The REU work was supported through the National Science Foundation: Division of Materials Research REU site program under grant number 0453554.

Acknowledgements:

Introduction

Investigation of Effect of Ammonia Treatment on Surface Morphology of

Platinum Catalysts for Use in “Swiss Roll” Reactors.

San Luis Obispo

Research Question

How is ammonia modifying the Pt catalyst surface and how does the modified surface morphology affect the catalyst’s affect on the ignition temperature, extinction limits vs Reynolds number, and thermal behavior?

Patrick J. Hyland and Dr. J. Ahn

School of Mechanical and Materials Engineering at Washington State University, Pullman, WA

Hydrocarbon fuels have a much higher energy storage density than batteries. (e.g. propane, 46.4 MJ/kg) >> batteries (≈ 0.5 MJ/kg for Li-ion)

Mesoscale or microscale fuel electrical power conversion devicewould provide much higher energy/weight than batteries for low power applications, even at very low efficiencies

Problems working at micro-scale that Swiss rolls reduce / eliminate

Heat losses to walls - flame quenching, efficiency loss

Friction losses in devices with moving parts

Precision manufacturing and assembly difficult

Swiss roll could be used as a power source for:MEMSmicro scale devicesmobile devices (cell phones, laptops, handheld GPS)

Applications

Swiss Roll Reactors are thermally insulating, have no moving parts and can use solid oxide fuel cells to generate electrical energy.

MethodSample treatment - Pt samples were placed in combustion chamber

of 1d Titanium reactor. Treatments involved combusting gaseous fuels (air, propane, ammonia) which were pumped into the Swiss roll reactor and ignited using an induction heating device.

Different factors were varied to affect the surface modification Air/Fuel/Ammonia Mixtures Combustion Durations Combustion Temperatures (between ~300 C and ~1200 C based

on varying fuel velocity and mixtures)

Flow Control System

PC control and data acquisition using LabView / NI data modules

Mass flow controllers for fuel, ammonia & air

Thermocouples to measure reactor temperature

Relevant LiteratureJeongmin Ahn, and Paul D. Ronney, Effect of Wall Thermal Conductivity and Thickness on the Performance of Heat-Recirculating Reactors, to appear in the Combustion and Flame, (2007).

Secondary Electron images from a Scanning Electron Microscope (SEM) were used to examine the morphological surface features of Pt relevant to this project.

SEM Imaging

3d Swiss Roll

1d and 2d designs had been developed for Swiss Roll reactors. It had not been discovered how to design one in 3d.

Theoretically, a spherical design would have the most efficient heat loss reduction. It would insulate the combustion chamber in every direction. A tetrahedral design was worked on because it was easier to design and manufacture.

Using Solidworks, a 3d tetrahedral model was developed. Using Blender and Pepakura Designer paper models were created. The next step will be to create a testable reactor out of Kapton film.

2-Dimensional

3-Dimensional

3-Dimensional (New)

Future Work

Analyze how NH3 concentration and Pt surface pretreatment affect surface etching,

Analyze effect of new surface morphology on combustion behavior

Examine Post treatment combustion natures

Observations

Some surface structures formed from: Plastic deformation Deposits (from combustion products or chamber materials

contribute to Pt etching) Etching of grains Etching of grain boundaries

Surface deposits affect etching Grain surface morphologies based on grain orientation and

crystallography Some grains reminiscent of twinned microstructures Surface changes may not always be affected by treatment history

Untreated Pt– microstructure based on rolling used to form foilAmmonia treatment etches surface of grains and grain boundaries under certain conditions.

Previous Work

Prior tests noted changes in the surface morphology possibly due to NH3 treatments. I observed similar structures in more recent work.

Grain Boundary / Surface Etching90 Air / 10 NH3, 30 min, 320 C

Deposits modify surface etching90 Air / 10 NH3, 30 min, 320 C

Surface deposits similar to prior work85 Air / 15 NH3, 30 min, 370 C

Possible non-crystallographic based etching90 Air / 10 NH3, 30 min, 320 C

Prior notes of modified surface morphology

Prior notes of possible crystallographic based etching / deposits

Grain / Boundary etching90 Air / 10 NH3, 30 min, 320 C

Grain Surface Etching90 Air / 10 NH3, 30 min, 320 C

Reminiscent of twinned microstructures90 Air / 10 NH3, 30 min, 320 C

Possible Porous Etching85 Air / 15 NH3, 30 min, 370 C

Surface structure orientation85 Air / 10 Propane/ 5 NH3, 30 min, 700 C

Crystallographic Based Morphology85 Air / 15 NH3, 30 min, 370 C

Grain Boundary / Surface Reformation85 Air / 14 Propane/ 1 NH3, 30 min, 350 C