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Forum Index : Microcontroller and PC projects : Not all mercury switches.....
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9750 |
Hiya.  I have received my two different types of mercury switches I plan to use to replace the problematic ball-switches covered in another thread. Not all mercury switches are the same!  Have a look at this photo:  The top one is a 5mm one from AliExpress, and the lower one is a 3mm one from eBay. The top one's mercury blob is nice and shiny as it should be, the lower one is not. The top one's closed resistance is about 0.1 Ohms, the lower one is 200 Ohms. Note how the lower one looks very frosted, whereas the upper one is nice and shiny as you would expect. The first one I picked out of the bag of the lower type had no circuit at ALL when closed, and the others were.....well, you get the idea. The AliExpress ones are very nice and work well. Crappy eBay switches Good ones from AliExpress I thought that mercury was a given constant, and that mercury was mercury, but it would seem not. Now, I know what some of you are saying: 'Crappy eBay or AliExpress - buy decent quality stuff from element14 etc.' There is certainly an argument for that, but I always like to push the envelope of what is achievable from China.  Smoke makes things work. When the smoke gets out, it stops! |
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Azure Guru  Joined: 09/11/2017 Location: AustraliaPosts: 446 |
It looks like that mercury in the small units is not pure, making them resistive. I agree with your comment re where to purchase. The price and shipping for most components on the eBay stuff makes them worth a try if your not in a hurry. For critical or time sensitive work I use element14. |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2171 |
Hey Grogs. can you try an experiment for me? take the crappy one and put it in your freezer. Does the "mercury" freeze? Gallium is molten at room temperature but it not as glossy or free-flowing as mercury. If it is mercury, it will not freeze at -25c... Gallium is cheaper to handle than mercury (being largely non-toxic compared to mercury) and i wonder if some crafty little wotsit has loaded them with gallium to shift them. Fake components and all, nothing surprises me. Cody has done a brilliant comparison here h |
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| Azure Guru Joined: 09/11/2017 Location: AustraliaPosts: 446 |
The eBay picture shows nice shiny mercury. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Thought the same; just not sure what would mix with it..... I do know my Grandfather used to store Alluvial Gold in Mercury.... Doubt that's happening in this case. Phil. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Just looking at it, melts at 29.76°C, so it's wouldn't be the pure element. But Wiki goes on to mention a few alloys, Galinstan; 11°C, and a Commercial version that melts at -18°C. Galinstan. Phil. |
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| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2171 |
what can I say? Wife controls the heating |
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atmega8 Guru Joined: 19/11/2013 Location: GermanyPosts: 727 |
May be the ebay switch ist "air penetrated", somewhat leaky ? Is this a process of oxidation?! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9750 |
Wow - lots of replies. @ Azure Re: Not Pure - Yes, that is also my prediction. @ CaptainBoing Re: Freezing - No, I can't. My freezer is bust, so I only have a fridge at the moment.  I do remember testing the temperature of my fan-assisted freezer when it was working, and it got no colder then about -11'C, so I don't think it would have helped anyway, as it would not get down to -25'C.....@ Azure Re: Shiny eBay picture: Yes it does! I noticed that myself. The picture and what you get are often not the same with eBay especially. I actually much prefer AliExpress these days, as they offer multiple shipping options, and things tend to be exactly what they say they are when you get them. I find that stuff from AliExpress arrives much faster too. Those eBay switches took one month to get here, the AliExpress ones too 1.5 weeks.@ Phil23 - Agree. @ atmega8 Re: Oxidation - Possibly. ALL the eBay ones are frosty looking like the first one. I could drop on in a glass of water and see if anything gets inside it... Smoke makes things work. When the smoke gets out, it stops! |
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redrok Senior Member  Joined: 15/09/2014 Location: United StatesPosts: 209 |
Hi All; I highly doubt that switch contains Gallium or other mixtures, often called Galistan, which readily wets things like glass. (Although there is a remedy for glass using gallium oxide coatings.) Anyway, gallium would tend to stick to the metal electrodes even if it doesn't wet the electrode material. I had a small sample of gallium used as for reversible electrical connections for very high density computer chip packages. The stuff was a nightmare to work with as it kind of stuck to any and every thing, the opposite of mercury which tends to repel things, (except metals). Anyway, stuff would be easy to freeze in a refrigerator's freezer. Also, gallium has a fairly low surface tension, the opposite of mercury which has a high surface tension. The dirty looking stuff in your picture is most likely Mercury that has a bunch of other metals dissolved in it. Mercury, as well as Gallium, is loosely defined as a solvent for metals and other chemicals. A solvent, generally, doesn't react with that which is dissolved. However, the impurities can form oxides which would make the electrical contact to the electrodes poor and unreliable. I suppose that switch has been made with fairly dirty mercury. As to the possibility of air or moisture entering through the glass frit sealed electrodes. If the seal is bad it is readily visible. Your picture sure looks good. I just think the mercury is dirty and should not change or get worse. I doubt the mercury gas could escape. BTW, I have 100 of those 5mm switches I got off ebay from China. They all look and work perfectly. They have very clear mercury blobs in them. I suppose I got lucky. redrok |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9750 |
I stuck one of the nasty ones under the microscope today, and here is what they look like at 30x zoom:  Nasty..... I will dispose of all of these little ones, as they are all the same in that the blob looks frosted at normal sight. Smoke makes things work. When the smoke gets out, it stops! |
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mikeb Senior Member Joined: 10/04/2016 Location: AustraliaPosts: 177 |
but I always like to push the envelope of what is achievable from China. And crap it still is. There are 10 kinds of people in the world. Those that understand binary and those that don't. |
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| kg4pid Regular Member  Joined: 08/03/2015 Location: United StatesPosts: 50 |
A couple of years ago on another forum a guy was talking about a trip he had made to china. He was getting quotes on having some specalized cables made. He said more than one factory he had been in had puddles of mecury in the floor. Maybe they decided to suck it up with a vacuum and put it into switches! I wouldn't be supprised if most of the factories in china are contaminated with some sort of nasty chemical. Max |
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Clockmanfr Guru Joined: 23/10/2015 Location: FrancePosts: 437 |
As part of my trade I work with Mercury. I work with scientific instruments, especially the stick barometers, which after a few hundred years are contaminated with atmospheric dust etc. A trick to clean mercury is to use a clean empty and fully dry clear plastic water bottle, put a small quantity of mercury, that you require cleaning, in it and then roll up a small ball of double sided sellotape and pop that into the water bottle. Put the cap back on and gently roll/shake carefully. You can see the sellotape is getting dirty, take the sellotape ball out and put another clean one in, and Just keep repeating the process until the mercury is bright and shiny again. Be warned Mercury vapour is dangerous work with appropriate safety equipment. Those dirty sellotape balls are contaminated so dispose with care. Most of the time I can re-use very old mercury. Everything is possible, just give me time. 3 HughP's 3.7m Wind T's (14 years). 5kW PV on 3 Trackers, (10 yrs). 21kW PV AC coupled SH GTI's. OzInverter created Grid. 1300ah 48v. |
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| Azure Guru Joined: 09/11/2017 Location: AustraliaPosts: 446 |
Back in my computer days I was involved in computer (Notebook, PC and Server) design and manufacturing. I used to visit and work with a lot of factories including several provinces in China. A lot of the better factories are very clean and conform to high strandards and are happy to be regularly visited on very short notice. That is not denying there are also lower quality factories the same as there are in most other parts of the world (which I have also visited many of). |
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| bigfix Senior Member Joined: 20/02/2014 Location: AustriaPosts: 129 |
China has a long History with Mercury... Tomb "And Qin Shi Huang's tomb is also thought to be encircled with rivers of liquid mercury, which the ancient Chinese believed could bestow immortality. "It's kind of ironic," Romey said. "This is probably how he died, by ingesting mercury. He was taking all these mercury pills because he wanted to live forever and it killed him by the age of 39." That moat of mercury also presents another reason why archaeologists are loath to explore the tomb just yet — doing so would likely be very dangerous, according to soil samples around the tomb, which indicate extremely high levels of mercury contamination." |
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