Synthesis of the Silver Nanofluid by ASNSS Process

第4卷增刊过程工程学报Vol.4 Suppl.2004年8月The Chinese Journal of Process EngineeringAug. 2004Synthesis of the Silver Nanofluid by ASNSS ProcessTa-Yu Chuang'，Tsung-Yeh Yang'，Hong-Ming Lin'，Wen-Chang Chen2(I. Depeartment of Materials Engineering, Tatung Universiy, Taipei 104, China; 2. Deaprtment of ChemicalEngineering, Yunin University of Technology, Yunin County, China)Abstract: Arc Spray Nanoparticle Synthesis System (ASNSS) has been used to prepare the silvernanofluids in this study. The metal electrodes under the electrical discharge will melt and evaporaterapidly and condense to form the nanoparticles in the dielectric fluid at lower temperature and producethe suspended nanoparticle fluid. Thus, the mechanism of the ASNSS process is superheating theelectrodes by plasma to form metallic nuclei and supercooling these nuclei by dielectric liquid toproduce nanofluid. This study considers the different controlling parameters such as discharge curent,discharge voltage, pulse-duration time, electrode diameter, and the temperature of dielectric liquid. Theoptimally operated parameters can be obtained to produce the finer particle size in nanofluid. Theresults indicate the silver electrodes in alcohol fluid will produce the spherical nanosilver particles. Themean particle size of siver in different dielectric liquid temperatures of -40, -20, 0, and 10°C is about13.4, 15.8, 17.5, and 21.6 nm, respectively. This indicates that the well suspended fuid can be obtainedby controlling the lower dielectric fluid temperature.Key words: ASNSS; nanoparticles; dielectric liquid temperatures; nanofluid; Ag1 NTRODUCTIONIn this study Ag raw material was used as the electrode to discharge in a chamber contains theelectrical discharge equipment and dielectric liquid. The electrodes material under the electricaldischarge will be melted and evaporated owing to introducing the current and voltage in between thetwo electrodes.Under this situation, the energy density is up to 3 J/mm't. The density of current reaches as high as10*~109 A/cm2[1. The temperature of plasma surrounding the spark is between 7000 K and 14000 K.This extreme temperature changes the metallurgy of the materials2, generates the phenomena ofmelting, evaporation and thermal spilling'), and produces the ultra fine particles. Preparing thenanoparticles that is dispersed in dielectric liquid by means of the ASNSS must go through three stages:nucleation, particle growth, and condensationl4.]. In order to prevent the growth of particles and obtainthe dispersion-well nanoparticles, the prepared particles need to be condensed immediately in thedielectric liquid with low temperature during the process5.o. Thus, the temperature of dielectric liquidis important in this process. In brief, the mechanism of the process is superheating of raw metal byplasma and super cooling of nanoparticles by dielectric liquid. There are many factors which influencethe formation of nanoparticles. These factors include the中国煤化工ation time, voltageand dielectric liquid temperatures... etc. Current densityfY HC N M H Gpeak value (Ip) andpulse duration time (tcN). According to the literature ilustration!", the current density is in propotion450过程工程学报第4卷to the value ofIp' Itow'(Jac (Ip Itow'); a<β ) and the importance of ton is more than Ip. The evaporationmass of the material increases when current density (I) is higher. For break down voltage, there is asimulation model!3l about the relationship between energy density and voltage. It indicates that thevoltage is inversely proportional to current. In general, high voltage will decrease the current strikingenergy on the surface of materials and results the effects on melt and evaporation of the material surface.To sum up, current density, pulse-duration time, voltage and current are closely linking to each other,and they are very important in the nanoparticle preparation. This study examines the major parametersthat may control the formation of nanoparticles Ag.2 EXPERIMENTAL PROCEDUREThe ASNSS system includes the vacuum system, electrical discharge system which isconventional electrical discharge machining equipment (EDM), cooling system, control system, fitersystem and dielectric liquid. The schematic diagram of ASNSS is shown in Fig.1. It can be described asfollows: (1) assembling the Ag rods in the electrical discharge system as the electrodes; (2) haven'tpumping the vacuum chamber and purging it by inert gasand controlling the final pressure at 1 atm; (3) starting thecontrol system of the process and feeding dielectric liquid(de-ionized water). The temperature is set at - -40, - -20, 0 and10°C; (4) heating the electrode by the submerged arc, andform nanoparticles through fusion, vaporized, nucleation andgrowth processes; (5) collecting the prepared nanoparticlesFig.l The schematic diagram of EDMand utilizing the instruments such as the particle sizeanalyzer, TEM, X-ray diffractometer, and SEM to examinethe particle size dstribution, structures and surface morphology of the nanoparticles; (6) finally,analyzing data to determine the optimal conditions of this experiment.3 RESULTS AND DISCUSSIONFigure 2 shows the relationship between the particle size, which is measured by particle sizeanalyzer LB500, and the electrical discharge energy (applied current). The experiment uses fiveparameters (current, pulse-duration time, voltage, and diameter) and dielectric liquid temperatures ineach trial run. Based on the analysis of variance, it shows all of the factors are important but majorfactor is temperature of dielectric in the experiment. In the other words, the effect of the five factors onelectrical discharge condition cannot be ignored. The result of Fig.2 shows that that particle sizeanalyzer measures the particle size which is obtained with experiment method. According to the resultin the figure, the particle size distribution is appeared Gaussian distribution. the particle size is largerwhile the dielectric liquid temperatures is high or low, t中国煤化工sedimentationcondition of the samples which prepared at different temperaHC N M H G the increasingorder of particle size: -40°C < -20°C<0°C<10C. Figure 3([(a), (b), (c), (d)] show the SEM photographs增刊Ta-Yu Chuang et al: Synthesis the Silver Nanofluid by ASNSS Process451of the particle under different dielectric liquid temperatures condition. After analyzing the samples, wefind the shape of the nanoparticles to have almost sphere structure. The reason of producing thenanoneedle is related to the property of Ag. So far we know that the thermal conductivity of silver ishigher than other materials. While preparing the nanoparticles based upon the electrical dischargeprocess, the condensation of the melted Ag is too rapid to form the sphere by means of surface tension.Therefore, the morphology of the prepared particles has almost sphere structure with unrough and evensurface. Figure 4.1[(a), (b), (C), (d)] shows the TEM photographs of the particle under differentdielectric liquid temperatures condition. 1 The X-ray diffraction pattern of prepared nanoparticles inFig.5 can also prove the result. If de ionized water is the dielectric fluid, in this experimentation thedecomposition reaction will be not carried out. As the result, pure silver is generated in the process.After calculating the particle size that is observed by TEM, the result is shown in Fig. 4.2: Particle sizeditribution of Ag in different dielectric fluid temperatures of (a) -40°C; (b)- -20°C; (C) 0°C; and (d)10°C with mean particle size about 13.4 nm, 15.8 nm, 17.5 nm, and 21.6 nm, respectively. The resultthe suspension is not well if the temperature ofdielectric liquid is too high. To gain the smaller particlesize we expect must introduce lower temperature ofdielectric liquid in the process. The result shows thatthe largest aspect ratio is approximately at appliedcurrent of 4 A, and the electrical discharge condition istmprunolaencdne boudhe . 20口at9A- 30 μs- 40 V-3 mm. The possible reason for abmpratureraectsquldbe 0它larger particle size is that under the low dielectric liquidtemperatures and an applied current of 9 A, the finerFig.2 Particle size distribution analyses byparticle size analyzerparticles can be obtained, and the thermal conductivityof the prepared particle is large. Furthermore, the condensation of particle is very fast. Thus, there isenough time to approach sphericity by surface tension. Thus, there is a high probability to get a smallparticle size at applied current of9 A.The structure of the Ag nanopowders can be examined by X-ray diffractometer and shown in Fig.5.Compared with X-ray pattemn of JCPDS card for Ag in Fig.6, it indicates the prepared Agnanoparticles are pure silver structure. It is shown that three peaks (38.98°, 44.5979, and 64.6749)on the X-ray patterm are similar to the JCPDS card of silver structure.细) -40°C(b)-20°C(d) 10°CFig.3 SEM images of the nanoparticles prepare ir中国煤化工。eraturesYHCNMHG452过程工程学报第4卷(间)-40°C(b)-20°C(c) 0°C(d) 10°CFig.4.1 TEM images of the nanoparticles prepare in different dielectric fluid temperatures(a) -40C(b) -20°CFig:.4.2 Particle size distribution of Ag in different dielectric fuid temperaturesEDS is the powerful technology to determine the quantity of the material. EDS graph in Fig. 7shows there are no oxidation on the surface of Ag particles. It means that the structure of the spherenanoparticle is similar to the structure of Ag without oxidation.30.144.28Fig.5 X-ray diffraction patterm of nanoparticles Fig.6 X-ray diffraction patterm of JCPDS card ofAg中国煤化工。Fig.7 EDS graph of prepared AgFig8Prr one weekMYHCNMHGFigure 8 shows the color change of nanofluids may cause by the aggregated Ag nanoparticles. The增刊Ta-Yu Chuang et al: Synthesis the Silver Nanofluid by ASNSS Process453different secondary particle size in fuid will affect the optical properties of solution. This experimentindicates that the well suspended fuid can be obtained by controlling the lower dielectric fuidtemperature. The color of Ag nanofiuids is gray, and changed ftom dark brown color slowly afterpreparation.To sum up the result, the suspension is not desirable if temperature of dielectic liquid is too lowor too high. To gain the finer and smaller particle size, we must introduce lower temperature ofdielectric liquid in the process.The phenomenon shows that the initial state of the nanofluid is stable. Ag particles do not reactionwith other elements or decompose with alcohol in the EDM process. The FTIR is applied to examinethe Ag nanofluids and is shown in Fig.9. Comparing the commercial nanopowders in alcohol with asprepared Ag nanofluids by EDM system, there is no obviously difference to be observed fromUV/Visible spectra as shown in Fig.10. These results indicate there is no decomposition of alcoholduring arc discharge that may contaminate the silver nanofluids. Comparing with UV/Visible and FTIRpattrns, it can help us find out what may happen during process. The major peaks in these spectra cannot tell the difference between the commercial Ag nanopowders and the Ag nanoparticles prepared byEDM system.s000- - PutAlconoMirnh2500三C30000 I1000200 3000 400100004000Wavelengh(nm)Wavelongth(nm)(a) Pure alcohol(b) Ag nanofluidFig.9 FTIR spectra& 120839003x00 400500600700800~ 000uvtiength(nm)Wviangth(nm)(a) Commercial Ag nanopowders in alcohol中国煤化工。rocessHCNMHGFig.10 UVVisible spwuu454过程工程学报第4卷4 CONCLUSIONSThe results of Ag nanofluids prepared by ASNSS process can be summarized as follow:(1) ASNSS is a novel process to prepare well dispersed powders in the dielectric fluid. The size ofparticles produces by this method can be reduced to nano scale.(2) From the related literatures and the test of EDM system in this study, the parameters of theexperimental design are determined. These parameters include current, pulse-duration time, voltage andthe diameter of the electrode.(3) This experimental study indicates that the current, voltage, pulse-duration time and electrodediameter and temperature of dielectric fluid will affect the particle size. Furthermore, the temperature ofdielectric liquid is especially considered as a major factor in this experiment.(4) The color of the Ag nanoparticles is gray, and changed from dark brown color slowly afterpreparation. This phenomenon indicates that the state of the nanoparticles may be unstable in the initialstate, which may be caused by the aggregation of nanosilver particles that changes the optical propertiesof silver nanofluid.(5) The mean particle size of Ag in different electrical discharge temperatures of -40°C, -20°C,0°C, and 10°C is about 13.4, 15.8, 17.5, and 21.6 nm, respectively. This indicates that the wellsuspended fluid can be obtained by contolling the lower dielectric fuid temperature.(6) FTIR results that indicate there are no decomposition of alcohol during arc discharge that maycontaminate the silver nanofluids.References[1] Daryl D. DiBitonto; Phili T. Eubank; MuKund R. Patel; and Maria A. Barufet. Theoretical Models of the ElecricalDischarge Machining Process. L. A simple cathode erosion model. J. Appl. Phys. 1989, 66(9), I November.[2] Lawrence, Rhoades. Understanding EDMed Surfaces. Cutting Tool Engineering, April, 1996.3] T. C. Lee and W. s. Lau. Some Characteristics of Electrical Discharge Machining of Conduction Ceramics. Materials andManufacturing Processes, 1991,6(4) 635-648.[4] 戴遐明，王家龙.等离子技术在高性能粉体制造之应用.中国粉体技术，1999, 5(6), 28- -32.[5]张组继，李厉兴.材料科学导论.上海科学技术出版社，1989.6]张立德，牟季美.纳米材料与纳米结构.科学出版社.[7]小林和彦，三菱電機技報45(10)33.8. Philip T. Eubank, Mukund R. Patel, Maria A.Bamufet, and Bedri Bozurt. TheoreticalModels of the Electrical Discharge Process. II. The Variable Mass, Cyindrical Plasma Model. J. Appl. Phys, 1993, 73(11),June I.中国煤化工MYHCNMHG