Al-doped ZnO varistors prepared by a two-step doping process
Qiuyun Fu a,b, Chunfeng Ke a,b, Yunxiang Hua,b†, Zhiping Zheng a,b, Tao Chena,b and Yongyan Xua,b
aSchool of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, People’s Republic of China; b Engineering Research Center for Functional Ceramics of the Ministry of Education, Wuhan, People’s Republic of China
ABSTRACT
It is difficult to dope Al into main grains of ZnO varistor ceramics, especially for small doping amount. Generally, all raw materials including Al dopant are directly mixed together and sintered into ceramics. However, in this direct doping process, Al is apt to stay in grain boundaries, and almost does not enter grains. This does harm to the electrical properties of ZnO varistors. In this paper, we proposed a two-step doping process. Al2O3 powder was first mixed only with a part of the ZnO powder and pre-sintered. The pre-sintered powder was mixed with other additives such as Bi2O3 and the rest ZnO. Then ZnO varistor ceramics were prepared via solid state sintering processes. Results showed that two-step doped ZnO varistors exhibited improved electrical properties with a significant increased nonlinear coefficient and a great decreased leakage current compared to directly doped ones because more Al was incorporated into ZnO grains.
KEYWORD S
ZnO varistors; two-step doping process; Al2O3 doping
Joining of SiC ceramic by using the liquid polyvinylphenylsiloxane
Bofang Zhoua,b, Keqin Fenga and Hongling Zhoua
aSchool of Manufacturing Science and Engineering, Sichuan University, Chengdu, People’s Republic of China; bSichuan Engineering Technical College, Deyang, People’s Republic of China
ABSTRACT
The joining of SiC ceramic using the liquid polyvinylphenylsiloxane at the high temperature was investigated. The characteristic evolution of polyvinylphenylsiloxane during heating process, shear strength and microstructure of joint were especially discussed. The results show that active groups Si-OH and CH=CH2 of polyvinylphenylsiloxane through cross-linking at low temperature (200°C) form the macromolecular structure, crosslinked polyvinylphenylsiloxane possess the higher ceramic yield and structure stability at high temperature. Shear strength of SiC joints increase with the joining temperature from 1000 to 1200°C, and then decrease when the joining temperature reaches to 1350°C. Combination with microstructure of fine grains of SiO2 and SiC dispersion in the Si–O–C ceramic of the join layer and new phase SiC formation on the joint interface through the gas–solid reactions, the shear strength of joint achieves the maximum at 1200°C. The defects of joint increase with temperature higher than
1200°C, and the shear strength of joint begin to decrease.
KEYWORD S
Joining; SiC ceramic; polyvinylphenylsiloxane; ceramic yield; shear strength
Methodology to evaluate variations in piezoelectric constants after aging
process
Mariana del Castillo a, Flávio Buiochib and Nicolás Péreza
aFacultad de Ingeniería, Instituto de Ingeniería Eléctrica, Universidad de la República, Montevideo, Uruguay; bDepartamento de Engenharia Mecatrônica, Universidade de São Paulo, São Paulo, Brazil
ABSTRACT
Piezoelectric ceramic properties change with time. Detected aging effects for PZT ceramics are; the difference in the value of the dielectric constants diminishes, whereas dielectric losses and elastic stiffness increases. In this work, an optimisation technique based on adjusting a finite element model to reproduce the complex impedance curves of a resonant piezoceramic disk is analysed aiming to detect changes due to aging. This technique allows estimating all material parameters, both their real and imaginary parts. The optimisation uses the constitutive equations of the piezoelectric effect in the linear regime. The evolution of elastic,
piezoelectric and dielectric constants is evaluated after 5 years of aging. To compute the ten complex parameters, the piezoelectric model is adjusted to minimise the difference between finite element simulations and the experimental data. Results presented here, show that the proposed technique is sensitive enough to detect changes in the individual parameters due to aging process.
KEYWORD S
Ceramics; aging; piezoelectric parameters; electromechanical resonances; complex impedance; FEM optimisation
Parametric study of a thin piezoelectric cantilever for energy harvesting
applications
T. Hoanga,b, G. Poulin-Vittrantb, G. Ferina, F. Levassortb, C. Bantigniesa, A. Nguyen-Dinha and M. Bavencoffeb
aAdvanced Research Department, Vermon S.A., Tours, France; bGREMAN UMR7347, Université de Tours, INSA-CVL, CNRS, Blois, France
ABSTRACT
Nowadays, bimorph piezoelectric cantilevers are commonly used in ambient vibrational piezoelectric energy harvesting. They are constituted of two thin layers of piezoelectric material separated by an inner shim material. To help the design process of these energy harvesting devices, analytical and numerical models have been developed. This work presents a parametric study to determine the effective coefficients of a thinned piezoelectric layer. To this aim, a one-dimensional analytical model and a three-dimensional finite element (FE) model are investigated: a thinned layer of PZT material in free mechanical boundary conditions is considered. The one-dimensional analytical admittance model allows the determination of the elastic, dielectric and piezoelectric coefficients ( sE11 , 1T33, d31 ) of the piezoelectric layer. Then, in order to determine the influence of all coefficients of the compliance, dielectric and piezoelectric tensors, a FE model is investigated.
KEYWORD S
Energy harvesting; parametric study; piezoelectricity; finite element model; electrical impedance; functional characterisation
Preparation of alumina ceramic template by the molten salt method
Xuezhu Luan, Jinhong Li and Xiang Wang
Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, School of Materials Science and Technology, China University of Geosciences, Beijing, People’ s Republic of China
ABSTRACT
Single-crystal alpha alumina (α -Al2O3) platelets were synthesised with aluminium sulphate in the study. Moreover, the effects of the heating temperature, holding time, and different power mixtures of γ-Al2O3 and sodium sulphate (Na2SO4) on the morphology of as-prepared α-Al2O3 platelets were explored. The crystalline phase evolution and morphology of the samples were characterised by X-ray diffraction and scanning electron microscopy. According to the further analysis results, most of α-Al2O3 platelets were hexagonal particles. After the power mixture of γ-Al2O3 and Na2SO4 (1:2) was heated at 1200°C for 1 h, the platelet size became relatively uniform with an average diameter of 3–5 μm and a thickness of 50–100 nm. This method is an easily controllable, simple, and green method to produce highquality α-Al2O3 platelets.
KEYWORD S
Alpha alumina; platelet; phase transformation; molten salt synthesis
Preparation of boron nitride-based coatings through thermal diffusion process
Eugene Medvedovski
Endurance Technologies Inc., Calgary, Canada
ABSTRACT
Preparation of boron nitride (BN)-based coatings for friction and corrosion conditions has been proposed and made through the thermal diffusion process following chemical vapour deposition principles. It includes the formation of gaseous B- and N-based species due to high-temperature reactions (decomposition) in the B- and N-rich powders with consequent deposition of B and N onto the heated substrate and their diffusion into the substrate with formation and consolidation of a thin BN layer. The proposed process can be used for complex-shape components employing simple production equipment.
KEYWORD S
Boron nitride; coating; surface structure; chemical vapour deposition; thermal diffusion
Solid-state reaction method to 6Li, Ce:YAG ceramics for thermal neutron
detection
Fusheng Zheng, Maobing Shuai and Wei Wang
Science and Technology on Surface Physic and Chemistry Laboratory, Jiangyou, People’ s Republic of China
ABSTRACT
The crystal structures and optical properties of 5% 6Li:Ce0.09Y2.91Al5O12 transparent ceramics prepared by solid-state reaction with different vacuum sintering temperature were investigated in this paper. The results reveal that with the increasing of sintering
temperature, the transmittance of 6Li,Ce:YAG ceramics increases from 36% (1680°C) to 82% (1780°C) at 1000 nm, and the intensity of absorption peaks at 340 and 460 nm increases. The emission peak wavelengths of 6Li:Ce0.09Y2.91Al5O12 ceramics have been measured as 534.5 nm, and there is no red shift. The high transmittance and emission peak (at 534.5 nm) suggested that this material could be a candidate for neutron detection applications.
KEYWORD S
6Li; ce:YAG; thermal neutron detection; sintering temperature
Virtual instrument to obtain electrical models of piezoelectric elements used
in energy harvesting
M. Vázquez-Rodríguez a,b, F.J. Jiménez a,b and J. de Frutosb
aDTE, ETSIST, Universidad Politécnica de Madrid, Madrid, Spain; bCEMDATIC-POEMMA R&D Group, Universidad Politécnica de Madrid, Madrid, Spain
ABSTRACT
A new virtual instrument (VI) has been designed to obtain the Fourier model of piezoelectric devices under test (PDUT) in road traffic environments, and the linear electrical model of the piezoelectric harvester circuit involved in energy harvesting applications. The VI provides a high grade of automatisation and high accuracy in the characterisation procedure of a piezoelectric harvesting system. The maximum power can be predicted and the number of piezoelectric elements can be calculated to achieve a given power value. The VI system controls the test bench (patent protected), which simulates the effect of the road traffic, and obtains the Fourier model of the PDUT. The VI controls the switched circuit’s matrix of the harvesting electronic hardware (HEH) to select the PDUTs and the rectifier topology. The VI also connects capacitors and load resistors of the HEH and computes the key parameters of the piezoelectric harvester model.
KEYWORD S
Virtual instrument; piezoelectric elements; energy harvesting; test bench; LabVIEW
