Experimental phase studies in the BaO-SrO-CeO2 oxide system

Energy requirement is rising day by day with developing technology. This phenomena has been becoming irreplaceable for begining of industurial life. Energy consumption is continuning with using fuels after using source of carbon. However, the flue gases and wastes is hazardous for nature. For all these reason, humankind set a target which is production of renewable, continuous and clean energy. Energy production from solar panel, wind turbine and the other clean energy production methods were explored in line with this purpose. These methods have advantages and disadvantages. These renewable energy systems effected from environment. For example solar systems are not productive in the cloudy climates. Powerfull water sources are essential for esthablish of hydroelectric dams and air circulation is necessary for production of wind energy. On the other hand, jeothermal energy is not found in every region. İn brief, environmental aspects have a crucial influence for energy production. Therefore, above-mentioned methods are not in use for continuous and critical energy production in every region. Fuel cell is a solution for this kind of problems. Fuel cells produces continuously clean energy with supplying fuel. These products known as enviromental friendly systems and works efficiently. Fuel cell is a device system which is continuously convert chemical energy to electric energy with electochemical reactions. It consists of anode, cathode and electrolyte like other battery systems. This electrolyte prevents the anode and cathode from electochemical reactions with eachother and transports ion or proton. Hydrogen, methanol, mixing of water and carbon dioxide uses for fuel in these systems. Water is the waste of the fuel cells. The most preffered fuel cells are the solid oxide fuel cells (SOFC) because of the following benefits;  All components are solid. Because of this situation, loosing of electrolyte and electrode corrosion is impossible.  Because of high operating temperature expensive catalyst (platinum and ruthenium) is not a necessity.  Natural gas can use as fuel.  SOFC wastes enviromental friendly.  High efficiency.  Using powerfull fuels.  Fuel cells are not affected from climatic factors. Disadvantages of SOFC are listed below;  High cost installation.  Complex manufacture structure.  Because of high operating temperature, procure the thermodynamicaly stability of anode, cathode and electrolyte are difficult.  Hydrogen is expensive.  Highly flammable systems.  Slow start and shut down process. Production of electrical energy is occured by results of reduction and oxidation. These processes produce electrons or ions. Capability of ion or electron transportation is conducted with high efficieny which is affected by temperature and other extrinsic factors. Ability of working in operating temperature, phase equilibrium and pysical characteristics effect to stability of the system. Type of electrolyte changes by fuel cell types. Generally, electrolytes are proton conducting membranes in the up the date systems. For example, ceramic proton conductor ceramics are used in the solid oxide fuel cells (SOFC). On the other side, polymer proton conductor electrolytes (such as Nafion) is used for low operating temperature fuel cells. Different electrolyte is used in solid oxide fuel cells for decreasing of operation temperature and increasing of conductivity like BaCeO3, SrCeO3, BaZrO3, CaZrO3, Y2O3 ve SrZrO3. Operating temperature of fuel cells can be on high temperature. Because of this situation, understanding of behavior of phases and the other characteristics are very important. There is a lot of study in the literature about phase diagrams and isothermal region. In this study, BaO-SrO-CeO2 ternary phase diagram is constituted for observe anod, cathode and electrolyte thermal stability, predict of interface diagram and conductivity. XRD, SEM and EDS analysis were used. In the experiments, (BaxSr1-x)CeO3 perovskite form is prepared with BaCeO3, CeO2, SrCO3 powders. Powders were prepared with conventional solid-state method. Powders were mixed with alcohol in polyacetal and put ball mill machine with 300 rpm and 3,5 hours parameters. Those specimens dried at 150 oC 24 hours for remowing of alcohol. After that specimens calcinated 775 oC 8 hours and heated to 1100 oC 12 hours. Than powders are pressed with cold izostatic press (CIP) under 400 MPa. Lastly those specimens are sintered 1100 °C, 1200 °C, and 1300 °C 48 hours. Some barium rich specimens melted on the 811 °C. Barium carbonate is heated to 775 °C for change of the structure and composition of this material. This application aims to get rid of from CO2 and obtain BaO. However, this method was not successful for every sample. On the other hand, some barium rich specimens can produced by sol-gel method without carbonate. For understanding of the process discrepancy some specimens are prerpared by sol-gel method which is started with nitrates. Because of this reason sol-gel method is used for synthesis of barium rich structures. Specimens were choosen form different regions of ternary phase diagram. XRD, SEM and EDS analysis were used. As a result, isothermal region is drawn for (BaxSr1-x)CeO3 in 1300 °C . The effect of temperature on solubility is limited. Three phase regions, two phase regions and single phase regions are observed in the isothermal region. In the X composition, it was tried to understand the solubility limits in this region with 0.1 mole changes. In some regions (Ba,Sr)O3 solid solutions are observed in accordance with results of the XRD, SEM/EDS analaysis. In the cerium corner region of phase diagram, (Ba,Sr,Ce)O3 solid solutions are observed. However, BaO and SrO solubility is limited in the CeO2 which is shown by SEM/EDS analaysis results. SrCeO3 and Sr2CeO4 solid solutions were observed in the strontium dense area. Low strength is observed in the some specimens because of the low resistation of hydration of the barium rich specimens.