Advanced Materials Research Vol. 502

Abstract: In order to understand dislocations in GaN grown on silicon using metal organic chemical vapor deposition (MOCVD), two samples with different film thickness were grown. The distribution of dislocations and its influence on epitaxial layer were studied. Wet etching can effectively reveal the dislocations in GaN, and the hexagonal etch pits are the emergence of dislocations. After etching in the aqueous KOH: H2O =3:20 (m:m), there are more pits with longer etch time. SEM shows that there are more hexagonal etch pits near the micro-cracks because many dislocations are induced by micro-cracks. In the experiment, ribbon slopes in the two sides of the pits are observed, and they are paralleled to each other. If the growth time prolonged, the ribbon slopes would disappear and the surface become flat, and this mechanism is discussed in this paper.

Abstract: The aim of this paper is to study the influence of manufacturing defects on coefficient of thermal expansion (CTE) of Plain Weave C/SiC by using the finite element computational micromechanics (FECM) method. Utilizing photomicrographs taken by scanning electron microscope (SEM), we established an accurate representative volume element (RVE) model for the plain weave C/SiC composites with consideration of manufacturing defects, which have different influence on CTE. The study shows that matrix cracks make CTE increase by 2.7% and matrix porosities make CTE decrease by 2.4% compared with the no defects RVE model. The variation law of CTE along with cracks density and porosity volume is also obtained: CTE of plain weave C/SiC is decreasing correspondingly while the speed gradually slows with the increasing of matrix crack density and matrix porosity volume fraction.

Abstract: The composition of FeS solid lubrication duplex layer on 45 steel surface was studied by using SEM, EDS, AES and XPS. The results show that the sulphurized surface layer of FeS solid lubrication duplex is composed of the sulphide aggradation layer deposited on the nitrocarburized sub-surface layer and the sulphide diffusion layer formed by some S element infiltrating the nitrocarburized surface. The sulphide aggradation layer is mainly composed of FeS and FeS2, the key composition of the sulphide diffusion layer is FeS, and Fe(2/3/4)N is the key composition of the nitrocarburized sub-surface layer. The result of friction reduction and wear resistance test combined with the composition of FeS solid lubrication duplex layer explains that the friction coefficient and wear volume of the duplex layer are lower than those of the plain surface, which attribute to the relatively softer sulphurized surface layer provided self-lubricating property while the harder nitrocarburized sub-surface layer provided sufficient load bearing capacity in view of resistance to plastic deformation, so that spallation failure of the sulphurized surface layer can be effectively avoided, and they exert excellent friction reduction and wear resistance functions in different moments during rubbing process respectively.

Abstract: Selective Laser Melting (SLM) technology can be used to fabricate plastic mould with complex conformal cooling channels directly and rapidly. In this paper, 316L stainless steel powders were used to produced a mould with an emphasis on attaining excellent mechanical properties.The precision, density and mechanical properties of parts were studied. Simulation and experimental results showed: the mould manufactured by SLM reveals good accuracy and performance, and the cooling efficiency of conformal cooling channels in mould has been greatly improved and the uniformity of cooling has been also upgraded.

Abstract: Al-doped ZnO (ZnO:Al) thin films were deposited on glass substrates by rf magnetron sputtering technique. The effect of discharge power on the structural, optical and electrical characteristics of ZnO:Al films was investigated by X-ray diffraction (XRD), four-probe meter and optical transmission spectroscopy. The results show that the films are polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The highest figure of merit of 5.58×10-3 -1 is obtained from the film prepared at the discharge power of 200 W. The average optical transmittance in the visible range of the films is over 78.2%.

Abstract: Indium tin oxide (ITO) thin films were deposited by RF magnetron sputtering on glass substrates employing a sintered ceramic target. The influence of substrate temperature on the structural, compositional, optical and electrical properties of the thin films were investigated by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), spectrophotometer and four-point probes. All the ITO thin films show a polycrystalline indium oxide structure and have a preferred orientation along the (222) direction. The substrate temperature significantly affects the crystal structure and optoelectrical properties of the thin films. With the increment of substrate temperature, the electrical resistivity of the deposited films decreases, the crystallite dimension, optical bandgap and average transmittance in the visible region increase. The ITO thin film deposited at substrate temperature of 200 °C possesses the best synthetic optoelectrical properties, with the highest transmittance, the lowest resistivity and the highest figure of merit.

Abstract: BiFeO3 (BFO) film is considered as relaxor ferroelectric film with a leakage current, and Bi3.25La0.75Ti3O12 (BLT) film is regarded as ferroelectric film with a leakage current. Maxwell- Wagner (M-W) theory has been used to study the dielectric relaxation behavior of BiFeO3 (BFO)/Bi3.25La0.75Ti3O12 (BLT) films grown on Pt/Ti/SiO2/Si substrate. Results show that the characteristics of BFO film significantly affect the dielectric relaxation behavior of the BFO/BLT film. The theoretical results agree well with the experimental data when the temperature is above 400K. It is inferred that the polycrystalline orientation of BFO film leads to the presence of disorganized polar nanoregions (PNRs) in BFO film. And BFO film exhibits relaxation characteristics at high temperatures.

Abstract: In this paper, Al₂O₃-Bi₂O₃ was choosed as chip fuse matrix material. Composition of Al₂O₃-Bi₂O₃ ceramics samples in different sintering temperature was studied by X-ray diffraction, and dielectric properties of samples under different frequency was measured. The results show that the mixture of Bi₂O₃ in Al₂O₃ ceramics can improve the sintering activity of Al₂O₃ ceramics, and thus greatly reduced the ceramic sintering temperature. It is concluded that the main crystalline phase is pure α-Al₂O₃ without miscellaneous phase distribution. The distribution of fracture morphology is uniform without the existence of apparent stomatal, the dielectric constant and dielectric loss was studied.

Abstract: In this paper, nano-copper/paraffin thermosensitive composite materials were prepared by high-energy ball milling, and pressed into the glass cylindrical tube by hot press molding. The micro-morphology and particle shape and microstructure of composite particles were observed by SEM, FI-IR, etc, the temperature sensibility of thermosensitive composite materials were tested by self-manufactured thermosensitive testing device. It shows that the way by which high-energy ball milling are prepared, the composite particle coated with good results, dense arrangement of particles, copper particles on the paraffin structure does not produce damage. With copper mass ratio increasing, the thermal conductivity of temperature sensitive composite is improved.

Abstract: According to the actual demand of scare coal resources in our country, there is a vital significance in the study on strengthening separated process of high ash and difficult floatable coal. In terms of the limitations and deficiencies of process intensification and flotation efficiency at home and abroad, by means of experimental and analytical approaches, the surface properties of scarce coal slime separation process and process intensification were focused on in this paper. The association between mineral dissemination and variation during flotation process was also focused on. The superficial properties of difficult floatable coal slurry and the existing problems of the traditional reagents in the separating process of difficult floatable coal were analyzed. The reagents dosages suitable for coal slime with high ash were proposed. In the process, kerosene and octanol were respectively taken as collector and frother. The conclusions were obtained that kerosene dosage was 320g/t, Octanol dosage was 110g/t, flotation concentration was 100g/L, and inflation volume was 0.37m3/m2•min.