Author Topic: Hydrogen poisoning in compact, quartz jacketed MH lamps?  (Read 1425 times)
dor123
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Hydrogen poisoning in compact, quartz jacketed MH lamps? « on: August 09, 2020, 09:07:24 AM » Author: dor123
At 2.Aug.2020, my Odyssea MHQ-T 70W 6500K aquarium MH lamp  that I bought from Aliexpress, failed prematurely after only a slightly more than 1 month, glowing continuously in starting mode .
No visible sputtering seen on the arctube at all, only mercury that condensed on the arctube wall, and no visible cracks on the arctube and the outerbulb (The lamp still looks brand new, despite it is EOL):


Is this possible that hydrogen impurities inside the lamp caused it to fail?
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Re: Hydrogen poisoning in compact, quartz jacketed MH lamps? « Reply #1 on: August 10, 2020, 04:03:42 PM » Author: Ash
(Dor posted elsewhere that the failure of this lamp was sudden, after the lamp worked normally in previous times. That is relevant for the question here)

I think it is unlikely :

If the lamp was ok initially it means that it had no Hydrogen trapped in it from manufacture, and no small leak that would let Hydrogen (the smallest atom of them all) to penetrate over the (typically) few months or longer time, when the lamp was in storage, before you got it

I dont think any gas can get *into* a HID lamp arctube, even when it is leaking, when the lamp is on, as the pressure inside is higher than outside. If anything, something would be leaking out...



If we suspect that the arctube selaling somehow got damaged (a micro crack appeared) after a few on/off cycles due to thermal stress :

1. I dont know how likely it is to get such small crack that would exactly only let through Hydrogen ?

2. If the crack is in the arctube, where would the Hydrogen come from ? The outer is not supposed to contain Hydrogen either...



This is not a leak of the outer either - since even with broken outer the lamp would still transition into full discharge and atleast partially warm up. It would not stay in starting like your lamp



My guesses are :

1. Micro crack after few thermal cycles that let some of the buffer gas out of the arctube (which it didn't care about when it was hot since there were enough other vapors to maintain the discharge), but is now unable to start properly since the buffer gas content is wrong

2. Variaton of 1 : A bubble in the arc tube wall (possibly in the vacuum pip) that contained air or some other contaminant popped into the inner volume of the arctube

3. Emitter depleted, if this lamp used any emitter at all to begin with ?
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Max
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Re: Hydrogen poisoning in compact, quartz jacketed MH lamps? « Reply #2 on: August 10, 2020, 04:17:16 PM » Author: Max
It is indeed likely that your lamp died of hydrogen poisoning. This happens if a quartz material of a low quality grade was used for the burner. The high hydroxyl content in the glass material results in the release of water vapor upon exposure to heat and UV light. Water molecules then decompose into oxygen and hydrogen, the former quickly reacts with any metal parts in the burner (additives, electrodes), leaving hydrogen which accumulates and form the highly electronegative HI molecules which cause ignition failure, or more commonly, glow-to-arc transition failure due to a too high glow discharge impedance (not enough current is drawn from the ballast, so the electrodes cannot reach the thermionic regime).
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Re: Hydrogen poisoning in compact, quartz jacketed MH lamps? « Reply #3 on: August 11, 2020, 05:50:55 AM » Author: dor123
Thanks Max. I'm guessed that this failure was caused by hydrogen poisoning, as it was abrupt and the conditions and the behavior of the lamp during the failure.
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Re: Hydrogen poisoning in compact, quartz jacketed MH lamps? « Reply #4 on: August 11, 2020, 11:19:59 AM » Author: dor123
Wait... But if it have a getter pellet inside, why it didn't absorbed all the hydrogen?
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Please forgive me if my choice of my words looks like offensive, while that isn't my intention.

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Medved
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Re: Hydrogen poisoning in compact, quartz jacketed MH lamps? « Reply #5 on: August 11, 2020, 01:11:39 PM » Author: Medved
(Dor posted elsewhere that the failure of this lamp was sudden, after the lamp worked normally in previous times. That is relevant for the question here)

I think it is unlikely :

If the lamp was ok initially it means that it had no Hydrogen trapped in it from manufacture, and no small leak that would let Hydrogen (the smallest atom of them all) to penetrate over the (typically) few months or longer time, when the lamp was in storage, before you got it

The water gets released from the quartz slowly, so it slowly poisoned the arctube. This caused the cold cathode glow voltage to rise slowly. Up to some limit the mains (= the ballast OCV) was still large enough to pass sufficient current to warmup the electrodes (it is a kind of unstable system - small heat causes electrodes to slightly warm up, that lowers the voltage a bit boosting the dissipated power, that warms up the electrodes even faster, so the system flips into the hot electrode mode when the electrodes are fully warmed up so have low voltage drop), so the lamp started apparently normally. Only when it just exceeded the critical concentration, the dissipated power in glow mode was insufficient to make the system to flip into the hot cathode mode, so "from the outside" it "suddenly" stopped working.



I dont think any gas can get *into* a HID lamp arctube, even when it is leaking, when the lamp is on, as the pressure inside is higher than outside. If anything, something would be leaking out...


Even when external gas leak isn't likely the cause here, you are wrong.
The gas will leak in (assume very small leak, more of a diffusion nature than real hissing), when the partial presure of that given gas is lower within the arctube than in the outside. The pressure of the other components does not matter there. So because there is supposed to be no hydrogen inside at all, even a small pressure outside is way greater than the H2 pressure inside of the artube, so the hydrogen will diffuse into it even when the other gasses have there 10atm... Of course, this is valid only for small, diffusion like leakages, when all flows are subsonic. If you have really a hole causing hiss, the hiss is a supersonic flow and there the supersonic flow really stop anything else going in the opposite direction.

In real life I've not heard about H2 going this way, but He poisoning is a real problem, becase He is a single atom gas with very ligt atom, so really diffuses through most practical construction materials. And there a small percentage of He in atmosphere (some He is leaking or even just in use in that room) has no problem contaminating a presurized container with another gas stored in that room. It takes time, but it does happen.
The same mechanism is actually able to save your day when He contaminates some MEMS structure (they are supposed to operate within vacuum, the leaked in He causes excessive damping so the MEMS fails; typically 32768Hz RTC oscillators used in modern smart watches or smart phones). When you move the affected thing outside to a clean air (not contaminated with the He), the He leakes back out from the mems component to the outside air (because the partial pressure outside will be lower) and the thing recovers and starts to operate again normally (unless the software collapses and cause havoc in the system over the time when the RTC did not work), even when the N and O make together 1atm difference in the total pressure.
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Re: Hydrogen poisoning in compact, quartz jacketed MH lamps? « Reply #6 on: August 24, 2020, 01:50:43 AM » Author: Alex
Wait... But if it have a getter pellet inside, why it didn't absorbed all the hydrogen?

The problematic hydroxyl is located in the quarz of the discharge tube. Some of the hydrogen that came out the quarz, went in the other envelope, in the Vacuum were it was absorbed by the getter. However the Part that went into the arc tube caused lamp failure, as it was sealed inside the arc tube.
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