Preparation and Investigation composite coating
(Ni-nano hydroxyapatite) on low carbon steel samples
dr. Nabaa Sattar Radhi Zainab S. Al-Khafaji
University of Babylon Al-Mustaqbal University College
E-mail: dr.nabbaa@gmail.com. Zainab_Alkafaji@mustaqbal-college.edu.iq.
Abstract:
In this work represents an attempt to introduce further improvement to the properties of Nickel coatings, by addition HA particle to electrodeposited solution. Low carbon steel samples were coated with Nickel and (Ni- HA) with different nanoscale particles size of hydroxyapatite once (20 nm) and another (40 nm). After electroplating, these samples were tested all specimen in Hank s solution to study the corrosion behavior. Then test the microhardness, surface roughness, and Topographic for Nickel coating and (Ni-HA) with (20 and 40) nm.
Keywords: Hydroxyapatite, orthopedic implant, biocompatibility, electrodeposited, nanoscale and Hank s solution.
1.1 Introduction:
Nickel is one of the most common metal that used in electroplating so as to enhance the usefulness, value and overall sales promotion for consumer goods and products manufacturing, [1]. As well as the nickel coating is also used to enrich the physical characteristics like resistance of wear, resistance of heat, resistance of corrosion. Nickel coatings are used in many important applications due to the ability of this coating to improve the resistance of the metal against corrosion with an improving in the functional properties as well as providing a decorative shape, [2-4].
1.2 Bio-active Coating
Bio-active materials is a term used to refer to the materials that will be active inside the human body and it will be interact with the bones around it or with the soft tissue in some cases depending on Bioactivity Index (IB) which introduced by (Hench) as shown in below to measure the level of bio-activity:
IB = 100/ t 0.5bb
Whereas: t 0.5bb = the time required to get bonding interface for more than 50%. And this usually occurs during the time depending on kinetic modification of the surface, generated by implantation of the bio-active material inside the live bone. Due to the reaction between the bio-active materials which inside the live bone and the surrounding body fluids there will be an ion exchange. And this ion exchange will lead to produce of a biologically active carbonate apatite (CHA) coat on the bioactive object which is equivalent to the bone mineral phase chemically and crystallographically. And the main examples for bio-active materials are synthetic hydroxyapatite (HA), and Bio-glass [5].
1.3 Hydroxyapatite

Hydroxyapatite (HA), usually written as Ca10(PO4)6(OH)2 is a member of the apatite group of ceramics. And apatite terms refer to deceit or deception and the main origin for this term is the Greek word (a pate) and the cause of this name return to the variation of the shape and colour [6]. It was chosen many times as an artificial bone due to it nature which is similar to live bone in spite of devoid of such organic constituents as collagen and polysaccharides. The chemical similarity of HA to bone and its excellent biocompatibility and bioactivity have attracted the attention of medical professionals [7,8].
HA has been synthesized and used to manufacture various forms of implants (solid and porous) and as a coating on other implants [9].
2. Experimental part:
2.1 Electroplating Process
The samples were low carbon steel (L.C.S.) with chemical composition as shown in Table (1). The chemical analysis was performed by using a spectroscopy device for metal.
The samples that used in all the tests were prepared by using cylindrical moulds and the finals samples have disc shape with the following dimension ( thickness = 2mm and diameter = 15mm) as well as the surface area for these samples are (447.667 mm2).
On the other hands, the samples surface was prepared as following:
1. Grinding the sample surface by using Grit silicon carbide papers which carried these grade (220,240,400,600,800,1000,1200). Then the sample surface will clean by using brines and acids to be ready for Electroplating process depending on the required period for each sample.
2. Electroplating process was carried out by using basin produced from polythene and has a rectangular shape (29x21x18 cm) as shown in figure (1); and power supply which can give the current up to (6Amp) and The voltage given up to (20 Volt).
2.2 Composition of Electroplating Baths:
The Watts Nickel Plating Solution The plurality of nickel plating solutions, especially those used for decorative plating, are depending on the ‘Watts’ formulation developed by Professor Oliver P. Watts in 1916. The Watts electrolyte gather nickel sulphate, nickel chloride and boric acid. While the proportions may vary according to the application, a typical formulation together with operating parameters is given in Table (2).
2.3 Tests:
In the research, the following tests were carried out to evaluate the performance of the coating layers:
2.3.1. Thickness Test
The thickness measuring device was used to measure the thickness of Ni and Ni-HA films, in (Babylon/College of Material Engineering/University of Babylon).
2.3.2. Light Optical Microscope (LOM)
Involved identification and measurement of the phases, shape and grain size are some characteristics of grain boundaries. Each of these has distinct characteristics. The microstructure evaluated with (100x) magnification using Olympus microscope manufactured by Japan.
2.3.3. Hardness Test
Vickers Hardness (TH-717 Digital Micro Vickers Hardness Tester) was measured the hardness of Ni and Ni-HA films, at load (200N) and holding time 20 seconds in (college of Material engineering /University of Babylon).
2.3.4. surface roughness test
The surface roughness of a nickel-coated steel sample (Ni-nHAP) was measured by using the (TR-100 surface roughness tester),which is located at the University of Babylon, Faculty of Materials Engineering. The device passes on the sample surface to measure the surface roughness. The device has a sensor that records the roughness of the sample surface and takes the reading directly from the device screen. The accuracy of the device (± m?0.01).
2.3.5. Electrochemical Test
The corrosive behavior of low carbon steel studied in Hank s solution. The chemical composition of Hank s solution is illustrated in Table (3) and pH of it at 37C° was 7.4.
2.3.5.1 Open Circuit Potential (OCP)
The experimental arrangement for the measurement of open circuit potential is described. A 500 ml capacity glass electrolytic cell is used. The tests were performed with the specimen submerged in a Hanks solution. The potential of the working electrode is measured with respect to a Saturated Calomel electrode (SCE).
2.3.5.2 Potentiostatic Polarization
Electrochemical experiments were performed in three electrode cell containing and electrolytes Hank s solution which chemical composition is shown in table (3), [10].
The test was carried out by stepping the possible using a scanning rate 0.4 mV/s from initial potential of 250 mV below the open circuit potential and the scan continued up to 250 mV above the open circuit potential. Corrosion rate measurement is got by applying the following equation [11].
Corrosion rate (mpy) = 0.13icorr(E.W.)/A.? …(1)
Where:
E. W. = equivalent weight (g/ eq)
A = area (cm2)
= ? density (g/ cm3)
0.13 = metric and time conversion factor.
icorr. = current density (?A / cm2).
The improvement percentage is calculated for coated samples, using the following equation [11]:
Improvement percentage =(CR0 _ CR / CR0)? 100 …(2)
Where:
CR° =the corrosion rate of master sample(without coated).
CR =the corrosion rate of coated sample (with Ni or (Ni-HAP)).
3. Results and discussion:
3.1 Thickness Results
For Ni sample the thickness is 25.7µm, while the thickness increased to (47.5, 48.7) µm for (Ni-20nHaP) samples with 10 and 20 g/L , and then the thickness reach to it is high value (49.7, 50.5) µm for (Ni-40nHaP) samples with 10 and 20 g/L. Anyhow with increasing amount and particles size of HAP, the rate of thickness increased also as shown in Table (4).
3.2 Light Optical Microscope (LOM)
The optical microscope is shown the topography behavior of coating layer for Ni and (Ni-HAP) as illustrated in figure (2(a,b,c,d,e)).
3.3. Hardness results
The hardness test was performed to determine the effect of (Ni) coating on the hardness values of low carbon steel. And finding out the effect of adding (HAP) in two different particles size on the hardness values of (Ni) coating and the low carbon steel values. Table (6) shows the results of hardness test for of the carbon steel sample, the Ni-coated steel sample, the Ni-20nHAP layers and the Ni-40nHaP layer.
The difference in hardness values observed between Ni-20nHAP and Ni-40nHAP is due to the difference in the volume of hydroxide uptake in both layers. The material hardness is clearly affected by the size of the particles, and mathematically can explain it by Hall-Petch relationship, which states, [4]:

whereas :
HV: Hardness of material with small granular size.
Ho: Hardness material is multi-size granular (polycrystalline grain size).
K: Constant, represents the slope of the Hv hardness when drawing against, and it depends on the type of material.
: Diameter of the particle.
Hall-Petch relationship is one theory that explains why ultra-fine microstructures have higher hardness values when compared to the coarser-grained ones and the same hardened material.
3.4 Surface roughness results
It is clear from table (6) the roughness of (Ni-40nHAP,20g) is the highest. This may be attributed to the bigger HAP particles size. This is idea is supported by the fact that (Ni) layer which is free of HAP particles possesses the lowest value of surface roughness. The surface roughness of the deposited layers are presented in table (6).
3.5 Corrosion Tests
3.5.1 Open Circuit Potential (OCP)- Time Measurements
The OCP - time was measured with respect to SCE in Hank s solution at 37°C for uncoated samples and coated samples (Ni and Ni-HA Coating). The data of OCP are shown in Table (4).
3.5.2 Potentiostatic Polarization
This test was done by using the Potentiostatic polarization test in Hank s solution) for uncoated, Ni and Ni-HA coated samples at 37 °C, as shown in table (7) and figure(3).
These results indicate stability behavior of HA coating layer. Along with an improvement of corrosion resistance, this HA coating is able to change the characteristics of the surface on the materials without affecting the characteristics of the bulk [12,13]. Also, the presence of HA in coatings can improve corrosion resistance of the coated implant in biological solutions which can decrease metallic release and promotes fixation via chemical bonding [12,14].
Conclusion:
1. The adding of hydroxyapatite to the electrolytic coating of metal (Ni) makes the coating layer has good properties.
2. Ni-20nHAP, 20 g / L) showed better results than (Ni-40nHAP, 20) due to the small size of the hydroxyapatite particles, which support the crystal structure by the interaction with the Crystalline structure.
3. The coating layer (Ni-20nHAP, 20 g / L) showed hardness and good corrosion resistance because hydroxyapatite is a chemically inert and has high hardness so as to it properties are reflected on the Ni coating layer. The results of the coating layer (Ni-20nHAP, 20 g / L) was much better than the results of the coating layer (Ni-40nHAP, 20 g / L) due to the small size of hydroxyapatite, which enter deeply in the alloy and its small size near the distance between the atoms in the crystal structure makes it as supporting particles for this Composition.
Tables:
Table (1) Chemical composition of the sample used.
C Si Mn Cr Fe
0.12 0.17 0.65 0.04 Rem
Table (2) Components of plating solution, [1].
Solution Chemical composition Condition of Deposition
Ni NiSO4.6H2O=240 g/l
NiCl2.6H2O=45 g/l
H3BO3=25 g/l pH = 3.5
Temp=55°C .
Coating time= 60 min.
Nickel Anodes=(99.9%)
Current density=2.5 (Amp/dm²(
Ni-nHAP NiSO4.6H2O=240 g/l
NiCl2.6H2O=45 g/l
H3BO3=25 g/l
HAP=10 g/l
Nano scale , d (20) nm pH = 3.5
Temp=55°C .
Coating time= 60 min.
Nickel Anodes=(99.9%)
Current density=2.5 (Amp/dm²(
Ni-nHAP NiSO4.6H2O=240 g/l
NiCl2.6H2O=45 g/l
H3BO3=25 g/l
HAP=20 g/l
Nano scale , d (20) nm pH = 3.5
Temp=55°C .
Coating time= 60 min.
Nickel Anodes=(99.9%)
Current density=2.5 (Amp/dm²(
Ni-nHAP NiSO4.6H2O=240 g/l
NiCl2.6H2O=45 g/l
H3BO3=25 g/l
HAP=10 g/l
Nano scale , d (40) nm pH = 3.5
Temp=55°C .
Coating time= 60 min.
Nickel Anodes=(99.9%)
Current density=2.5 (Amp/dm²(
Ni-nHAP NiSO4.6H2O=240 g/l
NiCl2.6H2O=45 g/l
H3BO3=25 g/l
HAP=20 g/l
Nano scale , d (40) nm pH = 3.5
Temp=55°C .
Coating time= 60 min.
Nickel Anodes=(99.9%)
Current density=2.5 (Amp/dm²(
Table (3): Chemical Composition of Hank s Solution [10]
NO. CONSTITUENT (mg/l)
1
2
3
4
5
6
7
8
9
NaCl
CaCl2
KCl
NaHCO3
Glucose
Mg Cl2.6H2O
Na2HPO4. 2H2O
KH2 PO4
Mg SO4. 7 H2O 8.0
0.14
0.4
0.35
1.0
0.1
0.06
0.06
0.06
Table (4): The Thickness of Ni and (Ni-HAP) Layer Coating.
Samples Thickness (µm)
Ni 25.7
Ni-20nHAP,10g 47.5
Ni-20nHAP,20g 48.7
Ni-40nHAP,10g 49.7
Ni-40nHAP,20g 50.5
Table (5) The hardness value
Layer coating hardness value
L.C.S 200
Ni 251
Ni-20nHAP,10g 304
Ni-20nHAP,20g 344
Ni-40nHAP,10g 295
Ni-40nHAP,20g 306
Table (6) Surface roughness value
Layer coating roughness value
L.C.S -
Ni 0.153
Ni-20nHAP,10g 0.265
Ni-20nHAP,20g 0.570
Ni-40nHAP,10g 0.293
Ni-40nHAP,20g 0.775
Table (7): Illustrate the Corrosion Potential (Ecorr.), Corrosion Current (Icorr.) and Improvement Percentage of coated Samples in Hank s solution at 37 °C
samples Icorr. µA/cm2 Ecorr. (-mV) Corrosion rate (mpy) Improvement percentage%
L.C.S 24.51 506.3 46.533 -
Ni 6.49 344.2 12.321 73.522
Ni-20nHAP,10g 1.35 255.1 2.563 94.492
Ni-20nHAP,20g 0.556 24.2 1.055 97.732
Ni-40nHAP,10g 1.47 354.8 2.790 94.004
Ni-40nHAP,20g 0.984 199.4 1.868 95.986

Figures:

Figure (1) electroplating cell.


(a) (b) (c)

(d) (e)
(a): Ni coating layer, (b): Ni-20nHAP,10g coating layer, (c): Ni-20nHAP,20g,
(d): Ni-40nHAP,10g, (e): Ni-40nHAP,20g
Figure (2) topographic morphology.

(a) Low carbon steel in Hank s solution.

(b)Low carbon steel coating with Nickel layer in Hank s solution.

(c) Low carbon steel coating with (Ni-40nHAP,10g/L) in Hank s solution.

(d) Low carbon steel coating with (Ni-40nHAP,20g/L) in Hank s solution.


(e) Low carbon steel coating with (Ni-20nHAP,10g/L) in Hank s solution.

(f) Low carbon steel coating with (Ni-20nHAP,20g/L) in Hank s solution.
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