Probe for plasma-based material analysis
Plasma researchers at the University of Applied Sciences and Arts (HAWK) and the University of Göttingen have developed a novel probe for non-destructive material analysis. The functional principle of this plasma-based material analysis is based on plasma spectroscopy. Since the elegant electrode configuration does not require a counter electrode on the specimen, no special sample preparation is necessary. With the help of a special plasma jet, a plasma is ignited towards the material surface, whose energy can be kept below the damage threshold of the material due to a special jet design. The sample composition is analyzed with a spectroscopic method, while the specimen-specific spectra are analyzed and correlated with reference spectra. In case of some methods, the examined sample may only have a certain thickness, since, for example, a counter electrode is required behind/under the sample (cf. plasma-assisted ionization spectroscopy) or the sample must have a certain shape, which either requires sample preparation or only allows an analysis of specific samples.
Common methods for material analysis are in most cases destructive. For example, in the case of laser-induced breakdown spectroscopy, a laser beam is used to irradiate the sample surface, whereby the sample material is evaporated into a plasma at the appropriate point and then spectroscopically analyzed. Other methods sometimes require the introduction of additives (cf. X-ray fluorescence) and/or a transmission of the sample (which usually only works with liquids, substances in solution or extreme thin samples). Hence, such methods can only be used in case of some material classes and/or have long integration times.
To realize a fast, versatile and especially non-destructive material analysis method, plasma researchers at HAWK and the University of Göttingen have developed a special probe which includes an atmospheric pressure plasma source in the form of a special plasma jet and a spectrometer. The plasma jet uses a honeycomb jet consisting of seven tubes (see Fig.1 B), in which only the inner one is exposed to a working gas, a protective gas is passed through the outer tubes that prevents an electrical flashover. Due to the special plasma jet configuration, the plasma energy can be kept so low that the sample surface is not damaged. A clever electrode configuration also allows the plasma to ignite without a counter electrode on or behind the sample, allowing the analysis of virtually any sample surface. With the help of an integrated spectrometer, the plasma spectra influenced by material-specific interaction are then analyzed and compared with corresponding reference spectra. With the help of the process, various types of wood, wood-plastic composites as well as polymers and polymer composites with detection rates of over 95% have already been successfully identified. By closing the lower opening of the probe and integrating corresponding inlets and outlets, the process could also be extended to gas or liquid analytical applications.
Abb.1: Probe for plasma-based material analysis (Source: Robert Köhler, HAWK)
- Non-destructive analysis of the material composition of samples
No sample preparation necessary
- Virtually possible on all sample surfaces and shapes
- Extension to the analysis of gases or liquids possible
- Analysis of organic and anorganic substances
Differentiation of wood species
- Analysis of wood-plastic composites, polymer materials and plastic composites
- Customs inspection (e.g. chemistry, medicines and drugs)
With a prototype of the probe, the process was successfully tested on various types of wood, wood-plastic composites as well as polymers and plastics. Detection rates of over 95% were achieved with the help of reference measurements.
Georg-August-University Göttingen Foundation under Public Law
Dr. Mirza Mackovic
Patent Manager Technology
Phone: +49 (0) 551 30 724 153
Tags: Plasma physics