Electroplating with Zinc (for under $10)

Electrolytic zinc-plating can be performed with common household & hardware store materials. Zinc is a cheerful light-colored metal, very much the “aluminum” of its day. I found this overview ( sorry, it’s a dead link now, try this one instead), and started working with it…

The preparations involve removing the zinc from batteries, making zinc chloride (zinc + HCL), making ammonium chloride (ammonia + HCL), etching the plating target slightly, then applying low voltage to both the “donor” zinc anode and the “target” metallic workpiece with both immersed in electrolyte solution made from water, zinc chloride and ammonium chloride. The results are easily achieved and can be used to apply a pattern of zinc to a larger piece of copper to produce a decorative pattern of brass.

Materials needed:

• Muriatic Acid (AKA about 30% HCL), $2.50/qt. at the hardware store
• 10% “janitorial strength”, non-sudsy plain ammonia, $2.50/qt. at the hardware/grocery store
• Several” dead” AA through D size batteries, both carbon-zinc (for zinc anode material) and alkaline (for granular zinc to make zinc chloride).
• Nitrile gloves (‘the alkali in “alkalines” is stiff enough stuff that you really should wear some’, sez the guy that bathes in corrosive reagents), respirator mask or goggles, gloves, an assistant (never enough hands when you juggle dangerous chemicals), an ambulance chaser (to bring the scurrilous purveyor of this illustrative article to justice for “making you hurt yourself”), good sense, and a well ventilated work area that can withstand moderate chemical, mechanical and metaphysical abuse.

Steps in the preparation:

A. Prepare the Zinc Chloride

1. Harvest zinc & hydroxide paste from alkaline batteries (see Steampunk and the Golden Penny post for one method). (This is a “gloves and goggles” process, no licking your fingers or rubbing your eyes, OK?
2. Put the zinc+hydroxide paste on a coffee filter in a funnel, and let a lot of water trickle through it slowly to get rid of the hydroxide. Then, give it a rinse or two with some sodium bicarbonate/water mixture (a tablespoon/quart), then another clean water rinse. We don’t want potassium hydroxide reacting with the HCL in the next step. (If you were doing this in a chemistry lab you would dry and weigh the zinc, and calculate the stoichometry to arrive at measures for the rest of this process. You can do this for extra credit, if you want to, but this isn’t chemistry class.
3. Pour a small quantity of muriatic acid into a suitable vessel (ceramic coffee cup or glass ashtray), then slowly add little bits (pinches) of the zinc granules to the acid until it stops dissolving. Undissolved zinc at the bottom of the vessel assures you have converted all the free HCL (and most of the Zn) to ZnCl2. (No tasting it or using as eye drops allowed, but it is now much less active than the precursor HCL was).

B. Prepare the Ammonium Chloride

Note: I just found that sellers of stained glass supplies carry blocks of sal ammoniac (ammonium chloride) for use as tip cleaners for soldering irons, and it’s really cheap there (a few dollars for a 1/4 pound cake), so that will be my source of choice.

But, otherwise, in the spirit of DIY: if you place a stoichometricly correct amount of ammonia in non-reactive (glass) container, then SLOWLY drip HCL (muriatic acid) into it, you will make ammonium chloride. Think “reverse double-boiler”, since the reaction is exothermic, okay?

Still, the “white smoke demo” (see this for details) is fun to show the kids, as long as you have the ammonia & HCL on hand.

The gang at finishing.com know more details and they are professionals at this stuff, okay?

But, to make a long story short, if you combine 30 parts (always by weight!) of zinc chloride with 120 parts of ammonium chloride with 1000 parts of water, you’ve got a workable solution for electroplating zinc. Run with the positive (+) wire on the zinc anode and the negative (-) wire on the item to be zinc plated. Add some (say 5% of total solution weight) of a glycol (like anti-freeze), and you’ get a brighter zinc finish… if you don’t apply more current that is needed (say 400 milliamps to 1200 milliamps at less than 12 volts). Calculations of coulombs are required (the Faraday Equation), ask a friend for help if you can’t work this out.

Tags: steampunk