Zhonghao Jiang

Synthesis and optical properties of S-doped ZnO nanowires

S-doped ZnO nanowires with an average diameter of 80 nm and length up to several tens of micrometers were produced through a simple physical evaporation approach. The nanowires had a single-crystal hexagonal structure and grew along the [102] direction. Photoluminescence (PL) measurements showed that the doping of sulfur shifted the PL spectrum peak towards short wavelengths, and the doping quantity was found responsible for the different characteristics.

A black phosphate coating for C1008 steel

This paper describes an effective metal finishing technology for obtaining black phosphate coatings on steel. The black conversion coating obtained on steel (C1008, AISI) and cast iron (No.35, ASTM) was dense and uniform with a thickness up to 18 μm. The coating shows better corrosion resistance; lubricating ability and higher efficiency of light-absorption than the traditional phosphate coatings. The black phosphate-forming mechanism was investigated. It is shown that sodium molybdate added to the black phosphate treatment bath can refine the microstructure. Corrosion tests showed that the corrosion rate was lower than that of traditional phosphating. The black phosphate coating, when employed as the pretreatment layer before laser heat-treatment, can remarkably improve the efficiency of light-absorption during laser heat-treatment. This phosphate technology had been employed successfully on the production line in the automobile industry.

Strain rate sensitivity of a nanocrystalline Cu synthesized by electric brush plating

A method for synthesizing bulk nanocrystalline Cu by an electric brush-plating technique is reported. This brush-plated nanocrystalline Cu has a fine (26nm) and quite uniform grain structure and predominant high-angle grain boundaries. A pronounced strain rate sensitivity of the stress with an m of 0.104 and the Coble creep and a subsequent transition to the power-law creep were observed in room temperature tensile and creep tests. The dominant grain boundary deformation due to the truly nanocrystalline structure of this nanocrystalline Cu is responsible for the observed strain rate sensitivity.

An analytical study of the influence of thermal residual stresses on the elastic and yield behaviors of short fiber-reinforced metal matrix composites

Abstract An analytical model was developed to study the influence of thermal residual stresses on the elastic and yield behaviors of aligned short fiber-reinforced metal matrix composites. Three-dimensional solutions of elastic stress field in the matrix of a circular cylindrical unit cell were first obtained based on the theory of elasticity. On this basis, an alternative analysis of the stress transfers between the matrix and the fiber was given by using the shear lag analysis, which provides the expressions for the stress distributions in the matrix and the fiber. The thermal residual stresses and the distributions of the stresses under tensile and compressive loadings as a function of the material parameters, such as fiber volume fraction, fiber aspect ratio and matrix yield stress, were calculated. Furthermore, simple expressions for the composite elastic modulus and yield strength under tensile and compressive loadings were derived. These expressions were used to study the influence of the thermal residual stresses and the material parameters on the elastic moduli and yield strengths under tensile and compressive loadings. Finally, the model predictions were compared with the experimental results on the SiC w /Al–Li T6 composite and several SiC w /Al T6 composites in literature and also with the other theoretical models.

Strain rate sensitivity of face-centered-cubic nanocrystalline materials based on dislocation deformation

The relationship between strain rate sensitivity and activation volume for face-centered-cubic metals is proposed based on the bow-out model of single dislocation from its source, which gives reasonable prediction of the enhanced strain rate sensitivity that occurs in nanostructured and ultrafine grained Ni and Cu.

Carbon-Encapsulated Co3O4 Nanoparticles as Anode Materials with Super Lithium Storage Performance

A high-performance anode material for lithium storage was successfully synthesized by glucose as carbon source and cobalt nitrate as Co3O4 precursor with the assistance of sodium chloride surface as a template to reduce the carbon sheet thickness. Ultrafine Co3O4 nanoparticles were homogeneously embedded in ultrathin porous graphitic carbon in this material. The carbon sheets, which have large specific surface area, high electronic conductivity, and outstanding mechanical flexibility, are very effective to keep the stability of Co3O4 nanoparticales which has a large capacity. As a consequence, a very high reversible capacity of up to 1413 mA h g−1 at a current density of 0.1 A g−1 after 100 cycles, a high rate capability (845, 560, 461 and 345 mA h g−1 at 5, 10, 15 and 20 C, respectively, 1 C = 1 A g−1), and a superior cycling performance at an ultrahigh rate (760 mA h g−1 at 5 C after 1000 cycles) are achieved by this lithium-ion-battery anode material.

Deformation mechanism transition caused by strain rate in a pulse electric brush-plated nanocrystalline Cu

Bulk nanocrystalline Cu was synthesized by a pulse electric brush-plating technique. A very large strength (at 2% plastic strain) increase from 644 to 1451 MPa was obtained by compression tests at room temperature and strain rates from 1×10−5 to 3×100 s−1. A transition in plastic deformation mechanism with strain rate from a combination of the thermally activated grain boundary sliding and the dislocation emission-absorption in grain boundaries to one dominated by the dislocation activity has been revealed by the significant changes in strain rate sensitivity and apparent activation volume with strain rate.

A unique porous architecture built by ultrathin wrinkled NiCoO2/rGO/NiCoO2 sandwich nanosheets for pseudocapacitance and Li ion storage

Hierarchical porous architectures assembled by ultrathin mesoporous nanosheets are attractive for electrochemical energy storage. Herein, we present a facile and scalable strategy where two ultrathin mesoporous NiCoO2 sheets (∼2 nm) are anchored on both sides of a rGO sheet to form an ultrathin sandwich nanosheet (∼6 nm) using a chemical co-precipitation method. The sandwich nanosheets are randomly wrinkled, thus the framework built up by such sheets is porous and has a high specific surface area. The high quality rGO endows the composite with excellent conductivity. And the firm adhesion between the NiCoO2 sheet and flexible rGO also guarantees the integration of the electrode during electrochemical cycling. The electrochemical tests on the electrode made by such ultrathin sandwich nanosheets validate that the strategy is effective to obtain high performance electrodes for supercapacitors and lithium ion batteries. As an electrode of a lithium ion battery, it shows excellent cycling performance with a specific capacity close to 998 mA h g−1 at a current density of 0.1 A g−1; and as an electrode of a supercapacitor, capacitance retention of 87.6% is achieved over 2000 cycles at a constant current density of 20 A g−1.

Strong work-hardening effect in a multiphase ZrCuAlNiO alloy

A bulk as-cast ZrCuAlNiO alloy consisting of Zr2Cu, B2-type ZrCu, and a small quantity of ZrCu martensite phase was prepared by copper mold casting. The multiphase alloy exhibits a remarkable work-hardening effect (Δσy=1196MPa, ΔE=5.6GPa, and Δee=2.11%) in the cycle loading-unloading compression test and possesses the high work-hardening capacity (Hc) of 1.66 and 1.58 at strain rates of 1×10−4 and 1×10−3s−1, respectively, under continuous deformation. The strong work-hardening effect of the alloy results from the continuous transformation of the ZrCu (B2, austenite) phase into the ZrCu martensite.

Influence of sodium metanitrobenzene sulphonate on structures and surface morphologies of phosphate coating on AZ91D

The gray phosphate coating was formed on AZ91D magnesium alloy from the zinc phosphating bath containing sodium metanitrobenzene sulphonate in about 4 min. The structure, surface morphologies and phase compositions of the phosphate coatings were observed and analyzed by using SEM, XRD and EDS. It is shown that the phosphate coating becomes denser and has less micro holes with increasing the concentration of sodium metanitrobenzene sulphonate in the bath in the range of 2.0 to 6.0 g/L. The addition of sodium metanitrobenzene sulphonate greatly increases the micro cathode sites for the formation of the phosphate coating and decreases the porosity of the coating.