The Preparation and Performance Study of a Phosphate-Free Corrosion/Scale Inhibitor

doi:10.4236/jwarp.2012.47056

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Journal of Water Resource and Protection, 2012, 4, 487-492

http://dx.doi.org/10.4236/jwarp.2012.47056 Published Online July 2012 (http://www.SciRP.org/journal/jwarp)

The Preparation and Performance Study of a

Phosphate-Free Corrosion/Scale Inhibitor

Defang Zeng*, Wei Zhang

School of Resource and Environmental Engineering, Wuhan University of Technology, Wuhan, China

Email: *[email protected]

Received November 29, 2011; revised April 3, 2012; accepted May 7, 2012

ABSTRACT

By using acrylic acid copolymer, sodium citrate, hydrolyzed polymaleic anhydride (HPMA), corrosion inhibitor D and

Zn2+ synergist as raw materials, a multi-component phosphate-free corrosion and scale inhibitor was developed. The

performance of the composite phosphate-free corrosion and scale inhibitor was evaluated using the rotary hanging sheet

corrosion test, the static scale inhibition test and the corrosion electrochemical test. And the surface morphology of the

carbon steel was observed by scanning electronic microscope (SEM). Orthogonal experiment results indicated that the

optimal mass ratios of amino acid: Zn2+ synergist: HPMA: corrosion inhibitor D: acrylic acid copolymer was

0.5:10:12:1:8. It was also observed that phosphate-free corrosion and scale inhibitor based on an anodic reaction

through the electrochemical corrosion experiment, its annual corrosion rate and scale inhibition rate reached 0.0176

mm·a–1 and 98.3%, respectively, showing excellent corrosion and scale inhibition performance.

Keywords: Phosphate-Free Corrosion/Scale Inhibitor; Static Scale Inhibition Method; SEM; Electrochemical Corrosion

1. Introduction

Industrial recirculating cooling water accounts for 60% -

70% in the industrial water, it will result in corrosion,

scaling and microbial slime of the equipment and the

pipeline as well as reduce their service life without treat-

ing. Thus, to treat recirculating cooling water has aroused

the concern from the whole society.

Organophosphorus compound was a type of corrosion

inhibitor extensively used since 1980s. However, it’s di-

minishing because of its toxic effects on aquatic and

other life [1]. Therefore, the public began to focus on the

development of low phosphorus, non-phosphorus and

heavy nonmetal salt corrosion and scale inhibitors. On

one hand, low phosphorus corrosion and scale inhibitor is

developing rapidly, such as 2-phosphono-1,2,4-tricarbo-

xylic acid butane (PBTCA) and hydrolyzed polymaleic

anhydride (HPMA) [2]. On the other hand, the non-phos-

phorus corrosion and scale inhibitor has also obtained

new achievements.

In this paper, a multi-component phosphate-free cor-

rosion and scale inhibitor blend composed of acrylic acid

copolymer, sodium citrate, hydrolyzed polymaleic anhy-

dride (HPMA), corrosion inhibitor D and Zn2+ synergist

was prepared [3-7]. The recirculating cooling water was

obtained from water treatment plant. The performance of

the phosphate-free corrosion and scale inhibitor was eva-

luated by rotary hanging sheet corrosion test and static

scale inhibition test. The mechanism of corrosion and

scale inhibition was preliminarily investigated by corro-

sion electrochemistry test and scanning electron micro-

scope (SEM) techniques [8-11].

2. Experimental

2.1. Main Materials

Acrylic acid copolymer, sodium citrate, hydrolyzed poly-

maleic anhydride (HPMA), sodium citrate, Zn2+ synergist

and anhydrous alcohol. All chemicals were of analytical

reagent-grade.

2.2. The Rotary Hanging Sheet Corrosion Test

The corrosion rate of A3 type carbon steel was deter-

mined by weight loss test. The carbon steel sheets were

polished with different grades of emery paper, degreased

with anhydrous alcohol, and rinsed with distilled water.

Having been dried by electric dry oven and accurately

weighed by electronic balance, the carbon steel were im-

mersed in a beaker with water sample and with or with-

out inhibitors. And the quality index of water sample was

presented in Table 1. The beakers were put into the ro-

tary hanging piece corrosion test instrument. Experi-

mental conditions as follows: 1) constant temperature

was 45˚C ± 1˚C; 2) rotating speed was 75 r·min–1; 3)

*Corresponding author.

D. F. ZENG, W. ZHANG

488

Table 1. Water quality index.

Project Analysis value

pH value 7.24

calcium ion/(mg·L–1) 92.57

magnesium ion/(mg·L–1) 61.28

chloride ion/(mg·L–1) 397.5

total hardness/(mmol·L–1) 4.54

total alkalinity/(mmol·L–1) 4.37

potassium ion/(mg·L–1) 15.24

conductivity/(μs·cm–1) 925

total dissolved solids content/(mg·L–1) 606

experimental period was 72 hours. After 72 hours, the

carbon steel sheets were taken out, washed, dried and

accurately weighed. Each set of experiments was re-

peated three times at least to ensure reproducibility. Ac-

cording to Technical Conditions of Standard Corrosion

Spool of Chemical Treatment in Cooling Water (HG/

T3523-2008), A3 type carbon steel with a size of 50 mm

× 25 mm × 2 mm and an area of 28 cm2 in the experi-

ment.

The annual corrosion rate and corrosion inhibition effi-

ciency was calculated by formulae (1) and (2), respec-

tively [12]:



0mm







8760

K (1)

where Ka is the annual corrosion rate, mm·a–1; m0 is the

weight of the carbon steel before experiment, g; m is the

weight of the carbon steel after experiment, g; s is the

surface area of the carbon steel, cm2; ρ is the density of

the carbon steel, g·cm–3; t is the test time, h.

100%

KKKK

 (2)

where K is the corrosion inhibition efficiency; K0 and K1

are the values of the weight loss of carbon steel after be-

ing immersed in solutions without and with inhibitors,

respectively, mm·a–1.

2.3. The Static Scale Inhibition Test

The mechanism of scaling inhibition mainly included la-

ttice deformation, complexation, dispersion effect and

dispersive active [13,14]. In the experiment, 0.5 L·min–1

of nitrogen was ventilated to the bottom of the container

with adding 30 mg·L–1 of inhibitor at 45˚C. The experi-

ment was ceased after six times diluted concentration.

100%





KKC





 (3)

where C2 is determined mass concentration of calcium

ion after adding chemicals, mg·L–1; C1 is determined

mass concentration of calcium ion without chemicals,

mg· L –1; C0 is initial mass concentration of calcium ion

without chemicals, mg·L–1; K is the concentration multi-

ple in the determined conditions of C2 and C1.

2.4 .Corrosion Electrochemical Experiments

Corrosion electrochemical methods consulted the re-

search methods and measurement techniques in other

fields. According to the characteristics and requirements

of corrosion metal electrodes, it has become a significant

method for the research and measurement of corrosive

electrochemistry with improvement and modification. In

particular, the dynamic potential polarization is the com-

mon method that evaluates inhibition efficiency of corro-

sion inhibitor [15]. Polarization curve obtained from the

dynamic potential polarization extrapolates corrosion po-

tential to obtain corrosion current density I and Tafel

parameters. The shape of cathode and anodic polarization

curve intuitively reflects the corrosion inhibition mecha-

nism of corrosion inhibitors, which is the main research

and evaluation method of corrosion inhibitors.

Electrodes were connected by three electrodes polari-

zation method in the experiment. A3 carbon steel was

used as the working electrode, saturated calomel elec-

trode (SCE) as the reference electrode and platinum sheet

as the auxiliary electrode. The sample was immersed in a

3.5% (w/w) NaCl solution for 30 min. When polarization

curve test was carried out, the potential scan rate was

adjusted to 0.01 v·s–1. Polarization curves could be achi-

eved after data process.

2.5. Scanning Electronic Microscopy (SEM)

Corrosion crystal morphology on the surface of A3 car-

bon steel was observed by JSM5610LV type SEM. In

this experiment, A3 carbon steel was immersed in water

sample with and without phosphate-free scale and corro-

sion inhibitor, respectively. Afterwards the test coupon

was washed with 98% (w/w) anhydrous alcohol and

treated for vacuum drying. Accelerating voltage of the

JSM5610LV type SEM was 25 kV, amplification factor

was 2000.

3. Results and Discussion

3.1. Rotating Hang-Parcel Weight-Loss

Experimental Performance Analysis

The inhibitor in this experiment composed of A (sodium

citrate), B (Zn2+ synergist), C (HPMA), corrosion inhibi-

tor D and E (acrylic copolymer). L16 (45) orthogonal

table was used to arrange experiment.Corrosion rate of

the carbon steel was determined after 72 hours, the final

result was the average values of three replicates. The re-

D. F. ZENG, W. ZHANG

489

HCO

sults were showed in Table 2. sion inhibition effect.

As shown in Table 2, the sequence of the influencing

factors was corrosion inhibitor D > Amino acid > Zn2+

synergist > acrylic copolymer > HPMA in order of im-

portance to the corrosion rate. According to orthogonal

experiment results, the optimum formula was D4A4B4E1C1

on corrosion inhibition. Based on the optimum formula,

the weight loss experiment was carried out. The mass

ratios of amino acid, Zn2+ synergist, HPMA, corrosion

inhibitor D and acrylic copolymer was 0.5:12:0:1:8 in the

optimum formula. The results were presented in Table 3.

3.2. Static Scale Inhibition Performance Analysis

Comparison experiments were conducted with and with-

out inhibitors. The relationship between the concentra-

tion of Ca2+, 3



and cycle of concentration was

showed in Figure 1.

When the solution concentration was concentrated by

1 - 1.8 times, the concentration of Ca2+ and 3

HCO



showed linear change, illustrating that Ca2+ and 3

HCO



were unsaturated in solution. The concentration of

The corrosion inhibition efficiency of optimized for-

mulation reached 96.6% (Table 3), showing good corro- 3

HCO



appeared increases linearly with the inhibitor,

Table 2. Design of orthogonal experiment L16 (45) and experiment results.

Experimental factor

Numbers A

Amino acid

/mg·L–1

Zn2+ synergist/

mg·L–1

HPMA/mg·L–1

Corrosion inhibitor/

mg·L–1

Acrylic copolymer/

mg·L–1

Average corrosion

rate/mm·a–1

1 0.3 9 10 0.8 5 0.0245

2 0.3 10 11 0.9 8 0.0225

3 0.3 11 12 1 7 0.0239

4 0.3 12 13 1.1 6 0.0214

5 0.4 9 11 1 8 0.0221

6 0.4 10 10 1.1 7 0.0260

7 0.4 11 13 0.8 6 0.0299

8 0.4 12 12 0.9 5 0.0230

9 0.5 9 12 1.1 6 0.0234

10 0.5 10 13 1 5 0.0229

11 0.5 11 10 0.9 8 0.0288

12 0.5 12 11 0.8 7 0.0310

13 0.6 9 13 0.9 7 0.0211

14 0.6 10 12 0.8 8 0.0205

15 0.6 11 11 1.1 5 0.0197

16 0.6 12 10 1 6 0.0271

17 0 0 0 0 0 0.5215

i/5 0.1064 0.1059 0.0921 0.0923 0.0901

ii/5 0.0953 0.0954 0.0919 0.1010 0.1029

iii/5 0.0908 0.0960 0.1023 0.1061 0.1010

iv/5 0.0943 0.0905 0.0926 0.0884 0.0918

R 0.0156 0.0154 0.0104 0.0207 0.0128

factors 2 3 5 1 4

Table 3. Optimizing formula experimental results.

Experiment Hang-parcel

number

Quality of hang-parcel

before experiment/g

Quality of hang-parcel

after experiment/g

Weight

loss/g

Annual corrosion rate

/mm·a–1

Inhibition

efficiency/%

1152 19.2498 19.2465 0.0033

1153 19.1601 19.1567 0.0034

Optimized

formulation

1154 19.0684 19.0655 0.0029

0.0176

1155 19.8299 19.7576 0.0945

1156 19.2922 19.2204 0.0940

Blank

1115 19.3625 19.2941 0.0938

0.5208

96.6

D. F. ZENG, W. ZHANG

490

Figure 1. Ca2+, conce ntr ation and conc e ntration multiple relationship chart.

HCO

while it increased slowly and even tended to decrease

without the inhibitor. And the concentration of Ca2+ ba-

sically showed increases linearly with and without in-

hibitor, respectively. Experimental results showed that

the concentrations of Ca2+ and in the solution

were stabilized after adding inhibitor.

According to the results of Table 4, the average scale

inhibition efficiency with phosphate-free corrosion and

scale inhibitor reached 98.3%, showing good scale inhi-

bition performance.

3.3. Corrosion Electrochemistry Results Analysis

Two specimens were immersed in 3.5% NaCl solution

with and without inhibitor, respectively. Then the test

method of electrochemical polarization curve was con-

ducted. The results were presented in Table 5 and Fig-

ure 2. And the inhibition efficiency of the inhibitor for

the carbon steel corrosion was calculated by formula (4):

corr

ηI

corr

100%







(4)

In Figure 2, the corrosion potential was shift to the

positive after adding the inhibitor. The increasing in an-

odic current density indicated that the dissolution of the

anode materials. Figure 2 showed the anode Icorr was

reduced from 201 μA·cm2 to 21 μA·cm2 after adding the

inhibitor. It indicated that the anode corrosion process

was inhibited. And the anode inhibition was more sig-

nificantly than the cathode with the inhibitor. Table 3

and Table 5 showed the consistent results with electro-

chemical test.

Figure 2. The polarization curve of blank and adding

phosphate-free scale corrosion inhibitor treated samples in

3.5% NaCl solution.

3.4. SEM Structure Analysis

The experimental conditions as followed: the bath tem-

perature was maintained at 50˚C for 48 h, the flow rate of

solution and the cycle of concentration were adjusted to

0.01 m·s–1 and 1.8 times, respectively. The concentration

of phosphate-free corrosion and scale inhibitor was 30

mg· L –1. Figures 3(a) and (b) were corrosion crystal on

A3 carton steel surface with and without phosphate-free

corrosion and scale inhibitor, respectively.

Figure 3 showed that the carbon steel was corroded

severely without the inhibitor, many apertures appeared

on its surface and some corrosion products deposited on

the surface with uplift shape. In comparison, the surface

of the carbon steel with 30 mg·L–1 of phosphate-free

D. F. ZENG, W. ZHANG 491

Table 4. Scale inhibition efficiency with different concentration multiple.

Concentration

multiple/K

Theoretical value

Ca2+/(mg·L–1)

Without chemicals

Ca2+/(mg·L–1)

Adding chemicals

Ca2+/(mg·L–1)

Scale inhibition efficiency

ηk/%

2.5 231.4 166.7 230.8 99.1

3 277.7 180.1 271.0 98.2

3.5 324.0 195.2 320.6 98.5

4 370.1 236.7 368.1 98.3

4.5 416.5 270.1 415.1 98.7

5 462.8 308.2 460.2 99.1

5.5 509.1 330.2 504.2 98.0

Average 98.3

Table 5. Electrochemical parameter with different concentrations of corrosion inhibitor in 3.5% NaCl solution.

Concentration of corrosion inhibitor/mg·L–1 Ecorr (vsSCE)/mV Icorr/µA·cm2 Corrosion rate η/%

0 –482 201 0

30 –443 21 89.56

60 –435 19 90.55

(a) (b)

Figure 3. The corrosion crystal on A3 carton steel surface.

corrosion and scale inhibitor was flat and smooth. It

caused some damage and few corrosion products accu-

mulation on the surface of the carbon steel because of

polishing hang-parcel. But there were basically no corro-

sion marks. Results illustrated that a complete compact

protective film formed on carbon steel surface after add-

ing phosphate-free corrosion and scale inhibitor. It effec-

tively cut off contact between the corrosive medium and

carbon steel surface so as to significantly inhibit the cor-

rosion of carbon steel in water sample.

4. Conclusions

1) A phosphate-free corrosion and scale inhibitor

composed of A (sodium citrate), B (Zn2+ synergist), C

(HPMA), corrosion inhibitor D and E (acrylic copoly-

mer). The optimized mass ratio of amino acid: Zn2+ syn-

ergist: HPMA: corrosion inhibitor D: acrylic acid co-

polymer was 0.5:10:12:1:8.

2) Annual corrosion rate tested by optimized rotating

hang-parcel corrosion experiment was 0.0176 mm·a–1

which was lower than 0.075 mm·a–1 of industry standard

according to Code for Design of Industrial Recirculating

Cooling Water Treatment (GB50050-2007). The experi-

mental results showed that the phosphate-free corrosion

and scale inhibitor was a kind of good corrosion and

scale inhibitor whose corrosion inhibition rate and scale

inhibition rate surpassed 96% and 98%, respectively.

3) Polarization curve test showed the phosphate-free

corrosion and scale inhibitor was a kind of corrosion and

scale inhibitor that mainly caused anode type reaction.

Based on the surface morphology of the carbon steel was

observed by SEM, it showed that a protective film was

formed on the surface of A3 carbon steel with optimized

phosphate-free corrosion and scale inhibitor.

5. Acknowledgements

The authors gratefully acknowledge School of Resource

and Environmental Engineering, Wuhan University of

D. F. ZENG, W. ZHANG

492

Technology institute of the facilities and test environ-

ments. We also thank the Science and Technology De-

partment of Hubei (China) to provide financial support.

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