Preparation of spherical submicronic nickel powders from rosin salts

Preparation of sphericalsubmicronicnickel powders from rosin salts ERICPONTHIEU1*, TETSUNORY KAWAKAMI2 and TETSUYA TSUTSUMI2 1Villecueve France d'Ascq, 2Harima Chemicals Tsukuba Research 5-9-3 Ibaraki Inc., Tokodai, 300-26, Laboratory, Tsukuba-City, Japan 15October 1993 Received forAPT 18June 1993; accepted fine(submicronic) nickel were inan Abstract-Extremely regular (spherical) powders synthesized andhypercritical from autoclave critical rosin nickel salts as conditions, upon 'hypocritical', starting The nature ofthesolvent used tosuspend therosin salt tobeofprimary precursors. appears importance; 2-Butanol better results than acetone. The are not believed to be essential since gave (T,P) parameters microstructures were obtained below thecritical of2-butanol. the adequate parameters Consequently, associated with fluids arenotthought toplay animportant role herein. In special properties supercritical thethermal oftherosin under conditions some comparison, degradation precursor atmospheric displays such asahigher aless microstructure anda drawbacks, significant processing temperature, satisfactory ofthepowder. heterogeneous macroscopic aspect 1.INTRODUCTION

_ fluids(SCFs) canbe advantageously usedasreaction media[1]. Supercritical onthespecific anSCFsolvent conditions, Depending mayeither actively participate and inthereaction orsolely actasthesolvent medium forthereactants, catalysts SCFs haveunique solvent andviscosity variations products. properties (large density versus smallchanges inpressure and/ortemperature) thatmaybeexploited to enhance reaction rates[1].Another concerns theiruseas important application media fluidchromatography) extraction/separation (i.e.supercritical [2]. SCFs areoftenconsidered asan'intermediate' stateofmatter between a liquid anda gas[3].SCFs obtained inclosed vessels (i.e.anautoclave) by maybereadily thetemperature andthepressure above thecritical point(1;"critical increasing theterminal pointoftheliquid-vapor temperature, pressure), being P , critical curve. Theresulting substance isagas-like fluidwhich has equilibrium compressible ofdiffusion densities andsolvating liquid-like power[2].Values (0.1-1 gcm-3) coefficients areintermediate between thoseofliquid andgasphases are [3].SCFs thusgoodsolvents fastmasstransfers. allowing Itisnowlargely thatthese fluids interest inthe recognized maybeofconsiderable fieldofmaterials Thesupercritical synthesis [3-5]. (orhypercritical) technique may beusedeither todrysolids ina liquid ortotakebenefit immerged phase (i.e.gels) fromthespecial ofSCFs todecompose witha better In properties precursors yield. inthe theSCFcontained theformer case,aerogels maybeformed onlybyventing

178 ofgels[6,7].Aerogels exhibit suchasunusually porosity unique properties, high surface andquitelowdensities Inthe areas,extremely highporevolumes [8-10]. of various materials latter,SCFsmaybeusedin transformation processes [3]. Pommieral.et[3]havesynthesized submicronic oxide from homogeneous powders suchasalkoxides. Intheirprocess, theformation ofthe metallorganic precursors results from thedecomposition oftheprecursor andnotfromitshydrolysis, product asforaerogels [6]. Toourknowledge, tothepreparation of veryfewpapers [11]havebeendevoted metallic inSCFs. Armor etal.[11] finecopper powders havesynthesized powders fromcupricacetate intoa methanol/water mixture. suspended Highly porous wereproduced ofthesolvent. The copper powders uponthesupercritical venting same wasusedherein inorder tosynthesize finenickel fromnickel principle particles rosinsalts.Theefficiency ofthisprocess wascompared witha moretraditional in anorganic solvent. route,i.e.thethermal preparation decomposition boiling tothepeculiar nature oftheprecursor section hasbeen According salt,thefollowing devoted tothechemistry ofrosinmetal salts. 1.1.Background aboutrosinmetal salts Rosin isobtained froma natural andrenewable resource: thepinetree[12]. Three rosinderivates tothenature oftheextraction maybeproduced according process: ofthecrude talloilproduced the (i)atalloilrosinisobtained bydistillation during theproduct collected byprocessing pulp-making process, (ii)agumrosinisobtained fromincisions intreetrunks made and(iii)a wood rosinisderived fromthesolvent extraction ofpinestump chips. Rosin isthenon-volatile resinous ofpine.Thethreeabovepartoftheoleoresin mentioned ofrosinconsist ofC20 resin acids. Rosin types monocarboxylic diterpene alsocontains small amounts ormore) orneutral andotheracidic (5-15%a components(e.g.fattyacids intalloilrosin). Inrosin,themostcommon resinacidsare oftheabietic andprimaric generally type. Muchoftheutilization ofrosintakesadvantage ofthecarboxyl andolefinic functionalities ofthecomponent resinacids. Ona commercial three pointofview, reactions areveryimportant: additions and(iii) (i)saltformation, (ii)Diels-Alder esterification. Eachofthesereactions consumes 200-300 million ofrosin pounds peryear. Resin acidsareknown to formsaltswithNa,Ca,Zn,Mg,Al,etc.Thefirst resinate tobeusedinanindustrial wasthesodium saltof application (paper sizing) theresin acids andofcertain derivatives. Resinates canbeprepared byprecipitation orfusion methods method involves theaddition (seeEqs1and2).Theprecipitation ofa solution oftheheavy metal salttoa soluble sodium resinate toproduce awater insoluble metal resinate. Theothermethod thefusion ofrosinwith heavy requires themetal oxide orthesaltofa volatile acid. hydroxide, organic

179 2.EXPERIMENTAL PROCEDURE 2.1.Materials solvents ethanol, BEE;tetraethylene TEG; Organic (2-(2-n-butoxyethoxy) glycol, werepurchased fromKanto Chemical 2-butanol, BUT; acetone, ACE;) Co.,Inc. These solvents werecertified puregrade. 2.2.Rosin nickel saltpreparation Thesynthesis ofnickel rosinsaltwasperformed fromgumrosin.Thissynthetic routetakesplace intwosteps: ofthesodium resinate and(ii)metal (i)formation Details ofthisprocedure arereported inFig.1.Inthisscheme, toluene exchange. issupposed toextract residues ofwater andtheinsoluble can exchange part,which bepartially rosinsodium salt. 2.3.Nickel powder preparation 2.3.1.Atmospheric route.Theprocedure totransform therosinNi(II) saltinto inFig.2.Different nickel isdescribed were the experiments operated bymodifying mostimportant ofthissynthetic thenature ofthesolvent parameters procedure: orBEE), therosinnickel solvent ratio(xly),the (TEG salt/organic weight percent time(z)oftheheating thetemperature increase rate(fastorslow) andthe treatment, useofultrasonic vibrations. which wasinvestigated extends from 2.3.2.Pressurized route. Thepressure range 15atmtopressures tothecritical oftheusedsolvents: BUTand superior pressure ACE.These solvents wereusedbecause oftheirrelatively goodsolvent properties andtheirmoderate critical 41.94 atm; ACE, parameters (BUT, 7§262.95°C, : controlled autoclave, bya thermal programmer 7§235.2°C, : P :47atm).A300 ml Asolution Chino Model ofrosinnickel salt DG,wasusedforthedegradation. ina 20mlglass wasfirstprepared (characterized bya xlyvalue equalto0.5/10) tube.Thistubewasputinthebottom Anadditional oftheautoclave. volume of 150 ml ofthesolvent totheautoclave. wasalsoadded Before a nitrogen wasmaintained for5minin the flow(50ml/min) heating, autoclave inordertogetridofthemajorpartoftheoxygen and/oratmospheric moisture. Thetemperature to T. andstabilized at thisvaluefor wasincreased

1.Flowchart ofthesynthesis oftherosin Ni(ii)salt. Figure

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2.Flowchart ofthesynthesis ofnickel Figure powder. ina vaporformbyslightly 120 min. Thesolvent wasevacuated theoutlet opening solvent inawater-cooled valve oftheautoclave andbytrapping theorganic condentheautoclave, thepowder waswashed withtoluene andthenwith sor.After cooling acetone toensure better purity. 2.4.Physico-chemical characterization Thechemical of synthesized nickelpowders wasdetermined composition by theService Central of theCNRS National dela Recherche d'Analyse (Centre Thelevels andsodium ofnickel wereobtained by Scientifique, Solaize, France). atomic emission Thedetermination of inductively couple plasma spectrometry. carbon andhydrogen wascarried outbyIRanalysis ofthegases released oxygen, by inagraphite combustion athightemperature ofthesample embedded crucible. The ofsolids wasexamined electron ona morphology byscanning microscopy (SEM) ABTDualStage model DS-130S. TheBrunauer-Emmet-Teller (BET) microscope, surface areaofsolids wasmeasured theadsorption ofnitrogen at77.5K through Jr fromAnkersmit). (Quantasorb 3.RESULTS AND DISCUSSION 3.1.Atmospheric route Themainresults theatmospheric routearedetailed in concerning preparation Table1.These results theimportance ofthenatureofthesolvent in emphasize thedegradation Thisisprobably themostcritical because it process. parameter thesolubilization conditions ofthenickel rosinsaltandthemaximal of temperature thedegradation treatment. onecansaythat"goodsolvents" Generally speaking, havea lowboiling tofindanadequate pointandviceversa.It isthusdifficult BEEhasgoodsolvent solvent forthisprocess. butitsboiling power point(231 °C) is ratherlow.Thistemperature isnotsufficient to complete thedegradation of therosinnickel withthissolvent salt,as indicated bythelowyieldobtained

181 1. Table nickel salt: main reaction andSEM ofrosin Atmospheric degradation experimental parameters, yield characteristics

was used inthese * Ultrasound experiments. theincrease ofthedegradation time(10to240min)andtheuse (experiment 5).Even toobtain a reasonable total ofultrasonic vibrations 6)didnotpermit (experiment yieldinthiscase. Thisisduetoitshigher TEGalways transformation yields. boiling gavehigher which isprobably moreconsistant withthedegradation temperature point(314°C) transformation wereobtained oftherosinnickel salt.Highest yields usinglong times(240 min). Theutilization of ultrasonic vibrations (without degradation tobedeleterious forthereaction mechanical wasshown yield. stirring) Themorphology ofsolids inatmospheric conditions israther variable. prepared time itisseenthattheincrease ofthedegradation Forthesynthetic routeusing BEE, vibrations (experiment 6)significantly (10to 240min)andtheuseof ultrasonic themicrostructure of theresulting improved powder (Fig.3 and4). Powder obtained inthiswayexhibits micron-sized spheroid particles. bettermicrostructures. The Nickel fromTEGexhibit powders synthesized to beessential The dilution andthedegradation timeappear parameters. degree shortdegradation times ofparticles morphology getsbetterbyusing (i.e.10min) saltintothesolvent andbyusing a highdilution oftherosinnickel (xly= 20/380 microstructures as instead of20/20) maybeconsidered (Fig.5 and6).However, ofagglomerates oflarge because oftheoccasional particules heterogeneous presence tothequality ofthepreparavibrations isdetrimental (Fig.6).Theuseofultrasonic intheformoflarge tion(Fig.7).Individual arefoundtobeagregated particles toacoustic cavitation. Thiseffect could berelated Doktycz (l0,um) agglomerates. induced flowandshockwaves andSuslick thatturbulent by [13]haveshown ina slurrytogether at a veryhigh cavitation coulddrivesolidparticles present Such Extensive fusionmayresultfromthesecollisions. velocity. interparticle ismoderately high phenomena mayoccurheresincethemelting pointofnickel (1453°C). Another synthesized important pointto benotedis thefactthatthepowders totheirmacroconditions areofheterogeneous under relatively atmospheric quality when thetotalyieldofthereaction ishigh(experiments scopic aspect, especially threetypesof forexperiment 3,which presents 2-4).Thisisparticularly striking foils(which adhere (ii)metallic macroscopic morphology: (i)hardagglomerates, In thissample, thelarge and(iii)fineparticles onthevessel (powder). walls)

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3.SEM inexperiment 5. ofthepowder Figure micrograph synthesized

4.SEM ofthepowder inexperiment 6. Figure micrograph synthesized increase andtothelong ofnickel foilcould beduetotheslow temperature presence duration ofthedegradation Theformation ofwell-ordered treatment. nickel foilsis timeis given formicrostructural indeed to befavored whensufficient supposed to occur. Onthecontrary, 5 rearrangements low-yield experiments (experiments and6)generally contain onlyfineparticles.

183

inexperiment 5.SEM ofthepowder 1. micrograph synthesized Figure

6.SEM ofthepowder inexperiment 3. Figure micrograph synthesized 3.2.Pressurized route Results inTable 2firstindicate thatnickel with maybeproduced presented powders a reasonable lowerthan300°C if thedegradation yieldat temperatures stepis Thetransformation carried outunderautogeneous pressure. yieldis foundto increase withthetreatment aslow slightly temperature. Degradation temperatures as250°C tobesufficient forproducing fineregular nickel (experiment 11)proved

184

7.SEM ofthepowder inexperiment 4. Figure micrograph synthesized Themorphology ofpowders tobemoreandmoreregular asa powders. appears function ofthedegradation assembled intheform temperature. Irregular particles, oflarge aremainly formed attemperatures lower than250°C agglomerates, (Fig.8) whereas areproduced veryfine(submicron) spherical slightly agglomerated particles attemperatures to250°C therearenosignificant difsuperior (Fig.9).Apparently, ferences between at250°C at powders produced (below andpowders produced 265°C inferthattheformation ofthesupercritical BUT isnot (above Onecould thekey-point toexplain thegoodmicrostructure obtained. Thereduction ofthetime ofthedegradation treatment togiverisetoregular and (experiment 13)alsoproves fineparticles, thereaction almost thereuse ofBUT yield being unchanged. Finally, froma previous isshown tobequiteacceptable (recovered batch) (experiment 13). Thepowders atatemperature below to250°C arehighly contaminated produced Table 2. Pressurized ofrosin nickel salt: main reaction andSEM degradation experimental parameters, yield characteristics

* The solvent hasnotbeen vented forthis sample. was carried outwith reused BUT. tThis experiment

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. 8.SEM ofthepowder inexperiment 7. micrograph synthesized Figure

9.SEM inexperiment 11. ofthepowder Figure micrograph synthesized residues 9: Ni= 38.6%, C= 35.2%, bycarbonandoxygen (e.g.experiment O= 14.4%, Na= 1.2%, Cl= 0.2%,H = 10.4%). Small levels ofcarbon remain inpowders attemperatures above 250°C 11:Ni= 92.8%, prepared (e.g.experiment = 0.02%, =H3.5%). C = 2.0%, 0 =1.7%, Na These carbon andoxygen residues beeliminated andHz,respectively. athermal under maynormally [14] through NH3 Such atreatment would thelevels Indeed, giverisetoextremely purenickel powders. inthesepreparations. ofNaandClarefound tobemarginal

186 of rosinNi(II)intoNimetalremains Themechanism forthetransformation inbothatmospheric thatthereduction atthisstage butitislikely unknown process the Thispointmayexplain isnottotally andpressurized environments complete. ofoxygen inthefinalproduct. residual impurities presence areas(experiment herein exhibit Nickel synthesized quitelargespecific powders = 9.5m2g-1)withrespect = 11.0 m2 tothemean 12,SBET 11,SBET g-1;experiment 11(Fig.9)andexperithatparticles ofexperiment Ifoneconsiders sizeofparticles. areamaybe theirtheoretical sizeofaround ment12havea mean 0.2jum, specific fromthefollowing formula: calculated andr themean radius ofNi(8.9gcm-3) thespecific withAbeing area,pthedensity observation determined electron (10-5 cm).The microscope (SEM) byscanning between the areavalue isequalto 3.37m2g-1.Thedifference calculated specific nature ofnickel totheporous calculated andexperimental values maybeattributed thatformed aresomeitcanbeseenfromSEM Indeed, particles pictures powders. treatment asaresult sinter whatrugose. Theparticles (at600°C, easily uponthermal thermal Armor ofthethermogravimetric analysis treatment). analysis/differential under thatporous metalparticles wereobtained noticed et al.[11]havealready some in conditions andthatthese displayed sintering, resulting powders supercritical soft,porous agregates. insupercritical withacetone conditions Ontheotherhand,experiments operated therosinnickel saltintonickel. Ata temperature totransform havenotallowed oftherosin 10and14),thetransformation closeto 240°C degree (experiments withBUT thanwithACE. used nickel saltwassignificantly Yet,thepressure higher 10(BUT). thaninexperiment inexperiment 14(acetone) wassignificantly higher Critical ofACEareveryclose tothoseofBUT(ACE: = 235.5°C, parameters = 41.4atm).Thispointclearly shows thatthe Pc= 47atm;BUT: = 263'C, Pc transformation oftherosinnickel saltis mainly governed bythenatureofthe of(T,P)parameters. rather thanbythevalues solvent 4.CONCLUSIONS saltoccurs atatemperature close to300°C when Thedegradation oftherosinnickel Thistemperature iscarried conditions. thedegradation outunder range atmospheric asthatforironorcobalt rosinsaltsbutislarger thanthat ismoreorlessthesame rosinsalt( -100°C) rosinsalt(-200°C) orsilver ofcopper [12]. Theexperiments, realized inanautoclave, showed thatthetemperature andthe ofthe tobeconsidered forthedegradation arenotthesingle parameters pressure roleplayed rosinnickel salt.Results obtained withBUTemphasize thepossible by isanexcellent solvent inthedegradation Itwasfound thatBUT thesolvent process. critical or toinduce thenucleation/growth ofnickel upon'hypocritical', particles conditions. hypercritical inthisspecific Theadvantages Thepressurized routeproofs itsefficiency process. onearenumerous: ofthisroutecompared withtheatmospheric and inthepressurized routearemuch finer(submicron) w Theparticles obtained inthebestatmospheric trials. moreregular thantheparticles obtained

187 w Thepressurized in since anddrying occur routeisaone-step degradation process thesamevessel. ismorehomogeneous thaninthecaseofthe ofthefinalproduct Thequality without areobtained, route:onlyfinepowders anymacroscopic atmospheric ornickel foil. hardagglomerates w Eventual or under treatments treatment hydrogen (e.g.thermal post-degradation inthesame vessel. ammonia) maybeaccomplished WIt is notnecessary intheautoclave because to usemechanical high stirring ofchemical induces could, Stirring quiteintimate mixing compounds. pressure of insomespecial cases beuseful homogeneization however, requiring perfect ofa carrier forcatalytic constituents different particles (e.g.coating bymetallic uses). can WThesolvent fromtheautoclave athighpressure andtemperature extracted bereused infurther experiments. WMetallic bedispersed intheautoclave onencascaneventually directly powders suchasopen-form vermiculite, (cordierite honeycombs, supports ingdevices wiremeshscreens, stones, etc). boiling Acknowledgements and Communities oftheEuropean E.P.would liketothank theCommission (CEC) for andTechnology Center Science theJapanInternational (JISTEC) Exchange ofa REES inJapanintheframe funded histraining (Research Experience having E.P.would alsoliketothankMrT.Kawakami, forEuropean Students) program. andfortheirhelp. fortheirhospitality MrT.Tsutsumi andDrH.Kondo REFERENCES Ind. Chem. insupercritical fluids-a review. and M.A.McHugh, Reactions 1.B.Subramaniam Eng. 1986. Process Des. Dev. 25,1-12, 1991. LC-GC Int.4,10-17, introduction. 2.R.E.Majors, fluid extraction-an Supercritical fluids asreaction medium for The useofsupercritical 3.C.Pommier, K.Chhor andJ.F.Bocquet, 1992. onElectroceramics, In:Proc. 3rdInt.Conf. ceramic France, Maubeuge, powder synthesis. 1991. 4.J.W.Tom andP.G.Debenedetti, J.Aerosol Sci. 22,555, etgravité, F.Cansell andC.Pommier, Fluides B.LeNeindre, P.Subra, 5.Y.Garrabos, critiques Fr.17, 55-90, 1992. Ann. Chim. fluides atmatériaux. supercritiques and and characterization of E. Elaloui and G. M. 6.E.Ponthieu, J.Grimblot, Synthesis pure Pajonk, 1993. Sci. alumina J.Mater. 3,287-293, yttrium-containing aerogels. and theproperbetween thesolution 7.E.Ponthieu, E.Payen and J.Grimblot, Correlation chemistry Int.Symp. onAdvances inSol-gel In:Proc. tiesofalumina Processing Applications, aerogels. IL,1993. Chicago, materials. Chem. Rev. and related 8.H.D.Gesser andP.C.Goswami, 89, 765-788, porous Aerogels 1989. 1991. 9.G.M.Pajonk, Catal. 72, 217-266, catalysts. Appl. Aerogel J.NON Solids solids with 10.J.Fricke, tenuous Cryst. 100, fascinating properties. Aerogels-highly 1988. 169-173, ofvery fine Metallic anovel 11.J.N.Armor, E.J.Carlson andG.Carrasquillo, synthesis aerogels: 1986. Lett. Mater. 4,373, copper powder. 12.J.Soltes andD.F.Zinkel, ofrosin. In:Naval UtilizaStores-Production, Chemistry, Chemistry 19??. Chemicals New York: D.F.Zinkel andJ.Russell Association, pp.261-234, Pulp tion, (Eds). Science driven collisions 13.S.J. Doktycz andK.S.Suslick, 247, byultrasound. Interparticle 1990. 1067-1069, residues from ceramic The of carbon or carbon J . removal 14.F.K.van andPluijmakers, powders Dijen 1989. with ammonia. J.Eur. Ceram. Soc. orgreenware 5,385-390,