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Mineral Adhesive Forces Measured by Atomic Force Microscopy
Cynthia Domergue
St. Mary’s University
Jacob Petersen, Jon Kellar, Albert Romkes, William Cross
South Dakota School of Mines and Technology
ABSTRACT: Adhesion measurements on surface treated silica surfaces were performed using atomic force
microscopy. Both a standard tip and a focused ion beam manufactured tip were used. These tips yielded similar
values for the adhesion of the tip with plasma cleaned, and silane treated silica surfaces. The adhesion found
corresponded well with literature values for adhesion found by our group for the plasma cleaned surfaces. The
silane treated surfaces exhibited lower adhesion by this technique than expected from the literature values.
INTRODUCTION
The mineral industry requires a significant amount of water
to extract valuable minerals from ores. A conventional
comminution-classification-flotation circuit to process, for
instance, copper sulfide ore, requires around 400 gallons
of water per metric ton of ore processed. [Bleiwas, 2012]
Furthermore, most copper mines in the US are located in
the southwest, such as Arizona and New Mexico, which
both have arid climates. Over 87% of the total US capac-
ity of approximately 1.9 million metric tons of copper
is mined in Arizona, Nevada and New Mexico [USGS
Minerals Yearbook, 2020]. Therefore, reducing water con-
sumption is critical to the sustainability of such operations.
This research is one step toward producing a dry particle-
separation process based on the control and exploitation of
adhesive forces, yielding more sustainable practice in the
processing of ores. In order to utilize a dry particle-separa-
tion process based on control and exploitation of adhesive
forces, there needs to be a technique for characterizing a
material’s adhesive forces. One such technique is the use of
an atomic force microscope (AFM). This research focuses
on the characterization of silica materials utilizing atomic
force microscopy as well as improving the microscopy tech-
nique, in order to create a more sustainable system of pro-
cessing ores in the future.
One issue with converting the atomic force microscopy
force (AFM force, FAFM) to work of adhesion (Wadh) is the
choice of the contact mechanics equations to use. Hertzian
contact mechanics was the first developed [Marti, 2000],
but does not consider adhesion forces. Bradley [1932],
Johnson, Kendall and Roberts (JKR) [Johnson Kendall
and Roberts, 1971], and Derjaguin, Muller and Toporov
(DMT) [Derjaguin, Muller and Toporov, 1975] have pro-
posed contact mechanics that do consider adhesion. Tabor
[1977] showed that JKR and DMT were limits to the extent
of the adhesion force. Thus, one can write the equation for
conversion of the AFM force to the work of adhesion as
F k RW
AFM adh (1)
where R is the AFM tip radius and k is a constant based on
the contact mechanics chosen and is 1.5 for JKR mechan-
ics and 2 for Bradley and DMT mechanics. In the software
used in this research, typically the DMT model is used.
JKR mechanics “represents the work done in completely
separating a unit area of the interface,” [Grierson, Flater
Mineral Adhesive Forces Measured by Atomic Force Microscopy
Cynthia Domergue
St. Mary’s University
Jacob Petersen, Jon Kellar, Albert Romkes, William Cross
South Dakota School of Mines and Technology
ABSTRACT: Adhesion measurements on surface treated silica surfaces were performed using atomic force
microscopy. Both a standard tip and a focused ion beam manufactured tip were used. These tips yielded similar
values for the adhesion of the tip with plasma cleaned, and silane treated silica surfaces. The adhesion found
corresponded well with literature values for adhesion found by our group for the plasma cleaned surfaces. The
silane treated surfaces exhibited lower adhesion by this technique than expected from the literature values.
INTRODUCTION
The mineral industry requires a significant amount of water
to extract valuable minerals from ores. A conventional
comminution-classification-flotation circuit to process, for
instance, copper sulfide ore, requires around 400 gallons
of water per metric ton of ore processed. [Bleiwas, 2012]
Furthermore, most copper mines in the US are located in
the southwest, such as Arizona and New Mexico, which
both have arid climates. Over 87% of the total US capac-
ity of approximately 1.9 million metric tons of copper
is mined in Arizona, Nevada and New Mexico [USGS
Minerals Yearbook, 2020]. Therefore, reducing water con-
sumption is critical to the sustainability of such operations.
This research is one step toward producing a dry particle-
separation process based on the control and exploitation of
adhesive forces, yielding more sustainable practice in the
processing of ores. In order to utilize a dry particle-separa-
tion process based on control and exploitation of adhesive
forces, there needs to be a technique for characterizing a
material’s adhesive forces. One such technique is the use of
an atomic force microscope (AFM). This research focuses
on the characterization of silica materials utilizing atomic
force microscopy as well as improving the microscopy tech-
nique, in order to create a more sustainable system of pro-
cessing ores in the future.
One issue with converting the atomic force microscopy
force (AFM force, FAFM) to work of adhesion (Wadh) is the
choice of the contact mechanics equations to use. Hertzian
contact mechanics was the first developed [Marti, 2000],
but does not consider adhesion forces. Bradley [1932],
Johnson, Kendall and Roberts (JKR) [Johnson Kendall
and Roberts, 1971], and Derjaguin, Muller and Toporov
(DMT) [Derjaguin, Muller and Toporov, 1975] have pro-
posed contact mechanics that do consider adhesion. Tabor
[1977] showed that JKR and DMT were limits to the extent
of the adhesion force. Thus, one can write the equation for
conversion of the AFM force to the work of adhesion as
F k RW
AFM adh (1)
where R is the AFM tip radius and k is a constant based on
the contact mechanics chosen and is 1.5 for JKR mechan-
ics and 2 for Bradley and DMT mechanics. In the software
used in this research, typically the DMT model is used.
JKR mechanics “represents the work done in completely
separating a unit area of the interface,” [Grierson, Flater