Wenzhe Chen

Graphene oxide–noble metal (Au, Pt, and Pd) nanoparticle composites as optical limiters

A series of graphene oxide (GO)/noble metal (Au, Pt, and Pd) nanoparticle (NP) composites were synthesized via a one-step hydrothermal reaction of HAuCl4, H2PtCl6, and Pd(C2H3O2)2 in the presence of GO. The metal NPs with different average sizes and distributions were uniformly deposited onto the GO surface. The GO structure was conserved after loading with Au, Pt, and Pd NPs. The corresponding nonlinear optical (NLO) and optical limiting (OL) properties were investigated using an open-aperture Z-scan technique with nanosecond pulses at 532 nm. The results show that the NLO and OL properties were significantly enhanced after the inclusion of metal NPs on the GO surface because of nonlinear scattering (NLS) effects. These enhancements depend on the type of loading metal NPs. The GO/Au-NP composite exhibits the optimal NLO and OL performances among the studied composites because of the surface plasmon resonance of the Au NPs. Thus, the NLO and OL effects of the two-dimensional GO can be effectively modified by absorbing different metal NPs on its surface. The synthetic NLO and OL properties in the GO/metal NP composites originate from the reverse saturable absorption in the GO sheets and the NLS in metal NPs. All of the results indicate that these composites can be used in optoelectronic applications.

In situ synthesis of metallophthalocyanines in inorganic matrix

Abstract Metallophthalocyanines (MPc) have excellent photoelectricity properties. However, their low solubility in the sol–gel precursor and their tendency to aggregate make it difficult to get their homogeneous composites with the traditional sol–gel schedule. To overcome this problem, a newly developed “in situ synthesis” technique during the sol–gel process was successfully used to synthesize transitional metallophthalocyanines in the silica xerogel matrix. As a result, a new kind of organic/inorganic nanocomposite was obtained. The characterizations of the glass sample and the extract were carried out by methods of IR, UV/Vis and fluorescence spectra. The microenvironment of MPc is inferred from the change of the pore structure of the matrix, and the reason why MPc exist in the form of a monomer is given. From the view of the different structures of transitional metallophthalocyanines and rare-earth metallophthalocyanines, it is also discussed why rare-earth metallophthalocyanines cannot be synthesized in the matrix while transitional metallophthalocyanines can.

Gas sensitivity of indium oxide

The yellow indium oxide nanoparticles were prepared by sintering the white deposition at 500 ℃. The crystalline indium chloride and ammonia were used as the starting material. The results show that, by analyzing the particles through X-ray diffraction and TEM, the particles are very small, spherical, and the particle size is about 40 nm. The direct-heat components made from indium oxide in Cl2 and NO2 was tested respectively, the component is far more sensitive to NO2 than to Cl2 at low heating temperature, and the status is reversed at high heating temperature..

Solution preparation of Li(Co, Fe)O2 coatings for molten carbonate fuel cell components

An aqueous solution process has been used for dip coating onto substrates of 316L stainless steel. Coatings of LiCoO2, Li(Co0.5Fe0.5)O2 and LiFeO2 were applied and heat treated to 650°C for 3 hrs. Thermal analysis, X-ray diffraction analysis, and SEM analysis were carried out to characterize the microstructure of the coatings. Results showed that the coatings transformed from a gel to a porous, crystalline layer between 270 and 350°C. Microhardness measurements at low load (50 g) were used as an indication of the surface coverage. Samples subjected to 10 thermal cycles at 10°C/min to 650°C and back to ambient, to simulate use in a molten carbonate fuel cell, showed no decrease in microhardness.

Dimerization of aluminum tetrasulfo-phthalocyanine chloride in sol-gel process

Abstract We report here the study of aluminum tetrasulfo-phthalocyanine chloride (AlTSPcCl)-doped silica xgel obtained by sol–gel technique. Because the issue of dimerization is vital in determining the optical properties of dye doped sol–gel materials and phthalocyanine offers an excellent opportunity to characterize dimers from monomers because of their identified absorption bands, we study the dimerization of different concentrations of AlTSPcCl-doped composites by electronic absorption spectra. Proceeding of the absorption spectra was correlated with various stages of the sol–gel process. The results show the composites AlTSPcCl concurrence in the forms of monomer and dimer. Dimerization behaves differently in the early and latter stage of sol–gel transition. Two reasons are given from the change of the micro-environment in which AlTSPcCl existed during the sol–gel process.

Encapsulation of zinc tetrasulfophthalocyanine in sol–gel materials

Abstract Metallophthalocyanines (MPc) exhibit, among many useful properties, the ability to protect sensors against short, intense pulse deleterious to efficient sensor operation. For the successful application of this optical-limiting property, an important issue is the incorporation of MPc molecules in a matrix to fabricate a solid-state system. We report here the study of different concentrations of zinc tetrasulfophthalocyanine (ZnTSPc) encapsulated in silica xerogel matrix obtained by sol–gel technique. The resulted composites were transparent and homogeneous with appropriate optical quality. The trapping effect was checked by the characteristic absorption bands of ZnTSPc in the UV/Vis spectra and the different pore structures of the doped and undoped composites. The optical-limiting properties of the composites were measured at 532 nm with 8-ns pulses.

Features of dynamic strain aging in high strength Al-Zn-Mg-Cu alloy

Abstract The present work investigates mainly the regulation and features of the occurrence of serrated yielding phenomenon of a high strength Al-Zn-Mg-Cu alloy LC4 under various heat treatments and loading conditions. The main results are: (1) In the serrated yielding temperature region a critical transition temperature T t exists. The critical plastic strain has a negative or positive temperature coefficient within the temperature region lower or higher than T t ; (2) The reason for this phenomenon might be the existence of an absorbed resource which diminishes the pinning effect of solute atoms to mobile dislocations; (3) in the positive coefficient region two reverse thermal activation processes occur simultaneously. One is the solute atoms diffuse to the moving dislocations and pin the dislocations. The other one is the absorbed resource absorbs the solute and diminishes the pinning effect; (4) for LC4, the activation energy of the first process is equivalent to the diffusion activation energy of Mg in Al matrix and the second one is equivalent to that of the interface absorbed solute atoms.

Microstructure evaluation during plastic deformation in a centrifugal spray deposition (CSD) Ti-48Al-2Mn-2Nb alloy

Abstract The microstructures and properties of Ti-48Al-2Mn-Nb alloy formed by centrifugal spray deposition (CSD) were investigated. Hot isostatic pressing was employed to remove the porosity of CSD samples. The tensile and compressive tests were carried out at ambient temperature and, especially, compression strains of 1, 3, 5, 10 and 20%, respectively, were also done. The results show that the ductility of CSD TiAl alloy is around 3%. On the other hand, an excellent compression behavior is achieved, which shows 2210–2310 MPa of compressive strength and 34–38% of compressive ratio. The scanning electron microscopy observations show that the character of slip bands is related to the lamellar structure of TiAl, which slips along the interfaces between the layers. Transmission electron microscopy observations show lots of twins and some dislocation lines built up in the boundaries between lamellar domains or between the lamellae.

Effect of Constrained Conditions on the Equivalent Strain and Microstructure of 5052 Al Alloy Deformed by Groove Pressing

Three-dimensional finite element simulation (3D FES) and experiments were carried out for analyzing the deformation behavior, homogeneity, microstructure and properties of 5052 Al alloy during groove pressing (GP) with two different processing conditions, that is, constrained groove pressing (CGP) and unconstrained groove pressing (UGP). The simulation results show that the values of the equivalent strain and its distribution depend strongly on the constrained conditions. Especially, the equivalent strain and its distribution are inhomogeneous along X direction, with lower strain regions located at both ends and larger strain regions with periodic variation located at intermediate section. CGP results in a higher accumulative rate of equivalent strain than that of UGP. The average strain is equal to the theoretical strain for CGP, but it is much lower than its theoretical strain for UGP. The experimental results show that grain sizes of 5052 Al alloy can be refined significantly by CGP or UGP, while CGP has a higher rate of grain refinement and finer grains than that of UGP. And the results of microhardness confirmed the prediction of 3D FES.

Effects of Forming Processing on Mechanical Properties of Ti-48Al-2Mn-2Nb Intermetallics

Ti-48Al-2Mn-2Nb alloy was produced by “centrifugal spray deposition” (CSD), and then hot isostatic pressing (HIP) was employed to remove the porosity formed by CSD. The effects of CSD and HIP processing on the mechanical properties and microstructure of the TiAl alloy were investigated. The results show that the CSD and HIP processing can both improve the strength, plasticity of the TiAl alloy, and the tensile elongation values of the CSD or HIP samples are around 3%, which are better than those of as-cast TiAl alloys in room temperature. Especially, they show more excellent compressive properties at ambient temperature with a compressive ratio of 33.8% and compressive strength of 2210MPa for the CSD samples, and a compressive ratio of 37.8% and compressive strength of 2348MPa for the HIP samples. The CSD processing also improves the fracture toughness of TiAl alloy, which is much higher than that of the HIP processing, while the HIP processing seems to be beneficial the ductility and plasticity as having a duplex structure. The effects of CSD and HIP processing on microstructure and properties of TiAl alloys are discussed to understand the deformation and fracture process of the alloy.