PCB Etching (again!) - chemicals used

[John Woodgate]

I read in sci.electronics.design that OBones

But does it leave the colouring of the fabric alone or does it make a
white spot instead of a orangish one?

Citric acid is not a reducing agent, so it won't have much effect on
many dyes, but acid-labile ones will fade. Also, bear in mind that the
iron will combine chemically with the fabric itself, in some cases,
acting as a self-mordanting orange dye. Even chlorine bleaches won't
shift that.

 

[[email protected]]

Ahhh, fair enough. I don't actually check RS and farnell, much - their
prices depress my poor uni student budget too much. ;-)

so try using toilet cleaner, the ones with HCl in them.


NT

 

[Chris]

I read in sci.electronics.design that Michael


Typical room temperature in Oz!

Yeah, but that's only in the south, I prefer it up in the tropics where it
gets
above boiling point ;-)

Cheers.

 

[John Woodgate]

Yeah, but that's only in the south, I prefer it up in the tropics where it
gets
above boiling point ;-)

Back in the Dark Ages, 1948 to be precise, my school's magazine included
a report from an Old Boy ('alumnus' in US English) from 'British
Malaria', where the LOWEST ambient temperature was inside the boiler of
the coconut-crusher's steam engine.

 

[Aubrey McIntosh, Ph.D.]

I read in sci.electronics.design that OBones



Citric acid is not a reducing agent, so it won't have much effect on
many dyes, but acid-labile ones will fade. Also, bear in mind that the
iron will combine chemically with the fabric itself, in some cases,
acting as a self-mordanting orange dye. Even chlorine bleaches won't
shift that.

I had forgotten that you can get ahold of oxalic in consumer products.
What about oxalic with a catalytic amount of KI, and some as yet
unidentified reducing agent? I'm thinking of the greensalt synthesis.

EDTA may work even better than oxalic. EDTA constants are mentioned on
http://www.cem.msu.edu/~cem333/EDTATable.html. It used to be a
component in Mr. Bubble, but I haven't seen it on any labels in the past
decade or so.

 

[John Woodgate]

I read in sci.electronics.design that "Aubrey McIntosh, Ph.D."

I had forgotten that you can get ahold of oxalic in consumer products.

Rhubarb, rhubarb?

What about oxalic with a catalytic amount of KI, and some as yet
unidentified reducing agent? I'm thinking of the greensalt synthesis.

I don't know the term 'greensalt synthesis'. Google doesn't help much.

EDTA may work even better than oxalic. EDTA constants are mentioned on
http://www.cem.msu.edu/~cem333/EDTATable.html. It used to be a
component in Mr. Bubble, but I haven't seen it on any labels in the
past decade or so.

Oxalic acid just forms colourless, soluble ferrous oxalate, I think.
Doesn't EDTA form complexes with Fe?

 

[Aubrey McIntosh, Ph.D.]

I read in sci.electronics.design that "Aubrey McIntosh, Ph.D."



Rhubarb, rhubarb?

A cleaning material for wooden decks contains mostly oxalic acid. I
have forgotten the brand name. When I read the price and the ingredient
list on the label, I thought a while, bought a stiff brush and a gallon
of vinegar, and the change in my deck was just short of miraculous.

I don't know the term 'greensalt synthesis'. Google doesn't help much.

No, I couldn't find it either. A few years ago there were dozens of lab
write-ups with the name, but it is archaic.

The formal name is potassium tris (oxalato) iron (III) trihydrate or
alternately potassium iron(III) tris-oxalate hydrate. It forms large
clear emerald green colored crystals. The color change is when the
solutions are mixed is immediate and dramatic, so it makes a nice
freshman chemistry lab. The toxicities and mess are low.

My memory was bad, it should be iron(III) and not iron(II) to be
soluble, so it should be easy.

There is a nice picture of the structure of the compound in this lab manual:

http://www.hmpublishing.com/hmplabscollection/Tatz123/Tatz123-137-144.pdf

A fairly short description of a synthesis, using Fe(Cl)3 is given at
http://www.wpi.edu/Academics/Depts/Chemistry/Courses/General/feoxalate.html

My thinking is that the oxalate's oxygen will grab the iron away from
the rust's oxygen, given good conditions. Also, the color change gives
immediate status on success.

Oxalic acid just forms colourless, soluble ferrous oxalate, I think.
Doesn't EDTA form complexes with Fe?

A compound with a central metal atom and other moieties around it that
have "lone pair electrons" is a "transition metal complex," so they both
the oxalates and the EDTA are correctly called "complexes" or
alternately "chelates." The oxalate is a "chelating agent" or a "ligand."

The key to having them be soluable is to have the complex carry a net
charge. So, if I made oxalates using Ni, Cr, Fe, Co, and try to walk
across the periodic table, I do end up with some beautiful colors, but
some are solutions and some are gunk.

 

[John Woodgate]

I read in sci.electronics.design that "Aubrey McIntosh, Ph.D."

No, I couldn't find it either. A few years ago there were dozens of
lab write-ups with the name, but it is archaic.

I found another 'green salt' with Google, Pt(NH3)3PtCl4. Nice, if you
can afford it!

The formal name is potassium tris (oxalato) iron (III) trihydrate or
alternately potassium iron(III) tris-oxalate hydrate. It forms large
clear emerald green colored crystals. The color change is when the
solutions are mixed is immediate and dramatic, so it makes a nice
freshman chemistry lab. The toxicities and mess are low.

My memory was bad, it should be iron(III) and not iron(II) to be
soluble, so it should be easy.

There is a nice picture of the structure of the compound in this lab manual:

http://www.hmpublishing.com/hmplabscollection/Tatz123/Tatz123-137-144.pd
f

A fairly short description of a synthesis, using Fe(Cl)3 is given at
http://www.wpi.edu/Academics/Depts/Chemistry/Courses/General/feoxalate.h
tml

That's helpful. But I'm not in favour of this niminy-piminy semi-micro
stuff. Let's have gallons (Imperial, of course) of reagents!

[snip]

A compound with a central metal atom and other moieties around it that
have "lone pair electrons" is a "transition metal complex," so they
both the oxalates and the EDTA are correctly called "complexes" or
alternately "chelates." The oxalate is a "chelating agent" or a "ligand."

Chelates hold on at both ends. They are a sub-set of complexes. Ammonium
and CN complexes, for example, are not chelates.

The key to having them be soluable is to have the complex carry a net
charge. So, if I made oxalates using Ni, Cr, Fe, Co, and try to walk
across the periodic table, I do end up with some beautiful colors, but
some are solutions and some are gunk.

Maybe even more fun with trans-uranics, but use a very long spoon!