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 • Results for Additives of SiO2, Al2O3 to ZrO2 • Theoretical Calculations • Experimental Results • OOF2: Finite Element Modeling (FEM) • Results • Conclusion
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
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?
YSZ Silica/ Alumina Preparation Methods Milling Drying Sieving Packing into Molds CIP’ing Bisque Firing Polishing Machining SEM Imaging Sintering Testing
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
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
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
Grain Size Analysis • Using ImageJ, we analyzed the grain size for all SEM Images. . • Smaller grain sizes should yield higher Flexural Strength
YSZ+ 20 vol% Al2O3 YSZ+ 10 vol% SiO2
OOF2: Finite Element Analysis • Modeling ofmicrostructures • Computes stresses, strain, and temperature gradients
Original SEM Image • YSZ +10 vol. % Al2O3 • Altered colors for easier processing and viewing Zirconia—Yellow Alumina—Blue
Finite Element Modeling • Microstructure of YSZ + 10 vol% Al2O3 • Creation of the Skeleton and FE Mesh
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
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!
Acknowledgements • Professor Martha Mecartney, Faculty Mentor • Jesse Angle, Graduate Student Mentor • Edward Su, Technical Support