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