Department of Metallurgical and Materials Engineering
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Browsing Department of Metallurgical and Materials Engineering by Author "ÖZTÜRK, Onur"
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Item ELECTROCHEMICAL NITRIDATION OF YTTRIA STABILIZED ZIRCONIA TO PRODUCE NITRIDE CONDUCTING SOLID ELECTROLYTES(2023-01-20) ÖZTÜRK, Onur; DOĞU, DorukThe gradual increase in the world population has many effects, both positive and negative, globally. Due to the increasing population, the amount of carbon emissions per capita is also increasing. If the carbon emissions continue to increase in this way, the world average temperature will increase by 4 ℃ by 2050. With the Paris Climate Agreement, which our country has also signed, this temperature is tried to be kept at 2 ℃. Ammonia is the second most produced chemical in the world, which is used in many fields from the food sector to the energy sector. Ammonia is currently produced by a process called Haber-Bosch. This process takes place at high temperatures and pressure. As a result, it is a production method with a high energy requirement and a high amount of carbon emissions. For these reasons, scientists are looking for alternative production methods. The production of ammonia using electrochemical methods is one of the most promising alternatives. These systems enable ammonia to be produced at low-pressure values. At the same time, the fact that these systems are easily scalable is another advantage. They ensure that the ammonia production can be done onsite and on demand where it is needed, and thus offers a great energy saving. The production method using high-temperature solid oxide electrolytes is one of the most popular methods. Currently, oxide conductive electrolytes and proton conductive electrolytes are used in studies using solid oxide electrolytes. These systems aim to ionize water vapor or hydrogen, which is the source of hydrogen in both systems, and react with nitrogen. But here, due to the strong triple bond between nitrogen atoms, the ionized hydrogens recombine instead of reacting with nitrogen and turn into H2. This reduces ammonia production rate and selectivity. On the other hand, if nitride conductive electrolytes are used, nitrogen can be fed to the reaction site in ionic form reducing hydrogen recombination and increasing ammonia selectivity. Within the scope of this thesis, nitrite conductive electrolytes, which can also solve the problem in the production methods mentioned above, have been developed for the first time. First of all, the reaction system was installed and designed, then the reactor was designed with the help of Autodesk Inventor 2019. 310 stainless steel material was used in the production of the reactor. Glass seal was used as sealing material in the system and crofer mesh was used. The experiments were carried out at 550 °C. Nitrogen ion conduction experiments were carried out using 8%YSZ electrolytes (127- 140-270 µm) of different thicknesses and using an LSM-YSZ (symmetric cell) catalyst. During these experiments, a current scan was made between 0.1-300 mA and it was observed that the cell cracked at high currents. In all experiments, 15 sccm of N2 gas was fed from the cathode side and 20 sccm of He gas was fed to the anode side. The anode gas outlet is connected to the mass spectrometer gas analyzer where the signals are monitored. Nitrogen ion transfer is observed starting around 200 mA. With the data taken at different currents with 40 minutes intervals, faradaic efficiency calculations were made and the maximum efficiency was found around 40% at 300 mA current value. Electrochemical nitridation was also performed using N-Mayenite and Ce-doped LaFeO3 anode catalysts. In addition to the electrochemical nitridation study, powder nitridation studies were also carried out. Nitridation of 8% YSZ and ZrO2 powders under different temperatures, time, and flow rates in N2 rich atmosphere has been tried. In addition to these, ZrO2 powder was tried to be reduced by the carbothermic reduction method.