30-08-2013, 01:27 PM
PHYSICAL CHEMISTRY OF SOLID SURFACES
[attachment=57604]
INTRODUCTION
Matter and Energy are manifestations of the universe they exist in a variety of forms and interact with each other in many ways.
Nano means 10-9. ( Nanometer is one thousand Millionth of a Meter)
Nano materials have large fraction of surface atom per unit volume.
Nano Materials differ significantly from Bulk materials. It is
due to the Increased relative surface area.
SURFACE ENERGY
Atoms and molecules on a solid surfaces possess fewer nearest neigbours and thus have unsatisfied bonds exposed to the surface.
Because of the dangling bonds on the surface, surfaces atoms are under an inwardly directed force .
Surface Energy γ = δG/ δA
γ = N ερ/2
SURFACE RELAXATION
The surface atom shift inwardly so that the distance between the surface atomic level and sub surface atomic layer would be smaller than that inside a bulk.
Occurs readily in Liquid phases.
The inward shift(Normal Relaxation) and lateral shift(lateral relaxation) of surface atom would result in the reduction of surface energy.
SURFACE RESTUCTURING
Surface restructuring through combining surface dangling bonds into new strained bonds.
The broken bond from the neighboring atom combine to form a highly structured bond.
SINTERING
Sintering is a method used to create objects from powders
The sintering temperature does not have to reach the melting point of the material, sintering is often chosen as the shaping process for materials with extremely high melting points such as tungsten and molybdenum.
OSTWALD RIPENING
Term refers to the growth of larger crystals from those of smaller size which have a higher solubility than the larger ones.
In the process, many small crystals formed initially slowly disappear, except for a few that grow larger, at the expense of the small crystals.
The smaller crystals act as fuel for the growth of bigger crystals.
[attachment=57604]
INTRODUCTION
Matter and Energy are manifestations of the universe they exist in a variety of forms and interact with each other in many ways.
Nano means 10-9. ( Nanometer is one thousand Millionth of a Meter)
Nano materials have large fraction of surface atom per unit volume.
Nano Materials differ significantly from Bulk materials. It is
due to the Increased relative surface area.
SURFACE ENERGY
Atoms and molecules on a solid surfaces possess fewer nearest neigbours and thus have unsatisfied bonds exposed to the surface.
Because of the dangling bonds on the surface, surfaces atoms are under an inwardly directed force .
Surface Energy γ = δG/ δA
γ = N ερ/2
SURFACE RELAXATION
The surface atom shift inwardly so that the distance between the surface atomic level and sub surface atomic layer would be smaller than that inside a bulk.
Occurs readily in Liquid phases.
The inward shift(Normal Relaxation) and lateral shift(lateral relaxation) of surface atom would result in the reduction of surface energy.
SURFACE RESTUCTURING
Surface restructuring through combining surface dangling bonds into new strained bonds.
The broken bond from the neighboring atom combine to form a highly structured bond.
SINTERING
Sintering is a method used to create objects from powders
The sintering temperature does not have to reach the melting point of the material, sintering is often chosen as the shaping process for materials with extremely high melting points such as tungsten and molybdenum.
OSTWALD RIPENING
Term refers to the growth of larger crystals from those of smaller size which have a higher solubility than the larger ones.
In the process, many small crystals formed initially slowly disappear, except for a few that grow larger, at the expense of the small crystals.
The smaller crystals act as fuel for the growth of bigger crystals.