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Electrolytic cell-free 57Co deposition for emission Mössbauer spectroscopy
Radiation Physics and Chemistry 146 (2018) 86–90
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Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Electrolytic cell-free
57
Co deposition for emission Mössbauer spectroscopy
a
a,⁎
b,c
Dmitry V. Zyabkin , Vít Procházka , Marcel Miglierini , Miroslav Mašláň a b c
T
a
Department of Experimental Physics, Faculty of Science, Palacký University in Olomouc, 17. Listopadu 12, Olomouc, Czech Republic Slovak University of Technology in Bratislava, Institute of Nuclear and Physical Engineering, Ilkovičova 3, 812 19 Bratislava, Slovakia Department of Nuclear Reactors, Czech Technical University in Prague, V Holešovičkách 2, 180 00 Prague, Czech Republic
A R T I C L E I N F O
A B S T R A C T
Keywords: 57 Co Electrolytic deposition Emission Mössbauer spectroscopy Cu Metallic glass
We have developed a simple, inexpensive and efficient method for an electrochemical preparation of samples for emission Mössbauer spectroscopy (EMS) and Mössbauer sources. The proposed electrolytic deposition procedure does not require any special setup, not even an electrolytic cell. It utilizes solely an electrode with a droplet of electrolyte on its surface and the second electrode sunk into the droplet. Its performance is demonstrated using two examples, a metallic glass and a Cu stripe. We present a detailed description of the deposition procedure and resulting emission Mössbauer spectra for both samples. In the case of a Cu stripe, we have performed EMS measurements at different stages of heat-treatment, which are required for the production of Mössbauer sources with the copper matrix.
1. Introduction Emission Mössbauer spectroscopy (EMS) is a powerful method for investigating different phenomena in physics. It has several advantages in comparison with a transmission geometry arrangement. In particular, it is at least 10,000 times more sensitive (Nath, 2010), in combination with a coincidence measurement it allows observation of chemical after-effects (Kamnev et al., 2017; Nagy, 1994) and quantity of the studied material commonly does not exceed 1 mg (Kamnev, 2013; Kamnev and Tugarova, 2017; Perfiliev, 2010). EMS is also suitable for investigation of diffusion processes. However, it is not widely applied due to a necessity of radioactive isotopes incorporation into the studied material that is a challenging task. The easiest way is to add 57 Co during the synthesis of the studied compound. In this case, 57Co is directly embedded into a crystalline structure. When the dynamic processes including solid-state diffusion are under a scope 57Co is added after the synthesis. For this purpose, different methods can be employed such as physical, chemical vapour deposition, direct alloying, and electrolytic deposition (Chackett et al., 1960; Cieszykowska et al., 2011a; Heyse et al., 2014; Severin, 1979). The latter is frequently used in the case of a compact conductive sample. Electrochemical deposition is also commonly used for preparation of Mössbauer sources. During this procedure, 57Co is deposited on appropriate substrates (Cu, Cr, Rh). Afterwards, 57Co atoms are diffused into a cubic structure of the matrix by annealing under inert atmosphere or in a vacuum. Electrolytic deposition of a natural isotopic mixture of Co (Kongstein et al., 2011; Palomar-Pardavé et al., 1998, 2005) is highly
⁎
sensitive to pH (Abd El Rehim et al., 1998), electrolyte composition (Kongstein et al., 2007b), (Frank and Sumodjo, 2014), (Grujicic and Pesic, 2004), cobalt concentration within the solution (Pagnanelli et al., 2015), applied voltage and/or electrodeposition current (Kongstein et al., 2007a). So far, in several studies describing the 57Co deposition electrolytes based either on sulphuric or hydrochloric acids were used (Fujimori et al., 1982; Kerfoot and Weir, 1988). However, in other works dedicated to that problem mainly citrate with additional hydrazine hydrate and ammonia hydroxide additives were utilized (Dézsi and Molnár, 1967; Mustachi, 1964; Stephen, 1964). Current densities were varied from 10 to 100 mA/cm2 with a time span up to 25 h and a maximal efficiency reaching 90%. They performed deposition onto steel and copper plates. Later, a method for low-activity-point-sources preparation was reported (Saxena et al., 2013). By virtue of using evaporation, 57Co as a cobalt chloride was subsequently diluted in H2SO4 and deposited with an addition of boric acid and ammonium hydroxide onto a tip of a cylindrical copper rod. A successful deposition of 3.7–5.18 MBq (∼100–140 μCi) under elevated temperature and current density of 45 mA/cm2 was demonstrated. Several researchers (Udhayakumar et al., 2012), (Ashutosh Dash et al., 2011) have described a mixed employment of non-radioactive Co and 57Co and its deposition onto a copper disc, with subsequent heat-treatment at 400 °C for 2 h. The activity was 1.48 MBq (~40 μCi) and 3 mCi/ml in 0.5 M HCl under current density 10–40 mA/cm2 and pH was kept at 3–4. The deposition yield of 57Co was 91%. The most recent works on source production have dealt with the production of rhodium-based sources, which utilized two electrolytes: alkaline (ammonium citrate, hydrazine
Corresponding author. E-mail address: [email protected] (V. Procházka).
https://doi.org/10.1016/j.radphyschem.2018.01.016 Received 17 November 2017; Received in revised form 10 January 2018; Accepted 17 January 2018 0969-806X/ © 2018 Elsevier Ltd. All rights reserved.
Radiation Physics and Chemistry 146 (2018) 86–90
D.V. Zyabkin et al.
demonstrate applicability of the method for the preparation of samples for emission Mössbauer spectroscopy and Mössbauer sources. For Mössbauer sources production 57Co deposited on the surface has to be incorporated into a cubic matrix of selected metals (Cu, Rh, Cr). Commonly, heat treatment is utilized within a defence atmosphere (argon (González-Ramírez et al., 1993), hydrogen (Mustachi, 1964), hydrogen mixed with carbon dioxide (Song and Mullen, 1977) and in vacuum (Dézsi and Molnár, 1967; Stephen, 1964)) which is kept inside a ceramic- or quartz-tube-based-furnace. Using of those tubes with a continuous argon flow and/or vacuum atmosphere showed almost the same results, except at high temperatures when on the surface Al2O3 and SiO2 presence was discovered at 1300 °C (Cieszykowska et al., 2011b). In some cases, the heat-treatment procedure was followed by rapid cooling in spite of an increasing number of vacancies within material with a following increase of the line width. (Cieszykowska et al., 2011b; Dézsi and Molnár, 1967; González-Ramírez et al., 1993; Stephen, 1964). Mössbauer spectra of sources in various states were presented rather rarely. Within this study, we show that the presented simplified deposition approach can be used for production of at least low activity Mössbauer sources. We report on the investigation of the 57Co atoms incorporation into the Cu matrix using EMS.
Fig. 1. The experimental conditions, the flat Cu cathode, the droplet of electrolyte with the Pt anode.
Table 1 Thermal treatment of the Cu strips. Temperature (°C)
Time (h)
350 450 470 490 530 550 570 590 600
1;2;3;5* 1;2;3;5* 1;5 1 1;3 1;5;7* 1;3; 5 1*
2. Experimental For the electrodeposition, the used solution consisted of 57CoCl2 in a 0.5 M HCl with specific activity of 5 mCi/ml (185 MBq/ml) produced by RITVERC, Saint-Petersburg, Russian Federation. A stripe of metal (Cu or metallic glass) representing the cathode was mounted on a holder in horizontal position. The desired amount of 57Co was deposited on the surface of the cathode in a form of 0.5 M HCl solution as illustrated in Fig. 1. It formed a small droplet due to the surface tension. The number of cobalt ions did not exceed 1015 within one droplet. Platinum wire 0.2 mm in diameter was inserted into the droplet as the anode. The rest of the metal stripe was covered by Parafilm M (by Bemis NA, USA) to avoid unwanted contact with the electrolyte. Prior to the experiment, the exposed surface was polished and degreased with acetone. Both the anode and the cathode were connected to a potentiostat OrigaStat - OGS100 by OrigaLys Electrochem SAS for a voltage control. In each experiment, the working volume of electrolyte varied from 30 to 60 μl. Regular additions of hydrazine hydrate were used to increase pH of the solutions up to 10–11 to prevent dissolution of the already deposited Co. Depositions were performed under ambient room conditions, pH of the solution during the deposition was controlled several times with the litmus paper. Deposition efficiency was studied within the interval of working voltage from 1.1 to 1.6 V (2.2 V
Note: Asterisks indicate the annealing time periods for which EMS spectra are shown in Fig. 3.
hydrate, ammonia solution) and acid (0.01 M HCl and 0.1 M NaCl). The maximum outcome reached almost 100% within 7 h of deposition. It was also pointed out that smaller volume of electrolyte and higher current density lead to higher efficiency in both cases, however the best result was obtained with a citrate electrolyte. Cells volumes were 5 and 10 μl, respectively (Cieszykowska et al., 2011a). All the above-mentioned experiments were carried out in special closed/sealed cells. Nevertheless, in many cases (including emission samples) the required amount of deposited 57Co has been rather small and using of such equipment inefficient due to low amount of the trace isotope and electrolyte.(Ashutosh Dash et al., 2011; Cieszykowska et al., 2011b) In this work, we present a simple approach of 57Co deposition without any specific cell using solely a droplet of an electrolyte on a surface of the cathode. This study focuses on electrolytic deposition of 57Co on a metallic glass and copper surface. These two examples have been chosen to
Fig. 2. (a) Impact of volume on the rate of deposition, (b) Effect of pH on current during deposition at different potentials.
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Radiation Physics and Chemistry 146 (2018) 86–90
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sufficient efficiency was achieved only with hydrazine hydrate added to Co in a form of 0.5 M HCl. The experiment with a Cu stripe was accomplished by a heat treatment procedure in an inert protective atmosphere of nitrogen. The sample in a ceramic crucible was placed into a furnace. One of the samples was repeatedly treated and after each heat treatment the emission Mössbauer measurement was performed at room temperature. The temperature and duration of thermal treatment is summarized in the Table 1. In the EMS experiments K2Mg[57Fe(CN)6] with 0.25 mg/ cm2 of 57Fe was used as a reference absorber. It was mounted to a transducer moving with triangular velocity and the spectrometer linewidth was 0.31 mm/s using a 28 µm calibration foil of alpha Fe. Mössbauer spectra were analyzed by VINDA (Gunnlaugsson, 2016) and CONUSS (Sturhahn, 2000) software. The Cu stripe width was 7 mm, its thickness was 0.25 mm. Nanoperm-type glass Fe76Mo8Cu1B15 was in the form of about 4.8 mm wide and about 20 µm thick ribbons (Miglierini et al., 2004, 2007). Deposition was made on the air (glossy) side of the glass and the sample was not thermally treated. Chemical composition of the copper stripe was characterized by means a scanning electron microscopy Vega 3 by Tescan equipped with an EDS detector. The presence of minor impurities was observed they consisted of 0.3% Ni and 0.07% Fe. 57
3. Results and discussion The impact of electrolyte volume on the rate of deposition was studied. The applied voltage was kept at 1.6 V. First, 30 and 60 μl droplets of electrolyte were deposited. The relative amount of the deposited 57Co was determined with respect to the deposition time. Fig. 2(a) clearly shows that the deposition proceeds faster in case of smaller volume of the droplet. Further, we were gradually increasing the amount of electrolyte during the deposition from 30 μl up to 60 μl. Within 3 h, 5 μl was added every 15 min. In this case, the deposition was approximately two times faster in comparison with the 60 μl droplet. Here, we would like to emphasize that usually the deposited amount is determined by measuring the activity of electrolyte. However, in our experiments it was the activity of the samples that was measured. Current with respect to the applied voltage was measured for different pH levels of electrolyte that varied from 5 to 11. Fig. 2(b) demonstrates that current increases with pH and the applied voltage. In the range 1.6–1.7 V we observed slight but continuous bubbling within the electrolyte on the cathode. The copper stripe with deposited 57Co was characterized using emission Mössbauer spectroscopy. Spectrum measured just after the deposition is presented in Fig. 3(a). Later, the sample was thermally treated according with the description shown in Table 1. The spectra measured after heat treatment marked by * in Table 1 and are plotted in Figs. 3(b)-3(e). From all EMS spectra, we have chosen typical examples which demonstrate pronounced changes in the shapes of spectra imposed by heat treatment. Spectra measured after heat treatment at 470, 490, 530, 570, and 590 °C are not presented as they exhibit negligible changes with respect to the spectra taken after the foregoing temperature treatments. Initially, with increasing of the heating temperature, the lines get broader. Then a new line occurs and after another heat treatment, it disappears again. The spectra in Fig. 3 were fitted using a three-component model. Here, the doublet C1 represents Co atoms in CoCl2 and its hyperfine parameters are in good agreement with those from literature (Cavanagh, 1969; Tamaki and Ito, 1977). The other two singlet components (C2 and C3) were assigned to metallic 57Co at different surroundings (Popov, 2012). All hyperfine parameters are listed in Table 2. After heat treatment at 600 °C, the spectrum exhibits one single line with a minor contribution (ca.8%) of a doublet component (C1). However, this spectrum contains additional contribution (about 12%)
Fig. 3. EMS spectra of 57Co deposited onto a Cu stripe at ambient conditions (a), recorded at room temperature after annealing 350 °C for 5 h. (b), 450 °C 5 h.(c), 550 °C 7 h. (d) and 600 °C 1 h. (e) with its magnified region showing the magnetic presence. Corresponding annealing times are marked in Table 1 by asterisks.
in case of the metallic glass due to much higher electrical resistance) and working current varied in an interval 3–10 mA/cm2. The total activity of the deposited 57Co was about 4.5 MBq for each sample. For determination of the deposited amount of cobalt, the electrolyte was every 30 min removed from the sample's surface and the surface activity was measured. The total time of the electrolytic deposition was three hours. Various combinations of acids, ammonium, and citrate solutions were tested during the development of this approach but 88
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Table 2 Hyperfine parameters of 57Co deposited on Cu after deposition and annealing. Isomer shifts are determined with respect to alpha-Fe, where C1-3 correspond to relative areas, IS1-3 to isomer shifts and QS1 to quadrupole splitting. State
C1 (%)
C2 (%)
C3 (%)
IS1 (mm/s)
IS2 (mm/s)
IS3 (mm/s)
QS1 (mm/s)
As-deposited 350 °C 450 °C 550 °C 600 °C
32 (1) 43 (2) 48 (2) 48 (2) 7.4(1)
67 49 36 63 80
0.2 (2) 6 (1) 15 (1) 24 (2) –
0.988 0.968 0.868 0.698 0.578
−0.002 (1) −0.042 (1) −0.112 (2) 0.008 (1) 0.028 (2)
0.868 0.858 0.868 0.808 –
2.52 2.73 2.76 2.48 2.13
Fig. 4. (a) Emission Mössbauer spectrum of
57
(2) (6) (1) (3) (3)
(3) (2) (2) (8) (9)
(8) (8) (3) (3)
(6) (4) (3) (2) (4)
Co deposited on the metallic glass. (b) Distribution of hyperfine field of the major contribution of the spectrum in Fig. 4(a).
of a ferromagnetic sextet with the isomer shift of −0.10(4) mm/s, quadrupole shift of 0.04(6) mm/s, and hyperfine magnetic field of 38.2(6) T as demonstrated by an inset in Fig. 3(e) where a spectrum of the sample after annealing under 600 °C with magnified y-axis is shown. The appearance of this magnetic component can be connected with the presence of magnetic atoms (Fe and Ni) that are present as impurities in technical copper that was used in our experiments. The process of 57Co deposition on the metallic glass was performed with the voltage of 2.2 V, the method of gradual increase of electrolyte was applied, the total amount of the electrolyte was 60 μl. The efficiency of deposition was 73%. Emission Mössbauer spectrum recorded from the metallic glass sample is shown in Fig. 4(a). It was fitted using a single sextet model. The major sextet exhibits large distribution of the hyperfine magnetic fields (see Fig. 4(b)), quadrupole interaction of 0.1 mm/s and isomer shift of −0.242 mm/s. Hyperfine parameters obtained after fitting agree with typical values observed in nanocrystalline glasses after the crystallization process of the original metallic glass (Conde et al., 2007). Thus, we can assign it to 57Co in contact with the nanograins that were formed on the surface of the ribbon-shaped sample. On the contrary, conversion electron Mössbauer spectroscopy (CEMS) spectra of the same compound exhibit much lower contribution of the surface crystallization (Cesnek et al., 2016). This discrepancy together with the shape of the EMS spectrum is a surprising result and further comprehensive investigation of this phenomenon is in progress. Here, we have checked only the feasibility of 57Co deposition upon surface of a metallic glass ribbon produced by the method of rapid quenching. as mentioned above, more systematic studies are envisaged and will be reported in a separate paper.
based incorporation of 57Co into a copper substrate was followed by means of emission Mössbauer spectroscopy. The results demonstrate that temperature of annealing after the deposition plays a key role in the whole process. It governs the incorporation of 57Co atoms into individual structural positions. Whilst at rather low temperatures of heat treatment some of the deposited material is still present on the surface in the form of the CoCl2, after 600 °C it is clear that the majority of Co atoms enters Cu. This sample exhibits a dominant single-line spectrum. Application potential of the deposition technique was demonstrated also by using a metallic glass ribbon. As the proposed method does not require any special and expensive equipment, it could be successfully utilized in many Mössbauer spectroscopy laboratories. Acknowledgements The authors gratefully acknowledge the support by internal IGA grant of Palacký University (IGA_PrF_2017_011) and projects VEGA 1/ 0182/16 and APVV-16–0079. The authors would also like to thank Helena Sedláčková (Palacký University Olomouc, Czech Republic) for her help with this paper. References Abd El Rehim, S.S., Abd El Wahaab, S.M., Ibrahim, M.A.M., Dankeria, M.M., 1998. Electroplating of cobalt from aqueous citrate baths. J. Chem. Technol. Biotechnol. 73, 369–376. http://dx.doi.org/10.1002/(SICI)1097-4660(199812)73:4<369::AIDJCTB971>3.0.CO;2-P. Ashutosh Dash, M.K., Udhayakumar, J., Gandhi, Shyamala S., Satpati, A.K., Nuwad, Sukla, Rakesh, Pillai, C.G.S., Venkatesh, Meera, Venugopal, V., 2011. On the application of electrochemical techniques for the preparation of 57Co source core, encapsulation and quality evaluation for radiometric assay of nuclear fuel rods. Radiochim. Acta 99, 103–111. http://dx.doi.org/10.1524/ract.2011.1799. Cavanagh, J.F., 1969. Mössbauer effect for Fe57 in CoCl2 and CoF2. Phys. Status Solidi (b) 36, 657–663. http://dx.doi.org/10.1002/pssb.19690360229. Cesnek, M., Miglierini, M., Bednarčík, J., 2016. 57Fe75Mo8Cu1B16 metallic glass studied by CEMS, CXMS and HEXRD. AIP Conf. Proc. 1781, 020002. http://dx.doi.org/10.1063/ 1.4965998. Chackett, G.A., Chackett, K.F., Singh, B., 1960. The processing of iron cyclotron targets in connexion with the Mössbauer effect in 57Fe. J. Inorg. Nucl. Chem. 14, 138–139.
4. Conclusions We have developed a low-cost method for 57Co electrolytic deposition that is easy to employ. It has been successfully tested using two examples, namely a copper stripe and metallic glass ribbon. The highest achieved efficiency reached ~ 90% after 3 h of deposition. Diffusion 89
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Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Electrolytic cell-free
57
Co deposition for emission Mössbauer spectroscopy
a
a,⁎
b,c
Dmitry V. Zyabkin , Vít Procházka , Marcel Miglierini , Miroslav Mašláň a b c
T
a
Department of Experimental Physics, Faculty of Science, Palacký University in Olomouc, 17. Listopadu 12, Olomouc, Czech Republic Slovak University of Technology in Bratislava, Institute of Nuclear and Physical Engineering, Ilkovičova 3, 812 19 Bratislava, Slovakia Department of Nuclear Reactors, Czech Technical University in Prague, V Holešovičkách 2, 180 00 Prague, Czech Republic
A R T I C L E I N F O
A B S T R A C T
Keywords: 57 Co Electrolytic deposition Emission Mössbauer spectroscopy Cu Metallic glass
We have developed a simple, inexpensive and efficient method for an electrochemical preparation of samples for emission Mössbauer spectroscopy (EMS) and Mössbauer sources. The proposed electrolytic deposition procedure does not require any special setup, not even an electrolytic cell. It utilizes solely an electrode with a droplet of electrolyte on its surface and the second electrode sunk into the droplet. Its performance is demonstrated using two examples, a metallic glass and a Cu stripe. We present a detailed description of the deposition procedure and resulting emission Mössbauer spectra for both samples. In the case of a Cu stripe, we have performed EMS measurements at different stages of heat-treatment, which are required for the production of Mössbauer sources with the copper matrix.
1. Introduction Emission Mössbauer spectroscopy (EMS) is a powerful method for investigating different phenomena in physics. It has several advantages in comparison with a transmission geometry arrangement. In particular, it is at least 10,000 times more sensitive (Nath, 2010), in combination with a coincidence measurement it allows observation of chemical after-effects (Kamnev et al., 2017; Nagy, 1994) and quantity of the studied material commonly does not exceed 1 mg (Kamnev, 2013; Kamnev and Tugarova, 2017; Perfiliev, 2010). EMS is also suitable for investigation of diffusion processes. However, it is not widely applied due to a necessity of radioactive isotopes incorporation into the studied material that is a challenging task. The easiest way is to add 57 Co during the synthesis of the studied compound. In this case, 57Co is directly embedded into a crystalline structure. When the dynamic processes including solid-state diffusion are under a scope 57Co is added after the synthesis. For this purpose, different methods can be employed such as physical, chemical vapour deposition, direct alloying, and electrolytic deposition (Chackett et al., 1960; Cieszykowska et al., 2011a; Heyse et al., 2014; Severin, 1979). The latter is frequently used in the case of a compact conductive sample. Electrochemical deposition is also commonly used for preparation of Mössbauer sources. During this procedure, 57Co is deposited on appropriate substrates (Cu, Cr, Rh). Afterwards, 57Co atoms are diffused into a cubic structure of the matrix by annealing under inert atmosphere or in a vacuum. Electrolytic deposition of a natural isotopic mixture of Co (Kongstein et al., 2011; Palomar-Pardavé et al., 1998, 2005) is highly
⁎
sensitive to pH (Abd El Rehim et al., 1998), electrolyte composition (Kongstein et al., 2007b), (Frank and Sumodjo, 2014), (Grujicic and Pesic, 2004), cobalt concentration within the solution (Pagnanelli et al., 2015), applied voltage and/or electrodeposition current (Kongstein et al., 2007a). So far, in several studies describing the 57Co deposition electrolytes based either on sulphuric or hydrochloric acids were used (Fujimori et al., 1982; Kerfoot and Weir, 1988). However, in other works dedicated to that problem mainly citrate with additional hydrazine hydrate and ammonia hydroxide additives were utilized (Dézsi and Molnár, 1967; Mustachi, 1964; Stephen, 1964). Current densities were varied from 10 to 100 mA/cm2 with a time span up to 25 h and a maximal efficiency reaching 90%. They performed deposition onto steel and copper plates. Later, a method for low-activity-point-sources preparation was reported (Saxena et al., 2013). By virtue of using evaporation, 57Co as a cobalt chloride was subsequently diluted in H2SO4 and deposited with an addition of boric acid and ammonium hydroxide onto a tip of a cylindrical copper rod. A successful deposition of 3.7–5.18 MBq (∼100–140 μCi) under elevated temperature and current density of 45 mA/cm2 was demonstrated. Several researchers (Udhayakumar et al., 2012), (Ashutosh Dash et al., 2011) have described a mixed employment of non-radioactive Co and 57Co and its deposition onto a copper disc, with subsequent heat-treatment at 400 °C for 2 h. The activity was 1.48 MBq (~40 μCi) and 3 mCi/ml in 0.5 M HCl under current density 10–40 mA/cm2 and pH was kept at 3–4. The deposition yield of 57Co was 91%. The most recent works on source production have dealt with the production of rhodium-based sources, which utilized two electrolytes: alkaline (ammonium citrate, hydrazine
Corresponding author. E-mail address: [email protected] (V. Procházka).
https://doi.org/10.1016/j.radphyschem.2018.01.016 Received 17 November 2017; Received in revised form 10 January 2018; Accepted 17 January 2018 0969-806X/ © 2018 Elsevier Ltd. All rights reserved.
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demonstrate applicability of the method for the preparation of samples for emission Mössbauer spectroscopy and Mössbauer sources. For Mössbauer sources production 57Co deposited on the surface has to be incorporated into a cubic matrix of selected metals (Cu, Rh, Cr). Commonly, heat treatment is utilized within a defence atmosphere (argon (González-Ramírez et al., 1993), hydrogen (Mustachi, 1964), hydrogen mixed with carbon dioxide (Song and Mullen, 1977) and in vacuum (Dézsi and Molnár, 1967; Stephen, 1964)) which is kept inside a ceramic- or quartz-tube-based-furnace. Using of those tubes with a continuous argon flow and/or vacuum atmosphere showed almost the same results, except at high temperatures when on the surface Al2O3 and SiO2 presence was discovered at 1300 °C (Cieszykowska et al., 2011b). In some cases, the heat-treatment procedure was followed by rapid cooling in spite of an increasing number of vacancies within material with a following increase of the line width. (Cieszykowska et al., 2011b; Dézsi and Molnár, 1967; González-Ramírez et al., 1993; Stephen, 1964). Mössbauer spectra of sources in various states were presented rather rarely. Within this study, we show that the presented simplified deposition approach can be used for production of at least low activity Mössbauer sources. We report on the investigation of the 57Co atoms incorporation into the Cu matrix using EMS.
Fig. 1. The experimental conditions, the flat Cu cathode, the droplet of electrolyte with the Pt anode.
Table 1 Thermal treatment of the Cu strips. Temperature (°C)
Time (h)
350 450 470 490 530 550 570 590 600
1;2;3;5* 1;2;3;5* 1;5 1 1;3 1;5;7* 1;3; 5 1*
2. Experimental For the electrodeposition, the used solution consisted of 57CoCl2 in a 0.5 M HCl with specific activity of 5 mCi/ml (185 MBq/ml) produced by RITVERC, Saint-Petersburg, Russian Federation. A stripe of metal (Cu or metallic glass) representing the cathode was mounted on a holder in horizontal position. The desired amount of 57Co was deposited on the surface of the cathode in a form of 0.5 M HCl solution as illustrated in Fig. 1. It formed a small droplet due to the surface tension. The number of cobalt ions did not exceed 1015 within one droplet. Platinum wire 0.2 mm in diameter was inserted into the droplet as the anode. The rest of the metal stripe was covered by Parafilm M (by Bemis NA, USA) to avoid unwanted contact with the electrolyte. Prior to the experiment, the exposed surface was polished and degreased with acetone. Both the anode and the cathode were connected to a potentiostat OrigaStat - OGS100 by OrigaLys Electrochem SAS for a voltage control. In each experiment, the working volume of electrolyte varied from 30 to 60 μl. Regular additions of hydrazine hydrate were used to increase pH of the solutions up to 10–11 to prevent dissolution of the already deposited Co. Depositions were performed under ambient room conditions, pH of the solution during the deposition was controlled several times with the litmus paper. Deposition efficiency was studied within the interval of working voltage from 1.1 to 1.6 V (2.2 V
Note: Asterisks indicate the annealing time periods for which EMS spectra are shown in Fig. 3.
hydrate, ammonia solution) and acid (0.01 M HCl and 0.1 M NaCl). The maximum outcome reached almost 100% within 7 h of deposition. It was also pointed out that smaller volume of electrolyte and higher current density lead to higher efficiency in both cases, however the best result was obtained with a citrate electrolyte. Cells volumes were 5 and 10 μl, respectively (Cieszykowska et al., 2011a). All the above-mentioned experiments were carried out in special closed/sealed cells. Nevertheless, in many cases (including emission samples) the required amount of deposited 57Co has been rather small and using of such equipment inefficient due to low amount of the trace isotope and electrolyte.(Ashutosh Dash et al., 2011; Cieszykowska et al., 2011b) In this work, we present a simple approach of 57Co deposition without any specific cell using solely a droplet of an electrolyte on a surface of the cathode. This study focuses on electrolytic deposition of 57Co on a metallic glass and copper surface. These two examples have been chosen to
Fig. 2. (a) Impact of volume on the rate of deposition, (b) Effect of pH on current during deposition at different potentials.
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sufficient efficiency was achieved only with hydrazine hydrate added to Co in a form of 0.5 M HCl. The experiment with a Cu stripe was accomplished by a heat treatment procedure in an inert protective atmosphere of nitrogen. The sample in a ceramic crucible was placed into a furnace. One of the samples was repeatedly treated and after each heat treatment the emission Mössbauer measurement was performed at room temperature. The temperature and duration of thermal treatment is summarized in the Table 1. In the EMS experiments K2Mg[57Fe(CN)6] with 0.25 mg/ cm2 of 57Fe was used as a reference absorber. It was mounted to a transducer moving with triangular velocity and the spectrometer linewidth was 0.31 mm/s using a 28 µm calibration foil of alpha Fe. Mössbauer spectra were analyzed by VINDA (Gunnlaugsson, 2016) and CONUSS (Sturhahn, 2000) software. The Cu stripe width was 7 mm, its thickness was 0.25 mm. Nanoperm-type glass Fe76Mo8Cu1B15 was in the form of about 4.8 mm wide and about 20 µm thick ribbons (Miglierini et al., 2004, 2007). Deposition was made on the air (glossy) side of the glass and the sample was not thermally treated. Chemical composition of the copper stripe was characterized by means a scanning electron microscopy Vega 3 by Tescan equipped with an EDS detector. The presence of minor impurities was observed they consisted of 0.3% Ni and 0.07% Fe. 57
3. Results and discussion The impact of electrolyte volume on the rate of deposition was studied. The applied voltage was kept at 1.6 V. First, 30 and 60 μl droplets of electrolyte were deposited. The relative amount of the deposited 57Co was determined with respect to the deposition time. Fig. 2(a) clearly shows that the deposition proceeds faster in case of smaller volume of the droplet. Further, we were gradually increasing the amount of electrolyte during the deposition from 30 μl up to 60 μl. Within 3 h, 5 μl was added every 15 min. In this case, the deposition was approximately two times faster in comparison with the 60 μl droplet. Here, we would like to emphasize that usually the deposited amount is determined by measuring the activity of electrolyte. However, in our experiments it was the activity of the samples that was measured. Current with respect to the applied voltage was measured for different pH levels of electrolyte that varied from 5 to 11. Fig. 2(b) demonstrates that current increases with pH and the applied voltage. In the range 1.6–1.7 V we observed slight but continuous bubbling within the electrolyte on the cathode. The copper stripe with deposited 57Co was characterized using emission Mössbauer spectroscopy. Spectrum measured just after the deposition is presented in Fig. 3(a). Later, the sample was thermally treated according with the description shown in Table 1. The spectra measured after heat treatment marked by * in Table 1 and are plotted in Figs. 3(b)-3(e). From all EMS spectra, we have chosen typical examples which demonstrate pronounced changes in the shapes of spectra imposed by heat treatment. Spectra measured after heat treatment at 470, 490, 530, 570, and 590 °C are not presented as they exhibit negligible changes with respect to the spectra taken after the foregoing temperature treatments. Initially, with increasing of the heating temperature, the lines get broader. Then a new line occurs and after another heat treatment, it disappears again. The spectra in Fig. 3 were fitted using a three-component model. Here, the doublet C1 represents Co atoms in CoCl2 and its hyperfine parameters are in good agreement with those from literature (Cavanagh, 1969; Tamaki and Ito, 1977). The other two singlet components (C2 and C3) were assigned to metallic 57Co at different surroundings (Popov, 2012). All hyperfine parameters are listed in Table 2. After heat treatment at 600 °C, the spectrum exhibits one single line with a minor contribution (ca.8%) of a doublet component (C1). However, this spectrum contains additional contribution (about 12%)
Fig. 3. EMS spectra of 57Co deposited onto a Cu stripe at ambient conditions (a), recorded at room temperature after annealing 350 °C for 5 h. (b), 450 °C 5 h.(c), 550 °C 7 h. (d) and 600 °C 1 h. (e) with its magnified region showing the magnetic presence. Corresponding annealing times are marked in Table 1 by asterisks.
in case of the metallic glass due to much higher electrical resistance) and working current varied in an interval 3–10 mA/cm2. The total activity of the deposited 57Co was about 4.5 MBq for each sample. For determination of the deposited amount of cobalt, the electrolyte was every 30 min removed from the sample's surface and the surface activity was measured. The total time of the electrolytic deposition was three hours. Various combinations of acids, ammonium, and citrate solutions were tested during the development of this approach but 88
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Table 2 Hyperfine parameters of 57Co deposited on Cu after deposition and annealing. Isomer shifts are determined with respect to alpha-Fe, where C1-3 correspond to relative areas, IS1-3 to isomer shifts and QS1 to quadrupole splitting. State
C1 (%)
C2 (%)
C3 (%)
IS1 (mm/s)
IS2 (mm/s)
IS3 (mm/s)
QS1 (mm/s)
As-deposited 350 °C 450 °C 550 °C 600 °C
32 (1) 43 (2) 48 (2) 48 (2) 7.4(1)
67 49 36 63 80
0.2 (2) 6 (1) 15 (1) 24 (2) –
0.988 0.968 0.868 0.698 0.578
−0.002 (1) −0.042 (1) −0.112 (2) 0.008 (1) 0.028 (2)
0.868 0.858 0.868 0.808 –
2.52 2.73 2.76 2.48 2.13
Fig. 4. (a) Emission Mössbauer spectrum of
57
(2) (6) (1) (3) (3)
(3) (2) (2) (8) (9)
(8) (8) (3) (3)
(6) (4) (3) (2) (4)
Co deposited on the metallic glass. (b) Distribution of hyperfine field of the major contribution of the spectrum in Fig. 4(a).
of a ferromagnetic sextet with the isomer shift of −0.10(4) mm/s, quadrupole shift of 0.04(6) mm/s, and hyperfine magnetic field of 38.2(6) T as demonstrated by an inset in Fig. 3(e) where a spectrum of the sample after annealing under 600 °C with magnified y-axis is shown. The appearance of this magnetic component can be connected with the presence of magnetic atoms (Fe and Ni) that are present as impurities in technical copper that was used in our experiments. The process of 57Co deposition on the metallic glass was performed with the voltage of 2.2 V, the method of gradual increase of electrolyte was applied, the total amount of the electrolyte was 60 μl. The efficiency of deposition was 73%. Emission Mössbauer spectrum recorded from the metallic glass sample is shown in Fig. 4(a). It was fitted using a single sextet model. The major sextet exhibits large distribution of the hyperfine magnetic fields (see Fig. 4(b)), quadrupole interaction of 0.1 mm/s and isomer shift of −0.242 mm/s. Hyperfine parameters obtained after fitting agree with typical values observed in nanocrystalline glasses after the crystallization process of the original metallic glass (Conde et al., 2007). Thus, we can assign it to 57Co in contact with the nanograins that were formed on the surface of the ribbon-shaped sample. On the contrary, conversion electron Mössbauer spectroscopy (CEMS) spectra of the same compound exhibit much lower contribution of the surface crystallization (Cesnek et al., 2016). This discrepancy together with the shape of the EMS spectrum is a surprising result and further comprehensive investigation of this phenomenon is in progress. Here, we have checked only the feasibility of 57Co deposition upon surface of a metallic glass ribbon produced by the method of rapid quenching. as mentioned above, more systematic studies are envisaged and will be reported in a separate paper.
based incorporation of 57Co into a copper substrate was followed by means of emission Mössbauer spectroscopy. The results demonstrate that temperature of annealing after the deposition plays a key role in the whole process. It governs the incorporation of 57Co atoms into individual structural positions. Whilst at rather low temperatures of heat treatment some of the deposited material is still present on the surface in the form of the CoCl2, after 600 °C it is clear that the majority of Co atoms enters Cu. This sample exhibits a dominant single-line spectrum. Application potential of the deposition technique was demonstrated also by using a metallic glass ribbon. As the proposed method does not require any special and expensive equipment, it could be successfully utilized in many Mössbauer spectroscopy laboratories. Acknowledgements The authors gratefully acknowledge the support by internal IGA grant of Palacký University (IGA_PrF_2017_011) and projects VEGA 1/ 0182/16 and APVV-16–0079. The authors would also like to thank Helena Sedláčková (Palacký University Olomouc, Czech Republic) for her help with this paper. References Abd El Rehim, S.S., Abd El Wahaab, S.M., Ibrahim, M.A.M., Dankeria, M.M., 1998. Electroplating of cobalt from aqueous citrate baths. J. Chem. Technol. Biotechnol. 73, 369–376. http://dx.doi.org/10.1002/(SICI)1097-4660(199812)73:4<369::AIDJCTB971>3.0.CO;2-P. Ashutosh Dash, M.K., Udhayakumar, J., Gandhi, Shyamala S., Satpati, A.K., Nuwad, Sukla, Rakesh, Pillai, C.G.S., Venkatesh, Meera, Venugopal, V., 2011. On the application of electrochemical techniques for the preparation of 57Co source core, encapsulation and quality evaluation for radiometric assay of nuclear fuel rods. Radiochim. Acta 99, 103–111. http://dx.doi.org/10.1524/ract.2011.1799. Cavanagh, J.F., 1969. Mössbauer effect for Fe57 in CoCl2 and CoF2. Phys. Status Solidi (b) 36, 657–663. http://dx.doi.org/10.1002/pssb.19690360229. Cesnek, M., Miglierini, M., Bednarčík, J., 2016. 57Fe75Mo8Cu1B16 metallic glass studied by CEMS, CXMS and HEXRD. AIP Conf. Proc. 1781, 020002. http://dx.doi.org/10.1063/ 1.4965998. Chackett, G.A., Chackett, K.F., Singh, B., 1960. The processing of iron cyclotron targets in connexion with the Mössbauer effect in 57Fe. J. Inorg. Nucl. Chem. 14, 138–139.
4. Conclusions We have developed a low-cost method for 57Co electrolytic deposition that is easy to employ. It has been successfully tested using two examples, namely a copper stripe and metallic glass ribbon. The highest achieved efficiency reached ~ 90% after 3 h of deposition. Diffusion 89
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