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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
Background: Anodization
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
Background: Anodization
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
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
~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.
20
(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.
20
(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.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 4hrs.)
Parameters: 1st Anodization (3wt.%, 12.5V, 4 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)
Updated Trend Analysis
2nd 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.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 4hrs.)
Parameters: 1st Anodization (3wt.%, 12.5V, 4 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)
Updated Trend Analysis
3rd 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.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 4hrs.)
Parameters: 1st Anodization (3wt.%, 12.5V, 4 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)
Updated Trend Analysis
Round Comparison - Membrane Thickness (First Anodization):
Parameters: 1st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 4hrs.)
Updated Trend Analysis
Round Comparison - Membrane Thickness (Second Anodization):
Parameters: 1st Anodization (3wt.%, 12.5V, 4 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)
Updated Trend Analysis
1st Round of Pore Diameter (First/Second Anodization):
Parameters: 1st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 4hrs.)
Parameters: 1st Anodization (3wt.%, 12.5V, 4 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)
Updated Trend Analysis
2nd Round of Pore Diameter (First/Second Anodization):
Parameters: 1st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 4hrs.)
Parameters: 1st Anodization (3wt.%, 12.5V, 4 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)
Updated Trend Analysis
Round Comparison – Pore Diameter (First Anodization):
Parameters: 1st Anodization (3wt.%, 12.5V, 2/4/6/8/10 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 4hrs.)
Updated Trend Analysis
Round Comparison – Pore Diameter (Second Anodization):
Parameters: 1st Anodization (3wt.%, 12.5V, 4 hrs.) 2nd Anodization, Pt.1 (2.7wt.%, 20V, 30 min.)
Transitional Time: 20 min.
Pt. 2 (2.7wt.%, 60V, 3/6/9/12/15 hrs.)