Sciencemadness Discussion Board

Titania ceramic

microcosmicus - 9-1-2008 at 01:26

In the thread on diamond electrodes,
( http://www.sciencemadness.org/talk/viewthread.php?tid=9628&a... )
12AX6 said
Quote:

I'm learning every day, more and more, just how fucking resilient TiO2 is.
Even to fluorides. . .


This comment fired my imagination. To about 2000K. :o This sounds
like just the thing for making crucibles, evaporating dishes, or anything
else which faces exposure to nasty chemicals.

Having obtained some TiO2 from the pottery shop the other day, it
was time to make some pottery. I took a bit of titania and mixed it
with water. Immediately I noticed how hydrophyllic it was --- it
sucked up the water like a sponge. I suppose this explained the
label "98% Titanium Dioxide, 2% moisture" as well.

I easily made up a slip and spread it upon a plaster bat to make a
slab of TiO2 and dried it over a radiator (about 50C or so) for an
hour. At that point, the slab was quite crumbly and fell apart at
the slightest touch.

To fire it, I used a MAPP torch. The first attempt failed because the
jet of hot gas simply blew the powder all over. The next time around,
I covered the titania slab with an alumina-mullite tile to keep it from
blowing about and succeded. I heated it until it was glowing bright
white ---hotter than molten iron, but not hot enough to melt the tile,
I would estimate 1700C--- for a few minutes, By then, the ceramic
had sintered and was more than solid enough not to be blown to
dust, so I removed the tile and heated it directly with the flame for
another five minutes or so. Upon cooling down, I noted that it was
a bright lemon yellow, but this color gradually faded away in the
next few minutes as it returned to the usual white.

At the end, I had a nice, hard, porous piece of ceramic, so it should
be possible to make dishes from it as well. However, it is not very
convenient working with a clay that practically turns to dust upon drying,
so I would prefer to do things a bit differently so as to have greenware
which stays in one piece. I suppose that adding a pinch of ball clay
would do the trick, but I don't like the idea of adding foreign material
(and presumably silica would compromise the resistance to fluorine)
so I am going to try something else; however, it is past my bedtime,
so that will have to wait for tomorrow. Just a preview for now.

The next thing I plan to do is fiddle around a bit with titanium compounds,
starting by synthesizing titanium carbonate according to a procedure I
found in an old book. From this, it should be easy enough to prepare
other compounds by acting with acids.

By the way, as I found out while researching on the web,. TiO2 has
some interesting uses other than as an inert material.

Upon exposure to UV light, it becomes an oxidizing agent with
a standard cell potential of 2.23V! As such, it is able to make
superoxide ions, hydroxyl radicals, and other such goodies --- it
sounds like an interesting and useful catalyst to have around the lab.
http://www.tekon.com/green/Photocatalyst.html
http://www.photocatalyst.co.jp/e/tukuru/tukuru.htm

It can decompose proteins:
http://www.eurekalert.org/pub_releases/2007-03/nios-tdi03300...

Also here is an experiment making a solar cell using TiO2 suitable
for home use --- they even sell kits.
http://mrsec.wisc.edu/Edetc/nanolab/TiO2/

Over and out,
R.S.P.

P.S. I also got some BaCO3 while I was at the store, so I will also have
to bake up some barium titanate. Even more fun stuff, ferroelectric
and all, but that will have to wait for another day and perhaps
another thread :)

[Edited on 9-1-2008 by microcosmicus]

[Edited on 9-1-2008 by microcosmicus]

[Edited on 9-1-2008 by microcosmicus]

[Edited on 9-1-2008 by microcosmicus]

[Edited on 9-1-2008 by microcosmicus]

12AX7 - 9-1-2008 at 03:00

To be more specific about my situation,

I had dissolved about 10 g NH4HF2 in 50ml H2O. To this I added an annealed titanium strip, complete with "scale", which is dark TiO2 / Ti2O3. After a few minutes, some minute bubbling was seen. About 10ml HCl (31%) was added, having little effect. The strip was left overnight. After 12 hours of soaking, there was no uniform effect on the surface, most of it being unaffected. There was deep pitting in areas, exposing craters of metallic titanium. The solution was turbid white.

Another solution of acid which I added fluoride to momentarily performed better, actually managing to clean and etch a piece of titanium uniformly. The solution turned black with a shade of green. My guess is it no longer has any effect because the fluoride is thoroughly complexed with titanium in solution. Does anyone know the Kf of TiF6(2-)? The activity and color do not change with extreme acidity.

As far as TiO2 as a ceramic, I would recommend using some clay or silica or whatever, just because it's easy to. Silica and titania don't get along real well (there is a range of immiscibility on the phase diagram, as I recall), but 5-10% silica/alumina should be soluble and have little effect on chemical properties.

SiO2 and TiO2 probably have similar overall reactivity, being very little (in fused or sintered form), but still forming MF6(2-) ions as a result of fluoride attack. Besides SiO2, mullite and Al2O3, MgO is certainly worth some consideration. Though it is a reasonably reactive hydroxide, it's my understanding that it's essentially unreactive in sintered form, and this should be no suprise given its insane melting point (2800C or so). It should be excellent for working with reactive metals. Some day when I get my induction heater up to full power, I'll have to purchase inert gas and a crucible and see if I can successfully melt titanium inside of the stuff.

Tim

not_important - 9-1-2008 at 09:12

TiO2 is resistant to acids but not alkalies, dissolving in fused sodium or potassium carbonates for example. It's also fairly easy to reduce to mixed oxides, which have a lower melting point.

The biggest problem, and likely the reason you don't see TiO2 labware being offered for sale, is that it has 4 allotropes, which often means size changes during heating and cooling, and may be why it is listed as have "rather poor thermal shock resistance"

The mixed oxide's lower melting point can be used to bond TiO2 into a solid. Heat the TiO2 to 1650 C or so, run the atmosphere into reduction to generate some Ti2O3 giving the molten mixed oxide, then slowly back into oxidation to convert that back into mostly TiO2.

The yellowing of TiO2 when heated is well know, there are thermochromic and photochromic glazes around based that use TiO2 for those effects.

microcosmicus - 9-1-2008 at 09:49

Quote:
Originally posted by 12AX7
To be more specific about my situation,

I had dissolved about 10 g NH4HF2 in 50ml H2O. . . .
The solution was turbid white.


I will have to try that with a bit of titania ceramic when I get the chance.
BTW, anybody out there have suggestions where to scrounge up a fluoride?
Quote:
Originally posted by 12AX7
As far as TiO2 as a ceramic, I would recommend using some clay or silica
or whatever, just because it's easy to.


Sure, a bit of binder wouldn't hurt, especially since one could also paint
a layer of pure TiO2 on the surface as a glaze. However, I am dong this
as much for the challenge as anything else ;) Also, it gives me an occasion
to play around with the chemistry of Ti. That said, I will also mix up a
few batches with clay and silica sometime to see how they turn out.
Quote:
Originally posted by 12AX7
Silica and titania don't get along real well (there is a range of immiscibility on the phase diagram, as I recall), but 5-10% silica/alumina should be soluble and have little effect on chemical properties.


Where did you find this phase diagram?
Quote:
Originally posted by 12AX7
MgO is certainly worth some consideration. Though it is a reasonably reactive hydroxide, it's my understanding that it's essentially unreactive in sintered form, and this should be no suprise given its insane melting point (2800C or so). It should be excellent for working with reactive metals. Some day when I get my induction heater up to full power, I'll have to purchase
inert gas and a crucible and see if I can successfully melt titanium inside of
the stuff.


Once I finish fiddling with titania (or sooner if I get impatient), I will have
a go with magnesia. In particular, magnesia cement looks promising:

http://www.premierchemicals.com/corner/articles/cements.htm

The materials are easy enough to obtain or make, and it sounds like
a good material for lining furnaces and the like. But what the heck
is a 22 Be solution of MgCl2 ???!!!!??!!!?! Why couldn't this fellow
use intelligent units for concentration, like g/l of molarity instead of
sending me on a wild goose chase through ancient tomes :mad:

Alright,. time to get back to work. Later on, I'll try my hand at synthesizing
some Ti(CO3)2 the old-fashioned way and be sure to keep y'all posted
on how it goes.

P.S. Some folks say titanium carbonate helps you get your pep on,

http://ci.nii.ac.jp/naid/110006200374/en/

but I'm not mad enough a scientist to try that --- instead. I'll stick to
safe toys like 2000 degree furnaces ;)

Ray

[Edited on 9-1-2008 by microcosmicus]

microcosmicus - 9-1-2008 at 10:28

Quote:

dissolving in fused sodium or potassium carbonates for example


Dissolving it in alkali is exactly what I plan to do tonight.
Quote:

is that it has 4 allotropes, which often means size changes during heating and cooling

I see . . . the stuff is bad as quartz with its inversions. While that might preclude
some uses and means having to be careful cooling it to avoid dunting problems, I'll at
least keep on trying this out of curiosity, to see what Ti ceramic looks like. Also, the
stuff about photocatalyst looks interesting.

Quote:

The mixed oxide's lower melting point can be used to bond TiO2 into a solid. Heat the TiO2
to 1650 C or so, run the atmosphere into reduction to generate some Ti2O3 giving the
molten mixed oxide, then slowly back into oxidation to convert that back into mostly TiO2.

Sounds like a plan --- this could form a basis for glazing titaniaware. For me, the problem
is not with the high temperatures but with the low temperatures --- how to keep the
stuff from falling apart before it gets hot enough that the particles stick together of their
own accord. My thought is to try gluing it together with some titanium salt. Hopefully, if I
pick the right salt, not only will it glue the dust together at room temperature, but, once
in the kiln, the salt will first melt, keeping the ceramic-to-be stuck together, then decompose
at higher temperature to make more TiO2. I won't speculate further, especially since I plan
to do the experiment soon enough.
Quote:

The yellowing of TiO2 when heated is well know, there are thermochromic and photochromic glazes around based that use TiO2 for those effects.

I learn something new every day :) Thanks

[Edited on 9-1-2008 by microcosmicus]

Xenoid - 9-1-2008 at 11:25

@ microcosmicus

I would like to know how titanium carbonate is made, as a precursor to other titanium compounds, notably the nitrate. Please let us into the secrets of your "old book".

EDIT: Duh!... I failed to read the previous posts fully. Yes, fusion with sodium/potassium hydroxide/carbonate. I always forget about the alkali fusion methods!

I was in the hardware shop the other day, and I noticed that all the gas mantles are now made using titanium nitrate (among a few other things, Al2O3, MgO - REE for activation). On intial combustion the the nitrate will decompose to form the oxide. I was interested in this as the nitrate could be used in anode coating formulations. I hadn't realised the nitrate was stable, does anyone know how to make it?

Incidentally when "Googling" titanium nitrate, it is amazing how many people confuse it with titanium nitride (eg. some guy wants to set up equipment for titanium nitrate coating of drills, etc.)
Quote:
Originally posted by microcosmicus
Also here is an experiment making a solar cell using TiO2 suitable
for home use --- they even sell kits.
http://mrsec.wisc.edu/Edetc/nanolab/TiO2/


This reference was posted over a month ago in the thread "Mad Science with Titanium Dioxide"!

http://www.sciencemadness.org/talk/viewthread.php?tid=9589

[Edited on 9-1-2008 by Xenoid]

[Edited on 9-1-2008 by Xenoid]

garage chemist - 9-1-2008 at 17:18

Cant you simply use diluted waterglass (sodium silicate) as both binder and flux?
It delivers both sodium and silica and should form a liquid phase nicely upon firing.

chloric1 - 9-1-2008 at 18:40

Considering the 4 allotropes, and the poor thermal characteristics, maybe a titania dope zirconia or aluminum oxide ceramic would be better. Maybe a blend would create a more unreactive composite. Thinking along the lines how aluminosilicates are less soluble than the corresponding aluminates and silicates.