Phosphoric Acid experiment

Ok this is probably of little interest to anyone but nonetheless

Have this old fragment of (what now appears to be) wrought iron. Been using it for years to open paint tins, lever out nails etc. You know the sort of thing.

Recently decided to try clearing rust off a section using Phos. Acid. (light grey area in above photo)

24hour immersed in acid reveals interesting striations in the structure of the metal - once the rust is 'dissolved'.

(I believe this is consistent with old wrought iron)

Will probably do some follow up exploration on this. Should it be of interest I may post more photos.

Regards.

Frank C.

I have one of these, though probably of high-carbon steel.

It might indeed have been simply a small crow-bar, but alternately could have been a "lewis" chisel - a stone-trade tool.

The "lewis" is an old tool for lifting blocks of stone, consisting of a double-sided wedge placed between two single-sided ones, all linked by a shackle-pin, into a mortice-like socket cut into the block by using a chisel of that shape.

The curve allows the mason or quarryman to cut the hole with the necessary vertical or inwardly-diverging, sides.

If wrought-iron it would not held an edge for long used as a chisel, though for centuries that was the only "tool-steel" available; apparently amenable to a degree of very crude hardening. It think it would more likely have been used on soft "freestones", rather than on the very hard, coarsely-crystalline, igneous rocks like Cornish Granite or rough stuff like conglomerate.

"Freestone" is a trade generic for, those rocks that are easy to cut in all directions when "new", though slowly harden by weathering. Most are species of limestone and sandstone; but the locally-quarried, slightly pumice-like volcanic lava used for the ashlar components of many of Exeter's old buildings may have been similar to work.

.

Yes please, Frank

MichaelG.

Looks like wrought iron to me. You can often see the same grain structure in old anchors and similar things dredged up from the sea bed. My father had one where you could see the way the grain changed where the smith had fire-welded the shaft.

My blacksmithing instructor in the 1970s said you can identify wrought iron by the smell, because it's all so old...

George

I had the same pattern happen on a small handrail bracket for a 5" gauge tender. The bracket was steel, and I left it in the acid overnight by mistake.

It came out looking just like that but on a much smaller scale.

I left a piece of mild steel in phosphoric acid (Chemtech Rust Off Remover - from local hardware store) overnight - because I forgot! Nothing to do with my age! Same effect. No "grey" finish, more a rusted orange colour. I will attempt to find it tomorrow and photograph it.

Different materials have varying reactions in phosphoric acid. I only paint it on not dunking things and sometimes it 'gells' almost immediately and sometimes does nothing, depending on the material, carbon content, presence of rust etc. After half an hour-ish I washi ti off and then get the grey appearance and milky white water. IN damp conditions I can get the grey in advance.

The striations in some wrought iron are the result of the old methods in an open hearth furnace which involved mixing in more iron ore. This produced a lot of slag mixed into the bloom which along with the oxide that formed on the surface of red hot iron as it was rolled gets pressed into the material. I think it is a characteristic of the metal being rolled into thin sections rather than the drawing that is now used,

Wrought iron or the end of a billet of rolled steel. About 45 years ago I had to repair the mounting plate on a attachment digger for a tractor, the boss came away, so rewelded it, it came away again so reweld ! At the 3rd break I studdied it closely and found that the sheet of 3/8"steel was in fact a series of layers of iron and slag. My guess at the time was it was the end of a billet and the mill scale and iron had been rolled so many times to form this coposit structure. It should have been scrapped at the mill and remelted. I gave up welding it and ordered a new mounting. Old chain ( big stuff ) will have this structure and is valuable as true wrought iron is seldom made now and it is re rolled. Noel.

This old plane iron had the phosphoric acid treatment a considerable number of years ago;

What I find interesting is that you can clearly see where the expensive cast/crucible steel cutting edge has been (presumably) fire welded to the wrought bulk of the iron.

Rod

Very cool!

phosphoric acid is also used in commercial vehicle wash bays to clean aluminium.

...and of course famously in Coca Cola. However I doubt it has anything to do with metallurgy.

In praise of Coca-Cola Original; not fit to drink because of high sugar, but a super bog cleaner! Due to Phosphoric acid content. A used toilet cleaner bottle with a bent neck design, re-filled with Coke, ideal for under rim cleaning. And a large bottle works out cheap. Try it sometime!

Edited By DMB on 05/07/2022 08:21:01

Considering just how little Phosphoric acid is in Coke, I doubt it's cheap compared to just buying the acid.

I usually use vinegar to clean the black oxide from steel when I have silver soldered parts. The other day I forgot about a small part and left it in the vinegar for 3 days. I found that the steel was eaten away just like in the pictures, in fact I had to make another it was so bad. So the same thing happens with acetic acid.

If Frank's object isn't Wrought Iron, I'll eat it!

The structure is due to the way the Iron was purified by repeated hammering.

Before about 1850, the chemistry of metal making was poorly understood and results depended on trial and error methods skillfully adapted to local conditions. The problem was impurities: Carbon and Manganese are 'good', Sulphur and Nitrogen are bad, and many others including Phosphorous, Silicon, Molybdenum, Nickel Silicon, Boron, Arsenic, Aluminium, Lead, Tungsten, Chromium, Vanadium, and Cobalt have good effects in carefully controlled proportions, otherwise bad. Understanding the chemistry makes an enormous difference.

Wrought Iron dates from the time when the best that could be done with dirty Iron was encourage impurities to dissolve into the slag in a low temperature furnace and then beat the slag out of the semi-molten metal/slag mix by repeatedly folding and hammering it. The more this was done the better and it's expensive.

The notion metals have more or less 'quality' come from the prescientific period because metals became purer the more they were skilfully re-heated and hammered or otherwise processed. More art than science, and more than a bit magical.

Buying metal for a purpose meant choosing it from a particular area and from the particular manufacturer who got closest to your requirement. Buyers had to understand the merits of iron variants produced by Carron, Buffery, Elsicar & Milton, Coed Talon and many other small makers, and why the iron was supplied in different forms: Best Bar Iron, Soft bar Iron, Cold Short Bar Iron, Hard Bar Iron etc. The amount of effort put into refining was often indicated by multiplying adjectives, such as 'Best Best Best Iron'. Processing often went wrong, and the accounts of early engineers are full of complaints about the random properties of what they got from the trade.

Between 1850 and 1860 Bessemer revolutionised the production of steel by realising that blowing air through a large charge of molten iron and coke would remove many impurities whilst also controlling the amount of Carbon in the mix. The resulting mild-steel was an excellent substitute for Wrought Iron: much cheaper, stronger, and without the layer structure that gives Wrought Iron high tensile strength along the grain but leaves it weak in other directions.

Mild-steel is also easier to machine, and can be mass produced even more cheaply simply by scaling up the furnace. The main disadvantage of mild-steel is it rusts.

A huge step forward but Bessemer almost came unstuck because he tested his new process with a low-phosphorous ore. It worked a treat, but the Bessemer process failed when tried with iron made high-phosphorous ore, a common type. Fixed by a chemist who analysed good and bad steels, and spotted Phosphorous was the problem and that it could be removed by lining the furnace with a suitable basic material.

The original Bessemer mild-steel was inferior to modern mild-steel because blowing air through the mix left Nitrogen in the alloy, another problem it took a chemist to identify. Fixed by blowing Oxygen extracted from air instead of compressed air.

Modern metal production is a far cry from melting stuff in a pot and relying on artisans to improve it! Although production can and does go wrong, it's far more reliable than earlier methods. For example, a rough analysis of the content of a molten mix with laboratory methods circa 1900 took over 30 minutes, too long to fix certain problems, whereas modern methods get an accurate analysis of the mix almost in real time, making it much easier to correct problems by adding chemicals, changing temperature, or whatever.

In it's day Wrought-Iron was a top engineering material, extremely useful and costly. Now rarely made and only in tiny quantities. It's almost exclusively used for high-end decorative iron-work, because it blacksmiths, looks good, and is low-maintenance.

Dave

Thanks, Chuck, your find is proving more interesting than you expected.

I read some years ago, perhaps when visiting the Ironbridge museum, that wrought iron isn't made any longer.

A brief search brought up: Wrought iron. I had expected that "old stock" might have been recycled, but they claim to be the only supplier in the world.

I recall seeing some large anchors at Portsmouth dockyards, with very significant grain visible.

I think that I read that sand or crushed glass was used as a flux, or was that blacksmith welds?

Thanks, Dave, for interesting details.

Bill

Yes - sand was used as flux, at least for hammer-welding flux.

Or crushed glass - chemically identical to all intents and purposes. (Silica: glass is fused sand. Its natural source is as quartz crystals weathered from igneous rocks such as granite, possibly recycled naturally via sand-stone over many millions of years.)

Wrought-iron was commonly used for rivets even when the structural material was mild-steel, until well into the 20C. There are probably thousands of millions of them still carrying out their unassuming duty, holding together any number of Victorian and Edwardian bridges, main-line railway termini, preserved machinery, and the like!

I recall a lecture on the paddle-steamer 'Waverley', recounting how the original paddle-wheels had come to the end of their lives. Her owners, the PSPS, tried to sell the salvageable wrought-iron as smithing material, but found no takers for it.