材料专业外文资料翻译--热处理对三种不同途径生产的纳米粉氧化锆晶体结构和形态的影响.doc

毕业论文外文资料翻译题 目 热处理对三种不同途径生产的 纳米粉氧化锆晶体结构和形态的影响学 院 材料科学与工程 专 业 材料科学与工程 班 级 学 生 学 号 指导教师 二一三年三月二一日- 7 -j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 5 ( 2 0 0 8 ) 178185journal homepage: /locate/jmatprotecEffect of thermal treatment on the crystalstructure and morphology of zirconiananopowders produced bythree different routesM.M. Rashad , H.M. BaioumyCentral Metallurgical Research and Development Institute, P.O. Box 87, Helwan, Cairo, EgyptarticleArticle history:infoabstractZirconia ZrO2 nanopowders have been successfully prepared via three processing routes,namely, conventional precipitation (CP), citrate gel combustion (CGC) and microemulsionrened precipitation (MRP). The formed zirconia particles were characterized using X-raydiffraction analysis (XRD), scanning electron microscope (SEM), Fourier transformer infrared(FT-IR) spectroscopy and UVvisible absorption spectrum. The results showed that the CProute led to the formation of tetragonal ZrO2 phase with low crystallinity at 700 C and theformed tetragonal phase was transformed to monoclinic ZrO2 phase at temperatures rangedReceived 24 May 2006Received in revised form22 April 2007Accepted 23 April 2007Keywords:ZirconiaSynthesisCrystal structureNanoparticlesCharacterizationfrom 1000 to 1200 C. The CGC route led to formation of monoclinic phase without presencetetragonal phase species in the temperatures range from 1000 to 1200 C. In contrast, MRPtechnique led to the formation of tetragonal phase with high crystallinity compared withthe other processing at 700 C and the produced tetragonal phase was inverted to cubicphase by increasing the calcination temperatures from 1000 to 1200 C. SEM showed that themorphology of the produced zirconia nanopowders changed according to synthesis routesand thermally treated temperatures. 2007 Elsevier B.V. All rights reserved.1.IntroductionAdvanced ceramics known as ne ceramics are a diversegroup of inorganic oxides such as zirconia, alumina, tita-nia and non-oxides like silicon carbide, boron carbide andsilicon nitride. These materials are drawing attention ashigh technology materials because of their superior mechan-ical, thermal, electrical, chemical and optical properties.Zirconia ne ceramics have an impressive combinationof properties such as high strength, hardness, toughness,corrosion resistance, low co-efcient of friction and biocom-patibility. Nearly 80% of produced zirconia in the world isused in conventional applications such as refractories, pig-ments, glazers, opaciers, abrasives, etc. The ever-increasingnumbers of ceramics applications have resulted in devel-oping of advanced technologies to process nanopowderszirconia (Galgali et al., 1995). The advanced applicationsof zirconia nanopowders are including transparent opti-cal devices, electrochemical capacitor electrodes, oxygensensors, fuel cells and catalysts including photocatalysts(Srdic and Omorjan, 2001; Kongwudthiti et al., 2003). Zir-conia catalyzes the hydrogenation of olens, isomerizationof olens and epoxides and the dehydrations of alco-hols. When zirconia is used as support, various reactions Corresponding author. Tel.: +20 2 5010642/213; fax: +20 2 5010639. E-mail address: (M.M. Rashad).0924-0136/$ see front matter 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.jmatprotec.2007.04.135j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 5 ( 2 0 0 8 ) 178185179such as Fischer-Tropsch synthesis, methanol synthesis andhydrodesulfurization have been reported to proceed withhigher activity and selectivity than with conventional sup-ports (Jung and Bell, 2000). It is well known that zirconiais a low absorption materials usable for coating in thenear-UV (300 nm) or IR (8 m) regions. Typical applica-tions include near-UV laser and dielectric mirror designs.In addition, about 95% of ferrule, the most important partof the optical ber connector is now made from zirconiane ceramics. It is known that high quality of the ceramicis based on the excellent performance of zirconia powder(5). Preparing a ne and an agglomerate free zirconia powderis the rst and perhaps the most important step in obtaininga sintered zirconia ceramic of desirable microstructure andtherefore mechanical properties. Various chemistry-basednovel approaches have been taken for the preparation of zirco-nia powders including co-precipitation, hydrothermal, sol gel,sonochemical method, microemulsion and thermal decom-position processing (Ma et al., 2004; Wu et al., 2003; Lee et al.,1999; Tai et al., 2001; Djuricic et al., 1995; Bourell and Kaysser,1993; Ward and Ko, 1993; Huang and Guo, 1992; Fang et al.,1997; Li et al., 1989; Juarez et al., 2000; Yashima et al., 1996;Yashima et al., 1994; Caruso et al., 1997; Chatterjee et al., 1992;Dodd and McCormick, 2002; Roy and Ghose, 2000; Kolenko etal., 2003; Noh et al., 2003; Somiya and Akiba, 1999; Piticescu etal., 2001). The chemical precipitation (CP) method is a suitablelow cost technique for the mass production compared withthe other mentioned technique. The main drawback is thatthe particle size is not small and has in wide size distribution.Microemulsion rened precipitation (MRP) gives better chem-ical homogeneity with controlling the particle size and sizedistribution. Citrate gel combustion (CGC) technique is usedto obtain highly uniform size and shape controlled nanopar-ticles. ZrO2 has three polymorphic phases; monoclinic (m), tetrag-onal (t) and cubic (c). Because of its phase transformationfrom tetragonal to monoclinic around the temperatures rangefrom 1100 to 2370 C, it is a challenging study with potentiallypractical applications to prepare stabilized tetragonal ZrO2powders at low temperatures. Stabilization of t-ZrO2 phaseis usually achieved by adding oxides of yttrium, magnesium,calcium, thorium, titanium, cerium and ytterbium (Piticescuet al., 2001; Jiang et al., 2001; Lascalea et al., 2004; Teterycz etal., 2003; Panda et al., 2003; Zhang et al., 2004; Ai and Kang,2004; Bhattacharjee et al., 1991). According to the change inthermal treatment, c-ZrO2 phase is stable at all temperatureup to the melting point at 2680 C. m-ZrO2 phase is stablebelow 1170 C and inverted to t-ZrO2 phase by increasing tem-perature over 1200 C. t-ZrO2 phase is stable between 1170and 2370 C by adding stabilized oxides (Stefanc et al., 1999).From our knowledge, little information in literature is foundabout the change in the phase transformation and the mor-phology of the formed ZrO2 nanopowders that are producedby CP, CGC and MRP techniques. The present work aims atcomparing the change in crystal structure, morphology, FT-IRspectra and UVvisible absorption spectrum of the producedZrO2 nanopowders which are obtained by these three process-ing routes at different calcination temperatures from 120 to1200 C.2.2.1.ExperimentalMaterials and processingThe materials used in the present work were, zirconyl chlo-ride ZrOCl2 8H2 O purchased from BDH Chemicals Ltd., Poole,England, sodium hydroxide and citric acid purchased from El-Nasr Pharmaceutical Chemical ADWIC, Egypt, n-pentanol andTriton X-100 (Serva Electrophoresis GmbH, Germany). To process ZrO2 powders by CP route, 10 g zirconiumoxychloride octahydrate was dissolved in 100 ml bidistilledwater using hot plate magnetic stirrer. The desired vol-ume of 2 M NaOH was added into the solution until pH10. After 15 min, the produced precipitate was ltered off,washed and dried at 120 C overnight. The dried ZrO2 nH2 Ocalcined at different temperatures from 500 to 1200 C at arate of 10 C/min and kept at the respective temperature for1 h. To process ZrO2 powders by CGC method, 10 g of zir-conium oxychloride octahydrate was dissolved in water. Astoichiometric amount of citric acid was added to the aque-ous solution. The mixture was evaporated to dryness at 60 C.Then, the produced precursor was dried to 120 C overnight.The formed precursor was heated again to 500, 700, 1000 and1200 C at a rate of 10 C/min and kept at the respective tem-perature for 1 h. For the MRP method, the authors employed n-pentanol asthe oil phase and triton X-100 as the surfactant. One molar ofTriton X-100 (non-anionic surfactant) was prepared by dissolv-ing in n-pentanol and the processed solution was divided intotwo parts, one part was added to 10 g zirconyl chloride octahy-drate dissolved in small amount of water and the other partwas used for preparation of 2 M sodium hydroxide. Both twosolutions were mixed together to precipitate zirconia hydrateat pH 10. The precipitated solution was ltered, washed, driedat 120 C, then calcined at different temperatures from 500 to1200 C.2.2.CharacterizationThe phase identication and the crystallite size of the pro-cessed ZrO2 nanopowders were characterized by Philips X-RayDiffractometer PW 1730 with nickel ltered Cu K radiation ( = 1.5406 A) at 40 kV and 30 mA. The crystallite sizes of ZrO2nanopowders were determined for the most intense peak(1 1 1) plane of ZrO2 crystals from the X-ray diffraction datausing the Debye-Scherrer formula:dRX =k cos (1)where dRX is the crystallite size, k = 0.9 is a correction factorto account for particle shapes, the full width at half max-imum (FWHM) of the most intense diffraction plane, the wavelength of Cu target = 1.5406 A, and is the Bragg angle. The change in crystal morphologies of the ZrO2 particlesproduced at heated temperature 700 and 1000 C for differ-ent processing routes were examined by scanning electronmicroscopy (JEOL-JSM 5410 SEM). Specic surface area (SBET ) of180j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 5 ( 2 0 0 8 ) 178185samples was determined by BET surface area analyzer (Nova2000 series, Quantachrome Instruments, UK). UVvisible absorption spectrums of the processed ZrO2powders using three processing routes at calcination temper-ature 1000 C were measured using CECIL CE 7200 UV doublebeam spectrophotometer. Vibration spectrum of the crystalline ZrO2 powders atcalcination temperature 1000 C for the different processingtechniques in KBr were recorded on Fourier Transformer andPye-Unicam SP 300 instrument.3.Results and discussionThe XRD patterns of the ZrO2 nanopowders products syn-thesized by precipitation (CP), citrate gel combustion (CGC)and microemulsion rened precipitation (MRP) techniques atdifferent thermal treatment from 120 to 1200 C were shownin Figs. 13. It is clear that the processed samples synthe-sized at temperature 120 C were amorphous in the threeprocessing techniques and it was also nearly amorphous forthe produced ZrO2 powders of the precursor sample pow-der which treated at the temperature 500 C in case of CPmethod. XRD studies also showed that the transformation ofZrO2 precursors to the crystalline tetragonal phase (JCPDS #49-1642) occurred as the calcination temperatures were increasedFig. 2 XRD patterns of the produced ZrO2 powders by CGCmethod at 120, 500, 700, 1000 and at 1200 C for 1 and 3 h.between 500 and 700 C for heating time 1 h. The crystallitesizes of formed single-phase t-ZrO2 nanopowders as calcu-lated from XRD analyses using Debye-Scherrer formula ofthe most intense peaks (1 1 1) plane were in the range of32.90, 10.18 and 20.97 nm at 700 C for CP, CGC and MRPmethods, respectively. The presence of tetragonal phase in as-prepared ZrO2 and the powder formed at low temperature isattributed to the fact that the specic surface free enthalpyof tetragonal ( = 0.77 J/m2 ) is smaller than that of mono-clinic ( = 1.13 J/m2 ). The large surface area of as-synthesizednanopowders becomes a thermodynamic barrier for t-ZrO2to m-ZrO2 phase transformation. Consequently, tetragonalphase is remained. Liang et al. (Liang et al., 2003) explained theformation of tetragonal phase at low temperature is attributedto that the structure of zirconia precursor is regarded ashydrous zirconia (ZrO2 nH2 O) and the schematic structure unithas 16 zirconium atoms, 20 non-bridging hydroxogroups, 22bridging oxide bond and 20 coordinated water and based onthis model, the following equations is obtained by increasedthe temperature up to 700 C:Zr16 O22 (OH)20 (H2 O)20 xH2 ONaturally driedZr16 O22 (OH)20 (H2 O)20 + xH2 O(2)Fig. 1 XRD patterns of the produced ZrO2 powders by CPmethod at 120, 500, 700, 1000 and at 1200 C for 1 and 3 h.Zr16 O22 (OH)20 (H2 O)20 16ZrO2 + 30H2 Oheat(3)j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 5 ( 2 0 0 8 ) 178185181Fig. 3 XRD patterns of the produced ZrO2 powders by MRPmethod at 120, 500, 700, 1000 and at 1200 C for 1 and 3 h. When ZrO2 nH2 O is heated up to about 300 C, themetastable tetragonal zirconia is observed compared to itsstable temperature around 11002370 C. The amorphous totetragonal phase transformation is attributed to the loss ofwater from the amorphous hydrous zirconia resulting fromthe release of water of hydration and the production of watervia oblation. Both processes lead to a reduction in the BET sur-face area of the calcined solid and a consequent increase inthe average particle size (Jung and Bell, 2000). Table 1 showedthat the relation between the crystallite size and the surfacearea of the obtained ZrO2 nanopowders produced by differ-ent techniques. For CP method, when the crystallite sizes ofthe produced powders increased from 7 nm for the precursorthermally treated at 500 C to 32.90 nm at 700 C. The surfacearea of amorphous zirconia produced at 120 C was 250 m2 /gwhich was decreased to 230 m2 /g for the precursor thermallytreated at 500 C and decreased again to 180 and 20 m2 /g for theprecursor thermally treated at 700 and 1000 C, respectively.For CGC method, the BET specic surface area of amorphouszirconia was 280 m2 /g then decreased to 210 m2 /g (crystallitesize was 10.18 nm) for the precursor treated at 700 C then to60 m2 /g for the sample treated at 1000 C (crystallite size was41.2 nm). Moreover, for MRP method, the BET specic surfacearea was also 280 m2 /g then decreased to 200 m2 /g (crystallitesize was 21 nm) and 45 m2 /g (crystallite size was 57.8 nm) forthe precursors annealing at 700 and 1000 C, respectively. The tetragonal phase then inverted to pure monoclinicphase (JCPDS #37-1484) by increasing the temperature up to10001200 C for 1 h in case of CP and CGC techniques. Trans-formation from the tetragonal to monoclinic phase have beenattributed to the relative stability of these two phases dependon the sum of the free energies from particle surface, bulkand strain contribution (Jung and Bell, 2000). Because of thelower bulk free energy of m-ZrO2 and the lower surface freeenergy of t-ZrO2 , the latter phase is stabilized below a criticalparticle size for a given temperature. This critical size is esti-mated to be 10 nm at 298 K. In the absence of particle strain,this thermodynamic description has been found to give thecorrect temperature for the tetragonal to monoclinic phasetransformation for the particles ranging from 9 nm to 10 m.The phase transformation occurred when the size of zirconiaparticles is equal to or greater than the critical size determinedfrom an analysis of the thermodynamic stability of small parti-cles of t- and m-ZrO2 . The validity of a purely thermodynamicexplanation has been questioned since several investigationshave observed t-ZrO2 that is larger than the critical particlesize by talking into account factors such as domain boundarystresses, nucleation embryos, anionic vacancies and adsorbedcations and anions, all of which contribute to the stabiliza-tion of t-ZrO2 . On these factors, the effects of external strainand the adsorbed ionic species on the surface free energy ofzirconia can be accommodated within the thermodynamictheory for the tetragonal to monoclinic phase transforma-tion. In addition, the phase transformation of zirconia startsfrom its surface region and then gradually develops into thebulk. The tetragonal phase in the surface region is difcultto stabilize. Treatment at progressively higher temperaturein absence of strain is accompanied by loss of surface area.Moreover, when hydrous zirconia inverted to t-ZrO2 , zirconiaTable 1 Crystallite size (Cs) and the specic surface area SBET values of zirconia nanopowders synthesized by CP, CGCand MRP methods at different calcination temperaturesTemperature ( C)Cs (nm) 120 500 7001000 732.964.5CP methodSBET (m2 /g)250230180 20CGC methodCs (nm) 8.510.241.2MRP methodCs (nm) 8.021.057.8SBET (m2 /g)280235210 60SBET (m2 /g)260240200 45182j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 5 ( 2 0 0 8 ) 178185Fig. 4 SEM micrographs of the produced ZrO2 powders by CP (a and b), CGC (c and d) and MRP methods (e and f) attemperatures 700 and 1000 C.still retained about one percent of water. On further heating, itinverted to m-ZrO2 , all identication hydrous ZrO