I need to find a reliable recipe for an aluminum alkoxide based Sol-Gel process to incorporate my CNT catalyst precursor in it and after calcination, put it in the CVD reactor for CNT growth. My intention is to put a layer of the gel containing the catalyst on a metal substrate and calcine it.
I need to know which Al alkoxide is the most reliable and frequently used one, and what are the corresponding concentrations, acidic or basic catalyzer and pH range, temperature range, duration and in general some information in this respect.
Simple and less complicated procedures are of course more welcome.
Maybe check in the literature B. Saruhan, she has been working on this topic for some year.
Regards
GC
I propose a method Yoldas, modified and described in the work:
Journal of Non-Crystalline Solids 01/2014; 402:128-134
aluminium isopropoxide as precursor
acetic acid as pH moderator
synthesis time 24h at 95 C deg.
aging time : 3-5 days
Regards
RP
Hi Mondragón,
Thanks for the comment. As far as I could find in the literature, B. Saruhan has mainly worked on Si based sol-gel systems, e.g., Mullite synthesis.
I think aluminum-tri-sec-butoxide is another good option. The sol-gel process can be performed in basic (e.g. pH=9) solution. Calcination can be done in between 700-900 C.
Hi Robert and thanks for your comments,
Going through your work, I came across a couple of questions that I have put below. Since I’m not expert in this field at all, some of the questions might seem primitive. But I would appreciate if you give your take anyway. Also others are welcome to take part in the discussion and put their comments.
1- Why Aluminium isopropoxide? Is there any specific characteristic in there that makes it a better choice? As you can see for instance in Umapada’s comment, aluminum-tri-sec-butoxide is suggested.
1*- Is Aluminium isopropoxide first dissolved in isopropanol and then in water or we directly hydrolyze it in water?
2- What could be the effect of addition of metal acetates (Co, Mo, Fe, etc.) dissolved in ethanol to the sol-gel precursor? These metals are my CNT synthesis catalysts that I need to have their oxides dispersed homogenously in the Al2O3 at the end.
3- When to add the catalyst metal acetates?
4- We need to put a thin layer of the precursor on a metal substrate (let’s say an Al foil) by dip-coating. When the viscosity of the system is good for such purpose (Sol? Gel?)? The xerogel is most probably not good for this and it should be done earlier.
5- In case of application of a thin film of the gel on a metal by dip coating, how will the process of drying change (the one that you did at 65 C for 72 h is for a bulk of the gel)? We need to avoid cracks and thus uncoated areas in both drying and calcination steps.
6- How long one can keep the prepared precursor when it is prepared (after all refluxing and stirring steps before drying and firing)? Does it degrade or undergo destruction by time?
Thanks again,
Hi Umapada and thanks for your comment,
Are there any papers working with the conditions you mentioned?
In the context of my work (CNT catalyst preparation) I have already found the following work dealing with aluminum-tri-sec-butoxide:
https://www.researchgate.net/publication/234842922_Comparative_Study_on_Effect_of_Iron_Oxide_Doped_Alumina-Based_Catalysts_via_Sol-Gel_and_LFS_Methods_on_CNTs_Growth_by_Methane_Decomposition
However in this work, the details of the sol-gel process are not discussed.
Article Comparative Study on Effect of Iron Oxide Doped Alumina-Base...
Hi Mazdak,
1- Why Aluminium isopropoxide?
Isopropoxide is hydrolyzed more slowly than butoxide and thus it’s hydrolysis reaction rate can be better controlled. Isopropoxide must be crushed in mortar into fine powder before used in reaction and sift . Grain fraction
Hi Robert,
Thank you very much for the comprehensive responses to all questions. Also for the nice photo of the transparent Gel with the symbolic Al in the background! I will be preparing the materials in the coming weeks to start the work ASAP and I hope my Gel will look the same, cross fingers! In case I come across queries, I’ll return to you.
Thanks again,
Mazdak
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