[ABSTRAK
Fe-Cr adalah paduan yang memiliki ketahanan temperatur tinggi danpotensial digunakan sebagai interkonektor pada sel bakar (SOFC=solid oxide fuelcell). Sintesis paduan Fe-Cr terus dikembangkan untuk mendapatkan metode yangefektif, dan efisien. Metode sintesis paduan Fe-Cr yang ada sekarang ini adalahmetode peleburan, metalurgi serbuk ataupun metode pemaduan mekanik. Metodemetodetersebut memiliki kelemahan misalnya paduan yang tidak homogen,terdapat oksida, proses panjang dan membutuhkan waktu lama. Untukmeminimumkan permasalahan ini, adalah penting untuk menghasilkan paduanmikro Fe-Cr yang memiliki kestabilan fasa dan sifat mekanis baik. Metodeultrasonik dapat dimanfaatkan untuk sintesis paduan mikro homogen melaluipenggunaan gelombang suara ultrasonik. Gelombang suara ultrasonikmenghasilkan gelembung-gelembung kavitasi, setiap runtuhan kavitasi dapatdianggap sebagai reaktor mikro yang mampu menghasilkan temperatur sekitar4737 oC dan tekanan sekitar 1000 atm dan yang terbentuk dengan sangat cepat,serta menghasilkan gelombang kejut. Dengan demikian metode ultrasonik dapatdimanfaatkan dalam pembuatan paduan mikro Fe-Cr yang homogen serta tanpaoksida dan diharapkan bisa mengatasi kelemahan metode pembuatan paduanberbasis Fe saat ini. Pada penelitian ini telah dilakukan sintesis paduan mikro Fe-Cr dengan metode ultrasonik pada frekuensi 20 kHz dalam cairan toluene.Tahapan yang telah dilakukan adalah perlakuan ultrasonik sebagai variasi waktuterhadap partikel prekursor (Fe, Cr), kemudian terhadap campuran partikelprecursor untuk mendapatkan paduan mikro Fe-Cr. Kemudian dilakukanpembuatan bongkah paduan Fe-Cr dari partikel hasil perlakuan ultrasonik melaluikompaksi tanpa lubrikan dan sintering dalam kapsul kaca kuarsa. Karakterisasiyang dilakukan adalah menggunakan Scanning Electron Microscopy (SEM)terhadap partikel precursor hasil rekayasa ultrasonic. Untuk partikel campuranprekursor Fe-Cr hasil perlakuan ultrasonik karakterisasi dilakukan menggunakanSEM-EDS (Energy Dispersive Spectroscopy), X-Ray Diffraction (XRD) disertaianalisis dengan metode Rietveld, Transmission Electron Microscopy-SelectedArea Electron Diffraction (TEM-SAED). Untuk bongkah Fe-Cr hasil konsolidasidengan menggunakan SEM-EDS, XRD disertai analisis dengan metode Rietveld,pengukuran densitas sebenarnya, pengujian kekerasan Vickers. Efek perlakuanultrasonik terhadap partikel Fe adalah pengurangan ukuran, penyatuan, danaglomerasi. Setelah perlakuan ultrasonik 40 jam terjadi peningkatan ukuranpartikel Fe (>2μm). Terhadap partikel Cr memberikan efek erosi permukaan,pengurangan ukuran dan pemecahan partikel aglomerasi. Partikel Cr aglomerasiterurai sepenuhnya menjadi partikel Cr kecil (< 2 m) setelah 63 jam. Terhadapcampuran partikel Fe dan Cr dapat menyatukan partikel kohesif (Fe-Fe, Cr-Cr)dan adhesif (Fe-Cr), terbentuk paduan mikro Fe-Cr seutuhnya (setelah 20 jam)ataupun paduan mikro Fe-Cr sebagian (setelah 50 jam). Pembentukan paduanmikro Fe-Cr diawali pada ukuran partikel Fe ataupun Cr < 2m. Bongkah paduan mikro Fe-Cr yang diperoleh adalah homogen dan tanpa oksida, dengankarakteristik densitas melalui sintering dua tahap yaitu tipe O = 8.655 gr/cm3, tipeB=8.179 gr/cm3, dan tipe A=8.196 gr/cm3, dan melalui proses sintering satu tahaptipe O = 7.678 gr/cm3, tipe B=7.587gr/cm3, dan tipe A=7.092 gr/cm3. Kekerasanbongkah Fe-Cr terbesar melalui sintering satu tahap yaitu 88 VHN adalah tipe B,sementara terbesar dua tahap yaitu 81 VHN adalah tipe A. Proses perlakuanultrasonik memberikan dampak positif baik dari sisi waktu proses maupunkualitas hasil paduan Fe-Cr. Dengan demikian metode ultrasonik bisa diandalkansebagai alternatif dalam pembuatan paduan berbasis Fe untuk mengatasi kendalahomogenisasi dan oksidasi yang dihadapi pada metode saat ini.;
ABSTRACT
Fe-Cr alloys have the potential for use as an interconnection material forsolid oxide fuel cell (SOFC) due to its being resistance to high temperatures.Synthesis methods of Fe-Cr alloy continue to be developed in order to obtain amethod that is both effective and efficient. Presently, the synthesis of Fe-Cr alloysinclude the casting, the powder metallurgy, and the mechanical alloying method.These methods have several drawbacks such as inhomogeneity in the resultingproducts, oxidation, and require a very time-consuming process to accomplish. Inorder to minimize this problem, it is important to produce Fe-Cr microalloys. Fe-Cr microalloys exhibit phase stability and good mechanical properties. Ultrasonicmethods can be used in the synthesis of homogeneous microalloys by employingthe ultrasonic sound waves. Ultrasonic sound waves will generate cavitationbubbles. Any cavitation collapse can be considered as a micro reactor in which atemperature of about 4737 oC and a pressure of about 1000 atm a very rapidlycreated, thereby generating a shock wave. Thus, the ultrasonic method can beused in producing homogeneous and free-oxide Fe-Cr microalloys and can beexpected to overcome the limitations imposed by the current methods. In thiswork the formation of Fe-Cr microalloys by ultrasonic treatment at a frequency of20 kHz in toluene liquid is presented. In the synthesis procedure, the proceduresteps followed were: (1) the treatment of precursor particles (Fe, Cr) throughultrasonic method with a time-variation, followed by (2) the same time-varyingultrasonic treatment on the admixture of these specially prepared precursorparticles in order to obtain the Fe-Cr microalloys, and (3) finally, the lubricantlesscompaction method was employed on these precursor particles admixturefollowed by sintering process inside quartz tubes to obtain a bulk of Fe-Cr alloy.Observations of the specially prepared precursor particles using ultrasonictechnique were carried out by scanning electron microscopy (SEM) method.Observation of the precursor mixture of Fe-Cr particles mixture treatedultrasonically was performed using a SEM-EDS (energy-dispersive spectroscopy)apparatus, a X-Ray diffractometer and accompanied by the Rietveld analysismethod, and transmission electron microscopy (TEM)-selected area electrondiffraction (SAED) apparatus. The bulk of Fe-Cr alloy were observed using SEMEDS,XRD accompanied by analysis by the Rietveld method, true densitymeasurement, and Vickers microhardness testing. Ultrasonic treatment has causedFe particles to form agglomerations, an interparticles neck formation, and a fusingamong the particles. The size of the Fe particles increased (>2μm) after 40 hourstreatment. The agglomerated Cr particles experienced fragmentation, surfaceerosion, and reduction of particle size. The agglometrated Cr particles fullydisintegrated into Cr microparticles (<2μm) after 63 hours treatment. The mixtureof Fe-Cr forming cohesive (Fe-Fe, Cr-Cr) and adhesive (Fe-Cr) particles, formingcompletely (after ultrasonic treatment for 20 hours) and partially (after ultrasonictreatment for 50 hours) Fe-Cr microalloys. The complete formation of Fe-Cr microalloy was possible with an equal particle size of the precursor Fe and Cr(approximately <2 μm). The bulk of Fe-Cr alloy results are homogenous andoxide-free. For two-step sintering, its density (in gr/cm3 unit) is 8.655 for type O,is 8.179 for type B, and is 8.196 for type A, and for one-step sintering its densityis 7.678 for type O, is 7.587 for type B, and is 7.092 for type A. The greatestmicrohardness number of 88 VHN is of type B (one-step sintering), and of 81VHN is of type A (two-step sintering). The ultrasonic treatment process has apositive impact, with respect to both of quality and time-consumption to finish theFe-Cr alloying process. Therefore the ultrasonic method can be relied upon as analternative method in the production of Fe-based alloys to solve problems inhomogenization and oxidation encountered in current methods;Fe-Cr alloys have the potential for use as an interconnection material forsolid oxide fuel cell (SOFC) due to its being resistance to high temperatures.Synthesis methods of Fe-Cr alloy continue to be developed in order to obtain amethod that is both effective and efficient. Presently, the synthesis of Fe-Cr alloysinclude the casting, the powder metallurgy, and the mechanical alloying method.These methods have several drawbacks such as inhomogeneity in the resultingproducts, oxidation, and require a very time-consuming process to accomplish. Inorder to minimize this problem, it is important to produce Fe-Cr microalloys. Fe-Cr microalloys exhibit phase stability and good mechanical properties. Ultrasonicmethods can be used in the synthesis of homogeneous microalloys by employingthe ultrasonic sound waves. Ultrasonic sound waves will generate cavitationbubbles. Any cavitation collapse can be considered as a micro reactor in which atemperature of about 4737 oC and a pressure of about 1000 atm a very rapidlycreated, thereby generating a shock wave. Thus, the ultrasonic method can beused in producing homogeneous and free-oxide Fe-Cr microalloys and can beexpected to overcome the limitations imposed by the current methods. In thiswork the formation of Fe-Cr microalloys by ultrasonic treatment at a frequency of20 kHz in toluene liquid is presented. In the synthesis procedure, the proceduresteps followed were: (1) the treatment of precursor particles (Fe, Cr) throughultrasonic method with a time-variation, followed by (2) the same time-varyingultrasonic treatment on the admixture of these specially prepared precursorparticles in order to obtain the Fe-Cr microalloys, and (3) finally, the lubricantlesscompaction method was employed on these precursor particles admixturefollowed by sintering process inside quartz tubes to obtain a bulk of Fe-Cr alloy.Observations of the specially prepared precursor particles using ultrasonictechnique were carried out by scanning electron microscopy (SEM) method.Observation of the precursor mixture of Fe-Cr particles mixture treatedultrasonically was performed using a SEM-EDS (energy-dispersive spectroscopy)apparatus, a X-Ray diffractometer and accompanied by the Rietveld analysismethod, and transmission electron microscopy (TEM)-selected area electrondiffraction (SAED) apparatus. The bulk of Fe-Cr alloy were observed using SEMEDS,XRD accompanied by analysis by the Rietveld method, true densitymeasurement, and Vickers microhardness testing. Ultrasonic treatment has causedFe particles to form agglomerations, an interparticles neck formation, and a fusingamong the particles. The size of the Fe particles increased (>2μm) after 40 hourstreatment. The agglomerated Cr particles experienced fragmentation, surfaceerosion, and reduction of particle size. The agglometrated Cr particles fullydisintegrated into Cr microparticles (<2μm) after 63 hours treatment. The mixtureof Fe-Cr forming cohesive (Fe-Fe, Cr-Cr) and adhesive (Fe-Cr) particles, formingcompletely (after ultrasonic treatment for 20 hours) and partially (after ultrasonictreatment for 50 hours) Fe-Cr microalloys. The complete formation of Fe-Cr microalloy was possible with an equal particle size of the precursor Fe and Cr(approximately <2 μm). The bulk of Fe-Cr alloy results are homogenous andoxide-free. For two-step sintering, its density (in gr/cm3 unit) is 8.655 for type O,is 8.179 for type B, and is 8.196 for type A, and for one-step sintering its densityis 7.678 for type O, is 7.587 for type B, and is 7.092 for type A. The greatestmicrohardness number of 88 VHN is of type B (one-step sintering), and of 81VHN is of type A (two-step sintering). The ultrasonic treatment process has apositive impact, with respect to both of quality and time-consumption to finish theFe-Cr alloying process. Therefore the ultrasonic method can be relied upon as analternative method in the production of Fe-based alloys to solve problems inhomogenization and oxidation encountered in current methods, Fe-Cr alloys have the potential for use as an interconnection material forsolid oxide fuel cell (SOFC) due to its being resistance to high temperatures.Synthesis methods of Fe-Cr alloy continue to be developed in order to obtain amethod that is both effective and efficient. Presently, the synthesis of Fe-Cr alloysinclude the casting, the powder metallurgy, and the mechanical alloying method.These methods have several drawbacks such as inhomogeneity in the resultingproducts, oxidation, and require a very time-consuming process to accomplish. Inorder to minimize this problem, it is important to produce Fe-Cr microalloys. Fe-Cr microalloys exhibit phase stability and good mechanical properties. Ultrasonicmethods can be used in the synthesis of homogeneous microalloys by employingthe ultrasonic sound waves. Ultrasonic sound waves will generate cavitationbubbles. Any cavitation collapse can be considered as a micro reactor in which atemperature of about 4737 oC and a pressure of about 1000 atm a very rapidlycreated, thereby generating a shock wave. Thus, the ultrasonic method can beused in producing homogeneous and free-oxide Fe-Cr microalloys and can beexpected to overcome the limitations imposed by the current methods. In thiswork the formation of Fe-Cr microalloys by ultrasonic treatment at a frequency of20 kHz in toluene liquid is presented. In the synthesis procedure, the proceduresteps followed were: (1) the treatment of precursor particles (Fe, Cr) throughultrasonic method with a time-variation, followed by (2) the same time-varyingultrasonic treatment on the admixture of these specially prepared precursorparticles in order to obtain the Fe-Cr microalloys, and (3) finally, the lubricantlesscompaction method was employed on these precursor particles admixturefollowed by sintering process inside quartz tubes to obtain a bulk of Fe-Cr alloy.Observations of the specially prepared precursor particles using ultrasonictechnique were carried out by scanning electron microscopy (SEM) method.Observation of the precursor mixture of Fe-Cr particles mixture treatedultrasonically was performed using a SEM-EDS (energy-dispersive spectroscopy)apparatus, a X-Ray diffractometer and accompanied by the Rietveld analysismethod, and transmission electron microscopy (TEM)-selected area electrondiffraction (SAED) apparatus. The bulk of Fe-Cr alloy were observed using SEMEDS,XRD accompanied by analysis by the Rietveld method, true densitymeasurement, and Vickers microhardness testing. Ultrasonic treatment has causedFe particles to form agglomerations, an interparticles neck formation, and a fusingamong the particles. The size of the Fe particles increased (>2μm) after 40 hourstreatment. The agglomerated Cr particles experienced fragmentation, surfaceerosion, and reduction of particle size. The agglometrated Cr particles fullydisintegrated into Cr microparticles (<2μm) after 63 hours treatment. The mixtureof Fe-Cr forming cohesive (Fe-Fe, Cr-Cr) and adhesive (Fe-Cr) particles, formingcompletely (after ultrasonic treatment for 20 hours) and partially (after ultrasonictreatment for 50 hours) Fe-Cr microalloys. The complete formation of Fe-Cr microalloy was possible with an equal particle size of the precursor Fe and Cr(approximately <2 μm). The bulk of Fe-Cr alloy results are homogenous andoxide-free. For two-step sintering, its density (in gr/cm3 unit) is 8.655 for type O,is 8.179 for type B, and is 8.196 for type A, and for one-step sintering its densityis 7.678 for type O, is 7.587 for type B, and is 7.092 for type A. The greatestmicrohardness number of 88 VHN is of type B (one-step sintering), and of 81VHN is of type A (two-step sintering). The ultrasonic treatment process has apositive impact, with respect to both of quality and time-consumption to finish theFe-Cr alloying process. Therefore the ultrasonic method can be relied upon as analternative method in the production of Fe-based alloys to solve problems inhomogenization and oxidation encountered in current methods] |
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