Silver Deposition on Alumina Membranes

Friday, July 01, 2005

Alteration from original chemical polishing procedure
In addition to chemical polishing using FeCl3 many other solutions can be used. Before trying the FeCl3 solution, I tried different molarities of nitric acid solutions. The first trial revealed a 10mM nitric acid solution was not at a high enough concentration to chemically polish the membrane and remove excess silver. Next, I tried a 5:1 dilution of nitric acid in distilled water. This also appeared to not chemically polish the membrane. Finally, a 2:1 dilution of nitric acid in distilled was tried. This resulted in very fast removal of silver particles from the membrane. That is why I chose another solution for chemical polishing. The FeCl3 solution takes a few minutes to take full affect so, there is more time to monitor the removal of the silver particles from the membrane.


Alteration from deposition procedure
Also, there is another solution/process for electroless deposition of silver on alumina membranes. It requires the membrane be placed in two initiator solutions before being immersed in the silver plating solution. The first initiator solution contained 0.9858g tin(II)chloride dissolved in 100mL distilled water. The membrane was immersed in the first initiator solution for five minutes, then it was placed in another containing silver nitrate dissolved in 100mL distilled water. The purpose of this extra initiator solution is to place a seed layer of silver on the membrane to improve electroless silver plating from the silver plating solution. The silver plating solution remained the same from the prior process I used, 0.6749g silver nitrate, 1.55g cobalt sulfate, 9.91g ammonium sulfate, and 16.33mL ammonium hydroxide. Trifluoroacetic acid can be used to stablize the initiator solution with tin(II)chloride.