Electroplating Nitinol for Soldering





Introduction: Electroplating Nitinol for Soldering

About: Chemistry and electronics have been a staple in my life since I was 8 and have pretty much been my only hobbies although I have dabbled in herbalism, art, music, and various other areas as well.

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!

Initial chemicals:

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:

  1. Copper chloride solution with an excess of hydrochloric acid
  2. Nitinol wire
  3. Sandpaper
  4. Power source (I used a 1500F supercapacitor charged up to ~1.7v)
  5. Multimeter for measuring voltage
  6. Soldering iron and stand
  7. Solder (I used 60/40 lead/tin electrical solder)
  8. Random bits of wire
  9. Scrap copper
  10. A small beaker or other suitable container
  11. Wire cutter
  12. Paper towels or a rag
  13. 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)
  14. 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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    2 Discussions

    In my experience, lead is a good electrode, but only for sulfates. I
    was doing an experiment a while back trying to generate electricity from
    carbon through a chemical process (charcoal is cheap especially when
    you have a way to make it and 10 acres of trees to work with haha).
    Basically what I was trying to do was use the charcoal to carbothermally
    reduce a metal oxide, then by essentially making an air battery,
    oxidizing that metal, generating electricity and the metal oxide thus
    completing the cycle and one of the metals I tried was lead considering
    it melts at an easily achievable temperature (although the reduction
    temperature is high (~1200C) which lead to the abandonment of lead in
    favor of copper which has a much higher melting point but a much lower
    reduction temperature (~250C)). One of the solutions I used to oxidize
    the lead was sodium chloride solution, it was rather slow and the power output was low but it did work. I've tried electrolysis using lead with the tap water I have and it disintegrates within a couple of hours, even with nothing added to the water to make it more conductive.

    lead electrodes work very well. I had an old car battery that I drained. probably doesn't last like platinum... but works much better than carbon.