16 Introduction to Sol-Gel

Question 1

Oxides from molecular precursors

Answer 1

Oxides can be synthesized from molecular
precursors. For example, SiO2
can be prepared
by hydrolysis and condensation of tetraethyl
orthosilicate.

Question 2

Gel

Answer 2

a porous, 3D continuous solid network
surrounding and supporting a liquid phase.

Question 3

Sol:

Answer 3

a colloidal solution.

Question 4

Sol-gel process:

Answer 4

The chemical synthesis of a gel
from a sol. Sol-gel is a bottom-up approach
involving polycondensation reactions of
molecular precursors in a liquid medium

Question 5

Physics of sols

Answer 5

van der Waals interactions cause the particles in
the sol to be attracted to each other. This
attraction can result in particle growth.

Question 6

barriers in sols

Answer 6

Steric barrier: adsorption of a steric layer on
the particles.
– Electrostatic barrier: Electrostatic repulsion
between particles due to charges on the
surface.
A stable sol is produced once repulsive and
attractive forces reach equilibrium.

Question 7

PZC

Answer 7

Point of zero charge

The pH at which the particle has no charge on its
surface. At a pH below the PZC, the particle’s
surface is positively charged. At a pH above the
PZC, the particle’s surface is negatively charged.

Question 8

sol-gel synthesis occurs in four
stages:

Answer 8

1. Hydrolysis and condensation
2. Gelation
3. Aging
4. Drying

Question 9

Hydrolysis: acidic conditions

Answer 9

pH < 2 is considered acidic conditions (PZC 1.5 –
4.5).

Question 10

Hydrolysis: basic conditions

Answer 10

pH > 4 is considered basic conditions (PZC 1.5 –
4.5)