Viesor Labs

Last week I faced a question whether to purchase an expensive piece of equipment for my research work at the graduate school or use something else. I desperately needed an Ultra-Violet cleaner - an oven that cleans surfaces off any organic contaminants.

First of all, for those who does not know ultra-violet light is a quite dangerous thing and definitely should not be played with without the appropriate protection gear. The ultra-violet that everyone (most people) are happily enjoying during sun bathing times is the most harmless (actually, not really, but not as dangerous as other types of UVs) - called UV-A range (around 400nm wave-lenght). Not that many people realize that there are other UV wavelengths that are way more dangerous than UV-A. Those are UV-B and UV-C ranges (other classifications exist). Luckily the ozone layer that surrounds the earth mostly protects us from those and, understandably, that is the reason why there is a fuss around this topic. If not for the ozone layer - we would be exposed to other UV ranges and they are deadly.

For example, 254nm wavelength excites chemical bonds in organic compounds and dissociates them, while 185nm emission creates ozone out of oxygen. The first wavelength is typically used in the germicidal lamps that are used to kill bacteria. Both of them will damage eyes and skin!!! ( eyes, unfortunately, permenantly!!!! so be very careful if you have to deal with it).

When both of 254nm and 185 nm are present an excellent cleaning effect of inorganic surfaces can be achieved. First decomposes organics while second creates ozone that reacts with decomposed molecules and forms volatile species. This cleaning method is well known in semiconductor industry.

Anyway, back to my problem …. several thousand dollars seemed like a big investment for me, therefore, I had decided to build a UV cleaner myself. Moreover, I did some research and found that some of the germicidal lamps (i think they are usually used for water cleaning and duct cleaning but not sure) are actually dual band (produce both wavelengths). Some are available in a small form factor.

I called the company that manufactures the lamp and asked to ship a balance and a lamp-holder in the package. Luckily that had those as well. Total cost was about 200$.

When the lamp arrived I had to find an enclosure for the UV cleaner.

The former router/hub housing was found in the junk in the lab and seemed like a great fit for the purpose.

Several drilled and routed holes for the power line connector and a power switch, a couple of holes for the lamp holder, a couple of holes for the lamp balance were made first. Next the electrical connections were done in accordance with the lamp and balance manuals.

Unfortunately, I did not make a picture of the bare lamp mounted in the enclosure and thus I am skipping that step. Next, I built a light reflector using bare PCBs: cut the appropriate sizes and soldered together to have a box-shaped frame. Then, I taped that frame to the housing using an aluminum tape.

Additionally, I have made a lamp fixator - something to hold the free end of the lamp in place. I used a battery holder I suppose (not sure) - part that fit :). The purpose of the 4 bolts with standoffs will be clear later - they are for making a sample drawer slide in/out horizontally and not tilt.

The front of the enclosure, thanks to its previous application, already had an opening:

This opening I decided to use as a slot in which a drawer with a sample will be sliding in/out. So the next step was to build that drawer. I used the same approach as for the reflector and used PCB material to build it. Finally, added a handle to it to be usable.

Added a PTFE sheet to protect the metal from the UV rays and the drawer was complete. Ah… forgot, I also put a note on the drawer to remind everyone to be careful.

At this point I tried everything ON and that is how it looked.

After I ran the system overnight I noticed a pretty bad smell inside the system (besides the ozone smell) and I realized that whatever decomposes in the system stayed inside the enclosure as there were no escape paths - so, I decided to build a ventilation into the system.

I used a computer fan - one of our old computers came with it and we never mounted it so it was laying around for ages. It was time to serve it’s purpose.

Drilling holes behind the lamp would serve a purpose of venting the whole enclosure (electronics etc.).

and the mounting holes for the reused part of the fan:

Now, I addressed the UV chamber itself. I drilled holes along the sides of the UV chamber:

Using the rectangular tubing I manufactured the exhaust channels:

Finally, making holes in the plastic fan enclosure and drilling mounting holes for the exhaust pipes completed the exhaust system of the UV cleaner.

The last part was the fan’s power supply - the easiest option for me was to reuse one of the 12V power supplies found in a junk pile in our lab. A “surgery” brought out a transformer with a rectifier and a capacitor - all that was needed.

The problem was that it was a bare transformer with no means of fixating it on/to anything. Brass sheets, a bender, and metal cutters came to help followed by drilling, hammering, and jamming.

Finally, mounting it inside and making the necessary electrical connections:

And that was a final step. Here is the final product

Additionally, for those who interested, here is the effect of the UV on gold:

In normal conditions gold is hydrophobic, in other words, does not wet and a water droplet on the golden surface looks similar to this:

This hydrophobic behavior is explained by organic contamination that present on the surface exposed to usual ambient conditions. However, after 10 minutes exposure to UV, same droplet looks like this:

This indicates that the organic layer has been removed and the surface is covered with a layer of gold oxide that changes the hydrophobic surface into hydrophilic.

Isn’t that fun!!

Tags: research, UV