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Advances in Ma terials Physics and Che mist ry, 2012, 2, 253-255 doi:10.4236/ampc.2012.24B064 Published Online December 2012 (htt p://www.SciRP.org/journal/ampc) Copyright © 2012 SciRes. AMPC Obtai ning the thi n Semic onductive Covering Re-Se From Sulphate Electrolyte E. A. Salakhova, A. M. Aliyev Institute of Chemical Problems of the ANAS 29, H. Javid ave., AZ1143, Baku, Azerbaijan Email: elza_salahova@mail.ru Received 2012 ABSTRACT There have been investigated the kinetics and mechanism of the cathode electrodeposition of thin coverings Re-Se from the sulphate electrol yte, cont aining NH4ReO4, Se O2 and H2SO4. On the base of X -ray phase analysis and by th e method of cyclic avometr y there have been det ermined th e con ten t of ob tai ned co verin gs, el ectro sett led at th e vario u s concen tr ation s of co mpon ent s in elect ro lyte. the co-deposition process was shown to be attended by depolarization, which is due to the energy release upon the formation of the alloy. Keywords: Electrodeposition; Alloys; Rhenium; Selen; Semiconductive Cover 1. Introduction Rhenium and its alloys have a unique physico-chemical prop- erty, which provides their application in the most important fields of modern technology [1,2]. The high temperature of melting and stable mechanical properties at the high tempera- tures provided its application in the heat-resistant alloys pro- duction. The alloys of rhenium with selenium in the form of thin photosensitive films are used in semi-conducting technol- ogy. The semi-conducting films of alloys of rhenium with sele- nium are usually obtained by the method of separate compo- nents meeting together [3,4]. As the mentioned above method is rather difficult, it demands complicated instruments and the process is going at the high temperatures, we tried to apply electroch emical method b ased on th e electro lysis of water s olu- tions of selenium dioxide and ammonium perrenate in sulphuric acid for obtaining the thin coverings of Re-Se alloys. In order to obtain Re-Se alloy from the sulphate electrolyte [5,6] we studied the joint electrodeposition of rhenium with selenium and there was found the optimal regime for obtaining a s emi-conducting alloy. Analysis of results of indicated works showed that films de- pend not only on the composition and nature of electrolyte, but also o n t he material o f cathode. The use of different according to the origin electrolytes in order to obtain the thin coverings Re-Se, is certainl y conn ected with the hardships which are usually met in every concrete occasion and it’s directed to the search of the electrolyte com- position, which gives the chance of obtaining the qualified ca- thode films, suitable for use in different fields of modern tech- nology. The present work is a continuation of our investigations in the field of electrochemical obtaining the semi-conducting al- loys Re-Se and it’s devoted to the study of scientific basis of the joint electrodeposition Re-Se alloy by the method of cycling avometry. 2. Methods of Experiment For making the experiment there have been used the following reactants : SeO2, H2SO4 (chemical p ure) and NH4ReO4 (pu re for analysis). The experiments have been made in a glass cell pro- vided with the water j acket . The cycling avometer curves’ have been reading taken by means of potentiostat P-5827M and 2D registering device PDP4-002. As a workin g electrode t here have been u sed a pla- tinum electrode with 0.15 square cm, and as comparative elec- trode there have been used a chlorine-silver plate electrode, as anode – the platinum plate with 4 square sm. The acidity of solution was determined by pH-meter 673M with the glass electrode. The temperature of electrolyte was regulated by means of thermostat UH. the content of Re-Se alloy compo- nents has been analyzed as the following: 10 ml of concentrated HNO3 were dissol ved whi le h eatin g and after rep eated evapo ra- tion in the water boiler-both there was added 5 n of H3PO4 to the solution. The obtained solution has been diluted in the measured retort till 50 ml and then by extraction with isoamyl spirit rhenium was separated from selenium. The rhenium has been determined by photometry of rodanide complex at the device FEK-56M [7], and selenium has been determined by thiocarbomide complex [8]. X-ray graphical investigations of thin films Re-Se have been carried out at difractometer URS-55 in CuKα-irradiation in RKD camera 57,3. 3. The Results and Their D iscus sion In order to study the mechanism of formation Re-Se allo y there have been measured cycling avometer curves in different ac- cording to composition electrolytes as well as there was held the chemical and X-ray difractive analysis of cathode settle- ments, obtain ed at the cert ain potentials. For detailed investigation of the process of obtaining the thin electrolytic coverings of Re-Se alloys you must have the infor- mation about kinetics of deposition of separate components and E. A. SALAKHOVA, A. M. ALIYEV Copyright © 2012 SciRes. AMPC 254 alloys. With this aim there were indicated the polar curves of Re-Se alloys extra ctions and of the sep arate metals at the pl ati- num electrode. As it is known the rhenium stays in sulphate electrolytes in the form of ReO4− and i ts reduction co nsists of several separ ate processes. ReO4− + 8H+ + 7e → Re + 4H2O According to the work [9] the degree of ReO4− -ions goes stage-by-stage and each stage of formation the intermediate produ cts is charact erized b y a certain el ectrod e potential , which becomes more negative in the process of rehabilitation, which can also provide the approach of Re and Se potentials settle- ment. ReO4− + 2H+ + e → ReO3 + H2O; E1 = +0,77V ReO3 + 2H+ + 2e → ReO2 + H2O; E2 = +0,4 V ReO2 + 4H+ + 4e → R e + 2H2O; E3 = +0 ,26V Thus, the rhenium reduction in strong acid electrolytes goes according to the stage, through the formation of intermediate oxides film, about which tell us red and blue sediments in the obtained film. In order to have a whole information about the joint electro- deposition o f Re with Se, there were measured the cycli ng polar curves of rhenium in sulfate electrolyte at the different involu- tions. There are two sharp waves on the curve of a cathode halfcycle. One of them is at the potential 0,2 - 0,3 V, the ot he r – at(-0,3)-(0,4)V (s.c.e). Formation of these waves can be ex- plained by the step mechanism of reduction the perrenate ions. The character of anode halfcycle also proves this suggestion. The anode wave forming at the potential 0,1-0,2V (s.c.e.) can be explained by Re dissolving, and distinctly expressed peaks – to dissolving of ReO3 and ReO 2 correspondingly. There have been studied the dependence of involution rate of potential on the rise of limited current value. Dependence of limited current from square root of potential involution rate has a rectilinear character, which is observed in those cases, when the deposition rate is controlled by ions diffusion to the surface of cathode. Then, in order to have additional information about the processes taking place while Se deposition, there were meas- ured cycling polar curves of Se in sulphate solutions at the dif- ferent involution. As it can be seen in the diagram on the cycling volt-ampere curves of cathode deposition and anode oxidation of Se there appears a wave, which refers correspondingly to rehabilitation of SeO32− till Se and to oxidation of the obtained product till SeO32−. As well as it can b e seen from the d iagram th at with th e rise of evolution rate the volt-ampere curves are shifted to the positive side and at the involution of 80 mV/seс the wave dis- appears and there is formed a maximum limited current. Perhaps, while formation the wave of reduction the main role plays the high resistance of cr eate d semi-cond u ctin g layer o f Se, and therefore the process velocity decreases. With shifting the pot ent ial to th e negative side a st ormy discharge of hydrogen on the cathode takes p lace. It’s been established, that electrochemical formation of thin layer films goes through a number of complicated electro- chemical reactions. One of the factors influencing simultaneous deposition of electrolyte components is the state of a platinum cathode. It’s also well-known, that electrocatalytic activity of electrode sur- face can change while depositing the other metals in a small quantity. There were suggested several various mechanisms of elec- trochemical rehabilitation of Se [10], in the field of positive potentials (from +0.75 to +0.35 V s.c.e.). As it follows from these works, deposition of H2SO3 is a multistage process. At the first stage the adsorption of se acid takes place, where on the surface of electrode the adsorbed compounds of Se with intermediate degree of oxidation are being formed. There have been sh own the typical avogrammes of Se O2 so- lution in sulphuric acid at the platinum electrode. According to the results of investigations [5], the processes concerning peaks C1 and C2 are connected with formation of adsorbed com- pounds of Se with intermediate degrees of oxidation on the electron surface: 1) deposition and reduction of Se compounds (IV) on the ac- tive surfac e of plati num electrode H2SeO3 + 2H+ + 2e → H2SeO2 (Pt) + H2O; E = +0.70V 2) the current of reduction C2 is co nnect ed with th e pr ocess an substrate surface, which reminds the deposition of amorph- ous Se: H2SeO2(Pt) + 2H + + 2e → OSe (Pt) + 2H2O; E = +0.35V Our results are coordinated with the literature information. In order to investigate the joint electrodeposition and to study kinetics and mechanism of the process of joint electrodeposi- tion of Re with We from sulphate electrolyte there were taken the cycling vo ltamper cu rves o f Se, Re and Re-S e alloy. The Re deposition on platinum electrode takes place at the potential about 0. 6 V (s.c . e), and Se – at 0.5 V ( s .c.e.). th e curves of alloy are quite different from the curves taken from solutions, having separate components. The joint deposition of Re with We takes place at the more positive potentials, than these metals extrac- tion separately, i.e. both components in alloy are extracted by depolarization. Such location of polar curves is observed in those cases, when it’s possible to form a chemical compound on the cat hode. The depol arization itself is a d irect evidence of the fact that at the joint deposition there is a chemical interac- tion between the components with formation of ReSe2 on the catho de. Re + 2Se → ReSe2 At the change of the direction of potential evolution on the anode semi-cycles of voltampere curves, being obtained for individual components, there is observed just one peak of anode oxidation. For rhenium the pear of oxidation starts at the poten- tial 0 .6 V (s.c.e.) and for S e about 0.95 V (s .c.e.). However, there have been observed 3 peaks of anode oxida- tion on the voltampere curve of the anode semi-cycle. The peaks of oxidation, observed at 0.60 and 0.95 V (s.c.e.) no doubt, are caused by Re and Se oxidation. The new peak of oxidation, observed at the potential 0.80 V (s.c.e.) refers to the oxidation of complex ReSe2, forming on the catho de according to the reaction ReSe2 = Re + 2Se + 2 e E. A. SALAKHOVA, A. M. ALIYEV Copyright © 2012 SciRes. AMPC 255 Hence, at the indicated potentials on the cathode the joint deposition of Re with Se doesn’t take place and the only ca- thodic product is Se. The joint deposition of Re with Se starts at the potential some about 0.20 V (s.c.e.) which is confirmed by the appear- ance on the curve the anodic semi-cycle of the second wave of anodic current at the potential 0.80 V (s.c.e.) connected with ReSe2 oxidation. The sedi ment v ery close to ReSe2 according to the composi- tion is obtained in the interval of potentials 0.15 V (s.c.e.). By shifting the potential to the negative side the content of Se in cathodic sediments is rising. These sediments consist of ReSe2+Se. according to X-ray phaseous analysis, the films, having surplus quantity of Se and obtained at the potentials more positive than 0.25 V, consist of two phases ReSe2 and Re. The information taken from microanalyser showed that Re is mostly in the lower layers of the films. And the films rich with Se, obtained at the potential 0.10 V, consist of two phases ReSe2 and Se. Here Se is located in the upper layers of the films. The films, very close to ReSe2 according to their composition are formed in the interval of potentials 0.25 V. There were analyzed the content and morphology of thin layers ReS e2, electrodep osited on the p latinum electrode. Fr om the X-ray phaseous analysis it follows the film consist from 54% of Re and 46% of Se (according to the mass). We have establi shed that the co mpound ReSe2 is cr ystallized in triclinic syngony with the parameters of the lattice: a=6.7275 Å; b=6.6065 Å; c=6.7196 Å. 4. Conclusion There have been in vesti gated th e kinetics an d mechani sm of the cathode electrodeposition of thin coverings Re-Se from the sulp hate electrolyte. Was shown, that co-deposition of rhenium and selenium occur with some depolarization, which is due to the energy release upon the formation of the alloy. REFERENCES [1] Speranskaya E.F. Electrochemistry of Rhenium. p.53. Gylym, Alma-Ata, (1990) [2] Obolonchik V.A., Yanaki A.A. Col. “Rhenium in the new Tech- nics”. p. 59. Publishing House “Nauka”, Moscow, (1970 ) [3] Obolonchik V.A., Mikhlina T.M. The Ukraine chemical journal, “Rhenium Selenide obtaining and properties” p. 1037-1040 , v.30, Kyev, (1964) [4] Opalovsky A.A., Fedorov V.Y., Lobkov Y.U. Journal Non-organic materials, “The new selenides and rhenium tellu- rides” . p. 1 44 -148, Publishing House of the USSR AS, v. 1, No 2, (1971) [5] Salakhova E.A. Az. Chem. Journal, “The joint reduction of rhe- nium and selenium in sulphuric acid solutions”, p.9-12, No 3, Baku, (1999) [6] Salakhova E.A. Az. Chem. Journal, “The main regularities of the joint electrodeposition of Re with Se from sulphate electrolyte”, No 4, Ba ku, (20 0 3) , p.140-144. [7] Borisova L.V., Yermakov A.N. “Analytic chemistry of rheniu m”. Publi shing Ho us e “Nau ka”, Mos co w, (1974), p. 9 5 . [8] Nazarenko I.I., Yermakov A.N. “Analytic chemistry of Se and Te”. Publishing House “Nauka”, Moscow, (1971), p.46 [9] Salakh ova E.A., Medjidzade V.A. at all “The electrodep osition of rhenium in alkalin and acidic electrolytes”, Journal of Che- mistry and Chemical Engineering, Volum 6, No 5, (2012), p.489-494. [10] Dikstiene N. Electrochemistry, “Deposition of thin films Cu-Cd-Se”, v. 39, No 12, Moscow, (2003), p. 1487-1493 |