glass question

[Jerboy]

The quartz glass on my halogen bulb has developed white, rough spots on its surface. It was smooth and clear when it was new.

PIC. What is this white stuff and what causes them to form on the surface?

 

[gsaldivar]

I believe that is grease from your fingerprints when you first installed the bulb.

If you read the package, there is usually a warning not to directly touch the halogen bulb during installation - to prevent this from happening.

 

[Evadman]

Originally posted by: gsaldivar
I believe that is grease from your fingerprints when you first installed the bulb.

If you read the package, there is usually a warning not to directly touch the halogen bulb during installation - to prevent this from happening.

 

[Jerboy]

Originally posted by: Evadman

Originally posted by: gsaldivar
I believe that is grease from your fingerprints when you first installed the bulb.

If you read the package, there is usually a warning not to directly touch the halogen bulb during installation - to prevent this from happening.

Evadman, I know you're not supposed to touch the bulb(if you do, you're supposed to clean it with alcohol), but I'd like to know the technical reason to why it loses clarity. By the way, that bulb wasn't touched and it was even wiped down with alcohol before it was installed just in case.

 

[Evadman]

The reason you do not touch it is the grease / beloved patriot on your fingers will slow down the heat transfer of the bulb and actually melt the glass or corrode it. If you look at that picture colsely, you can see just where your 4 fingers were when you put the bulb in. It probably was not cleaned well enough to remove the film put there by your fingers.

As for the chemical make up of that white crossion, ya got me. I would guess some kind of silica oxidation made when the glass got hot enough to oxidize with the air, but that is only a guess.

 

[Jerboy]

Originally posted by: Evadman
The reason you do not touch it is the grease / beloved patriot on your fingers will slow down the heat transfer of the bulb and actually melt the glass or corrode it. If you look at that picture colsely, you can see just where your 4 fingers were when you put the bulb in. It probably was not cleaned well enough to remove the film put there by your fingers.

I sure as hell didn't touch it. Must have been someone else. I used an old sock to handle the bulb and no part of bulb was touched by my bare fingers.

As for the chemical make up of that white crossion, ya got me. I would guess some kind of silica oxidation made when the glass got hot enough to oxidize with the air, but that is only a guess.

The glass on this halogen lamp is no ordinary glass. It is made of special glass called fused quartz, which has a melting point of about 1700°C, about 200°C hotter than steel. I'm not sure if quartz could oxidize any further.

Quartz already is the most stable oxide of silicon. Si(Silicon)+O2(oxygen)=SiO2(quartz glass). I've never heard of formation of silicon trioxide or silicon pentoxide.

 

[Evadman]

That would be why I said it was a guess 🙂

as for handling it, it sure looks like 4 fingerprints to me. I would smack your brother / sister 🙂

 

[CTho9305]

interesting thread - i never knew any of this 🙂. but if it is getting up to 1700C, i think you'd be seeing other problems too 😉

evadman - interesting sig

 

[Evadman]

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Thanks! Well, I think, anyway 😀