EDL/DLVO and Hydrothermal Synthesis

Question 1

What is the feed required for hydrothermal synthesis?

Answer 1

1) Aqueous metal salt solution
2) Amorphous solid slurry

Question 2

What is the temperature range for hydrothermal synthesis?

Answer 2

100-300C

Question 3

Explain the “thermal” part of hydrothermal synthesis

Answer 3

100-300C to remove liquid from the feed

Question 4

Explain re-crystallisation in hydrothermal synthesis

Answer 4

At lower temperatures, crystallisation may occur
These then dissolve, and re-crystallise as larger crystals when higher temperatures are reached
Further growth also occurs

Question 5

Name two conditions for hydrothermal synthesis

Answer 5

High temperature
High pressure (100-300C)

Question 6

What is the purpose of electrostatic stabilisation in sols?

Answer 6

To minimise/prevent flocculation through manipulation of the sol

Question 7

Outline the DLVO theory through an equation

Answer 7

G_Total = G_Repulsion + G_Attraction

Question 8

What contributes to the attraction in the DLVO Theory?

Answer 8

Van der Waals Forces between particles

Question 9

What contributes to repulsion in the DLVO Theory?

Answer 9

EDL Overlap

Question 10

What does EDL mean?

Answer 10

Electrical Double Layer

Question 11

What are the two layers in the EDL?

Answer 11

Stern Layer
Diffuse Layer

Question 12

Explain the effect of changing concentration in a sol?

Answer 12

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

Question 13

What is the relationship between sol concentration and particle EDL?

Answer 13

Inverse relationship
Conc ↑ = EDL Thickness ↓
Conc ↓ = EDL Thickness ↑

Question 14

How could sol concentration be manipulated to increase stability?

Answer 14

The concentration should be decreased to minimise the ionic strength (cz^2), and therefore maximise the thickness of the EDL

Question 15

How can pH be used to ensure maximum suspension stability?

Answer 15

The pH should be as far away from the IEP as possible

Question 16

What is the Isoelectric Point (IEP)?

Answer 16

The pH at which neutral/near-neutral zeta potential is observed

Question 17

What is the relevance of the IEP to stabilisation?

Answer 17

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

Question 18

In the EDL theory, what is kappa a function of?

Answer 18

K = f(cz^2) → Ionic Charge

Question 19

What does total system energy represent in a solution?

Answer 19

The total amount of energy required to flocculate and destabilise the system

Question 20

State 2 methods to increase repulsion

Answer 20

1) Decrease concentration
2) Deviate the pH from the IEP

Question 21

What is the relationship between EDL overlap and repulsion?

Answer 21

For a given separation distance, if there is more overlap of individual EDLs then there is greater repulsion