Performance Characteristics of Electroless Plating Baths for Nickel-Ceramic Composite Membrance fabrication

Thesis submitted in partial fulfillment of the Thesis submitted in partial fulfillment of the Thesis submitted in partial fulfillment of the Thesis submitted in partial fulfillment of the.

DOCTOR OF PHILOSOPHY

Vijaya Kumar Bulasara

Department of Chemical Engineering Indian Institute of Technology Guwahati

Guwahati – 781039, India July 2011

CERTIFICATE

Introduction and literature review 1–50

Performance characteristics of membrane fabrication methods 12

Performance characteristics of conventional electroless plating baths

Performance characteristics of hydrazine baths 86

Performance characteristics of agitated electroless plating baths

Agitated hypophosphite electroless plating baths 101
Agitated hydrazine electroless plating baths 116

Performance characteristics of ultrasonic electroless plating baths

Ultrasonic hypophosphite electroless plating baths 133 .1 Efficacy of sonication assisted electroless plating 133
Ultrasonic hydrazine electroless plating baths 148 .1 Efficacy of sonication assisted electroless plating 148

Performance characteristics of electroless plating baths under hydrothermal conditions

Electroless plating process characteristics 163

Conclusions and future work 179–188

Symbols

CB average bulk concentration of nickel ions in the plating bath (mol/l) CS average nickel ion concentration at the liquid-substrate interface (mol/l) CM average metallic nickel concentration on the substrate (mol/l).

INTRODUCTION AND LITERATURE REVIEW

Introduction to metal membranes

Palladium membranes
Silver and nickel membranes

Therefore, palladium membrane technology addresses the fabrication of a dense palladium membrane with minimal palladium film thickness on a structured asymmetric support. Therefore, palladium membrane technology is proposed supplemented with an automated control system that prevents the membrane from coming into contact with hydrogen up to 300°C (heating in an inert environment).

Metal membrane fabrication methods

Physical vapor deposition
Thermal evaporation
Magnetron sputtering
Chemical vapor deposition
Electroplating
Electroless plating
Summary

Activation of the support prior to deposition is required to initiate this autocatalytic deposition process. As described above, the traditional technique for preparing metal composite membranes by electroless deposition consists of two steps; activation of support and lining.

Performance characteristics of membrane fabrication methods

Chemical vapor deposition (CVD)
Magnetron sputtering
Electrodeposition

They found that the stirring rate of the electroless plating bath affected the Pd deposition and also affected the crystalline growth of Pd. They found that the pore size shrinkage of the hydrothermally deposited palladium membrane was significant.

Prominent issues in literatures .1 Membrane support parameters

Fabrication process variables
Mass transfer enhancements
New generation supports

The final thickness of the metal layer is strongly dependent on the pore size distribution of the support. They reported that the final thickness of palladium was about three times the diameter of the largest pore on the surface. Also in their work, the authors did not investigate the influence of the loading degree on the performance characteristics of the electroplating baths.

In summary, both process parameters and mass transfer coupling effects can contribute significantly to the permeation properties of the metal-ceramic composite membranes. On the other hand, porous stainless steel support has been used to improve the mechanical strength of the support.

Possible scope for further research

They found that the Pd/Nb40Ti30Ni30/Pd/porous nickel support composite membrane exhibited excellent permeability and satisfactory mechanical properties. In summary, nickel membranes appear to be promising as new generation supports for thin and dense Pd film integrated composite membranes. There is a need to address the capability of electroless plating to prepare this new generation of supports that have nickel layer as the intermediate diffusion barrier.

It is important to note that the existing nickel powder impregnation method may not offer such flexibility and thus further engineering of dense Pd membranes may be limited. In summary, it is expected that mass transfer enhanced electroless plating process characteristics for nickel deposition on porous supports will provide a good technical overview with which further engineering of thin dense Pd composite membranes can be easily accomplished.

Objectives of present study

The choice of nickel as a plating precursor is due to the hypothesis that nickel membrane deposition characteristics are inferior to palladium membrane deposition characteristics, so the greater role of mass transfer enhancements can be thoroughly investigated. Alternatively, an additional goal of this work is to prepare nickel ceramic composite membranes with different average pore size values (5–100 nm), metal film thickness (5–50 microns), to serve as diverse membrane supports for ultra-thin deposition palladium films on these supports. To critically examine and identify potential mass transfer enhancement techniques that may enable higher pore densification values at lower metal precursor concentrations.

Organization of the thesis

Chapter 2 presents the preparation and characterization of ceramic membrane support along with the experimental procedure for electroless plating process adopted in this study

Chapter 3 addresses the performance characteristics of conventional electroless plating baths for nickel–ceramic composite microfiltration membranes

Support preparation and characterization .1 Raw materials

Support fabrication
Support characterization
Summary

Evaluation of plating characteristics .1 Plating parameters

Titration analysis
Permeation analysis of composite membrane
Kinetic studies

Summary

As shown in the figure (Figure 2.6), the slope and intercept values for the ceramic support. The average pore diameter and the effective porosity of the ceramic support as obtained from the above analysis were 275.46 nm and 0.4497 respectively. From the air permeation experiments, the average pore diameter and the effective porosity of the ceramic membrane support were obtained as 275 nm and 0.44, respectively.

The average pore size and porosity of the composite membranes were estimated from gas permeation experiments. The average pore diameter of the metal-ceramic composite membrane is evaluated using the expression: 2.19).

PERFORMANCE CHARACTERISTICS OF CONVENTIONAL ELECTROLESS PLATING

BATHS

Performance characteristics of hypophosphite baths

Efficacy of electroless plating
Surface characterization
Permeation characteristics of composite membrane
Cost tradeoffs
PPD and efficiency tradeoffs
Summary

The deposition rate is found to increase non-linearly with solution concentration and loading ratio. The nature of the spectrum indicates that nickel films deposited using plating baths without hypophosphite electrolytes are amorphous. The effective porosity (Figure 3.5b) of the deposited nickel layer increased with increasing solution concentration, but a decrease in porosity values is observed with increasing loading ratio.

This may be because the surface of the porous substrate is uneven. From Figure 3.9, it is clear that the plating efficiency (η), which minimizes the metal loss during the electroless plating, is favored by a lower initial concentration of nickel, while the pore densification (PPD), which improves the separation performance of the plated membrane, is favored. at a higher concentration.

Performance characteristics of hydrazine baths

Efficacy of electroless plating
Permeation characteristics of composite membrane
Cost tradeoffs
PPD and efficiency tradeoffs
Summary

To confirm that the membrane fabrication is crystalline, the surfaces of the composite membranes were subjected to X-ray diffraction (XRD) study. Based on experimental observations, it can be concluded that the performance characteristics of the electroless plating baths are significantly affected by the solution concentration as the loading ratio. The optimal values of the initial NiSO4 solution concentration (Ci, opt) obtained by maximizing the objective function (fmax) through a non-linear regression analysis for various combinations of f and 1 f for a 2 loading ratio of 393 cm2/ L is presented in Table 3.7.

From Figure 3.18, it can be seen that plating efficiency (η), which minimizes metal loss during electroless plating, is favored by a lower initial nickel concentration, while pore compaction (PPD) that improves the separation performance of the plated membrane is favored. due to a higher concentration. The fabricated nickel-ceramic composite membranes are porous in nature and this may be due to the larger pore size of the membrane support.

Conclusions

The average pore diameter of the nickel-ceramic composite membrane, as obtained from gas permeability experiments, can also be shown from FESEM surface micrographs (Figure 3.19). These photomicrographs show the presence of micropores on the surfaces of nickel-ceramic composite membranes fabricated in hypophosphite and hydrazine electroless plating baths.

PERFORMANCE CHARACTERISTICS OF AGITATED ELECTROLESS PLATING BATHS

Agitated hypophosphite electroless plating baths .1 Efficacy of electroless plating

Metal–ceramic membrane characteristics

Permeation characteristics

PPD and Efficiency tradeoffs

From this figure (Fig. 4.3), it can be seen that the average nickel deposition rate increases as the stirrer speed increases for the initial solution concentrations of 0.04 and 0.08 mol/L and is higher than that of the base case (0 rpm). for both loading ratios. However, this is not the case at the higher initial solution concentration (0.16 mol/L) where the average nickel deposition values occur under stirring. It is observed that the effective porosity of the metal layer is strongly influenced by all three parameters.

Further, it can be observed that the average thickness of the porous nickel layer is inversely proportional to the loading ratio of the bath. Either of the two optimal combinations can be used, namely an initial nickel concentration of 0.08 mol/L at a stirrer speed of 100 rpm or 0.04 mol/L at 200 rpm.

Agitated hydrazine electroless plating baths .1 Efficacy of electroless plating

Permeation characteristics .1 Pore diameter

It can be observed that the surface texture is strongly influenced by the concentration of the solution as a loading ratio. Greater uniformity of the metal coating is observed at a concentration of 0.08 mol/L, and coarser nickel grains are formed at a higher solution concentration (0.16 mol/L) for all stirrer speeds. The effect of loading ratio on PPD is insignificant compared to the concentration of the metal solution.

The observed PPD trends are similar to those obtained for conversion, i.e. improvement of PPD with stirring speed is evident for both 0.04 and 0.08 mol/L initial nickel metal solution concentrations, but not for 0.16 mol/L initial nickel solution concentration. The PPD improvement with stirring speed is estimated to be approximately 6% and 1.7% for initial metal solution concentrations of 0.04 and 0.08 mol/L, respectively.

Summary and conclusions

A comparative assessment of the performance of the two reducing agents in stirred baths for electroless plating is shown in Table 4.9. From this table (Table 4.9), it can be seen that the hydrazine-based electroless plating baths result in higher values of conversion, efficiency, PPD, metal film thickness and average mass transfer coefficient, indicating that they are superior to hypophosphite baths. The lack of competence of hypophosphite-based baths for electroless plating with hydrazine-based baths, even under stirring, is due to the fundamental problem of hydrogen formation in the earlier case.

Based on thorough experimental research, it has been found that stirring the bath using membrane stirring improves the performance of electroless plating baths, but results in lower plating efficiency compared to the base case. The next chapter (Chapter 5) presents the effect of sonication on the performance of electroless plating baths.

PERFORMANCE CHARACTERISTICS OF ULTRASONIC ELECTROLESS PLATING BATHS

Ultrasonic hypophosphite electroless plating baths .1 Efficacy of sonication assisted electroless plating

Film thickness

Summary

For example, sonication gave 230% excess selective conversion compared to the base case at an initial nickel solution concentration of 0.08 mol/L and a loading ratio of 196 cm2/L. Sonication greatly improves the metal film thickness independent of the solution concentration due to improved plating speed and efficient. Further, it can be observed that identical permeability coefficient profiles exist for both membrane stirring cases of 100 rpm and 200 rpm at a lower solution concentration of 0.04 mol/L (Figure 5.6a).

Therefore, it is clear that the permeation properties of the metal film are largely influenced by the type of mass transfer enhancement and by the concentration of the solution. In all cases, the effective porosity values obtained for a lower loading degree (196 cm2/L) are almost twice as large as those obtained for the higher loading degree (393 cm2/L) and increase with the concentration of the solution.

Ultrasonic hydrazine electroless plating baths .1 Efficacy of sonication assisted electroless plating

Film thickness

Summary

Bath loading slightly affects the plating efficiency and a higher loading ratio (393 cm2/L) is recommended for efficient plating. Bath loading ratio (θ) has no significant effect on the model parameters for ultrasonic electroless plating. As shown in the figure, the surface morphology of the deposited metal layer depended on the solution concentration as well as the loading ratio.

It can be observed that both bath concentration and loading ratio significantly influence the effective porosity values. In all cases, the effective porosity values obtained for a lower loading ratio (196 cm2/L) are approximately 50% higher than those obtained for the higher loading ratio (393 cm2/L) and increase with the concentration of the solution.

Conclusions

Based on several experimental investigations, this work addresses the effect of process parameters and mass transfer enhancement techniques on the morphological and transport properties of porous nickel metal films fabricated using ultrasonic hydrazine baths for electroless plating. Selective conversions of nickel and hydrazine electroplating baths are in the acceptable range for industrial use (>60% at higher mol/L nickel solution concentrations) with sonication at a loading ratio of 393 cm2/L). It can be observed that all process as well as morphological parameters including conversion, efficiency, PPD, average pore size, average effective porosity and average mass transfer coefficient for hydrazine-based baths are significantly higher than those obtained using hypophosphite-based baths.

Selective conversion values for hydrazine-based baths varied and are higher than those obtained for hypophosphite baths especially at higher concentrations. The presence of micropores on the surfaces of nickel-ceramic composite membranes is also confirmed by FESEM surface micrographs (Figure 5.19).

PERFORMANCE CHARACTERISTICS OF ELECTROLESS PLATING BATHS UNDER

HYDROTHERMAL CONDITIONS

Electroless plating process characteristics