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

nickel ceramic composite membranes optimization of hydrazine based electroless plating process parameters vijaya kumar bulasara harjyoti thakuria ramgopal uppaluri mihir kumar purkait department of chemical engineering indian institute of technology guwahati guwahati 781039 india a b s t r a c ta r t i c l ei n f o article history received 21 october 2010 received in revised form 1 march 2011 accepted 2 march 2011 available online 26 march 2011 keywords nickel membrane solution concentration loading ratio conversion effi ciency hydrazine bath effective porosity pore densifi cation 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 effi ciency 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 effi cient 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 2011 elsevier b v all rights reserved 1 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 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 tio2recovery 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 fi eld of nickel composite membranes is benefi cial 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 uniformityinplating susceptibilityforscaleup simpleexperimentalset up etc to date many experimental investigations aimed at providing theperformancecharacteristicsofthecompositemembranesatvarious 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 valueswithoutindicatingtheireffi cacy collinsandway 17 usedahigh 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 tubularstainlesssteelporoussupports ontheotherhand experimental studies involving disc type membranes did not adopt a v ratios as high desalination 275 2011 243 251 corresponding author tel 91 361 2582262 fax 91 361 2582291 e mail addresses ramgopalu iitg ernet in r uppaluri mihir iitg ernet in m k purkait 0011 9164 see front matter 2011 elsevier b v all rights reserved doi 10 1016 j desal 2011 03 009 contents lists available at sciencedirect desalination journal homepage 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 m 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 al2o3substrate 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 solutionconcentrationof0 0307 mol l ataloadingratioof527 cm2 l from their work a general rule of thumb that could be deduced is that whenthemetalsolutionis increased 10folds theloadingrationeedsto 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 ongoingefforts tosystematically 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 n2molecules but not the lighter h2molecules 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 fi nal outcome of the study along with the specifi cation of the confi dence 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 2 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 mem brane supports is available in our recent article 22 for all electroless plating experiments 8 sequential depositional plating steps of one hour duration each were carried out using fresh solutions and chosen loading ratio values 196 393 cm2 l and nickel solution concentrations 0 04 0 16 mol l eventually the prepared membrane was subjected to both surface and fl ux characterization studies the solution concentration of nickel after plating was evaluated using titration method thereby the combinatorial impact of plating process parameters on both metal depositional effi ciency andporedensifi cationwasevaluated finally foroptimalconditionsof plating tradeoffs associated to cost pore densifi cation and metal plating effi ciency were evaluated to provide further details upon the effi cacyofhydrazinebasedplatingbaths thenextsectionsummarizes the experimental procedure adopted in this study 2 1 electroless plating after cleaning the substrate ultrasonically sensitization and activation were carried out to seed palladium metal on the support surface selectively by covering the other surfaces with tefl on tape before nickel plating conventional procedure involving sequential steps of sensitization activation and rinsing was deployed to carry out the pd seeding process the ceramic membrane was dipped in the sensitization bath containing tin chloride solution 1 0 g l for 5 min rinsed with de ionized water and then dipped in the activation bath containing palladium chloride solution 0 1 g l followed by acid bath 0 1 m hcl for 5 min each and fi nally rinsed with de ionized water the operation was repeated 4 5 times to get suffi cient seeding of pd over the ceramicsubstrate after seeding the membranewas dried for 6 h in an oven at 373 k to measure its dry weight w1 plating experiments were carried out using typical compositions summarized in table 1 the plating experiments were designed to evaluateplatingcharacteristicsforawiderangeofinitialnickelsolution concentration 0 04 0 16 mol l and loading ratio 196 393 cm2 l hydrazine hydrate was chosen as the reducing agent 100 excess hydrazine was used and the ph of the plating bath was maintained around 10 11 using naoh trisodium citrate was used as the complex ingagenttocontroltherateofreleaseoffreemetalionsforthereduction reaction and the plating temperature was maintained at 353 k using silicone oil bath eight sequential steps one hour each involving intermediate rinsing of membrane with de ionized water were carried out to yield the nickel ceramic composite membrane then the membrane was rinsed with de ionized water for 30 min and dried for 6 h at 373 k in a hot air oven the weight of the membrane after drying was measured w2 2 2 evaluation of plating characteristics the effect of metal ion ni 2 concentration and bath loading ratio on the process parameters such as conversion plating effi ciency and ineffi ciency plating thickness and pore densifi cation during electroless nickel plating using hydrazine baths was studied the expressions to evaluate these parameters had been presented in our previous work 22 analysisoftheplatingbath aftereightsequentialonehourplating steps was carried out by complexometric titration with ethylenedia minetetraacetic acid edta at 353 k using xylenol orange as indicator to estimate the average concentration of ni 2in the solution average porediameterandeffectiveporosityofthecompositemembraneswere determined from air permeation experiments the procedure to evaluate average pore diameter of the composite membranes is presented in the next section 2 3 gas permeation experiments the membrane performance and presence of defects in the interior portion of the support membrane was evaluated using both gas air and liquid water fl uxcharacterization a laboratorymadepermeation setup shown in fig 1 of 200 ml capacity was used for the permeation experiments the setup consisted of a tefl on tubular cell with a fl at circular tefl on base plate containing the membrane housing the membrane was placed in a tefl on casing and was sealed with epoxy resin and then placed in the membrane housing provided on the base plate the cell was pressurized with compressed air and the outlet was connectedtoagasfl owmeterformeasuringthegasfl owrateforvarious trans membrane pressures of air for water permeation experiments table 1 compositions and parameters for electroless nickel plating baths along with retail unit costs s no componentamount mol l unit cost g 1nickel sulfate niso4 7h2o 0 04 0 160 070 2hydrazine hydrate n2h4 h2o 0 08 0 320 046 3trisodium citrate na3c6h5o7 2h2o 0 05 0 200 012 4sodium hydroxide naoh ph 10 110 032 plating temperature k 353 loading ratio cm2 l 196 393 244v k bulasara et al desalination 275 2011 243 251 thepermeatefl owratewasmeasuredusingadigitalweighingmachine the hydraulic permeability and the corresponding pore diameter of the membranes were also determined all permeation experiments were conducted at room temperature 298 k for the metal ceramic composite membrane the air permeation data can be represented as a function of volumetric fl ow rate and pressure using the following expressions eqs 1 5 23 k qp2 s p b apavg 1 a 0 4 d2 o g q2 film 2 b 1 066 dov q2 film 3 the average pore diameter of the nickel ceramic composite membrane do is evaluated using the expression do 2 666a b v g 4 the effective porosity of the metal ceramic composite membrane is evaluated using the expression q2 film b 1 066dov 5 in the above expression corresponds to the thickness of the porousnickel fi lm whichitself is a function of effective fi lm porosityas shown below 22 w2 w1 niam 1 1 q2 film 6 substituting the above expression in eq 5 we get q2 film b w2 w1 1 066dov niam 1 1 q2 film 7 this is in the form q2 film k 1 q2 film 8 where k b w2 w1 1 066dov niam 9 hence the fi lm effective porosity can be estimated as q2 film 1 ffiffi ffiffi ffiffi ffiffi ffiffi ffiffi ffi 1 4k p 2 10 this expression eq 10 is valid only when k 0 25 percent pore densifi cation ppd is evaluated using the following expression 22 ppd d2 i d 2 o d2 i 100 11 3 results and discussion in this section we presented the results in four sub sections the fi rst sub section summarizes the characteristics of the electroless plating process in terms of conversion and plating effi ciency the second sub section presents the characteristics of nickel ceramic composite membrane in terms of average membrane pore size and percent pore densifi cation the third sub section presents associated cost tradeoffs with respect to ppd and average membrane thickness finally a comparative assessment of the results obtained in this work with those obtained previously 22 is presented in the fourth sub section 3 1 effi cacy of electroless plating figs 2 and 3 summarize the variation of conversion x and plating effi ciency with nickel solution concentration ci and loading ratio respectively as shown nickel conversion varied from 14 5 to 46 8 16 to 49 8 and 17 5 to 54 for a variation in nickel sulfate solution concentration of 0 04 0 16 mol l and values of 196 262 and 393 cm2 l respectively corresponding plating effi ciencies varied from 97 2 to 82 0 98 3 to 82 3 and 99 9 to 82 6 for a variation in nickel sulfate solution concentration of 0 04 0 16 mol l and values of 196 262 and 393 cm2 l respectively the plating effi ciency trends 1 2 3 4 1 compressor 2 permeation cell 3 membrane 4 flow meter fig 1 setup for permeation experiments initial niso4 solution concentration mol l 0 040 080 120 16 conversion x 10 20 30 40 50 60 196 cm2 l 262 cm2 l 393 cm2 l fig 2 variation of conversion with niso4solution concentration and 245v k bulasara et al desalination 275 2011 243 251 indicate that the loading ratio did not infl uence the effi ciency signifi cantly for a chosen nickel plating solution concentration in summary the plating characteristics are indicative of a low to moderate conversion 14 5 54 and good effi ciency profi les 99 9 82 0 with variation in solution concentration and loading ratio parameters the selectiveconversionvalues defi nedas theproductof fractional conversion and effi ciency presented in table 2 increased with concentration as well as loading ratio the plating reaction was assumed to follow a pseudo parallel reaction scheme expressed as ni 2 nimem 12 ni 2 nisol 13 wherenimemandnisolcorrespondtothemetaldepositiononmembrane surface referring to effi cient plating and in solution including the surroundings referring to ineffi cient plating respectively the pseudo kinetic constants at an average nickel solution concentration c were expressed as re kec ne 14 ri kic ni 15 where ke ki neand nicorrespond to the pseudo kinetic constants evaluatedfortheaverageeffi cient re andineffi cient ri platingreaction ratesrespectively thekineticconstantsforthepseudo reactionschemes were evaluated using non linear regression technique fig 4 presents the variation of average effi cient nickel plating rate mol l s with the electroless plating process parameters it can be observed that the average effi cient nickel plating rate varied from 1 57 to 17 05 1 75 to 18 20 and 1 94 to 19 82 10 6mol l s with a variation in initial nickel solution concentration of 0 04 0 16 mol l and loading ratio valuesof196 262and393 cm2 lrespectively thevariationintheaverage nickel ineffi cient plating rate mol l s with electroless plating not shown wasevaluatedtovaryfrom0 04to3 73 0 03to3 92and0 002 to 4 18 10 6mol l swithavariationininitialnickelsolutionconcentration of 0 04 0 16 mol l and loading ratio of 196 262 and 393 cm2 l respectively psuedo kinetic constants evaluated using expressions eqs 14 and 15 along with r2values are summarized in table 3a the effi cient plating kinetic constant ke was observed to vary between 1 16 and 1 38 10 3 1 mol l 1 01 0 98s with the pseudo reaction order ne varying from 2 01 to 1 98 for a variation in loading ratio from 196 to 393 cm2 l on the other hand the ineffi cient plating kinetic constant ki wasevaluatedtovarybetween0 06and50 10 1 1 mol l 2 65 5 47s with the pseudo reaction order ni varying from 3 65 to 6 47 for a variation in loading ratio from 196 to 393 cm2 l table 3b presents the variation of the ratio of the av