Download Study of Stainless Steel Surface Cleanability

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Study of Stainless Steel Surface Cleanability
Nuttha Thongyai, Siriporn Daowphiset and Narong Pungwiwat
King Mongkut’s Institute of Technology North Bangkok, Bangkok 10800
Phone 0-2913-2500, E-Mail: [email protected]
Abstract
Stainless steel surface cleaning is very simple and important
method that can prevent corrosion from environmental
and after aging 1 week and 2 weeks respectively. The affect of
aging time to surface energies of treated stainless steels were
studied.
contamination. Wettability and cleanability can be evaluated by
The interpretation of the contact angle ( θ ) in terms of
contact angle measurement. It also leads to calculate surface energy
interfacial energy relies on Young’s Equation [3]. The contact
of treated stainless steel surface. From our work, it was found that
angle of liquid drop on a solid surface is defined by mechanical
surface treatments had influenced on surface energies but after aging
equilibrium of the drop under the action of three interfacial
2 weeks surfaces were contaminated and caused reduction of
energies, as illustrated in Figure 1.
surface energy resulted in low wettability and cleanability. Stainless
steel coated with TiO2 can improve hydrophilic property and
enhance cleanability by water rinsing. The fascinating resulted found
on composite (of TiO2 and SiO2) coated stainless steel surface also
showed highly wettability (even after 2 weeks) due to the acidity of
the mixed oxides.
Introduction
Figure 1 contact angle of liquid on solid surface
The surface energy and the contact angle are related by equation (1)
Stainless steel was used for building structure; in practice
surface cleaning is considerable trouble i.e., high consumption of
γ
SV
= γ
SL
+ γ
LV
cos θ
(1)
energy and expenditure. One approach has indeed been to make the
where γ is a surface or interfacial energy and the subscript LV,
surface highly hydrophilic so that a stream of water would replace
SV and SL refer to liquid-vapor, solid-vapor and solid-liquid,
stains. Enhancement of water wettability has been found on stainless
surface boundary, respectively. However, contact angle from
steel [1]. In the field of adhesion science, the concept of surface
Owens and Wendt method [4] has relationship with the surface
wettability is a commonly employed to monitor the cleanliness of
energy as in equation (2)
surface [2]. Surfaces are classified into two types as high energy
surface and low energy surface [3]. High energy surface is
1/ 2
essentially synonymous with hydrophilic and low-energy surface
γ LV × (1 + cos θ ) ⎡ γ Lp ⎤
= ⎢ d ⎥
2 × ( γ Ld ) 1 / 2
⎣γ L ⎦
with hydrophobic.
From the equation above, when the left-hand side term is plotted as a
In this work, surfaces of stainless steel 304 RB sheets
were treated surface by 6 methods and surface energies were
determined from contact angle measurements for fresh preparation
× ( γ Sp ) 1 / 2 + ( γ Sd ) 1 / 2
(2)
function of (γPL/γdL)1/2surface energy can be calculated from the sum
of γ Sd and γ Sp (where d and p means dispersive and polar part.)
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Experimental procedures
Polar
In this work, stainless steel AISI 304 RB was investigated. The
angles were measured by Krüss contact angle goniometer equipped
with a camera monitor at 20 ºC.
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Surface Energy (mJ/m2)
surfaces were treated in 6 different ways as shown below. Contact
Disperse
80
60
50
40
30
20
10
Method
Details
Chemically Cleaned
0
Chemical
Ar-plasma
TiO2
SiO2
Bi-layers
Composite
ethanol:acetone in ultrasonic bath
Ar-plasma
plasma treatment in argon gas
TiO2
from TiO2 solution.*
SiO2
from SiO2 solution*
Bi-layers
TiO2/SiO2 *
Composite
40mol%SiO2+TiO2*
Figure 2 Comparison of polar and dispersive part of surface
energies of different treated stainless steel surfaces from fresh
preparation, aging 1 week and aging 2 weeks
*Collabolated with Siriwan Permpoon at Laboratorie de Thermodynamique et
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γ LV , γ Lp and γ Ld for different liquids were obtained from literature [1]
and were used in equation (2) to determine γ Sd and γ Sp . The treated
stainless steels were also kept for 1 week and 2 weeks followed by
the contact angle measurements and surface energies calculation.
Water Contact Angle (Degree)
Physcio-Chemie Matallurgique, INPG, France.
No aging
50
Aging 1 w eek
Aging 2 w eeks
40
30
20
10
0
Chemical
Results and Discussion
Ar-plasma
TiO2
SiO2
Bi-layers
Composite
Figure 3 Comparison of contact angles of different treated
A comparison of surface energies represented in Figure 2.
stainless steel surfaces against aging time.
Each surface treatment has 3 bar graphs from left to right which
represent surface energies of fresh preparation, aging 1 week
Chemical cleaning of stainless steel surface with mixture of
and 2 weeks, respectively. Surface energy of fresh preparation
ethanol and acetone performed less hydrophilic surface. The
was affected by the surface treatment. Surface energies are
principle problem encountered with solvent cleaning was that the
2
greater than 70 mJ/m for all treated surfaces except chemically
drying process lead to recontamination spots [1]. Stainless steel
2
cleaned was at 55 mJ/m . Fresh preparation created
treated by Ar-plasma composed of many species such as argon
hydrophilicity on the treated surface due to polar part was higher
atom (Ar), excited argon (Ar*(4s) and Ar**(4p) and argon ion
than dispersive part. After one week aging, all specimens had
(Ar++) [5] physically colliding to the surface, breaking bonds and
slightly changed in polar part of surface energies but after 2
releasing the surface material. For the third method,
weeks the surface energies were greatly declined in the polar
hydrophilicity of TiO2 could be explained by dissociation of
part while the dispersive part was still the same. From Figure 3,
water from reaction with oxygen adatoms at the vacancy sites.
it would be clearly seen that the contact angles for all treated
The co-adsorption with H2O resulted in two equivalent OH
surfaces were significantly increased when the time period
groups [6]. The aim of coating by SiO2 for the fourth method, as
extended but the exception was found on composite coating
barrier to prevent diffusion of Fe3+ and Fe2+ during calcination
which can maintain 0º from the beginning until 2 weeks.
which decreased super-hydrophilic property [7]. For coating by
SiO2, one possible explanation is a partial SiO- . . . H3O+ ionic
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interaction [8]. This reason was found in agreement with water
the dependent on surface treatment for freshly prepared
contact angle data which showed that water wet on SiO2 coated on
specimen. After aging two-weeks, it was found that surface
stainless steel surface. Bi-layers of TiO2/SiO2 on the stainless steel
energy reduction occurred because contamination adsorption on
surface also showed that polar part of surface energy was higher
the surface. Surface coated by composite showed very high
than dispersive part. For the structure of TiO2-SiO2, where TiO2 is
wettability due to acidity of the mixed oxides.
the major component oxide, in the interfaces of TiO2-SiO2, silica
atoms may enter the titanium lattice [9]. In this case, the Lewis
acidity is assumed to appear upon the presence of an excess of
positive charge as show in Figure 4.
Acknowledgement
I would like to thank Miss Siriwan Permpoon, Prof. J.-C.
Joud and Prof. B. Baroux for their advises., INPG’s laboratory
where I did my research and Thai-France Cooperative Program
for financial support.
References
[1] Wightman, J.P. and Mantel M., Surface and Interface
Science Analysis, 21, (1994): 595- 605.
[2] Matsunaga T., Surface Contamination, Plenum Press,
Figure 4 Model of TiO2-SiO2 structure and charge difference [9].
NewYork, 1979.
[3] Wu S., Polymer Interface and Adhesion Marcel Dekker, Inc.
After aging 2 weeks the increase of contact angle was revealed.
At the beginning all treated specimen surfaces may create oxide
layer thickness instead of carbon contamination layer. However,
with exposure to air, the surfaces were inevitably contaminated by
some contaminants in air, for examples, dust, CO2 and
hydrocarbons [10]. Aging time caused lowering surface energy
since oxide film occurred on the surface was gradually covered by
carbon contamination and resulted in increasing of the contact
angle. For the composite coating there is a competitive adsorption
process from contaminated compounds and water on the surface.
Because of the enhance acidity on the surface as mentioned above,
the water (OH- group) is preferentially adsorbed and the
contamination is decreased on the surface [11] leading to the
surprising result of 0º contact angle even though the time has
already extended.
1982.
[4] Ponsonnet L., et al., Materials Science and Engineering C. 28
(2003): 551-560.
[5] Vasenkov A. V., J. Vacuum Science Technology A, 22
(2004): 511-530.
[6] Diebold U., Surface Science Reports, 48 (2003) 53-229.
[7] Yu C., et al., Environmental Science & Technology, 37,
(2003): 2296-2310.
[8] Sneh O., Cameron M. A. and George S. M., Surface Science,
364 (1996): 61-78.
[9] Guan K., Lu B. and Y. Yin., Surfaces and Coatings
Technology, 173 (2003): 219-223.
[10] Tang S., Kwon O-J., Lu N. and Choi H-S., Surface &
Coating Technology, 195, 2005.
[11] Guan K., Surface and Coatings Technology, 191 (2005):
155-160.
Conclusion
The wettability and cleanability of stainless steel AISI 304 RB
surface was improved by using hydrophilic coatings. Surface energy
obtained from contact angle by Owens and Wendt method revealed