Search results for "Microstructure"
showing 10 items of 707 documents
Phase separation as a key to a thermoelectric high efficiency
2012
This work elucidates the possible reasons for the outstanding, but never reproduced thermoelectric properties of the doped Ti(0.5)Zr(0.25)Hf(0.25)NiSn Heusler compounds. The structural investigations done via synchrotron X-ray diffraction measurements and scanning electron microscope measurements, which clearly show that the microstructure consists of three temperature stable C1(b) phases with possible semi-coherent interfaces, are presented. The exceptional thermoelectric properties are due to this intrinsic phase separation. It is possible to reproduce the high Figure of Merit values with ZT = 1.2 at 830 K. Furthermore, the influence of doping different elements on the Sn position in this…
STACKING-FAULTS IN VERY FINE PALLADIUM PARTICLES SUPPORTED ON PUMICE
1990
By means of an X-ray diffraction study, carried out with best-fitting procedures, of the asymmetry and peak maximum shifts of some reflections, stacking-faults in the FCC lattice of very fine palladium particles supported on pumice were detected using the Warren-Wagner-Cohen theoretical approach.
Stochastic multiscale model for carbonate rocks.
2007
A multiscale model for the diagenesis of carbonate rocks is proposed. It captures important pore scale characteristics of carbonate rocks: wide range of length scales in the pore diameters; large variability in the permeability; and strong dependence of the geometrical and transport parameters on the resolution. A pore scale microstructure of an oolithic dolostone with generic diagenetic features is successfully generated. The continuum representation of a reconstructed cubic sample of sidelength $2\phantom{\rule{0.3em}{0ex}}\mathrm{mm}$ contains roughly $42\ifmmode\times\else\texttimes\fi{}{10}^{6}$ crystallites and pore diameters varying over many decades. Petrophysical parameters are com…
Market efficiency and price discovery relationships between spot, futures and forward prices: the case of the Iberian Electricity Market (MIBEL)
2016
ABSTRACTThis paper analyses the relationships between prices from three different markets within the Spanish zone of the Iberian Electricity Market (MIBEL), namely futures, spot and over the counter (OTC) forward markets. The study focuses on three items: (i) contrasting the Weak-form efficiency hypothesis of the markets involved in the study, (ii) analysing the Semi-strong-form efficient market hypothesis (EMH) of the MIBEL futures market and (iii) examining the price discovery relationships between the series of prices of the considered markets.The empirical results confirm that 1-month-, 1-quarter-, 1-year-ahead futures and spot markets satisfy, generally, the Weak-form efficiency hypoth…
The timeline of trading frictions in the European carbon market
2012
We evaluate the quality of prices of EU-ETS, the most active European derivative market for greenhouse gas emissions allowances (EUAs). So far, this market has had two phases, a trial phase (from 2005 to 2007) and a commitment phase (from 2008 to 2012). The true value of a trial-phase EUA at the beginning of 2008 was inevitably zero because it could not be used in the commitment phase to cover emission targets. However, continued rumors of over-allocation of EUAs led to an early collapse of the market by May 2007. We study whether this market breakdown and the subsequent outbreak of the international financial crisis had a persistent effect on the quality of the commitment phase. We provide…
Why is equity order flow so persistent?
2015
Abstract Order flow in equity markets is remarkably persistent in the sense that order signs (to buy or sell) are positively autocorrelated out to time lags of tens of thousands of orders, corresponding to many days. Two possible explanations are herding, corresponding to positive correlation in the behavior of different investors, or order splitting, corresponding to positive autocorrelation in the behavior of single investors. We investigate this using order flow data from the London Stock Exchange for which we have membership identifiers. By formulating models for herding and order splitting, as well as models for brokerage choice, we are able to overcome the distortion introduced by bro…
Dissimilar joining of copper to stainless steel and TA6V to stainless steel by high power beams : understanding and modeling of physicochemical pheno…
2010
The present study is dedicated to the comprehension of the mechanism of materials mixing during dissimilar welding by high power beam sources. We have been interested in joining of two couples of metallic materials which present different metallurgical problems: •copper- stainless steel (miscibility gap, important difference in physical properties);•TA6V- stainless steel (oxidation on air, formation of intermetallic phases which made the joint brittle).For the first couple of materials, continuous laser Nd:YAG welding and electron beam welding have been applied. The experimental study of morphology evolution, composition, microstructure and mechanical properties has allowed establishing the…
Friction stir welding: a solid state joining process
2007
A wide experimental investigation on the friction stir welding of AA6082-T6 sheets is presented. In particular the influence of some of the most relevant process parameters was taken into account, with the aim to maximize the joint strength; furthermore the joint fatigue behavior was considered too. An accurate analysis on the obtained parts was carried out, with particular attention to the material microstructure evolution. The obtained results permitted to develop a proper FSW process engineering.
Analysis of the chemical and microstructural modifications effects on the hydro-mechanical behaviour of a lime-treated clay
2019
The paper presents the results of a characterization of kinetic characteristics of pozzolanic reaction with the aim to investigate the time-dependent modification of clay properties as a consequence of mixing with lime. Results of chemical analyses are in agreement with the increase of mechanical properties and with the observed microstructure modifications up to one year of curing time. The rate of development of pozzolanic reactions seems to be almost constant while the time required for their completion is dependent on the lime content. Pozzolanic products are responsible for the time reduction of swelling strain upon saturation as well as for the increases of yielding stress, stiffness …
Mechanical properties and microstructural study of homogeneous and heterogeneous laser welds in α, β,and α + β titanium alloys
2018
International audience; Heterogeneous welding has been investigated for three different couples of titanium alloys: α/α + β, α/β,andα + β/β. Plates of 100 × 60 mm and 1.6 or 1.8 mm thick were welded with a Yb:YAG laser. Tensile tests show that the resistance of the heterogeneous welded specimens was generally controlled by those of the weakest material except for the α + β/β where the ultimate tensile strength was approximately equal to the average value of both materials. In every case, the elongation of the welded sample was found to be smaller than that of the base metals. The rupture generally took place outside the weld metal and was found to be most of the time located in the alloy ha…