Sciencemadness Discussion Board

lab maintenance

Magpie - 23-10-2012 at 12:58

Periodically I find it necessary to repair lab equipment. Successfully repairing an item gives me nearly as much thrill as a successful synthesis. So, for you other maintenance freaks out there I am showing three such recent successful repairs.

The first shows the Ag resoldering of my phosphorus condenser. After 9 runs it had been severely eaten away by heat/chemicals:

resoldered condenser.JPG - 95kB
resoldered condenser

The second shows a rare Kontes 2-A stopcock on a 125mL pressure equalized addition funnel (19/22). I had been looking for this plug for years and had seriously considered using the funnel for target practice. I found the plug in a 14/20 funnel bought at surplus for $10.


rare Kontes 2-A stopcock.JPG - 83kB
rare Kontes 2-A stopcock

The third item is another item bought at surplus for $1. It is a small, almost micro sized, bunsen burner. The valve wheel had worn loose and was non-functional.

Ag soldered Bunsen burner valve wheel.JPG - 94kB
Ag soldered bunsen burner valve wheel



[Edited on 23-10-2012 by Magpie]

bahamuth - 23-10-2012 at 14:22

Well grown up in a garage so to speak I to find great joy in fixing/building things, though I don't have pictures to show for it..
Quote: Originally posted by Magpie  

The first shows the Ag resoldering of my phosphorus condenser. After 9 runs it had been severely eaten away by heat/chemicals:


Is the heat the problem, or is the degradation corrosive? We have a very high heat solder we call "phosphorous solder" in Norway which "hardens" after initial soldering and increases the melting point. The initial mp is around 750-850 degrees C., and is impossible to remelt with propane after that. An old Castolin table listed it as very high phosphorous alloy but can't recall the percentage. Maybe it will withstand the P better than Ag...? Worth to mention that the solder "sticks" are always square and brass-like in color.

Working a lot with silver solder I know that the best silver solder is about 55% silver and that it isn't very resistant against corrosive stuff, the common silver solder is about 15% silver and is really poor for soldering anything..


Wish I could afford a glass torch to work all my broken Kontes stuff....

Magpie - 23-10-2012 at 14:48

Quote: Originally posted by bahamuth  


Quote: Originally posted by Magpie  

The first shows the Ag resoldering of my phosphorus condenser. After 9 runs it had been severely eaten away by heat/chemicals:


Is the heat the problem, or is the degradation corrosive?


I really don't know. Before rebuilding much of the solder was gone and what was left was spongy looking. I'm thinking that heat is a factor but also the 5% NaOH bath that I place it in for cleaning for 2 or 3 days may well be a factor too. The outside surface of the solder really should not be exposed to the P vapor that is internal to the condenser.

watson.fawkes - 23-10-2012 at 15:34

Quote: Originally posted by bahamuth  
We have a very high heat solder we call "phosphorous solder" in Norway which "hardens" after initial soldering and increases the melting point. The initial mp is around 750-850 degrees C., and is impossible to remelt with propane after that. An old Castolin table listed it as very high phosphorous alloy but can't recall the percentage. Maybe it will withstand the P better than Ag...? Worth to mention that the solder "sticks" are always square and brass-like in color
As I recall, it's around 6-8% P alloy with copper. It's a fairly standard brazing alloy (also called hard soldering) for joining copper to copper. I have some stamped "0" on it, indicating 0% silver, though P is usually present in silver-bearing alloys as well. The "hardening" behavior happens because the alloy composition changes when used, with more copper from the brazement diffusing into the filler metal. This lowers the percentage of P in the joint, raising its subsequent melting temperature.

bahamuth - 23-10-2012 at 15:48

The silver solder alloy you got sounds like something that gets dissolved in alkaline sol., which I find very strange since silver solder is supposed to be versatile and strong.. Do you have the designation on the solder sticks, or the color (of the outside flux) and the producer? One can check the alloy and see if something there is the problem.. But still, 5% NaOH wouldn't hurt aluminum much even....

From the color of the solder it really looks like the "low" % silver solder, which is more or less useless if you want the silver properties of the solder. IIRC it is brittle and sort of hard to flow where one wants to...


Not really a repair and perhaps not worth mention in this thread but me and a business partner is building a 3-axis cnc since my city (read town) doesn't have the shops around to do prototyping for us.

Other than that I can only mention in the passing what I have done at the university labs in the field of repairs.. As most Norwegians just throw away stuff that is damaged and buy new, or hire repairmen to change a fuse and similar, I have customized a lot of equipment to function (IMO better than supplied) with simple and reasonable cheap stuff the times I could convince the guys with the funds to trust me fixing the instrument or the item. But in the other direction I've got a lot of free equipment needing just a cleanup or resoldering because it was to expensive to hire repairmen and the item would end up on the land fill if not I've saved it... This items are include but are not limited to a; Büchi rotavapor with an old worn vacuum seal, a stirrer hotplate needing a connection cleanup, Pfeiffer-Balzer vacuum pump with slight corrosion damage, an old HPLC, an all glass water still and so. Unfortunately my job and my private company work leaves me little or no time to pursue chemistry. Working with CAD design of instrumentation within molecular biology (company stuff) and as a lab tech in the local uni.

By god, I derail when I get drunk...



-All spelling errors if any are intentional and only to confuse.

bahamuth - 23-10-2012 at 15:51

Quote: Originally posted by watson.fawkes  
Quote: Originally posted by bahamuth  
We have a very high heat solder we call "phosphorous solder" in Norway which "hardens" after initial soldering and increases the melting point. The initial mp is around 750-850 degrees C., and is impossible to remelt with propane after that. An old Castolin table listed it as very high phosphorous alloy but can't recall the percentage. Maybe it will withstand the P better than Ag...? Worth to mention that the solder "sticks" are always square and brass-like in color
As I recall, it's around 6-8% P alloy with copper. It's a fairly standard brazing alloy (also called hard soldering) for joining copper to copper. I have some stamped "0" on it, indicating 0% silver, though P is usually present in silver-bearing alloys as well. The "hardening" behavior happens because the alloy composition changes when used, with more copper from the brazement diffusing into the filler metal. This lowers the percentage of P in the joint, raising its subsequent melting temperature.


Oh, just used 20 min. to write the previous response..

I see, it is also called "hard solder" here to...

I've found it to bond tightly to low alloy steel as well if certain Castolin fluxes are used (don't remember which) in conjunction.

Magpie - 23-10-2012 at 16:13

Quote: Originally posted by bahamuth  
The silver solder alloy you got sounds like something that gets dissolved in alkaline sol., which I find very strange since silver solder is supposed to be versatile and strong.. Do you have the designation on the solder sticks, or the color (of the outside flux) and the producer? One can check the alloy and see if something there is the problem.. But still, 5% NaOH wouldn't hurt aluminum much even....

From the color of the solder it really looks like the "low" % silver solder, which is more or less useless if you want the silver properties of the solder. IIRC it is brittle and sort of hard to flow where one wants to...


I don't have any idea about the specifications of the silver solder used. I hire a machinist/welder to do that kind of work as I don't have an acetylene torch. On this last job he was feeding a silver wire to the weld after first fluxing it heavily. On my autoclave he was feeding a skinny silver bar. Again I don't know the specifications. I will see if I can find out what he was using on the condenser.

watson.fawkes - 23-10-2012 at 20:22

Quote: Originally posted by Magpie  
I don't have any idea about the specifications of the silver solder used. [...] I will see if I can find out what he was using on the condenser.
The liquidus temperature of copper-silver is 780 °C. The spongy look you reported might be a symptom of gas escaping through a partially-molten joint. Given that phosphorus is used to lower the melting point of such alloys, there's a good chance that the filler metal is simply liquifying.

Probably needs to be welded. Nickel brazing would likely work, but welding would be cheaper.