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Cathodic production of zirconium
J. Electroanal. Chem., 122 (1981) 279--283
279
Elsevier Sequoia S.A., L a u s a n n e - Printed in The Netherlands
CATHODIC PRODUCTION OF ZIRCONIUM *
A.S. F O U D A and M.M. E L S E M O N G Y
Chemistry Department, Faculty of Science, Mansoura University, Mansoura (A.R. Egypt) (Received 16th June 1980; in revised form 7th N o v e m b e r 1980)
ABSTRACT Zirconium was deposited on the cathode at controlled pH from a n u m b e r of solutions containing the metal salt and a complexing agent. The current density ranged from 25 to 1 0 0 m A cm -2. Both the s p e c t r o p h o t o m e t r i c analysis and chemical analysis indicate that the purity of the metal is better t h a n 99.8%.
INTRODUCTION
Zirconium is often thought of as a rare element but with its c o m p o u n d s is now finding a number of applications, for example, ferro-Zr is used in the steel industry, the metal is being used in radio valves and in photo-flash bulbs, and it has been used as an oxygen scavenger in the manufacture of special steels and in the construction of some wireless valves. Zirconium occurs in very small concentrated deposits, Hf being found naturally in all Zr minerals, and because of the lanthanide contraction the separation of the metal from Hf is extremely difficult. This fact motivated us to try to deposit Zr in concentrated form by a simple electrochemical method. Information on the electrodeposition of zirconium is scarce. Zirconium has been prepared by deposition on to a m o l y b d e n u m cathode [ 1 ] from fused equimolecular KNO3 + NaNO3 containing 0.7--5.3 mol% ZrC14 at 700--900°C and current density from 10 -4 to 10 A cm -2. It is also reported [2] that electrodeposition occurs at low current densities at 600--700 ° C and at a concentration of zirconium ~:0.49 wt.%. The metal can also be prepared [ 3 ] by electrolysis of KZrF4 melts in equimolecular mixtures of KC1 and NaC1 at 760--800°C and current density between 0.01 and 0.1 A cm -2. The element was prepared [4] by electrolysis of melts containing Cs2ZrC16 and CsC1 and in the presence of KF, and also [5] from the electrolysis of mixtures of NaC1, KC1 and ZrC1 in the presence of KF. Zirconium was deposited from the vapour phase [6] on tungsten by heating a mixture of ZrCL and H2.
* Dedicated to Mrs. Eltifat A. Elshafie. 0 0 2 2 - 0 7 2 8 / 8 1 / 0 0 0 0 - - 0 0 0 0 / $ 02.50, © 1981, Elsevier Sequoia S.A.
280 EXPERIMENTAL Standard solutions of zirconyl chloride were prepared by dissolving the AR material in twice-distilled water. The metal content was analysed by the m e t h o d given by Vogel [7]. Other chemicals used were also of AR grade and were used without further purification. For the electrodeposition of Zr, an electrolytic cell with an asbestos diaphragm was used to separate the catholyte from the anolyte. The cathode comp a r t m e n t was provided with a platinum sheet electrode, whereas the anode was a platinum wire electrode. The electrolysis current was supplied from a 6 V storage battery. Current regulation was maintained by a resistance box connected in series. The electrodeposition was carried out at 25 + 0.05 ° C. For each experiment 10 ml of 0.33 M zirconyl chloride solution was electrolysed in the presence of a complexing agent. RESULTS AND DISCUSSION
Cathodic deposition of zirconium A number of experiments was carried out in order to determine the optim u m conditions necessary for the cathodic deposition of zirconium using different complexing agent solutions, pH, current density and additives, such as a m m o n i u m chloride, sodium chloride and absolute alcohol. The most suitable baths are given in Table 1. Chemical analysis confirmed that the purity of zirconium was 99.8%.
Reactants in the deposition of zirconium The existence of zirconyl complex species in solution indicated in Table 1 has recently been proved in this laboratory by conductometric titration. The plots of conductance vs. a m o u n t of complexing agent added exhibited breaks corresponding to the formation of the indicated complex (e.g. plots of conductance vs. a m o u n t of complexing agent added exhibited breaks corresponding to the formation of the 2 : 1 zirconyl : sulphate complex). Also, these confirmed the presence of the positively charged complex species. This procedure has recently been used in this laboratory for similar purposes [ 8,9 ]. The structure of zirconyl complexes of the type [(ZrO)2SO¢] 2÷ was proved [10]. Also, the fluoride [ 11 ], citrate, tartarate, EDTA, malonate, cysteine, oxalate [ 12 ], G.P., diacetylmonoxime G.P. [ 13 ] and G.T., diacetylmonoxime G.T. [ 14 ] zirconyl complexes were identified and proved conductometricaUy.
Effect of the concentration of the zirconyl solution Smooth deposition was found to take place in the concentration range 0.1-0.33 M zirconyl solution. At higher concentrations (>0.5 M zirconyl solution) deposition of double salts may be obtained [ 15 ]. On the other hand, at very low concentrations of zirconyl solution (<0.05 M solution) no deposition takes place. This may be due to the very small concentration of Zr ions produced.
281 TABLE 1 C a t h o d i c p r o d u c t i o n o f zirconium Bath
Composition of electrolyte solution
Sulphate
4 g NHaCI + 4 g NaC1 + 0.2 g Na2SO+ 5 ml C2HsOH 4 g NH4C1 + 4 g NaCI + 0.1 g NaF + 10 ml C2HsOH 5 g NH4C1 + 4 g NaC1 + 3 ml H3PO4 + 5 ml C2HsOH 5 g NH4C1 + 4 g NaC1 + 5 ml d i c h l o r o a c e t i c acid + 5 ml C 2H 5OH 5 g NH4C1 + 4 g NaCI + 0.1 g NaCN + 10 ml C2HsOH 5 g NH4C1 + 3 g NaC1 + 0.5 g tartaric acid + 3 ml C2HsOH 6 g NH4C1 + 3 g NaC1 + 0.4 g citric acid + 5 ml C2HsOH 4 g NH4C1 + 4 g NaCI + 0.3 g oxalic acid + 3 ml C2HsOH 5 g NH4C1 + 3 g NaC1 + 0.1 g cysteine + 3 ml C2H sOH 3 g NH4CI + 4 g NaCI + 2 g malonic acid + 5 ml C2HsOH 4 g NH4C1 + 4 g NaCI + 0.5% E D T A + 10 ml C2HsOH 5 g NH4CI + 3 g NaCl + 0.5 g sodium acetate + 5 ml C2HsOH 5 g NH4C1 + 4 g NaC1 + 0.2 g G.P. + 5 ml C2HsOH 3 g NH4C1 + 4 g NaC1 + 0.2 g d i a c e t y l m o n o x i m e G.P. + 5 ml C2HsOH 5 g NH4C1 + 4 g NaC1 + 0.2 g G.T. + 3 ml C2HsOH 4 g NH4CI + 4 g NaCl + 0.2 g d i a c e t y l m o n o x i m e G.T. + 3 ml C2HsOH
Fluoride Phosphate Dichloroacetic acid Cyanide Tartarate Citrate Oxalate Cysteine Malonate EDTA Acetate Girard's reagent P Diacetylmonoxime G.P. Girard's reagent T Diacetylmonoxime G.T.
pH
C o m p l e x species
70
5.0
[(ZrO)2SO4] 2+
65
5.0
(ZrOF) +
73
5.0
ZrO(H2PO4) +
60
6.0
ZrO(HC202C12)+
40
5.0
ZrOCN ÷
100
6.5
Z r O ( H s C 40 6) +
100
8.0
ZrO(HTC 6) +
100
5.0
ZrO(HC204) +
60
6.5
ZrO(H6C302NS) +
80
5.0
ZrO(H3C304) +
80
5.0
ZrO(HlsC10N2 O6) ÷
100
8.0
ZrO(H3C 20 2) +
75
6.0
ZrO(HgCTN30)C1 +
75
5.0
ZrO(H14C11N40)Cl +
60
6.0
ZrO(H13CsN30)C1 +
60
5.0
Z r O ( H I sCgN40)C1 +
Current density/mA crn -2
Effect of complexing agents It was noted that no deposition takes place in the absence of, or at very low concentrations of, the complexing agent (at about 0.05 g). Complexing agents have an i m p o r t a n t role in ensuring the presence of a sufficiently small ZrO 2+ ion concentration at the cathode so that this concentration m a y be suitable for the reduction and s m o o t h deposition of the element [ 15 ]. S m o o t h deposition was found to take place at the cathode in the presence of moderate concentrations of the complexing agent.
282
Effect of pH The o p t i m u m pH values obtained for the cathodic deposition of Zr from different baths are shown in Table 1. It was found experimentally that no deposition of zirconium occurs from any bath below pH = 2. This is because of the attack on the element by hydrogen ions resulting in dissolution, and may also be due to the absence of complex formation at these lower pH values. On the other hand, at higher pH values, deposition of Zr salts (hydrous oxide) takes place, hindering the deposition of the element at the cathode (Table 2).
Effect of ammonium salts It has been found that a m m o n i u m salts has an important role in the cathodic deposition of zirconium. It acts as a buffering medium for the bath, assists the stability of the zirconyl complexes and prevents the precipitation of zirconium hydroxide as the pH is raised.
Effect of current density It was noted experimentally that at lower current density (<10 mA cm -2) no deposition takes place in any bath. Increase of current density to 100 mA cm -2 assists the rapid discharge of H ÷ ions leading to the rapid reduction of ZrO, favouring the formation of a crystalline deposit regularly oriented on the cathode [4]. At current density > 1 5 0 mA cm -2 the deposit formed was not adherent and was randomly oriented over the surface of the cathode (Table 2). The o p t i m u m current densities necessary for the cathodic deposition of zirconium are also shown in Table 1.
Effect of ethyl alcohol It was found experimentally that ethyl alcohol was a necessary addition to the bath in order to obtain the Zr deposit and also to help in the process of TABLE 2 Effect of pH and current density on the deposition of Zr from a bath containing 0.33 M Zr ion and 1.4 M Na2SO 4 Current density m A c m -2 Experiments made at a series of pH values of the range 1.5--7 pH unit
Experiments made at a series of current density in the range 10--160 m A c m -2 .
70 70 70 70 70 10 50 70 100 130 160
pH
A m o u n t of Zr metal produced
1.5 4 5 6 7
None Very small Large Small None
5 5 5 5 5 5
None Very small Large Large Small None
283
dissolution of zirconyl chloride. Metal with lower oxygen content was obtained in the absence of ethyl alcohol. Effect o f some additives It was observed that the addition of sodium chlorides increases the conductance and helps in the formation of a coherent deposit. The final pH of the solution was not greatly affected, but the efficiency of the cathodic deposition of Zr was improved. REFERENCES
1 M.V. S m i m o v , A.N. B a x a b o s h k i n a n d V.E. K o m a r o v , Zh. Fiz. K h i m . , 3 7 ( 8 ) ( 1 9 6 3 ) 1 6 6 9 . 2 P. Pint a n d S.N. Flengas, Trans. Inst. Min. Metl., Sect. C, 87 ( 1 9 7 8 ) 29. 3 L.E. Ivanovskii a n d O.S. L e t e m e v , Tr. i n s t . E l e k t r o k h i m . , Ural. Fil. A k a d . N a u k S.S.S.R., 2 ( 1 9 6 1 ) 71. 4 I . F . N i c h k o v , S.P. R a s p o p i n a n d V.I. D e v y a k k i n , Tr. Ural. P o l i t e k h . Inst., 121 ( 1 9 6 2 ) 18. 5 I.N. S h e i k o , Ukx. K h i m . Zh., 29 ( 1 9 6 3 ) 57. 6 British T h o m s o n - H o u s t o n Co., L t d . , Brit. 1 8 2 , 1 9 t h J u l y 1 9 2 1 . 7 A.I. Vogel, Q u a n t i t a t i v e i n o r g a n i c A n a l y s i s , L o n g m a n , L o n d o n , 3rd ed., 1 9 6 8 , p. 547. 8 A.S. F o u d a , J. E l e c t r o a n a l . C h e m . , 1 1 0 ( 1 9 8 0 ) 3 5 7 . 9 M.M. E l s e m o n g y , M.M. G o u d a a n d Y . A . E l e w a d y , J. E l e c t r o a n a l . C h e m . , 76 ( 1 9 7 7 ) 3 7 6 . 10 V . F . S a k s i n , N a u c h . D o k l . V y s s h . Shk., K h i m . i K h i m . T e k h n o l . , 1 ( 1 9 5 9 ) 75. 11 V.M. K o l i k o v a n d V.N. R y b c h i n , Zh. Prikl. K h i m . , 3 6 ( 7 ) ( 1 9 6 3 ) 1 4 1 0 . 12 K ' u e i Wang, H u a H s u e h Pao, 2 9 ( 6 ) ( 1 9 6 3 ) 3 9 5 . 13 M.E.M. E m a m , M.Sc. Thesis, Mansouxa Univ., E g y p t , 1 9 7 4 . 14 G.M. I b r a h i m , M.Sc. Thesis, M a n s o u r a Univ., E g y p t , 1 9 7 8 . 15 M.M. E l s e m o n g y , Y.A. E l e w a d y , M.M. G o u d a a n d A. E l a s k l a n y , J. E l e c t r o a n a l . C h e m . , 84 ( 1 9 7 7 ) 3 5 9 .
279
Elsevier Sequoia S.A., L a u s a n n e - Printed in The Netherlands
CATHODIC PRODUCTION OF ZIRCONIUM *
A.S. F O U D A and M.M. E L S E M O N G Y
Chemistry Department, Faculty of Science, Mansoura University, Mansoura (A.R. Egypt) (Received 16th June 1980; in revised form 7th N o v e m b e r 1980)
ABSTRACT Zirconium was deposited on the cathode at controlled pH from a n u m b e r of solutions containing the metal salt and a complexing agent. The current density ranged from 25 to 1 0 0 m A cm -2. Both the s p e c t r o p h o t o m e t r i c analysis and chemical analysis indicate that the purity of the metal is better t h a n 99.8%.
INTRODUCTION
Zirconium is often thought of as a rare element but with its c o m p o u n d s is now finding a number of applications, for example, ferro-Zr is used in the steel industry, the metal is being used in radio valves and in photo-flash bulbs, and it has been used as an oxygen scavenger in the manufacture of special steels and in the construction of some wireless valves. Zirconium occurs in very small concentrated deposits, Hf being found naturally in all Zr minerals, and because of the lanthanide contraction the separation of the metal from Hf is extremely difficult. This fact motivated us to try to deposit Zr in concentrated form by a simple electrochemical method. Information on the electrodeposition of zirconium is scarce. Zirconium has been prepared by deposition on to a m o l y b d e n u m cathode [ 1 ] from fused equimolecular KNO3 + NaNO3 containing 0.7--5.3 mol% ZrC14 at 700--900°C and current density from 10 -4 to 10 A cm -2. It is also reported [2] that electrodeposition occurs at low current densities at 600--700 ° C and at a concentration of zirconium ~:0.49 wt.%. The metal can also be prepared [ 3 ] by electrolysis of KZrF4 melts in equimolecular mixtures of KC1 and NaC1 at 760--800°C and current density between 0.01 and 0.1 A cm -2. The element was prepared [4] by electrolysis of melts containing Cs2ZrC16 and CsC1 and in the presence of KF, and also [5] from the electrolysis of mixtures of NaC1, KC1 and ZrC1 in the presence of KF. Zirconium was deposited from the vapour phase [6] on tungsten by heating a mixture of ZrCL and H2.
* Dedicated to Mrs. Eltifat A. Elshafie. 0 0 2 2 - 0 7 2 8 / 8 1 / 0 0 0 0 - - 0 0 0 0 / $ 02.50, © 1981, Elsevier Sequoia S.A.
280 EXPERIMENTAL Standard solutions of zirconyl chloride were prepared by dissolving the AR material in twice-distilled water. The metal content was analysed by the m e t h o d given by Vogel [7]. Other chemicals used were also of AR grade and were used without further purification. For the electrodeposition of Zr, an electrolytic cell with an asbestos diaphragm was used to separate the catholyte from the anolyte. The cathode comp a r t m e n t was provided with a platinum sheet electrode, whereas the anode was a platinum wire electrode. The electrolysis current was supplied from a 6 V storage battery. Current regulation was maintained by a resistance box connected in series. The electrodeposition was carried out at 25 + 0.05 ° C. For each experiment 10 ml of 0.33 M zirconyl chloride solution was electrolysed in the presence of a complexing agent. RESULTS AND DISCUSSION
Cathodic deposition of zirconium A number of experiments was carried out in order to determine the optim u m conditions necessary for the cathodic deposition of zirconium using different complexing agent solutions, pH, current density and additives, such as a m m o n i u m chloride, sodium chloride and absolute alcohol. The most suitable baths are given in Table 1. Chemical analysis confirmed that the purity of zirconium was 99.8%.
Reactants in the deposition of zirconium The existence of zirconyl complex species in solution indicated in Table 1 has recently been proved in this laboratory by conductometric titration. The plots of conductance vs. a m o u n t of complexing agent added exhibited breaks corresponding to the formation of the indicated complex (e.g. plots of conductance vs. a m o u n t of complexing agent added exhibited breaks corresponding to the formation of the 2 : 1 zirconyl : sulphate complex). Also, these confirmed the presence of the positively charged complex species. This procedure has recently been used in this laboratory for similar purposes [ 8,9 ]. The structure of zirconyl complexes of the type [(ZrO)2SO¢] 2÷ was proved [10]. Also, the fluoride [ 11 ], citrate, tartarate, EDTA, malonate, cysteine, oxalate [ 12 ], G.P., diacetylmonoxime G.P. [ 13 ] and G.T., diacetylmonoxime G.T. [ 14 ] zirconyl complexes were identified and proved conductometricaUy.
Effect of the concentration of the zirconyl solution Smooth deposition was found to take place in the concentration range 0.1-0.33 M zirconyl solution. At higher concentrations (>0.5 M zirconyl solution) deposition of double salts may be obtained [ 15 ]. On the other hand, at very low concentrations of zirconyl solution (<0.05 M solution) no deposition takes place. This may be due to the very small concentration of Zr ions produced.
281 TABLE 1 C a t h o d i c p r o d u c t i o n o f zirconium Bath
Composition of electrolyte solution
Sulphate
4 g NHaCI + 4 g NaC1 + 0.2 g Na2SO+ 5 ml C2HsOH 4 g NH4C1 + 4 g NaCI + 0.1 g NaF + 10 ml C2HsOH 5 g NH4C1 + 4 g NaC1 + 3 ml H3PO4 + 5 ml C2HsOH 5 g NH4C1 + 4 g NaC1 + 5 ml d i c h l o r o a c e t i c acid + 5 ml C 2H 5OH 5 g NH4C1 + 4 g NaCI + 0.1 g NaCN + 10 ml C2HsOH 5 g NH4C1 + 3 g NaC1 + 0.5 g tartaric acid + 3 ml C2HsOH 6 g NH4C1 + 3 g NaC1 + 0.4 g citric acid + 5 ml C2HsOH 4 g NH4C1 + 4 g NaCI + 0.3 g oxalic acid + 3 ml C2HsOH 5 g NH4C1 + 3 g NaC1 + 0.1 g cysteine + 3 ml C2H sOH 3 g NH4CI + 4 g NaCI + 2 g malonic acid + 5 ml C2HsOH 4 g NH4C1 + 4 g NaCI + 0.5% E D T A + 10 ml C2HsOH 5 g NH4CI + 3 g NaCl + 0.5 g sodium acetate + 5 ml C2HsOH 5 g NH4C1 + 4 g NaC1 + 0.2 g G.P. + 5 ml C2HsOH 3 g NH4C1 + 4 g NaC1 + 0.2 g d i a c e t y l m o n o x i m e G.P. + 5 ml C2HsOH 5 g NH4C1 + 4 g NaC1 + 0.2 g G.T. + 3 ml C2HsOH 4 g NH4CI + 4 g NaCl + 0.2 g d i a c e t y l m o n o x i m e G.T. + 3 ml C2HsOH
Fluoride Phosphate Dichloroacetic acid Cyanide Tartarate Citrate Oxalate Cysteine Malonate EDTA Acetate Girard's reagent P Diacetylmonoxime G.P. Girard's reagent T Diacetylmonoxime G.T.
pH
C o m p l e x species
70
5.0
[(ZrO)2SO4] 2+
65
5.0
(ZrOF) +
73
5.0
ZrO(H2PO4) +
60
6.0
ZrO(HC202C12)+
40
5.0
ZrOCN ÷
100
6.5
Z r O ( H s C 40 6) +
100
8.0
ZrO(HTC 6) +
100
5.0
ZrO(HC204) +
60
6.5
ZrO(H6C302NS) +
80
5.0
ZrO(H3C304) +
80
5.0
ZrO(HlsC10N2 O6) ÷
100
8.0
ZrO(H3C 20 2) +
75
6.0
ZrO(HgCTN30)C1 +
75
5.0
ZrO(H14C11N40)Cl +
60
6.0
ZrO(H13CsN30)C1 +
60
5.0
Z r O ( H I sCgN40)C1 +
Current density/mA crn -2
Effect of complexing agents It was noted that no deposition takes place in the absence of, or at very low concentrations of, the complexing agent (at about 0.05 g). Complexing agents have an i m p o r t a n t role in ensuring the presence of a sufficiently small ZrO 2+ ion concentration at the cathode so that this concentration m a y be suitable for the reduction and s m o o t h deposition of the element [ 15 ]. S m o o t h deposition was found to take place at the cathode in the presence of moderate concentrations of the complexing agent.
282
Effect of pH The o p t i m u m pH values obtained for the cathodic deposition of Zr from different baths are shown in Table 1. It was found experimentally that no deposition of zirconium occurs from any bath below pH = 2. This is because of the attack on the element by hydrogen ions resulting in dissolution, and may also be due to the absence of complex formation at these lower pH values. On the other hand, at higher pH values, deposition of Zr salts (hydrous oxide) takes place, hindering the deposition of the element at the cathode (Table 2).
Effect of ammonium salts It has been found that a m m o n i u m salts has an important role in the cathodic deposition of zirconium. It acts as a buffering medium for the bath, assists the stability of the zirconyl complexes and prevents the precipitation of zirconium hydroxide as the pH is raised.
Effect of current density It was noted experimentally that at lower current density (<10 mA cm -2) no deposition takes place in any bath. Increase of current density to 100 mA cm -2 assists the rapid discharge of H ÷ ions leading to the rapid reduction of ZrO, favouring the formation of a crystalline deposit regularly oriented on the cathode [4]. At current density > 1 5 0 mA cm -2 the deposit formed was not adherent and was randomly oriented over the surface of the cathode (Table 2). The o p t i m u m current densities necessary for the cathodic deposition of zirconium are also shown in Table 1.
Effect of ethyl alcohol It was found experimentally that ethyl alcohol was a necessary addition to the bath in order to obtain the Zr deposit and also to help in the process of TABLE 2 Effect of pH and current density on the deposition of Zr from a bath containing 0.33 M Zr ion and 1.4 M Na2SO 4 Current density m A c m -2 Experiments made at a series of pH values of the range 1.5--7 pH unit
Experiments made at a series of current density in the range 10--160 m A c m -2 .
70 70 70 70 70 10 50 70 100 130 160
pH
A m o u n t of Zr metal produced
1.5 4 5 6 7
None Very small Large Small None
5 5 5 5 5 5
None Very small Large Large Small None
283
dissolution of zirconyl chloride. Metal with lower oxygen content was obtained in the absence of ethyl alcohol. Effect o f some additives It was observed that the addition of sodium chlorides increases the conductance and helps in the formation of a coherent deposit. The final pH of the solution was not greatly affected, but the efficiency of the cathodic deposition of Zr was improved. REFERENCES
1 M.V. S m i m o v , A.N. B a x a b o s h k i n a n d V.E. K o m a r o v , Zh. Fiz. K h i m . , 3 7 ( 8 ) ( 1 9 6 3 ) 1 6 6 9 . 2 P. Pint a n d S.N. Flengas, Trans. Inst. Min. Metl., Sect. C, 87 ( 1 9 7 8 ) 29. 3 L.E. Ivanovskii a n d O.S. L e t e m e v , Tr. i n s t . E l e k t r o k h i m . , Ural. Fil. A k a d . N a u k S.S.S.R., 2 ( 1 9 6 1 ) 71. 4 I . F . N i c h k o v , S.P. R a s p o p i n a n d V.I. D e v y a k k i n , Tr. Ural. P o l i t e k h . Inst., 121 ( 1 9 6 2 ) 18. 5 I.N. S h e i k o , Ukx. K h i m . Zh., 29 ( 1 9 6 3 ) 57. 6 British T h o m s o n - H o u s t o n Co., L t d . , Brit. 1 8 2 , 1 9 t h J u l y 1 9 2 1 . 7 A.I. Vogel, Q u a n t i t a t i v e i n o r g a n i c A n a l y s i s , L o n g m a n , L o n d o n , 3rd ed., 1 9 6 8 , p. 547. 8 A.S. F o u d a , J. E l e c t r o a n a l . C h e m . , 1 1 0 ( 1 9 8 0 ) 3 5 7 . 9 M.M. E l s e m o n g y , M.M. G o u d a a n d Y . A . E l e w a d y , J. E l e c t r o a n a l . C h e m . , 76 ( 1 9 7 7 ) 3 7 6 . 10 V . F . S a k s i n , N a u c h . D o k l . V y s s h . Shk., K h i m . i K h i m . T e k h n o l . , 1 ( 1 9 5 9 ) 75. 11 V.M. K o l i k o v a n d V.N. R y b c h i n , Zh. Prikl. K h i m . , 3 6 ( 7 ) ( 1 9 6 3 ) 1 4 1 0 . 12 K ' u e i Wang, H u a H s u e h Pao, 2 9 ( 6 ) ( 1 9 6 3 ) 3 9 5 . 13 M.E.M. E m a m , M.Sc. Thesis, Mansouxa Univ., E g y p t , 1 9 7 4 . 14 G.M. I b r a h i m , M.Sc. Thesis, M a n s o u r a Univ., E g y p t , 1 9 7 8 . 15 M.M. E l s e m o n g y , Y.A. E l e w a d y , M.M. G o u d a a n d A. E l a s k l a n y , J. E l e c t r o a n a l . C h e m . , 84 ( 1 9 7 7 ) 3 5 9 .