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Thermal Shock Resistance of Oxygen Sensors

Thermal Shock Resistance of Oxygen Sensors. Marvin Chan, SURF IT Fellow Jesse Angle, Graduate Student Mentor Professor Mecartney, Faculty Mentor. Outline. Introduction Oxygen Sensors Problem of Thermal Shock Preparation and Test Methods

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Thermal Shock Resistance of Oxygen Sensors

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  1. Thermal Shock Resistance of Oxygen Sensors Marvin Chan, SURF IT Fellow Jesse Angle, Graduate Student Mentor Professor Mecartney, Faculty Mentor

  2. Outline • Introduction • Oxygen Sensors • Problem of Thermal Shock • Preparation and Test Methods • Results for Additives of SiO2, Al2O3 to ZrO2 • Theoretical Calculations • Experimental Results • OOF2: Finite Element Modeling (FEM) • Results • Conclusion

  3. Oxygen Sensors • Oxygen sensors • Made of yttria-stabilized zirconia (YSZ) ceramic • Used to determine correct fuel to air ratio in internal combustion engines • Problems • Oxygen sensor operates most efficiently at 900°C • System must be heated slowly from ambient to optimal operating temperature • fuel is wasted • carbon emissions are high

  4. Problem of Thermal Shock • YSZ will fracture if heated or cooled too quickly. • The property that measures resistance to fracture upon heating/cooling is called thermal shock resistance. • Research Question: How to improve and predict the thermal shock resistance of YSZ?

  5. YSZ Silica/ Alumina Preparation Methods Milling Drying Sieving Packing into Molds CIP’ing Bisque Firing Polishing Machining SEM Imaging Sintering Testing

  6. Test Methods • Samples analyzed via: • SEM imaging of Microstructure • Thermal shock quenching and 3-Point bend tests for strength • Compare strength after quenching to unquenched samples

  7. Calculations of Thermal Shock Resistance σ=Strength E=Elastic Modulus α=Thermal Expansion Coefficient ν=Poisson’s Ratio • Thermal Shock Parameter (R): • Improve thermal shock resistance by: • Increasing fracture strength(σ) • Decreasing Poisson’s ratio (ν) or elastic modulus (E) or thermal expansion coefficient (α) • Idea: Make a composite! Use Rule of Mixtures

  8. SEM Experimental Results • Grain Size Analysis using ImageJ software YSZ Smaller grain size for ceramics usually gives higher strength. YSZ with 10 vol. % SiO2 Average Grain Size 9.2 µm Average Grain Size 2.4 µm

  9. Grain Size Analysis • Using ImageJ, we analyzed the grain size for all SEM Images. . • Smaller grain sizes should yield higher Flexural Strength

  10. YSZ+ 20 vol% Al2O3 YSZ+ 10 vol% SiO2

  11. OOF2: Finite Element Analysis • Modeling ofmicrostructures • Computes stresses, strain, and temperature gradients

  12. Original SEM Image • YSZ +10 vol. % Al2O3 • Altered colors for easier processing and viewing Zirconia—Yellow Alumina—Blue

  13. Finite Element Modeling • Microstructure of YSZ + 10 vol% Al2O3 • Creation of the Skeleton and FE Mesh

  14. Modeled for Strain • Enter Boundary Conditions and Material Parameters Max Stress • Boundary Conditions: • *Apply compressive stresses left, right and from below Min Stress 10 vol. % Al2O3; Strain Field

  15. Conclusions • YSZ + 20 vol% Al2O3 had the highest Flexural Strength and highest Thermal Shock Resistance • YSZ + 10 vol% SiO2 and YSZ +10 vol% Al2O3 had less than ideal results—led to negligible improvements • OOF2 models areas of stress, i.e. compression and tension for thermal shock-continuing work in the fall!

  16. Acknowledgements • Professor Martha Mecartney, Faculty Mentor • Jesse Angle, Graduate Student Mentor • Edward Su, Technical Support

  17. Questions ?

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