Search results for "Microstructure"
showing 10 items of 707 documents
Low temperature catalytic combustion of propane over Pt-based catalyst with inverse opal microstructure in microchannel reactor
2007
A novel Pt-based catalyst with highly regular, periodic inverse opal microstructure was fabricated in a microchannel reactor, and catalytic testing revealed excellent conversion and stable activity for propane combustion at low temperatures.
Spray pyrolytic deposition of ZnO thin layers composed of low dimensional nanostructures
2010
Abstract ZnO nanolayers composed of fine nanostructures have been successively grown by spray pyrolytic deposition at 300 ∘ C over amorphous glass substrates. As deposited samples were analysed by scanning electron microscopy (SEM), showing a granular morphology with grain size in the limit of the microscope resolution. CL measurement shows a broad near band edge (3.4 eV) emission of ZnO in the UV region and the defect level emissions in the green region of the spectrum. The use of intermittent spray pyrolytic deposition is shown as an alternative to increase the homogeneity of the samples when temperatures near to the precursor pyrolytic decomposition is selected, long depositions times a…
The Effect of Building Direction on Microstructure and Microhardness during Selective Laser Melting of Ti6Al4V Titanium Alloy
2021
AbstractDuring the last few years, additive manufacturing has been more and more extensively used in several industries, especially in the aerospace and medical device fields, to produce Ti6Al4V titanium alloy parts. During the Selective Laser Melting (SLM) process, the heterogeneity of finished product is strictly connected to the scan strategies and the building direction. An optimal managing of the latter parameters allows to better control and defines the final mechanical and metallurgical properties of parts. Acting on the building direction it is also possible to optimize the critical support structure. In particular, more support structures are needed for the sample at 0°, while very…
Effect of additives on the crystallization of cordierite-based glass-ceramics as glazes for floor tiles
2003
Abstract The effect of several additives such as fluxes and/or nucleants on a parent glass with composition located in the primary field of cordierite within the quaternary system CaO–MgO–Al 2 O 3 –SiO 2 has been examined. Crystallization path of glasses was determined by differential thermal analysis (DTA) and X-ray powder diffraction (XRD). Pressed pellets of powdered glasses containing different additives were submitted at thermal treatments up to 1200 °C. The microstructural development at several temperatures was followed by field emission scanning electron microscopy and energy-dispersive X-ray analysis. The results shown that additions of TiO 2 as nucleant and/or B 2 O 3 as flux to a…
Crystallization behaviour and microstructural development in ZrSiO 4 and V-ZrSiO 4 solid solutions from colloidal gels
2000
Abstract Zircon and vanadium-doped zircon blue pigments were prepared by heat treatment of gel precursors. Gels with nominal compositions Vx-ZrSiO4 with x=0.0, 0.002, 0.004, 0.02 and 0.2 were prepared by formation of a silica coating on zirconia colloidal particles previously obtained. The crystallization behavior and microstructural evolution were studied using X-ray powder diffraction (XRD), energy dispersive X-rays microanalysis (EDX), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The results indicated that the vanadia loading in the precursor gels speeds up the crystallization of the vanadium-co…
Synthesis of self-assembled α-GaOOH microrods and 3D hierarchical architectures with flower like morphology and their conversion to α-Ga2O3
2015
Abstract This report reveals the methodology for the fabrication of α-GaOOH micro rods and micro flowers from gallium nitrate with two different complexing agents. α-GaOOH self-assembled 3D hierarchical architecture, comprising of nanorods and nanoribbbons with a flower like morphology, is fabricated under benign hydrothermal conditions. Calcination of α-GaOOH results in formation of α-Ga 2 O 3 with the retention of morphology. Both gallium oxyhydroxide and gallium oxide microstructures were analyzed with SEM, EDX, TEM and powder X-ray diffraction. α-Ga 2 O 3 micro flowers are furnished with nanorods having ordered diamond like cross section with a diagonal length proportion of 2:1. The hyd…
Tailoring the microstructure and mechanical properties of Ti–Al alloy using a novel electromagnetic stirring method
2006
The effect of melt convection during the solidification of Ti45Al55 alloys was investigated in terms of microstructure evolution and the resulting mechanical properties. The samples were subjected to conventional induction melting as well as enhanced melt stirring by an external magnetic field using a specially designed floating zone arrangement. The stirred samples showed a significant improvement of plastic deformability. A strong change in the morphology from dendritic to spherical and an increased properitectic phase fraction were observed after stirring.
Particle size and morphology control of the negative thermal expansion material cubic zirconium tungstate
2009
Cubic ZrW2O8 is a negative thermal expansion (NTE) material that is of interest as filler in controlled thermal expansion composites. It is easily accessible from a hydrated precursor, ZrW2O7(OH)2·2H2O, which can be obtained by hydrothermal synthesis. Different reaction conditions were investigated to gain control over the morphology, and to minimize the particle size. Optimized procedures resulted in rod-shaped particles with widths of 10–30 nm and lengths of 200–500 nm, which showed little agglomeration. The particle size and morphology of the precursor are preserved during conversion to the NTE phase at 600–650 °C.
An X-ray powder diffraction study of the microstructural evolution on heating 3:2 and 2:1 mullite single-phase gels
2006
Single-phase gels with compositions 3Al2O3·2SiO2 and 2Al2O3·SiO2 were prepared by gelling mixtures of aluminium nitrate and tetraethylorthosilicate. Gels were fast heated at different temperatures between 900°C and 1600°C. The phase transformation and microstructural changes of both mullite precursor gels over the temperature range were followed by X-ray powder diffraction (XRD), lattice parameter determination (LP), and scanning and transmission electron microscopies (SEM and TEM). The distribution of crystallite sizes and strains were determined by linewidth refinements of X-ray diffraction patterns using the integral breadth method of Langford and the Warren-Averbach analysis. XRD of bot…
Extremely efficient evaluation of chromatic dispersion in realistic photonic crystal fibers
2004
We present a fast and accurate procedure for the evaluation of chromatic dispersion in photonic crystal fibers. It combines an iterative Fourier technique to compute the propagation constant at any fixed wavelength and an analytical approach to calculate its derivatives.