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Relationship between surface coverage @ and concentration of Nin, KI and combination of them.

Table 2 Relationship between surface coverage @ and concentration of Nin, KI and combination of them.

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ninhydrin (2,2-Dihydroxyindane-1,3-dione) Electrodeposition of zinc was carried out using an acid sulfate bath containing: 0.15 M ZnSO,’ 6H20, 0.15 M Na2SO, at pH 3.5 anc at 25 °C. The pH of the electrolyte was adjusted by addition of 1:1 H2SO4. The additive tested was ninhydrin (Nin) in the presence and absence of KI. The Nin solution was prepared by dissolving the appropriate amount in 250 ml doubly distilled water, and ther added the required amount to the electrolyte.
ninhydrin (2,2-Dihydroxyindane-1,3-dione) Electrodeposition of zinc was carried out using an acid sulfate bath containing: 0.15 M ZnSO,’ 6H20, 0.15 M Na2SO, at pH 3.5 anc at 25 °C. The pH of the electrolyte was adjusted by addition of 1:1 H2SO4. The additive tested was ninhydrin (Nin) in the presence and absence of KI. The Nin solution was prepared by dissolving the appropriate amount in 250 ml doubly distilled water, and ther added the required amount to the electrolyte.
Fig. 1. Potentiodynamic cathodic polarization curves during zinc electrodeposition in the absence (blank) and presence of different concentrations of Nin at pH 3.5.
Fig. 1. Potentiodynamic cathodic polarization curves during zinc electrodeposition in the absence (blank) and presence of different concentrations of Nin at pH 3.5.
Fig. 2. Potentiodynamic cathodic polarization curves during zinc electrodeposition in the absence (blank) and presence of different concentrations of KI at pH 3.5. To investigate the effect of the tested additives on the electrode kinet- ics, Tafel parameters were derived from the corresponding i-E curves (Figs. 1-3) using the Software CorrView 2. The Tafel slopes, b, were calcu- lated from the straight lines at high polarization (— 1.168 to — 1.327 V) in the absence and presence of Nin and iodide ions, in addition, the values of the electrokinetic parameters i, (exchange current densities), a, (the transfer coefficient) are listed in Table 1. The data indicate that Tafel
Fig. 2. Potentiodynamic cathodic polarization curves during zinc electrodeposition in the absence (blank) and presence of different concentrations of KI at pH 3.5. To investigate the effect of the tested additives on the electrode kinet- ics, Tafel parameters were derived from the corresponding i-E curves (Figs. 1-3) using the Software CorrView 2. The Tafel slopes, b, were calcu- lated from the straight lines at high polarization (— 1.168 to — 1.327 V) in the absence and presence of Nin and iodide ions, in addition, the values of the electrokinetic parameters i, (exchange current densities), a, (the transfer coefficient) are listed in Table 1. The data indicate that Tafel
Tafel kinetic parameters obtained for zinc sulfate solutions in absence and presence of Nin and/or KI and combination between them at pH 3.5. Table 1
Tafel kinetic parameters obtained for zinc sulfate solutions in absence and presence of Nin and/or KI and combination between them at pH 3.5. Table 1
Fig. 3. Potentiodynamic cathodic polarization curves during zinc electrodeposition in the absence and presence of Nin, KI and a combination of them at pH 3.5.
Fig. 3. Potentiodynamic cathodic polarization curves during zinc electrodeposition in the absence and presence of Nin, KI and a combination of them at pH 3.5.
Fig. 4. Plot of 6/(1-6) against concentration [C] to evaluate AG$'(a) Nin and (b) KI. ina similar way as reported for organic molecules where R is the univer- sal gas constant, T is the absolute temperature and 55.5 is the molarity of water. The large value of free energy change of — 25.9 kJ/mol for Nin and — 38.0 kJ/mol for KI confirms the extent of the chemisorption at the metal-solution interface [25]. Also, the large value of AG°, and its negative sign indicate that the adsorption of Nin or iodide ions on
Fig. 4. Plot of 6/(1-6) against concentration [C] to evaluate AG$'(a) Nin and (b) KI. ina similar way as reported for organic molecules where R is the univer- sal gas constant, T is the absolute temperature and 55.5 is the molarity of water. The large value of free energy change of — 25.9 kJ/mol for Nin and — 38.0 kJ/mol for KI confirms the extent of the chemisorption at the metal-solution interface [25]. Also, the large value of AG°, and its negative sign indicate that the adsorption of Nin or iodide ions on
Fig. 6. Cyclic voltammetric curves recorded at GC electrode in the absence and pres- ence of different concentrations of KI (scan rate = 100 mV/s). Fig. 10a-c depicts the effect of adding Nin, iodide ions and a combination between them to the plating bath on the anodic linear stripping responses. The addition of Nin alone to the sulfate bath de- creased the height and the area of the anodic stripping peak. A larger decrease in the anodic stripping peak was observed as a result of the iodide ion addition. It is worthwhile to mention that the large effect
Fig. 6. Cyclic voltammetric curves recorded at GC electrode in the absence and pres- ence of different concentrations of KI (scan rate = 100 mV/s). Fig. 10a-c depicts the effect of adding Nin, iodide ions and a combination between them to the plating bath on the anodic linear stripping responses. The addition of Nin alone to the sulfate bath de- creased the height and the area of the anodic stripping peak. A larger decrease in the anodic stripping peak was observed as a result of the iodide ion addition. It is worthwhile to mention that the large effect
Fig. 5. Cyclic voltammetric curves recorded at GC electrode in the absence and pres- ence of different concentrations of Nin (scan rate = 100 mV/s).
Fig. 5. Cyclic voltammetric curves recorded at GC electrode in the absence and pres- ence of different concentrations of Nin (scan rate = 100 mV/s).
The nucleation overpotential (NOP) as a function of concentrations of Nin, KI and < combination of them.
The nucleation overpotential (NOP) as a function of concentrations of Nin, KI and < combination of them.
Fig. 7. Cyclic voltammetric curves recorded at GC electrode in the absence (blank) and pres- ence of different concentrations of Nin, KI and combination of them (scan rate = 100 mV/s).
Fig. 7. Cyclic voltammetric curves recorded at GC electrode in the absence (blank) and pres- ence of different concentrations of Nin, KI and combination of them (scan rate = 100 mV/s).
Fig. 8. Cyclic voltammetric curves recorded at GC electrode in the absence and presence of 2.8 x 10-4 M Nin at different scan rates. The insert shows the relation between the ca- thodic peak (ip) as a function of the scan rate (Vv).
Fig. 8. Cyclic voltammetric curves recorded at GC electrode in the absence and presence of 2.8 x 10-4 M Nin at different scan rates. The insert shows the relation between the ca- thodic peak (ip) as a function of the scan rate (Vv).
Fig. 9. Cyclic voltammetric curves recorded at GC electrode in the absence and presence of 2.5 x 10~° M K1 at different scan rates. The insert shows the relation between the ¢ thodic peak (icp) as a function of the scan rate (v). increases, suggesting that the rate of growth of the nuclei is controlled by mass transfer of the depositing metal ions towards the electrode sur- face [36]. These results agree well with those obtained by the ALSV tech- nique (Fig. 10). The most interesting part of the i-t transients is the rising portion (the first 20% of the rising part), which corresponds to the density of the first monolayer of the growth of nuclei and therefore can be used to determine the kinetics of nuclei growth [37]. Only the first 20% of the rising current of the transient is free from overlap of nu- clei. However, the overall shape of the transient and its dependence on potential then becomes important. Scharifker and Hills [38] considered two types of nucleation, proposed that for instantaneous nucleation in which the nuclei are formed at the beginning of the pulse, and for pro- gressive nucleation in which the nuclei are continuously formed during Several characteristic regions in this current-time profile were no- ticed. The first region, where the current decreased is attributed to the charging of the double layer [36]. This is followed by a second region where a short and nearly constant current is seen indicating an induc- tion period. As zinc began to nucleate and grow on the GC electrode the current increased with time. This rising current was mainly related to an increase in the electroactive sites where each independent zinc nucleus grew in size (instantaneous growth) and/or the number of zinc nuclei increased (progressive) on the steel substrate surface. Final- ly, the rising current tended toward a steady-state value when the cath- ode surface was completely covered with zinc and the relative area of growth became constant. The data in Fig. 12 shows that, as the cathodic step potential is made more negative, the steady-state current value
Fig. 9. Cyclic voltammetric curves recorded at GC electrode in the absence and presence of 2.5 x 10~° M K1 at different scan rates. The insert shows the relation between the ¢ thodic peak (icp) as a function of the scan rate (v). increases, suggesting that the rate of growth of the nuclei is controlled by mass transfer of the depositing metal ions towards the electrode sur- face [36]. These results agree well with those obtained by the ALSV tech- nique (Fig. 10). The most interesting part of the i-t transients is the rising portion (the first 20% of the rising part), which corresponds to the density of the first monolayer of the growth of nuclei and therefore can be used to determine the kinetics of nuclei growth [37]. Only the first 20% of the rising current of the transient is free from overlap of nu- clei. However, the overall shape of the transient and its dependence on potential then becomes important. Scharifker and Hills [38] considered two types of nucleation, proposed that for instantaneous nucleation in which the nuclei are formed at the beginning of the pulse, and for pro- gressive nucleation in which the nuclei are continuously formed during Several characteristic regions in this current-time profile were no- ticed. The first region, where the current decreased is attributed to the charging of the double layer [36]. This is followed by a second region where a short and nearly constant current is seen indicating an induc- tion period. As zinc began to nucleate and grow on the GC electrode the current increased with time. This rising current was mainly related to an increase in the electroactive sites where each independent zinc nucleus grew in size (instantaneous growth) and/or the number of zinc nuclei increased (progressive) on the steel substrate surface. Final- ly, the rising current tended toward a steady-state value when the cath- ode surface was completely covered with zinc and the relative area of growth became constant. The data in Fig. 12 shows that, as the cathodic step potential is made more negative, the steady-state current value
Effect of Nin and/ or KI on the throwing power (TP%) throwing index (TI), and Wagner number (Wa) for zinc electrodeposition from sulfate bath at pH 3.5. Table 4
Effect of Nin and/ or KI on the throwing power (TP%) throwing index (TI), and Wagner number (Wa) for zinc electrodeposition from sulfate bath at pH 3.5. Table 4
Fig. 10. Anodic linear stripping voltammograms for zinc electrodeposits: (a) in absence and presence of different concentrations of Nin (b) in absence and presence of different concentrations of KI (c) in absence and presence of combination between KI and Nin; and (d) in presence of 1.4 x 10~* M Nin at different deposition potentials.
Fig. 10. Anodic linear stripping voltammograms for zinc electrodeposits: (a) in absence and presence of different concentrations of Nin (b) in absence and presence of different concentrations of KI (c) in absence and presence of combination between KI and Nin; and (d) in presence of 1.4 x 10~* M Nin at different deposition potentials.
Fig. 11. Metal distribution ratio M versus the linear ratio L in the presence and absence of additives, (a): blank. (b) 2.8 x 1074 M Nin, (c) 6.5 x 107° MKI (d) 2.8 x 10-4 M Nin +6.5 x 107° M KI. Morphological examination using SEM of the as-deposited zinc was carried out to better understand the electrochemical results.
Fig. 11. Metal distribution ratio M versus the linear ratio L in the presence and absence of additives, (a): blank. (b) 2.8 x 1074 M Nin, (c) 6.5 x 107° MKI (d) 2.8 x 10-4 M Nin +6.5 x 107° M KI. Morphological examination using SEM of the as-deposited zinc was carried out to better understand the electrochemical results.
Fig. 12. Potentiostatic current-time transients from the sulfate bath at different deposition potentials.
Fig. 12. Potentiostatic current-time transients from the sulfate bath at different deposition potentials.
Fig. 13. The relationship between current density and t'/? at different depositior potentials. X-ray diffraction analysis showed a difference in the crystallographic orientation of the deposits in the presence and absence of Nin and/ or iodide ions as shown in Fig. 17. The results indicate that the zinc depos- ited from the additive-free solutions, exhibited a hexagonal structure, with a strong (101) diffraction peak (preferred growth orientation) in addition to (002) and (110) peaks with relatively low intensities. This crystallographic orientation is in accordance with that usually detected for these deposits [21,34]. The presence of Nin or iodide ions in the plat- ing solution causes an increase in the full width height maximum
Fig. 13. The relationship between current density and t'/? at different depositior potentials. X-ray diffraction analysis showed a difference in the crystallographic orientation of the deposits in the presence and absence of Nin and/ or iodide ions as shown in Fig. 17. The results indicate that the zinc depos- ited from the additive-free solutions, exhibited a hexagonal structure, with a strong (101) diffraction peak (preferred growth orientation) in addition to (002) and (110) peaks with relatively low intensities. This crystallographic orientation is in accordance with that usually detected for these deposits [21,34]. The presence of Nin or iodide ions in the plat- ing solution causes an increase in the full width height maximum
Fig. 14. Potentiostatic current-time transients from the sulfate bath in presence and absence of Nin, KI and combination between them.
Fig. 14. Potentiostatic current-time transients from the sulfate bath in presence and absence of Nin, KI and combination between them.
Fig. 15. The relationship between current density and t'? in presence of Nin, KI and combination between them.
Fig. 15. The relationship between current density and t'? in presence of Nin, KI and combination between them.
Fig. 17. X-ray diffraction analysis of zinc deposits in the absence and presence o additives.
Fig. 17. X-ray diffraction analysis of zinc deposits in the absence and presence o additives.
Fig. 16. Photomicrographs of zinc deposited in the absence and presence of different concentrations of Nin, KI and a combination of them (a) Blank, (b) 2.8 x 1074 M Nin (c) 2.5 x 107° M KI, (d) 1.5 x 107° MKI + 2.8 x 1074 M Nin.
Fig. 16. Photomicrographs of zinc deposited in the absence and presence of different concentrations of Nin, KI and a combination of them (a) Blank, (b) 2.8 x 1074 M Nin (c) 2.5 x 107° M KI, (d) 1.5 x 107° MKI + 2.8 x 1074 M Nin.
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