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indigotwilight
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Quote indigotwilight Replybullet Topic: Zinc oxide nano crystals in a silica matrix
    Posted: 06 May 2008 at 10:11am
Some of you may remember me from last year - that new PhD student who studies the sol-gel process with Anomalous Small Angle X-ray Scattering. Then, of course, I was developing a method of producing clear, homogenous YSZ that would gel over the course of a few hours. The experiment was a huge success - particularly in the sintering of YSZ gels to ceramics. And in a few weeks we are taking this one step further with an in situ grazing incidence experiment on coated substrates. 
 
My next mission is to grow zinc nanoparticles in a silica matrix, and orientate them in an electric field. Initial attempts have been puzzling to say the least. Literature suggested dissolving Zinc Acetate in Methoxythanol and Ethanolamine to produce the zinc sol. This is widely used in dip coatings to produce 2-0-0 orientated ZnO crystals. 
 
I thought, at least, that by mixing this sol with a straight TEOS-alcohol-0.1M nitric sol-gel would give me the desired product. However - it seems I was wrong! The zinc did not crystalise as I hoped it would. What occured instead was either a clear gel, or a white precipitate (more than likely a silicon compound) with "larger" quantities of Ethanolamine.
 
What is more, XRD revealed no crystals, even on sintering, which surprised me. I also discovered quite early on that Zinc Acetate was not as soluble in MEA as I had originally been led to believe. It dissolves a treat in Citric acid solution though - however, Zinc Acetate and Citric acid produced a rapid precipitation with alcohol - not so good for trying to grow the crystals in a silica matrix.
 
Now... The matrix does not have to be silica - in fact, I've considered using Alumina instead (though the alkoxide precursor materials appear to be far more reactive than TEOS)  I just want to grow zinc nano-crystals in a sol and orientate them in a field during an in-situ experiment.
 
Do you have any ideas or suggestions as to what I could try? I have all of summer to try out various methods and precursors before the beamtime at Diamond Light Source in September.
 
 
Thanks,
 
Twi
 
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s_v_g
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Quote s_v_g Replybullet Posted: 06 May 2008 at 11:44am
What conditions do they used to produce ZnO crystals (in literature)?
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indigotwilight
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Quote indigotwilight Replybullet Posted: 07 May 2008 at 11:14am
From what I can tell, most of the crystals are produced by evaporating a (say) citric acid - Zinc acetate solution - itself made in ambient conditions.
The Zinc Acetate - MEA - Ethanolamine is used for coatings of orientated crystals. In such cases, the coated substrate is placed in a furnace to secure the oxide film.
 
As I want to make a bulk gel with the crystals grown as a sort of colloidal suspension (in the gel) I was hoping to use a similar method - however it did not quite work out as I anticipated.
I had previously made Yttria stabilised Zirconia and Zirconia in Silica - heating the Xerogel in a furnace resulted in the growth of zirconia nano crystals within the ceramic silica matrix.
 
However, the system I am trying to devise now has different properties. I want long, hair-like crystals to grow in the sol as it gels. Actually, it does not really even have to be zinc. I chose this simply because the K edge (X-ray absorption) is 9Kev, which is good for ASAXS experiments at synchrotron radiation sources. Another element will do if you can suggest one, and it has a K (or an LIII) edge between 5KeV and 20KeV.
There has also been a lot of interest in zinc oxide, particularly due to its high absorption of Ultra Violet. (Zinc Oxide is the active ingredient in sun block) and the ease of which one can coat substrates with crystals of a particular alignment.
 
Zinc is also relatively cheap and abundant in nature - making it a viable alternative to rare elements such as Indium - which I believe has similar properties.
 
Twi
 
 
 
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s_v_g
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Quote s_v_g Replybullet Posted: 07 May 2008 at 1:06pm
"From what I can tell, most of the crystals are produced by evaporating a (say) citric acid - Zinc acetate solution - itself made in ambient conditions."
Do I correctly understand you? This is variant of crystal growth in gel.

"The Zinc Acetate - MEA - Ethanolamine is used for coatings of orientated crystals."
In that case, Crystals are produced since orientated crystals is nucleator for crystal growth (I think).  Maybe you test similarly method. 
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