M.S. Thesis Presentation

Tapered Porous Structure in Anodic Aluminum Oxide (AAO) Tubular Membrane using a Two-Step Hard

Anodization Process

Elkin Mejia

February 5, 2008

Outline

BackgroundObjectiveProcedureProcessing ParametersTrend Analysis/ConclusionsFuture Work

Background: Hemodialysis

Semi-permeable Membrane: Separates waste from needed proteins and blood cells BLOOD: Enters Tube Side Red Blood Cells White Blood Cells Albumin (Protein)

WASTE: Urea (small) Creatinine B2 Microglobin (middle) Phosphate

Dialysate: Enters Shell Side, removes

Background: Anodization

Electrolyte process used to increase thickness of the natural oxide layer on the surface of a metal

Source: Elizabeth Grasing

Anodic Aluminum Oxide (AAO)

Contains an array of nanometer-sized pores

Anodizing of an Aluminum Substrate:

Porous Material: Extremely well ordered honey comb structure pore arrays

Anodization ranges:

(A) Low Field Anodization (0 to 10 V)

(B) Mid-Field Anodization (10-40 V)

(C) High Field Anodization (40-150 V)

Background: Membrane Comparison

Current Membranes acting as artificial kidneys: Synthetic Polymers

Anodic Aluminum Oxide (AAO) Membranes:

Non-uniform and Irregular shape

Circular and Regular shape

Objective

Study the effect of transitioning the anodization of aluminum from low to high voltage

• Pore structure/diameterRemove a larger percentage of waste at a faster rate. Restrict a wide range of molecules that are needed by the human body

• Membrane thickness Facilitate mechanical handling Compliments fluid separation applications

Goal: Pore size ~ 20 nm

Goal: Thickness ~ 60 µm

Procedure: Processing Stages

As-Received Tube

After Electro-polishing

Addition of Polymer Coating

1st Anodization: (Pore Diameter/ Dimple formation)

Barrier Layer Etching

2nd Anodization :Pt.1 (Protective Porous Oxide

Layer is produced)Pt. 2 (Membrane Thickness

Growth)

Removal of polymer

Ends Sealed with Parafilm

Aluminum Etching

Removal of Parafilm

Source: Elizabeth Grasing

Main Chamber

Procedure: Processing Parameters

1) Electrolyte Solution: H2SO4 (1st Anodization) H2C2O4 (2nd Anodization)

2) Electrolyte Concentration: 3wt.% H2SO4 (1st Anodization) 2.7wt.% H2C2O4 (2nd Anodization)

3) Voltage: 12.5 V (1st Anodization)

20 – 60 (2nd Anodization, Part 2)

20 V (2nd Anodization, Part 1)

4) Time: 2-3hours (1st Anodization)

3-4 hours, 10 hours (2nd Anodization)

Procedure: Instruments

• Scanning Electron Microscope (SEM): Inner/Outer Pore Structure/Diameter

3) Membrane Morphology

• Light Optical Microscope (LOM): Membrane Thickness

2) Mercury-in-GlassThermometer: Temperature

1) NI USB-6008 DAQ/Lab View: Current

Trend Analysis

(A) Transitional Time: Trials C(S11), D(S12)

Parameters: 1st Anodization (3wt.%, 12.5V, 2 hours) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)

Pt. 2 (2.7wt.%, 60V, 3 hours)

Trend Analysis

(A) Images of Trials,

C(S11)

D(S12)

~14 µm

~23 µm

Trend Analysis

(B) First Anodization Time: Trials G(S15), E(S13)

Parameters: 1st Anodization (3wt.%, 12.5V) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)

Transitional Time: 20 min. Pt. 2 (2.7wt.%, 60V, 4

hours)

Trend Analysis

(B) Images of Trials,

G(S15)

E(S13)

~24 µm

Trend Analysis

(C) Second Anodization Time: Trials D(S12), G(S15), H(S16)

Parameters: 1st Anodization (3wt.%, 12.5V, 2 hours) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)

Transitional Time: 20 min.

Pt. 2 (2.7wt.%, 60V)

Trend Analysis(C) Images of Trials,

D(S12)

G(S15)

H(S16)

~23 µm

~24 µm

~57 µm

Parameter/Result TableParameters Results

Trials Stages Electrolyte Concentration Voltage Time Transitional Time (min.) Pd (nm) Mt (µm)

C(S11)/D(S12) 1st Anodization 3wt.% 12.5 2 hrs.

2nd Andozation

(Part 1) 2.7wt.% 20 30 min.

8 20 14

20 20 23

(Part 2) 2.7wt.% 60 3 hrs.

G(S15)/E(S13) 1st Anodization 3wt.% 12.5 2 hrs. 20 24

3 hrs. 20 24

2nd Andozation

(Part 1) 2.7wt.% 20 30 min.

(Part 2) 2.7wt.% 60 3 hrs.

D(S12)/G(S15)/H(S16) 1st Anodization 3wt.% 12.5 2 hrs.

2nd Andozation

(Part 1) 2.7wt.% 20 30 min.

(Part 2) 2.7wt.% 60 3 hrs. 20 23

4 hrs. 20 24

10 hrs. 22 57

Trend Analysis

Conclusions:

Variation of time in the first anodization did not affect the pore diameter/membrane thickness

A pore diameter of 20nm and a thickness of 57µm was obtained at a voltage greater than 12.5 V in the 2nd Anodization under 24 hours

A linear growth rate of the membrane thickness to the 2nd Anodization (Part 2) time was confirmed

Future Work

Repeat previous experiments to determine an error bar

Objective: Optimize pore diameter (~ 20 nm) and membrane thickness (~ 60 µm) at a high voltage (60V) in an efficient process by varying the time parameters

The following are experiments to be conducted in order to conclude a trend analysis in the variation of time (anodization, transitional) and provide sufficient data to prove the above contribution

Complete further experiments to complete trend analysis charts

Utilize image J software to accurately measure pore diameters

Vary the transitional time to determine if the membrane thickness increases

Vary the first anodization to study the affect of the pore structure

Vary the second anodization time to determine the optimal membrane growth rate

Updated Trend Analysis

1st Round of Membrane Thickness (First/Second Anodization):

Parameters: 1st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)

Pt. 2 (2.7wt.%, 60V, 4hrs.)

Parameters: 1st Anodization (3wt.%, 12.5V, 4 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)