Claude Merlet

An accurate computer correction program for quantitative electron probe microanalysis

The aim of this paper is to present a practical and accurate program of correction based on a new mathematical description of φ(ϱz), which allows a global correction combining atomic number and absorption correction [ZA]. Characteristic and continuum fluorescence corrections are also included to complete the program. Elements of atomic number in the range 4 <Z < 92 and X-ray emission linesKα,Kβ,Lα,Lβ,Mα andMβ are taken into account by the program which is especially designed for difficult cases (light elements, low overvoltages, low accelerating voltages).This correction program written in Fortran is designed to work off line under DOS or WINDOWS graphic operating systems on PC compatible microcomputers. The WINDOWS user interface environment makes the software easy to use. The computation and plot of φ(ϱz) depth distribution function as well as the printing of physical parameters enable the user to easily optimize the experimental conditions.This procedure has been tested on various databases (Pouchou and Pichoir, Love et al. and Bastin et al.) for medium to heavy elements. For the light elements (O, C andB) Bastins database has been used. The results presented furthermore reveal the good accuracy of the method and allow a comparison with other correction procedures.

Distribution of niobium, tantalum, and other highly incompatible trace elements in the lithospheric mantle: The spinel paradox

Because its crystal structure is unfavorable to large cations, the contribution of chromium-spinel to the trace-element budget of mantle rocks is generally thought to be negligible. Here we present a conflicting picture of trace-element distribution in spinel peridotites, emphasizing the strong capacity of this mineral to trap highly incompatible elements, such as Nb, Ta, Rb, Ba, and U. This paradox is due to the existence of a very thin reactional layer (<10 μm thick) coating the surfaces of spinel crystals and concentrating these elements. Our detailed study of a peridotite from the Ronda massif, Spain, and five xenoliths from the East African Rift, Ethiopia, has revealed that this layer is dominantly composed of titanium oxides and phlogopite, hardly detectable by optical methods. In spite of their extremely low abundance in the rocks (e.g., 0.002–0.015% niobium rutile), these microphases account for 45–90% of the whole-rock budget for Rb, Ba, Nb, and Ta. The spinel rims are attributed to a metasomatic process involving pervasive percolation of silica-rich and K-rich small melt fractions in the lithospheric mantle. This process bears major implications for the genesis of the continental crust and Nb-Ta-depleted magmas such as arc lavas.

HFSE residence and Nb/Ta ratios in metasomatised, rutile-bearing mantle peridotites

We have constrained the residence of high field strength elements (Nb, Ta, Zr, Hf, Ti) in metasomatised peridotite xenoliths in basalts from SE Siberia using high-precision electron-microprobe analyses of accessory Ti-rich oxides and solution inductively coupled plasma mass spectrometry analyses of whole rocks and clinopyroxene. Highest Nb abundances (0.9^4.5%) were found in rutile, compared with 6 0.5% in armalcolite and loveringite and 6 0.1% in ilmenite. Mass-balance calculations indicate that only 1^5% of Nb and Ta in the rocks reside in major minerals and that the rest may be hosted by the Ti-oxides. The Nb/Ta values in the Ti-oxides ( ˛ 2^5% accuracy at Tav 1000 ppm) range significantly between individual grains in each sample (e.g. 11^37) but their averages are close to Nb/Ta in the bulk rock. Thus, the whole-rock Nb/Ta can be constrained from analyses of the Nb-rich phases. High ZrO2 (1^7%) was found in loveringite and rutile. However, these minerals alone do not control whole-rock Zr/Hf in the peridotites because, unlike the Nb^Ta pair, much of Zr and Hf also resides in pyroxenes. Loveringite typically has high La and Ce (up to 1.6 wt%) and may be an important light rare earth element host. Overall, the Ti-oxide micro-phases may be essential components in nondescript grain boundary materials that are believed to host much of the highly incompatible elements in some mantle rocks and play a role in the behaviour of those elements during melting and metasomatism. Whole-rock Nb/Ta values in most of the peridotites are higher than the chondritic ratio (17.5). A literature review finds largely chondritic and subchondritic Nb/Ta and Zr/Hf in abyssal and massif peridotites, consistent with an origin as partial melting residues (based on peridotite/melt partition coefficients). By contrast, superchondritic Nb/Ta, as well as high La/Yb, is common in mantle xenoliths, indicating that metasomatism may increase Nb/Ta, together with La/Yb, in the initially depleted peridotites. If the high Nb/Ta predominates in the lithospheric mantle (assuming most of it has been metasomatised), it may provide a reservoir complementary to those of asthenospheric mid-ocean ridge basalt-type mantle and continental crust, which both have subchondritic Nb/Ta. However, the lithospheric mantle is not likely to counterbalance the subchondritic reservoirs in the bulk earth, firstly, because of a much higher mass of the asthenospheric mantle and higher Nb and Ta in the crust, and secondly, because many metasomatised peridotites (including all samples in this study) have subchondritic Nb/La. fl 2002 Elsevier Science B.V. All rights reserved.

Quantitative Electron Probe Microanalysis: New Accurate Φ (ρz) Description

This study presents a new method of matrix correction, combining atomic number and absorption correction [ZA]. The procedure requires an accurate knowledge of the Φ(ρz)-distribution with mass depth (ρz) of primary X-rays generated in the target. The Φ(ρz)-expression is evaluated using experimental measurements based on tracer layers and a theoretical approach involving the Monte Carlo method.

Measurements of absolute L- and M-subshell x-ray production cross sections of Pb by electron impact

Absolute L- and M-subshell x-ray production cross sections of Pb have been measured for incident electron energies ranging from 3 to 38 keV. The experimental cross sections were obtained by measuring Lα, Lβ, Mα, Mβ and Mγ x-ray intensities emitted from ultrathin Pb films deposited onto self-supporting thin C films. Measurements were performed on two electron microprobes using wavelength-dispersive spectrometers. X-ray intensities were converted into x-ray production cross sections by using estimated values of the number of incident electrons, target thickness and spectrometer efficiency. Experimental results are compared with calculated cross sections obtained using different predictive formulae, and, whenever possible, with experimental data from the literature.

Combustion synthesis: a new route for repair of gas turbine components—principles and metallurgical structure in the NiAl/RBD61/superalloy junction

A new technique for repairing turbine blade materials based on combustion synthesis is described in this article. This process uses a local internal generation of heat provided by the NiAl combustion synthesis in order to rebuild damaged turbine components. In this study, a nickel base braze was inserted between a substrate of nickel base superalloy and a powders compact (Ni+Al). The heat released during the combustion synthesis gave rise to interdiffusion of the elements and consequently to formation of a metallurgical bonding. The nature of the phases formed during this process was investigated by the combination of the results of chemical analysis and thermodynamic calculations. In addition to the negligible energy requirement and rapidity of the combustion synthesis, this process allows the local treatment of the turbine components and thus minimises the temperature undergone by the whole piece.

Electron Probe Microanalysis of Thin Films and Multilayers Using the Computer Program XFILM

XFILM is a computer program for determining the thickness and composition of thin films on substrates and multilayers by electron probe microanalysis. In this study, we describe the X-ray emission model implemented in the latest version of XFILM and assess its reliability by comparing measured and calculated k-ratios from thin-film samples available in the literature. We present and discuss examples of applications of XFILM that illustrate the capabilities of the program.

Standardless semi-quantitative analysis with WDS-EPMA

A standardless semi-quantitative method for wavelength dispersive spectrometry (WDS) electron probe microbeam analysis was developed with a view to simplifying the analytical procedure required with this apparatus. Based on spectrum acquisition, this method is a way to obtain the sample composition in a short time with the advantages of the WDS system and maintaining reasonable accuracy. To this end, three specific algorithms were designed. The first algorithm was constructed to find automatically all the elements present in the sample and to select the appropriate X-ray line for each element. It needs to index automatically, with a good confidence level, all the peaks which are detected. The second was constructed to convert the X-ray peak area from the measured spectrum into X-ray peak intensity (normally used in WDS procedures) with a Gaussian function which is governed both by the characteristics of the crystal and by the X-ray line itself. This is essential to prevent any underestimation of the concentration due to the measurement of truncated peaks related to low sampling frequencies, and to improve the counting statistics by using all the information given by the spectrum. Finally, the sample composition was obtained with the calculation of the absolute intensity of the selected line which takes into account the spectrometer efficiency.

M-subshell ionization cross sections of U by electron impact

M-subshell ionization cross sections of U by electron impact with kinetic energies between 4 and 38 keV were determined experimentally. The cross sections have been deduced from high-resolution measurements of the M x-ray emission spectra resulting from the radiative decay of M-subshell vacancies. The experimental cross sections are compared with cross sections calculated within the plane- and distorted-wave Born approximations. The predictions of the distorted-wave Born approximation represent experimental measurements well within experimental errors.

Combustion synthesis: a new route for repair of gas turbine components—achievements and perspectives for development of SHS rebuilding

Abstract Repair techniques such as brazing diffusion remetalling (BDR) are extensively and successfully used in the aeronautical industry to extend the life of damaged turbine blades. Nevertheless, the development of new repair processes able to generate a reduction of costs and/or of the duration of the treatment cycles is a permanent objective. The basic advantages of the repair process based on the self-propagating high-temperature synthesis (SHS) are the rapidity, the self-generation of energy, the local treatment of the turbine component and the reduction in temperature by turbine component. This process ensures similar mechanical properties as traditional processes or at least sufficient for some applications. The purpose of this paper is to explain the principle of the SHS build-up process and through some examples to show the possibilities and the economical advantages offered. The build-up of a turbine blade tip and the simultaneous synthesis and joining of a NiCrAlY layer to a superalloy substrate are described.