence spectrum of aqueous MnCl2 solution. The calculated temperature is about 3300 K and consistent with the temperature estimated earlier using Swan molecular bands for aqueous solution of benzene (Didenko Y. T., McNamara III W.B., Suslick K. S., J. Am. Chem. Soc., 1999, V. 121, P. 5817).
Key words: Cavitation, Ornstein method, Emission temperature, Sonoluminescence
Ultrasound irradiation of liquids is accompanied by cavitation, i. e. nonlinear pulsations of vapor-gas bubbles. The energy accumulated by the bubble during expansion in the negative phase of sound pressure is realized in a rapid almost adiabatic collapse, when the concentration of low density of sound energy reaches about 1012 . As a result, cavitation is accompanied by acoustic noise, shock waves, chemical reactions and weak light radiation in the range from the near UV to the IR region, i. e. sonoluminescence (SL). The SL is materialized in the form of nanosecond flares correlated with the final phase of the collapse, when the temperature and pressure inside the bubble reach thousands of Kelvin and hundreds of atmospheres.
Since ultrasound is widely used in production and medicine, the study of the processes accompanying ultrasonic cavitation is relevant. The extreme conditions formed during the bubble collapse determine the intensity of these processes, in particular, the erosion of materials, the destruction of living cells, and the yield of products of sonochemical reactions. Spectroscopy methods were effectively used to determine pressures and temperatures during ultrasonic cavitation in non-aqueous solutions [2–6]. An analysis of the work on the estimation of the plasma temperature in cavitation bubbles showed that the results obtained by spectroscopic methods in aqueous solutions are few. In , the SL temperature was determined by the mutual intensity of the Swan bands, for which a small amount (0.01%) of benzene was added to the water.
In this research, we applied the atomic spectroscopy method (Ornstein method) to estimate the effective SL temperature from two Mn emission lines in the spectrum of an aqueous MnCl2 solution.
An experimental setup for measuring SL spectra was previously described many times [8, 9]. The central part of the setup is a thermostatic flow-through ultrasonic cell. The tip of the ultrasonic emitter was placed at one end of the cell, the other end was covered with a quartz window connected to the entrance slit of the MDR‑23 monochromator (diffraction grating of 1200 lines / mm with a maximum brightness of 500 nm, the spectral width of the slit was 2.9 nm). The ultrasound frequency of 20 kHz, the output power of 23 W (intensity of 17 W / cm2) was determined by the readings of the VC‑750 generator. The temperature of the solution was maintained equal to ~ 10 °C. The solution was saturated with argon an hour before and during the entire experiment. The light flux was recorded by FEU‑100 photomultiplier. We used a 0.5 M solution of MnCl2 in distilled water with the addition of 0.5 mM ethoxylated alcohol (C14E15). The spectra were measured at an additional static pressure of 0.5 atm. Additional pressure and surfactant helped increase the intensity of metal emission [8, 9].
The experimental spectrum of an aqueous solution of 0.5 M MnCl2 is shown in Fig. 1 with a dashed line. The spectrum is a continuum over which a OH radical band is imposed (about 310 nm). The spectrum contains Mn atomic lines. Two spectral lines are observed: 403 nm (3d54s2 a6S – 3d5(6S)4s4p(3P°) z6P°) and 280 nm (3d54s2 a6S – 3d5(6S)4s4p(1P°) y6P°). These lines are tight multiplets. Each multiplet has the brightest (significant) line, which we rely on in our calculations.
The Ornstein method allows one to determine the electronic temperature of the radiation Te from the ratio of the intensities of two emission spectral lines that do not belong to one multiplet:
where g1,2 is the statistical weight of the excited state, A1,2 is the probability of a spontaneous transition, k is the Boltzmann constant, E1,2 is the level excitation energy, I1,2 is the intensity of the emission lines in the spectrum, λ1,2 is the wavelength. The atomic constants g1,2, A1,2, E1,2 are taken from .
The intensities of the experimental lines I1,2 were determined as follows. The spectrum was corrected for the spectral sensitivity of the recording system (grating + photomultiplier). The correction function was obtained by taking emission spectra of calibrated lamps with the same spectrometer configuration. Since the MnCl2 solution has pronounced absorption bands, a correction was also made for the absorption spectrum of MnCl2. From the corrected spectrum presented in Fig. 1 solid line, cut out the area near the lines, sufficient for a Gaussian approximation of the peak. The cut region of the spectrum for each line was aligned by subtracting the underlying background, followed by tilt correction. The approximation of the obtained peak of the Gauss curve gave the position, amplitude and width of each peak. The amplitude ratio was taken as the ratio of the intensities of the observed lines I1 / I2.
The results of calculations by formula (1) and the constants used are shown in Table 1. The calculations yielded an electron temperature of Te about 3300 K. This value corresponds to the temperature at which Mn emission occurs under SL under our experimental conditions.
For the first time, the Ornstein method was used to estimate the temperature of metal emission during the SL of an aqueous solution of MnCl2 in an Ar atmosphere. The obtained value of about 3300 K is consistent with the result of  (about 4300 K) obtained using Swan molecular bands under similar experimental conditions (aqueous solution, ultrasound of 20 kHz, intensity of 50 W / cm2, solution temperature of 5ºС).
The research was carried out as part of the state task «Studying the Basic Foundations of the Origin, Development, Transformation and Interaction of Hydroacoustic, Hydrophysical and Geophysical Fields of the World Ocean». Registration number: AAAA-A20-120021990003-3.
Contribution of authors:
M. V. Kazachek – design and conduction of the experiment, discussion of the results, writing of the article; T. V. Gordeychuk – setting of the task, discussion of the results, writing of the article; A. S. Pochinok – processing of the results, numerical experiment.
Kazachek M. V., Cand. of Scien. (Chemistry), e-mail: email@example.com, senior scientist, V. I. Iljichev Pacific oceanological institute FEB RAS, Vladivostok, Russia.
area of interest: spectroscopy, physical chemistry.
Gordeychuk T. V., Cand. of Scien. (Physics and mathematics),
e-mail: firstname.lastname@example.org, senior scientist, V. I. Iljichev Pacific oceanological institute FEB RAS, Vladivostok, Russia.
area of interest: spectroscopy, physical acoustics.
Pochinok A. S., Master student of FEFU, e-mail: email@example.com, engineer, V. I. Iljichev Pacific oceanological institute FEB RAS, Vladivostok, Russia.
area of interest: physical acoustics, atomic spectroscopy.