[show abstract][hide abstract] ABSTRACT: In this paper, bi-layered magnetoelectric (ME) composites laminated with the bonded Tb1−xDyxFe2−y (Terfenol-D) prepared by means of magnetic warm compaction and (Pb(Zr0.52Ti0.48)O3 (PZT-5H) ceramics were developed. The results show that the transverse ME voltage coefficient of ME composite is about 6 V/cm Oe, 3 times of that prepared by traditional room temperature pressure molding, implying that the magnetic warm compaction technology is an promising way to prepare the bonded Terfenol-D laminated ME composites. Additionally, the enhanced ME voltage coefficient is related to the preferred orientation of the Terfenol-D, and the magnetic field is key factor in the magnetic warm compaction technology.
Journal of Alloys and Compounds 01/2014; 587:287–289. · 2.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: Passive films play an important role in corrosion and stress corrosion cracking of titanium. Correlation between passive film-induced stress and film mechanical properties on α-Ti in methanol solution with varying water content was investigated. Film-induced stress in the methanol solution was measured by the flow stress differential method, and thin film fracture properties were determined by nanoindentation. For small amounts of water (⩽0.15%), both film-induced tensile stress and film fracture load were higher. However, the film-induced tensile stress and fracture load decreased significantly in more dilute solutions. Thus, water reduces Ti SCC susceptibility in methanol solution.
[show abstract][hide abstract] ABSTRACT: The duplex stainless steel passive film electrical properties before and after passivation were investigated by current sensing atomic force microscopy and X-ray photoelectron spectroscopy (XPS). The current maps and band gap energies extracted from I–V curves show that the conductivity of passive film covering austenite and ferrite is different and decreases with increasing film formation potential due to the changes in the passive film thickness and composition, confirmed by XPS analysis. I–V curves reveal that the passive films exhibit p-type or n-type semiconducting properties depending on the film formation potential, attributed to different film chemical composition, supported by XPS results.
[show abstract][hide abstract] ABSTRACT: Two-dimensional and three-dimensional crack morphologies of stress corrosion cracking (SCC) were studied by serial-sectioning and synchrotron-based X-ray computed tomography. Discontinuous surface cracks were actually continuous inside the specimen, which matched typical river-like fractographs and finite element simulations. A low stress SCC model was created, where a main crack continuously grew along the main propagation direction (MPD) due to anodic dissolution; then, discontinuous secondary microcracks emanated from MPD, angularly extending to the two sides of MPD. Finally, some of the secondary microcracks reached the sample surface, resulting in the formation of discontinuous surface cracks.
[show abstract][hide abstract] ABSTRACT: This paper demonstrates the impact of composition on the electrocaloric effect in lead-free (1−x)BaZr0.2Ti0.8O3−xBa0.7Ca0.3TiO3 ceramics, especially on the morphotropic phase boundary. The samples exhibited typical diffused ferroelectric-paraelectric phase transition, which was diffused the most around the tricritical point of rhombohedral, tetragonal, and cubic phases at x = 0.3. The x = 0.3 sample had the highest ΔTmax of 0.30 K under 20 kV/cm field and the widest cooling peak within a wide composition range, which endowed it with the best refrigeration capacity. Although the x = 0.7 sample had even higher ΔTmax, less diffused phase transition narrowed the cooling peak, which reduced the refrigeration capacity.
[show abstract][hide abstract] ABSTRACT: This paper compares the effects of Co dopants into lanthanum strontium titanate (LST) anodes on phase structures, stability and electrochemical measurements in solid oxide fuel cells (SOFCs) employing H2S-containing H2 as fuel. The Co-doped LST (LSCT) with perovskite structure was synthesized via solid state approach, achieving excellent phase purity and refined particle size. The catalytic activity and electrochemical performances is significantly improved by introducing Co. A maximum power density of 300 mW cm-2 was achieved at 900 oC with 5000 ppm H2S-H2 in a fuel cell having a 300 μm thick YSZ electrolyte. Trace amounts of metallic Co nano-particles with sizes typically no larger than 10 nm in diameter were detected on the LSCT surface after reduction in H2 at 900 oC. The nano-sized Co clusters could reduce the anode polarization resistance, as well as improve cell performance, compared with undoped LST anodes. LSCT anode catalyst was electrochemically stable in 5000 ppm H2S-H2 during the test time at high operating temperature. LSCT anode catalyst also had relatively high redox stability in reversible oxidation-reduction cycles.
[show abstract][hide abstract] ABSTRACT: Performance and longevity of artificial joints are highly correlated with the surface properties of the prosthesis materials. In view of the importance of this research area, this article consolidates the research work with some fundamental aspects to build up a comprehensive picture of the current state of knowledge. Tribofilm containing organometallic compounds can form on the surface of artificial joints through biotribocorrosion processes. Tribofilm can act as a barrier to prevent further ionic release and can also act as a solid lubricant. Some test methods are presented, being applied both in vivo and in vitro. A review of recent work in this area is provided, focussing on the constitution and microstructure of the artificial joints surface. The future perspective of this research area is summarized.
[show abstract][hide abstract] ABSTRACT: BaTiO3 has a giant electrocaloric strength, |ΔT|/|ΔE|, because of a large latent heat and a sharp phase transition. The electrocaloric strength of a new single crystal, as giant as 0.48 K·cm/kV, is twice larger than the previous best result, but it remarkably decreased to 0.18 K·cm/kV after several times of thermal cycles accompanied by alternating electric fields, because the field-induced phase transition and domain switching resulted in numerous defects such as microcracks. The ceramics prepared from nano-sized powders showed a high electrocaloric strength of 0.14 K·cm/kV, comparable to the single crystals experienced electrocaloric cycles, because of its unique microstructure after proper sintering process. Moreover, its properties did not change under the combined effects of thermal cycles and alternating electric fields, i.e. it has both large electrocaloric effect and good reliability, which are desirable for practical applications.
[show abstract][hide abstract] ABSTRACT: The effects of annealing temperature on the microstructure and the magnetic domain structures of duplex stainless steel 2507 were investigated by the magnetic force microscopy (MFM), X-ray diffraction (XRD), and electron backscattered diffraction (EBSD). The MFM and XRD results indicated that the volume fraction of ferrite phase increased with increasing annealing temperature, but the lattice constants kept constant. Moreover, with the rise of annealing temperature, the magnetic domain structure in the ferrite phase varied gradually, where the magnetic domain became thinner and the distribution turned more homogeneous. These results gave a direct evidence for the changes of microstructure and magnetic domain structure induced by the annealing treatment. EBSD analysis showed that the orientation of ferrite grains changed after annealing treatments, which coincided with the changes of the microstructure and the magnetic domain structures.
[show abstract][hide abstract] ABSTRACT: The water adsorption behavior on the surfaces of chromium, copper and
gold and its effect on the surface potential at various relative
humidity were studied by in situ scanning Kelvin probe force microscopy
(SKPFM) combined with force calibration. The thickness of water layer on
different surfaces was obtained from the force-distance curve. It
increases with the rise of humidity. The Volta potential map was
measured using SKPFM within a wide humidity range of 20-100% as a
function of the thickness of water layers. The surface potential
decreases with the increasing thickness of water layers on the metal
surfaces. The difference in the water adsorption behavior and its effect
on surface potential originates from the different surface properties of
three metals, such as the roughness and contact angle.
[show abstract][hide abstract] ABSTRACT: This paper demonstrates the electrocaloric effect (ECE) around BaTiO3's orthorhombic-tetragonal first-order phase transition. By manipulating a field-induced transition of a metastable phase in the thermal hysteresis zone, a huge exothermic or endothermic peak appears after first applying or removing electric fields because of the energy change of lattice structure. A large ECE of ΔT/E = 1.4K·m/MV, equaling to latent heat, is achieved under 10kV/cm at 10°C. The entropy change for polarization ordering alone induces an ECE two orders of magnitude lower under the same condition. It confirms the dominant factor to ECE of the energy flow due to the structural phase transition.
[show abstract][hide abstract] ABSTRACT: The wear resistance of silicon probe is a crucial issue to assure the quality and reliability of atomic force microscope (AFM) measurements. In order to reduce the artifacts created by worn tip, the composite diamond and diamond-like-carbon (DLC) deposition on the silicon probe was investigated in this paper. The composite diamond-DLC film was deposited on the standard AFM silicon probe by the method of plasma-enhanced chemical vapor deposition. The morphology and composition of the coatings were characterized by scanning electron microscopy, AFM, and Raman spectroscopy. The wear resistance and scanning image quality of the composite diamond-DLC deposited probes were measured, as well the adhesive force under various humidity levels. The results showed that the composite diamond-DLC deposition reduced the adhesion and wear of the silicon probe, and extended the effective service life.
[show abstract][hide abstract] ABSTRACT: The stability of nano-scale ferroelectric domains in a LiNbO3 single crystal under varied atmospheric humidity levels was studied using piezoelectric force microscopy. Experimental results showed that the nano-scale domains fabricated by the tip field of the atomic force microscope changed as the environmental humidity changed; the c− domains expanded or shrank with increases or decreases in the environmental humidity (that is, with the amount of adsorbed H2O molecules on the domain surface), while the c+ domains transformed in the opposite sense. The surface energy of the domains is responsible for these transformations.
Journal of Applied Physics 05/2012; 111(9). · 2.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper presents the surface potential distributions of pores, grain boundaries (GBs) and indentation cracks of lead zirconate titanate piezoceramics. The pores, GBs and indentation cracks in poled samples are higher potential regions in comparison to other regions. However, GBs and indentation cracks have no distinguishing potential feature in unpoled samples. Coupled with an investigation of the fracture modes, the role of the electrostatic repulsive force induced by charges accumulated in GBs on the ferroelectric fracture is discussed.