Thread: Painting Black Steel

In this case, 'inhibited' means that there is a (often organic) compound added to the acid which severely decreases the acid attack on mild steel by "adsorbing on the cathodic sites of mild steel and decreases the evolution of hydrogen. The adsorption on anodic sites occurs through pi-electrons and lone pair of electrons on nitrogen atom of the active alkaloids found in extracts" (or words to that effect).

Killed spirits references the end product of the acid/zinc reaction, zinc chloride.

I looked up Inhibited Hydrochloric acid on Wiki some time ago and got lost in the whole explanation .
Its seems there are some fancy doings going on to inhibit the effects of the acid on mild steel .Not sure if your method is the correct one to inhibit the acid or not.
I have been thinking of buying the Septone Hydroclean and giving it a try.

http://www.septone.com.au/detail.asp...398&page_num=1
Kev

Inhib HCl seems to change formula depending almost in every chemistry book that has it mentioned

This source gives the constituents as

The inhibited acid solution shall be formulated as follows:
Hydrochloric acid, 23 Baume (Sp. 1.19, Assay 37 percent) 240 ml
Ferric chloride hydrated (FeCl3 . 6H2O) 50 g
Cupric chloride hydrated (CuCl2 . 2H2O) 0.62 g
1, 3 Diethylthiourea (DETU) 10.4 g
Inhibitor, concentration 0.2 percent by weight
(of total solution)
Distilled water Sufficient to obtain 500 ml of solution not to exceed.

Another chemistry book I have says it is a combo of HCl, Sb2O3 and SnCl4

If you can get 3m scotch brite wheels for an angle grinder they are good for taking scale off without taking away the metal

The first batch was made with 500 g in 5 litres (100 g/l).

After 8 hours the black scale could be significantly removed by rubbing with a cloth.
It will be left overnight.
As there is very slight gas evolution, the batch is in a covered container in the middle of the yard.

A visit to the local Bunnings will provide a wire brush, and I will look for the 3M Scotch Brite wheel suggested by old_fella.

John.

At 20 hours there were sporadic gas bubbles still being produced.

The items were rinsed and hand wire brush cleaned.
There was a black goo that the brush would move around, but not remove.
A cloth removed the goo easily and it stained heavily into the skin like grease.
The finish was perfectly OK for painting.
The goo is probably the oil/dust/grease residue from the mill scale.

I noticed that any surface proud of the brew would quickly rust.
Re-immersion removed the rust just as quickly.

Put in again, removed at 25 hours, rinsed and power brush cleaned.
I used a sctoch-brite style brush generally with a wire brush to get into some of the corners.

One strut was originally painted and the brew removed significant amounts of paint.

Bright shiny metal was the end result.
Attaced is a photo, the various shades come from the attack angles of the brushes, some P80 paper I used in some corners, and sky reflection through the doorway.

Citric Acid can clearly be used to removed mill scale, probably at lower strength solutions than what I used (100g/l).
Happy Christmas to all,
John.

What no before shots?
They came up nice John. I'll have to remember that one as I've only ever used Citric acid to remove flux after silver soldering S/S.
Stuart