Instructables
Picture of Corrosion Resistant Micro-Bath Heater
This instructable will show you how to make a miniature heating element which is resistant to corrosion. I'm hoping to use it in conjunction with cupric chloride for etching printed circuit boards. You can either screw it into a side-hole of an HDPE container, with teflon tape acting as a washer, or you can lower it into the bath.

I decided to use very small containers, which I found in the form of powdery makeup for little girls at a local dollar store. If you want to go smaller, perfume sample vials may be used. If you want to go larger, baby food jars may work.

As a minimum, you will need an assortment of NiChrome wire, which can be purchased online from various vendors since it is the primary mechanism for converting electrical energy into heat. Everything else assists in getting power to the container and in distributing the heat.

Step 1: Size Dowel

Picture of Size Dowel
05D - Cut Dowel.jpg
05E - Sand Edges.jpg
In this step, you will need to find a small container and a dowel with a diameter smaller than the mouth of the container. It is important that:
  1. The container be made of glass so that it's resistant to corrosive liquid -AND- has good thermal conductivity.
  2. The dowel is made of hardwood since lots of tension will be present with the nichrome wire.
After, saw a piece off the dowel which will fit nicely into the container.

Step 2: Make Pattern

Picture of Make Pattern
06B - Tangent.jpg
06C - Tangent.jpg
06D - Tangent.jpg
06E - Divide.jpg
In this step, create a template for drawing side notches on the dowel.
  1. Trace the dowel along its circumference.
  2. Use a right-angle to draw a tangent on two edges of a circle.
  3. Use a right-angle to complete the square around the circle.
  4. Draw a line from opposite corners of the square.
 
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wow this is really interesting, can you elaborate a little more about boiling the dowl in a laxative mineral oil to carbonize it? what oil did you use? do you have a link?
vreinkymov (author)  amandaghassaei2 years ago
You can get the mineral at most pharmacies and some Walmarts. It's usually in the laxative isle and is used as a stool softener. Here's a link I found to one online:

http://www.walgreens.com/store/c/walgreens-mineral-oil-intestinal-lubricant/ID=prod5593964-product

If you were to heat up the dowel with the nichrome wire without treating it, it would create smoke by burning the wood. Additionally, wood is VERY porous (even hardwood), so it would start releasing gasses when heated. This would push whatever you have out of the little glass jar.

To treat the wood, I increased the temperature over 1-2 hours from 250 - 450 or 500F (not sure exactly) while having the piece of wood floating in the oil.

The idea here boils down to this:

1. Oil will displace any gases that are released.
2. Heat will burn off anything that would smoke.

What you should notice is that as you ramp the temperature up, at first there are LOTS of bubbles, but then, as time goes on there are fewer and fewer as the wood carbonizes.

Since the heating element won't nearly get as hot as the treatment, the carbonized piece should not emit any gasses when heated. Surprisingly, the wood is STILL very hard, even after the treatment. I wouldn't try sawing it, but it's definitely nowhere to being as brittle as a piece of charcoal.
ironsmiter2 years ago
if we're better off NOT building it... :-)

Try the heating element from a travel hair dryer.
It's already shaped, and has that nifty x-board of insulator material in place.
Make sure the container is highly heat resistant. maybe a small canning jar?