Revista Romn de Materiale / Romanian Journal of Materials 2014, 44 (3), 283 291 283

STABILITATEA MASELOR FOSFATICE FLUORURATE PE ALIAJE DE CoCrMo

ABOUT STABILITY OF ELECTRODEPOSITED FLUORIDATED PHOSPHATE MASSES ON CoCrMo ALLOYS

DANIELA COVACIU ROMONI, GEORGETA VOICU, DANIELA IONI, IOANA DEMETRESCU Universitatea POLITEHNICA Bucureti, str. G. Polizu, nr. 1, 011061, sect. 1, Bucureti, Romania

CoCrMo alloys are extensively used in

tissue engineering in both dental and orthopaedic applications and are highly recommended due to the good ratio quality /price comparing with other metallic biomaterials. The present approach is related to electrodeposition of fluoridated phosphate masses with good ratio calcium to phosphorus close to the one existing in bone.

SEM and EDX analysis confirm that the electrochemical method for deposition of fluoridated apatite on CoCrMo is efficient and the results were quantified using electrochemical and mechanical measurements.

Aliajele de CoCrMo sunt des utilizate n ingineria

tisular, att n aplicaiile stomatologice ct i n cele ortopedice i sunt recomandate datorit raportului bun calitate/ pre comparndu-le cu alte biomateriale metalice. Abordarea actual este legat de electrodepunerea maselor fosfatice fluorurate cu raport bun calciu fosfor, apropiat de raportul molar existent n os.

Analizele SEM i EDX confirm c metoda electrochimic pentru depunerea maselor apatitice pe aliajul de CoCrMo este eficient iar rezutatele au fost cuantificate prin msurtori electrochimice i mecanice.

Keywords: CoCrMo alloys, electrochemical deposition, SEM, EDX, artificial saliva, physiological serum 1. Introduction

Having very good mechanical properties as

castability, corrosion and wear resistance CoCrMo alloys [1] noowdays, are extensively used in tissue engineering in both dental and orthopaedic applications [2,3]. Even as heads in artificial joints. CoCrMo alloys have been introduced in bioapplications at the begging of the last century, but due especially to its problems with ion release for a period of time was used with limitations. A remarkable comeback was known in its using after introducing largely the surface engineering procedures [4,5] and the type of Ni-free alloy according to ASTM F-75 standard [6]. In medicine regeneration, CoCrMo alloys are highly recommended due to the good ratio quality /price and comparing with other metallic biomaterials as stainless steels [7] which have disadvantage in corrosion resistance or with titanium alloys which have demerit in wear resistance [2], despite the large variety of surface modifications proposed for enhancing their performance especially at the surface level [8].

The wear resistance of the CoCrMo alloys is due to the carbide structure found in both cast and wrought alloys. The hardness and elongation is attributable to the martensite transformation induced by strain [9]. The resistance to corrosion is

due to its passive film formed at the surface in various bioliquids [10]. The existence of a small amount of nickel as an impurity, despite the fact International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) estimates that nickel is carcinogenic [11], is able to maintain workability. More recently, taking into account the bacteria extension, and knowing the silver effect in enhancing antibacterial function new coatings having antibacterial inhibition effect were elaborated on the CoCrMo alloy surface [12] including hydroxyapatite (HA) as bioactive component and silver as antibacterian agent as well. Hydroxyapatite as bioactive coating was elaborated via various procedures [13,14] leading to various properties. It has been reported that plasma-sprayed HA coatings dissolve and degrade quickly, resulting in the weakening of the coating-substrate bonding or the implant fixation to the host tissues [15]. For this reason any changes to the HA that result in a higher chemical stability would be an advantage.

Impregnations to the HA crystal structure the chemical elements such as Fluoride by substituting OH groups was performed successfully on various alloys [16,17].

The present approach is related to electrodeposition of fluoridated phosphate masses with good ratio calcium to phosphorus close to the

Autor corespondent/Corresponding author, E-mail: getav2001@yahoo.co.uk

284 D.C one existingto dissolutiotrying to electrochemcorrosion prelease evacomparisoncoated allosolution is d

2. Experim

For

were used polished on1200) and aFor 15 minuacetone anfrom the Srinsed in dtemperaturewas (NH4)2CaCl22H2Oelectrolyte ufluoridated titanium [18order to encoating by thydroxyl ioCoCrMo all

2.1. Coatin

The different te22oC (sam(Figure 1.)electrode (aand CoCrMWorking pathe experimpotentiostatequipped w

Aftecalcinated Thermal trethe crystalCoCrMo safor strengthFigure 2 selectrochemcoatings on

CoP

Covaciu Romon

g in bone, inon. Firstly the

establishmical behavparameters ialuation withn of electrooy in saliva discussed as

ental

r electrodeposamples o

n SiC abrasafter that etcutes the sam

nd ethanol inSiC paper. distilled watee. The cont2HPO4 0.025

O 0.042 M,used in litera

hydroxyap8]. A volumenhance the dthe release oons. The oy its accord

ng process coating proc

emperatures:mple B) usi) with a panode), Ag/AMo as worarameters arments were pt/ galvanosta

with Volta Maer electrode

at 4000C eatment wasllinity and amples. Calchening the shows variatmical deposn CoCrMo sa

WorkoCrMo Sample

Proba CoCrMo

A B

ni, G. Voicu, D. order to proe aim of pres a relaiour of sucn bioliquids

h mechanicaochemical sand in phy

s well.

osition of phoof CoCrMo. sive papers hed in HF 4%

mples were un order to reFinally the er and drietent of elec5 M, NH4F , almost siature for elecatite on s

e of H2O2 3%deposition prof H2 gas anchemical c

ding to ASTM

cess was pe 28oC (samng a electr

platinum plaAgCl as referking electrre presentedperformed usat controlled ster 4 Softwa

eposition all temperature

s made in orthe purity

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ing parameters Cur

Densi

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ovide resistasent researction betwh coating frand from i

al propertiesstability of ysiological N

osphate masSamples w(600, 800

% for 2 minuultrasonicatedemove partic

samples wed at the roctrolyte solu 0.012 M milar with

ctrodepositiostainless s

% was addedrocess of dend productioncomposition M F75 [6].

erformed at mple A) androchemical

ate as counrence electroode (cathod

d in Table 1.sing a PGZ

by a compuare. samples w

e for 1 horder to increof the coaalso, benefi

patite coatinntial in timeoridated apa

for coating procrrent Density itate de curent[mA/cm2]

-1

etrescu / About CoCrM nce

ch is een rom ons

s. A the

NaCl

sses were and tes. d in cles

were oom tion and the

n of teel d in nse n of

of

two d at cell nter ode de). . All 301 uter

were our. ase

ated icial ngs. e of atite

F(Cpoce(Cpo

F

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yy

cre

cess/ ParametriEle

time / Tim

t stability of elecMo alloys

ig. 1 - ElectrolyCoCrMo), 2-REotentiostat/ galvelulei electrochCoCrMo), 2-ERoteniostat/ galv

ig. 2 - Coating p

Curvehown below8oC have stecond equaave standard

= - 0.80368 += - 0.88625 +

The man be descrieactions.

i de lucru pentruectrodeposition

mp de electrodep[min]

60

ctrodeposited flu

ytic cell scheme E (Ag/AgCl), vanostat, 6-magimice folosite

R (Ag/AgCl), 3-vanostat, 6-agita

process/ Proces

e equations w; equation (tandard devition (2) for d deviation, R

+ 0.1388 e0.07+ 0.43206 e-0

mechanism ofbed as a ser

u procesul de de

punere

uoridated phosp

used in coating3-CE (Pt), 4

gnetic stirrer, 7n procesul de CE (Pt), 4-soluator magnetic, 7

sul de depunere

for coating 1) for coatediation, R2 = coated CoCR2 = 0.92

7442x

0.02516x

f electrolytic ries of electro

epunere Deposition tem

Temperatura de[oC] 28 22

phate masses on

g process: 1-W4-electrolyte, 57-stirrer/ Schem

depunere: 1-Euie electrolit, 57-agitator.

e.

process ard CoCrMo a0.65 and th

CrMo at 22oC

(1) (2)deposition ochemical

Table

mperature e depunere

n

WE 5-

ma EL 5-

re at e C

) )

1

D.Covaciu Romoni, G. Voicu, D. Ioni, I. Demetrescu / Stabilitatea maselor fosfatice fluorurate pe aliaje de CoCrMo 285

The possible sources of OH- at the cathode are [19] O 2H O 4e 4HO (3) NO H O 2e 2HO NO (4) 2H O 2e H 2HO (5)

Hydroxide ions, generated during the electrodeposition process, resulted in an increase of the pH in the vicinity of the cathode; which led to the occurrence of the following reactions: H PO e HPO H (6) H PO 2e PO H (7) H PO HPO H (8) HPO PO H (9)

The precipitation of phosphate ions occurred due to the acid-base reactions, which are vital for the crystallization process of formation of FHA coating film according to the following reaction: H PO HO HPO H O (10)

H PO H O 2e H PO 2HO (11)

The suitable local chemical environment in the vicinity of the cathode enabled the HPO42- ions to react with the Ca2+ ions [17]. Ca HPO H O CaHPO 2H O (12)

The coating, after alkaline treatment, was converted to HA according to the following reaction: 10CaHPO 2HO Ca PO OH 4PO 10H (13)

Calcium deficient hydroxyapatite was formed as follows [20] 10 x Ca 6 x PO

xHPO 2 x HO Ca HPO PO OH (14) where 0 < x 2.

Addition of NaF into the electrolyte led to the occurrence of the following reactions. At the early stage, Ca2+ ions rapidly consumed the F ions in the electrolyte to form CaF2 which can be expressed as follows [20] Ca PO OH 10F 7 n H

5CaF H O 3 n H PO nH PO (15)

CaF2 particles reacted with the HPO42- ions in the solution to form FHA [20] 5CaF 3 n H PO nHPO

1 x H O Ca PO OH F 10 x F 7 x n H

where (0 < x < 1, 0< n < 3) (16) Combining reactions (15) and (16) resulted in the formation of FHA via the following reaction: 10Ca 6PO xF 2 x HO Ca PO F OH (17)

3. Results and discussions 3.1. X-Ray Diffraction Analysis X-Ray Diffraction analysis was performed for the coated samples of CoCrMo at 22C with Empirean PANalytical Diffractometer with radiation Cu (=1.5406). The acquisition was done from 10 to 80 degrees 2 with 0.02 degres step and acquisition time with 2 seconds step. Incidence angle was 1 degree. In Figure 3 is presented XRD analysis for coated CoCrMo samples.

From the XRD analysis it can be observed the deceleration of the mineralogical crystalline phases of fluorohydroxyapatite and CaHPO4.

Fig. 3 - XRD analysis of coated CoCrMo/ Analiza XRD a probelor acoperite de CoCrMo.

3.2. Scanning electron microscopy analysis

Coated samples of CoCrMo alloy were investigated with a scanning electron microscope HITACHI, S-2600N Model coupled with energy-dispersive X-ray spectroscopy (EDX) for morphology determinations. In Figure 4 are presented images with SEM characterization.

The coated CoCrMo samples shows morphologies which are characteristic to hydroxyapatite according to literature data and the synthesized deposit on CoCrMo alloy consists of spherical particles formed of plaques with very small dimensions (Figure 4). The coating is not uniform on all over the surface probably due to deposition conditions.

The fluoride presence was not observed in elemental analysis, due to the fact that the scanning electron microscope used was limited and does not detect halogens, but the fluoride existence in the coating was confirmed from FT-IR spectra at 719 cm-1. In the literature, Freund, describes a relation between the introduction of fluoride in hydroxyapatite and the increase of a band around 720-740 cm-1 [21].

The difference between coated CoCrMo at 28oC and the coated CoCrMo at 22oC shows a better adherence on the metallic substrate and a more uniform deposition for the electrochemical deposition carried at 22 degrees.

286 D.C

Fig. 4 - SEM ia), b)

Fig. 5 -EDX

FiguCoCrMo saraports Ca/

Covaciu Romon

images of apatiCoCrMo acope

spectra of apati

Fig. 6 - T

ure 5 showamples and pP.

ni, G. Voicu, D.

te coatings: a), erit la 28oC, c), d

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ity of CoCrMses in salina trochemicalication of 0(PO4)6(OH)2fluoridation , could providelectrochemons. CrMo samp

were charac% wt %) amical methomical impedammetry. Thiva Afnor is pfel plots e Tafel plots val 200/+ 2tential and ds. The detesame three ed for coatipsysiologicals. e polarizatir 4 Software

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oC.

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< x < 2 is thcomparison wability as cannd ions relel

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rding to obvious that coed alloy andith fluoridat

anticorrosion corrosion raed and in sficial saliva,

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the so-called

urface porosy potentiodyequation:

e Rp and Rof the barate pair, re

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he protectives shown in Fcoating shophysiologican be seen roved, after Fe action of

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de CoCrMo

btained datarrosion rate we can conted phosphproperties.

ates are lowaline solutio, the latterresistances aand corrosiofrom electro

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287

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Fig. 10 - Cylicacope

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290 D.C

In bin artificial resistance values are Tafel plotsmaterials ccorrosion rserum. Canphysiologicaof magnitudsaliva, indcharacter on2 we can electrolyte interface odiffusive ch

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Fig. 12 - ConCoCpen(b).

Covaciu Romon

both cases, saliva, the of the subscorrelated

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ni, G. Voicu, D. in physiologcoating layetrate (Rp vawith valuescial saliva, uncovered,

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much mo. From the vhe interface acitive charaFHA/electrolyugh obtained

metry ammetry detwere: E0 = -0 mV anure 10 arefor uncoateolutions, artif

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Ioni, I. Deme

gical serum er improves alues). Also obtained fr

both studshows a beo physiolog

ase of CoCrs with an oroCrMo/ artifiore aggressalues of n1 of the CoCr

acter and at yte we haved porous laye

erminations -800mV, E1nd scan re shown cyd and coaficial saliva

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3.4. Contact The d

erformed wrocedure sudrop) of dis

Figure 12 theetermination

For ngle values

s 96.30 whichIn c

hosphate mangle is 15uperhydrophelation with bngles the bio

3.5. MicroharThe V

eterminationwith Buehler

for 10 secoVickers units

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with the speeBy co

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4. Conclusio

SEM lectrochemichosphate m

Diffraction amineralogical uorohydroxy

An esing ele

measurementhosphate mlloy is morealiva and ph

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D.Covaciu Romoni, G. Voicu, D. Ioni, I. Demetrescu / Stabilitatea maselor fosfatice fluorurate pe aliaje de CoCrMo 291

The mechanical properties meaning microhardness and adherence are better for nanosized coatings as well.

Acknowledgements

The work has been funded by the Sectoral Operational Programme Human Resources Development 2007-2013 of the Ministry of European Funds through the Financial Agreement POSDRU/ 159/1.5/S/134198.

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