Gaorong Han

Tribological Behavior of Carbon-Nanotube-Filled PTFE Composites

Carbon nanotube/polytetrafluoroethylene (CNT/PTFE) composites with different volume fractions were prepared and their friction and wear properties were investigated using a ring-on-block under dry conditions. It was found that CNTs signifi-cantly increased the wear resistance of PTFE composites and decreased their coefficient of friction. PTFE composites with 15–20 vol.% CNTs exhibited very high wear resistance. The significant improvements in the tribological properties of CNT/PTFE composites are attributed to the super-strong mechanical properties and the very high aspect ratio of CNTs. The CNTs greatly reinforce the structure of the PTFE-based composites and thereby greatly reduce the adhesive and plough wear of CNT/PTFE composites. The CNTs are released from the composite during sliding and transferred to the interface of the friction couples. They thus serve as spacers, preventing direct contact between the mating surfaces and thereby reducing both wear rate and friction coefficient.

From clusters to phase diagrams: composition rules of quasicrystals and bulk metallic glasses

Metallic elements having negative enthalpies of mixing tend to form characteristic local atomic clusters. In this review, we use the structural information in the first nearest neighbour shell level, or first-shell atomic cluster, to derive the composition rules of two types of complex alloy phases, quasicrystals and bulk metallic glasses, both being composed of elements with negative enthalpies of mixing. We first show the composition phenomena in quasicrystal-forming systems, where major composition rules such as cluster line, electron concentration and atomic size criteria are derived. Then we analyse the composition rules of bulk metallic glasses using the very same approaches. Finally, we summarize their common composition rules into more general rules and basic theories.

Facile synthesis of single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods as anode materials for lithium-ion batteries

In this work, single-crystalline α-FeOOH nanorods with a length of 400–700 nm and a diameter of 20–80 nm were successfully synthesized via a facile template-free hydrothermal method. Single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods could be obtained from these α-FeOOH precursors after calcining at 350 °C in air and 500 °C in nitrogen, respectively. The as-prepared single-crystalline mesoporous α-Fe2O3 and Fe3O4 nanorods exhibited a large specific surface area and porosity, effectively enhancing the electrochemical reaction area and accommodate the strain during the charge–discharge cycling process.

Percolative conductor/polymer composite films with significant dielectric properties

A percolative film with conductive acetylene black introduced into β-polyvinylidene fluoride was prepared by dip-coating method. Percolation theory was employed to explain the dielectric behavior of polymer/conductor composite films. Experimental results showed that the dielectric constant of polymer/conductor composite films can reach 56 and the dielectric loss is below 0.15 when acetylene black concentration is in the neighborhood of percolation threshold (fc). The experimental results are in good agreement with classic percolation power law, with fc≈1.3% and exponent q≈0.53. Such composite films have a potential to become capacitors and can be easily fabricated due to its flexibility.

Fabrication and characterization of anodic aluminum oxide template

In this paper, anodic aluminum oxide (AAO) templates were fabricated using a two-step oxidization method, pore-widening was then fulfilled in 5 wt% phosphoric acid at 37 °C. The AAO template prepared under 40 V constant potential presents the optimum ordering. The pore diameter and spacing are proportional to the forming voltage, which is due to the alternative migration velocity of reactive ions under electric field according to the growth-dissolution model. Further pore adjustment depends on the time of pore-widening in phosphoric acid. The characterization of the AAO template was measured by atomic force microscopy (AFM) and X-ray diffraction (XRD).

Sol-gel preparation of bioactive apatite films

The surface of biomedical metallic implants covered by a bioactive apatite film can create bioactivity of the implant and shorten healing time. In this work, apatite films on Ti6Al4V were prepared by sol–gel route using Ca(NO ) , P O and HPF as 32 2 5 6 the precursors, in vitro evaluations of the resulting hydroxyapatite (HA) and fluorapatiteyhydroxyapatite solid solution (FHA) films were done in Kokubo’s simulated body fluid and citric acid modified phosphate buffer solution (CPBS). HPF showed a 6 good reagent for the incorporation of fluorine into apatite films. The FHA film demonstrated to have good bioactivity, and to have better stability in CPBS and higher adhesion strength than the HA film. When fluorine is incorporated into the film, an increase in crystallinity of the apatite film and a decrease in intrinsic solubility of the FHA film could make significant contributions to the improvement in the stability; the thermal expansion coefficient of the FHA film getting closer to that of Ti6Al4V could be responsible for the increase in adhesion strength. 2002 Elsevier Science B.V. All rights reserved.

Band structures of TiO2 doped with N, C and B

This study on the band structures and charge densities of nitrogen (N)-, carbon (C)-and boron (B)-doped titanium dioxide (TiO2) by first-principles simulation with the CASTEP code (Segall et al., 2002) showed that the three 2p bands of impurity atom are located above the valence-band maximum and below the Ti 3d bands, and that along with the decreasing of impurity atomic number, the fluctuations become more intensive. We cannot observe obvious band-gap narrowing in our result. Therefore, the cause of absorption in visible light might be the isolated impurity atom 2p states in band-gap rather than the band-gap narrowing.

Self‐Templated Synthesis of Single‐Crystal and Single‐Domain Ferroelectric Nanoplates

Low-dimensional nanomaterials, such as nanowires and nanotubes, 3] have received extensive attention because of their fascinating catalysis, optics, and electronics 7] properties, which offer the opportunity to fabricate nanodevices. Much attention has been paid to materials with two-dimensional (2D) nanostructure because of their unique electronic, magnetic, and storage properties. In particular, the recent development of stable graphene has stimulated great interest in studying free-standing 2D nanomaterials. So far, a variety of 2D free-standing materials with nanostructure, such as PbS nanosheets, WO3 nanoplates, [10] CeO2 nanoplates, [11] MoS2 nanoflakes, 13] and TiO2 nanosheets, [4] have been successfully synthesized. Compared to these simple compounds, 2D free-standing, single-crystal multicomponent oxide nanomaterials, such as ferroelectric oxides, have been rarely reported because of the relatively complex crystal structures and rigid crystalline properties of these oxides. Ferroelectric oxide nanomaterials, such as PbTiO3 (PT), Pb(Zr,Ti)O3, and BaTiO3, have versatile properties for various technical applications ranging from nonvolatile ferroelectric random access memories (NFERAMs) to electromechanical applications. 15] Among these nanomaterials, 2D free-standing, single-crystal ferroelectric materials are highly attractive because of their potential performances. For example, ultrathin single crystals of BaTiO3 [16,17] prepared by focused ion beam (FIB) microscopy have been used as single-crystal capacitors with thicknesses down to about 65 nm. These ferroelectric platelets fabricated by FIB have greatly improved our understanding of the fundamental properties of thin films. However, recent theoretical research predicts that ferroelectric nanodiscs could even favor an ultimate NFERAM density of 60 10 bits per square inch as well as a new toroid moment. In contrast to the conventional properties, the surface chemistry of ferroelectric oxides only gradually became an active field of research. In particular, it has been predicted that CO and NO catalysis could be favored on ultrathin Pt(100) films supported on ferroelectric PbTiO3. [22] Various methods have so far been applied to fabricate 0D and 1D ferroelectric nanomaterials, including templated methods, sol-gel processing, 28] soft-chemistry routes, solvothermal/hydrothermal reactions, 31] and electrospinning techniques. 33] Despite much effort, there is still an absence of a simple wet-chemistry method to prepare 2D single-crystal ferroelectric nanomaterials, such as nanoplates and nanodiscs. Here we report, for the first time, that freestanding, single-crystal PT nanoplates can be synthesized by a facile hydrothermal method. The characterization of the microstructure by X-ray diffraction (XRD) and high-resolution transmussion electron microscopy (HRTEM) demonstrates that these PT nanoplates, with side lengths of 600– 1100 nm and heights of about 150 nm, grow along the ab plane of the tetragonal perovskite structure and that {001} facets at the top and bottom surfaces are exposed. The “self-templated” crystal growth has been employed to discuss the mechanism for the formation of PT nanoplates under hydrothermal conditions. Electrostatic force microscopy in the dynamic contact mode (DC-EFM) of operation was also used to study the ferroelectric properties of the PT nonaplates. Furthermore, the catalytic performance of the nanoplates for the oxidation of carbon monoxide (CO) has been evaluated. In brief, tetragonal-phase PT nanoplates were synthesized by a hydrothermal method at 200 8C by using 6m KOH. Figure 1a shows a typical XRD pattern (JCPDS 70-0746) of PT nanoplates prepared by the hydrothermal process at 200 8C for 12 h with 6m KOH, and indicates that the product has a pure tetragonal perovskite PT structure. More importantly, the intensity of the (001) diffraction peak is dramatically higher than that of (100), which is opposite to the case in conventional perovskite PT (JCPDS 70-0746). This observation reveals that {001} crystal planes are prevailent in the sample. Scanning electron microscopy (SEM) and TEM analysis show that the products consist of well-defined structures with a rectangular outline and a side length of 600–1100 nm (Figure 1b,c). The HRTEM image (Figure 1d) of a PT nanoplate shows a clear crystal lattice with uniform interplanar spacings of 0.390 nm and 0.390 nm, which correspond to the tetragonal (100) and (010) planes, respectively, and indicate that the PT nanoplates grow along the ab plane of the perovskite structure. The effect of the KOH concen[*] C. Y. Chao, Dr. Z. H. Ren, Z. Xiao, Z. Y. Liu, Dr. G. Xu, J. Q. Mai, Dr. X. Li, Dr. G. Shen, Dr. G. R. Han State Key Laboratory of Silicon Materials Department of Materials Science and Engineering Cyrus Tang Center for Sensor Materials and Application Zhejiang University, Hangzhou 310027 (P.R. China) E-mail: renzh@zju.edu.cn hgr@zju.edu.cn

PbTiO3 nanofibers with edge-shared TiO6 octahedra.

A new tetragonal phase of PbTiO(3) was discovered, in which each TiO(6) octahedron pair shares an edge and stacks over following pairs in an interlaced manner to form a one-dimensional (1D) columned structure along the c-axis. This new tetragonal phase of PbTiO(3) transforms into a normal perovskite phase in air at elevated temperature.

The effect of citric acid addition on the formation of sol-gel derived hydroxyapatite

In order to improve the gelation in sol–gel preparation of hydroxyapatite by using Ca(NO3)2 and PO(OH)3−x (OEt)x precursors, citric acid was selected as an enhancing gelation additive. Hydroxyapatite derived from the mixed precursor solutions (Ca/P molar ratio of 1.67) with citric acid showed a different reaction path from that without citric acid. The addition of citric acid led to formation of amorphous as-prepared powder, the powders calcined at 650 ◦ C contained three phases: hydroxyapatite, carbonated hydroxyapatite and a small amount of -tricalcium phosphate. The powders calcined at 800 ◦ C contained only a single phase of oxy-hydroxyapatite. It is suggested that citric acid plays a role in enhancing gelation through a strong coordination ability of Ca ions with citrate groups.