EDL/DLVO and Hydrothermal Synthesis Flashcards
What is the feed required for hydrothermal synthesis?
1) Aqueous metal salt solution
2) Amorphous solid slurry
What is the temperature range for hydrothermal synthesis?
100-300C
Explain the “thermal” part of hydrothermal synthesis
100-300C to remove liquid from the feed
Explain re-crystallisation in hydrothermal synthesis
At lower temperatures, crystallisation may occur
These then dissolve, and re-crystallise as larger crystals when higher temperatures are reached
Further growth also occurs
Name two conditions for hydrothermal synthesis
High temperature
High pressure (100-300C)
What is the purpose of electrostatic stabilisation in sols?
To minimise/prevent flocculation through manipulation of the sol
Outline the DLVO theory through an equation
G_Total = G_Repulsion + G_Attraction
What contributes to the attraction in the DLVO Theory?
Van der Waals Forces between particles
What contributes to repulsion in the DLVO Theory?
EDL Overlap
What does EDL mean?
Electrical Double Layer
What are the two layers in the EDL?
Stern Layer
Diffuse Layer
Explain the effect of changing concentration in a sol?
Change in concentration = Change to cz^2
Given that k is a function of cz^2, then 1/k also changes
Since 1/k = x = Particle Spacing, then:
Concentration Change = Change in EDL thickness
What is the relationship between sol concentration and particle EDL?
Inverse relationship
Conc ↑ = EDL Thickness ↓
Conc ↓ = EDL Thickness ↑
How could sol concentration be manipulated to increase stability?
The concentration should be decreased to minimise the ionic strength (cz^2), and therefore maximise the thickness of the EDL
How can pH be used to ensure maximum suspension stability?
The pH should be as far away from the IEP as possible
What is the Isoelectric Point (IEP)?
The pH at which neutral/near-neutral zeta potential is observed
What is the relevance of the IEP to stabilisation?
The IEP is the pH with (near) neutral zeta potential, such that the particles have zero surface charge//stern potential and therefore repulsion is minimal
In the EDL theory, what is kappa a function of?
K = f(cz^2) → Ionic Charge
What does total system energy represent in a solution?
The total amount of energy required to flocculate and destabilise the system
State 2 methods to increase repulsion
1) Decrease concentration
2) Deviate the pH from the IEP
What is the relationship between EDL overlap and repulsion?
For a given separation distance, if there is more overlap of individual EDLs then there is greater repulsion
