relevance between marine biofouling and physical...
TRANSCRIPT
Relevance between marine biofouling and physical
properties of porous ceramics coated with oxide powders
Sang-won Lee1, Seung-gu Kang
1
1Dept. of Advanced Materials Engineering, Kyonggi University
Iui-dong, Yeongtong-Gu, Gyeonggi-do 154-42, KOREA
Corresponding Author : [email protected]
Abstract. Recently, the eliminating methods of red tide organisms has been at-
tempted by filtering method using the porous ceramic bodies. The marine bio-
fouling, however, can be developed on the outer surfaces of porous ceramic
body after use for long period of time, decreasing the function of the porous
bodies. In this paper, the effect of ceramic coating to porous ceramic body upon
inhibiting marine bio-fouling has been examined. The ceramic powders tried as
coating materials were Al2O3, TiO2, and ZrO2. In the primary stage about for
one month, the amount of bio-fouling decreased with increased water absorp-
tion rate of specimens. During the early stage, the bio-fouling was caused by
mostly from light-weight organisms such as red algae or microbes. After two
months later, however, the amount of bio-fouling increased with decreased sur-
face roughness of the specimen due to larger fouling organisms such as barna-
cle. The Al2O3 proved as the optimum coating materials among three ceramic
powders to prevent the marine bio-fouling owing to offering lower water ab-
sorption and higher surface roughness to the specimens. It was confirmed that
the amount of bio-fouling could be reduced by controlling the water absorption
and the surface roughness of the porous ceramic through the oxide coating
without using the environmentally hazardous materials.
Keywords: Ceramic porous ceramic, bio fouling, oxide coating
1 Introduction
Recently, the waste water discharged from various industrial and household sites
seriously contaminates river and ocean. As a result, the water-bloom and red tide
occurrence become a serious social problem. Especially the red tide turned out to a
exorbitant damage to fish cage farms during the every summer [1-2]. Several methods
such as dusting ocean with the ocher to reduce the red tide have been tried in Korea,
but perfect and safe method to control red tide has not been yet established. The elim-
inating methods of red tide organisms has been recently attempted by filtering them
using the porous ceramic bodies [3]. The marine bio-fouling, however, can be devel-
oped on the outer surfaces of porous ceramic body after use for long period of time,
and it could decrease the function of the porous bodies. Bio-fouling is often occurred
Advanced Science and Technology Letters Vol.116 (Bioscience and Medical Research 2015), pp.254-260
http://dx.doi.org/10.14257/astl.2015.116.52
ISSN: 2287-1233 ASTL Copyright © 2015 SERSC
at the bottom of a ship, power station turbines or marine structures. At first a light
weight life such as micro-organisms attached to marine structures and consequently a
variety of species being attached to feed them which gradually increase amount of bio-
fouling [4]. Attached large algae accelerates to increase the weight of vessel or marine
structure and cause problems of structural safety [4]. The anti-biofouling paints devel-
oped contain a wide variety of materials such as organic tin compounds. But the or-
ganic tin compound exert a fatal toxicity even with concentration of 1 ppt (part per
trillion, 10-12) to marine organisms, so its use is prohibited now around the world [5].
Accordingly, environmental-friendly methods for inhibiting bio-fouling have been
continuously studied. Most methods are modifying surface character of body to give
hydrophilic or hydrophobic character, the plus or minus charge, and large or slight
roughness. Cho et. al. showed that the aluminum substrate surface with hydrophobic
character had anti-biofouling effect at the initial step [6]. Benbi Bai and Jones
changed the surface charge through the surface modification of polymeric membranes
to show effect of preventing bio-fouling [7]. Kim and Lovitt have reported the results
of controlling bio-fouling by change surface charge and surface roughness for the
filtration membrane [8,9]. The previous research, however, has focused mostly on
anti-biofouling of metal or polymer, so anti-fouling of porous ceramic materials has
not been much studied. In this research, environmentally friendly method for anti-
biofouling on porous ceramic bodies without the use of toxic materials was examined.
The factors tried were the surface charge, the surface roughness and absorption of the
porous ceramic bodies controlled through the various oxides coating.
2 Experimental procedure
Three kinds of oxides of Al2O3, TiO2, and ZrO2 were coated on porous ceramics
whose main constituent is SiO2. The most porous ceramic specimens used were of
spherical shape and the mean diameter is 17.5±2 mm. Oxide powder reagent were
used Al2O3 (High Purity Chemicals, Japan, 99.9%), TiO2 (High Purity Chemicals,
Japan, 99.9%), and ZrO2 (Junsei Chemical Co., Japan, 99.0%), and average particle
size of the oxide powders was 1.8±0.7 ㎛. A method of coating of oxide powder on
the surface of porous ceramic body is as follows. First, soaking the porous ceramic
body for 10 seconds in 1.0 wt% PVA (polyvinyl alcohol) solution giving sticky sur-
face was performed, and then placed the specimens into a vessel rotating for 10
minutes at a speed of 70 rpm to mixed with the oxide powder. The amount of the
oxide coating was from 0.1 to 1.0 wt%. The specimens then was dried for 24 hours at
105 ℃, and heat-treated at 1200 ℃ for 10 minutes to bond completely the oxide pow-
der to the specimen surface. Absorption of the porous ceramic body was measured in
accordance with Korea Industrial Standard as “KS F 2503: test method density and
water absorption of coarse aggregate.” In addition, surface roughness was observed
using a confocal laser microscope (Confocal Laser Scanning Microscope, OLS3000-
300mm autostage, OLYMPUS), and the average roughness value was obtained from
four measurements. Porous ceramic body was attached on acrylic plate of width 15 cm,
and length 21 cm using an organic adhesive. The specimens attached to plate were
Advanced Science and Technology Letters Vol.116 (Bioscience and Medical Research 2015)
Copyright © 2015 SERSC 255
installed in the sea of 1 m depth, located in Geoje-si, Gyeongsangnam-do during from
July to October in 2014. The amount of bio-fouling generated were measured at every
month, and calculated using the following equation (1).
(1)
Where, Wa is a weight of the specimen after one month and Wb is a weight of the
specimen before installation into the sea.
3 Result and discussion
Fig. 1 shows that the water absorption of the porous ceramic bodies used in this study.
The water absorption of the oxide coated porous ceramics has too low values. Com-
paring the absorption value for three type of specimens, the Al2O3-coated sample
showed the lowest value and the ZrO2-coated one had the highest value. In addition,
increasing amount of oxide coating from 0.1 wt% to 1.0 wt%, except for Al2O3, in-
creased slightly the absorption of specimen. The lowered absorption of the coated
specimen is due to filling-up of fine powders into cracks or open pores presented in
the specimen surface.
Fig. 1. The water absorption of porous ceramics coated with various oxide powders.
Advanced Science and Technology Letters Vol.116 (Bioscience and Medical Research 2015)
256 Copyright © 2015 SERSC
Fig. 2 shows that an average roughness value by measuring the four points random-
ly selected from a confocal microscopic images for the porous ceramic body. Rough-
ness of the no-coated specimens showed a value of about 100 ㎛, while the specimen
coated with oxide powders showed increased roughness regardless of the type and the
amount of coating.
Most specimens showed roughness of 120~140 ㎛ which is 20~40% higher com-
pared to the no-coated specimen except the case of 1 wt% of Al2O3. In particular, 1
wt% Al2O3 coated specimen had about 220 ㎛ roughness which is significantly 120%
higher value compared with no-coated specimen.
Fig. 2. Surface roughness of porous ceramics coated with various oxides.
Fig. 3 shows the pictures for appearance of porous ceramic bodies bio-fouled as a
function of time and amount of coating powders and kinds of oxides. The specimens
were first installed in the marine of Geoje-si, Gyeongsangnam-do in July, 2014.
All specimen surface can be seen as light red color which means red algae are
weakly attached. After two months later, biological styela clava seems to attatch and
after three months, the barnacle and shellfish such as mussels was very firmly attached.
Fig. 4 shows the amount of bio-fouling measured at every month during three
months. First, the amount of bio-fouling, regardless of the type of oxide coating on the
specimens, showed a tendency to increase greatly with time. But it was not large
amount of bio-fouling for any specimens with the time elapsed until the first month.
The microbial fouling organisms film usually occurs at the early stage. However,
the amount of fouling organisms began to increase after one month and rapidly in-
creased in all specimens after two months. The increased weight is due to large mus-
sels or barnacles attached to the specimen after two months.
Advanced Science and Technology Letters Vol.116 (Bioscience and Medical Research 2015)
Copyright © 2015 SERSC 257
Time
Specimen
As-installed 1 month 2 months 3 months
No-
coated
Al2O3
Fig. 3. Pictures for appearance of bio-fouling with time developed at porous ceramics with
various oxide; (a) no-coated, and (b) 1.0 wt% Al2O3-coated. The specimens were first installed
in the marine of Geoje-si, Gyeongsangnam-do in July, 2014.
Fig. 4. Amount of bio-fouling for porous ceramics coated with 1wt% coated. The specimens
were first installed in the marine of Geoje-si, Gyeongsangnam-do in July, 2014.
The amount of fouling in the specimen after two months was much higher com-
pared to that of first month later. The amount of bio-foulng for ZrO2 and Al2O3 were
Advanced Science and Technology Letters Vol.116 (Bioscience and Medical Research 2015)
258 Copyright © 2015 SERSC
lower than that of no-coated specimen, except TiO2 coated specimens showing a high-
er amount of bio-fouling. After three months elapse, overall amount of bio-fouling
was much higher than that of 2 months after. The specimens coated with ZrO2 and
Al2O3 showed a lower amount of fouling than that of no-coated specimen. The speci-
mens with the highest fouling resistance was proved as Al2O3 coated specimen.
When analyzing the amount of bio-fouling after one month (Fig. 4) and water ab-
sorption (Fig. 1) of coated specimen, the lower the water absorption, the lower the
amount of bio-fouling in the specimen can be seen. That means that the coating shows
a lowering effect to suppress biological fouling for 1 month due to lower water ab-
sorption.
When associating amount of bio-fouling and the surface roughness of specimen
(Fig. 2), the larger surface roughness value showed greater controling effect on bio-
fouling during 2 months. Especially, the surface roughness of the 1 wt% Al2O3 coated
specimen had the highest, and consequently had lowest bio-fouling among all speci-
mens. The greater the roughness, the greater inhibitory effect on microbial adhesion in
the seawater for the long term exposure. The bio-fouling starts with attachment of the
microorganisms and then large algaes such as barnacles or prey become to attach to
the specimen. These hard large algae was proven to not grow easily to the specimen
surface of larger roughness value.
4 Conclusion
By coating the oxide powder on porous ceramic bodies to study the anti-fouling effect,
the following results were concluded. The ceramic powders tried as coating materials
were Al2O3, TiO2, and ZrO2. In the initial stage about one month, the amount of bio-
fouling decreased with increased water absorption rate of specimens. In the early stage,
the bio-fouling was mostly caused by light-weight organisms such as red algae or
microbes. After two months later, however, the amount of bio-fouling decreased with
increased surface roughness of the specimen because the fouling at the later stage was
due to by larger fouling organisms such as barnacle. It showed the Al2O3 was the op-
timum coating materials among three ceramic powders to prevent the marine bio-
fouling because it offered lower water absorption and higher surface roughness to the
specimens. It was confirmed that the amount of bio-fouling could be reduced by con-
trolling the water absorption and the surface roughness of the porous ceramic through
the oxide coating. It is expected that, therefore, this result could be applied to future
marine structures without using the environmentally hazardous materials.
Advanced Science and Technology Letters Vol.116 (Bioscience and Medical Research 2015)
Copyright © 2015 SERSC 259
Acknowledgment: This work was supported by the National Research
Foundation of Korea (NRF) grant funded by the Korea government (MEST) (No.
NRF-2013R1A2A2A04014978).
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