Proper acetone procedure

Thanks for the clarification. As I wrote: VC disappears from a coin's surface when it dries so you cannot see it. CC does not disappear and leaves a wet look. If you don't have a "sniffer" in your house, you will not know VC was put on your coin because it disappears. You can tell that Care was used - unless, it was removed in another step of the conservation process.

If the TPGS decides to analyze your coin, @JMGallego writes that both will be detected.

 

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Great information. I thought that the sniffer just caught residual organics that did not fully evaporate. I can see why a simple dip in acetone or other solvent won't get rid of this. Are there other reaction products that can form during the "conservation" process, or is Copper BTA the only one?

 

Calling @BadThad

 

JMGallego said:

Yes, the so-called "sniffer" (can be an analysis instrument called Surface Enhanced Raman Scattering, SERS http://jes.ecsdl.org/content/129/8/1716.short or even by Infrared reflectance spectra, http://www.sciencedirect.com/science/article/pii/S0010938X70800269 ) will detect films of benzotriazole (BTA) on the surface of a coppe coin or in a coin contains copper (such a 90% silver coins). BTA does not "disappear", it creates CuBTA by covalent bonds with copper atoms.

Do you have references for the part "BTA does not "disappear", it creates CuBTA by covalent bonds with copper atoms."

BTA does combine with copper, but the copper can not then maintain the metallic bonding with the coin. That is why references also refer to this as a "passive layer". The passive layer is insoluble in water, and in most but not all organic solutions, which leads me to believe that it is not permanent then it can be removed. I know its use has been explored for other coins, especially ancient coin bronze disease problems. I am not saying you are incorrect, just where you found the info as last I read on this a while back the bonding and structure of the cu-BTA was somewhat controversial. Thanks

 

Benzotriazole/tolytriazole (isomeric mixture of triazoles) will remain on the surface after using a solution and drying. It's a pretty good corrosion inhibitor but a harsh cleaner.

The sensitivity of the Sniffer is not very good being an ATR technique. Detection would depend on the thickness of the layer and instrument sensitivity. BZT is also a pretty easy target, it has a lot of "stuff" on the molecule to make IR detection easy. I can easily test a coin with BZT residue in my lab, will give it a shot sometime, I'm curious.

 

I've always considered metal-surface reactions as ionic not covalent. Nitrogen is a tricky thing, it does strange things with electrons. @Kentucky is the PhD, I'll leave it to him to explain lone pairs and pi orbitals.

BZT can be easily removed from a metallic surface, the pka is like 8. You just have to give a better place to go using some chemistry.

 

[QUOTE="BadThad, post: 2665805, member: 17261..Nitrogen is a tricky thing, it does strange things with electrons. @Kentucky is the PhD, I'll leave it to him to explain lone pairs and pi orbitals.[/QUOTE]
I bow to experience..."I'm not that kind of doctor, Thad."

 

I know of your lab Thad! Chem Disneyland!! When are you going to finish the book Jim

 

Ran a quick experiment today on the FTIR-ATR. As I already knew, BZT produces a strong IR spectrum. I made a strong solution of BZT in methanol and let it produce a dry film on the ATR, this is what I got:


As a control, I ran a RB Lincoln and nothing was obtained, basically just noise. Then I applied the BZT/methanol solution to the entire surface of the Lincoln and dried it using house air. It left a slightly sticky fiim on the surface so coverage was very good. The FTIR scan of the coin only revealed the two strongest IR bands at 1222 and 752 cm-1. Definitely not enough information to match to ANYTHING conclusively. It's my opinion that BZT residue on the coin surface is undectable on a coin surface by FTIR-ATR.

 

Great clarification, thanks.

Yes, it is still there but cannot see it because it is a very thin film. I have, somewhere, the thickness of the film, I will try to locate it.

In an indirect way, you can see the effect of the BTA. If you put a small drop of distilled water on the surface of the treated copper coin you will see that the drop is almost a small sphere, not oval, or smears, this is the hydrophobic effect of the BTA on copper. I have some photos from research/test articles showing this effect, I will try to locate them too. However, I can see that effect on the coins I have conserved.

 

Thanks.

The main reaction product is copper BTA, however, if present, there will copper chloride BTA and copper oxide BTA. The copper chloride BTA is of great interest, if the coin was not properly clean before the treatment leaving minute copper chlorides, the BTA will prevent those copper chlorides from coming into contact with water (or humidity) because it creates a hydrophobic film over the copper chlorides. This prevents the verdigris disease which is a cycle of creating hydrochloric acid out of the chlorides and corroding the copper metal.

 

Hi @desertgem,

Yes, several scientific articles describing the bonding and structure of the CuBTA. One of this article published back in 1989 entitled "COORDINATION POLYMERIZATION OF BENZOTRIAZOLE ON THE SURFACE OF METALLIC COPPER". In this article, the authors explain the chemistry and explain the film composition. They conclude: "We have shown that BTAH can react with copper metal other than copper cations or oxides in extremely mild conditions. The reaction product is mainly bis ( benzotriazolato ) copper ( II ), which covers the surface in the shape of a polymeric material." They used infrared (middle) and X- ray photoelectron spectroscopies and elemental analysis.

Another interesting one is the 2009 article "A review of the effects of benzotriazole on the corrosion of copper and copper alloys in clean and polluted environments". In it, it has a section called "Benzotriazole: its chemistry and mode of action" that explains in detail the how the bond is created. Another section is the "Inhibiting effects of benzotriazole, its derivatives, and blends". Very interesting article.

And there are plenty of articles on analyzing BTA film on the surface of copper. Just to mention a couple, one is the 1970 "Reflection infra-red studies of films formed by benzotriazole on Cu", the 1990 "The use of near-infrared Fourier Transform techniques in the study of surface enhanced Raman spectra" and the 1985 "A photoemission study of the adsorption of benzotriazole on copper"

These are just a few articles, there are many more and recent ones.

 

Agree, but as explained in some of the articles, the bond is covalent because of the lone pair of the nitrogen. I will look at my references and double check it. Thus, too, it should be easy to remove, but I have not found an article describing how to remove it, except for abrasive method, agh! not good for coins. I tried several common organic solvents and I can still see the hydrophobic effect of BTA. I recently purchase DMSO to see if it is strong enough to remove it, but I have not had a chance to test it.

 

Hi @BadThad,

Here is a shot of the IR spectra from the 1989 article "COORDINATION POLYMERIZATION OF BENZOTRIAZOLE ON THE SURFACE OF METALLIC COPPER":

For Surface-Enhanced Raman Spectras of BTA film on copper, I have notes regarding the article "A surface enhanced Raman spectroscopy study of the corrosion-inhibiting properties of benzimidazole and benzotriazole on copper", published in Langmuir Y. 1991, vol. 7, No. 1, pages 2-4. But I do not have this article, I will try to get a copy from the University later on.

Hopes this helps.

 

By the way, great questions!

Thanks for the interest, I have been working on conservation of copper and silver coins with BTA for a while. I wanted to make sure that my valuable coins were properly conserved and slabbed.

TPGs are not doing surface analysis on coins submitted for grading unless it is a high valued coin, very high value... anyone knows how high before they "sniff" the coin?

 

Sounds very much like the upper spectrum in @JMGallego's posted snippet. I wonder if those two bands are enough of a signal to make a TPG throw a flag on the coin?

 

@BadThad,

You may want to try leaving the coin for about 20-30 minutes in your BTA/ethanol solution to allow the protective film to form. I would recommend a diluted solution not higher than 5% (2-3%) and the pad dry it with a clean microfiber cloth.

 

It may, your spectra shows the BTA peaks quite nicely. The interesting part would be if it shows the band drifts too on the copper-treated coin like in the article.

 

The article is ~30 years old, check out their IR spectra and compare to a modern FTIR (mine above, 2 years old). LOLOLOL