Design and characterization of low-heat and low-alkalinity cements

SYNTHESIS AND CHARACTERIZATION OF LOW COSTMAGNETORHEOLOGICAL (MR) FLUIDSVK Sukhwani and H Hiraniv_sukhwani@iitb.ac.in , hirani@iitb.ac.inDepartment of Mechanical Engineering, Indian Institute of Technology BombayMumbai-40007, INDIAABSTRACTMagnetorheological fluids have great potential for engineering applications due to their variable rheological behavior. These fluids find applications in dampers, brakes, shock absorbers, and engine mounts [1].However their relatively high cost (approximately US$600 per liter) limits their wide usage. Most commonly used magnetic material “Carbonyl iron” cost more than 90% of the MR fluid cost [2]. Therefore for commercial viability of these fluids there is need of alternative economical magnetic material. In the present work synthesis of MR fluid has been attempted with objective to produce low cost MR fluid with high sedimentation stability and greater yield stress. In order to reduce the cost, economical electrolytic Iron powder (US$ 10 per Kg) has been used. Iron powder of relatively larger size (300 Mesh) has been ball milled to reduce their size to few microns (1 to 10 microns). Three different compositions have been prepared and compared for MR effect produced and stability. All have same base fluid (Synthetic oil) and same magnetic phase i.e. Iron particles but they have different additives. First preparation involves organic additives Polydimethylsiloxane (PDMS) and Stearic acid. Other two preparations involve use of two environmental friendly low-priced green additives guar gum (US$ 2 per Kg) and xanthan gum (US$ 12 per Kg) respectively.Magnetic properties of Iron particles have been measured by Vibrating Sample Magnetometer (VSM). Morphology of Iron particles and additives guar gum and xanthan gum has been examined by Scanning Electron Microscopy (SEM) and Particles Size Distribution (PSD) has been determined using Particle size analyzer. Microscopic images of particles, M-H plots and stability of synthesized MR fluids have been reported. The prepared low cost MR fluids showed promising performance and can be effectively used for engineering applications demanding controllability in operations Keywords: Smart fluids, MR fluid, Magnetorheology, Particle distribution, Guar gum, Xanthan gum, PDMS, Low cost.1.INTRODUCTIONMagnetorheological (MR) fluids are known for their ability to change their rheological behavior by several orders of magnitude within milliseconds under the influence of magnetic field and therefore have been regarded as controllable fluids for engineering applications. Typically these fluids are non colloidal suspensions of micron sized magnetic particles (generally Iron particles) in nonmagnetic carrier medium (mineral oil, synthetic oil or water). Under the influence of magnetic field, these particles polarize and forms columnar structure parallel to the applied field, thus increases the apparent viscosity of the fluid which develops the yield stress in the structure. This viscosity change is rapid and completely reversible. Therefore MR fluid can be converted from a free flowing liquid to a plastic like solid by applying magnetic field and vice versa and can be used in different applications to bring dynamic change in performance measures like damping resistance as in MR-dampers, braking torque in MR-brakes and minimum film thickness in MR-bearings [3].Performance of any MR fluid in any application depends upon the magnetic properties of the solid phase, volume fraction, size and distribution of the magnetic particles, and viscosity of the carrier fluid etc.The synthesis of MR fluid involves many challenges. Two critical factors are the problem of gravitational sedimentation and agglomeration of particles and relatively high cost of MR fluids (approximately US$ 600 per liter). The large density difference between magnetic particles (i.e., ρ =7.86 g/cm3) and carrier fluid (i.e. ρ =1 g/cm3) is responsible for sedimentation problem. The problem of sedimentation has been mainly solved by three approaches, by adding Behavior and Mechanics of Multifunctional and Composite Materials 2007, edited by Marcelo J. DapinoProc. of SPIE Vol. 6526, 65262R, (2007) · 0277-786X/07/$18 · doi: 10.1117/12.720870surfactants, by adding nano particles or using nano magnetizable particles and by coating magnetizable particles with polymers .The addition of nano particles or use of nano magnetizable particles improves sedimentation stability effectively but at the same time it also reduces the MR effect produced by MR fluids. [4]High cost of MR fluid is mainly due to the high cost of magnetic material. Most commonly used magnetic material is Carbonyl iron obtained by thermal decomposition of Iron penta carbonyl .This material costs more than 90 % of the MR fluid cost [2, 5] Therefore for commercial viability of these fluids there is need of alternative economical magnetic material. In addition, an important functional requirement to produce more MR effect is the high dynamic yield stress. Use of alternative materials to reduce the cost has been reported in literature. Foister et al [5] in their patent have described the synthesis of low cost MR fluid using low cost water atomized Iron powder, multi component organoclay and multi component additive. Also the use of green additives like guar gum as thixotropic agent to solve the problem of sedimentation and agglomeration of MR fluids has been reported in literature. Chen et al [4] and Wu Wei Ping et al [6] successfully employed guar gum for improving sedimentation stability of MR fluids but they used the expensive carbonyl iron powder for synthesis of MR fluid. Similarly use of xanthan gum for achieving sedimentation stability of particles in MR fluid has been described by JD Carlson and JC Jones Guion in their patent. [7]As per authors knowledge no one has attempted use of both the economical Iron powder and additives like guar gum or xanthan gum in a single MR fluid composition. This has been attempted in the present work. In the present work synthesis of MR fluids have been carried out with objective to produce low cost MR fluid with high sedimentation stability and large yield stress. Low cost electrolytic Iron powder as magnetic material and variety of additives has been used for the present synthesis.2. SELECTION OF MAGNETIC PARTICLESThe magnetic particles for MR fluids should have high saturation magnetization and low coercivity. Carbonyl iron powder [8, 9, 10, 11], Nickel Zink ferrite [12], Iron oxide coated polymer composite particles [13], and Iron Cobalt alloy [14, 15] go well with these requirements. Saturation magnetization of Nickel Zink ferrite, Iron powder and Iron Cobalt alloy are 0.4T, 2.1 T and 2.43 T respectively [12,15] i.e. Iron Cobalt alloy has highest saturation magnetization but its density (8.1 g/ cm3) is greater than Iron therefore it aggravates gravitational settling. All the above mentioned magnetic materials are costly and therefore don’t suit the present synthesis of low cost MR fluid. Therefore for present synthesis Iron powder produced by electrolytic process has been chosen as this process yields the Iron of very high purity at very economical price (US$ 10 per Kg).The electrolytic Iron (EI) powder of relatively larger size 300 mesh (SD Fine-Chem, India) has been ball milled by suitable stainless steel grinding media in stainless steel pot to reduce the size to the order of few microns (1 -10 micron). This milled Iron powder was used for synthesis of all three MR fluids..3. SELECTION OF CARRIER FLUIDThe function of carrier or base fluid is to provide liquid phase in which magnetically active phase can be suspended. The carrier fluid should be non magnetic, nontoxic, non corrosive and non reactive. As most of lubricant with their additives packages suits these requirements, the commercial lubricants can be used for synthesis of MR fluid. In the present synthesis work, PAO (Poly Alfa Olefin) based high temperature synthetic oil with density 0.87 gram /cm3 and viscosity 20 cSt (0.01 Pa s) at 40°C has been selected. This oil can withstand operating temperature up to 180°C.4. SELECTION OF ADDITIVESAs discussed earlier, many additives have been attempted by researchers for synthesis of MR fluid. Generally thixotropic agents are added to prevent particle sedimentation. In addition, anti wear, anti corrosion, friction modifier and antioxidant agent are also added. Following are some important additives used in the synthesis of MR fluids for different purposes as reported in the literature:•To overcome sedimentation,o Fumed Silica [11], Lithium stearate, Aluminum distearate, Thiophosphorus, Thiocarbomate, Phosphorus, Guar gum [4], Organoclay[16] Poly vinyl pyrolidone [17], Poly vinyl butyl [18]•To overcome agglomeration,o Fumed silica [11], Fibrous carbon [19], Stearic acid [20], Sodium dodecyl sulphate [15], Viscoplastic media[21] o To increase abrasion wear resistance,o ZDDP (Zink dialkyl dithio phosphate ) [22-23]•To reduce oxidation,o ZDDP [23]• To reduce friction resistance.o Organomolybydnums (Moly) [22]Most of the above additives are not only expensive they are harmful to environment also. Therefore two environmental friendly additives, guar gum and xanthan gum have been chosen to prevent sedimentation of particles in the present synthesis. However for comparison purpose one organic polymer Polydimethylsiloxane (PDMS) has also been used as additives in one MR fluid composition.Guar gum is a high molecular weight hydro colloidal polysaccharide. It is extracted from guar bean (Cyamopsistetra gonoloba). It consist of linear chains of (1→4) linked ß-D mannose residue with a-D-galactopyranosyl units attached by (1.6) linkages. There is no polar group on the main chain of the guar gum, and most of the hydroxyl group is located outside. Furthermore, the side chain of the a-D-galactopyranosyl units does not hide the active alcoholic hydroxyl group; therefore it has a very large area of hydrogen bond. These characteristics make it useful as a thickening agent, suspension agent and stabilizing agent [4]. Its main application is found in food industry, where it is used as thickener, suspending agent and binder agent of free water in sauces, Ice cream, salad dressings etc.Similarly xanthan gum is a biosynthetic gum similar to natural gum. Xanthan gum is a long chain polysaccharide. It is prepared by fermentation of corn sugar with a microbe called Xanthomonas campestris. Xanthan gum has a special molecular structure. Its most important property is its very high viscosity at low-shear and relatively low viscosity at high shear. High viscosity at low shear provides stability to colloidal suspensions and therefore it is used as thickener and stabilizer for emulsions and suspensions.In the present work guar gum with approximate particle size 300 mesh (Premcem Gums India) and xanthan gum (Sienokem USA) have been used as thixotropic additives in two different preparations. In another preparation organic additive Polydimethylsiloxane (PDMS) with viscosity 100 cSt and Stearic acid are used. In addition an additive pack consists of anti wear, anti rust, anti corrosion, friction modifier and anti oxidant agent has also been used in all three preparations.5. CHARACTERIZATIONThe solid phase of MR fluid i.e. magnetic material was characterized before it is used in synthesis. Typically characterization includes analysis of particle size and its distribution, morphology and magnetic characterization. Additives guar gum and xanthan gum were also checked for their morphology.5.1 Particle size distribution analysisParticle size distribution analysis is very important for synthesis of MR fluid as particle size and size distribution influence the important properties i.e. Sedimentation stability, yield stress and magnetic properties of MR fluids [24]. Ota and Miyamoto [25] using two particle sizes calculated the static yield stress for a theoretical ER fluid and concluded that “ER Fluid consist of only same particle size gives the higher yield stress”. Lemaire et al [26] reported the influence of particle size on MR effect “It is better to have monodisperse sample in order to optimize the MR effect”. This indicates that narrow size distribution leads to more MR effect. But Wereley et al [13] in their study concluded that use of bidisperse particles in MR fluid increases their sedimentation stability. They also suggested a favorable tradeoff of proportion of particle sizes to increase the yield stress of MR fluid. Often particle size ranging 0.1 micron to 10 micronsis preferred [27]. Particle lesser than 0.1 micron will be subjected to random Brownian forces which destroy the chain like structure leading to decrease in the yield stress. On the other hand particles larger than 10 microns create the sedimentation problem. Kordonski et al [24] reported that particle size growth results in quadratic decrease of stability. Magnetic particles were analyzed using a particle size analyzer (GALAI computerized inspection system CIS-1, Particle size analyzer, Israel). Particles were dispersed in de ionized water with few drops of polyelectrolyte stabilizer to prevent the agglomeration of particles. Sodium Hexa Meta Phosphate was used as a medium to disperse the particles in this case. Sonication was also done to disperse the particles thoroughly. Fig-1 and Fig-2 show the particle size distribution of magnetic Electrolytic Iron (EI) particles before and after milling.Fig 1 Probability Volume density Graph for Electrolytic Iron powder before millingFig 2 Probability Volume density Graph for Electrolytic Iron powder after millingResults show that magnetic particle have broad size distribution (3.94 -77.50 microns ) with mean size 39 micron before milling and narrow size distribution (1.11-9.50microns) with mean size 4.27 micron after milling. This size range is recommended size range (1-10 micron) and therefore they are suitable for synthesis of MR fluids. These particles will have relatively lesser tendency to settle down.5.2 Morphology of magnetic particles and gum powdersThe morphology of the particles was studied by scanning electron microscopy (SEM facility S-3400 N, Hitachi Science Systems Japan). The powder sample was prepared by placing very small amount of powder on double sided carbon tape and pressing with the tip of spatula. The tape was then placed on brass stub. Gold plating was done on the samples to make the samples conducive. High vacuum was used and SEM was operated at 6-10 KV.Fig 3 SEM Image of Electrolytic Iron Particles before millingThe SEM image of the electrolytic Iron particles is shown in fig-3 .It shows the characteristic morphology of the particles .The electrolytic iron particles are of dendrite shape with a size distribution. Also they are in well dispersed state. SEM was also done for additives guar gum and xanthan gum. Fig-4 shows the SEM images (×500) obtained.(a) Guar gum (b) Xanthan gumFig 4 SEM Images of Guar gum and Xanthan gum powder5.3 Magnetic properties of particlesMagnetic properties of Iron particles were measured using vibrating sample magnetometer (VSM) technique. The VSM facility used for this purpose is Lakeshore VSM (Model 7410) interfaced with Lakeshore Cryotronics, Inc.VSM software.The Iron powder weight was measured with the accuracy of 0.0001 g by electronic balance (Precisa, Switzerland). The powder sample is pressed in to a small pellet. Small part of pellet (10-100 mg) is weighed and wrapped tightly in a butter paper /Teflon tape to avoid the movement of powder inside the sample holder. The magnetic field up to 20 K Oe was applied and operating frequency was 82 Hz.VSM was also done for costly carbonyl Iron (CI) powder to compare the magnetic properties of economical electrolytic Iron (EI) with costly carbonyl Iron (CI). Figure-5 shows M-H curves of the EI powder and CI powder obtained at room temperature (210C). The VSM results show that saturation magnetization of the electrolytic Iron powder is quite high (204.54emu/g) and approximately is of the same order of saturation magnetization of costly carbonyl Iron powder which is mostly used in synthesis of MR fluids. The saturation magnetization of carbonyl Iron (CI) powder has been found 212.08 emu/g. Slightly lower value of saturation magnetization of electrolytic iron powder in comparison to carbonyl Iron may be due to the fact that the electrolytic Iron used has 95.0 % purity while examined carbonyl Iron has 97-98 % purity. Moreover electrolytic Iron powder has also been milled to reduce the particle size which may also induce some impurities in the powder. Therefore more saturation magnetization will be obtained if EI powder having more purity is used.Coercivity was also determined from VSM data. Measured coercivity for electrolytic Iron is 26 O e and for carbonyl Iron it is 22 Oe. This shows that coercivity of electrolytic iron is only a little higher than the coercivity of carbonyl Iron. Moreover its value is still lower than 50 Oe and therefore can be considered as soft magnetic materials [28]Fig 5 M-H curves for Electrolytic Iron and Carbonyl Iron6. SYNTHESIS ROUTEIn present work three MR fluids are prepared using same base fluid (PAO based synthetic oil) and same magnetic phase i.e. electrolytic Iron (EI) powder but with different additives. These MR fluids are:MR Fluid-1: It has thixotropic agent Polydimethylsiloxane (PDMS) which is silicon based organic polymer and is known for its anti caking properties, Stearic acid as stabilizer additives and an additive package consist of anti wear, anti corrosion, friction modifier and anti oxidant agent.MR Fluid-2: It has green additive guar gum as thixotropic agent and above additive package. MR Fluid-3: It has additive xanthan gum as thixotropic agent and above additive package.6.1Coating of guar gum/xanthan gum on Iron particlesAdditives guar gum /xanthan gum were coated on the milled EI powder. Wu Wei Ping et al [6] reported that additive guar gum will be more effective when it is coated over the iron particles rather than co ball milling it with the Iron powder therefore first approach has been used in this work. For coating guar gum /xanthan gum over Iron particles the measured quantity of guar gum /xanthan gum was added to some quantity of water and mixed by mechanical stirrer for 30 minutes at 500 rpm. Iron powder was then added and mixture was agitated for 30 minutes at 1000 rpm. Ethanol was then added gradually to the mixture which leads to guar gum or xanthan gum forming a coating on the Iron powder. Precipitate was washed with acetone and filtered and dried to remove the water and then milled. These coated particles were used for synthesis. The weight percentage of guar gum /xanthan gum in the MR fluids is 3 %.6.2 Preparation of MR fluidsTo prepare MR fluid, first the appropriate amount of additive package consist of anti wear, anti rust, anti corrosion, friction modifier and anti oxidant agent was added to the measured quantity of base oil and mixed appropriately for 15 minutes by mechanical stirrer. The Iron particles (uncoated in case of MR fluid-1 and coated in case of MR fluid-2 and MR fluid-3) were then directly dispersed with specified volume fraction (0.36) in the above mixture. This mixture was homogenized by agitation of a mechanical stirrer at 1000 RPM for twenty-four hours to make MR fluid homogeneous. Appropriate amounts of PDMS with viscosity100 cSt and Stearic acid were also added in addition to the above additive package to the base oil for synthesis of MR fluid MRF-1. Fig-6 shows the flow chart for synthesis route of Magnetorheological fluid. The compositions of different MR fluids synthesized are given in table-1.Fig 6 Flow chart for Synthesis route of MR fluidsTable -1, Compositions of synthesized MR Fluids7. RESULTS & DISCUSSIONSIn present study three MR fluids have been synthesized using synthetic oil as base fluid, economical electrolytic Iron (with purity > 95.0 %) particles as magnetic phase and different additives. The prepared MR fluids were checked for their magnetic properties, expected MR effect and stability against sedimentation. Results of the study are as follows:7.1 Magnetic properties of uncoated particlesAs discussed earlier, magnetic properties of uncoated EI particles has been determined by VSM. Results indicate that saturation magnetization which is most important factor for producing MR effect i.e. yield stress developed , of low cost electrolytic iron powder (204.54 emu/g) is slightly lower (3.5%) than that of costly Carbonyl iron powder (212.084 emu/g). Similarly measured coercivity of EI powder (26 Oe) is slightly greater than Coercivity of CI powder (24 Oe).Therefore electrolytic Iron (EI) can be used for synthesis of MR fluid to reduce the cost of MR fluid significantly without significant reduction in MR effect.MRF-1 MRF-2 MRF-3 Ingredients Weight % Approx.Vol % Weight % Approx.Volume % Weight % Approx.Volume %Syntheticoil 16 64 15.5 64 15.5 64 Iron Powder81 36 81 36 81 36PDMS 2 ------ ------ ------ ------ ------ Stearicacid0.5 ------ ------ ------ ------ ------Guar gum ---- ------ 3.0 ------ ------ ------ Xanthangum ---- ------ ------ ------ 3.0 ------ Additive package0.5 ------ 0.5 ------ 0.5 ------7.2 Magnetic properties of coated particlesTo observe the effect of the additives coating on the magnetic properties of iron particles the magnetic properties of guar gum and xanthan gum coated particles were also checked by VSM. M-H curves for guar gum and xanthan gum coated particles are shown in figure-7. M-H curves show that saturation magnetization of guar gum coated and xanthan gum coated Iron particles are 198.52 emu/g and 198.14 emu/g respectively. Theses values are slightly lower (3%) than magnetic saturation of uncoated iron particles (204.54 emu/g). Measured Coercivity of these guar gum coated and xanthan gum coated Iron particles are 26 Oe and 28 Oe respectively which are almost same as that of coercivity of uncoated EI particles (26 Oe). This shows that coating of additives guar gum and xanthan gum on Iron particles has negligible effect on magnetic properties of Iron particles and therefore it can be concluded that MR effect produced by MR fluid will not reduce due to additive coating.Fig 7 M-H curves for Guar gum and Xanthan gum coated Electrolytic Iron7.3 MR effect expected (Yield stress developed)Magnetorheological (MR) effect produced by any MR fluid is the measure of its performance and is judged by maximum yield stress developed on application of magnetic field. For a MR fluid of known particle loading, particle size and known viscosity of base fluid the maximum yield stress depends upon the saturation magnetization of the magnetic material.The yield stress developed in MR fluid can be determined by performing magnetorheological measurement using a rheometer with an arrangement to produce magnetic field. Alternatively maximum yield stress developed in any MR fluid can be determined by measuring the saturation magnetization of the magnetic particles using VSM (Vibrating Sample Magnetometer). The relation between maximum obtainable yield stress and saturation magnetization of the magnetic particles has bee reported in the literature [29] as 20524()(3)()5yd s sat M τξφµ⎛⎞=⎜⎟⎝⎠(1)Where, yd τ is the yield stress, 0s M µ is saturation magnetization, φ is the particle volume fraction, 0µ is permeability of the free space and (3) 1.202ξ=(a constant)Table-2 shows the maximum yield stress expected to develop in three MR fluids obtained by using Eqn-1, based on their saturation magnetization values obtained by VSM .The values of yield stresses obtained for MRF-1, MRF-2 and MRF-3are quite high and are comparable to the value of yield stress (108 KPa) obtained for MR fluid using carbonyl Iron powder (2.09 T).Table 2- Expected Yield Stress for synthesized MR FluidsMR Fluid Saturation Magnetization Yield stress (KPa)MRF-1 204.54 emu/g (2.01 T) 99.59MRF-2 198.52 emu/g (1.96 T) 94.70MRF-3 198.14 emu/g (1.95 T) 93.737.4 Sedimentation stabilityPrepared MR fluids were put in graduated cylindrical flasks and observed over period of time for their sedimentation behavior i.e. settling of particles due to gravity. It was found that all three MR fluids remain in a well dispersed and stable state without significant settling of particles for quite long time. This is due to use of different thixotropic additives in MR fluids which reduces the sedimentation by forming weakly bonded structure in the fluid .These three dimensional structures have high apparent viscosity at low shear which prevents particle settling in the suspension. These structures collapse under shear leading to significant reduction in viscosity but reform again on removal of shear. Though all three MR fluids show very good stability against sedimentation but the MR fluids prepared by using additives guar gum and xanthan gum (MR fluid-2 and MR fluid-3) have better stability in comparison to MR fluid prepared using PDMS and Stearic acid (MR fluid-1). Sedimentation stability obtained are in the decreasing order from MRF-3 to MRF-1 i.e. lowest sedimentation tendency among three fluids was observed for MR fluid with xanthan gum and the highest sedimentation tendency was observed for MR fluid with PDMS. The result shows that the coating of guar gum and xanthan gum on iron particles gives better results in comparison to adding PDMS to the base fluid. This shows the utility of low-cost environmental friendly additives guar gum and xanthan gum in synthesis of MR fluids.8. CONCLUSIONS(01) Economical Iron powder produced by electrolytic process has very good magnetic properties, almost as good as costly carbonyl Iron powder which is most commonly used magnetic material for synthesis and therefore electrolytic Iron can be used as magnetic material to reduce the cost of MR fluid considerably without any significant reduction of MR effect produced.(02) Environmental friendly additives like guar gum and xanthan gum have been found more useful in comparison to organic polymer PDMS for preventing sedimentation of the particles in the MR suspension. Lowest sedimentation tendency has been observed for MR fluid with xanthan gum and the highest sedimentation tendency has been observed for MR fluid with PDMS.(03) The effect of coating of additives guar gum and xanthan gum on saturation magnetization and coercivity of Iron particles has almost been negligible. Therefore these additives can be used to improve the sedimentation stability without reducing MR effect produced by the MR fluids.(04) All three synthesized low cost MR fluids show very good stability against sedimentation and large yield stress therefore can be used in different commercial applications for achieving controllability in operation at relatively low cost..ACKNOWLEDGEMENTAuthors would like to thank their institute IIT Bombay for providing all the necessary facilities required for this workREFERENCES[1] Li W H, Du H and Guo NQ , “Finite Element Analysis and Simulation Evaluation of a Magnetorheological Valve”, Int. Journal of Advance Manufacturing Technology, Vol. 21, pp.438–445, 2003[2] Goncalves F D, Koo, J H, and Ahmadin M, “A review of the state of art in magnetorheological fluid technology – Part 1: MR Fluid and MR fluid models”, Shock and Vibration Digest, Vol.38, pp. 203-219, 2006,[3] Sukhwani VK and Hirani H, “Synthesis of a Magnetorheological lubricant” 5th International conference on Industrial tribology, ICIT-06, IISc Bangalore, Nov.30 –Dec. 02, 2006.[4] Fang Chen, Zhao Bin Yuan, Chen Le Sheng, Wu Qing, Liu Nan and Hu Ke Ao , “The effect of the green additive guar gum on the properties of magnetorheological fluid” , Smart materials structure, Vol.14, pp. N1-N5,2005.[5] Foister, Robet T, Iyanger, Vardarajan R, Yurgelvic and Sally M “Low cost MR fluid” US Patent No 6787058 , 2004[6] Wu Wei Ping , Zhao Bin Yuan , Wu Qing , Chen Le sheng and Hu Ke Ao, “The strengthening effect of guar gum on the yield stress of magnetorheological fluid” , Smart materials structure,Vol.15, pp. N94-N98,2006.[7] Carlson J D and Jones Guion J C, “Aqueous magnetorheological materials” U S Patent No 5670077, 1997.[8] Rabinow J, US Patent No 2575360, 1951.[9] Rabinow J, “The magnetic fluid clutch”, AIEE Trans, Vol. 67, pp.1308, 1948[10] Park J H, B yung Doo Chin and Ook Park , “Rheological properties and stabilization of magnetorheological fluid ina water in oil emulsion”, Journal of Colloid and Interface science, Vol. 240, pp 349-354 ,2001.[11] Lim S T, Cho M S, Jang I B and Choi H J, “Magnetrheological characterization of carbonyl iron suspension stabilized by fumed silica”, Journal of magnetism and magnetic materials, Vol. 282, pp .170-173, 2004.[12] Phule P P and Ginder J M “Synthesis and properties of novel magnetorheological fluids having improved stability and redispersibility”, 6th International conference on ER Fluids , MR suspensions and their applications, Yonezawa, Japan, World scientific, pp 445-453,1997.[13] Werely N M, Chaudhuri A , Yoo J H , John S, Kotha S, Suggs A , Radhakrishnan R, Love B J and Sudarshan T S, “Bidisperse magnetorheological fluids using Fe particles at nanometer and micron scale” ,Journal of Intelligent Materials, Systems and Structures, Vol. 17, pp. 393-401,2006.[14] Margida A J , Wiess K D and Carlson J D , “Magnetorheological materials based on Iron alloy particles”, Int. 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Characterization of microstructure,mechanical properties and corrosion resistance of dissimilar welded joint between 2205duplex stainless steel and 16MnRShaogang Wang *,Qihui Ma,Yan LiCollege of Material Science and Technology,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,Chinaa r t i c l e i n f o Article history:Received 23March 2010Accepted 10July 2010Available online 16July 2010Keywords:A.Ferrous metals and alloys D.WeldingF.Microstructurea b s t r a c tThe joint of dissimilar metals between 2205duplex stainless steel and 16MnR low alloy high strength steel are welded by tungsten inert gas arc welding (GTAW)and shielded metal arc welding (SMAW)respectively.The microstructures of welded joints are investigated using scanning electron microscope,optical microscope and transmission electron microscopy respectively.The relationship between mechanical properties,corrosion resistance and microstructure of welded joints is evaluated.Results indicate that there are a decarburized layer and an unmixed zone close to the fusion line.It is also indi-cated that,austenite and acicular ferrite structures distribute uniformly in the weld metal,which is advantageous for better toughness and ductility of joints.Mechanical properties of joints welded by the two kinds of welding technology are satisfied.However,the corrosion resistance of the weldment produced by GTAW is superior to that by SMAW in chloride solution.Based on the present work,it is con-cluded that GTAW is the suitable welding procedure for joining dissimilar metals between 2205duplex stainless steel and 16MnR.Ó2010Elsevier Ltd.All rights reserved.1.IntroductionDuplex stainless steel (DSS)consists of approximately equal amounts of austenite and ferrite,which results in the favorable mechanical properties and corrosion resistance.The higher strength properties allow weight savings,which reduce fabrication costs and enable lighter support structures to be used.The higher corrosion resistance,in particular against stress corrosion cracking,makes them preferably applied in certain environments such as chemical tankers,pressure vessels,pipes to heat exchangers,paper machines and ocean engineering [1–3].With the growing applica-tion of new materials and higher requirements for materials,a great need occurs for component or structure of dissimilar metals.However,the joining of dissimilar metals is generally more chal-lenging than that of similar metals,which is usually due to several factors such as the differences in chemical compositions and ther-mal expansion coefficients,resulting in different residual stresses situation across the different regions of weldments as well as the migration of carbon element from the steel with higher carbon content to the steel with relatively lower carbon content.If the welding process is not well controlled,some weld defects such as dilutions and cracks will generate in the weld metal and leadto great decrease of properties of the welded joint.There are some researches about failure analysis or mechanical performance for dissimilar metals joints.Ul-Hamid et al.[4]have addressed that carbon diffusion in the dissimilar joint between carbon steel pipe and type 304stainless steel elbows resulted in cracking after a rel-atively short period of usage.Lee et al.[5]have also reported creep–fatigue damage of dissimilar weldment of modified 9Cr–1Mo steel (ASME Grade 91)and 316L stainless steel in a liquid me-tal reactor.In order to overcome the technical problems and take full advantage of the properties of different metals,it is necessary to pay more attention to the joining of dissimilar metals,so as to produce high quality welded joints between them.At present,some investigations have been conducted on weld-ing of duplex stainless steel,almost all common fusion welding techniques can be used to weld duplex stainless steel through selecting appropriate filler metals and parameters such as heat in-put [6,7].Explosive welding can be thought as a feasible method to produce composite plates.Kaçar and Acarer [8]have addressed that explosive welding process can be used successfully for clad-ding duplex stainless steel on the vessel steels without losing prop-erties such as corrosion resistance and mechanical properties.However,compared to the welding of similar metals,there is lim-ited information about microstructure/property relationships in dissimilar material welds between duplex stainless steel and low alloy high strength steel.Increasing application of these steels will0261-3069/$-see front matter Ó2010Elsevier Ltd.All rights reserved.doi:10.1016/j.matdes.2010.07.012*Corresponding author.Tel.:+8602552112901;fax:+8602552112626.E-mail address:sgwang@ (S.G.Wang).require a better understanding of the mechanics associated with welding of dissimilar metals.Since GTAW and SMAW are widely employed in engineering application,in the current work,a few at-tempts have been made to produce dissimilar material welded joint between DSS and low alloy high strength steel.At the same time,some results are presented as reference for the practical welding of these types of dissimilar metals.2.Experimental material and procedureThe base metals employed in this presentation are duplex stain-less steel2205and low alloy high strength steel16MnR.The chem-ical compositions of base metals andfiller metals are given in3.Results and discussion3.1.Microstructure of welded jointsThe preparation of microstructure samples of dissimilar metals joint is much difficult.Therefore,special operation procedure should be used.Both of the weld metal(WM)and2205base metal are etched by aqua-regia.However,the bonding region at the side of16MnR is etched by5%nital solution alone,and16MnR base me-tal should be prevented from being etched by aqua-regia.The interfacial microstructure of16MnR–WM is shown in Fig.2.It is a region with about30l m width near the fusion line.The existing of this region can be attributed to the thermal conductivity of theTable1Chemical compositions of base metals andfiller metals(wt.%).Elements C Mn P S Si Cr Ni Mo NBase metal SAF22050.0160.820.0240.0010.3622.48 5.46 3.120.16 16MnR0.15 1.380.0160.0140.32––––Filler metal ER22090.013 1.540.0180.0070.4922.928.61 3.180.17 E22090.0260.900.0250.0020.9022.1010.00 2.840.18 832S.G.Wang et al./Materials and Design32(2011)831–837Moreover,some short rod-like carbides,granular carbides and is-land-like carbides are observed at higher amplification electron microscope,as shown in Fig.4c and d respectively.However,the result shows that no carbides such as M23C6or martensite are ob-served in the unmixed zone.Therefore,it can be concluded that the development of such a morphology is attributed to decomposition of pearlite at16MnR side and formation of Fe3C at the WM side. The decomposition model is shown in Fig.5.The optical micrograph of weld metal is shown in Fig.6.From Fig.6,the morphology of acicular ferrite in austenite matrix has been observed,which is characterized by large amount of austen-ite.However,in terms of ferrite content in the joint,there is not much variation between the two weld metals in welded joints A and B,and the ferrite volume fraction is only17.3%and14.5%(ob-improving joint crack resistance and reducing the inhomogeneous distribution of weld structure during multi-pass welding.Generally,the formation of martensite,M23C6(chromium car-bide),Cr2N and r phase depends on the base materials joined and welding conditions according to Refs.[15,16].Therefore,X-ray diffraction analysis is carried out on the weld metal and the re-sults are shown in Fig.7.There are only a and c phases in both of the weld metals,and no precipitation of M23C6(chromium car-bide),Cr2N or r phase is found in the weld metal,which is advan-tageous to mechanical properties and corrosion resistance of the joint.3.2.Mechanical properties834S.G.Wang et al./Materials and Design32(2011)831–837si-cleavage fracture,as shown in Fig.9d.Microhardness profile across the joint interface is shown inFig.10.The microhardness distributions of two kinds of welded joints are almost the same.Obviously,the hardness value of weld metal is higher than that of the16MnR base metal and the 16MnR HAZ.With the distance increasing away from interface, the microhardness values vary to a certain extent.The highest hardness values of the two joint interface are approximately 224HV and220HV respectively.It is because the carbon element migrates from the16MnR side to weld metal during welding due to the difference of chemical compositions between16MnR and weld metal.Similar result is reported by Kaçar and Acarer[8],studied the explosively welded joint between DSS andCorrosion behaviororder to evaluate the corrosion resistance of weldis sealed with A/B glue,leaving about10mmÂ10mm area,3.5%NaCl solution is used as corrosion solution,the sche-matic diagram is shown in Fig.11.Electrochemical corrosion test results of2205DSS base metal and weld metal are shown in Fig.12and Table4respectively. These samples display more or less similar behaviors in terms of In general,the higher the value is,the better corrosion resistance of the material is.Therefore,in3.5%NaCl solution,corrosion resis-tance order of the samples is:2205DSS BM>joint A>joint B.The pitting corrosion resistance of the DSS BM is much better compared to the two weld metals,as can be seen from the polari-zation plot.The DSS BM sample does not display any corrosion in 3.5%NaCl solution and there is no pit in the sample examined after the potentiodynamic cyclic scanning.And the good pitting resis-tance behaviors of weld metal are attributed to the addition of Cr,Ni,elements[19].The alloying element Cr could improve the stability of passivefilms,and the Ni would decrease the overall dis-solution rates of Fe and Cr[20].Moreover,the heat input of joint A is different from that of joint B,which affects the weld microstruc-ture and results in the difference of formation condition of metal surface passivefilm.Generally,thefiner the grain is,the more eas-ily the compact passivefilm forms.As a result,the corrosive ions cannot readily diffuse through the passivefilm and the metal pre-sents better corrosion resistance,so the joint A has better corrosion resistance compared to joint B.When welded joint is etched in chloride solution,defects gener-ated in the welding process(such as welding spatter or inclusion) possibly make it lose its ability to protect the surface passivefilm. As a result,a chromium-depleted zone appears around weld metal, which makes the surface activated,and the joint presents an ac-tive–passive behavior.The initiation sites for the pits are located at the ferrite–austenite grain boundaries and once formed they rapidly propagate from ferrite to austenite,as described in Ref.[21].It can be seen from Fig.13that ferrite grains are etched,leav-ing lots of grooves at the ferrite–austenite grain boundaries,and the remaining white strips are austenite.This selective localized corrosion is attributed to difference of the electrochemical poten-tial,caused by the ratio of biphase in weld metal.It is concluded that the austenite grains are by far more resistant to the chloride environment than that of the ferrite grains.4.ConclusionsThe investigation of welding between2205DSS and16MnR by GTAW and SMAW respectively reach the following conclusions:Fig.10.Hardness curves of16MnR–WM interface. Fig.12.Polarization curves of DSS BM and weld metals.Attribute to decomposition of pearlite at16MnR side and for-mation of Fe3C at the WM side,a decarburization layer and an un-mixed zone are observed at the interface of16MnR/WM.The microstructure of weld metal consists of austenite and acic-ular ferrite,and both of the two kinds of joints are characterized by a high content of austenite,which is beneficial to mechanical prop-erties and corrosion resistance.Sigma phase or M23C6intermetallic compounds are not observed in current case through analysis of XRD.The impact toughness of the weld metal is similar to that of 16MnR,but it is much higher than that of16MnR HAZ.The weld metal and16MnR HAZ welded by GTAW present a ductile mode of fracture,while the pattern of16MnR HAZ welded by SMAW be-longs to quasi-cleavage fracture.The fracture of the joint welded by GTAW occurs in the zone of 16MnR base metal,while the fracture position of the joint welded by SMAW is in16MnR HAZ.However,the average tensile strength of welded joints is582.4MPa,564.6MPa respectively.Both of them can meet the tensile strength requirements of engineering structure.The joint produced by SMAW has higher susceptibility to pitting corrosion in chloride solution than that of weldment produced by GTAW.Based on the present work,it is summarized that GTAW with filler metal ER2209is the suitable welding procedure for dissimilar metals joining between2205duplex stainless steel and16MnR in the practical application.References[1]Sieurin H,Sandström R.Austenite reformation in the heat-affected zone ofduplex stainless steel2205.Mater Sci Eng A2006;418:250–6.[2]Olsson J,Snis M.Duplex–A new generation of stainless steels for desalinationplants.Desalination2007;205:104–13.[3]Kurt B.The interface morphology of diffusion bonded dissimilar stainless steeland medium carbon steel couples.J Mater Process Technol2007;190:138–41.[4]Ul-Hamid A,Tawancy HM,Abbas NM.Failure of weld joints between carbonsteel pipe and304stainless steel elbows.Eng Fail Anal2005;12:181–91. [5]Lee HY,Lee SH,Kim JB,Lee JH.Creep–fatigue damage for a structure withdissimilar metal welds of modified9Cr–1Mo steel and316L stainless steel.Int J Fatigue2007;29:1868–79.[6]Ureña A,Otero E,Utrilla MV,Munez CJ.Weldability of a2205duplex stainlesssteel using plasma arc welding.J Mater Process Technol2007;182:624–31. [7]Muthupandi V,Bala Srinivasan P,Seshadri SK,Sundaresan S.Effect of weldmetal chemistry and heat input on the structure and properties of duplex stainless steel welds.Mater Sci Eng A2003;358:9–16.[8]Kaçar R,Acarer M.Microstructure–property relationship in explosively weldedduplex stainless steel–steel.Mater Sci Eng A2003;363:290–6.[9]Naffakh H,Shamanian M,Ashrafizadeh F.Dissimilar welding of AISI310austenitic stainless to nickel-based alloy Inconel657.J Mater Process Technol 2009;209:3628–39.[10]Sireesha M,Shankar V,Albert SK,Sundaresan S.Microstructural features ofdissimilar welds between316LN austenitic stainless steel and alloy800.Mater Sci Eng A2000;292:74–82.[11]Srinivasan PB,Muthupandi V,Dietzel W,Sivan V.Microstructure and corrosionbehavior of shielded metal arc-welded dissimilar joints comprising duplex stainless steel and low alloy steel.J Mater Eng Perform2006;15:758–64. [12]Srinivasan PB,Muthupandi V,Dietzel W,Sivan V.An assessment of impactstrength and corrosion behaviour of shielded metal arc welded dissimilar weldments between UNS31803and IS2062steels.Mater Des 2006;27:182–91.[13]You YY,Shiue RK,Shiue RH,Chen C.The study of carbon migration indissimilar welding of the modified9Cr–1Mo steel.J Mater Sci Lett 2001;20:1429–32.[14]Migiakis K,Papadimitriou GD.Effect of nitrogen and nickel on themicrostructure and mechanical properties of plasma welded UNS S32760 super-duplex stainless steels.J Mater Sci2009;44:6372–83.[15]McPherson NA,Chi K,Mclean MS,Baker TN.Structure and properties of carbonsteel to duplex stainless steel submerged arc welds.Mater Sci Technol 2003;19:219–26.[16]Rajeev R,Samajdar I,Raman R,Harendranath CS,Kale GB.Origin of hard andsoft zone formation during cladding of austenitic/duplex stainless steel on plain carbon steel.Mater Sci Technol2001;17:1005–11.[17]Badji R,Bouabdallah M,Bacroix B,Kahloun C,Belkessa B,Maza H.Phasetransformation and mechanical behavior in annealed2205duplex stainless steel welds.Mater Charact2008;59:447–53.[18]Palmer TA,Elmer JW,Babu SS.Observations of ferrite/austenitetransformations in the heat affected zone of2205duplex stainless steel spot welds using time resolved X-ray diffraction.Mater Sci Eng A 2004;374:307–21.[19]Tavares SSM,Pardal JM,Lima LD,Bastos IN,Nascimento AM,de Souza JA.Characterization of microstructure,chemical composition,corrosion resistance and toughness of a multipass weld joint of superduplex stainless steel UNS S32750.Mater Charact2007;58:610–6.[20]Olsson C-OA,Landolt D.Passivefilms on stainless steels-chemistry,structureand growth.Electrochim Acta2003;48:1093–104.[21]Kordatos JD,Fourlaris G,Papadimitriou G.The effect of cooling rate on themechanical and corrosion properties of SAF2205(UNS31803)duplex stainless steel welds.Scripta Mater2001;44:401–8.S.G.Wang et al./Materials and Design32(2011)831–837837。

Materials Characterization Materials characterization is a crucial aspect of materials science and engineering, as it involves the study and analysis of the properties and behavior of materials at the microstructural and macroscopic levels. This process is essential for understanding the structure-property relationships of materials, which ultimately impacts their performance and functionality in various applications. In this response, we will delve into the significance of materials characterization, the techniques and methods involved, and the impact it has on different industries. First and foremost, materials characterization plays a pivotal role in the research and development of new materials. By thoroughly analyzing the composition, structure, and properties of a material, researchers can gain valuable insights that inform the design and synthesis of advanced materials with tailored properties. This is particularly important in industries such as aerospace, automotive, and electronics, where the demand for high-performance materials is constantly growing. For example, the development of lightweight yet durable materials for aircraft construction relies heavily on materials characterization to ensure the materials meet stringent safety and performance standards. Moreover, materials characterization is essential for quality control and assurance in manufacturing processes. By employing techniques such as microscopy, spectroscopy, and thermal analysis, manufacturers can assess the uniformity, purity, and integrity of materials, thereby ensuring that thefinal products meet the desired specifications. This is critical in industrieslike semiconductor manufacturing, where even minor variations in the material properties can lead to significant defects and malfunctions in electronic devices. Through meticulous materials characterization, manufacturers can mitigatepotential risks and uphold high standards of product quality. In addition, materials characterization is instrumental in understanding the degradation and failure mechanisms of materials. By examining the microstructural changes, surface alterations, and mechanical properties of materials over time, researchers and engineers can identify the root causes of degradation and develop strategies to enhance the durability and reliability of materials. This is particularly relevant in the field of infrastructure and construction, where the long-term performanceof concrete, steel, and composites is essential for ensuring the safety and sustainability of buildings, bridges, and other civil structures. Furthermore, materials characterization contributes to the advancement of nanotechnology and biomaterials, where the unique properties and behaviors of materials at the nanoscale are of paramount importance. Techniques such as atomic force microscopy, X-ray diffraction, and electron microscopy enable researchers to investigate the structure and properties of nanomaterials with exceptional precision, paving the way for innovations in drug delivery systems, tissue engineering, and nanoelectronics. The ability to characterize and manipulate materials at the nanoscale opens up new possibilities for developing novel technologies with unprecedented functionalities. From a practical standpoint, materials characterization also has significant implications for environmentalsustainability and resource conservation. By understanding the environmental impact of materials and their life cycles through techniques like life cycle assessment and environmental impact analysis, researchers and policymakers can make informed decisions regarding the selection, use, and disposal of materials. This holistic approach to materials characterization contributes to the development of eco-friendly materials, recycling processes, and waste reduction strategies, ultimately promoting a more sustainable and circular economy. In conclusion, materials characterization is an indispensable aspect of materials science and engineering, with far-reaching implications for research, industry, and society as a whole. The diverse techniques and methods employed in materials characterization enable a comprehensive understanding of materials, from their atomic and molecular structure to their macroscopic properties and behaviors. This knowledge not only drives innovation and advancements in various industries but also fosters a deeper appreciation for the role of materials in shaping the world we live in. As we continue to push the boundaries of materials science, the significance of materials characterization will only grow, leading to new discoveries and applications that benefit humanity in profound ways.。

2024-2025学年上外版英语高三上学期期末模拟试卷及解答参考一、听力第一节（本大题有5小题，每小题1.5分，共7.5分）1、W: Which book are you reading, John? M: I’m reading Twilight. It’s very interesting. W: Can I have a look at it? M: Certainly. You can read it now. Q: What are the two speakers talking about?•A: A movie. (Wrong: They were discussing a movie.)•B: A book. (Correct: John is reading a book called Twilight, and they are discussing this book.)•C: A TV show. (Wrong: They were not talking about a TV show.)2、M: I wonder what you think of this new board game. Do you take an interest in it? W:I haven’t tried it, but I think it’s not a good one. It is quite difficult and boring. M: That sounds bad. Q: What does the woman think of the game?•A: It’s interesting. (Wrong: The woman thinks the game is difficult and boring.)•B: It’s difficult and boring. (Correct: The wom an thinks the game is difficult and boring.)•C: It’s not enjoyable. (Correct: The woman considers the game difficult and boring, which means it’s not enjoyable.)The questions are designed to test the students’ ability to understand conversations indifferent contexts and to infer the speakers’ thoughts and feelings based on the dialogue.3.W: I can’t find my textbook. Do you think it could be in the library?M: I think you should check your bag first. We left it there this morning.Question: Where does the conversation hint that the textbook was last seen?A)In the library.B)In the speakers’ bag.C)During the morning.Answer: B) In the speakers’ bag.Explanation: The man suggests that the woman first checks her bag, implying that they left the textbook there earlier that morning.4.M: How was your job interview? Did everything go smoothly?W: It went okay, but I didn’t get the job. The company is looking for someone with more experience than I have.Question: What is the main concern expressed by the woman about the job interview?A)She believes the interview didn’t go well.B)She didn’t receive any feedback on the interview.C)She doesn’t have the required experience.Answer: C) She doesn’t have the required experience.Explanation: The woman explicitly states that the company is looking for more experienced candidates, indicating that her lack of experience is the concern that prevented her from getting the job.5、听下面一段对话。

高熵合金催化剂制备流程## English Answer: ##。

High-entropy alloys (HEAs) have emerged as promising catalytic materials due to their unique properties, such as exceptional stability, high catalytic activity, and tunable composition. The preparation of HEA catalysts involves several key steps:1. Materials Preparation: The first step involves selecting and preparing the precursor materials for the HEA catalyst. These materials can include pure metals, metal oxides, or other compounds. The desired composition and properties of the final HEA catalyst are determined at this stage.2. Alloying Process: The precursor materials are then combined and subjected to an alloying process, which typically involves high-temperature melting and rapid cooling. This process promotes the formation of ahomogeneous HEA structure with a random distribution of elements. Different alloying techniques can be employed, such as arc melting, induction melting, or mechanical alloying.3. Catalyst Activation: After the alloying process, the HEA catalyst may undergo additional steps to enhance its catalytic activity. These steps can include surface modification, reduction, or oxidation treatments. The specific activation methods depend on the intendedcatalytic application and the nature of the HEA catalyst.4. Characterization: The prepared HEA catalyst is then characterized to determine its structural, morphological, and compositional properties. This characterization typically involves techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).5. Catalytic Evaluation: The final step involves evaluating the catalytic performance of the prepared HEA catalyst. This is typically done through standard catalytictests, which assess the catalyst's activity, selectivity, and stability under specific reaction conditions.The development of HEA catalysts is still in its early stages, but these materials have shown great potential for various catalytic applications. By optimizing the composition, structure, and activation methods, HEA catalysts can be tailored to meet the specific requirements of different catalytic processes.## 中文回答， ##。

Materials Science and Engineering A361(2003)36–44Characterization of a thermomechanically processed powdermetallurgy Al–5wt.%Mg–1.2wt.%Cr alloyM.Eddahbi ∗,M.Cars´ı,O.A.RuanoDepartamento de Metalurgia F´ısica,Centro Nacional de Investigaciones Metalúrgicas,CSIC,Avda.de Gregorio del Amo 8,Madrid 28040,SpainReceived 19August 2002;received in revised form 12May 2003AbstractA thermomechanical processing (TMP)was carried out in a powder metallurgy extruded Al–5wt.%Mg–1.2wt.%Cr alloy to obtaina fine-grained material.The extruded billets showed elongated (sub)grains,oriented towards the ␤-fiber orientations,where the intensity maximum was located at the brass component (Bs).After annealing at 550◦C for 48h,the (sub)grains remained elongated toward the extrusion direction,whereas the intensity of the Bs component increased.After TMP which consisted of various reductions by cold rolling up to 90%with intermediate annealing,the microstructure developed a banded structure,composed of elongated (sub)grains of size 0.5–1␮m,and the intensity of orientations along the ␤-fiber decreased considerably.After annealing at 500◦C for 48h,the TMP material showed recrystallized grains 5–8␮m in size with a weak rotated cube texture.©2003Elsevier B.V .All rights reserved.Keywords:Thermomechanical processing;Powder metallurgy;Microstructure;Texture;Mechanisms;Aluminium alloys1.IntroductionThermomechanical processing (TMP)is usually con-ducted to achieve fine microstructures in ingot cast metal-lurgy alloys (IM).It is also important in powder metallurgy alloys (PM)because the intrinsic fine structure is changed to generate superplasticity at elevated temperatures.This property is found in materials having an extremely fine grain size and fine second phases that can be maintained during deformation at elevated temperatures.Although the most important factor,however,a fine grain size is not the only condition to have superplasticity.Other microstruc-tural features such as the presence of high angle boundaries and a homogeneous distribution of second phases are also important to achieve high ductility.A global microstructure analysis of the processed mate-rials should be conducted in order to reach special prop-erties.This analysis involves the initial microstructure and the thermomechanical variables that influence the mecha-nisms controlling the evolution of the microstructure dur-ing TMP and so the microstructure and the behavior of the material [1–7].It is also important to establish the correla-∗Corresponding author.Tel.:+34-91-553-8900;fax:+34-91-534-7425.E-mail address:eddahbi@cenim.csic.es (M.Eddahbi).tions between the various aspects of the microstructure such as grain size,grain shape,dislocation density,macrotexture and microtexture [8–11].Special attention has been paid in recent years to the texture analysis to reveal new aspects of the microstructure that are not identifiable by other tech-niques [12,13]and to relate them to macroscopic features and properties.The texture analysis allows,for example,to differentiate among the different mechanisms such as static recrystallization [14,15],dynamic recrystallization [16–20],slip or grain boundary sliding that may occur during TMP or high-temperature deformation [21,22].The large distance from equilibrium solute solubility that can be attained in Al alloys through the use of controlled atomization and fabrication techniques via TMP,such as rolling or extrusion,enhances the development of new al-loys having improved mechanical properties [23–25].The addition of slow solid-state diffusion elements such as Fe,Li,Cr,Zr and Sc allows the attainment of a considerable volume fraction of small particles.For example,Al–Mg–Cr (PM)alloys produced by rapid solidification and consoli-dated by extrusion show improvements of properties over a wide range of temperatures compared to conventional ingot metallurgy (IM)processing [26,27].The Al 18Mg 3Cr 2and Al 7Cr particles present in these alloys are resistant to coars-ening and exercise a pinning effect on the grain boundaries,increasing strength and ductility of the material [28,29].On0921-5093/$–see front matter ©2003Elsevier B.V .All rights reserved.doi:10.1016/S0921-5093(03)00502-1M.Eddahbi et al./Materials Science and Engineering A361(2003)36–4437the other hand,these particles play a primordial role in gen-erating deformed zones which stimulate the nucleation of new grains during annealing or high-temperature deforma-tion by a particle-stimulated nucleation (PSN)mechanism [30–33].Aluminium alloys usually develop during cold defor-mation ␣-and ␤-fiber orientations.The ␤-fiber orienta-tions are predicted to be stable by the Taylor model under full-constraint conditions,FC model,and its modifications under relaxed constraint conditions,RC models [34–38].Fig.1illustrates the different simulation models discussed widely by Hirsch and Lücke [36]and proposed to predict the deformed microstructure (grain structure and texture)after rolling in a polycrystalline aggregate.The shear strains and the single letters given in the figure indicate the associ-ated three main rolling texture components,Cu,S and Bs,while the subscripts define the shearplane.Fig.1.Shape changes of grains under full constraints conditions (FC):(a)undeformed crystal and (b)deformed crystal giving D orientation.Shape changes of grains under relaxed constraints (RC):(c)εNR =εCu shear relaxed giving the copper component,(d)εCu and εNT =εs shear relaxed giving the S component and (e)εTR =εBs shear relaxed giving the Brass component [34].The FC model is considered an approximation for the be-havior of equiaxed grain microstructures where plastic com-patibility is a primordial requirement (Fig.1(b)).However,for highly non-equiaxed grains,as for example after large deformation during rolling,the FC model fails to describe the global microstructure.This is because the change of cer-tain strain components during rolling does not correspond to the macroscopic strain.Those strain components are said to be relaxed which may indicate that less than five strain com-ponents are necessary to strain the material.The microstruc-tural changes associated to these conditions are discussed consequently in the models illustrated in Figs.1(c)–(e).The aim of the present investigation is the microstructural characterization of the extruded PM Al–5wt.%Mg–1.2wt.%Cr alloy before and after TMP.An approach on the mecha-nisms governing the evolution of grain structure and texture during rolling is proposed.It is to note that in this paper all compositions are given in wt.%.2.Materials and experimental procedureRapidly solidified powders of composition 4.89Mg,1.19Cr,0.14Fe,0.06Si,0.007Be and balance aluminium were prepared and supplied by Kaiser Aluminium and Chemical Corporation,Pleasanton,CA.The solidifica-tion rate was 104K s −1using an air (95%N 2–5%O 2premixed)-atomizing nozzle.Powders less than 149␮m in diameter were sieved from the bulk powders for use in billet preparation.The powders were cold iso-statically pressed to about 70%density,degassed at 520◦C during 8h and then compacted to 100%density at 480◦C.The compact was then extruded at 270◦C into a billet,at 4:1reduction,of cross-section of 26.7mm ×101mm.The extruded billet was subjected to an overaging anneal at 520◦C for 24h and then furnace-cooled to 200◦C.A TMP procedure was carried out on the overaged an-nealed material to develop a fine-grained microstructure.The scheme of the processing route is illustrated in Fig.2and consists,basically,of three rolling steps with intermediate annealing.An annealing treatment at 500◦C for 48h was carried out to obtain a recrystallized microstructure.The microstructure was revealed by conventional grinding and polishing techniques,followed by etching in Barker’s reagent.Optical microscopy (OM),scanning electron mi-croscopy (SEM)and transmission electron microscopy (TEM)were used to characterize the initial (before rolling)and the final (after rolling)microstructure.Texture measurements were carried out by means of an au-tomated X-ray texture in the Schulz reflection method using a Siemens diffractometer equipped with a D5000goniome-ter and an opened Eulerian cradle.Incomplete pole figures {111},{200},{220}and {113}were measured over a range of azimuthal angles χfrom 0◦to 75◦in the step mode with increment of χ=5◦.For both polar coordinates,χand φ,a textureless standard sample of pure Al was used for38M.Eddahbi et al./Materials Science and Engineering A361(2003)36–44Fig.3.Microstructure of the extruded billet(ED is horizontal):(a)trans-verse plane(surface of the billet)(OM)where the grains are elongatedtoward ED,(b)transverse plane(middle of the billet)(OM)and(c)trans-verse plane(TEM)showing deformed(sub)grains confined by particles.Fig.5(a)is an optical micrograph obtained on the extrudedplane of the microstructure of the extruded billet annealedat550◦C during48h.It is observed that the microstructureis slightly coarser than that of the extruded billet.Further-more,the(sub)grains maintain their directionality towardsED,despite the extended annealing treatment.Fig.5(b)isan OM image of the transverse section of the annealed bil-let showing that the microstructure is a mixture of elongatedM.Eddahbi et al./Materials Science and Engineering A361(2003)36–4439Fig.4.Texture of the extruded billet(surface):(a)(111)polefigures, (b)(200)polefigures and(c)ODF.and equiaxed(sub)grains.However,the volume fraction of the former is larger than that of the latter.Fig.5(c)shows a TEM image where dislocation motion is estimated to occur from the subboundaries toward the original grain boundaries. Other TEM images have shown that,globally,the structure appears to be pinned by particles and some subboundaries are not dissolved after such annealing.Texture measurements at both the surface and the middle of the billet show that no new texture is developed after such annealing.Nevertheless,at the surface,the texture intensity of the main component(Bs)increases compared to that cor-responding to the extruded billet.In turn,along the S–Cu orientations the intensity remains constant.At the middle of the billet the intensity was close to that of the extruded billet.In the case of the cube texture the intensity increases onlyslightly.Fig.5.Microstructure of the annealed billet:(a)extruded plane(surface) (OM)showing elongated structure toward ED(ED is horizontal),(b) transverse plane(OM)showing some elongated grains containing small equiaxed(sub)grains(ED is vertical)and(c)transverse plane(TEM) showing microstructure of the annealed billet.3.2.Characterization of the thermomechanically processed materialFig.6(a)is a TEM image showing the microstructure of the TMP material revealed on the transverse section(steps 1,2and3in Fig.2).It is observed that the(sub)grains are elongated toward RD.Globally,this microstructure should40M.Eddahbi et al./Materials Science and Engineering A361(2003)36–44Fig.6.Microstructure of the TMP material:(a)transverse plane (TEM)with banded structure showing elongated (sub)grains toward RD and (b)rolling plane (TEM)in which deformation zones around an Al 18Mg 3Cr 2particle are indicated by symbols X.be considered as a banded structure containing (sub)grains.A deformed substructure with small (sub)grains,0.5–1␮m around the particles,is formed as shown in Fig.6(b).Fig.7(a)is the ODF of the TMP material obtained on the rolling plane close to the surface.It is observed that the in-tensity of the Bs and the Cu components has dramatically decreased during rolling.The orientation intensity is con-stant along the ␤-fiber with a slight tendency toward the S component.At the middle plane of the sheet the texture is also a ␤-fiber;however,the intensity of orientations is higher than that at the surface (Fig.7(b)).Fig.8shows the ODF density,f (g ),along the ␤-fiber as a function of Euler’s angle,ϕ2,for the TMP material at the surface and the middle of the sheet.For comparison,the Fig.7.ODF of the TMP material:(a)rolling plane (surface of the sheet)and (b)middle plane.data corresponding to the surface and the middle of the ex-truded and the annealed billets are included.The Cu,S and Bs components are given in the figure.For the annealed bil-let,it is observed that the intensity of the Bs orientation at the surface has increased,whereas the intensity along the S–Cu orientations remained constant.In turn,the orienta-tion intensity along the ␤-fiber has increased only slightly at the middle of the billet.However,during rolling the in-tensity of the main orientations (Bs and Cu)has decreased considerably at both the rolling and the middle plane of the sheet.Furthermore,it is observed that the gradients of tex-ture intensity between the surface and middle plane in the TMP material is less pronounced than that observed in the annealed billet.M.Eddahbi et al./Materials Science and Engineering A361(2003)36–4441Fig.8.Orientation density,f(g),as a function ofϕ2of the Al–5wt.% Mg–1.2wt.%Cr alloy in the three states:extruded billet,annealed billet and thermomechanicallyprocessed.Fig.9.Microstructure of the recrystallized material showing clean grains (rolling plane)(TEM).Fig.9shows the microstructure obtained on the rolling plane of the TMP material after annealing at500◦C for48 h.The microstructure is characterized by small recrystal-lized equiaxed grains of5–8␮m and low dislocation den-sity.The grains are oriented toward a45◦ND-rotated cube orientation,{100} 011 ,as evidenced by Fig.10.It is to note that the intensity of this orientation decreases from the surface to the middle of the rolled sheet.4.Discussion4.1.Extruded billetThe microstructure of the Al–5wt.%Mg–1.2wt.%Cr ex-truded billet consists of elongated(sub)grains in ED as shown in Fig.3[26].This microstructure is stronglyconfined Fig.10.ODF corresponding to the rolling plane of the recrystallized material.in a homogeneous distribution of Al18Mg3Cr2and Al7Cr particles.The elongated microstructure with␤-fiber orien-tations may indicate that the original grains developed an amount of shear strainsεs,εCu andεBs.In addition,the sta-bility of each component requires that certain spatial distri-bution of orientations should be present.The formation and stability of Bs orientation which is the main component de-scribing the texture of the extruded billet is associated to the formation of the shear strainεBs.However,this shear strain is difficult to develop in elongated grain structure and requires specific conditions(Fig.1(e)).For instance,the presence of a Goss component,{110} 001 ,before cold extrusion could lead to this component[41,42].However,the texture of the Al–5wt.%Mg–1.2wt.%Cr alloy before cold extrusion should have been random.Other possibility is the activation of two highly unfavorable slip systems with respect to the external stress as suggested in a previous investigation[37]. This may be the case of the Al–5wt.%Mg–1.2wt.%Cr alloy if we assume that the particles introduced by the PM proce-dure may induce the activation of such systems that lead to the formation and stability of the Bs component.In the case of the Cu component,a correlation of ad-jacent Cu-oriented grains in symmetrically complementary Cu-oriented variants may result in a full compensation of42M.Eddahbi et al./Materials Science and Engineering A361(2003)36–44theεCu shear strain enhancing its stability as described in Fig.1(c).In the case of the S component,its deformation behavior should be similar to that of the Cu and the Bs com-ponents.For this reason,it should be considered as a tran-sition orientation between the Cu and the Bs orientations and should rotate along the␤-fiber orientations.The devel-opment of the S orientation requires the relaxation of theεs shear strain,but it does not lead to its stability.In addition to the elongated(sub)grains,small equiaxed (sub)grains are also observed in the extruded billet.These could be confined in the small powder particles that recrys-tallize during extrusion.It is our contention that these small equiaxed(sub)grains are responsible for the recrystallization cube texture{100} 001 .4.2.Annealed billetThe microstructure of the annealed billet remains elon-gated toward ED and contains some subboundaries(Fig.5). This indicates that the microstructure of the annealed billet is stable against annealing.This may be mainly attributed to the particle distribution,which in a manner confines the sub-structure.This means that only an extended recovery mech-anism occurs during such annealing since no new texture was observed[1,16,19].TEM analysis on the long trans-verse sections of the annealed billet showed that the original grain boundaries,which are parallel to ED,did not mani-fest any curvatures towards the direction normal to ED;an example is shown in Fig.5.It is expected,therefore,that the dislocation density may decrease during such anneal-ing,principally,by elimination of dislocations and disap-pearance of low subboundaries inside the original elongated grains.In addition,provided that the(sub)grains inside the original grains are small and the diffusion processes are im-portant,we assume that part of the decrease of subbound-ary density may result from subgrain coalescence inside the original elongated grains.This coalescence process,in our proposal,may be supported by dislocations climb along the subboundaries that should induce a slight rotation of the ad-jacent subgrains[26].These dislocations are then absorbed at the original boundaries,mainly,those that are parallel to ED.Therefore,an increase in grain boundaries misorienta-tion is expected.4.3.Thermomechanically processed materialTMP drastically changes the state of the extruded mi-crostructure resulting in a new distribution of particles and orientations.The formation of a heavily banded structure with elongated(sub)grains(Fig.6)is a common feature of high strain deformation at low temperature.It is expected that some relaxation ofεCu andεs shear strains should be developed during rolling[36].Furthermore,since the mi-crostructure shows a mixture of coarse and small particles, it is to be expected that the deformation should be heteroge-neous around the coarse particles and homogeneous around the small particles as found in previous studies[44].We sug-gest that such heterogeneous deformation around the coarse particles is responsible for the drastic decline of the texture intensity during rolling,particularly that of Bs and Cu ori-entations(Fig.10).This may be interpreted as reorientation along the␤-fiber by rotation around a given orientation re-lationship.As an approximation,if we consider the rotation path from Bs toward S,it can be shown that the Bs compo-nent gives,in addition to other orientations,the S component by a rotation around an axis located60◦from ND toward RD ( 110 ).Similarly,the rotation of the Cu component may give the S component.Such rotation relationships can eas-ily be seen by means of the(111)polefigures.However,it is difficult to follow the microstructural processes involved in such orientation relationships.This requires several mea-surements of local lattice rotations by means of EBSD,es-pecially in the deformation zones.With regard to the lattice rotation near the particles,it was observed that two slip systems were activated and a rotation around 112 was observed in a rolled Al–Cu single crys-tal with Bs orientation[44].However,in crystals with other orientations,such as{110} 001 orientation,no 112 ro-tation was operated.Similar 112 rotations near the par-ticles were obtained in strained Al–Cu[45]and Al–Cu–Si single crystals[30].Other studies in f.c.c.metals,assuming single slip,predicted that the orientation of the(sub)grains inside the deformed zones are rotated around the 112 axis lying in the slip plane and normal to the slip direction[46]. However,such prediction is more complicated in polycrys-tals.Generally,a more or less random orientation distribu-tion of(sub)grains in the deformation zones is observed.In this investigation,we determined that 112 rotations could not describe the texture changes during TMP as reported re-cently by Engler et al.[43].Perhaps,it is too early to support such rotational relationship in the Al–5wt.%Mg–1.2wt.% Cr alloy.This requires numerous measurements of local ori-entations near the particles by EBSD.In this context,we have tried to conduct such EBSD analysis but the measure-ments were not satisfactory,owing to the deformation state near the particles and the undesirable conditions of the sam-ple patterns.4.4.Recrystallized materialIn general,the cube texture,{100} 001 ,and the ND-rotated cube texture,{100} 013 ,are the main tex-tures developed during recrystallization in aluminium and its alloys[15,47].The origin of such textures in various materials,and in particular aluminium alloys,has been the subject of many studies.However,the intrinsic aspects of the development of this texture are not understood. It was suggested that a fraction of original cube grains do not transform during rolling and maintain their cube orientation[48–53].These cube grains form a40◦ 111 orientation relationship with respect to the deformed ma-trix that allows them to grow easily at the expense ofM.Eddahbi et al./Materials Science and Engineering A361(2003)36–4443the surrounding(sub)grains giving rise to the exact cubetexture.Nevertheless,the annealed TMP material shows,ratherthan{100} 001 and/or{100} 013 orientation(s),a45◦ND-rotated cube texture{100} 011 (Fig.9).This texturewas not observed previously in aluminium and aluminiumalloys.Even if one admits that the TMP material contains alow density of cube grains,supposed retained during rolling,however,the orientation relationship40◦ 111 cannot serve to explain the formation of the{100} 011 orientation.Wepropose that a correlation should exist between the defor-mation state and the development of such orientation.Thisdeformation–orientation correlation is favorable to give a {100} 011 orientation in some regions of the TMP mate-rial,probably close to the particles.Attempts are going on to reveal this correlation by means of the EBSD technique.It is to note,however,that the{100} 011 orientation is weak indicating that the major part of the recrystallized grains are randomly oriented[54–58].In summary,the high deformation introduced by theTMP results in a new microstructural and textural state.The(sub)grains are elongated toward the rolling directionand the intensity of the initial␤-fiber orientations decreasesdrastically after rolling.The presence of coarse and smallparticles induces a heterogeneous deformation behavior,i.e.heavily deformed zones are developed around the coarserparticles,whereas homogeneous deformed zones are ex-pected in the surroundings of thefine particles.5.Conclusions(i)The Al–5wt.%Mg–1.2wt.%Cr extruded billet showselongated(sub)grains toward ED with␤-fiber orientations.The billet is heavily deformed near the surface and the tex-ture is intense.At the middle of the billet,however,the ma-terial is less deformed and the texture is weaker than that atthe surface.(ii)After annealing at550◦C for48h,some recoveryoccurs but the microstructure is similar to that of the extrudedbillet.At the surface,the intensity of the Bs orientationincreases,whereas that of the rest of the orientations remainsconstant along S–Cu orientations of the␤-fiber.The textureintensity increases only slightly at the middle.(iii)The TMP results in a new deformed microstructureconsisting of a banded structure with(sub)grains of0.5–1␮m in size.The texture intensity of the␤-fiber orientations decreases drastically,especially at the surface of the rolled sheet.(iv)After annealing for48h at500◦C,the TMP materialshows afine-grained recrystallized microstructure,5–8␮min size,with a weak rotated cube texture{100} 011 . 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三氟乙酰肼的合成及应用研究进展李伟;徐卫国;杭晓春【摘要】The general properties, synthesis and applications of 2,2,2-trifluoroacetohydrazide were reviewed.%对三氟乙酰肼的概况、合成及应用进行了详细的综述。

【期刊名称】《浙江化工》【年(卷),期】2015(000)004【总页数】6页(P1-6)【关键词】三氟乙酰肼;合成;应用【作者】李伟;徐卫国;杭晓春【作者单位】浙江省化工研究院有限公司，浙江杭州 310023;浙江省化工研究院有限公司，浙江杭州 310023;浙江省化工研究院有限公司，浙江杭州 310023【正文语种】中文三氟乙酰肼是一种常用的有机氟化工原料，主要用于合成三氟甲基三氮唑及其衍生物以及其它一些常见的五元或六元含氮杂环化合物，在农药、医药及有机金属配合物中用途广泛。

三氟乙酰肼是一种白色粉末状固体，CAS号为1538-08-5，分子式为C2H3F3N2O，分子量为128．05，常压下熔点为111℃，沸点为192．3℃。

肼类化合物一般性质比较活泼，引入-CF3这一强吸电子基团，更增强了分子的活性，本文对三氟乙酰肼的主要制备方法及其在合成中的应用进行综述。

2.1 以三氟乙酸乙酯为原料和水合肼反应文献报道较多的制备三氟乙酰肼的方法是三氟乙酸乙酯和水合肼反应，反应路线见式1：Groth R H[1]等早在1960年就报道了采用此路线来合成三氟乙酰肼的方法，他采用0．75 mol的三氟乙酸乙酯和0．825 mol 85%的水合肼在150 mL 95%乙醇中回流3 h，得到96 g粗品，然后用丁醇重结晶得到该产品。

Sitzmann M E[2]等报道了以三氟乙酸乙酯和80%水合肼为原料，在25℃下，在甲醇中反应16 h得到该产品。

D．Searle等[3]在专利US6423713、US6514977及US6979686报道了采用0．10 mol的三氟乙酸乙酯和0．11 mol 80%的水合肼在25 mL乙醇中回流6 h，以96%的收率得到该产品。