Optics: measuring and testing – By dispersed light spectroscopy – With sample excitation
Patent
1997-02-24
1998-08-25
Nelms, David C.
Optics: measuring and testing
By dispersed light spectroscopy
With sample excitation
356318, G01N 2163
Patent
active
057988323
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for determining the composition and concentration of elements in material samples, in particular for determining the concentration or the presence of precious metals in unsorted metal scrap by means of laser-based plasma emission spectroscopy, as well as a device therefor comprising a high-power laser, a spectrometer and a measuring head including integrated radiation optics.
BACKGROUND OF THE INVENTION
The detection of element concentrations near the surface through spectral analysis of laser-induced plasma is discussed in the relevant literature under the key words of LIBS (=laser-induced breakdown spectroscopy) and laser spark spectroscopy. Such processes are used in particular for analysing metal particles. The specification of German laid-open patent application DE-OS 37 18 672 A1 for example discloses a process for determining or analysing the composition of metal particles which one after the other pass through a test line, in which said particles are subjected to a pulsed laser beam, partly evaporated to plasma and the plasma spectral lines are analysed to identify the metal particles. In this known process, a certain small wavelength range or a certain wavelength is filtered out of the total radiation emitted by the plasma and only the intensity of the partial radiation filtered out, i.e. only a certain wavelength or wavelength range is compared with an example to obtain a qualitative analysis of the elements contained in the sample.
A process described in the specification of German laid-open patent application DE-OS 40 28 102 A1 likewise relates to the analysis of metal particles of different material compositions. By means of a pulsed laser, a plasma is generated, thus ablating metal from the metal to be analysed. Discrete spectral lines or spectral line ranges are also filtered out of the plasma line spectrum. In doing so, a characteristic value is formed according to an algorithm based on the radiation intensities of the wavelengths of the spectral lines or spectral line ranges filtered out, and a sorting signal is obtained by comparing said characteristic value with given limits. Also in this process the metal particles are subjected to a qualitative analysis.
The disadvantages of these known processes are that they are merely intended for conducting qualitative analyses, with low accuracy of the resulting analyses. A high accuracy of the analysis is not required for said known processes since they are only aimed at producing a sorting signal for coarsely categorizing particles of different metals into certain element groups. However, it has turned out that a merely qualitative analysis of materials such as metal particles or metal scraps is no longer sufficient to ensure an economically reasonable separation and reclaiming of e.g. metallic raw materials.
The specification of German patent DE 41 18 518 C2 describes a process for conducting the laser-based emission spectroscopy in which plasma parameters such as plasma temperature and plasma density are measured. In order to obtain a quantitative analysis, the emission spectra are only to be measured in defined plasma states which are produced by influencing the intensity of the laser radiation which forms the plasma. One shortcoming of this process is that a lot of constructive work and calculations are required for carrying out the process, resulting in a noticeably increased fault liability of the process and the required device.
It is the object of the present invention to provide a process of the above specified type by means of which a simple quantitative and qualitative analysis of high accuracy can be conducted.
It is a further object of the invention to provide an device of the above specified type.
Known devices for determining the composition and concentration of elements by means of laser-based plasma emission spectroscopy comprise a source of laser light generating pulsed laser beams, one or several spectral filters with respective spectral detectors as well as
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Time-Resolved Laser Induced Breakdown Spectroscopy of Iron Ore--K.J. Gant et al. Dec. 10, 1990, vol. 44 No. 10.
Hnilica Klaus D.
Schneider Klaus
Nelms David C.
NIS Ingenieurgesselschaft MBH
Smith Zandra V.
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