An Electroluminescent RectifierNorman Stanley,16 November 2001
Lead and aluminum electrodes are placed in a saturated solution of borax (sodium tetraborate, Na2B4O7). Passing alternating current through the cell (at 120 V AC) oxidizes the aluminum on the positive half cycles. (No reduction takes place in aqueous solution.) The cell becomes a rectifier since the layer of aluminum oxide is a semiconductor. If the plates are observed in a darkened room they will be seen to glow with a uniform soft white luminescence. Presumably this is caused by reverse current leakage, though no individual sparking is seen. Whether it is due to micro-sparking or some more esoteric effect I don't know. Investigating this by making a cell that can be observed microscopically should make an excellent amateur project.
Little note seems to have been taken of this phenomenon but when I reported it in an amateur chemistry journal way back in the late thirties I received a letter from an enthusiastic teen-aged amateur physical chemist in Seguin, Texas by the name of Roland Schmitt. He thought the luminescing rectifier was intriguing. He proposed directing his research to find out what was happening. A war came along about then, we fell out of touch, and I never did learn if Roland had solved the mystery. What he did do was to go on to a distinguished career in physics and public service. He was at one time or another Vice Presidentof Science and Technology at General Electric, President of Rennselaer Polytechnic Institute, and Chairman of the National Science Board. There is nothing wrong with amateur science as a springboard to a professional career.
Condensed and slightly adapted from Norman Stanley's article on the web at...