Search results for "Mechanical engineering"
showing 10 items of 4245 documents
Sixfold coordinated phosphorus by oxygen in AlPO4 quartz homeotype under high pressure.
2007
International audience; AlPO4 belongs to the berlinite quartz homeotype family, which has been the subject of intense high pressure research triggered by the supposed existence of reversible pressure induced amorphization. New x-ray diffraction experiments, complemented with ab initio calculations, demonstrate the existence of two high pressure crystalline polymorphs and show that AlPO4 share the same two stage densification mechanism as silica. In first place a compact hexagonal sublattice of oxygen atoms is formed. In a second step the cations redistribute in the interstices giving rise to a monoclinic distorted CaCl2 phase. The most outstanding feature of the new phase is that phosphorou…
Iron Doped-ZrSiO4: Structural, Microstructural and Vibrational Characterization
2015
Fex-ZrSiO4 is known for the applications in the ceramic industry such as ceramic pigment. In this article, we focus our attention to the structural, microstructural and vibrational changes of Fex-ZrSiO4 from free-mineralizer precursors, treated at different temperatures in the range of 1100-1600 °C. The refinements of X-ray diffraction patterns show that Fe3+ cations were distributed into tetrahedral sites replacing Si4+. The evolution of the shape distribution analyzed by transmission electron microscopy, reveal a polyhedral morphology at 1100 °C during 3h. In comparison, well-rounded and homogeneous particle size was determined in the sample heated at 1600 °C during 24 h. On the other han…
Mechanically Activated SHS Reaction in the Fe-Al System: In Situ Time Resolved Diffraction Using Synchrotron Radiation
1998
The Mechanical Activation Self propagating High temperature Synthesis (M.A.S.H.S.) processing is a new way to produce nanocrystalline iron aluminide intermetallic compounds. This process is maily the combination of two steps ; in the one hand, a mechanical activation where the Fe - Al powder mixture was milled during a short time at given energy and frequency of shocks and in the other hand, a Self propagating High temperature Synthesis (S.H.S.) reaction, for which the exothermicity of the Fe + Al reaction is used. This fast propagated MASHS reaction has been in -situ investigated using the Time Resolved X - Ray Diffraction (TRXRD) using a X - ray synchrotron beam and an infrared thermograp…
Investigation of mechanically activated field-activated pressure-assisted synthesis processing parameters for producing dense nanostructured FeAl
2003
The parameters of the mechanically activated field-activated pressure-assisted synthesis (MAFAPAS) process, which were recently developed and patented for producing dense nanostructured materials, were studied in the case of the B2-FeAl intermetallic. Based on x-ray diffraction (XRD) experiments, residual stresses XRD analysis, relative density measurement, and secondary-electron microscopic observations, the optimal synthesis conditions (time, current intensity, and pressure) were studied. Fe + Al powders were comilled in a specially designed planetary mill to obtain a mixture of reactants at the nanoscale without the formation of any product. The milled mixtures were then subjected to a h…
Enhancement of self-sustaining reaction by mechanical activation: case of an FeSi system
1999
Mechanical high energy ball milling of an Fe2Si elemental powders mixture was used to activate a self sustaining combustion reaction or so-called self-propagating high-temperature synthesis (SHS) to form iron disilicide, a reaction for which the thermodynamic criterion is not favorable. A complete characterization of the milled powders before reaction was performed with energy dispersive X-ray spectrometry, specific surface measurements and X-ray diffraction profile analysis. Thermal and structural information describing the combustion front initiated by heating up a sample to 400°C in a Fe‐Si system is communicated. In order to isolate the phases involved in the gasless reaction, a time-re…
Which tool to distinguish transient alumina from alpha alumina in thermally grown alumina scales?
2005
International audience; Alumina scales constitute excellent protective barriers when they form on alumina-forming steels. If they keep tightly adherent to the underlying substrate, they isolate it from the surrounding aggressive atmosphere at high temperature. The protectiveness of the alumina scale is highly dependant upon its growth mechanism. The nucleation and transformation of transient alumina (mainly g-Al2O3 and y-Al2O3) is known to play an important role on alumina scale formation. It is therefore fundamental to characterise these transient alumina especially during the early stages of the oxidation process. The morphology of the transient alumina was observed by scanning electron m…
Extractive-Pyrolytic Method for Au/MeO<sub>x</sub> Nanocomposites Production
2014
Au/MeOx(MeOx- SiO2, Al2O3and TiO2) nanocomposites have been produced by the extractive-pyrolytic method. An organic extract – a solution of n-trioctylammonium tetrachlorolaurate ([Oct3NH]AuCl4) in toluene – was used as a gold-containing precursor. The produced samples were analyzed by IR spectroscopy, X-ray diffraction and scanning electron microscopy. The performed studies have shown that the mean size of the metal crystallites vary within wide limits: on Al2O3from 60 nm to 35 nm; on SiO2from 33 nm to 23 nm; on TiO2from 50 nm to 13 nm.
128-Channel Silicon Strip Detector Installed at a Powder Diffractometer
2004
Silicon strip detectors represent a new class of one-dimensional position-sensitive single photon counting devices. They allow a reduction of measurement time at the powder diffractometers by a factor up to 100 compared to instruments with a single counter, while maintaining comparable count statistics. Present work describes a 128-channel detector working with a standard diffractometer. The detector is 12.8 mm long and covers the angular range of 3.2 deg. We discuss the diffraction geometry in real and reciprocal space, the FWHM of diffraction peaks, and the background level. Measurements were made on standard samples and on complex samples of industrial importance (e. g., portland clinker…
COMPARING PARTICLE SIZE DISTRIBUTION ANALYSIS BY SEDIMENTATION AND LASER DIFFRACTION METHOD
2009
In this paper a brief review of the laser diffraction method is firstly carried out. Then, for 30 soil samples having a different texture classification sampled in Sicilian basin, a comparison between the two techniques is developed. The analysis demonstrated that the sand content measured by Sieve-Hydrometer method can be assumed equal to the one determinated by laser diffraction technique while an overestimation of the clay fraction measured by Sieve-Hydrometer method respect to laser diffraction technique was obtained. Finally a set of equations useful to refer LD measurements to SH method was proposed.
NUMERICAL-EXPERIMENTAL METHOD FOR THE ANALYSIS OF RESIDUAL STRESSES IN COLD-EXPANDED HOLES
2012
Hole cold expansion is a technique widely used to improve the fatigue life of components with holes, e.g. bolted or riveted joints. As it has been demonstrated in literature by analytical, numerical and experimental analyses carried out by several authors, the compressive residual stresses introduced by the hole cold expansion have a beneficial influence on both the static and the fatigue strength of the treated component, because they reduce significantly the typical stress peaks around the hole due to stress concentration. In the literature, various analyses of the residual stresses introduced by the hole cold expansion have been performed by using several methods such as X-ray diffractio…