Search results for "Metallurgy"
showing 10 items of 1419 documents
Preliminary study on the laser cleaning of stainless steels after high temperature oxidation
2000
Abstract The objective of the present work was to estimate the influence of pulsed laser irradiation on the removal of the oxide layer, which is developed on the surface of stainless steels during their exposure to high temperature oxidation. In general, this layer is a protective one, mainly against corrosion. However, in many manufacturing applications or maintenance work, the removal of the oxides is necessary; for example, the metallic surfaces should be cleaned before welding, otherwise the presence of oxides increases the tendency to brittle behaviour of the joint. In this study, a pulsed Nd:YAG laser (λ=1.064 μm, 10 ns) was used for the surface cleaning of three stainless steels with…
Ti-Al Membranes for Microfiltration
2016
Porous membranes made of Ti – 48 at. % Al intermetallic compound was obtained by elemental powder synthesis. These disks can be used as microfiltration membranes due to their low pores size and interconnected porosity. During this study titanium (purity 99.5%) and aluminum (purity 99 %) with low particle size range were mixed in corresponding ratios. The powder mixture was pressed at 500 MPa and the samples were heat treated in two stages. In the first step is the forming of Al3Ti compound by a solid state reaction at a temperature of 640 °C, slightly below the melting point of aluminum. In the second step the Ti-Al compound was formed at the temperature of 1300 °C and the sintering the por…
Properties of spark plasma sintered nanostructured Zn1+xSb
2011
Engineering materials with specific physical properties has recently focused on the effect of nanoscopic inhomogeneities at the 10 nm scale. Such features are expected to scatter medium and long-wavelength phonons lowering thereby the thermal conductivity of the system without simultaneously decreasing the charge transport (phonon–glass electron–crystal concept). A new Zn1+xSb nanophase obtained by a wet chemical approach was densified by spark plasma sintering (SPS). Investigations on compounds subsumed as “Zn4Sb3” always suffer from its low thermal stability and the contamination of the nanoparticles with solvents and additives used in the synthesis. In order to gain insight into this com…
Control of barium ferrite decomposition during spark plasma sintering: Towards nanostructured samples with anisotropic magnetic properties
2014
Abstract The sintering of barium ferrite (BaM) nano-sized powders by spark plasma sintering was studied. At the surface of the samples, an iron-rich layer (magnetite) was formed due to the decomposition of BaM and segregation in the secondary phases. To prevent the formation of secondary phases different protection layers between the graphite mould and the sample were used. Their effect on the sample microstructure was studied by X-ray diffraction and scanning electron microscopy. The most suitable protection layer was a highly dense sintered disc of aluminium oxide. Using this dense protection layer, sintered discs of BaM with 82% of theoretical density and grains of 90 ± 50 nm were obtain…
Nanostructured Alumina from Freeze-Dried Precursors
2010
Nanocrystalline alumina has been obtained on the 100 g scale by thermal decomposition of precursors resulting from the freeze-drying of aqueous solutions of different aluminum-containing products, namely aluminum acetate and aluminum L-lactate. Samples prepared at different temperatures (from 873 to 1573 K in steps of 100 K) were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and surface area measurements. In the acetate case, the transformation sequence involves the formation of θ-Al 2 O 3 as an intermediate phase between γ-Al 2 O 3 and α-Al 2 O 3 , whereas this θ phase is not observed in the lactate case. TEM…
Characterization of the Solid State Properties of Anodic Oxides on Ta-Nb Alloys as a Function of the Anodizing Conditions
2011
Tantalum oxide, niobium oxide and Ta-Nb containing mixed oxides were grown by anodizing sputter-deposited TaxNb(1-x) alloys with 0 ≤ x ≤ 1. A photoelectrochemical investigation was performed in order to estimate the band gap values of the oxides as a function of their composition as well as to estimate their flat band potential. Differential capacitance curves were recorded for all the investigated oxides in a wide range of electrode potential and for several frequencies of the alternative signal. The dependence of C on the applied potential and a.c. frequency was interpreted on the basis of amorphous semiconductor Schottky barrier, and allowed to estimate the dielectric constant of the inv…
Ohmic contacts on n-type and p-type cubic silicon carbide (3C-SiC) grown on silicon
2019
This paper is a report on Ohmic contacts on n-type and p-type type cubic silicon carbide (3C-SiC) layers grown on silicon substrates. In particular, the morphological, electrical and structural properties of annealed Ni and Ti/Al/Ni contacts has been studied employing several characterization techniques. Ni films annealed at 950 degrees C form Ohmic contacts on moderately n-type doped 3C-SiC (N-D similar to 1 x 10(17) cm(-3)), with a specific contact resistance of 3.7 x 10(-3) Omega cm(2). The main phase formed upon annealing in this contact was nickel silicide (Ni2Si), with randomly dispersed carbon in the reacted layer. In the case of a p-type 3C-SiC with a high doping level (N-A similar …
Changes of lead silicate glasses induced by leaching
1998
Abstract The structural differences in the surface region between freshly fractured and leached silicate glasses containing 16.7, 18.8 and 44.4 mol% PbO, respectively, were investigated by photoelectron spectroscopy (XPS). The optical properties and the thicknesses of leached layers were determined by reflection measurements. The binding energies of the O1s signal components for untreated samples can be ascribed to non-bridging (NBO) and bridging (BO) oxygen and oxygen associated with lead as network former (OPb). The binding energy of OPb was found to be 529.1 ± 0.2 eV. For quantitative conclusions, relative XPS sensitivity factors were determined for oxygen, silicon and lead in these glas…
Effect of silicon on corrosion resistance of Ti–Si alloys
2011
Abstract The corrosion resistance of Ti–Si alloys has been studied in acid solutions and the alloys exhibit a high resistance to corrosion. SEM examinations combined with EDAX allowed to conclude that the passive films on Ti–Si alloys are mainly composed of TiO 2 /SiO 2 oxides. XPS analysis indicated the formation of Si–O and Si–O–Ti bonds in the passive film, respectively corresponding to SiO 2 and Si-doping TiO 2 . The effect of silicon on the corrosion was correlated to the formation of a stable SiO 2 film, Si-doping on TiO 2 and the extended lattice imperfections formed along TiO 2 /SiO 2 grain boundaries and phase-boundaries. The calculated donor densities based on the point defect mod…
Residual crystalline silicon phase in silicon-rich-oxide films subjected to high temperature annealing
2002
Structural properties of silicon rich oxide films (SRO) have been investigated by means of micro-Raman spectroscopy and transmission electron microscopy (TEM). The layers were deposited by plasma enhanced chemical vapor deposition using different SiH4/O2 gas mixtures. The Raman spectra of the as-deposited SRO films are dominated by a broad band in the region 400-500 cm-1 typical of a highly disordered silicon network. After annealing at temperatures above 1000°C in N2, the formation of silicon nanocrystals is observed both in the Raman spectra and in the TEM images. However, most of the precipitated silicon does not crystallize and assumes an amorphous microstructure. © 2002 The Electrochem…