porous peo coatings on titanium, obtained under dc regime ... · keywords: plasma electrolytic...
TRANSCRIPT
Available online at www.worldscientificnews.com
( Received 20 January 2018; Accepted 07 February 2018; Date of Publication 08 February 2018 )
WSN 94(2) (2018) 99-114 EISSN 2392-2192
Porous PEO coatings on titanium, obtained under DC regime, enriched in magnesium, calcium, zinc,
and copper
Krzysztof Rokosza, *Tadeusz Hryniewiczb, Kornel Pietrzakc, Łukasz Dudekd
Division of BioEngineering and Surface Electrochemistry, Department of Engineering and Informatics Systems, Faculty of Mechanical Engineering, Koszalin University of Technology,
Racławicka 15-17, PL 75-620 Koszalin, Poland
a-dE-mail address: [email protected] , [email protected] ,
[email protected] , [email protected],
*Corresponding authors: [email protected]
ABSTRACT
In the present paper, the analysis of SEM and EDS results of porous and enriched in calcium,
magnesium, zinc, copper and phosphorus coatings, obtained during 3-minute treatments performed by
Plasma Electrolytic Oxidation (PEO)/Micro Arc Oxidation (MAO) processes on CP Titanium Grade
2, is presented. The PEO process was carried out at DC potentials of 500 VDC, 575 VDC, and 650 VDC
in electrolytes containing 125 g Ca(NO3)2·4H2O, and 125 g Mg(NO3)2∙6H2O, and 125 g
Zn(NO3)2∙6H2O, and 125 g Cu(NO3)2∙3H2O in 1 L H3PO4. It was found that obtained coatings have
pores with different shapes and diameters and/or size/dimentions. The Ca/P, Mg/P, Zn/P, Cu/P, and
M/P ratios (M=Ca+Mg+Zn+Cu) were equal to 0.074, 0.046, 0.056, 0.042, and 0.218, respectively.
The highest value of each of these ratios was recorded for 650 VDC. It may be concluded that the
obtained PEO coatings structures most likely are similar to hydroxyapatite-like structures, in which the
Ca2+
may be replaced with Zn2+
, Mg2+
, Cu2+
.
Keywords: Plasma Electrolytic Oxidation (PEO); Micro Arc Oxidation (MAO); CP Titanium Grade 2;
calcium nitrate Ca(NO3)2·4H2O; magnesium nitrate Mg(NO3)2∙6H2O; zinc nitrate Zn(NO3)2∙6H2O;
copper nitrate Cu(NO3)2∙3H2O
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1. INTRODUCTION
Metal surface treatments by electrochemical processing have been steadily developed
since many decades. Standard electropolishing (EP) [1-5], considered as a surface finishing
performed on a plateau current density level has been recently modified by extending the
treatment conditions to the high-current density electropolishing (HCEP) [6-8] or high-
voltage electropolishing (HVEP) [9] with the improved results concerning nano-films of
nano-coatings. Another electrochemical surface technique acquires a magnetic field [10] with
the process named magnetoelectropolishing (MEP) [10-24] in which, apart from improving
surface finishing [13-24], nanohardness [12], corrosion resistance [13-16], biological response
[26], and fundamental about 90-percent de-hydrogenation is obtained [25].
On the other hand, Plasma Electrolytic Oxidation (PEO) [27] also known as Micro Arc
Oxidation (MAO) has been developed to form micro-coatings on metals and alloys [28-64].
These coatings are usually porous and may be enriched in chemical elements, such as
phosphorus and calcium to form the hydroxyapatite-like structure [38-46]. Moreover, another
elements, such as bactericidal copper [47-56], magnesium, which may accelerate the healing
of wounds [41,58,59] as well as zinc with antibacterial properties [40,60-63], capable for
improving osteogenic characteristics and bone regenerating capacity [64-67], may be
introduced into the porous coatings.
The aim of this work is to characterize porous and biocompatible hydroxyapatite-like
surface coatings (calcium-phosphorus structures) created on titanium by Plasma Electrolytic
Oxidation; these coatings are enriched with antibacterial zinc and copper as well as with
magnesium. The additives, used to enrich the porous coatings on metallic implants, are
helpful with wound healing.
2. METHOD
The samples of CP Titanium Grade 2, with dimensions 10 10 2 mm, were treated by
Plasma Electrolytic Oxidation (Micro Arc Oxidation) for the surface studies. The plasma
electrolytic oxidation (PEO) was performed at the voltages of 500 VDC, 575 VDC and
650 VDC. For the studies, the electrolyte containing 125 g calcium nitrate Ca(NO3)2·4H2O,
and 125 g magnesium nitrate Mg(NO3)2∙6H2O, and 125 g zinc nitrate Zn(NO3)2∙6H2O, and
125 g copper nitrate Cu(NO3)2∙3H2O, in 1 L concentrated 85% analytically pure
orthophosphoric acid H3PO4, was used. For each run, the electrolytic cell made of glass was
used, containing up to 500 ml of the electrolyte.
For the studies, the scanning electron microscope Quanta 250 FEI with Low Vacuum
and Environmental Scanning Electron Microscope (ESEM) mode and a field emission
cathode as well as the Energy-Dispersive X-ray Spectroscopy (EDS) system in a Noran
System Six with nitrogen-free silicon drift detector, were employed.
3. RESULTS AND DISCUSSION
In Figures 1 and 2, the SEM images of coating formed on Titanium after PEO
treatment at 500 VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, 125 g
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Mg(NO3)2∙6H2O, 125 g Zn(NO3)2∙6H2O, and 125 g Cu(NO3)2∙3H2O in 1 L H3PO4, are
presented.
Fig. 1. SEM pictures with magnification 500 times spectrum for coating formed on Titanium
after PEO treatment for 3 min at 500 VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O,
125 g Mg(NO3)2∙6H2O, 125 g Zn(NO3)2∙6H2O, and 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
It may be seen that during Plasma Electrolytic Oxidation process, irregular surface with
common micrometers size pores were developed which in general is beneficial to bone tissue
growth [59] and can be employed as local drug delivery systems where polymer matrix
containing bioactive substances is applied as thin layer also filling pores [60-62]. (This is also
known as smart materials). In Figure 3 and Tables 1 and 2, EDS results of coating formed on
Titanium after PEO treatment at 500 VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O,
and 125 g Mg(NO3)2∙6H2O, and 125 g Zn(NO3)2∙6H2O, and 125 g Cu(NO3)2∙3H2O in 1 L
H3PO4, are displayed.
These EDS peaks of phosphorus, titanium, calcium, magnesium, zinc and copper show
that formed PEO coating is built mainly of phosphorus-titanium-calcium and calcium
substituted by magnesium zinc and copper compounds what may suggest the hydroxyapatite-
like structure has been formed. In PEO coating, apart from the titanium (36.3 ± 0.2 at%)
which is substrate, and of which signal may partly come from matrix, phosphorus (54.4 ± 0.4
at%), calcium (1.8 ± 0.1 at%), magnesium (2.0 ± 0.1 at%), zinc (1.9 ± 0.2 at%) and copper
(1.8 ± 0.2 at%) were also recorded. Thus metal-to-phosphorus ratios for calcium, magnesium,
zinc, copper and sum of metals equal 0.066, 0.037, 0.034, 0.033, and 0.170, respectively.
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Fig. 2. SEM pictures with magnification 10 000 times spectrum for coating formed on
Titanium after PEO treatment for 3 min at 500 VDC in electrolyte containing of 125 g
Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O, 125 g Zn(NO3)2∙6H2O, and 125 g Cu(NO3)2∙3H2O
in 1 L H3PO4
Fig. 3. EDS spectrum for coating formed on titanium after PEO treatment for 3 min at 500
VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O, 125 g
Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
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Table 1. EDS results of coatings formed on Titanium after PEO treatment for 3 min at 500
VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O, 125 g
Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
Atomic Concentration [%]
P Ca Mg Zn Cu Ti
54.4 ± 0.4 3.6 ± 0.1 2.0 ± 0.1 1.9 ± 0.2 1.8 ± 0.2 36.3 ± 0.2
Table 2. Metal-to-phosphorus ratios of coatings formed on Titanium after PEO treatment for
3 min at 500 VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O,
125 g Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
Metal-to-phosphorus ratio
Ca/P Mg/P Zn/P Cu/P M/P
0.066 0.037 0.034 0.033 0.170
Table 3. EDS results of coatings formed on Titanium after PEO treatment for 3 min at 575
VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O, 125 g
Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
Atomic Concentration [%]
P Ca Mg Zn Cu Ti
49.4 ± 0.4 2.6 ± 0.1 2.2 ± 0.1 2.0 ± 0.3 1.8 ± 0.2 42.0 ± 0.3
Table 4. Metal-to-phosphorus ratios of coatings formed on Titanium after PEO treatment for
3 min at 575 VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O,
125 g Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
Metal-to-phosphorus ratio
Ca/P Mg/P Zn/P Cu/P M/P
0.053 0.043 0.043 0.039 0.177
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In Figures 4 and 5, the SEM pictures of coating formed on Titanium after PEO
treatment at 575 VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, and 125 g
Mg(NO3)2∙6H2O, and 125 g Zn(NO3)2∙6H2O, and 125 g Cu(NO3)2∙3H2O in 1 L H3PO4, are
presented. One may notice, that during plasma electrolytic oxidation process, irregular surface
with common micrometers size pores were developed, which in general is beneficial to bone
tissue growth [59] and can be employed as local drug delivery systems where polymer matrix
containing bioactive substances is applied as thin layer also filling pores [60-62].
In Figure 6 and Tables 3 and 4, EDS results of coating formed on Titanium after PEO
treatment at 575 VDC in the electrolyte containing of 125 g Ca(NO3)2·4H2O, and 125 g
Mg(NO3)2∙6H2O, and 125 g Zn(NO3)2∙6H2O, and 125 g Cu(NO3)2∙3H2O in 1 L H3PO4, are
presented. These EDS peaks of phosphorus, titanium, calcium, magnesium, zinc and copper
show that formed PEO coating is built mainly of phosphorus-titanium-calcium and calcium
substituted by magnesium zinc and copper compounds what may suggest, the hydroxyapatite-
like structure may exist.
In the PEO coating, apart from the titanium (42.0 ± 0.3 at%) which is substrate, and of
which signal may partly come from matrix, phosphorus (49.4 ± 0.4 at%), calcium (2.6 ± 0.1
at%), magnesium (2.2 ± 0.1 at%), zinc (2.0 ± 0.3 at%) and copper (1.8 ± 0.2 at%), were also
recorded. Thus metal to phosphorus ratios for calcium, magnesium, zinc, copper and sum of
metals equal 0.053, 0.043, 0.043, 0.039, and 0.177, respectively.
Fig. 4. SEM pictures with magnification 500 times spectrum for coating formed on Titanium
after PEO treatment for 3 min at 575 VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O,
125 g Mg(NO3)2∙6H2O, 125 g Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
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Fig. 5. SEM pictures with magnification 10 000 times spectrum for coating formed on
Titanium after PEO treatment for 3 min at 575 VDC in electrolyte containing of 125 g
Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O, 125 g Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in
1 L H3PO4
Fig. 6. EDS spectrum for coating formed on titanium after PEO treatment for 3 min at 575
VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O, 125 g
Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
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In Figures 7 and 8, the SEM images of coating formed on Titanium after PEO
treatment at 575 VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, and 125 g
Mg(NO3)2∙6H2O, and 125 g Zn(NO3)2∙6H2O, and 125 g Cu(NO3)2∙3H2O in 1 L H3PO4, are
presented. One can easily notice, that during plasma electrolytic oxidation process, irregular
surface with common micrometers size pores were developed, which in general is beneficial
to bone tissue growth [59] and can be employed as local drug delivery systems where polymer
matrix containing bioactive substances is applied as thin layer also filling pores [65-67].
In Figure 9 and Tables 5-6, EDS results of coating formed on Titanium after PEO
treatment at 575 VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, and 125 g
Mg(NO3)2∙6H2O, and 125 g Zn(NO3)2∙6H2O, and 125 g Cu(NO3)2∙3H2O in 1 L H3PO4, are
presented. These EDS peaks of phosphorus, titanium, calcium, magnesium, zinc and copper
show that formed PEO coating is built mainly of phosphorus-titanium-calcium and calcium
substituted by magnesium zinc and copper compounds, what may suggest the hydroxyapatite-
like structure is formed. In the PEO coating, apart from the titanium (38.5 ± 0.2 at%) which is
a substrate, and of which signal may partly come from matrix, phosphorus (50.3 ± 0.4 at%),
calcium (4.7 ± 0.1 at%), magnesium (2.2 ± 0.1 at%), zinc (2.4 ± 0.3 at%) and copper (1.9 ±
0.3 at%), were also recorded. Thus metal-to-phosphorus ratios for calcium (Ca/P), magnesium
(Mg/P), zinc (Zn/P), copper (Cu/P), and the ratio of sum of these metals (M/P) were equal to
0.074, 0.046, 0.056, 0.042, and 0.218, respectively.
Fig. 7. SEM pictures with magnification 500 times spectrum for coating formed on Titanium
after PEO treatment for 3 min at 650 VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O,
125 g Mg(NO3)2∙6H2O, 125 g Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
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Fig. 8. SEM pictures with magnification 10 000 times spectrum for coating formed on
Titanium after PEO treatment for 3 min at 650 VDC in electrolyte containing of 125 g
Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O, 125 g Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in
1 L H3PO4
Fig. 9. SEM pictures with magnification (a) 500 times, (b) 10 000 times and (c) EDS
spectrum for coatings formed on Titanium after PEO treatment for 3 min at 650 VDC in
electrolyte containing of 125 g Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O, 125 g
Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
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In Figure 10, the summary EDS results for 500 VDC, 575 VDC and 650 VDC, are
presented. One can note that all of M/P ratios (for M = Ca, Mg, Zn, Cu) decrease for 500 VDC
and 575 VDC, with some mixed results referred to 650 VDC. On the other hand, however, the
ratio of the sum of all four metals (Ca+Mg+Zn+Cu) to phosphorus increases with the growth
of PEO voltage from 500 up to 650 VDC.
Fig. 10. EDS results for coatings formed on Titanium after PEO treatment for 3 min in
electrolyte containing of 125 g Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O, 125 g
Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
Table 5. EDS results of coatings formed on Titanium after PEO treatment for 3 min at 650
VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O, 125 g
Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
Atomic Concentration [%]
P Ca Mg Zn Cu Ti
50.3 ± 0.4 4.7 ± 0.1 2.2 ± 0.1 2.4 ± 0.3 1.9 ± 0.3 38.5 ± 0.2
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Table 6. Metal-to-phosphorus ratios of coatings formed on Titanium after PEO treatment for
3 min at 650 VDC in electrolyte containing of 125 g Ca(NO3)2·4H2O, 125 g Mg(NO3)2∙6H2O,
125 g Zn(NO3)2∙6H2O, 125 g Cu(NO3)2∙3H2O in 1 L H3PO4
Metal-to-phosphorus ratio
Ca/P Mg/P Zn/P Cu/P M/P
0.074 0.046 0.056 0.042 0.218
4. CONCLUSIONS
The following conclusions may be drawn from the studies:
it is possible to obtain the porous surface on titanium, enriched in magnesium, calcium,
zinc and copper as well as phosphorus in electrolyte containing: 125 g Ca(NO3)2·4H2O,
and 125 g Mg(NO3)2∙6H2O, and 125 g Zn(NO3)2∙6H2O, and 125 g Cu(NO3)2∙3H2O, in 1
L H3PO4 at the voltage ranging from 500 VDC until 650 VDC during 3 min PEO process
the ratios Ca/P, Mg/P, Zn/P, Cu/P, and M/P, where M=Ca+Mg+Zn+Cu, were equal to
0.074, 0.046, 0.056, 0.042, 0.218, respectively
the highest values of all those ratios were recorded for 650 VDC
most likely the obtained coatings are similar to hydroxyapatite-like structures, in which
the Ca2+
may be replaced with Zn2+
, Mg2+
, Cu2+
.
Acknowledgements
This work was supported by subsidizing by Grant OPUS 11 of National Science Centre, Poland, with
registration number 2016/21/B/ST8/01952, titled "Development of models of new porous coatings obtained on
titanium by Plasma Electrolytic Oxidation in electrolytes containing phosphoric acid with addition of calcium,
magnesium, copper and zinc nitrates".
Prof. Winfried Malorny from Hochschule Wismar-University of Applied Sciences Technology, Business and
Design, Faculty of Engineering, DE 23966 Wismar, Germany, is given thanks for providing access to the
SEM/EDS apparatus allowing to perform the studies.
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