CC BY
12Chemical Journal of Kazakhstan
ISSN 1813-1107, elSSN 2710-1185 https://doi.org/10.51580/2022-1/2710-1185.54
Volume 1, Number 77 (2022), 25-36
УДК 544.6:544.653.22
ELECTROCHEMICAL DISSOLUTION OF TITANIUM ELECTRODES POLARIZED BY ALTERNATING CURRENT IN A HYDROBROMIC ACID AQUEOUS SOLUTION
Nurdillayeva R.N.1*, Bayeshov A.2, Abdikerim A.Zh.1, Zhylysbayeva G.N.1
Khoja Akhmet Yassawi International Kazakh-Turkish University, Turkistan, Kazakhstan; 2 "D.V. Sokolskiy Institute of Fuel, Catalysis and Electrochemistry " JSC, Almaty, Kazakhstan. E-mail: raushan.nurdillayeva@ayu.edu.kz
Abstract. The work shows the patterns of electrochemical dissolution of titanium elecro-des polarized by alternating current in an aqueous solution of hydrobromic acid. The current density (200-1200 A/m2), hydrobromic acid concentration (1.0-5.0 M), electrolysis duration (0.25-2.0 hours), and electrolyte temperature depend on the current rate of the titanium electrode in the alternating current source (20°C-80°C) were considered. The maximum value of current yield was obtained at a current density of 400 A/m2 when titanium electrodes were polarized by an alternating current and it was recorded that the current yield is reduced at a high current density. It is shown that the current output for titanium increases directly proportional to the concentration of hydrogen bromide, i.e., hydrogen ion content. The order of the reaction which occurs during the electrolysis of hydrobromic acid is determined. It is proved that the current output of dissolving titanium in the alternating current source decreases when the electrolysis time is increased, as the eletrolysis products in the electrolyte settle down on the electrode surface. It is shown that as the temperature of the electrolyte solution is increased, the current output value for dissolving titanium rises to 48%. The activation energy determined according to the temperature kinetic regime was 17.76 kJ/mol, the process was carried out according to the diffusion-kinetic regime. It was shown that titanium is dissolved in hydrobromic acid aqueous solution to form titanium (III) ions. The influence of the main parameters on the electrochemical dissolution of a polarized alternating current titanium electrode in hydrobromic acid is investigated and effective ways of titanium dissolution are considered.
Keywords: titanium electrode, hydrobromic acid, alternating current, current output, electrolysis, current density
Citation: Nurdillayeva R.N., Bayeshov A., Abdikerim A.Zh., Zhylysbayeva G.N. Electrochemical dissolution of titanium electrodes polarized by alternating current in a hydrobromic acid aqueous solution. Chem. J. Kaz., 2022, 1(77), 25-36. DOI: https://doi.org/10.51580/2022-1/2710-1185.54.
1. Introduction
Currently, titanium and its alloys are of great interest due to their important mechanical properties such as high strength and flexibility, low elastic modulus characteristics, corrosion resistance, and biocompatibility [1-2].
The corrosive properties of titanium are characterized by the fact that its surface is covered by a passive film of titanium dioxide which prevents metal from further oxidation while interacting with water or atmospheric air [3]. The physicochemical properties of the passive film are influenced by the electrolysis conditions, the composition of the electrolyte [4] and the pH of the solution [5], and the electric polarization [6].
In recent years, there has been increasing interest in experimental work to study and determine the dissolution patterns of the titanium electrode in various aqueous solutions. The properties of electrodes made of titanium powders and catalytically active titanium-based material in an aqueous solution of hydrochloric acid were studied using the voltammetric method. Electrochemical sensors have developed new methods for treating titanium used in gas-diffusion electrodes, and as a result, it was found that metallic titanium in the potential range of 0.5-1.7 can act as a conductor for catalytically active materials in HClO4 solutions [7]. The methods of cyclic voltammetry and potentiometry were used to study electrchemical processes occurring on the surface of a porous titanium electrode in H3PO4 acid with heavy metal ions, as a result of which it was shown that titanium metal has limited corrosion properties in phosphate acid solutions [8-9]. In citric acid with a pH value of 2.0, containing halogen ions, the property of Ti and Ti6Al4V alloys was investigated by voltammetric method, and a passive state at the electrode surface in the presence of chloride, bromide, and iodide ions were established. However, it was observed that the primary passive film on the electrode surface dissolves under the influence of fluoride ions [10]. Corrosion properties of the oxide film formed on the surface of titanium metal under anodic current in acid H2SO4 and acid H3PO4 solutions were studied by the methods of potentiodynamic polarization and scanning electron microscopy. The study proved that the oxide layer formed on the surface of the titanium electrode is thin and amorphous [11]. To determine the electrochemical properties of titanium metal, there were conducted an experiment consisting of two stages which determine the influence of alternating current on the corrosion properties of the titanium in a solution containing halogen ions as a result, good metal surface solubility was observed under the action of low-voltage alternating current in HCl and HBr acid solutions [12]. The cathodic property of Ti (III) ions in NaCl-2CsCl melt is determined by cyclic voltammetry and chronopotentiometry methods in the presence of a tungsten electrode and it is shown that the reduction of Ti (III) ion is an irreversible process consisting of two diffusion-controlled stages [13]. The effect of 1.0 m chloric acid solution HClO4 containing fluoride ions on the corrosion properties of titanium metal has been studied by potentiodynamic polarization methods. As a result, the influence of the concentration of fluoride ions on the electrochemical dissolution of the oxide film formed on the surface of titanium was observed [14]. The aggressive halogenated medium was also studied
in the presence of a passivator in acidic solutions of H2SO4 and HCl to determine the electrochemical and corrosion properties of Ti and its compounds. The study proved that the passivity plays an important role in slowing down the corrosion of titanium metal in an acid solution [15]. To study the electrochemical properties of the oxide film formed in titanium and alloys, a potentiostatic anodization process in HBr solution was performed. The study proved that titanium metal tends to form a thick layered oxide film compared to its alloy [16]. Polarization of titanium electrode in solution containing 1.0 M H2SO4 fluoride ions was studied by dynamic voltammetry, resulting in a 3D electrochemical map that comprehensively characterizes the formation and transformation of new products in the dissolution process [17].
Our earliest research result reveals that the titanium electrode polarized by non-stationary currents can form titanium (III) ions in solutions with sulfate-, chloride-, phosphate-[18], fluoride-[19] ions. In our previous studies, it was established the regularities and mechanisms of electrochemical dissolution of titanium via taking cyclic and anodic potentiodynamic polarization curves in potassium bromide solution oxidized by sulfuric acid. [20]. In addition, the effects of direct and alternating current in an aqueous solution of 1.0 M potassium bromide oxidized with 0.5 M H2SO4 solution were comparatively studied [21-22].
Having analyzed scientific papers on the study of the electrochemical properties of titanium and titanium-based alloys in the scientific database, it was found that the electrochemical properties of the titanium electrode in bromic acid solutions have not been fully studied. In this regard, the present study examined the patterns of electrochemical dissolution of titanium in an aqueous solution of hydrobromic acid on an alternating current source.
2. Experimental Part
In this work, to study the dissolution of the titanium electrode in hydrobromic acid, the electrolysis mode with connection to an alternating current source was used. The experiment was performed on a glass electrolyzer without electrode space. Two titanium plates paired as working electrodes were used in the study. Aqueous HBr acid solutions of different concentrations were used as electrolytes. Before each experiment, the titanium electrodes were cleaned with sandpaper, washed with distilled water, and dried. The study considered the influence of the main electrochemical parameters: current density, electrolyte concentration, solution temperature, and duration electrolysis on the current dissolution rate of titanium.
Preliminary studies revealed that titanium electrodes dissolved during alternating current electrolysis to form purple trivalent titanium ions.
The current output (CO) of titanium dissolution polarized by alternating current was calculated by determining the dissolved mass of the electrodes during the anodic half-period of alternating current.
Qualitative analysis of the electrolyte composition is used in the electrochemical dissolution of titanium in hydrobromic acid solution. It is known that solutions of titanium (III) salts have purple color. The formed titanium (III)
ions are gradually oxidized in the atmosphere to the valence state (IV). Titanium ions were quantitatively studied using the colorimetric method. The concentration of titanium ions was determined by constructing a standard calibration curve. During electrolysis, the mass of dissolved titanium electrodes was determined.
3. Results and discussion
Previous research results revealed that titanium is insoluble during anodic polarization because of titanium dioxide films which prevent it from electrolysis dissolution [19]. This research results show that titanium is dissolved intensively when polarized by alternating current. When titanium is covered with oxide layer is affected by alternating current, there occur cathodic and anodic processes on the surface of titanium electrode (Figure 1). When titanium is polarized by an alternating current at 50 Hz frequency, TiO2 oxide layer is reduced at cathodic half period, and titanium is dissolved at anodic half period. As a result, titanium electrodes are dissolved and trivalent titanium ions and bromides are formed.
Figure 1 - Oscillogram current-time passing alternating current with a frequency of 50 Hz in
hydrobromic acid.
When titanium electrodes are polarized with an alternating current in hydrobromic acid solution during the half-cycle of the anode, an oxidation reaction takes place and titanium (III) ions are formed (1st reaction):
Ti - 3e- ^ Ti3+ E= - 1.37 V (1)
During the cathodic half-cycle period, hydrogen ions are discharged (2nd reaction):
2H+ + 2e- ^ H2 (2)
Titanium (III) ions in solution react with bromide ions to form titanium (III) bromide (3rd reaction):
Ti3+ + 3Br = TiBr3 (3)
Titanium ions formed in an aqueous solution of hydrogen bromide gradually pass into the tetravalent state.
The effect of current density on the electrochemical dissolution of a titanium electrode in an aqueous solution of hydrobromic acid in the alternating current mode is considered (Figure 2). The study showed that at a current density value of 200-400 A/m2, the current output (CO) has high values, and within 600-1200 A/m2, a decrease in current output. These data indicate that the titanium electrode dissolves much better than at high current densities. This can be explained by the fact that at high current densities, an oxide film is formed on the surface of the titanium electrode, which prevents titanium from dissolving.
The output increases at current densities up to 400 A/m2 according to the Tafel equation, and at high current densities, it decreases due to the coating of the surface of titanium electrodes with oxide films.
[HBr]=2,0 M, t=0,5 h.
Figure 2 - The current density effect on the current output of titanium dissolution is polarized by alternating current.
The effect of hydrobromic acid concentration on the electrochemical dissolution of a titanium electrode polarized by alternating current was studied (Figure 3). As a result, it was shown that with an increase in the concentration of hydrobromic acid in the range of 1.0-5.0 M, the current output also increases from 6% to 22%. The reaction order of electrochemical dissolution of titanium in hydrobromic acid is calculated, accounting for 0.85 (table 1).
Table 1 - Calculation results of electrochemical reaction sequence in hydrobromic acid
№ C, M CO, % lgC=x lgCO=y X2 xy
1 1 6 0 0.778 0 0
2 2 13.5 0.301 1.13 0.09 0.34
3 3 16 0.477 1.2 0.288 0.574
4 4 20.5 0.602 1.31 0.363 0.7936
5 5 22 0.699 1.34 0.488 0.94
S - - 2.079 5.758 1.169 2.647
Reaction sequence was calculated using values in 1st table
_ nlxy -Ix-Iy _ 5 • 2.647 - (5.758 • 2.079) _ b = nix2 - (Ix)2 = 5 • 1.169 - (2.079)2 =
Preliminary experiments have shown that the titanium electrode is chemically insoluble in hydrogen bromide concentrations in the range of 2.0-5.0 M.
ix,=400 А/м2, x=0,5 h
Figure 3 - Hydrobromic acid concentration effect on current output of titanium electrode dissolution polarized by alternating current.
The influence of the electrolysis time on the dissolution of the titanium electrode in hydrobromic acid in the presence of alternating current is considered. As shown from Table 2, the current output of the titanium electrode decreases with increasing electrolysis time. This phenomenon can be explained by the fact that as the electrolysis time increases, accumulated titanium ions are formed and concentration inhibition occurs.
Table 2 - The electrolysis duration effect on current output of titanium electrode dissolution polarized by alternating current, i=400 A/m2, [HBr]=2,0 M
r, h. 0.25 0.5 1.0 1.5 2
CO, % 15.0 13.5 12.5 12.0 11.0
The effect of temperature on the electrochemical dissolution of a titanium electrode polarized by the alternating current is considered (Figure 4, a). The current output of the titanium electrode increases from 13.5% to 48% in the temperature range of 20°C-80°C for hydrobromic acid. An increase in the rate of a chemical reaction with an increase in the temperature of the solution is a natural phenomenon. The activation energy value determined by the temperature-kinetic
method (lgCO - 1/T- 103) was 17.76 kJ/mol (Figure 4, b; Table 3). This value showed that the electrochemical process proceeds in the diffusion-kinetic mode.
It should be noted that titanium electrodes are chemically dissolved in an aqueous solution of hydrobromic acid at a temperature of 60°C, 0.0005 g, and at 80°C, 0.001 g each.
o
0 20 -tO 60 SO 100
i=400 A/m2, [HBr]=2,0 M, r=0.5 h.
Figure 4 - The solution temperature effect on the current output of titanium electrode polarized by alternating current (a); Inverse temperature dependence of the current output logarithm of the
titanium electrode current (b).
Table 3 - Results of calculation of the electrochemical reaction mode in hydrobromic acid
№ t,°C T,K CO,% x=--103 T y=lgCO x-y X2
1 20 293 13,5 3.4129 1.130 3.857 11.6479
2 40 313 18 3.1949 1.255 4.01 10.2074
3 50 323 23 3.096 1.361 4.216 9.5852
4 60 333 29 3.003 1.462 4.391 9.018
5 70 343 37 2.9154 1.568 4.572 8.4995
6 80 353 48 2.8328 1.681 4.762 8.0247
S - - - 18.455 8.457 25.808 56.9827
Using the values in 3rd table the corresponding coefficients were calculated and the values were -0,9364 and 4,2897, respectively (1.2).
nXxy-Xx-Xy 6-25,808-18.455-8.457 „„^s.
a = —, , =-:---—=-0.9364 (1)
nXx2-(Xx)2 6-56.9827-(18.455)2 v '
¿y-aXx _ 8.457-(-0.9364)-18.455 _ ^ ^
The equation of a straight line is expressed by 3rd equation:
y = -0.9364x + 4.2897 (3)
The experimental error of the method was determined by 4th formula and its value was 0,0063.
2
o = l(y- (ax + b)) = I(y - ((-0.9364)* + 4.2897))2 « 0.0063 4)
The activation energy of the reaction was determined using these values and its value was 17,76 KJ/mol
Ea=-2.33-8.314—-—(-0.9364)=17.76 KJ/mol
mol K
The optimal electrochemical solubility of the titanium electrode in an aqueous solution of hydrobromic acid was recorded at a current density of 400 A/m2, a concentration of 5.0 M, and a temperature of 60°C. The melting current of titanium electrodes at these parameters was 48%.
4. Conclusion
For the first time in the research work, the patterns of dissolution of titanium electrodes polarized by alternating current in an aqueous solution of hydrobromic acid were studied. The influence of the main parameters on the consumed current of the electrochemical dissolution of a titanium electrode in hydrobromic acid solutions is considered. The study showed that the current output of the titanium electrode slowly decreases with increasing current density and electrolysis time. During the electrochemical dissolution of titanium, it was found that the current output increases directly proportional to the concentration and temperature of hydrobromic acid. It was established that the electrolysis process proceeds in the diffusion-kinetic mode and the order of the reaction was calculated.
The research results showed that a titanium (III) bromide can be synthesized by the polarization of titanium electrodes using an alternating current in an aqueous solution of HBr.
The results of scientific research can be used to improve the treatment of titanium-based wastes and the synthesis of important titanium compounds in production.
Funding: The research was conducted at Khoja Akhmet Yassawi International Kazakh-Turkish University as part of initiative research work (State Registration number No0120RKI0185, registered at NCSTE RK).
Acknowledgements: The research was carried out in the research laboratory of Ecology and Chemistry Department of the Natural Science Faculty of Akhmet Yassawi University.
Conflict of Interest: The authors have no Conflict of Interest declared between the authors requiring disclosure in this article.
Information about authors:
Nurdillayeva Raushan N. - Candidate of Chemical Science, Professor, Head of Ecology and Chemistry Department of Natural Sciences Faculty, Khoja Akhmet Yassawi International Kazakh-Turkish University, Turkistan, Kazakhstan; E-mail: raushan.nurdillayeva@ayu.edu.kz; ORCID ID: https://orcid.org/0000-0001-9444-737X
Bayeshov Abduali - Doctor of Chemical Science, Professor, Academician of the National Academy of Sciences of the Republic Kazakhstan, «D.V. Sokolskiy Institute of Fuel, Catalysis and Electrochemistry» JSC, Almaty, Kazakhstan; E-mail: bayeshov@mail.ru; ORCID ID: https://orcid.org/0000-0003-0745-039X
Abdikerim Aliya - Khoja Akhmet Yassawi International Kazakh-Turkish University, master student of educational program 7M05324-Chemistry, II course, Turkistan, Kazakhstan; E-mail: aliya.abdikerim@ayu.edu.kz; ORCID ID: https:// orcid.org/0000-0002-9243-8450
Zhylysbayeva Gulkhan - Candidate of Technical Science, Associate Professor, Khoja Akhmet Yassawi International Kazakh-Turkish University, Turkistan, Kazakhstan; E-mail: gulkhan.zhylysbayeva@ayu.edu.kz; ORCID ID: https://orcid.org/0000-0002-9800-3896
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Тушндеме
бромсутек ;ыш;ылыньщ сулы ершндюнде айнымалы
ТОКПЕН ПОЛЯРИЗАЦИЯЛАНГАН ТИТАН ЭЛЕКТРОДТАРЫНЬЩ ЭЛЕКТРОХИМИЯЛЫ; ЕРУ1
Нурдгллаева Р.Н.1*, Баешов А.2, дбдшерт Э.Ж.1, Жылысбаева Г.Н.1
1 Кржа Ахмет Ясауи атындагы халыцаралыц цазац-mYpiK yuueepcumemi, TYpKicmaH, Казацстан;
2 «Д.В. Сокольский атындагы Жанармай, катализ жэне электрохимия институты» АК, Алматы, Казацстан.
E-mail: raushan. nurdillayeva@ayu. edu.kz
Берiлген ж^мыста бромсутек кыш^ылыньщ сулы ертндюшде айнымалы токпен поляризацияланган титан электродтарыныц электрохимиялык; еру занды-лыщтары керсетшд^ Титан электродынын айнымалы ток кезшде ерушщ ток бойын-
ша шыгымына ток тыгыздыгынын (200-1200 А/м2), бромсутек кышкылынын кон-центрациясынын (1,0-5,0 М), электролиз уакытынын (0,25-2,0 саг.) жэне электролит температурасыныц (20°С-80°С) эсерлерi карастырылды. Айнымалы токпен поля-ризацияланган титан электродынын ток тыгыздыгы 400 А/м2 болганда, ток бойынша шыгымынын ен максимал мэш тiркелдi жэне жогары ток тыгыздыктарында титан-нын еруiнiн ток бойынша шыгымы твмендейтiнi аныкталды. Бромсутек кышкылы-нын концентрациясынын артуымен, ягни сутек иондарынын мвлшерi арткандыктан титаннын ерушщ ток бойынша шыгымы да жогарылайтыны кврсетiлдi. Бромсутек кышкылында электролиз барысында жYретiн реакциянын ретi аныкталды. Айнымалы ток квзiнде титаннын ерушщ ток бойынша шыгымы электролиз уакыты вскен сайын электролит курамындагы электролиз внiмдерi электрод бетше кайта отыра-тындыктан твмендейтiнi дэлелдендi. Электролит ертндга температурасы арткан сайын, титаннын ерушщ ток бойынша шыгымы 48%-ке дешн всетiндiгi кврсетiлдi. Температуралык-кинетикалык режиммен аныкталган активтендiру энергиясынын мэнi 17,76 кДж/моль курап, процестiн диффузиялык-кинетикалык режимде журе-тiндiгi аныкталды. Бромсутек кышкылынын сулы ерiтiндiсiнде титан (III) иондарын тузе электрохимиялык жолмен еритiндiгi кврсетiлдi. Айнымалы токпен поляри-зацияланган титан электродынын бромсутек кышкылында электрохимиялык еруiне непзп параметрлердiн эсерi зерттелiп, титан ерушщ тиiмдi жолдары карастырылды.
ТYЙiн сездер: титан электроды, бромсутек кышкылы, айнымалы ток, ток бойынша шыгым, электролиз, ток тыгыздыгы
Резюме
ЭЛЕКТРОХИМИЧЕСКОЕ РАСТВОРЕНИЕ ТИТАНА ПРИ ПОЛЯРИЗАЦИИ ПЕРЕМЕННЫМ ТОКОМ В ВОДНОМ РАСТВОРЕ БРОМОВОДОРОДНОЙ КИСЛОТЫ
Нурдиллаева Р.Н.1 *, Баешов А.2, Абдикерим А.Ж.1, Жылысбаева Г.Н.1
1 Международный казахско-турецкий университет имени Ходжи Ахмеда Ясави, Туркестан, Казахстан;
2АО «Институт топлива, катализа и электрохимии им. Д.В.Сокольского»,
Алматы, Казахстан;
E-mail: raushan. nurdillayeva@ayu. edu.kz
В данной работе показаны закономерности электрохимического растворения поляризованным переменным током титанового электрода в водном растворе бро-моводородной кислоты. Рассмотрены влияния плотности тока (200-1200 А/м2), концентрации бромоводородной кислоты (1,0-5,0 М), продолжительности электролиза (0,25-2,0 ч.) и температуры электролита (20°С-80°С) на выход по току растворения титанового электрода в источнике переменного тока. При плотности поляризованного переменным током титанового электрода 400 А/м2 зафиксировано максимальное значение выхода по току и установлено, что при высоких плотностях тока выход по току растворения титана уменьшается. Было показано, что с увеличением концентрации бромоводородной кислоты, т.е. с увеличением содержания ионов водорода, выход растворения титана по току также увеличивается. Определен порядок реакции, протекающей в процессе электролиза в бромово-дородной кислоте. Доказано, что выход по току растворения титана в источнике переменного тока уменьшается по мере увеличения времени электролиза, так как продукты электролиза в составе электролита вновь оседают на поверхности
электрода. Установлено, что по мере повышения температуры раствора электролита выход по току растворения титана увеличивается до 48%. Доказано, что значение энергии активации, определяемое температурно-кине-тическим режимом, составляет 17,76 кДж/моль и процесс протекает в диффузионно-кинетическом режиме. Обнаружено, что в водном растворе бромоводородной кислоты параллельно растворяются ионы титана (III). Исследовано влияние основных параметров на электрохимическое растворение поляризованного переменным током титанового электрода в бромоводородной кислоте и рассмотрены эффективные способы растворения титана.
Ключевые слова: титановый электрод, бромоводородная кислота, переменный ток, выход по току, электролиз, плотность тока
