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ChiangAST
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Quote ChiangAST Replybullet Posted: 25 February 2003 at 11:25pm
Quote: Originally posted by xyuan on 15 February 2003

There are streaks emanating from the center of the wafer for SPIN-coated TiO2 films. Does anyone know how to solve the problem? The sol is transparent and can last at least a week or even longer. Thanks very much.

****

This is because of uneven temperature distribution. The rotor of the spin coater is hot. The centr of the coated sol is dried faster.


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Barrie
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Quote Barrie Replybullet Posted: 26 February 2003 at 8:17am

Hello,

I am attempting to dip coat TiO2 onto a polycarbonate (Lexan®) substrate (withdrawal speed variable).  The problem is that the thin film cracks during the curing process (100C/1hour).  These cracks do not present themselves when using a glass substrate.  Any advice on how to eliminate or reduce these cracks would be much appreciated. 

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Barrie                                                                                                                               

Researcher, UMCS

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Quote ChiangAST Replybullet Posted: 26 February 2003 at 9:23pm

Coating on hydrophobic polymer such as PC with alcohol/aqueous sol is more difficult then on glass. Some have suggested the use of plasma to creat hydroxyl on the surface to increase bonding.

The problem is strongly related to the titania sol used. There are commercial product that is made of PC coated with TiO2, or TiO2-SiO2 AR layer.

Silane coupling agent would also be helpful. Dilution of the sol so that the coated layer is thinner always reduce chance for cracking.

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Quote waterace Replybullet Posted: 07 May 2003 at 10:15am

New to the world of sol-gel but trying to coat glass slides, have tried a few different methods for preparing sol-gel but not had too much success! what do you all find to be the most reproducible?

Has anyone tried to coat sand? If so did you have any luck?

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gabonino
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Quote gabonino Replybullet Posted: 16 July 2003 at 10:41am

I have a question about the proccess for titania:

After hydrolysis and condensation, a big precipitate appears due to the formation of TiO2. Is it possibleto remove this precipitate and peptize it in some other media? If it is, what is the mechanism of this peptization process?

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Oscar Gabriel Niño A.
Chemical Engineer
Universidad Nacional de Colombia
M. Sc. Process and Energy Engineering
Technische Universität Berlin
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Quote gabonino Replybullet Posted: 23 July 2003 at 8:38pm

Regarding the recipes given above, is it possible to use basic catlysts such as ammonia for the proccess? How would this coating differ with the one prepared with Acids?

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Oscar Gabriel Niño A.
Chemical Engineer
Universidad Nacional de Colombia
M. Sc. Process and Energy Engineering
Technische Universität Berlin
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Quote gabonino Replybullet Posted: 02 September 2003 at 5:28pm

Once again I ask the forum the same thing:

I tried using aqueous ammonia as a catalyst and peptizing agent for hydrolysis and condensation. A white suspension is formed, but I am not sure if it will become traslucent after some time....so I ask: Is it possible to use ammonia fdor coatings? How much would the properties of the coating differ from those prepared with acid catalysts?

Oscar Gabriel Niño A.
Chemical Engineer
Universidad Nacional de Colombia
M. Sc. Process and Energy Engineering
Technische Universität Berlin
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Quote administrator Replybullet Posted: 03 September 2003 at 11:28am
Try peptizing with strong acids. This will probaly leads to transparent to translucent (depending of the ratio acid/TiO2) solutions ready for coating.
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Quote ChiangAST Replybullet Posted: 09 September 2003 at 12:08am
Quote: Originally posted by Administrator on 03 September 2003
Try peptizing with strong acids. This will probaly leads to transparent to translucent (depending of the ratio acid/TiO2) solutions ready for coating.
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Quote ChiangAST Replybullet Posted: 09 September 2003 at 12:10am

Our experience is to peptize TiO2 at about pH=1.5. This will give a transparent sol. However, leaving the sol at this pH too long will cause the growth of TiO2 crystals.

 

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