How Electrodeposition Works - University of Tulsa
How Electrodeposition Works
for
The University of Tulsa
Nanomaterials Workshop
Presented by
Dr. Saibal Mitra
Associate Professor of Physics
Dr. Winton Cornell
Senior Professor Associate of Geosciences
With Help From
Richard Portman
Life Sciences
Michael DeShazer
Vanessa Russo
Suchitra Mutlur
Zhijng Zhang aka Peter
Lora L. Marschall
Nathan Hale High School
Tulsa, OK
How Electrodeposition Works
Electrodeposition is a fairly old technique used to plate metals on metals. The one used here at the University of Tulsa is at least 15 years old. The technology is run by an old DOS computer program called “Headstart.” It has a copyright of 1986 and 1989 but still gets the job done. It was originally run on an XT PC computer using and A and B drives, 8½” floppies and no hard drive. It is now run on a newer computer, which uses PC DOS 2.1 as its operating system and a hard drive. (The DOS window in the new Windows programs will not run this program successfully.)
The computer is connected to an EG & E Princeton Applied Research Model 273 Potentiostat/Galvanostat machine that controls the electron potential across the electrodes. Plugged into that is a box that connects the wires to the electrodes.
In the fume hood there are three electrodes present in a glass beaker filled with distilled water. We will exchange this water filled beaker with one with our electrolyte salt solution. One electrode is the reference electrode that measures and controls the voltage. The second is the counter or positive electrode. (The original second and third electrodes are broken and have been replaced.) It is ingeniously made out of a plastic pipette with a plastic covered copper wire running through it. The third or active electrode is made of the same material as the second except it has an alligator clip attached to the lower end. Very carefully attach the edge of a small substrate steel plate with the alligator clip and make sure about half of it is submerged in the salt solution. We connect the black plastic covered alligator clip to the active negative electrode to complete the circuit. If we touch the substrate or it drops on the floor, we must wash with isopropyl alcohol and rinse with distilled water. (Grease interferes with deposition. If bubbles form around the substrate, we must gently tap the glass container to remove them.)
How Electrodeposition Works
The salt solution is made up of the ionized metal that will plate upon the substrate. In this case the salt solution is made from NiSO4·6H2O or hydrated Nickel II sulfate. We measured out .0526g of NiSO4·6H2O per 200ml of solution and added 1 drop of .1M HCl for the proper pH of 3. We use about 40 ml of this solution per run.
Start the program Headstart by typing “headstrt” and hit enter twice. Select Setup/Run the experiment from the menu and hit enter. Hit the F2 key and type “CA” and hit enter at the prompt for file name. For E1 and E2 type in
”–1500” in mV, current range “-2”, seconds per point “1” and total # of seconds for deposition of “3600” or your variable. Hit enter after each value and deposition begins after you hit enter for the time value. (Make sure the voltage potential number goes from negative to positive as the deposition begins.)
After your sample has run, the program asks for a file name. Do not save but view data by hitting Esc followed by a F4. You are now at the Display Data Menu. In the Plot Format Menu (F1) use the arrow key to select Time in the left most menu and hit enter. Hit F3 to plot current data
for deposition. Read your average current off of the graph and write this down on your data table.
Unhook the black plastic clamp from the active electrode breaking circuit. Remove the active electrode and gently rinse clip with substrate attached with distilled water and let dry. Remove glass beaker with electrolyte solution in it and place another empty beaker there. Using a bottle of distilled water wash counter electrode and reference electrodes with distilled water. Empty the rinse water. And fill again with distilled water and place electrodes in it. Used nickel solution may be poured down the drain.
Place dry substrate in a small, clear plastic box lined with Kimwipe® and label with your initials, date and time. Repeat using different times.
How Electrodeposition Works
In the above experiment every Ni+2 carries 2 electrons.
The current in milliamps varies during the process.
The equation below shows the relationships between the variables. We do not know “n.”
T = (1/nFA)(itM/ς)
T = thickness
n = # of electrons transferred
F = Faraday’s number or 96,485 C/mol
A = Area of electrode or substrate submerged
i = applied current
t = deposition time
M = formula weight (Ni only)
ς = density
By varying the time and trying to keep the other variables constant we hope to get the correct thickness. Voltage is kept constant. Area of submerged electrode varies from sample to sample. Current varies during the process so we use an average. Hence, getting good results is not only a science but is also an art.
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