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Effect of fruit juices and chloride ions on the corrosion behavior of orthodontic archwire Manu Rashmi Sharma, Neelima Mahato, Moo Hwan Cho, Thakur Prasad Chaturvedi & Madan Mohan Singh To cite this article: Manu Rashmi Sharma, Neelima Mahato, Moo Hwan Cho, Thakur Prasad Chaturvedi & Madan Mohan Singh (2018): Effect of fruit juices and chloride ions on the corrosion behavior of orthodontic archwire, Materials Technology To link to this article: https://doi.org/10.1080/10667857.2018.1473992
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MATERIALS TECHNOLOGY https://doi.org/10.1080/10667857.2018.1473992
Effect of fruit juices and chloride ions on the corrosion behavior of orthodontic archwire Manu Rashmi Sharmaa*, Neelima Mahato*b,c, Moo Hwan Choc, Thakur Prasad Chaturvedia and Madan Mohan Singhb a
Division of Orthodontics, Faculty of Dental Sciences, Institute of Medical Sciences, Varanasi, India; bDepartment of Applied Chemistry, Institute of Technology, Varanasi, India; cSchool of Chemical Engineering, Yeungnam University, Gyeongsan-si, Republic of Korea ABSTRACT
ARTICLE HISTORY
Electrochemical and surface analytical study on the corrosion behavior of AISI 316L stainless steel orthodontic archwire in different fruit juices was carried out. The electrochemical parameters were measured after immersing the wires for approx. 24 h in artificial saliva (AS) containing different fruit juices and separately in fruit juices with 1% NaCl in AS. All the fruit juices used in this study increased the rate of corrosion process in AS in the presence or absence of salt. Addition of 1% NaCl to the AS, all experiments exhibited pitting. Solanum lycopersicum (Tomato) and Durio zibethinus (Amra) are rated as most detrimental to the surface followed by Prunus domestica Linn. (Plum) juice. SEM Micrographs of the specimens show formation of blisters onto the steel surface which are remnants of passive film.
Received 16 February 2018 Accepted 3 May 2018
Introduction Orthodontic appliances are exposed to physical, chemical, mechanical and biological stresses when placed in an aggressive oral environment. Various dietary constituents, such as common salt (mainly NaCl), spices, fruit juices, carbonated drinks act as promoters of corrosion [1–3]. Pitting corrosion has been observed to occur primarily within crevices or other protected areas on metal surfaces exposed to corrosive environment. It may occur at the sites where irregularities are formed during manufacturing or handling by the orthodontists. It may also occur at the bracket-archwire sites where the surfaces contact one another or coated with plaque and food remnants. This results in the formation of micro- sites or corrosion environment [4]. Pitting is the most destructive type of corrosion seen in the orthodontic appliances placed in the oral cavity [5]. Its effect is localized and forms holes or pits in the metal. These pits sometimes occur scattered or isolated and sometimes so close together so that they appear like rough surface. Stainless steel archwires are most popular and readily used archwire appliances during orthodontic treatment due to low cost and outstanding mechanical properties that include considerably high strength, modulus of elasticity, resistance to corrosion, excellent formability and lower bracket-wire friction [6,7]. Acidic medium and presence of CONTACT Neelima Mahato
[email protected]; Moo Hwan Cho University, Gyeongsan-si, Gyeongsanbuk-do, Republic of Korea-38541 *Contributed equally as first author Supplemental data for this article can be accessed here. © 2018 Informa UK Limited, trading as Taylor & Francis Group
KEYWORDS
Orthodontic appliances; archwires; stainless steel; pitting corrosion; passive film; fruit juices
aggressive ions, such as chloride ions can accelerate the rupture of the protective passive film and induce corrosion [2,8,9]. Corrosion of orthodontic appliances requires a special concern because of its potential health implications, deterioration of physical properties and the clinical performance [10,11]. Corrosion can lead to weakening of the appliances, and liberation of elements from the metal or alloy, and ultimately, leading to mechanical failure of the orthodontic materials [12–14]. Fruit juices are most commonly preferred, included in everyday diet structure and recommended due to their nutritional value. In tropical countries, these juices are extensively consumed in many ways, e.g., as condiments, digestives, electrolyte or health drinks, nutritional supplements, and so on. These are either consumed as raw, soon after extraction from fruits, or in the form of processed drinks containing salts, or pickles, jams, marmalades, etc. Present work deals with the in vitro effects of ten most commonly consumed natural fruit juices on the corrosion behavior of steel orthodontic wires, viz., Prunus domestica Linn. (Plum), Spondias mombin (Amra or yellow mombin or hog plum), Vitis vinifera (Grapes), Carissa carandas (Karaunda or bengal currant), Citrus limon (Lemon), Citrus sinensis (Musambi or sweet lime), Ananas comosus (Pine apple), Punica granatum (Pomegranate), Tamarindus indica (Tamarind), and Solanum lycopersicum (Tomato). Influence of the addition of salt
[email protected]
School of Chemical Engineering, Yeungnam
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M. R. SHARMA ET AL.
(NaCl) was also studied. The after effect of corrosion tests on the surface of the stainless steels was studied using scanning electron microscopy.
Materials and methods Experimental material Stainless steel (AISI 316L) orthodontic archwire of diameter 0.018 inches (0.04572 cm) was taken for the study. The alloy composition determined by EDAX (Energy dispersive X-ray analysis) was Cr (20.42%), Ni (12.82%), Fe (67.19%), Mo (3.12%), Mn (0.50%). Preparation of test solutions AS was prepared in double distilled water with the following composition in g/L (16): K2HPO4 (0.340), NaH2PO4.2H2O (0.445), KHCO3 (1.500), NaCl (0.585), MgCl2.6H2O (0.031), citric acid (0.032), CaCl2 (0.012). All the chemicals were procured from Merck, India Ltd. The selected fruits were washed thoroughly and rinsed with distilled water and wiped with the help of clean cotton cloth. The edible parts of the fruits were then cut into smaller pieces and crushed in a juicer followed by filtration to obtain clear transparent juice of each fruit separately. Test solutions containing 20% fruit juice by volume in AS were prepared. An additional set of test solutions containing 1% salt (NaCl) was also prepared. Preparation of electrodes Wire specimens of length 5 cm were cut from the as received orthodontic archwire sample and were covered with lacquer leaving 3.48 cm length to be exposed to the electrolyte solution. These were used as working electrode and prepared in a way so that a surface area of 1 cm2 is exposed to the electrolyte solution. The three-electrode electrochemical cell consisted of a Pt grid as Counter electrode and Ag/ AgCl (Orion, Beverly, MA, USA) as the reference electrode. Electrochemical experiments and surface analysis All the electrochemical experiments were carried out at 37º Celsius using an Electrochemical analyzer (CH Instrument 604C). The wires were immersed in the test solution for approx. 24 h at 37 º Celsius prior measurements. This step was performed in order to stabilize the solution-surface equilibrium or achieving a stable open circuit potential. Open circuit potential (OCP) measurements were performed on the electrochemical analyse for 1 h. When the rate of change of potential becomes less than 5 mV/h, the OCP was
considered to be attained. It usually took 12–16 hours to reach equilibrium potential (OCP). All the electrochemical experiments were carried out in an electrochemical cell containing 15 mL volume of unstirred aqueous test solutions. Potentiodynamic Polarization curves (or Tafel’s plots) of log current (log i/Acm−2) vs. potential (V/Ag-AgCl) were scanned in the range of – 0.4 V (Ag/AgCl) (cathodic potential) to + 1.2 V (Ag/AgCl) (anodic potential), at a rate of 1 mVs−1. The usual meaning of the corrosion parameters can be found in [15–18]. All the experiments were performed for three times and the mean values of the obtained results are recorded in Table 1. The corresponding graphical parameters were within error limits of ± 0.2 – 0.3 V. The surface features of the orthodontic wires after corrosion experiments were examined under Scanning Electron Microscope (JEOL SEM: JSM-5600) before and after the experiments to study the morphological changes.
Results and discussion Electrochemical behaviour The open circuit potential (OCP) recorded for 1 h after immersing the orthodontic archwire specimens for approx. 24 h are shown in Figure 1. The individual effect of fruit juices and chloride ions on the open circuit potential shows near stable values after 2000 seconds. An overlay plot of polarization curves of stainless steel wire in AS and effects of chloride ion is shown in Figure 2 (a, b). Effects of different fruit juices on the potentiodynamic polarization measurements are shown in Figure 3 (a-d). The curves show a small active region followed by a distinct passive region for all the fruit juices. The shift of Ecorr values towards more negative potential on the addition of 1% NaCl and fruit juices to AS indicates an early onset of anodic process and an increased tendency for corrosion. Also, the addition of different fruit juices to AS and AS containing 1% NaCl caused an increase in the Icorr values indicating an accelerated rate of corrosion process. Depending upon the Icorr values, the order of aggressiveness of the fruit juices to the steel archwire in AS are as follows: Prunus domestica Linn. (Plum) > Ananas comosus (Pine Apple) > Citrus limon (Lemon) > Tamarindus indica (Tamarind) > Solanum lycopersicum (Tomato) > Vitis vinifera (Grapes) > Carissa carandas (Karaunda) > Spondias mombin (Amra) > Citrus sinensis (Musambi) > Punica granatum (Pomegranate) > AS. It is evident that the anodic current density has been increased with the addition of fruit juices to AS. The property of the passive film on the stainless is protective in nature and implies corrosion resistance. The anodic current density at the passive region of polarization curve corresponds to the charge transfer resistance through the surface passive film. The latter may form spontaneously on
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Table 1. Corrosion parameters of AISI 316L in AS containing fruit juice and 1% NaCl. Polarization βa βc resistance, Rp Medium (V/decade) (V/decade) ECorr (V) (×10−6) (Ω) Saliva 0.25 0.10 −0.12 41.21 saliva + NaCl 0.27 0.09 −0.21 6.46 Prunus domestica 0.21 0.14 −0.16 0.63 Linn. (Plum) Prunus domestica 0.13 0.10 −0.12 2.10 Linn. (Plum) + NaCl Spondias mombin 0.16 0.09 −0.19 1.26 (Amra) Spondias mombin 0.20 0.06 −0.19 0.83 (Amra) + NaCl Vitis vinifera (Grapes) 0.20 0.13 −0.13 1.27 Vitis vinifera (Grapes) 0.18 0.14 −0.19 0.79 + NaCl Carissa carandas 0.19 0.13 −0.15 1.47 (Karaunda) Carissa carandas 0.16 0.08 −0.19 1.28 (Karaunda) + NaCl Citrus limon (Lemon) 0.18 0.14 −0.12 0.88 Citrus limon (Lemon) 0.19 0.14 −0.08 1.08 + NaCl Citrus sinensis 0.13 0.09 −0.18 1.42 (Musambi) Citrus sinensis 0.14 0.18 −0.16 0.76 (Musambi) + NaCl Ananas comosus (Pine 0.19 0.14 −0.16 0.59 apple) Ananas comosus (Pine 0.14 0.15 −0.12 0.76 apple) + NaCl Punica granatum 0.16 0.14 −0.24 1.30 (Pomegranate) Punica granatum 0.13 0.10 −0.19 0.74 (Pomegranate) + NaCl 1.27 Tamarindus indica 0.19 0.14 −0.09 (Tamarind) Tamarindus indica 0.14 0.10 −0.18 1.21 (Tamarind) + NaCl Solanum lycopersicum 0.20 0.16 −0.12 1.22 (Tomato) Solanum lycopersicum 0.13 0.08 −0.20 0.87 (Tomato) + NaCl
ICorr (×10−8) Corrosion rate (A) Epit (V) (×10−2) (mil/yr) 0.09 absent 0.04 0.63 0.75 0.29 8.05 absent 4.06
the corrosion resistant alloys, such as stainless steels. A low anodic current density corresponds to high charge transfer resistance through the passive film. Addition of fruit juices to the AS solution must have decreased this resistance, thus causing an increase in the anodic current density in the passive region. Upon adding NaCl to the AS, the Icorr increased from 0.09 to 0.63 (×10−8) A/ cm2. This is due to an increase in the conductivity of the electrolytic medium. However, not all the fruit juices in AS showed an increase in Icorr values on the addition of 1% NaCl. In the cases of Prunus domestica Linn. (Plum), Carissa carandas (Karaunda), Citrus limon (Lemon), Ananas comosus (Pine Apple), Tamarindus indica (Tamarind) and Solanum lycopersicum (Tomato), the Icorr values decreased on addition of salt. Also we obtain a different order of aggressiveness: Citrus sinensis (Musambi) > Vitis vinifera (Grapes) > Ananas comosus (Pine Apple) > Citrus limon (Lemon) > Punica granatum (Pomegranate) > Solanum lycopersicum (Tomato) > Spondias mombin (Amra) > Tamarindus indica (Tamarind)> Carissa carandas (Karaunda) > Prunus domestica Linn. (Plum) > AS. This might be due to the interaction of salt with a
Corrosion rate (×10−8) (gram/h) 0.097 0.66 9.31
pH (Before test) 7.4 7.37 3.8
pH (After test) 7.41 7.43 3.84
1.01
0.40
1.66
3.79
3.79
3.95
1.81
0.98
3.19
5.76
3.86
3.87
2.24
0.52
2.51
7.31
3.84
4.06
3.01 4.84
absent 0.85
2.67 3.34
6.11 7.64
4.04 4.03
4.1 4.27
2.26
absent
5.89
3.33
3.51
1.82
0.90
1.92
4.40
3.32
3.44
4.57 3.71
absent absent
2.08 1.69
4.75 3.87
2.77 2.74
2.9 2.84
1.46
absent
0.67
1.53
4.46
4.66
5.20
0.97
2.36
5.42
4.44
4.86
7.02
absent
3.19
7.31
4.28
4.58
4.30
0.86
1.96
4.48
4.27
4.4
0.98
absent
0.45
1.02
4.36
4.82
3.33
0.87
1.51
3.46
4.37
4.93
3.25
absent
1.48
3.39
2.97
3.33
1.87
absent
1.7
3.89
3.04
3.12
3.10
0.65
1.41
3.23
4.14
4.28
2.34
0.45
1.06
2.44
4.11
4.26
13.5
constituent of fruit juice resulting in the formation of some compound which might have favored delayed corrosion reaction. Pitting potential or Epit was seen in all the cases where chloride ions were added to the electrolyte medium. Chloride ion reacts with metal ion present on the steel surface to form metal chloride and cause dissolution of the latter. Once the dissolution of metal ions begins, the pitting process propagates in an autocatalytic manner. Since pitting is the main reason for the destruction and failure of the material, Epit values provide an apparent viewpoint of the aggressiveness of test solutions. Depending on the pitting tendency, fruit juices are arranged in decreasing order as: Prunus domestica Linn. (Plum) > Solanum lycopersicum (Tomato) > Spondias mombin (Amra) > AS > Vitis vinifera (Grapes) > Ananas comosus (Pine Apple) > Punica granatum (Pomegranate) > Carissa carandas (Karaunda) > Citrus sinensis (Musambi) > Tamarindus indica (Tamarind) ~ Citrus limon (Lemon). Plum juice in AS containing 1% NaCl is most detrimental in terms of pitting corrosion, as pitting occurred at a much
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Figure 1. Open circuit potential measurements for orthodontic wire in (a) AS and (b) AS containing 1% NaCl.
Figure 2. Potentiodynamic polarization curves measured for orthodontic wire in AS and the same containing 1% NaCl. Chloride ions cause pitting of the wire surface.
lower potential (Epit = 0.35 V). The presence of Vitis vinifera (Grape juice), Carissa carandas (Karaunda), Ananas comosus (Pine apple juice), Citrus sinensis (Musambi) and Punica granatum (Pomegranate juice) in AS containing 1% NaCl showed Epit higher compared to that obtained in AS containing 1%
NaCl. This indicates that the presence of these juices decreases the tendency of pitting corrosion of stainless steel wire. Solanum lycopersicum (Tomato) and Spondias mombin (Amra) are the most aggressive for the wire as far as the pitting is concerned as these fruit juices exhibited pitting even in the absence of
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Figure 3. Overlay of polarization curves of orthodontic wire in AS containing (a, b) Fruit juice, (c, d) Fruit juice and 1% NaCl.
salt. Addition of 1% NaCl to these solutions further increased the aggressiveness of the medium and the pitting occurred at a relatively lower potential value. Cathodic Tafel constant or βc values fall within two different ranges. βc values near 120 mV/d indicate involvement of four electron transfer during the reduction reaction, mainly oxygen reduction reaction, and near 60 mV/d values indicate involvement of two electron transfer correspond to hydrogen gas evolution during the reduction reaction. The βa values appear to be scattered and mainly attributed to the variation in the nature of anodic reactions. The change in the pH values of the electrolyte before and after the completion of the corrosion experiments was not found to have varied significantly.
Surface analysis The Scanning Electron Micrographs of the after test steel archwire specimens are shown in Figure 4. The surface shows blister like appearance which might be the accumulation of corrosion products onto the surface because of loss of material.
Mechanism The chemical composition of the fruit juices is largely a composition of two or more organic acids. For example, pomegranate juice contains both citric acid and ascorbic acid along with sugars, pectin and amino acids. Similarly, tamarind juice (obtained from the pulp) contains citric acid, tartaric acid and malic acid. The chemical composition of different
Figure 4. Surface of orthodontic wire showing pits and blisters obtained in AS containing (a) plum with 1% NaCl and (b) tomato juice with 1% NaCl.
fruit juices has been given in the supplementary information. The corrosion mechanism of the metallic surface in the presence of organic acid medium takes place by means of adsorption of the acid
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M. R. SHARMA ET AL.
Figure 5. The probable mechanism of corrosion of stainless steel surface in the AS containing fruit juices. The corrosion begins with adsorption of acid anions onto the steel surface.
molecules onto the surface [19]. For example, malic acid is a di-carboxylic acid capable of furnishing two protons into the electrolyte medium as shown below. Therefore, adsorption of malic acid molecules can take place at two different sites simultaneously on the steel surface. Dissociation of malic acid (or 2-Hydroxybutanedioic acid) C4 H6 O6 Ð C2 H4 O2 ðCOOH ÞðCOOÞ þ H þ þ Ð C2 H4 O2 ðCOOÞ2 2 þ H 2Fe þ CH2 CHOH ðCOOH Þ2 2 ! ½Fe2 ðCH2 CHOH ðCOOÞ2 Þads þ 2e
½Fe2 ðCH2 CHOH ðCOOÞ2 Þads ! ½Fe2 ðCH2 CHOH ðCOOÞ2 Þ2þ þ 2e ½Fe2 ðCH2 CHOH ðCOOÞ2 Þ2þ þ 2H þ ! 2Fe2þ ðaq:Þ þ CH2 CHOH ðCOOH Þ2
Eq:1
Fe2 C2 H4 O2 ðCOOÞ2 ads 2þ ! Fe2 C2 H4 O2 ðCOOÞ2 þ 2e
Eq:9
Eq:2
½Fe2 C2 H4 O2 ðCOOÞ2 2þ þ 2H þ ! 2Fe2þ þ C2 H4 O2 ðCOOH Þ2
Eq:3
Eq:4
Eq:5
Dissociation of tartaric acid (or 2,3-Dihydroxybutanedioic acid) þ C4 H6 O6 ! C2 H4 O2 ðCOOÞ2 2 þ 2H
2Fe þ C2 H4 O2 ðCOOÞ2 2
Eq:8
þ
C6 H8 O7 Ð C3 H5 OðCOOHÞ2 ðCOOÞ þ H þ Ð C3 H5 OðCOOH ÞðCOOÞ2 2 þ H 3 Ð C3 H5 OðCOOÞ3 þ H þ
The adsorption of acid anions on to the steel surface can be represented as ! ½Fe2 C2 H4 O2 ðCOOÞ2 ads þ 2e
Similarly, tartaric acid is also a dicarboxylic acid whereas citric acid is a tricarboxylic acid. On the other hand ascorbic acid or vitamin-C is a diacid which undergo dissociation as shown below: Dissociation of citric acid (or 2-Hydroxypropane1,2,3-tricarboxylic acid)
þ 2 þ C6 H8 O6 Ð C6 H7 O 6 þ H Ð C6 H6 O6 þ H Eq:7
Eq:6
Dissociation of ascorbic acid or vitamin-C (or (R)3,4-dihydroxy-5-((S)- 1,2-dihydroxyethyl)furan-2 (5H)-one)
Eq:10
Fe þ C3 H5 OðCOOH Þ2 ðCOOÞ ! ½Fe C3 H5 O COOHÞ2 ðCOOÞ ads þ e Eq:11 ½Fe C3 H5 O COOHÞ2 ðCOOÞ ads þ Fe ! ½Fe2 C3 H5 OðCOOH Þ COOÞ2 ads þ e Eq:12 ½Fe2 C3 H5 OðCOOH Þ COOÞ2 ads þ Fe ! ½Fe3 C3 H5 O COOÞ3 ads þ e
Eq:13
½Fe3 C3 H5 O COOÞ3 ads ! ½Fe3 ðC3 H5 O COOÞ3 3þ þ 3e
Eq:14
½Fe3 ðC3 H5 O COOÞ3 3þ þ 3H þ ! 3Fe2þ þ C3 H5 OðCOOH Þ3
Eq:15
2Fe þ C6 H6 O2 6 ! ½F2 ðC6 H6 O6 Þads ! ½Fe2 ðC6 H6 O6 Þ2þ þ 2H þ ! 2Fe2þ þ C6 H8 O6 Eq:16 The corresponding cathodic reactions with evolution of hydrogen molecule can be represented as
MATERIALS TECHNOLOGY
2Fe þ C2 H4 O2 ðCOOH Þ2 þ 2e ! 2FeHads þ C2 H4 O2 ðCOOÞ2 2
Eq:17
2FeHads þ 2FeHads ! 4Fe þ 2H2 "
Eq:18
3Fe þ C3 H5 OðCOOH Þ3 þ 3e ! 3FeHads þ C3 H5 OðCOOÞ3 3
Eq:19
3FeHads þ 3FeHads ! 6Fe þ 3H2 "
Eq:20
2Fe þ CH2 CHOH ðCOOH Þ2 þ 2e ! 2FeHads þ CH2 CHOH ðCOOÞ2 2
Eq:21
2FeHads þ 2FeHads ! 4Fe þ 2H2 "
Eq:22
The mechanism of corrosion of stainless steel surface in the AS containing fruit juices has been summarized in Figure 5.
Conclusion The findings suggest that corrosion behavior of stainless steel orthodontic archwire is influenced by the presence of fruit juices and salt (NaCl). All the fruit juices used in this study increased the rate of corrosion process in AS in the presence or absence of salt. Addition of 1% NaCl to the AS increased the corrosion rate. Epit presents more realistic picture of material corrosion rather than corrosion rate (Icorr). On the addition of 1% NaCl, all experiments exhibited pitting. Solanum lycopersicum (Tomato) and Durio zibethinus (Amra) are rated as most detrimental to the surface followed by Prunus domestica Linn. (Plum) juice. Tomato and Amra juices induced pitting even in the absence of salt. Measures should be taken to prevent the corrosion of orthodontic appliances in oral cavity which include maintenance of good oral hygiene and improvement of the material composition and manufacturing process of the appliances to make them more corrosion resistant.
Acknowledgments Authors acknowledge UGC, India for financial support.
Disclosure statement All the authors hereby declare no conflict of interest.
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