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rammahipal
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Quote rammahipal Replybullet Posted: 06 September 2004 at 4:00pm

hi

i just wanted to know as u mentioned that by thermal treatment of film the film becomes less porous, what u suggest me as i want to make highly porous film of Tio2 and thin film

do u want me to make the film with out thermal treatment.

Quote: Originally posted by gabonino on 19 July 2004


Holger,

regarding your questions:

First: Probably the purpose of the aging of the sol is to achieve more viscous sols, that will lead into thicker layers of the coating. I am not sure on such affirmation, but probably someone more involved with the process can contradict this theory.

Second: Thermal treatment is made on coatings in order to achieve several purposes; on those, I can mention densification, which will lead to a more densified coating, less porous and probably more resistant in mechanical matters. On the other side, thermal treatment can be used in order to achieve some specific structure for the coating. For instance, if you want rutile coatings, you should do a thermal treatment, so that you can get a complete transformation into this phase. Later on I hope to send you some other aspects that you can get once you make thermal treatment on a coating

Best regards


Ram
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University of arkansas
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gabonino
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Quote gabonino Replybullet Posted: 06 September 2004 at 5:04pm

Ram Mahipal Kouda,

the better and more delicate the drying conditions, the mor porous material you will get...you can go from supercritical drying up to strong thermal treatment.....my suggestion is to try to remove solvents, each time getting one with higher vapor pressure...that might work, though structure will not remain monolitic.

Oscar Gabriel Niño A.
Chemical Engineer
Universidad Nacional de Colombia
M. Sc. Process and Energy Engineering
Technische Universität Berlin
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rammahipal
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Quote rammahipal Replybullet Posted: 06 September 2004 at 5:15pm

hi gabonino

i would like to know what do u mean by delicate conditions, and what is supercritical drying conditions

Quote: Originally posted by gabonino on 06 September 2004


Ram Mahipal Kouda,

the better and more delicate the drying conditions, the mor porous material you will get...you can go from supercritical drying up to strong thermal treatment.....my suggestion is to try to remove solvents, each time getting one with higher vapor pressure...that might work, though structure will not remain monolitic.


Ram
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University of arkansas
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gabonino
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Quote gabonino Replybullet Posted: 06 September 2004 at 5:51pm

ram mahipal,

I see you're online right now, have you got msn or yahoo messenger? if so, write me to my email and send it to me

Oscar Gabriel Niño A.
Chemical Engineer
Universidad Nacional de Colombia
M. Sc. Process and Energy Engineering
Technische Universität Berlin
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pourqoi
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Quote pourqoi Replybullet Posted: 07 September 2004 at 1:57am
Quote: Originally posted by Nai74 on 19 February?003

Urgent!

hi, I had deposited thin film of TiO2 on sapphire. But, It 's important for me to remove in order to use the sapphire crystal. What's the mean manner or technique used?

thank you for help..


I have similar problem. I have deposited TiO2 on silicon wafer by spin-coating. However, i don't know how to etch it to expose the botton electrode.

Anyone have suggestions on that? wet etching is preferable.

Thanks!!!

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Quote Guests Replybullet Posted: 09 September 2004 at 2:14am

Dear forum,

I am studying about TiO2 fabrication using sol gel method. Many researchers concern to explore alkoxide (Titanium Tetra iso Propoxide -TTIP) since the alkoxide offer the high pure material for Sol gel method. However, I found that it is not easy to control the Ti sol since the alkoxide is very reactive.The basic sol gel method that I know is based on the hydrolysis method. As I know, hydrolysis means reacting with water. Direct reaction of TTIP and water will result white precipitation soon after adding water into TTIP. This is the reason why people use alcohol as a steric hindrance to avoid the direct contact between TTIP and water. However, I could not understand, why researcher use acid (usually HCl) and even base (ammonia) during the hydrolysis reaction? 

Could any body help me?

Thx!

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Quote gabonino Replybullet Posted: 09 September 2004 at 12:27pm

Elly,

the reason for the usage of some electrolytes is not the hydrolysis reaction, biut the peptization process of the TiO2 generated; electrolytes help particles achieve de double layer neccesary for the stabilization of the colloid.

Oscar Gabriel Niño A.
Chemical Engineer
Universidad Nacional de Colombia
M. Sc. Process and Energy Engineering
Technische Universität Berlin
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Quote Guests Replybullet Posted: 09 September 2004 at 8:18pm

Gabriel,

Thx for your reply. The first assumption I've ever tried to understand the adding of some electrolite is based on the knowledgment that some chemical reaction might be occur with specific condition (pH, temperature, etc). Then, I assume that the TTIP hydrolysis reaction will occur only in the relatively low temperature (T room) and specific pH. I realized that this 'specific pH' is unreliable reason because it could be acid or base. :( And, I think that your explanation about "electrolite help particle to stabilize the colloid" is reliable reason because it could explain the using of both acid and base electrolite during the reaction.

However, would you please tell me where I could find any literature about the double layer? I dont know what you mean by the 'double layer'.

thx.

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Quote eexie Replybullet Posted: 09 September 2004 at 10:52pm

Hi, all experts

I am a freshman.  I shall be very grateful if you could explain my experimental phenomena!

By adding PEG (polymer) into TiO2 (3 nm; 2 mol/L) water suspension  solution, a transparent sol-gel could be fomed. After high T therm-treatment, a transparent film was obtained.

However, if TiO2 size was about 25 nm  I only got pale ink-like solution. After high T therm-treatment, a pale film was formed.

How to get transparent sol-gel by using a suspensive solution of TiO2 (25nm) 40 wt% in water?

And then how to get transparent TiO2 film?

Thanks for help

Xie
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Quote adam1979 Replybullet Posted: 10 September 2004 at 2:37am

J materials Science28(1993)2353-2360

the paper is one of the most great works in titania sol-gel processing.

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