coal
Harmless
Posts: 15
Registered: 13-10-2007
Member Is Offline
Mood: No Mood
|
|
zirconium oxide from zirconium silicate
right. my first ever post! 
i need some zirconium oxide to experiment with makeing lead zirconium titanate ceramic, but i can only find zirconium silicate. some googling has
reveled this is done industrialy by mixing with coke and iron and getting it damn hot, the silicate being reduced to silicon and alloying with the
iron (http://www.madehow.com/Volume-1/Zirconium.html).
this would be a bit of a pain in the arse. is there an easy way? can i simpley desolve it in NaOH? i supose i could try some sort of thermite type
reaction... if i had any Al powder. its this silicate i don't realy know what to do with, once i'm at a hydroxide or sulphate i can go from there
easily enough.
i also have a worying little voice in my head telling me if i can't work this out i don't have much hope of makeing fun piezoelectric PZT ceramics.
ho well 
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
The silicate will combine with aluminum (not very vigorously), but don't bet on the zirconia part.
NaOH isn't going to touch it; it's much too refractory a compound. Cooking in an autoclave might work. Fusing with NaOH might have more success.
You still have to seperate the components while preventing them from forming the original compound.
In preparative terms, the best way is going to be dissolving it all in hydrofluoric acid and seperating the ZrF6(2-) and SiF6(2-) ions.
Industrially, a reductive chlorination is in order. ZrSiO3 + 3C + 4Cl2 --> ZrCl4 + SiCl4 (+ etc.) + 3CO. This has the advantage that the
chlorides can be seperated by distillation, and the chloride can be reduced to Zr metal in the Kroll process, as with Ti. If you hydrolyze the ZrCl4,
you will get high purity Zr(OH)4, perfect for something as tricky as piezoelectric materials.
Naturally, the same goes for Ti. You could take Ti- and Zr-rich ores, feed them to the chlorinator and distill out your two components.
The problem with technical ceramics such as piezoelectrics, ferrites, phosphors and others is, they often require high purity and tight tolerances to
get the right properties. In many materials, the special properties are due to the minute impurities in the structure, rather than the structure
itself.
Reduction with Fe and C is interesting, and I can see that working. You get a mostly-ZrO2 slag, which could be further processed. I wonder if much
ZrC is made in the process. You can hook graphite rods to a welding box, poke them into a mixture and make an improvisational arc furnace, but don't
expect to get much yield or anything. I would expect a glassy, very hard, very refractory slag from such a process.
Tim
|
|
|
Xenoid
National Hazard
Posts: 775
Registered: 14-6-2007
Location: Springs Junction, New Zealand
Member Is Offline
Mood: Comfortably Numb
|
|
If you obtained your zirconium silicate from a pottery supply shop, you should also be able to obtain zirconium oxide. Most of the pottery suppliers
around here sell it for about 50% more in price.
Interestingly, zircon (zirconium silicate) is extremely refractory and resistant to attack and Zr was often reported low in early wet analytical
techniques compared to modern non-destructive XRF analyses. One method to get it in solution was HF in a small, heated, teflon lined bomb.
Zircon is capable of surviving one or even more complete tectonic cycles lasting 100's of millions of years. That's original formation in a granite
melt, intrusion into the crust, erosion, incorporation into say a sandstone, melting and incorporation into a granite again. This shows up as zircons
with irregular crystalline overgrowths, each layer of which can be dated with modern ion probes.
As of 2001 the oldest dated thing in the world was a zircon from Western Australia with an age of 4,400 million years, but I have a vague recollection
that an even older age was obtained recently for a zircon from Greenland or Canada.
A very resistant material indeed!
Regards, Xenoid
[Edited on 17-10-2007 by Xenoid]
[Edited on 17-10-2007 by Xenoid]
|
|
|
garage chemist
chemical wizard
Posts: 1803
Registered: 16-8-2004
Location: Germany
Member Is Offline
Mood: No Mood
|
|
Zirconium silicate is worked up industrially by fusion with NaOH.
I cite Ullmanns:
Caustic Fusion. Caustic fusion of zircon with a slight excess of sodium hydroxide at 650 °C (or sodium carbonate at 1000 °C) is the usual zircon
decomposition process [8], [9]:
ZrSiO4 + 4 NaOH ---> Na2ZrO3 + Na2SiO3 + 2 H2O
The cooled reaction mass is crushed and slurried in water. Water dissolves the sodium silicate and hydrolyzes the sodium zirconate to soluble sodium
hydroxide and insoluble hydrous zirconia. The hydrous zirconia, recovered by filtration, can be fired to oxide, dissolved in mineral acid for further
conversion to aqueous zirconium compounds, or dissolved in mineral acid for feeding to a hafnium extraction process.
A variant of the caustic fusion process uses less caustic to produce an acid-soluble sodium zirconium silicate
ZrSiO4 + Na2CO3 ---> Na2ZrSiO5 + CO2
The frit from this reaction is added to strong acid to yield a solution containing sodium and zirconium salts and silica gel:
Na2ZrSiO5 + 4 HCl ® 2 NaCl + ZrOCl2 + SiO2 + 2 H2O
[8] H. L. Gilbert, C. Q. Morrison, A. Jones, A. W. Henderson, Bur. Mines Invest. 5091 (1954).
So melt your zirconium silicate with NaOH at 650°C and leach the product with water to get sodium silicate solution and hydrous zirconia. The product
should however be purified further, e.g. via the tetrachloride etc...
Ullmanns gives other procedures as well, like the already mentioned chlorination in presence of carbon, but this does not look to be feasible on a
small scale because the chlorination process needs 1100°C! The NaOH process is the one with least heat required.
The HF method also sounds very promising for lab use!
[Edited on 18-10-2007 by garage chemist]
[Edited on 18-10-2007 by garage chemist]
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
garage chemist has given the simplest process for more home experimenters. A minor variation is to use 2 moles, or a bit more, of Na2CO3 in place of 4
moles of NaOH. You'll have to heat it to 850-1000 C, but you get away with using the cheap and easily accessible carbonate instead of the more
expensive abd sometimes difficult to find hydroxide.
|
|
|
coal
Harmless
Posts: 15
Registered: 13-10-2007
Member Is Offline
Mood: No Mood
|
|
Thanks for the replys! lots of helpfull infrmation 
think the best route might to be to try harder to get the oxide and save a lot of hassle. if that fails, i might try fuseing with NaOH if i can find
a suitable container
does anyone happen to know what temperature lead zirconium titanate materals need to be fired at? there doesn't seem to be alot of information about
them on the net. if its more than about 1200 degC than i'm stuffed anyway as my various firnaces won't go to more than about that 
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
The early methods that started with mixed oxides would do a hot press and then sinter at 1000 to 1350 C. Unreacted ZrO2 is unwanted, extended milling
of the oxide powders before pressing and sintering is useful
Later crystals of PZT were grown in molten salt baths at 800 to 1100 C.
More recently PZT films have been made by various processes using organic compounds such as alkoxides of Zr and Ti and lead acetate. After formation
of the films they are heat treated to develop the crystal structure, temperatures from 800 to as low as 450 C have been used.
There are a lot of patents related to PZT that should give you more information.
Attachment: 751892.pdf (411kB)
This file has been downloaded 573 times
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
