Introduction: Electroplating Nitinol for Soldering
Nickel titanium alloy or nitinol can be about impossible to solder to with out fancy fluxes or ultrasonic wave soldering equipment. One way to get around this to at least get an electrical connection is to plate it with a coat of copper. Mechanically, this coat of copper doesn't have quite enough strength but its good enough for lower stress applications and will be strong enough for a good electrical connection as long as you don't pull on it too hard.
The main reason that I use nitinol as an electrode is its the only one I have found to hold up in electrolysis with our tap water so far. Carbon dissolves, gold oxidizes and forms a nice white powder, and there's no hope for nickel, lead, copper, aluminum, iron, zinc, tin, magnesium, or stainless steel. Those are some of the cheaper ones used in the high corrosion environment of electrolysis(except gold). I haven't tried straight titanium, platinum, rhodium, or palladium yet but I'm sure they would work as well. The latter three are quite expensive and I didn't have any titanium electrodes laying around so I went with superelastic nitinol wire considering I had about 20ft of it laying around doing nothing at the time.
One thing to note is that for electrode use, nitinol is good only for oxidizing conditions such as the positive electrode in electrolysis but not so good as the negative electrode unless very low currents are used. The reason for this is that the titanium will form titanium hydride, a very brittle compound, which will result in flaking and eventual disintegration of the electrode (personal experience).
I originally tried a copper acetate electroplating solution but after that didn't work, I switched to a copper (II) chloride solution with an excess of hydrochloric acid which produced excellent results in my opinion
Disclaimer: I hold no liability for anything resulting from your use of the information or lack of information contained within this instructable. You have been warned!
1. Hydrochloric Acid (C.A.S # : 7647-01-0)
2. Water (yes it is considered a chemical) (C.A.S#: 7732-18-5 IUPAC Name: Oxidane)
3. Copper (C.A.S#: 7440-50-8)
4. Copper (I) Chloride (C.A.S#: 7758-89-6)
5. Copper (II) Chloride (C.A.S#: 7447-39-4)
6. Nickel (C.A.S#: 7440-02-0)
7. Titanium (C.A.S#: 7440-32-6)
Step 1: Gather Materials
Its time to gather up the materials!
You will need:
- Copper chloride solution with an excess of hydrochloric acid
- Nitinol wire
- Power source (I used a 1500F supercapacitor charged up to ~1.7v)
- Multimeter for measuring voltage
- Soldering iron and stand
- Solder (I used 60/40 lead/tin electrical solder)
- Random bits of wire
- Scrap copper
- A small beaker or other suitable container
- Wire cutter
- Paper towels or a rag
- A way of holding the electrodes in place (I used what is called a "third hand" in electronics. Its basically a couple of clamps on a stand to hold things in place while soldering and such)
- A solderless breadboard (not essential but very handy)
Step 2: Prepare the Electrodes
Sand off any oxidation on the scrap copper to get a good electrical connection and sand what you're going to plate on the nitinol until its shiny.
This step is quite important to the adhesion and quality of the coating. To my knowledge, there are only two coatings that come with nitinol wire, black oxide and uncoated, but even in the uncoated version there is still a layer of titanium dioxide on the surface which must be sanded off prior to plating.
Step 3: Set Up the Electrodes and Wire Them Up
Just as with any electroplating setup, the sacrificial electrode must be connected to the positive and the item to be plated must be attached to the negative. Its also important to check for short circuits before adding electrolyte. Nobody wants a meltdown haha
Step 4: Add the Electrolyte Solution and Hook Up the Power
See pictures. I let it run for about 5 min in the copper chloride solution.
Step 5: Solder the Wire On
Wipe the copper oxide off of the outside of the wire and polish up the copper layer a little, then wrap the copper wire around the electrode and solder. See pictures.
Step 6: Testing
I tested the electrode with one of my electrolyzers and I must say that I'm pleased with the result.
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