Effect of Pozzolanic Materials and Poling Field on Electromechanical Coupling Coefficient of Cement-Based Piezoelectric Composites

Effect of Pozzolanic Materials and Poling Field on Electromechanical

Coupling Coefficient of Cement-Based Piezoelectric Composites

Dung-Hung Lin

, Huang Hsing Pan

, Chang-Geng Jiang

and Hui-Chuan Hung

1

Department of Civil Engineering, Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan 2

Wanchi Steel Industrial Co. Ltd., Kaohsiung, Taiwan a

[email protected], [email protected], [email protected], d

[email protected]

Keywords: Electromechanical coupling, Cement, Pozzolana, Polarization, Impedance.

Abstract. Electromechanical coupling coefficient of cement-based piezoelectric composites affected by pozzolanic materials and poling field are investigated. Specimens, through a pressure approach, are manufactured by combining PZT powders and cement-based binder with the same volume fraction. Pozzolanic materials including fly ash, slag and silica fume replace 20% cement in the binder. Three poling fields are considered to induce piezoelectricity of 0-3 cement-based composites. Results show that electromechanical coupling coefficients do not have many fluctuations in terms of material ages for any cement-pozzolanic piezoelectric composites. With the same volumetric substitutes of pozzolanic materials, the electromechanical coupling coefficient with pozzolanic materials except fly ash is lower than that with plain cement, especially for silica fume having a 7.9% decrease. Raising poling field can increase electromechanical coupling coefficients. Polarization of cement-based piezoelectric composites containing silica fume in low poling fields such as 0.5kV/mm and 1kV/mm is not easy to complete.

Introduction

Piezoelectric composites consisting of piezoelectric ceramics and cement have been attracted considerable attention more than ten years [1-6]. For applications of sensors and actuators in civil engineering structure, 0-3 cement-based piezoelectric composites developed to overcome the matching problem that traditional piezoelectric ceramics or polymers do not contact synchronously with concrete [7-9].

For 0-3 cement-based piezoelectric composites, most literatures have discussed the piezoelectric and dielectric properties affected by volume fraction and particle size of piezoelectric ceramics, poling time, poling temperature, poling field, curing time, the thickness and the forming of specimens [1,3,4,7-14]. For the properties of piezoelectricity, the thickness electromechanical coupling coefficient Kt on cement-based piezoelectric composites has less concerned.

Electromechanical coupling coefficient is a measure of the conversion efficiency between electrical and acoustic energy in piezoelectric materials. To enhance the electromechanical coupling coefficient of cement-based piezoelectric composites is important for the applications of engineering and energy. Researches [6,11] indicated that increasing volume fraction of piezoelectric ceramics in cement-based piezoelectric composites, such as lead zirconate titanate (PZT), can raise Kt.

Electromechanical coupling coefficient also depends on forming pressure of specimens. While the applied forming pressure increases on the specimen, Kt will decrease [12]. In the polarization, high

poling voltage, temperature and time applied to the composites are beneficial for Kt [8]. Chaipanich

and Jaitanong [13] found that Kt approached to the optimum state at poling time of 45 minutes, and

became lower for exceeding 45 minutes. Gong et al [15] pointed out that adding 0.4 vol % carbon black into 0-3 cement-based composites can obtain the maximum value of Kt.

Advanced Materials Research Vols. 512-515 (2012) pp 2867-2872 Online available since 2012/May/14 at www.scientific.net

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frequence (kHz) 0 200 400 600 800 1000 im p e d a n c e ( k ΩΩΩΩ ) 0 20 40 60 80 0.5kV/mm 1 kV/mm 1.5kV/mm sample:SL frequence (kHz) 138 140 142 144 146 im p e d a n c e ( k ΩΩΩΩ ) 18 20 22 24 26 28 frequence (kHz) 0 200 400 600 800 1000 im p e d a n c e ( k ΩΩΩΩ ) 0 20 40 60 80 0.5kV/mm 1 kV/mm 1.5kV/mm sample:FA frequence (kHz) 130 131 132 133 134 135 136 im p e d a n c e ( kΩΩΩΩ ) 20 22 24 26 28

Fig. 8 Poling effect for SL materials Fig. 9 Poling effect for FA materials Table 4. Frequency at minimum and maximum impedance [kHz].

poling voltage frequency PC SF SL FA

0.5 kV/mm fm 140.573 135.980 140.975 131.869 fn 141.477 136.583 141.829 132.623 1.0 kV/mm fm 139.578 135.176 141.427 132.472 fn 140.533 135.980 142.432 133.377 1.5 kV/mm fm 138.623 135.126 141.276 132.673 fn 139.628 135.980 142.332 133.678 Conclusions

We considered the effect of pozzolanic materials and poling fields to the electromechanical coupling coefficient of the 0-3 cement-based piezoelectric composites by the pressure method. After the tests, we conclude the results as follows.

(1) The fluctuations of the electromechanical coupling coefficient are pretty small with increasing the material ages for the cement piezoelectric composites with or without pozzolanic materials. (2) The electromechanical coupling coefficients of cement piezoelectric composites containing

pozzolanic materials except fly ash are less compared with the PC composite. The reduction of

Kt for adding slag and silica fume is 1.6% and 7.9%, respectively.

(3) Increasing poling field is effective to the electromechanical coupling coefficient.

(4) The cement-based piezoelectric composites containing silica fume need higher poling voltages to induce the piezoelectric properties.

Acknowledgments

The author greatly thanks for the financial support to this study from the Taiwan National Science Council under Grant number NSC 99-2625-M-151-001.

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Effect of Pozzolanic Materials and Poling Field on Electromechanical Coupling Coefficient of Cement-Based Piezoelectric Composites