marvin chan, surf it fellow jesse angle, graduate student mentor professor mecartney, faculty mentor
TRANSCRIPT
Marvin Chan, SURF IT FellowJesse Angle, Graduate Student MentorProfessor Mecartney, Faculty Mentor
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 ◦ 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
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?
Sintering
Bisque Firing
Machining
CIP’ing
Testing
YSZSilica/
Alumina
Milling
Drying
Sieving Packing into
Molds
SEM Imaging
Polishing
Samples analyzed via: ◦ SEM imaging of Microstructure
◦ Thermal shock quenching and 3-Point bend tests for strength
◦ Compare strength after quenching to unquenched samples
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 Mixturesν E (GPa) α (1/K) k
(W/m*K)
YSZ 0.31 230 10E-6 2
SiO2 0.17 73 0.55E-6 1.4
Al2O3 0.26 370 8E-6 35
σ=Strength E=Elastic Modulusα=Thermal Expansion Coefficientν=Poisson’s Ratio
Grain Size Analysis using ImageJ software
YSZ
YSZ with 10 vol. % SiO2
Average Grain Size 2.4 µmAverage Grain Size 9.2 µm
Smaller grain size for ceramics usually gives higher strength.
Using ImageJ, we analyzed the grain size for all SEM Images. .
Smaller grain sizes should yield higher Flexural Strength
Specimen Avg.
Grain Size (µm)
YSZ 9.2
YSZ+10 vol% Al2O3 5.5
YSZ+ 20 vol% Al2O3 4.2
YSZ+ 10 vol% SiO2 2.4
YSZ+ 20 vol% Al2O3
YSZ+ 10 vol% SiO2
Modeling ofmicrostructures
Computes stresses, strain, and temperature gradients
YSZ +10 vol. % Al2O3
• Altered colors for easier processing and viewing
Zirconia—YellowAlumina—Blue
Microstructure of YSZ + 10 vol% Al2O3
•Creation of the Skeleton and FE Mesh
• Enter Boundary Conditions and Material Parameters
10 vol. % Al2O3; Strain Field
•Boundary Conditions:
*Apply compressive stresses left, right and from below
Max Stress
Min Stress
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!
Professor Martha Mecartney, Faculty Mentor
Jesse Angle, Graduate Student Mentor
Edward Su, Technical Support