How to make a diode?

[electronicsounds]

I mad quite a bit of research but the only results I got were not satisfactory, except for the 'valve metals'. If I were to put an aluminum (as cathode) and iron(as anode) together will it serve as a diode. Another idea is; will it work in a spark gap with two different metals on the two sides without enclosing it in a tube? The only reason I don't want ready made diodes is because I want to build them in a custom shape.
thanks in advance, Karl

[SuperCaviTationIstic]

If you want to construct a high voltage spark gap diode, electrons leave a pointed surface more easily, and collect on a flat surface. Also, electrons are drawn to a magnetic field. put a strong magnet on one side of a plate or rounded surface, and on the opposite side put a point or pyramid shape/array directed at the flat surface. the pointy one is your cathode

[Jetijs]

Here are my observations. I took aluminum and tungsten electrodes and put them in conductive water. If I apply positive voltage to the aluminum and negative to the tungsten, there is a big current flow and much gas is produced, if I reverse the polarity and now the tungsten is positive and aluminum negative, even at 4 times larger input voltages only some miliamps of current will flow. Works kinda like a diode.

[electronicsounds]

thanks

thanks for your help, really appreciate, Karl

[lamare]

Here are my observations. I took aluminum and tungsten electrodes and put them in conductive water. If I apply positive voltage to the aluminum and negative to the tungsten, there is a big current flow and much gas is produced, if I reverse the polarity and now the tungsten is positive and aluminum negative, even at 4 times larger input voltages only some miliamps of current will flow. Works kinda like a diode.

That is how they made diodes in the old days. Benitez talks about this in this patent:
http://www.tuks.nl/pdf/Patents/Benitez/GB121561A.pdf
The last line on page 9 and on.

Also see:
Borax or Baking Soda Rectifier and the glow.
Baking Soda Variable Electrolytic Capacitor.

[tellli]

For Jetijs,

In Benitez patent aluminium is cathode and iron or steel is anode, so I'm puzzled.