Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
Browse
3 results
Search Results
Master Thesis Coating of La0.3sr0.7fe0.7cr0.3o3-Δ and La0.3ca0.7fe0.7cr0.3o3-Δ Cathode Layers on Gdc Ceramics by Electrospray Deposition (esd)(01. Izmir Institute of Technology, 2023) Erğen, Emre; Akkurt, Sedat; Ahmetoğlu, Çekdar VakıfHigh temperatures are needed to rapidly transfer of oxygen ions between layers during the chemical energy to electrical energy conversion in solid oxide fuel cells (SOFC). Nevertheless, intermediate-temperature SOFCs are preferred to increase their lifetime and reduce maintenance and production costs. The performance of IT-SOFCs depends particularly on the microstructure and electrochemical properties of the cathode layer. In this study, cobalt-free La0.3Sr0.7Fe0.7Cr0.3O3-δ and La0.3Ca0.7Fe0.7Cr0.3O3-δ cathode layers were coated on GDC ceramic pellets by ESD method. The aim of the thesis was to have better structural and electrochemical properties of coatings than the literature. ESD provides the atomization of liquids with the help of electrical forces. ESD is an effective method for forming coatings with desired compositions. By changing ESD parameters, different structural properties such as reticular, cracked, and dense were obtained. Reticular structures are useful for easier oxygen transfer with increased surface area. Effects of parameters were examined by Plackett-Burman design, and the most effective parameter was found as flow rate. The quality of the coatings was evaluated by quantitative scoring. The 16th sample, which was coated with solution E, got the best score. Parameters of 16th sample were used in the investigation of the effects of different solutions on the coatings. 8 different solutions named A to H were prepared with different solvents and precursor salts. Coating by solution E shows better EIS results than the literature as 0.22 Ω.cm2. Coatings by solution G and A show close values to the literature as 0.29 Ω.cm2, and 0.34 Ω.cm2, respectively.Master Thesis Sintering and Densification Behavior of Gdc Infiltrated Porous Gdc Electrolyte(01. Izmir Institute of Technology, 2021) Tekin, Sinem; Akkurt, Sedat; Ebil, ÖzgençIt is desired that the electrolytes used in solid oxide fuel cells have a dense structure. Ceria-based electrolytes require temperatures of 1400-1500oC to densify. High densification temperatures make this material less in demand despite its good ionic conductivity. In this study, it was aimed to sinter and densify porous GDC scaffolds made of GDC (Gd0.10Ce0.90O1.95) material at low temperatures using infiltration technique. A porous GDC scaffold is first produced by sintering the GDC pellet around 1000oC to obtain an intermediate product ready to be infiltrated by a GDC-bearing solution. Multiple infiltration and drying cycles were intended to fill the pores by GDC nanoparticles which are expected to densify at lower temperatures. Two different groups (infiltrated and non-infiltrated) were formed and their densification behaviors with temperature and infiltration repetition cycles were investigated using a vertical dilatometer. The porous GDC scaffold was infiltrated with a polymeric solution prepared from Ce(NO3)3.6H2O and Gd(NO3)3.6H2O. The prepared samples were sintered at 1400oC. As a result of the experiments, it was observed that the densification decreased with the increase in temperature and infiltration cycles. This is thought to be because the porous scaffold could not be completely dried during the infiltration cycles. This led to the formation of a dense outer layer of GDC and porous inner layer. This dense layer inhibited shrinkage of the pellet during dilatometric analysis. Further studies need to be conducted to fully evaporate the solvent during drying of the infiltrated pellets.Master Thesis Catalytic Combustion of Methanol on Structured Catalysts for Direct Methanol Fuel Cell(Izmir Institute of Technology, 2011) Dönmez, Emel; Şeker, ErolThe major goal of this study is to investigate the effect of metal loading, space velocity and the outside temperature on both the steady state temperature of the alumina supported platinum catalysts and on time to reach at the temperature of 60 oC of a typical direct methanol fuel cell operating temperature in methanol combustion reaction. Alumina supported platinum catalysts were synthesized by using impregnation method and sol-gel made alumina. The methanol combustion reaction was performed in a tubular reactor.The characterization of the catalysts was performed by XRD and BET techniques. Particle size of Pt and surface area of the catalysts were compared before and after the reaction. In this study, it was found that the pure alumina was not active in methanol combustion whereas Pt/Al2O3 catalysts with varying loadings were active starting at room temperature. 2, 3 and 5% Pt loading catalysts showed the similar activity so it is possible that the average crystallite size and the crystallite size distribution of Pt on these catalysts would be similar. The space velocity tests indicated that low space velocity is required to quickly reach at 60 oC and also to achieve the highest steady state temperature for fresh catalyst whereas high space velocity is required to quickly reach at 60 oC and to achieve the highest steady state temperature for reused catalyst. The activity of the catalyst was also tested at sub-room temperatures. It was observed that the steady state temperature of the catalyst decreased and the time to reach at 60 oC increased when the outside temperature was below the room temperature. In addition to the tubular reactor, plate reactor was prepared for the methanol combustion. For this purpose, varying concentration alumina sols were coated on the stainless steel plates. However, optimum coating thickness could not be obtained because of the crack formation and peeling offs; thus, further detailed studies are necessary for obtaining stable coating suitable for the catalytic combustion.