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Prips Flux preparation problems


#1

I have always used Prips flux to prevent firescale on my silver. I
have bought the Prips commercially and also used that made by others
in our shop.

Recently I have tried mixing up some myself. Using a 3:2:2 ratio of
boric acid, TSP, and borax, and I can not get it all to go into
solution. The three parts amounts to about 48 grams of boric acid
and the twos around 32 grams each, in a quart of water.

The mixture remains cloudy through boiling, and then allowing it to
stand and cool the solution clears, but there is sediment on the
bottom of the container. Is this normal or am I doing something
wrong? I have used this clear solution while soldering and it seems
to work OK.

I have tried different brands of borax and both powdered and
granular boric acid, with the same results. The TSP is trisodium
phosphate. I have also tried increasing the amount of water.

Can anyone help?
Thanks, Don


#2

I had the same problem with Pripps and more or less gave up on it. I
finally figured out the problem: Most TSP on the market today also
contains sodium silicate. Sodium silicate only remains soluable in
basic solutions. When you add the boric acid, the sodium silicate
precipates out as silica gel, a form of silicon dioxide. (Silicic
acid is formed by the dissolution of silicon dioxide in water. It is
an equilibrium reaction that strongly favors the SiO2 phase) I
believe that if you can find some TSP that does not contain sodium
silicate, you would not have the precipitation problem.

Howard Woods
Eagle Idaho


#3

Your TSP has to be regent. Lloyd.


#4

The times I’ve seen TSP on the market that contained Sodium
Silicate, it turned out that the stuff in the container was not
actually TSP at all. There are a many substitutes for TSP sold as
general cleaners, etc, that do not use actual tri-sodium phosphate
(TSP) in order to comply with water pollution regulations regarding
phosphates in detergents/cleaners. Instead, they generally use
Sodium Metasilicate, which may work fine as a cleaner in many of the
situations traditionally emplying TSP, but as you note, it’s a
totally different chemical, and does not work for making Prips.

I believe the problem is not one of finding TSP that doesn’t contain
"some" sodium Silicate, it’s that of finding a product that is
actually TSP at all. Most of the substitutes are confusingly labled.
Things like “TSP-90” or the like. No actual TSP in there. Only the
Sodium Metasilicate. What you have to do is very carefully read the
ingredients listing and labels. Just because the letters TSP are in
the product name does not mean that is what it contains. 46ind a
product that actually contains tri-sodium phosphate. From what I’ve
seen, when it’s sold, it’s not generally mixed with anything else of
any significance to making Prips flux. In my location, when i go to
the local Home Depot stores, in the paint department one finds, at
eye level shelves, several versions of the substitutes, many of
which, from quickly reading the labels, look like they should be TSP,
and which will be fine for washing walls before painting. But
they’re the wrong chemical. Stepping back, getting on my knees, and
searching the floor level bottom shelf, I often can find a rather
less fancy looking “generic” sort of carboard box product that is
labled, and actually contains, TSP. That’s the stuff you need for
Prips. Read the fine print to be sure.

Peter