How exactly does mercury increase Nixie lifetime?

[Kevin Keith]

I've seen references and claims to this fact, but never an explanation of the exact mechanism? So, with that said, how *does* mercury actually reduce cathode poisoning/sputtering damage? Are there any potential alternatives? Would something like gallium work?

[Dalibor Farný]

Hi, the mercury adheres to cathode surface and because its molecule is
heavy, it is less likely to be relieved from the cathode by electrons
bombarding the cathode (compared to relatively light molecules of Fe,
Ni, Cr - stainless steel).. The lifetime of mercury doped nixies is
200.000 hrs, tubes without mercury have 5.000 hrs (MTBF value from
datasheets). This is a theory.. The lifetime otself depends on many
other parametrs, eg. size of the hole in anode grid or shape of the
ceramic insulators between numbers..

My experimental tube without mercury is at ~1500 hrs, no signs of
metal deposit on glass, some deposit of shiny metal on ceramic
insulators - the resistivity is not measurable yet (>300 Mohms).
photo: http://tinyurl.com/n5o5bau

Dalibor

2014-02-13 8:44 GMT+01:00 Kevin Keith <krfk...@gmail.com>:
> I've seen references and claims to this fact, but never an explanation of the exact mechanism? So, with that said, how *does* mercury actually reduce cathode poisoning/sputtering damage? Are there any potential alternatives? Would something like gallium work?
>

> --
> You received this message because you are subscribed to the Google Groups "neonixie-l" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+...@googlegroups.com.
> To post to this group, send an email to neoni...@googlegroups.com.
> To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/61e65e8a-43ac-4cc4-824b-04c7f4039731%40googlegroups.com.
> For more options, visit https://groups.google.com/groups/opt_out.



--
Dalibor Farny
----------------------------------------
phone: +420 724 321 571
http://www.daliborfarny.com
blog: http://dalibor.farny.cz

[John Rehwinkel]

> My experimental tube without mercury is at ~1500 hrs, no signs of
> metal deposit on glass, some deposit of shiny metal on ceramic
> insulators

Where did you get the ceramic insulators?

- John

[Dalibor Farný]

Hi,

I got some 2mm spacers from eBay (cant find the auction now) and let
some 0.9mm thick insulators be made in China (not used yet)..

Dalibor

> --
> You received this message because you are subscribed to the Google Groups "neonixie-l" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+...@googlegroups.com.
> To post to this group, send an email to neoni...@googlegroups.com.

> To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/A139F719-1079-439A-A21D-E77FB01CF0AE%40mac.com.

[Kevin Keith]

Do you know of any papers or studies detailing this discovery? Patents even? Surely someone had to have discovered this, but it is just taken as fact in the few references I find. Not that I'm doubting that mercury does indeed extend tube life, but I have to wonder who first happened upon this.

[NoCampersFluffy]

Hello
From my chemistry days I think there is a complementary explanation to the coating of cathodes with Mercury and for mercury vapor inside the Nixie.  It takes less energy to energize mercury atoms than energizing the atoms in the penning mix (Neon and Argon).  This principle also led to the development of the fluorescent tube.  In this way the mercury atoms form part of the thermionic emission releasing electrons with UV wavelenghths which collide with and ionize the noble gas atoms inside the tube to form the resulting plasma by the process of impact ionization.  As a result of avalanche ionization the ionized gas increases its conductivity rapidly and a current is able to flow.  Mercury also has the benefit of stabilizing the ionization voltage as well as increasing the life of the cathode.