Effect of Pozzolanic Materials and Poling Field on Electromechanical Coupling Coefficient of Cement-Based Piezoelectric Composites
Dung-Hung Lin
1, a, Huang Hsing Pan
1,b, Chang-Geng Jiang
1,cand Hui-Chuan Hung
2,d1
Department of Civil Engineering, Kaohsiung University of Applied Sciences, Kaohsiung, Taiwan
2
Wanchi Steel Industrial Co. Ltd., Kaohsiung, Taiwan
a
[email protected],
b[email protected],
c[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 K
ton 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 K
t. Electromechanical coupling coefficient also depends on forming pressure of specimens. While the applied forming pressure increases on the specimen, K
twill decrease [12]. In the polarization, high poling voltage, temperature and time applied to the composites are beneficial for K
t[8]. Chaipanich and Jaitanong [13] found that K
tapproached 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 K
t.
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enhance the strength and durability. The dielectric and piezoelectric properties of cement-based piezoelectric composites containing pozzolantic materials are seldom studied [16]. It is interesting to investigate the effect of pozzolantic materials and poling voltage on electromechanical coupling coefficient of cement-based piezoelectric composites here. In this work, four cement-based binders of the composites containing 100% cement (PC), 20% replaced by silica fume (SF), 20% replaced by blast furnace slag (SL) and 20% replaced by fly ash (FA) in volume were investigated.
Experiments
The 0-3 cement-based piezoelectric composites consists of 50% PZT and 50% cement-based binder in volume. The particle diameter of PZT is 75~150 µm with specific gravity of 7.9. Cement is type I Portland cement with the fineness of 349m
2/kg and specific gravity of 3.16. The specific gravity, particle diameter and the fineness of silica fume are 2.2, 0.15 µm and 20,000m
2/kg, in turn. Blast furnace slag was produced from CHC Resources Corporation (Taiwan), where the fineness is 572m
2/kg and the specific gravity is 2.87, respectively. F type fly ash produced by Hsinta thermal power plant was also used, where the fineness is 326m
2/kg and the specific gravity is 2.11. The main chemical components are shown in Table 1.
Table 1. Main chemical components of materials.
chemical components cement silica fume slag fly ash
SiO
2(S) 21.24 95.01 33.36 46.26
Al
2O
3(A) 4.44 - 14.19 19.47
Fe
2O
3(F) 3.44 - 0.37 5.72
CaO 64.51 - 42.63 4.90
MgO 2.35 - 5.80 1.53
PZT power was drily mixed with four binders to produce mixed materials. Then the mixed materials were pressed into disks of 15mm diameter and 10mm thickness under 80 MPa for 3minutes.
The specimens were put in a curing room with a temperature of 90˚C and relative humidity of 100%
for 7 days before polarizations. After curing, the surfaces of the disks were polished to 2mm ± 0.05mm thickness, and coated with silver paint baked 30 minutes at 150˚C. The poling was carried out three poling voltages of 0.5, 1 and 1.5kV/mm each, in a stirred silicone oil bath. The poling temperature and time are 150˚C and 45 minutes respectively. During the polarization, voltage increase was applied stably to prevent from current breakdown of the specimens.
After poling, the composites were aged for 24 h prior to the measurements. We use impedance analyzer to measure frequency at minimum impedance f
mand frequency at maximum impedance f
n, and follow [11]
2 ) 2 tan(
2
n m n n
m
t
f
f f f
K π f π －
= (1) to calculate the thickness electromechanical coupling coefficient K
t.
Results and Discussion
Material Age Effect. We measured the impedance spectra of the composites subjected to 1.5kV/mm
at the 0 day, 10
th, 14
thand 28
thdays for four kinds of composites, shown in Figs. 1 ~ 4. The results on
the impedance of four cement-based piezoelectric composites show that the measured values of
impedance decrease with the material ages. Obviously, the impedances after 10 days become stable
because the hydration products gradually complete filling the pore in the composites.
frequence (kHz)
0 100 200 300 400
im p e d a n c e ( k ΩΩΩΩ )
0 10 20 30 40 50 600day 10days 14days 28days sample:PC
frequence (kHz)
0 100 200 300 400
im p e d a n c e ( k ΩΩΩΩ )
0 10 20 30 40 50 60
0day 10days 14days 28days sample:SF
Fig. 1 Age effect for PC materials Fig. 2 Age effect for SF materials
frequence (kHz)
0 100 200 300 400
im p e d a n c e ( k ΩΩΩΩ )
0 10 20 30 40 50 60
0day 10days 14days 28days sample:SL
frequence (kHz)
0 100 200 300 400
im p e d a n c e ( k ΩΩΩΩ )
0 10 20 30 40 50 60
0day 10days 14days 28days sample:FA
Fig. 3 Age effect for SL materials Fig. 4 Age effect for FA materials
From the impedance spectra and Eq. (1), we calculated the electromechanical coupling coefficient for four composites, shown in Fig. 5. Although the impedance spectra alter with the materials ages, the fluctuations of K
tare small. The electromechanical coupling coefficient is independent of the material age.
after polarization (days)
0 5 10 15 20 25 30
K t (% )
11 12 13 14 15 16
PC SF SL FA
Fig. 5 Electromechanical coupling coefficient vs. material ages
Pozzolanic Materials Effect. To compare the effect of pozzolanic materials, we applied the poling voltage of 1.5kV/mm to the composites and calculated K
tat 28 days, shown in Table 2. The electromechanical coupling coefficient of FA (fly ash inside the composite) is 13.58%, higher than the others materials. However, the K
tvalues of the composites containing slag (SL) and silica fume (SF) are both lower compared with PC (without any pozzolanic materials), especially for silica fume-cement piezoelectric composite with 7.9% reduction.
Table 2. Electromechanical coupling coefficient at 1.5kV/mm.
coefficient PC SF SL FA
K
t(%) 13.48 12.41 13.27 13.58
Poling Field Effect. Three poling voltages, 0.5kV/mm, 1.0 kV/mm and 1.5kV/mm, were applied to the composites. Results of K
tafter the polarization of 24 hours (0 day) are shown in Table 3, where PZT is the 100% piezoelectric ceramic. The K
tvalues for all materials shown in Table 3 increase with increasing poling voltages. This result coincides with Dong et al [8].
Table 3. Electromechanical coupling coefficients for 24 hours after the polarization [%].
poling voltage PC SF SL FA PZT
0.5 kV/mm 12.77 10.89 12.53 12.47 18.26 1.0 kV/mm 13.40 12.5 13.17 12.9 54.05 1.5 kV/mm 13.65 12.5 13.45 13.58 55.81
From the relation between impedance spectra and poling fields shown in Figs. 6~9, the resonant frequency and anti-resonance frequency of the composites become obvious if the poling voltages increase. Table 4 is the frequency at the minimum and maximum impedances of four piezoelectric composites under different poling voltages. The composites containing silica fume (SF) show no obvious the resonant frequency and anti-resonance frequency under 0.5kV/mm and 1kV/mm, shown in Fig. 7 or Table 4. The polarization for the composites with silica fume is not completed when the lower poling voltages are applied. Therefore, the minimum poling fields to successfully achieve the polarization will not be the same for the cement-based piezoelectric composites containing pozzolanic materials. The poling field and the additions control the electromechanical coupling coefficient of cement-based piezoelectric composites, but the material ages do not.
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:PC
frequence (kHz) 136 138 140 142 144 impedance (kΩΩΩΩ)
16 18 20 22 24
frequence (kHz)
0 200 400 600 800 1000
im p e d a n c e ( k ΩΩΩΩ )
0 20 40 60
0.5kV/mm 1 kV/mm 1.5kV/mm sample:SF
frequence (kHz) 132 134 136 138 140 impedance (kΩΩΩΩ)
6 8 10 12 14 16 18 20 22
Fig. 6 Poling effect for PC materials Fig. 7 Poling effect for SF materials
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
impedance (kΩΩΩΩ)
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 impedance (kΩΩΩΩ)
20 22 24 26 28
![Table 4. Frequency at minimum and maximum impedance [kHz].](https://thumb-ap.123doks.com/thumbv2/9libinfo/9165853.447757/5.892.364.763.128.359/table-frequency-minimum-maximum-impedance-khz.webp)
