Re: Re: Re: Re: Re: Re: Re: synthetic opal synthesis
You want the purest grade of TEOS you can find. Grades below 95% have silica polymers in them and may not produce good spheres. Last I checked (a decade ago), you could get 99% for a reasonable price.
Ethanol is actually preferred, but methanol is usually easier to get. You need to check that it does not contain denaturants, or it will not work.
Household ammonia is about 5% solution. It has to be concentrated to ammonium hydroxide (can't remember the actual percent, but much higher).
Only work with TEOS outside or under a hood. Even then I recommend a chemical respirator be worn. Normal precautions with alcohol and ammonia fumes should be observed. Wear gloves and eyeglasses.
I don't have any formulas on hand (they are all packed up in storage), but will make a note to look them up for you. The terminology in Moles is a bit confusing. I've found that the proportions are not real critical and you can produce good spheres with reasonable attention to measurements. I normally use volume rather than weight.
Once you select a set of conditions, the spheres will form and will be uniform in size and shape automatically.
My suspensions would begin to form diffractive layers in about a week and would settle out a 5-6 mm layer in 4-6 weeks (this was using a 25-30 cm column of suspension).
From Henry Barwood - July 24, 2007 at 11:12:56