Optics: measuring and testing – With plural diverse test or art
Reexamination Certificate
1999-12-13
2001-12-25
Evans, F. L. (Department: 2877)
Optics: measuring and testing
With plural diverse test or art
C356S301000
Reexamination Certificate
active
06333784
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The Government has rights in this invention pursuant to a contract awarded by the Department of Energy.
This invention relates to the field of analytical testing of the chemical composition of a sample. In particular, the present invention relates to a device for performing Electron Spectroscopy for Chemical Analysis (ESCA) and Raman spectroscopic studies.
2. Background of the Invention
The molecular composition of corrosion films and deposits on metal surfaces has been of interest for many years. In particular, it is well known that the life of a power generation plant can be extended if corrosion can be controlled to a point of minimization or elimination. To control corrosion, the corrosion products must first be accurately identified. This information can then be used with supplemental process information to identify and arrest the chemical mechanism from which corrosion products form in a system. Typically, corrosion products on metal surfaces are characterized by a combination of a host of analytical techniques which include, in part, Auger, X-ray Diffraction (XRD), Electron Spectroscopy for Chemical Analysis (ESCA), and most recently, Raman spectroscopy. Each of these analytical techniques provides a limited amount of information and neither technique alone can be used to unambiguously identify the compounds present in a corrosion film or deposit. For example, Auger provides elemental information that requires the analyst to hypothesize a molecular composition which must be confirmed by a secondary technique. XRD provides molecular composition information but is highly sensitive to (1) material concentration (the limit of detection is approximately 2-3%), (2) material composition (the technique cannot detect. amorphous material), and (3) sample geometry (sample face curvature and roughness degrade the spectra). As a result, the XRD technique cannot be used to unambiguously determine the true molecular composition of a corrosion product. The ESCA technique provides direct molecular composition information on all types of materials (including amorphous materials) by measuring molecular field dependent binding energies of atoms, but can not readily distinguish between various oxidization states of some elements such as iron (ESCA cannot accurately distinguish between Fe
2+
and Fe
3+
). Because most corrosion products in a power generation plant consist of iron oxides and various doped iron oxides, the ESCA technique can only be used to speculate on the true molecular nature of iron oxide compounds present in a corrosion product from such a system. Finally, Raman spectroscopy provides molecular information on all types of materials (including amorphous materials and glasses) but cannot detect molecules that are not amenable to an internal dipole change (such as Cu
2
S). As a result, it cannot be guaranteed that the Raman technique will detect all compounds present in a corrosion product.
ESCA and Raman spectroscopy synergistically complement each other in the chemical analysis of corrosion products on metal surfaces. In this case, molecular composition analysis information that cannot be obtained by one technique can be obtained by the other to give the most complete and unambiguous analysis of a corrosion product sample. For example, ESCA cannot readily distinguish between Fe
2+
and Fe
3+
based compounds whereas Raman spectroscopy produces well resolved unique vibrational fingerprint. spectra for most Fe
2+
and Fe
3+
corrosion product compounds such as &agr;-FeOOH, &bgr;-FeOOH, &ggr;-FeOOH, Fe(OH)
2
, Fe
2
O
3
and Fe
3
O
4
. As a second example, ESCA can identify that a material contains phosphorus and oxygen but cannot distinguish between the various types of phosphates such as PO
4
3−
, HPO
4
2−
, and phosphate from NaFePO
4
. Raman, on the other hand, produces clearly defined spectra for these species. Finally, and in contrast, ESCA can identify compounds such as Cu
2
S which cannot be detected by the Raman technique because such symmetrical compounds are not amenable to internal dipole changes which are needed for Raman analyses. Therefore, these two techniques synergistically complement each other and the integration of these two techniques results in a powerful analytical tool what will enable rapid, accurate, and unambiguous identifications of the chemical compositions of corrosion films or deposits in one single analysis without the need to use any other analytical techniques to confirm the results.
It is impractical to perform ESCA and Raman measurements on separate ESCA and Raman instruments because (1) the need to break the high vacuum of the ESCA instrument to transfer the sample to the Raman spectrometer will subject any newly exposed corrosion product to oxidizing room air which will compromise the sample integrity and produce erroneous results, and (2) the inability to accurately position the sample on both instruments so that both techniques are obtaining data from precisely the same location on the specimen.
Accordingly, a need remains for an integrated analytical instrument in which both ESCA and Raman measurements can be performed without exposing samples to air, and without the need for repositioning the sample between ESCA and Raman measurements. An integrated ESCA/Raman analytical instrument is one in which both ESCA and Raman analyses are performed on corrosion products on specimens located in a vacuum chamber. The ESCA/Raman system enables the rapid acquisition of molecular corrosion films and deposits on metal specimens.
SUMMARY OF THE INVENTION
In order to meet this need, the present invention is an integrated ESCA/Raman analytical instrument in which both ESCA and Raman analyses are performed on corrosion products on specimens located in a vacuum chamber. The instrument contains the hardware required to perform both techniques, including an X-ray source, an electron lens, an electron detector, an ion gun, a fiber optic probe linked to a laser light source, and a fiber optic probe linked to a monochromator and a visible light detector. The ion gun is used to sputter through films and deposits on metal surfaces. The sputtering can be done incrementally, so that both ESCA and Raman results can be obtained at various levels within the sample to obtain a cross-sectional composition profile. In ESCA analysis of a given level, the X-ray source produces X-rays of various energies which, when aimed at a sample, cause the sample to eject electrons. These ejected electrons are collected and counted by the electron lens and detector, respectively. The energies of the ejected electrons are used to identify the elements present, and the numbers of the ejected electrons are used to quantify the elements present. Monochromatic light from the laser, transmitted through a laser fiber optic cable, is directed through a laser light delivery probe and focused by lenses onto the sample. The resulting Raman scattered light emitted by the sample is collected by lenses and transmitted into a scattered light collection probe and a monochromator fiber optic cable to a monochromator and a detector. The absolute energies of the Raman shift peaks are used to identify the molecular composition of the material causing the Raman spectrum, and the intensities of the peaks can be used to quantify the material.
The ESCA/Raman analytical instrument can be used to obtain rapid chemical molecular information from films and deposits on any material surface. In particular, an ESCA/Raman system is of value for, among other applications, evaluating corrosion deposits and films formed on metal component surfaces from power generation plants. Typically, ESCA is used to sputter through films and deposits on metal surfaces and to perform molecular compound profiling of the corrosion material which may be layered. Sputtering is performed in step increments through the films or deposits. ESCA is performed at each step increment to obtain molecular composition depth profiling. This process is r
Allison David A.
Blasi Raymond J.
Caress Virginia B.
Evans F. L.
Gottlieb Paul A.
The United States of America as represented by the United States
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