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Message Icon Topic: Preparation of transparent TiO2 films. Post Reply Post New Topic
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sagebob
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Quote sagebob Replybullet Posted: 07 April 2006 at 4:42pm

howdy Oscar,

You are correct, the TIPT, TPT, TET, TMT are generally too reactive in their native state to be of use.  The TBT is also too reactive alone but as you see, there are chelating agents to modify the material.

TMT and TET are fairly useless for coatings. OK for generating suspensions of particles and the like.   Acidifying the solution (i have seen several acid based solutions mentioned here) helps keep the solution clear and may allow some kind of film to form but i have never found it to be a good source of smooth, homogenous, uniform films.  TIPT with chelating agents works moderately well but 20 years of dip coating showed me that there are no advantages of TIPT (TPT) over TBT.

It is possible to get slightly denser and thus higher refractive index films with TPT but nowhere near the theoretical maximum.  You need proportionately more chelating agents for more reactive alkoxides and the presence of sodium and the typically slow heating rates prevents any rutile formation.

Dupont and others sell titanium acetylacetonate and other pre-chelated materials that can simplify making solution.

Something around 30 grams per liter oxide equivalent is a nice solution concentraqtion in the middle of the process window (20-40 g/l are practical limits).  This also gives a reasonable draw speed for dip coating.  Relative humidity in the 20-40% (70degrees F) is best.  30% RH being a nice spot to operate at.

Thickness for a single layer without cracking has a practical limit of about 1000nm QWOT (d=120nm).  I have not done too much experimentation with thick TiO2 films.  Thin films with the more diluted solution can be made easily at a QWOT down to 200nm (d=25nm).  Again, I have done much work with thin TiO2 films.

TiO2 films are very prone to pinholes and other defects.  Substrate wetting is an issue with thin films in particular.  Whitish coatings or cracks just tell me the starting solution is inadequate (given you are trying to operate within the process windows I have mentioned above).

For thicker films, coat and bake multiple times is the generally accepted procedure.  The TiO2 films should bond to a clean soda-lime glass surface very well.  Much less to to borosilicate and quartz.  Interestingly, these films do not stick to rutile particularly well.  

There is quite a bit of stress in the final films so do not expect microns of thickness regardless of what you do.  The general failure mechanism for multiple films is adhesive failure at layer interfaces.  An etch between layers helps.  You can think of a water wash and rinse as a very mild etch with caustic and sulfuric as an extreme etch.  Something that helps generate thick layers is to reduce oven temperature as each layer is applied.  I.e. first layer is applied and baked at 500C, second layer is baked at 490C, etc.  You can get a higher total thickness using thin layers rather than thick layers.  If you are making precision optical films, the calculations can get messy since the refractive index will vary by layer.

FYI - The waste or spent solution is good for waterproofing concrete if you do not mind a slight yellowing and patchiness

-bob.

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rammahipal
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Quote rammahipal Replybullet Posted: 10 April 2006 at 6:05pm

hi

i am tring to coat the film on quartz tube which is smooth ,but it wasn't coming up, as i can wipe the surface off.

but it came well on fristed slides.

do any of you think will sandblasting the tubes work it.

any particular for coating TiO2 film on quartz tube

thankz

Ram
Chemical Engineering)
University of arkansas
USA
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sagebob
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Quote sagebob Replybullet Posted: 11 April 2006 at 11:16am

howdy

in general, glassy surfaces need to be very well cleaned for adequate adhesion.  Caustic wash, rinse, acid wash, rinse, dry- works well.  for difficult to wet substrates like borosilicate, quartz, saphire, etc. and etch is recommended.  5% HF works.  Be careful this is tricky dangerous stuff.

1- If deionized water will not wet the surface uniformly, it is not clean.

2- as the water drains off during the drying process, if you see any streaks or other imperfections in the thin film, it is not clean.

15+ meg-ohm water, .2 micron absolute filter for rinse.  Application dependant of course.

 

-bob

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fancy
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Quote fancy Replybullet Posted: 08 June 2006 at 5:33am

Hi all,

I'm the new comer and i'm glad to find this webpage, it is so useful for me and i know more about the details of sol-gel method in making TiO2 film.

However, i do have question in making the TiO2 film.  I would like to ask for details in making TiO2 film start from TiO2 powder (p-25), how can i make it become semi-solid and hence coat it to the surface?

Many thanks for all your help.

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sagebob
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Quote sagebob Replybullet Posted: 08 June 2006 at 10:13am

howdy

 

this topic has recently been covered in one of the related forum threads here.

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Splanky
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Quote Splanky Replybullet Posted: 23 June 2006 at 2:33pm
Has anyone tried to make thin ( less than 10nm) TiO2 films.   Can TiO2 films be made on gold substrates?? Thanks for any help
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sagebob
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Quote sagebob Replybullet Posted: 23 June 2006 at 6:39pm

howdy Splanky,

Diluting the solutions (around 5-10 gram per liter) and using spin coating can get you down to single digits.  The tricky part is measuring them.  It is also difficult to know if they are continuous.

I am sure you can deposit by a vacuum process on gold.  Might not stick too well. 

I have never tried it by solution methods.  You can coat stainless steel, mild steel and aluminum by solution methods but of course these surfaces have alot of active sites for the film to bond too.

 

-bob

 

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nawfal
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Quote nawfal Replybullet Posted: 04 July 2006 at 10:36am
hello evry bady,
I would like to make tests of hydrophilcity on film of TiO2 and I have a lamp in tungsten which irradiates my films as much in the visible one that in UV, but I do not manage to have modiffication of the contact angle and according to certain authors this come from the lamp because is needed used a lamp which that irradiates in UV!! somebody would have it thank you more information
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sagebob
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Quote sagebob Replybullet Posted: 04 July 2006 at 12:20pm

howdy Nawfal,

A UV only lamp is not necessary.  Visible light does not reduce the photoactive properties of TiO2.  However, you might check the actual output of UV from your tungsten lamp.  Unless it was designed for enhanced UV, there may not be much there.  A standard  commercial mercury arc lamp or metal halide lamp emits large quantities of UV.  Make sure you do not a "safety" type lamp.  they have a UV absorber in the glass envelope. There are many flourescent almps made for sun tanning.  These emit alot of UV also.

I have seen this as a recurring topic in the forums.  TiO2 is NOT always photoactive.  With special attention to structure and doping, it can be.  I worked with TiO2 sol-gel films for many years.  Occasionally, my experiments would create a film that was photoactive.  (There are other materials that have similar properties)

  I would say that generating particles and putting them on a surface might be a better path than trying to generate an optical film.

Several glass companies (i.e. Pilkington, PPG) sell a "self-cleaning" glass now. This is based on a photoactive film.  You might look up the literature on this for some hints.  I recently put a reference in one of the forums that covers doped TiO2.

-bob

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kutty
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Quote kutty Replybullet Posted: 14 July 2006 at 9:06am

 hai friends,

                  i am doing in sol-gel field.i had no idea to form the TiO2 solution.please any one friends  give the details of preparation of TiO2 solution.if u know variety of  steps to preparing TiO2 solution,please give to me.

   friends, i am awaiting yours replay

  my mail id is : krishpdf@yahoo.co.in

.if u give  i am realy very happy.

thanking u.

 



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s.r.krishnamoorthy
s.r.krishnamoorthy
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