Ravi Pamu

In the sol-gel process, you first obtained a sol or, more precisely, a dispersion of nanoparticles of hydroxides of the listed oxides. Over time, during aging, hydroxides formed a gel network by dehydration. It is transparent and looks like glass. After heating, you got a dry gel or xerogel powder. To obtain glass, you need to select the mode of water removal under vacuum with or without heating or gradual drying in a desiccator over phosphorus pentoxide, anhydrous calcium chlorides. It is not necessary to remove all the water, but only part of it.

Dear Ravi, many thanks for posting this very interestig technical question. In addition to the expert advice provided by Yuri Mirgorod I would like to add is that what you observed is the transition form a wet gel to a dry gel / xerogel. The formation of dense transparent glass requires subsequent calcination / sintering at high temperatures.

For a potentially useful literature reference in which this process is described please have a look at the following interesting article:

Characterization of Bioactive Glass Synthesized by Sol-Gel Process in Hot Water

Article Characterization of Bioactive Glass Synthesized by Sol-Gel P...

This article has been posted by the authors as public full text on RG. Thus you can freely download it as pdf file.

I also suggest that you search the "Publications" section of RG in order to find and access other helpful articles about this topic. Just search e.g. for the term "bioactive glass by sol-gel process":

https://www.researchgate.net/search.Search.html?type=publication&query=bioactive%20glass%20by%20sol-gel%20process

As you can see, this will provide you with many other relevant references wich have been posted by RG members, some of them even as public full texts.

Good luck with your research and best wishes, Frank Edelmann

Hi;

The sol-gel process allows, as its name indicates, the evolution of a liquid phase towards a solid phase through different stages.

The textural properties of the final solid depend strongly on the drying step. If the gel is dried under mild conditions, it densifies and forms a xerogel, resulting in compact glasses. The other option is drying under severe conditions, with a high and constant evaporation rate. A very low density gel can be formed: the aerogel

The drying step allows the evaporation of solvents. During the thermal treatment, the shrinkage of the gel is due to the reduction of the interstitial spaces between the secondary particles, as the sol evaporates. This reduction of the interstitial spaces allows the aggregation of the particles thanks to the condensation of the surface OH groups.

Densification occurs during calcination in which a macroscopic 3D network is formed. This step is possible thanks to the fusion of secondary particles, via a viscous flow due to the relatively high temperature of the thermal treatment.

With my best regards

Hello,

Hope this message finds you best!

As a main disadvantage of sol-gel method in comparison to conventional ones, is the huge shrinkage which is produced during conversion from polymeric state to inorganic state.

That increases the possibility of extended crack formation inside the bulk.

I suggest the addition of fillers to your system or substitution of sol-gel method with polysiloxane-based PDC technique.

Regards,

Sorosh