Applied Mechanics and Materials Vol. 455

Abstract: Alumina was prepared from NaOH-NaAlO₂-Na₂CrO₄-H₂O solutions (chromate alkali solutions) by carbonization process. The effect of seed ratio, carbon dioxide (CO₂) volume fraction, reaction temperature, and initial sodium hydroxide (NaOH) concentration on the removal efficiency of Al was investigated in detail. High removal efficiency of Al was obtained following the increase of CO₂ volume fraction and temperature. While, initial NaOH concentration increases the stability of solution and reduces the removal efficiency of Al. Bayerite (Al (OH)₃) with small content of Cr (VI) and Na₂O was obtained from alkali metal chromate solutions at 50 °C with no seed. Particle size of bayerite (d₅₀) was about 24 μm. Al₂O₃ was obtained after calcination at 1050 °C for 1.5 h.

Abstract: The radiation damage and its distribution in the type-Ib diamond film implanted by B ion have been investigated by means of Raman scattering and X-ray diffraction spectra. It is of significance during the applications of diamond materials due to several phenomena related to B-doped diamond, such as the superconductivity, the conversion of p-type to n-type conductivity and the low resistivity. The Raman scatting spectra indicated that the radiation damage in implantation layer was various with implantation depth. The top layer was damaged badly and graphitized completely. There existed small damage in nether layer, which resulted in partly amorphous carbon. It was noted that the volume was expanded in diamond film implanted by B ion. By x-ray diffraction pattern, it was reckoned that the lattice parameter was enlarged in B-implanting diamond layer, which expanded the volume of diamond film.

Abstract: With the development of micro/nanoelectronic technology and the miniaturization of IC (Integrated Circuit) packaging, the interfacial characteristics of the nanoscale interface structure in IC packaging become more and more serious on the whole performance of IC or devices. The FEM (finite element method) is used to estimate the thermodynamics properties of the Al-Cu interface structures at the macroscopic scale. Meanwhile, the NEMD (non-equilibrium molecular dynamics) method is used to investigate the interfacial heat transfer at the nanoscale. In the macroscopic scale, the deformation and nanocracks always appear at the outside edge of interface between Cu solder and Al pad due to the dissimilar thermal expand expansion coefficients. In the nanoscale, there is diffusion between different atoms at the interface, the diffusion thickness increases with the temperature increasing. The diffusion between Al and Cu atoms enhances the heat transfer with the temperature increasing. The results reveal the mechanism of the interfacial heat transfer and interfacial crack, which also supply a multiscale analysis method to evaluate the interfacial properties in the IC packaging, which is helpful to design and manufacture of IC assembly.

Abstract: The crystal structure of (La,Mg,Nd)₅Ni₁₉ alloy has been investigated using powder x-ray diffraction. A Rietveld refinement is used to determine the phase structures for tying to find out the correlations of lattices among the phases in this hydrogen storage alloy. The results show that the alloy consists of three phases, which correspond to (La,Mg)₃Nd₂Ni₁₉ with a Pr₅Co₁₉-type structure, La (Mg,Nd)Ni₇ phase with a Ce₂Ni₇-type structure and (La,Mg)₃Nd₂Ni₁₉ with a Ce₅Co₁₉-type structure. Mg and Nd substitute for La atom at the 4f position for Pr₅Co₁₉-type and Ce₂Ni₇-type structures and the 6c position for Ce₅Co₁₉-type structure, respectively. It induces a good lattice match along the a-axisand b-axis among the three phases. The three kinds of structures might form a rod-like shape structural unit by stacking along the c-axis. This phase constitution seems to be beneficial for the cyclic stability of the hydrogen storage alloys.

Abstract: The dynamic recrystallization (DRX) behavior of GH80A superalloy was investigated by isothermal compression tests on a Gleeble1500 thermomechanical simulator. True stress-strain curves and deformed specimens were obtained at the temperature range of 1273-1473K and the strain rate range of 0.01-5s^-1. Experimental results show that the stress-strain curves at low strain rate display a typical DRX characteristic. By regression analysis of experimental results, Materials constant n, activation energy Q and Zener-Hollomon (Z) parameter were determined, and the critical strain model and austenite grain size model for dynamic recrystallization were established as a function of deformation temperature and strain rate. The dynamic recrystallization kinetic model for GH80A was established on the basis of the Avrami equation.

Abstract: In the present work, a new composite gold-supported chitosan-silica (Au/CS-SiO₂) nanomaterial has been synthesized via organic modification and chemical reduction method. Firstly, the hybrid chitosan-silica (CS-SiO₂) material was synthesized by modification of silica with chitosan under suitable reaction conditions. Furthermore, based on the ligand effect of chitosan molecule and the reduction ability of organic alcohols and ascorbic acid, gold nanoparticles were generated and fixed on the surface of hybrid CS-SiO₂ material, which successfully leading to production of the composite Au/CS-SiO₂ nanomaterial. The obtained samples were characterized by the infrared spectroscopy, X-ray diffraction and transmission electron microscopy. Moreover, thermogravimetric analysis was also used to examine their thermal stabilities. It was found that the reducing agent is closely related to the size, shape and amount of gold nanoparticles, and the modification of chitosan decides the stability of the material. These materials can exhibit promising application as the catalyst in chemical field.

Abstract: Micro-arc spark deposition with Stellite6 alloy as the coating material on SCH13 steel substrates was carried out using high-energy micro-arc process with different processing parameters. The microstructure, chemical compositions and phase identification of the deposition layers were examined by using scanning electron microscopy (SEM), energy dispersive Xray spectroscopy (EDS) and X-ray diffraction (XRD), respectively. Meanwhile the form and growth mechanism of a single pulse deposit were focused on. The results show that the morphology of the single pulse deposit is splashshape. A large number of single pulse deposits deposited and superimposed continuously and then deposition layers with a certain thickness were formed. The epitaxial growth coating with columnar grains was then achieved by the micro-arc spark deposition. The prepared Stellite6 alloy coating has a good metallurgical combination with the SCH13 steel substrate and the elements at the interface are smooth transition. Because of the effects of the temperature gradient and the solidification rate, the microstructure of the deposition layer is slightly coarser with the increasing of the processing voltage. The coatings are consisted of γ-Co solid solution and chromium carbides.

Abstract: A three-dimensional (3D) simulation system is developed for the moving mask UV lithography of thick photoresist. The exposure simulation model is obtained with consideration of the mask moving function, the refraction and energy loss of the UV light at the surface of photoresist, and the reflection at the photoresist/substrate interface. The development model is calculated by the fast marching method. In addition, the energy deposition distributions and the three-dimensional development profiles are presented under different conditions to study the effect of various parameters and to verify the accuracy by experiment. The results will be useful to understand the effects and to control the exposure conditions in the design process of moving mask UV lithography for thick-photoresist in the future.

Abstract: A two-dimensional pseudo-homogenous mathematical model was established according to the Au-Cu non-mercury catalytic reaction kinetics. The Crank-Nicholson method was used to solve the equations on the basis of experimental data. The results showed that a violent reaction at the entrance of the fixed bed reactor led to a hot spot in the acetylene hydrochlorination reaction over the Au-Cu Non-mercury catalyst. The conversion increased rapidly initially, and then flattened gradually in the axial direction. The result of simulation provided valuable data to optimize the design of reactor and the industrial operation conditions.

Abstract: Aluminium spinel MAl₂O₄ (M = Mg, Zn, Cu) photocatalysts were prepared by a sol-gel method. The prepared samples were characterized by X-ray diffraction and transmission electron microscope. The results indicated that the samples possess a single spinel-type structure. Ultraviolet-visible diffuse reflectance spectra showed an extension of light absorption into the visible region. The spinel MAl₂O₄ photocatalysts exhibited high photocatalytic activity for the degradation of industrial dyes under high pressure mercury lamp and visible light irradiation, especially CuAl₂O₄. With the decrease of band gap of MAl₂O₄ (M = Mg, Zn, Cu), the photocatalytic activity increases. The possible reasons are discussed from the crystal field theory and energy band theory. These characteristics make the aluminium spinel MAl₂O₄ (M = Mg, Zn, Cu) photocatalysts to be promising candidates for the photocatalytic degradation of dyes.