Papers by Keyword: HR-TEM

Abstract: Aluminium alloys are somehow the workhorse among light metals: spreading from castable, work hardenable to age-hardenable alloys, a wide panel of alternatives is available for the users. Nevertheless, continuous improvement of these alloys is ongoing, looking for higher strength, wider service temperature ranges, and suitability for new manufacturing processes.Likewise, a better knowledge of microstructure and ‘finer’ effects have to be encompassed.A proper multiscale approach and competent preparation are advisable for the best interpretation of the performances of new or ‘revised’ alloys.In this work a case study is presented in which multiscale approach has been used in order to explain the behavior of relatively widely used alloys, and also the problems and solution adopted in order to obtain the best results from microstructural analyses.Wrought age hardenable alloys were analyzed to have a better comprehension of ‘high temperature’ evolution of microstructure. The overall appearance of the microstructure was first identified by optical microscopy. Scanning Electron Microscopy (SEM) was involved to analyze grain size, type and size of secondary phases and texture. The results supported modeling studies related to the effect of grain size and texture. Finally, High Resolution Transmission Electron Microscopy (HR-TEM) investigations helped to understand the modification in the decay of mechanical properties upon extended overaging.

Abstract: A poly(propyleneimine) based dendrimer was synthesised and successfully functionalised with a copper centre within its branches. The dendrimer and corresponding metallodendrimer were successfully characterised using FTIR, HR-TEM and HR-SEM in order to determine the effect of the inclusion of copper into the dendritic structure. The incorporation of copper caused crystallinity as revealed in the HR-TEM and a sheet-like morphology as shown in the HR-SEM images. The resulting metallodendrimer was then applied as an electrocatalytic platform for the sensing of a first line TB drug called isoniazid. This method was compared to a routine laboratory detection using UV-Vis and was found to be much more sensitive to trace amounts of isoniazid in solution. The electrochemical detection was found to have a limit of detection (LOD) of 0.233 nM compared to 11.47 nM using the Ultraviolet-visible spectroscopy method.

Abstract: The nanocrystalline orthorhombic LiMnO2 was successfully synthesized with the raw materials of MnO2, Mn (CH3COO)2 and LiOH by hydrothermal synthesis method, which has the properties of small size, less stacking faults and single phase. High resolution electron microscopy images show that along the b axis of the orthogonal LiMnO2, MnO6 and LiO6 octahedron arrange alternately and regularly. The orthorhombic LiMnO2 is proved to be p-type semiconductor by the Hall test. XPS tests indicate that the trivalent Mn in the o-LiMnO2 is in the high-spin state. And the magnetic study shows that there is reentrant spin glass behavior in o-LiMnO2. The contrast study of Raman spectroscopy and magnetic susceptibility shows that the characteristic mode softening of structural phase transition corresponds to the magnetic phase transition temperature, indicating a possible interaction between phonons and spin.

Abstract: Flame synthesis of carbon nanotubes and nanocapsules is demonstrated via a pyramid-shaped pyrolysis flame. The mixture of CO, H₂, and nebulized catalyst raw material reacts in a high temperature environment formed inside the frustum of pyramid-shaped reactor heated by premixed flame of C₂H₂ and air outside. A sampling substrate inserted into the incomplete combusting flame of central reacting mixtures can gain the samples of carbon nanotubes and nanocapsules. The effect of sampling time and catalyst concentration is revealed via Field emission scanning electron microscope (FE-SEM) and High-resolution transmission electron microscopy (HR-TEM). 5-mins sampling time and 0.5/50 (Fe(CO)₅/C₂H₅OH, volume ratio) of catalyst concentration is the most appropriate for carbon nanotubes synthesis. In addition, it is to say that catalyst concentration is the most important one among all the factors that can be used to determine whether the main products are carbon nanotubes or nanocapsules, and the structures of nanocapsules are also analyzed in detail.

Abstract: Pyramid shaped pyrolysis flame is a new method for carbon nanotubes synthesis. Oxy-acetylene flame outside the frustum of pyramid shaped reactor provides the necessary high temperature environment, while carbon monoxide is used as the source of carbon, iron pentacarbonyl (Fe(CO)5) as the source of catalyst precursor in reactor. In this experimental, substrate is the platform on which carbon nanotubes produced. The locations of 304 stainless steel and 201 stainless steel as substrates stayed in flame, 304 stainless steel pretreated or not, and different thickness of red copper and brass were studied. The results of 304 stainless steel substrate at the height of 10mm are the best, comparing with others at 7mm, 5mm, and 0mm heights. Although using 201 stainless steel as substrates has the same results, the results of it are not as good as 304 stainless steel. Pretreated 304 stainless steel as substrate can gain better properties of carbon nanotubes. Different thickness of brass and red copper can not get carbon nanotubes, only copper oxide on the surface of red copper while particles on brass.

Abstract: This article describes the analysis of the polytype transformation of SiC ingot. We analyzed the sample by Raman spectroscopy and TEM observation. The result of the analysis shows the polytype is transformed from 4H-SiC to 6H-SiC, and then returned to 4H-SiC. We found that the direction of the c-axis is not the same as the growth direction of the ingot. And also we found the existence of 8H-SiC at the interface between 6H-SiC and 4H-SiC region by the selected area diffraction pattern and confirmed it by HR-TEM observation.

Abstract: We have achieved the first successful growth of 2H-SiC single crystals using the C-Li-Si melt system. Li-Si melt, whose melting point is lower than 1000 oC, was chosen because the 2H-SiC polytype is more stable at lower temperatures than other polytypes such as 3C-, 4H-, and 6H-SiC. Many hexagonal-shaped crystals of approximately 100 m in diameter were observed via a scanning electron microscope (SEM). A high resolution transmission electron microscope (HR-TEM) lattice image of the grown crystals showed a periodical structure with A-B stacking along the <0001> direction. These results indicated that the Li-based flux was useful for growing bulk 2H-SiC single crystals.