Monday, July 04, 2005

LATERAL SECOND ANODIZATION

For the reanodization, we implemented the experimental portion of our research. Rather than using the same stainless steel plate, we instead used a thin stainless steel wire. The diameter of the wire was measured to be 508 micrometers. The same setup was used in terms of securing the aluminum metal as before. However, for the stainless steel a new setup was necessary since the plate was now replaced with a thin wire. So, we decided to mount the wire on a plastic panel of the same proportions as the ones used to secure the aluminum metal (The matching panel sizes would help in aligning the wire with the aluminum metal). The wire was secured to its panel using hydroxyy glue. Since the design of the panel was porous, we were able to protrude a small portion of the wire through one of the holes in the panel. The wire's end was cut off close to the surface to ensure that, once combined, the stainless steel wire and the aluminum metal do not touch. The panel with the steel wire was then combined with the panels securing the aluminum metal. The "device," now different from before, was set for reanodization.
The point of using the thin wire as opposed to the plate was to see whether or not the pores would radially arrange in terms of their diameters and density. Since the cathode is much smaller this second time around, the amount of pores and their respectice diameter would theoretically decrease radially across the metal from the point where the wire is pointed. Whereas the stainless steel plate was applying a uniform amount of voltage across the aluminum metal, the wire is pointed at the center of the sample. It will be interesting to observe the results of the second anodization under the scanning electron microscope.

Sunday, July 03, 2005

STEPS FOR LATERAL ANODIZATION

The steps for our experimental lateral anodization procedure involved basically the same standard steps for the regular anodization. Like the standard, electropolishing was done to level out the surface. And, like the standard, a setup for securing the metal in close range to the cathode was used. However, the variation from the standard was in that we needed to do everything from a lateral direction. So, we electropolished the metal's edge rather than its surface (To ensure that the surface would level properly, we mechanically polished the edges as well prior to electropolishing).
For the first anodization, we would keep the current density constant. Our setup included two panels and two gaskets (The extra gasket was used to ensure that water would not reach the "vertical" aluminum surface from either direction). Screw arrangements were designed so that they would not block the edge of the aluminum metal (the sample) from being exposed. The cathode would we a stainless steel wire wrapped around an arrangement of three screws. The wire would thus essentially provide uniform current to the sample.
For the second anodization, our test for the current density principle will be performed. This time around, we will simply use the wire to point at one end of the aluminum sample. The current would thus continuously decrease as the distance from a point on the sample to it increased. The results of this, we expect, will produce the desired drop in pore size and density across the sample.


Saturday, July 02, 2005

CURRENT DENSITY

In conjunction with our idea to grow pores laterally, we decided to see the effects of current density during the anodization process. What would happen, if we used a cathode, such as a stainless steel wire for example, with a notably small surface area, on a much larger aluminum surface? Since the wire would be aimed at one end of the membrane, there would be a difference in current density across the membrane. In effect, since the current applied over the sample will be nonuniform, we would predict that pore size and density would demonstrate similar variation. Of course, it is not as if the current will be randomly uneven across the sample. As the distance from the wire increases, the current should then effectively decrease. So, in theory, we should see a continuous drop in pore size and density as the distance from the wire increases. This type of concept can be very useful in potentially controlling pore sizes across a piece of aluminum. With control, it can open the door to creating more variation of wires within the same sample of aluminum.

Friday, July 01, 2005

LATERAL ANODIZATION

On March 1, 2005, Cojocaru et. al proposed a novel way of anodizing alumina membranes. Their idea was to grow pores parallel to the surface of the aluminum metal rather than the standard vertical growth of pores. By lining the cathode perpendicular to the aluminum thin film, the desired direction of pore growth was achieved. Their results were strikingly similar to the norm: A uniform, organized arrangement of pores.
Using their findings, we decided to attempt the same procedure in our laboratory. Our intentions, however, are not to exclusively grow pores laterally. But, rather, try to successfully grow pores in both directions on the same sample. Such a structure, with both lateral and longitudinal pores, would provide a potentially very effective nanostructure. Of course, we must first be able to successfully grow lateral pores. This, in itself, is quite an obstacle since the procedure has only yet been introduced. Then, we must be able to deposit metal inside the pores, another roadblock to be weary of.

Tuesday, June 28, 2005

VIEWING IMAGE UNDER SEM

Using the Scanning Electron Microscope (SEM), we were able to observe the results of the aluminum membrane synthesis. The images clearly show that the pores formed and that the anodizations went smoothly. However, we were unable to conclude whether our "radial" experiment worked. Since the sample is so large on a nanoscale, we could not find a specific area of the sample to examine whether the current density and pore size decreased radially as predicted. With more time with the microscope and careful planning prior to that, I think we will be able to later determine more accurate results of our experiment. We did notice that there were smaller pores within the larger ones, similar to the results often seen by applying different voltages to each separate anodization. However, again, our main objective to determine whether current density and pore size decreased radially was not determined conclusively. I think there is an important lesson to be learned here. Time with the SEM is limited and costly. I think careful preparation of the sample prior to microscope use is very important. I think that we should have developed a means of marking the area of the membrane where we targeted the 508 micron stainless steel wire. That way, we would not need to spend relative any time in trying to determine the area perpendicular to the anodization, which could be timely on a nanoscale. Below are two of the images taken from the SEM of the membrane:




Monday, June 27, 2005

REANODIZATION

For the reanodization, the same procedure will be used. The purpose for reanodization, again is to get a uniform arrangement of the pores. Setting up the panels and gasket with respect to the membrane will be unchanged. The procedure will go in similar fashion to the first anodization. The voltage will remain the same as well as the duration of anodization.


Sunday, June 26, 2005

PREPARING FOR REANODIZATION

Re-anodization of the aluminum metal is important so that the pores arrange uniformly and meet the desired configuration. Therefore, the alumina membrane must be removed, restoring the aluminum metal (This would make it possible to re-anodize). We immersed the membrane in 50 mL of chromic acid solution. A regular flask was used to hold the solution and the membrane. The flask was then placed under a condenser, where it would be heated. The reaction with the chromic acid would remove the membrane, preparing us for a second anodization.