Like others, I discovered Nyle Steiner's Main Page a while back and soon became excited about several of his experiments. One in particular describes making a homemade device that strongly resembled a Memristor. A Memristor is a two-wire electrical device that stores a binary state (either on or off) in a non-volatile manner. That is, it remembers to stay on or to stay off even when all power is removed from it.
Mr. Steiner starts out telling how he found several brass gun cartridges in an area that smelled of sulfur and that the brass cartridges had acquired a dark coating. He took a few home to study and soon discovered the electrical characteristics that would later lead him to describe his Homemade Memristor.
Follow up experimentation led him to discover that placing brass or copper metal in powdered sulfur caused the black coating to appear on the metal over time. This black coating behaved essentially the same as that on the cartridges. Mr. Steiner tells how to place a piece of aluminum in contact with the coating to create his memristor-like device and how to demonstrate its behavior.
I set out to duplicate the project and have done so on several occasions. Like Mr. Steiner, I started by inserting pieces of metal (copper in my case) into powdered sulfur and found that they slowly acquired the dark coating. I tried other ways to get the copper to take on the black coating. For one, I tried simply rubbing the sulfur powder against the clean copper surface using my fingers, thinking that perhaps a little abrasion of the sulfur particles with the copper would speed things up a bit. That did seem to move the process along a bit more quickly.
Then it occurred to me to try making a slurry of sulfur and water and using that instead of dry sulfur. That simply did not work. When I tried that again, however, substituting Denatured Alcohol for the water, I found that the process suddenly took place in a matter of a few seconds. Therefore, rubbing a slurry of denatured alcohol and powdered sulfur against a clean copper surface causes the black coating to appear right before your eyes. The coating appears to accumulate in thickness rather quickly and seems to be rather soft. If you are not careful, you will soon find it being destroyed by the same rubbing action. Using a light touch can help.
I am not a chemist at all and I have no clue as to why this works so well. So I am just passing it along to anyone who would like to perform similar experiments.
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