Lecture 10 - Surface Reactivity Flashcards
(16 cards)
What is mineral reactivity controlled by in low temperature systems?
By surface reactivity (with water in aqueous systems) (surface roughness)
What large scale properties do surface properties dictate?
Energetic benefits associated with fracturing and transportation of fluids via the wettability of the surface
What do mineral surfaces control?
Electronic and vibrational properties of the surface control ability to bond with ions in solution. Surface roughness controls reactivity (more rough, more unstable) and surfaces allow species to sorb or diffuse.
What determines crystal shape?
Final shape dictated by interacting surfaces with lowest energy. Crystal assumes shape with lowest Gibbs free energy (Wulff construction)
Wulff construction
a droplet or crystal inside a separate phase will arrange itself such that its surface Gibbs free energy is minimised
Euhedral
a crystal that has well defined, sharp and distinct faces due to uninterrupted growth without external interference
What determines surface stability?
Bonds per surface atom, surface roughness and charge neutrality
Why do pyrite and pyrope have different surfaces in the euhedral form?
This is due to differences in chemical groups which are lying on different planes; pyrite has strong covalent and ionic bonds which prefer sharp corners and smooth faces. On the other hand pyrope has more complex chemistry, forming irregular and less defined surfaces.
How many PBC do F,S and K surfaces have?
2 (flat),1 (step) and 0 (kink) respectively
How can water change surface energy?
Absorption onto a surface can satisfying some bonds thus reducing surface energy. This is accounted for by chemical potential
How may earth of gotten water?
As adsorption of water is energetically favourable, it may have adsorbed to dust particles which condensed from gas phase in early solar nebula
Presence of defects would help adsorption (steps, corners)
What is the height of steps and kinks related to?
Size of unit cell perpendicular to surface plane
what is a stern layer?
Related to PZC - a diffusion profile is created due to formation of a charge compensation layer. Fluids at the mineral surface are chemically distinct and layers are 3 or more molecules thick
How do surfaces with interphases open fractures?
Due to negative interactions between structured water films at each new surface
How does water adsorption impact friction?
Can significantly lower a minerals frictional strength
How can surface energy be lowered?
By hydration which generates structured water layers at the surface
