Elsevier

Desalination

Volume 275, Issues 1–3, 15 July 2011, Pages 243-251
Desalination

Nickel-ceramic composite membranes: Optimization of hydrazine based electroless plating process parameters

https://doi.org/10.1016/j.desal.2011.03.009Get rights and content

Abstract

Based on the experimental investigation, this article addresses optimization of nickel hydrazine electroless plating process parameters for the fabrication of mesoporous nickel-ceramic composite membranes. An inexpensive sintered ceramic support with an average pore size of 275 nm was used for all the experiments. Parametric optimization was experimentally investigated for a wide range of nickel solution concentrations (0.04–0.16 mol/L) and loading ratios (196–393 cm2/L). Process parameters such as conversion, plating efficiency and membrane morphological parameters such as average thickness, pore size and effective porosity were evaluated. Based on these evaluated parameters, the optimal process parameters have been evaluated as 0.12 mol/L and 393 cm2/L respectively. In general, it was also observed that hydrazine electroless plating baths are efficient from both processes as well as membrane perspective as they have been observed to provide a maximum selective conversion and PPD of 38% and 98.8% respectively.

Research Highlights

► Hydrazine electroless plating is efficient process. ► Plating efficiency increases with increasing membrane stirring speed. ► The optimal conditions of plating have been identified. ► The variation in loading ratio did not provide significant variation in conversion.

Introduction

Metal composite membranes such as nickel/silver/palladium composite membranes have numerous applications in process engineering. Among these, dense palladium composite membranes have been extensively studied for their performance characteristics due to several possible applications as an essential component in fuel cells, portable hydrogen generators and membrane reforming [1], [2], [3], [4], [5], [6], [7], [8]. A critical issue of the palladium membranes is their high cost that is primarily contributed by the noble metal. On the other hand, porous silver composite membranes have been suggested to be applicable for producing pathogen free water for special medical applications [9], XRD analyses media and analyses of dissolved organic carbons or coke oven emissions [10]. Nickel composite mesoporous and microporous membranes have also been indicated to be applicable for numerous applications including TiO2 recovery from waste water streams [11] and production of ultrapure gases for special applications [12] etc. Also, it was suggested that nickel membranes could serve as supports for palladium dense membranes [13], [14]. Due to these many applications, metal composite membranes made of palladium, silver and nickel are commercially manufactured. Among these classes of membranes, research in the field of nickel composite membranes is beneficial in many ways. Firstly, nickel being inexpensive could provide conceptual physical insights into the plating process when a noble metal is used with the similar conditions. Secondly, nickel composite membranes can be also applicable for gas separation [15] and membrane reactor applications [16] and much research is awaited in the years to come.

Among several methods for the preparation of metal composite membranes, electroless plating has numerous advantages such as uniformity in plating, susceptibility for scale up, simple experimental set up etc. To date, many experimental investigations aimed at providing the performance characteristics of the composite membranes at various temperatures. Nonetheless, experimental investigations that relate the effect of electroless process parameters (such as metal concentration and loading ratio) on membrane morphological parameters have not been addressed.

To deduce upon the proper choice of plating process parameters from much investigated research towards palladium membrane fabrication is cumbersome and confusing. As far as loading ratio is concerned, various researchers used various values of loading ratio values without indicating their efficacy. Collins and Way [17] used a high A/V ratio of 527 cm2/L whereas Yeung et al. [18] used a moderate A/V ratio of 350 cm2/L during the electroless deposition of Pd on tubular membrane supports. In agreement with these values, Bhandari and Ma [6] used an A/V ratio of 460 cm2/L while Ayuturk and Ma [7] used a lower A/V ratio of 250 cm2/L for electroless Pd and Ag deposition on tubular stainless steel porous supports. On the other hand, experimental studies involving disc type membranes did not adopt A/V ratios as high as those used for tubular membranes. Altinisik et al. [19] used a bath loading value of 30 cm2/L while Dogan and Kilicarslan [20] used a loading ratio of 80 cm2/L for Pd electroless plating on porous (2.6 μm) glass disks of 2.5 cm diameter. In a similar way, Huang et al. [21] used a bath loading ratio of 60 cm2/L in the electroless co-deposition of Pd–Ag alloy membrane on a γ-Al2O3 substrate. Some of the above researchers also used diverse metal solution concentrations. For instance, Huang et al. [21] used a metal solution concentration of 0.00307 mol/L (at a loading ratio of 60 cm2/L) whereas Collins and Way [17] used a metal solution concentration of 0.0307 mol/L (at a loading ratio of 527 cm2/L). From their work, a general rule of thumb that could be deduced is that when the metal solution is increased 10 folds, the loading ratio needs to be as well increased ten folds. However, such general rules of thumb need to be experimentally validated beyond doubt with technical insights.

Considering this primary limitation in the available literatures, we have recently addressed the effect of process parameters on porous membrane as well as process performance characteristics for nickel sodium hypophosphite electroless plating baths [22]. In conclusion, it was observed that hypophosphite plating baths are not promising due to providing higher average membrane pore sizes and lower selective conversions. Continuing our ongoing efforts to systematically quantify the performance characteristics of nickel electroless plating baths, in this work, we address these experimental studies for hydrazine based nickel electroless plating baths. This is also due to the fact that hydrazine could serve better as a reducing agent and would provide lower surface shear stress during deposition due to the release of heavier N2 molecules but not the lighter H2 molecules that are released when sodium hypophosphite is used as a reducing agent. The purpose of this experimental investigation is to visualize the general characteristics associated to both plating process and membrane morphology. Thereby, an optimal combination of process parameters is anticipated as a final outcome of the study along with the specification of the confidence levels of using hydrazine based metal plating baths for membrane fabrication. The major objective of this work is to identify suitable plating process parameters that indicate superior process as well as membrane morphological parameters.

Section snippets

Materials and methods

Attempting to identify optimal electroless plating conditions, this work adopts the following experimental procedure. Disk type ceramic membranes whose nominal pore size is about 275 nm were prepared in our laboratory and were used as substrates for the electroless plating experiments. Detailed information about the raw materials, fabrication methodology and characterization of the ceramic membrane supports is available in our recent article [22].

For all electroless plating experiments, 8

Results and discussion

In this section we presented the results in four sub-sections. The first sub-section summarizes the characteristics of the electroless plating process in terms of conversion and plating efficiency. The second sub-section presents the characteristics of nickel-ceramic composite membrane in terms of average membrane pore size and percent pore densification. The third sub-section presents associated cost tradeoffs with respect to PPD and average membrane thickness. Finally, a comparative

Conclusions

In this work, we attempted to quantify the performance characteristics of hydrazine based electroless plating baths for metal-ceramic composite membrane fabrication. Firstly, it was observed that the optimal conditions of plating have been identified as 0.12 mol/L initial concentration of nickel, 393 cm2/L of loading ratio, which provided 41.5% conversion, 91.6% plating efficiency and 98.8% PPD. Under these conditions, the ratio of desired to undesired reaction rates was observed to be 10.9. The

Nomenclature

    K

    Effective permeability factor (m/s)

    Q

    Volumetric flow rate (m3/s)

    P2

    Membrane pressure at permeate side (kPa)

    S

    Effective membrane area (m2)

    ΔP

    Trans-membrane pressure drop (kPa)

    A

    Slope in Eq. (1) (m/(s kPa))

    B

    Intercept in Eq. (1) (m/s)

    Pavg

    Average pressure (kPa)

    di

    Average pore diameter of the ceramic membrane support (m)

    do

    Average pore diameter of the nickel-ceramic composite membrane (m)

    δ

    Thickness of porous nickel film (m)

    ηg

    Viscosity of gas (kPa s)

    εq2film

    Effective porosity of the nickel-ceramic composite

Acknowledgments

This work is partially supported by a grant from Council of Scientific and Industrial Research (CSIR), New Delhi. Any opinions, findings and conclusions expressed in this paper are those of the authors and do not necessarily reflect the views of the CSIR.

References (24)

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