Best way to easily make positive ions?


by Kopachris
Tags: easily, ions, positive
Kopachris
Kopachris is offline
#1
Mar8-09, 10:08 PM
P: 13
How do you make positive ions? I found a kit device that is made of a bunch of capacitors and diodes that's supposed to make negative ions (it says to reverse the diodes to make positive ions) how does this work? Wikipedia and HowStuffWorks weren't much help. Wikipedia explained what diodes do, but it didn't explain why it's direction-specific. In other words, what makes the cathode a cathode and the anode an anode?
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alxm
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#2
Mar9-09, 05:11 AM
Sci Advisor
P: 1,867
The simplest way to create positive ions is usually to hit atoms with an electrical arc discharge. When the fast-moving electrons in the discharge hit the electrons in the atoms/molecules of matter, they knock other electrons 'out of orbit', which then head towards to positive anode. Leaving a positively charged, i.e. ionized, molecules.

This (Electrical Ioniziation, or IE) is known as a 'hard' ionizing technique. It tends to blast apart molecules. If you look up and read about mass spectrometry (MS), it's essentially all about ionizing molecules so they can then be sorted and detected according to weight. (their acceleration in an electric field will depend on charge and mass) So the area of MS has developed a bunch of different ionization methods for different molecules. E.g. MALDI for big biomolecules which would fragment into tiny pieces if blasted by an electrical arc.

As for what a cathode is, it depends on who you ask.
In most electrical contexts, it's the negative terminal. (I.e. defined as the more negatively charged end)
In electrochemical contexts, it's the positive terminal of a galvanic cell and the negative terminal of an electrolytical cell. The definition then is the end where chemical reduction occurs.
Kopachris
Kopachris is offline
#3
Mar9-09, 07:17 AM
P: 13
Well, that helps. Thanks!

Modey3
Modey3 is offline
#4
Mar13-09, 10:08 PM
P: 136

Best way to easily make positive ions?


Kopachris,

Can you post a link to that "kit" because "reversing diodes" will not stop the generation of positive ions and create negative ions. It may change whether a positive or negative ion is detected, but nothing else. Electron Impact Ionization is the type of ionization process that alxm is referring to. I do ion implantation and secondary ion mass spectroscopy as part of my research. Given an atom, such as nitrogen, the ionization probability depends on how tightly the electrons are bound and the size of the atom - that goes without saying! Whether it ionizes as a positive or negative ion depends on the chemical environment that the atom is in. If nitrogen is in a highly electronegative bonding state with say oxygen. The probability of forming a positive nitrogen ion is increased. At the same time, the probability of forming a negative oxygen ion increases. You can change your ion abundances by changing the chemistry of your gas mixture.

modey3
Kopachris
Kopachris is offline
#5
Mar15-09, 12:08 PM
P: 13
Modey3:
Here's the kit I was talking about. What I need is just positively ionized hydrogen -- protons. Preferably ionized in a vacuum to prevent accidentally igniting the hydrogen (although I'd only be using a tiny amount, about 50mL, and I'd keep it away from stuff, just in case).


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