Sciencemadness Discussion Board - Beautiful Titanium-based Multilayer Precipitate.

Beautiful Titanium-based Multilayer Precipitate.

I am a fish - 16-6-2005 at 12:08

I dissolved an excess of titanium granules in dilute hydrofluoric acid (generated in situ, by placing the titanium in 10% hydrochloric acid, and then adding sodium fluoride solution). The reaction proceeded slowly, and at first, resulted is a green solution, presumably due to the presence of [TiF6]3- ions. A day later, the colour had changed to purple, presumably due to a drop in hydrogen fluoride concentration, causing the presence of uncomplexed titanium 3+ ions (strictly speaking [Ti(H2O)6]3+ ions).

I decanted the solution off, and started experimenting with coordination complexes. I noticed that basic compounds produced a thick, grainy and very dark precipitate. (I first noticed this with ethylene diamine, and then produced exactly the same result with ammonia, and finally with potassium hydroxide).

In order to investigate this precipitate further, I added the remainder of my titanium solution to an excess of potassium hydroxide solution, and left the mixture to settle overnight.

The following day, I was confronted with the most beautiful precipitate I have ever seen. It was divided into four layers. The top layer was snowy white, the second layer was a light grey-blue colour, the third layer was a deeper grey-blue colour and the bottom layer was a blue-black colour. It should be noted that the the colours did not form a continuum, but instead were divided into four discrete layers.

I don't know what the precipitate is, and will investigate it further. Also, the author of Science Made Alive briefly mentions a similar precipitate, but makes no mention of layering.

Pyridinium - 16-6-2005 at 14:29

This sounds great. Do you have any pictures of it? I'd really love to see it.

Four layers, wow. I love chemistry.

Have you tried oxidation of Ti with 5-10% sulfuric acid and 3% H2O2? If it's free of fluoride, Fe, Ni, Cr, it will make a nice colored complex. (can't remember offhand what the formula is).

I am a fish - 17-6-2005 at 07:51

Hydrofluoric acid oxidizes titanium to the Ti3+ state. However, I think a mixture of sulphuric acid and hydrogen peroxide would oxidize it further, to the Ti4+ state. When I added hydrogen peroxide to my titanium(III) fluoride solution, it turned bright red, which is the distinctive colour of Ti4+ complexed with hydrogen peroxide.

Nevertheless, I will see what happens when I prepare the titanium solution in this manner. I am currently dissolving the titanium, but the reaction is progressing very slowly, and so I have nothing yet to report.

Lambda - 17-6-2005 at 09:39

Quote:

Originally posted by I am a fish
I dissolved an excess of titanium granules in dilute hydrofluoric acid (generated in situ, by placing the titanium in 10% hydrochloric acid, and then adding sodium fluoride solution).

I am a fish, personly I would rather keep the titanium granules. Titanium dioxide and aluminium trioxide are one of the most used white pigments. Titanium dioxide, having a overwelming white appearance, is as pigment incredibly cheap. Hughe quantaties can be obtained via any paintstore that mixes it's own pigments.

Could this not be a cheap resource to conduct your very interesting experiment with ?

Just adding my two cents. I to, look foreward in seeing pictures of your results.

Good luck !

Pyridinium - 17-6-2005 at 13:28

Quote:

Originally posted by Lambda
I am a fish, personly I would rather keep the titanium granules. Titanium dioxide and aluminium trioxide are one of the most used white pigments. Titanium dioxide, having a overwelming white appearance, is as pigment incredibly cheap. Hughe quantaties can be obtained via any paintstore that mixes it's own pigments.

Could this not be a cheap resource to conduct your very interesting experiment with ?

It depends on how the TiO2 was made. Precipitated TiO2 (from aqueous solutions) will dissolve in acid. TiO2 made by high temperature ignition will not, at least not very well.

I don't know why there's a difference, except maybe there's an alpha and beta modification or something.

I am a fish, I looked up that H2O2 complex formula with sulfuric acid. It's TiO2(SO4)2(2-). Orange to red. Apparently you may also get some H4TiO5.

It sounds as though at least one of your precipitate layers is a hydrogel, made by neutralizing an acidic Ti ion solution with excess alkali. I have a 1940 reference here that says this gel has been analyzed with X-ray diffraction, and they say that, if it's allowed to age, the pattern is the same as the anatase form of TiO2. Interesting!

The bottom layer may also have Ti(OH)3, slowly turning to TiO2. Just a guess though.

12AX7 - 17-6-2005 at 17:28

Quote:

Originally posted by Pyridinium
It depends on how the TiO2 was made. Precipitated TiO2 (from aqueous solutions) will dissolve in acid. TiO2 made by high temperature ignition will not, at least not very well.

Probably surface area, same thing with alumina and magnesia, big refractory products. Calcined (and dead burned, respectively) are pretty inert.

Tim

I am a fish - 21-6-2005 at 11:41

Quote:

Originally posted by Pyridinium
Have you tried oxidation of Ti with 5-10% sulfuric acid and 3% H2O2?

I added titanium to such a mixture (see above), and after a few days I obtained a deep red solution. However, on adding potassium hydroxide solution, I merely obtained a plain white precipitate, which I assume is hydrated titanium dioxide.

This result in unsurprising, as the precipiation was from a Ti4+ solution (rather than a Ti3+ solution). However, I will try reducing the solution with zinc first, and then see what precipitate I get.

It has also occured to me that Ti3+ ions are oxidized by the oxygen in air. Therefore, my four layer precipitate may have contained mixed oxidation states.

Quote:

This doesn't matter a great deal, as I usually work on a semi-microscale. However, I will look into using this route (see below).

Quote:

Originally posted by Pyridinium
Precipitated TiO2 (from aqueous solutions) will dissolve in acid. TiO2 made by high temperature ignition will not, at least not very well.

I will try dissolving pottery grade titanium dioxide in sulphuric acid. I will also try dissolving it in a mixture of sulphuric acid and hydrogen peroxide. (Although the hydrogen peroxide is not needed as an oxidizer (as the titanium is already in a Ti4+ state), it may help dissolution, by forming a complex with the product.)

[Edited on 21-6-2005 by I am a fish]

Update:

I am a fish - 17-7-2005 at 09:15

The four layer precipitate has now become a two layer precipitate. The blue-black bottom layer has remained the same, whilst the rest of the precipitate has turned white. This could be because the intermediate layers consisted of mixtures of the upper and lower components, which have now fully seperated. However, if this was the case, I expect that a continuum between white and deep blue would have initially formed, rather than discrete layers. Another possibility is that the intermediate layers have been oxidised into the same substance (probably TiO2

as the top layer.

Quote:

I added pottery grade TiO2 to 10% sulphuric acid about a week ago. Yesterday, when I added hydrogen peroxide to the mixture, it turned a faint orange/yellow colour. I assume that this is due to low concentration of the strongly coloured Ti4+ / H2O2 complex. This indicates that a reaction had occured, but only to a very small extent. Since adding the H2O2, I have not noticed any increase in the colour's intensity, and so its presence cannot be significantly accelerating the reaction.

Quote:

I will try reducing the solution with zinc first, and then see what precipitate I get.

I added an excess of zinc powder to my Ti4+ / H2O2 solution. I decanted off a liquid, which was the characterstic purple colour of Ti3+. I then added potassium hydroxide solution. However, instead of the previous result, I obtained a dark grey metallic-looking sheet-like precipitate, which later faded to white.

Titanium chemistry is starting to baffle me. I will try the experiment with my original setup, to see if I can repeat the original result.

woelen - 29-8-2005 at 14:28

I'm new to scimad and found this topic. I'm also very interested in titanium chemistry and I found an even more interesting phenomenon. Titanium (III) and titanium (IV) form a mixed-valence complex with multiple titanium ions in a single ion. The exact nature of the stuff, I did not yet determine. I added some pictures on my site about the titanium experiment. See here.

I also did more experiments with the blue/black precipitate of titanium (III). It is oxidized by water, forming hydrogen gas, itself being converted to white hydrous titanium (IV) oxide. It is most remarkable that a metal hydroxide forms hydrogen gas with water! Nice and detailed pictures of this will follow in due time on my site.

The layered structure of the precipitate, I indeed did not observe, but what I sometimes did observe is that the precipitate is changing color from dark to white slowly, starting at the surface of the liquid. This probably is due to oxidation by oxygen from the air.

[Edited on 29-8-2005 by woelen]

chloric1 - 29-8-2005 at 18:14

I am fish, I am thinking some of your layers contained Ti+3 and these, like the ferrous ion, are much more suseptible to oxidation by air when in an alkaline state. If you can reduce vanadium to the bivalent state add alkali and I am sure you would find simular results.

As far as titanium white goes, I think it shares the property with niobium and tantalum oxides in that a bisulfate fusion shall make them soluble.

Woelen, if I knew trivalent Ti was that beautiful I would have tried long ago! Where did I put my Titanium sheet !?!

[Edited on 8/30/2005 by chloric1]

[Edited on 8/30/2005 by chloric1]

woelen - 30-8-2005 at 12:55

This is a detailed picture of the precipitate of titanium (III) hydroxide, which reacts with water to form hydrogen gas:

http://81.207.88.128/science/chem/solutions/tiIIIoh.jpg

This is the same precipitate a little later. You can already see it turn lighter near the surface of the liquid.
http://81.207.88.128/science/chem/solutions/tiIIIoh-2.jpg

When it is shaken:
http://81.207.88.128/science/chem/solutions/tiIIIoh-3.jpg

When it is shaken in contact with air for a longer time:
http://81.207.88.128/science/chem/solutions/tiIVoh-2.jpg

The following also is nice. It is the complex of titanium (IV) with hydrogen peroxide at moderate concentration:

http://81.207.88.128/science/chem/solutions/tiIVh2o2.jpg

These pictures are part of a section in my website about many transition metals (all first row and many second and third row). I want to make an overview of all colors of all oxidation states, all precipitates of hydroxides, many common complexes and all solutions of higher oxidation states. This is a large job and it may take a few more months, but if it is finished, then I'll certainly let you know. Pictures from it will be published sometimes earlier, when appropriate.

I most like titanium, vanadium and chromium. These are really interesting

.

[Edited on 30-8-2005 by woelen]

WOW!

chloric1 - 30-8-2005 at 15:01

Those are really great! I especially like how the Ti+3 hydroxide on shaking with air turns into the white dioxide.

Speaking of the dioxide I know that the dioxide mixed with carbon will react with dry chlorine gas at about 500 to 600 C, do you know what are the conditions of the chlorine on the pure metal? Is it very dangerous? To me it would be impractical like heating aluminum in chlorine.

I am a fish - 6-9-2005 at 11:58

My original precipitate is now completely white. The two middle layers were presumably different mixed-valence complexes, which were both highly susceptible to oxidation (hence their short lifespan). The bottom layer was presumably titanium(III) hydroxide, whislt the white top layer was always titanium dioxide.

Quote:

Originally posted by woelen
When it is shaken in contact with air for a longer time:
http://81.207.88.128/science/chem/solutions/tiIVoh-2.jpg

The colours in this image are very similar to those of my original precipitate. The particles suspended in the liquid appear to have different colours (although this could be an illusion caused by them being at different distances from the surface of the tube, and so being occluded by different amounts), and so could be of differing chemical composition. I expect that my coloured layers formed from a mixture of very similar composition to that shown in the image. If you had sealed the tube at this point, and had let the mixture settle, you may have ended up with the same multi-layer phenomenon.