(Part 2) Tests for PbF / SnPb solder

Just checked a day later and the SnPb boiled in vinegar for 20 seconds plus potassium iodide shows a slight yellow colour compared to the PbF sample. What other non-license source of a strong acid other than car battery acid? drain cleaner is clobbered by elfin safety these days.

Citric acid should be widely available, and you might want to try phosphoric acid if you can find a source for a small amount. Phosphoric acid is used in foods, but also as a diluted solution to etch and clean metals before applying paints or other corrosion-preventive coatings. Most autobody repair/refinishing shops will be familiar with diluted phosphoric acid as a preparatory step in applying primer to steel or aluminum (aluminium?) parts. A typical generic term here in the US is "metal prep". A paint distribuor should have a way to get diluted PA for you, but you may have to buy a quart (1L sized bottle).

Diluted PA isn't particularly dangerous to handle, but it stings if it gets into a cut in the skin, avoid any conact with eyes.

I don't know if either of these acids would be useful for detecting lead, or lead-free solders.

-- Cheers, WB .............

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2 days on and a more definite but pale yellow colouration , after shaking, so a precipitate. Tin heavy sample still clear liquid. Perhaps it is just picking up lead carbonate or something as contaminant on the surface, but old SnPb is likely to be the only such to be found in the UK these days. Will try boiling for 10 minutes in vinegar , i doubt you can grind down solder in a mortar and pestle (another test maybe, perhaps high tin solder will so grind down and not leaded version).

Will try getting phosphoric acid . Isn't there formic acid for de-calcifying or something ? The problem trying to get around is not post 2006 boards with PbF on the overlay and green stickers on the casing but identifying boards like Yamaha from 2001 or Marshall from 2003 but with PbF soldering

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

phosphoric

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The PA I found as rust remover (hardware and car spares shops) probably has dye/colour change stuff in it, so defeating the purpose here

I have seen clear metal prep/phosphoric acid, but a colored product would complicate testing, as others may find differently colored solutions.

The reason I didn't mention muriatic acid (swimming pool chemical, concrete cleaner/etcher, and good for removing rust from steel) because the muriatic I've seen has had a dark amber color.

-- WB .........

Conc Sulphuric Acid (95%+) and Conc Hydrochloric Acid (35%) are available from many sources (such as Robert Dyas). The H2SO4 is used for unblocking drains. But even though boiling H2SO4 attacks lead, it forms the insoluble sulphate which inhibits further action (and being insoluble, it is difficult to test it for lead). Boiling HCl attacks lead, and forms the soluble chloride, which would be ideal to test for lead. But I wonder how long it would be before Elf'n'safety appeared when your neighbours start choking?...

I doubt the purity of either acid would help ascertain the Pb content of solder. They may contain lead as an impurity anyway.

--
Jeff

Hmmm... odd.

The quart of muriatic acid I bought at a local hardware store (to make PC-board etchant) is water-clear. No color at all, until after I etched... at which point the copper(II) chloride makes a lovely blue-green.

--
Dave Platt                                    AE6EO
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Put some hydrogen peroxide in the HAc and it will go after the lead pronto.

Tom

concrete

muriatic

I tried repeating the leaded solder + vinegar heated and potassium iodide and no yellow colour after a day.

Remembered I had some 10 yearold car-body treatment Loctite Rust Remedy in the shed. With SnPb solder shavings and water ,boiled up for 30 seconds turned to a clear strong orange colour over a cloudy mass , if left to settle. Boiling the loctite and water on its own remained cloudy cream colour throughout, no settling out. Sn/Ag/Cu gave a cloudy very slight yellow colour. Tried some iron filings, as there is supposed to be a colour change to blue for rust treatement, and the test tube sample went via grey-green to black. Will try Cu and Zn filings and Sn filings and then repeat the set again to see if there is consistency

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Given up on chemical tests , no consistency/ lack of differentiation. Mortar and pestle idea goes no where.

Had to decide this week whether a 2003 board had failed solder due to SnPb or PbF and excess heat , where it was used. Could not decide by appearance, good mirror finish, lack of pastiness but solder joints too shallow to tell domed from conical, so probably SnPb. Low temp soldering iron test, melted - SnPb Paper test - SnPb and indentation test much nearer Pb diameter than Al so - SnPb

You need this, expensive though, or find out whats in the tester chemicals.

JC

or this

Got some spirit of salts (32 percent hydrochloric acid) from a traditional hardware shop. No colour reaction found heated with leaded solder and then KI. Also got a pot of sulphur and may try excessive heating as there seems to be some sort of test that way producing a black lead sulphide colour.

I increased sample sizes to about 3cc of 32% HCl and about 30 cu-mm of solder wire. About 1/3 of the wire scraped into scrapings and remainder added as round and the part round remnant . After boiling and cooling twice then perhaps about 5 to 10 cu-mm of KI added and repeated boiling and cooling. For the leaded one bright orange crystals? soon appear on forced cooling and flecks of glistening gold colour the second time of heating cooling after KI . The glistening gold agrees with my chemistry book for lead testing with KI, don't know about the orange. The colours and crystals disappear on boiling.

The lead free one , no colours at all in the liquid but the metal goes black. With repeated boiling then still a lot of gas comes off the metal for some time after removing from the heat , unlike the leaded sample. Maybe acting on the 5 percent silver content.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

The KI came from a kids chemistry set in a charity shop. One way around kids and chemistry and product liability, absolutely no name. Nothing on the box and nothing in the accompanying book for makers name or even country of origin.

Looks as though regular flicking of the test tube is important. Repeated samples and again nothing appearing in the non-lead sample. The odd flecks that would appear when shaken were probably reduced flakes of the original scrapings, again black colour. Looks as though 30 cu-mm is about the right amount of KI with 30 cu-mm of solder and initially 3cc of HCl. I can only estimate using a small spatula that is in fact a stainless steel lobster pick, fork+spoon. The 4mm wide spoon end is ideal for this. No orange colour this time (initially) . Once a very slight yellow tinge to the liquid appears and at boiling and through cooling , much flicking of the tube with a finger, then instead of flecks that look like golden flakes of skin you get a dense mass of more like cream-coloured soap flakes. Reheat and all this dissolves well before boiling point. Allow to cool untouched and then just a small scattering of fine gold-coloured flecks when you flick the tube. The orange colour seems to only appear after repeated heating and cooling, the second SnPb sample is now starting to show this orange colour after 5 or 6 heat/cooling cycles. The colour of the residual bits of SnPb solder masked by the crystals/precipitate , but not obviously black.

followup Looks as though the orange colouration is due to tin/stannic iodide, from the Sn in SnPb and PbF. After a week or so the orange colouration appeared in the solution in the PbF test tube also. Even more convincing collection of scintillating gold flecks in the SnPb test tubes