FLORENCE J F, RAJENDRAN S, SRINIVASAN K N*

【電鍍】

指甲花萃取物對鎳從瓦特鍍液中電沉積的影響

FLORENCE J F, RAJENDRAN S, SRINIVASAN K N*

采用赫爾槽試驗、分散能力測定法、掃描電鏡、X射線衍射、能譜分析、硬度測量及交流阻抗譜，研究指甲花萃取物(主要成分為 2–羥基–1,4–萘醌)對鎳從瓦特鍍液中電沉積(以低碳鋼為基體)的影響。在溫度40 ～ 50 °C和pH 4.5 ～ 5.0的條件下，從含60 mL/L指甲花萃取物的瓦特鍍鎳液中得到的鍍層具有良好的耐蝕性和硬度。指甲花萃取物作為瓦特鍍鎳液的添加劑，極大地提高了鍍液的分散能力和電流效率。在最佳指甲花萃取物濃度下所得的鍍鎳層為晶態(tài)，結(jié)晶細(xì)致。

低碳鋼；瓦特鍍鎳；添加劑；指甲花萃取物；羥基萘醌；赫爾槽試驗；耐蝕性

1 Introduction

A large number of technical innovations regarding nickel electroplating have been accredited and documented in many scientific publications since before 1900[1]. Starting as a relatively small scale industry in the United States, France, Germany, and Russia, nickel electroplating technology and industry today is mature and popular in almost all parts of the world with an annual consumption approaching 100, 000 metric tones[2]. Watts bath is still widely used and its impact on the development of modern nickel electroplating cannot be overstated[3]. There are large numbers of publications on the Watts electrolyte application. Many electrolyte formulations are based on the classical composition proposed by Watts[4]which yields dull nickel deposits. To obtain decorative deposits with a mirror like surface finish, special additive formulations have been developed[4], which contain organic substances like surfactants, brighteners, and levelers. For nickel plating from Watts bath, two types of additives, such as aromatic sulfones or sulfonates and their compounds containing unsaturated groups like＞C═O, ＞N─C═S, and ─C═N are recognized as brighteners[5]. Environmentally friendly inhibitors have attracted several researchers. Nontoxic natural products have been widely used as corrosion inhibitors. The main constituent of the aqueous extract of henna is lawsone. It has excellent inhibition efficiency in controlling corrosion of carbon steel. It contains benzene unit, p-benzoquinone unit, and phenol group[6]. The structure of henna extract as found from the FTIR spectra is given below.

2-hydroxy-1,4-naphthoquinone

In this work, the effect of henna extract on electrodeposition of nickel in Watts electrolyte was studied with respect to various properties of the deposit.

2 Experimental

2. 1 Preparation of bath solution

Watts electrolyte was prepared using double distilled water by adding 300 g/L of nickel sulfate, 60 g/L of nickel chloride, and 40 g/L of boric acid in a glass container. The electrolyte pH was maintained at 4.5-5.0 by adding dilute sulfuric acid. In order to complete the dilution of electrolyte constituents and obtain a homogenous solution, the electrolyte was subjected to mild agitation overnight.

2. 2 Preparation of henna extract

A stock solution of 5% henna extract (as additive) was prepared by refluxing 25 g of dry henna leaves powder with 500 mL of 0.1N HCl for 3 h. The refluxed solution was then allowed to stand overnight and filtered through ordinary filter paper. The residue was repeatedly washed with 0.1N HCl and the filtrate was made up to 500 mL. This solution was used for plating purposes.

2. 3 Hull cell test

A 267-mL Hull cell made of PVC was used for studying the effect of henna extract on deposit characteristics at various current densities[7-8]. Mild steel panels of 100 mm × 75 mm were mechanically polished, degreased, alkaline cleaned, acid dipped, and then used as cathodes. Electrolytic nickel was used as anode. A current of 1 A was applied from a regulated power supply for duration of 10 min. Hull cell patterns were recorded.

2. 4 Measurement of throwing power

The determination of throwing power followed the procedure proposed by Haring and Blum[9]in a double jacketed cell. Nickel was deposited from an unstirred electrolyte at various current densities (1, 2, and 3 A/dm2) for 30 min on two mild steel substrates with the distance of 5:1 relating to a perforated Ni anode. The mass of the deposited nickel was determined by weighing the substrate before and after deposition. The throwing power was calculated by using the following equation.

Throwing Power = (L ? M) / (L + M ? 2) × 100% Where, L is the ratio of distance of two cathodes from anode and M is the ratio of the deposited masses.

2. 5 Other studies

Scanning electron microscopy (SEM), energydispersive X-ray analysis (EDAX), and X-ray diffraction (XRD) were performed. Hardness values were measured using a Vickers hardness test with 100 g load for a test duration of 20 s. The corrosion resistance of the deposits obtained with and without henna extract was analyzed by AC impedance measurements using IM6 electrochemical impedance analyzer with a three-electrode cell assembly. A frequency of 100 kHz to 10 mHz was impressed on the system. The AC voltage was superimposed on the rest potential on electrodeposited electrode immersed in 5% NaCl solution. Using the Nyquist plot, the values of charge transfer resistance and double layer capacitance were calculated.

3 Results and discussion

3. 1 Hull cell studies

Figure 1 shows the Hull cell pattern obtained with different concentrations of henna extract in the Watts bath.

Figure 1 Hull cell patterns for the nickel deposits obtained with different concentrations of henna extract圖1 不同指甲花萃取物濃度下所得赫爾槽鍍鎳試片的外觀

It is found that, without any additive in the bath, bright deposits are obtained up to a current density of 3 A/dm2. Addition of henna extract increases the brightening range up to 60 mL/L of the additive. Further addition reduces the effective current density range. Hence further experiments were conducted with 60 mL/L of henna extract.

3. 2 Properties of Watts bath containing henna extract

3. 2. 1 Current efficiency at various current densities

Table 1 shows the effect of current density on current efficiency of the bath with 60 mL/L of henna extract at different bath temperatures. It is seen from the table that there is an increase in current efficiency of the bath with current density up to 4 A/dm2. Further increase in current density reduces the current efficiency at all temperatures studied. This may be due to the hydrogen evolution at higher current densities and also burnt/dull deposit characteristics as evidenced from the Hull cell studies.

Table 1 Current efficiency of Watts bath containing 60 mL/L henna extract at different bath temperatures and current densities表1 不同溫度及電流密度下含60 mL/L指甲花萃取物的瓦特鍍鎳液的電流效率

3. 2. 2 Throwing power at various current densities

Table 2 shows the throwing power of the Watts bath with and without additives at different current densities. It is seen from the table that without any additive, Watts bath shows a throwing power from 15% to 10% as increasing the current density from 1 to 3 A/dm2. Addition of henna extract improves the throwing power evidently. This may be due to the preferential adsorption of p-benzoquinone and hydroxyl group existing in henna extract.

Table 2 Throwing power of Watts bath with and without henna extract at different current densities表2 不同電流密度下含與不含指甲花萃取物的瓦特鍍鎳液的分散能力

3. 3 Effect of henna extract on properties of nickel deposit

3. 3. 1 Hardness test

The effect of henna extract on the hardness of the deposits shows that there is an increase of hardness value from 437 HV to 706 HV. The increase in hardness may be due to fine-grained structure of the deposits obtained in presence of the extract.

3. 3. 2 Corrosion resistance evaluation

Figure 2 shows the impedance spectra for the deposits obtained with and without henna extract. Table 3 shows the charge transfer resistance and double layer capacitance values obtained from the impedance spectra. It is found from the table that there is an improvement in corrosion resistance of the deposit obtained with henna extract. The increased corrosion resistance of the deposit may be also due to the fine-grained structure of the deposit.

Figure 2 AC impedance spectra for nickel deposits obtained from Watts bath with and without henna extract in 5% NaCl solution圖2 從含與不含指甲花萃取物的瓦特鍍鎳液中得到的鎳鍍層在5% NaCl溶液中的交流阻抗譜

Table 3 Effect of henna extract on corrosion resistance of nickel deposit表3 指甲花萃取物對鍍鎳層耐蝕性的影響

3. 3. 3 XRD measurements

Figure 3 shows the XRD spectra for the deposits obtained with and without henna extract. Crystalline nickel deposits are obtained in both cases. XRD data also indicate that the deposit of Ni obtained from Watts bath has a face-centered cubic structure, and exhibits a (111) growth orientation with reflections assigned to (200) and (220) as well. For the Watts bath in presence of henna extract, the deposit has also a (111) growth orientation with pronounced (200) and (220) reflections. The particle sizes calculated using Scherer equation based on Figure 3a and 3b are 44 nm and 17 nm respectively, thus there is a considerable reduction in particle size by using the Watts bath containing henna extract.

Figure 3 XRD patterns of nickel deposits obtained from the Watts bath with and without henna extract圖3 含與不含指甲花萃取物的瓦特鍍液中所得鎳鍍層的X射線衍射譜圖

3. 3. 4 SEM studies

It is seen from Figure 4 that there is a considerable reduction in grain size in the deposit obtained with henna extract which is in agreement with the XRD spectra.

Figure 4 SEM images of nickel deposits obtained from Watts bath with and without henna extract圖4 含與不含指甲花萃取物的瓦特鍍液中所得鎳鍍層的掃描電鏡照片

3. 3. 5 EDAX characterization

The result of EDAX analysis (see in Table 4) shows the inclusion of carbon and sulfur in the deposit obtained with henna extract, indicating that there is an inclusion of the additive in the deposit. The hardness increase in presence of extract may be due the inclusion of these elements in the deposit.

Table 4 EDAX analysis of nickel deposits obtained from the Watts bath with and without henna extract表4 含與不含指甲花萃取物的瓦特鍍液中所得鎳鍍層的能譜分析

4 Conclusion

The following is the optimal bath composition and operating conditions:

Henna extract plays a major role as an additive in Watts bath. Addition of henna extract greatly improves the corrosion resistance and hardness of nickel deposit. The throwing power and current efficiency of Watts bath are evidently improved in the presence of henna extract. Under the optimal conditions, the nickel deposit was found to be crystalline and fine-grained as evidenced from XRD and SEM studies. The particle size of nickel deposit is greatly reduced in the presence of henna extract as calculated using Scherrer equation. Hence the nickel coating can be used for engineering applications where high anticorrosion and hardness are required.

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Effect of henna (Lawsonia inermis) extract on electrodeposition of nickel from Watts bath

J. Felicita Florence1, Susai Rajendran2, K. N. Srinivasan3,*
(1. GTN Arts College, Dindigul-624005, Tamil Nadu, India; 2. RVS School of Engineering and Technology, Dindigul-624005, Tamil Nadu, India; 3. CSIR—Central Electrochemical Research Institute, Karaikudi-630006, Tamil Nadu, India)

The effect of henna extract (mainly composed of 2-hydroxy-1,4-naphthoquinone) on electrodeposition of nickel in Watts bath on mild steel was evaluated by Hull cell test, throwing power determination, SEM, XRD, EDAX analysis, hardness measurement, and AC impedance spectroscopy. The deposit obtained from the Watts bath with 60 mL/L of henna extract at temperature 40-50 °C and pH 4.5-5.0 has good corrosion resistance and high microhardness. Henna extract plays a major role as an additive in the Watts bath, greatly improving the throwing power and current efficiency of the bath. At the optimal concentration of henna extract, the nickel deposit obtained was found to be crystalline and fine-grained.

mild steel; Watts nickel plating bath; additive; henna extract; hydroxynaphthoquinone; Hull cell test; corrosion resistance

TQ153.12

A

1004 – 227X (2012) 07 – 0001 – 04

date:2011–11–05 Revised date: 2012–03–19

Dr. K. N. Srinivasan, (E-mail) k_n_srinivasan@yahoo.com.

Biography:J. Felicita Florence (1980–) is doing her PhD under the guidance of Prof. Dr. S. Rajendran. Presently she is working as Assistant Professor in chemistry, Holy Cross College (Autonomous), Tiruchirappalli. She has guided 5 MSc students for completion of their project work.

[ 編輯：溫靖邦 ]