In this paper we focus on the investigation of the transient cavitation activity evolution during the sonochemical treatment of magnesium aqueous suspensions. We investigated the nonlinear behavior of cavitation activity that can be related with the influence of hydrogen gas released in the reaction of magnesium with water. Ultrasound causes the modification of the magnesium particles leading to the formation of the nanostructured Mg(OH)2 phase (brucite) resulting from both chemical and sonochemical impacts on the magnesium

Brezhneva, N.

Dezhkunov, N. V.

Mazheika, S. O.

Nenashkina, A.

Skorb, E. V.

Дежкунов, Н. В.

Belarusian State University of Informatics and Radioelectronics Repository

International Journal of Nanoscience W tPVol. is, Nos. з &  4 (2019) 1940071 (4 pages) w f i  World ScientificW orld SHentifir Publishing C,rm im nv  ™  w w w .w o rld sc ie n tific .co m©  orl  cie tific blis i g o pa y DOI: 10.1142/S0219581X19400714Evolution of Cavitation Activity During Ultrasonic Nanostructuring of MagnesiumN. Brezhneva*’^ ,  N. V. Dezhkunov^, S. O. Mazheika*, A. Nenashkina^ and E. V. Skorb'*Faculty o f Chemistry, Belarusian State University Leningradskaya Street 14, 220030 Minsk, Belarus +ITM O University, Lomonosova Street 9 191002 St. Petersburg, Russia %Research and Development Unit Belarusian State University o f Informatics and Radioelectronics P. Brovki Str. 6, 220013 Minsk, Belarus %rezh,NY@bsu. byReceived 22 December 2018 Accepted 14 January 2019 Published 13 May 2019In this paper we focused on the evolution of transient cavitation activity during the sono- chemical treatment of magnesium aqueous suspensions. We have investigated the non-linear behavior of the cavitation activity related to the hydrogen released in the reaction of magnesium with water. Ultrasound modifies magnesium particles leading to the formation of nanostructured Mg(OH)2 phase (brucite) resulting in the chemical and sonochemical impacts on magnesium.Keywords: Transient cavitation; sonochemical nanostructuring; magnesium particle; hydrogen storage.1. IntroductionNowadays, ultrasonic (US) processing provides new possibilities in the synthesis o f new nanomaterials, structuring solid surfaces for creating materials with the desired properties with proper control at the microlevel and nanolevel.1,2 Am ong the benefits o f sonochemical method, one could mention an ability to create non-equilibrium conditions during the synthesis in a specific manner. For example, the collapse o f cavitation bubbles is accompanied by creating local areas o f extremely high temperatures& Corresponding author.(ca. 5000 K) and pressures (ca. 500 bar)3 while the system treated by US remains on macrolevel at ambient conditions. The type o f cavitation that deals with the phenomenon o f bubble collapse on the final stage o f the bubble cycle is called the transient cavitation.4 Moreover, microbubbles that appeared during the sonochemical treatment o f aqueous solutions can appear as microcontainers with free radicals and active ions that are appro­priate species for the synthesis o f nanostructures and modification o f solids.1940071-1N. Brezhneva et al.Sonochemical treatment o f metals and alloys surface leads to an enhancement o f different mate­rials’ properties in comparison with non-treated original materials. For instance, the activation of electrocatalytic water splitting by A l-N i alloy,5,6 improvement o f the T i biocompatibility,7-9 and formation o f active aluminum surfaces10 were observed. Recently, the use o f sonochemically trea­ted Mg for reactive hard templating has been demonstrated.11 In addition, an interest to the Mg activation is caused by the perspectives o f its application as a hydrogen storage material due to the light weight o f and large content o f hydrogen in Mg hydride structure.12In this paper, we present experimental results on the evolution o f the cavitation activity during US treatment o f Mg aqueous suspensions.2. ExperimentalAqueous suspensions o f Mg powder (Alfa Aesar; 99.8%; —325 mesh) with different concentrations (0.003, 0.007 and O .Olg/m L) were prepared by adding the appropriate amount o f powder to 100 mL of distillated water.In the experimental setup schematically shown in Fig. 1(a), the sonotrode was connected to an ultrasonic generator UZG 55-22 (20kHz). The cav­itation activity was registered with the hydrophoneconnected to a cavitometer ICA 5D and placed under the sonotrode tip at a distance o f 1 cm. The probe at the hydrophone end acted as a waveguide coupling the acoustic signal from the cavitation zone to the piezoceramic plate. The electronic block o f the cavitometer allowed displaying and proces­sing the electric signal produced by the piezoelectric probe in response to the acoustic stimulation.133. Results and DiscussionDuring the sonochemical treatment o f magnesium the following reactions occur:H20  =  H+ +  0 H - ,  (1)Mg +  2H20  =  M g(O H )2 +  H2. (2)The reaction (1) is attributed to water sonolysis and the reaction (2) is related to the modification o f Mg during sonication. Magnesium is affected by the chemical and sonomechanical impacts resulting in the etching o f the metal surface and formation of the porous structure and magnesium hydroxide.The transient cavitation is the main factor o f US treatment when cavitation bubbles reach their critical size and violently collapse [Fig. 1(b)] producing extreme conditions with local areas o f high temperatures.3 For aqueous suspensions with different contents o f Mg particles, various dependencies o f cavitation activity were detected.ч: ^ O OОЙх): Hч. О-О  ,r>{ I ) ’■' J  -'U '(iwater4 5 6 7 8 9 1011 1 2 1 3 1 4 1 5  Time, min(V)>EMg 0.003 g/ml Mg 0.007 g/mlMg 0.01 g/ml6 7 8 9 1011 12 1314 15 Time, min(d)Fig. 1. (a) The setup for cavitation intensity measurements during the sonochemical treatment o f Mg aqueous suspensions; (b) theevolution o f the cavitation bubbles size; (c) and (d) the cavitation intensity during the US treatment o f pure water and the Mg suspensions of different concentrations, respectively.1940071-2Cavitation Activity Evolution During Ultrasonic Nano structuring o f MagnesiumIn the case o f 0.003-g/m L suspension, the cavitation intensity increased till the third minute o f treat­ment [Fig. 1(d)]. This fact can be connected with the formation o f small bubbles that detach from the metal particles’ surface and contribute to the cavi­tation intensity. During the US treatment o f this suspension, the number o f small bubbles increases and the cavitation intensity reaches its maximum. The increase in the amount o f small bubbles can result in production o f big bubbles by the possible coalescence mechanism [Fig. 1(b)] responsible for the decrease in the cavitation intensity. This phe­nomenon can be explained as the screening by the large bubbles the cavitation intensity 011 its way to be detected with hydrophone. After reaching its maximum, the intensity o f cavitation further decreases and reaches the equilibrium value, when the rates o f formation and destruction o f large cavitation bubbles get equal.Interestingly, when the amount o f Mg is larger, the cavitation activity oscillations can be noted. In the case o f 0.007-g/m L and 0 .01-g/m L suspensions [Fig. 1(d)], after the stage o f  decrease in the cav­itation intensity, the cycles o f enlargem ent- reduction in the cavitation activity are observed and the increase in the concentration o f the reac­tive metal leads to the formation o f more hydro­gen. W e assume that the gas evolved by this chemical reaction influences the formation and collapse o f cavitation bubbles. Gaseous hydrogen has the highest diffusivity in comparison with other gases.14 H2 bubbles released to liquid can generate more efficient cavitation than other dis­solved gases due to its high diffusivity observed in w ater.14Thus, in our case the in situ production o f H2 due to the chemical reaction o f magnesium particles with water can affect the size o f cavitation bubbles. These hydrogen bubbles can influence the bubble size through diffusion o f gas molecules into the bubbles, leading to their enlargement and growth of the partial gas pressure inside the bubble making it more difficult to be collapsed by the external pres­sure. The following increase in the cavitation ac­tivity can be related to destruction o f the larger bubbles and to the reformation stage o f the smaller bubbles.15 In the case o f pure water such effect of cavitation intensity oscillations was not observed [Fig. 1(c)].4. ConclusionThe analysis o f transient cavitation activity in aqueous suspensions o f Mg particles was carried out. The cavitation intensity increase can be at­tributed to the formation o f small bubbles. The further decrease o f cavitation intensity can be re­lated to the formation o f large bubbles by coales­cence o f small bubbles or the hydrogen diffusion produced during the chemical reaction o f magne­sium with water.AcknowledgmentsThe work was supported by RSF Grant No. 17-79- 20186 and by the Government o f Russian Federa­tion (Grant 08-08).References1. K. S. Suslick, T. Hyeon and M. Fang, Chem. Mater. 8, 2172 (1996).2. K. S. Suslick, T. Hyeon, M. Fang and A. A. Cichowlas, Mater. Sci. Eng. A 204 , 186 (1995).3. K. S. Suslick, Science 247 , 1439 (1990).4. С. K. Holland and R. E. Apfel, J. Acoust. Soc. Am. 88, 2059 (1990).5. P. V. Cherepanov, I. Melnyk, E. V. Skorb, P. Fratzl, E. Zolotoyabko, N. Dubrovinskaia, L. Dubrovinsky, Y. S. Avadhut, J. Senker, L. Leppert, S. Kiimmel and D. V. Andreeva, Green Chem. 17 , 2745 (2015).6. P. V. Cherepanov, M. Ashokkumar and D. V. Andreeva, Ultrason. Sonochem. 23 , 142 (2015).7. Y. Zhukova, S. A. Ulasevich, J. W. C. Dunlop, P. Fratzl, H. Mohwald and E. V. Skorb, Ultrason. Sonochem. 36 , 146 (2017).8. J. Kopf, S. Ulasevich, O. Baidukova, Y. Zhukova, J. W. C. Dunlop, P. Fratzl, P. Rikeit, P. Knaus, S. K. Poznyak, D. V. Andreeva and E. V. Skorb, Adv. Eng. Mater. 18 , 476 (2016).9. Y. Zhukova, C. Hiepen, P. Knaus, M. Osterland, S. Prohaska, J. W. C. Dunlop, P. Fratzl and E. V. Skorb, Adv. Healthc. Mater. 6, 1601244 (2017).10. J. Gensel, T. Borke, N. Pazos Perez, A. Fery, D. V. Andreeva, A. H. E. Muller, H. Mohwald and E. V. Skorb, Adv. Mater. 24 , 985 (2012).11. O. Baidukova, H. Mohwald, A. S. Mazheika, D. V. Sviridov, T. Palamarciuc, B. Weber, P. V. Cherepanov, D. V. Andreeva and E. V. Skorb, Chem. Commun. 51 , 7606 (2015).1940071-3

Evolution of Cavitation Activity During Ultrasonic Nanostructuring of Magnesium

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Evolution of Cavitation Activity During Ultrasonic Nanostructuring of Magnesium

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