clays as colloids
DESCRIPTION
Clays as Colloids. R. F. Giese Geology [email protected]. Meaning of “clay”. Engineering small particles of any material Geological small particles of layer silicate minerals. Outline. Uses. Structure. Chemistry. Surface properties. Stability of clay-water systems Landslide. - PowerPoint PPT PresentationTRANSCRIPT
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Meaning of “clay”
• Engineering– small particles of any material
• Geological– small particles of layer silicate minerals
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Outline
• Uses.
• Structure.
• Chemistry.
• Surface properties.
• Stability of clay-water systems
• Landslide
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Importance of clays• Industrial
– thickeners (paints, drilling muds)– catalysts (cracking of hydrocarbons)– fillers (rubber, plastics)– adsorbents
• Geological– alteration products of rock– formation of hydrocarbons
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Importance of clays
• Scientific– large surface area– known surface structure– nano-composites– insulators– designer surfaces
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Clay Minerals
• Layer silicates
• Silicates are oxides of silicon and other elements:
• Aluminum, magnesium, iron, calcium, sodium
• Oxygen (anion) is larger than the other elements (cations)
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Origin and calculation of the layer charge for 2:1 clay minerals.
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Kaolinite: TEM replica
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Kaolinite: TEM
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Halloysite: TEM
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Micas
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Smectites
Vermiculites
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Organo-clays
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Montmorillonite: TEM replica
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Montmorillonite: TEM
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Allophane
TEM replica
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Allophane
TEM replica
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Surface tension measurements
• Single crystals (micas)
• oriented films (smectites)
• thin layer wicking (kaolinite)
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Generalities for clays
2
2
2
35 45mJ/m
0 3mJ/m
5 45mJ/m
LW
$
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For all natural clays:
difference between hydrophobic and hydrophilic
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Natural and modified clay materials
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Coverage of talc by a long chain amine (in wt%)
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0 5 10 15
Chain length
0
5
10
15
20
25
30
35
40
-n-alkyl ammonium cations
Coverage of smectite by organic matter
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Interactions in water
• Flocculation
• Adsorption
• DLVO versus XDLVO
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F r e e E n e r g y o f I n t e r a c t i o n :
1 2 1 1 2
1 1 2 2 1 2 1 2
2
4
A B A BG
$ $ $ $
1 2 1 1 2
1 2 1 2
2
2 2
L W L W
L W L W L W L W
G
21 2 1
1l n 1 e x p
2E LG R
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XDLVO plot
-1000
0
1000
2000
3000
4000
5000
6000
0 10 20 30 40 50 60
Distance (A)
De
lta
G (
kT
)
Series1
Series2
Series3
Series4
Series5
Series6
Series7
Montmorillonite: XDLVO
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Stability of montmorillonite
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Quick clays
• Clays deposited in marine environment
• sea level drops
• rain leaches out the salty pore water
• attraction between particles is weakened
• soil becomes unstable
• Canada, Scandinavia