| 1. |
- Alberts, D., et al.
(author)
-
In-depth profile analysis of filled alumina and titania nanostructured templates by radiofrequency glow discharge coupled to optical emission spectrometry
- 2010
-
In: Analytical and Bioanalytical Chemistry. - : Springer Science and Business Media LLC. - 1618-2642 .- 1618-2650. ; 396:8, s. 2833-2840
-
Journal article (peer-reviewed)abstract
- The development of highly ordered and self-assembled magnetic nanostructures such as arrays of Fe or Ni nanowires and their alloys is arousing increasing interest due to the peculiar magnetic properties of such materials at the nanoscale. These nanostructures can be fabricated using nanoporous anodic alumina membranes or self-assembled nanotubular titanium dioxide as templates. The chemical characterization of the nanostructured layers is of great importance to assist the optimization of the filling procedure or to determine their manufacturing quality. Radiofrequency glow discharge (RF-GD) coupled to optical emission spectrometry (OES) is a powerful tool for the direct analysis of either conducting or insulating materials and to carry out depth profile analysis of thin layers by multi-matrix calibration procedures. Thus, the capability of RF-GD-OES is investigated here for the in-depth quantitative analysis of self-aligned titania nanotubes and self-ordered nanoporous alumina filled with arrays of metallic and magnetic nanowires obtained using the template-assisted filling method. The samples analysed in this work consisted of arrays of Ni nanowires with different lengths (from 1.2 up to 5 μm) and multilayer nanowires of alternating layers with different thicknesses (of 1-2 μm) of Ni and Au, or Au and FeNi alloy, deposited inside the alumina and titania membranes. Results, compared with other techniques such as scanning electron microscopy and energy-dispersive X-ray spectroscopy, show that the RF-GD-OES surface analysis technique proves to be adequate and promising for this challenging application. © 2009 Springer-Verlag.
|
|
| 2. |
- Bengtson, Arne, et al.
(author)
-
Comparison of GD-MS and LA-ICPMS direct solid sampling techniques for trace elemental analysis of steels
- 2013
-
Reports (peer-reviewed)abstract
- The objective of this project is to evaluate commercially available techniques for trace elemental analysis of steels using direct solid sampling. Such methods have the potential to increase sample throughput and thereby reduce analysis costs. Glow Discharge Mass Spectrometry (GD-MS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) were evaluated. Five certified reference materials (CRM) were selected for the experimental work; a high purity iron, a carbon steel and three high alloy steels. For both types of instruments, the sample set was first used for calibration, then run as unknowns several times in order to get sufficient statistics for the evaluation. The GD-MS measurements were carried out at the Thermo Fisher Scientific applications laboratory in Bremen. The LA-ICPMS work was carried out at KIMAB. Prior to the measurements reported here, the effects of varying instrumental parameters of LA-ICPMS were investigated in order to develop a suitable method for steels. The results show that both techniques are powerful methods for simultaneous determination of a large number of trace elements in steels. A limitation is that none of the techniques is capable of analysing C, N and O, due to gas leaks and contamination from materials in the sources. The overall performance in terms of precision and detection limits is better for GD-MS, but for several applications LA-ICPMS provides sufficient performance. Both techniques have instrumentally limited detection limits at the ppb level or below, but the results on the test samples mostly give considerably higher standard deviations, also at very low concentration levels. Therefore, the analytical accuracy for traces is more limited than one would expect based on the instrumental capabilities; typically in the low ppm range or slightly below. The most likely reason for this is the combination of material inhomogeneity and small sampling volumes. This affects LA-ICPMS the most, due to considerably lower sampling volume than GD-MS.
|
|
| 3. |
- Bengtson, Annika, et al.
(author)
-
Evolution and diversification related to rainfall regimes : diversification patterns in the South African genus Metalasia (Asteraceae-Gnaphalieae)
- 2015
-
In: Journal of Biogeography. - : Wiley. - 0305-0270 .- 1365-2699. ; 42:1, s. 121-131
-
Journal article (peer-reviewed)abstract
- AimThe Cape region is known for its exceptional species richness, although much remains unknown regarding the appearance of the modern Cape flora. One explanation is that floral diversification was influenced by the establishment of winter rainfall/summer arid conditions hypothesized to have occurred towards the end of the Miocene. We studied the evolution and diversification of the plant genus Metalasia (Asteraceae-Gnaphalieae), with the aim of testing whether radiation patterns may have been influenced by the climatic changes. LocationSouth Africa, with emphasis on the south-west. MethodsThe radiation of Metalasia was investigated using two approaches: a species diffusion approach, which estimated the ancestral areas by means of a relaxed random walk while sampling from extant distributions; and a discrete approach, in which distributions were defined according to the phytogeographical centres of the Cape region. Secondarily derived clock rates from an earlier Gnaphalieae study were used for calibration purposes. ResultsOur analyses date Metalasia to approximately 6.9Ma, after the Miocene-Pliocene boundary and the establishment of the winter rainfall/summer arid conditions. Metalasia consists of two sister clades: Clade A and Clade B. Clade B, which is endemic to the winter rainfall area, is estimated to have diversified c. 6.4Ma, whereas Clade A, with a main distribution in the all-year rainfall area, is considerably younger, with a crown group age estimated to 3.3Ma. Diversification rates suggest an early rapid speciation, with rates decreasing through time both for Metalasia and for clades A and B separately. Ancestral area estimations show a possible scenario for the radiation of Metalasia to its current diversity and distribution, with no conflict between results inferred from diffusion or discrete methods. Main conclusionsThe diversification of Metalasia is estimated to have begun after the establishment of the winter rainfall/summer arid conditions, consistent with its radiation having been influenced by changes in the climatic regime.
|
|
| 4. |
- Bengtson, Arne, et al.
(author)
-
Further Development of GD-OES for Surface and Depth Profile Analysis
- 2014
-
Reports (peer-reviewed)abstract
- Glow Discharge Optical Emission Spectroscopy (GD-OES) is a well established technique for Compositional Depth Profiling (CDP), very useful for in-depth elemental analysis of surface layers from 10 nm to 100 µm. It is fast, sensitive and fully quantitative. However, there are a few artefacts requiring further study to improve the accuracy and trueness of the method further, primarily for near-surface applications. Outgassing of volatile compounds present inside the source, mainly water and hydrocarbons, has been established to be a major cause of such artefacts. The most “problematic” element is hydrogen, for the following two reasons: 1) it “cools” the plasma even when present in small quantity and thereby affects the intensities of the emission from almost all other elements; 2) it is very reactive and forms molecular species with other light elements e.g. CH, NH and OH, having emission spectra overlapping several atomic analytical lines; causing “false” or exaggerated surface peaks of the corresponding elements. In this work, methods to reduce the outgassing of volatile compounds have been studied. Attempts to dry and clean the argon gas flowing into the source by means of a chemical filter gave no significant improvement. On the other hand, replacing the “standard” anode made of a copper-beryllium alloy with a pure copper anode was shown to reduce the outgassing significantly. To be more specific, the background signal from atomic hydrogen and associated artefacts are reduced, it is still possible that the amount of molecular hydrogen remains almost constant, without observable effects on the analytical signals. Since molecular emission can originate from the sputtered material of the sample itself, particularly organic coatings, an in-depth study of molecular emission in GD-OES was carried out. It was shown that background signals from such emission can be significantly reduced, provided that the instrument has spectral channels for the emitting molecular species installed. With such channels available, conventional “line interference correction” methods was found to be effective in reducing false elemental signals from molecular emission. Application of the pure copper anode and reduction of molecular background techniques to a heat treated zinc-base coating showed expected improvements in the near-surface part of the depth profile. However, for the major elements of technical importance, the difference compared with the original anode and analytical method was marginal. This is reassuring, since it means that the near-surface artefacts normally do not cause major analytical errors. The element that is most difficult to establish the “trueness” of depth profiles is nitrogen, especially if the surface layer is slightly porous. There are samples where an elevated signal from nitrogen in the top surface cannot be correlated to a vacuum leak, trapped air or molecular emission (CO). Investigations where samples are measured for total nitrogen with conventional techniques are very difficult, since the surface layers showing an elevated content are very thin. Further investigation of such samples with high vacuum techniques, e.g. SIMS, would be of interest. A second part of the project deals with advanced evaluation of depth profile data by means of “expert systems”. An expert system is a computer application that is able to perform tasks which are normally performed by human experts; in this case the aim is to be able to perform e.g. quality control with GD-OES without the need for a qualified human expert to interpret the data. There are several types of “computational statistics” methods that can be employed for such purposes, the most well known is probably multivariate analysis. Other methods can evaluate both numerical and other types of input related to classification based on technical properties, e.g. paint adhesion, scratch resistance etc. The objective of this work is to be able to classify samples according to such technical properties. All such systems need a “training set” of samples with known technical properties. In this work, a relatively large set of steel sheet samples with various zinc-based coatings were classified according to corrosion resistance. Form the GD-OES depth profiles, the coating weights of zinc, aluminium and magnesium were extracted in a data pre-treatment step. Using the rule-based classification algorithm “decision tree” 25 out 29 samples was correctly classified. This “proof of concept” work has shown that it is possible to predict certain technical properties based on a multi-element depth profile. This opens up the possibility for e.g. automated quality inspection of complex coating systems, but also the possibility to use GD-OES depth profiling more effectively as a tool in product development.
|
|
| 5. |
- Bengtson, Arne, et al.
(author)
-
Investigation of computational statistics for evaluation of PDA-OES data – final report of the project Innestyr 3
- 2014
-
Reports (peer-reviewed)abstract
- The aim of this project was to investigate the potential of applying computational statistics (“data mining”) methods to PDA – OES data to find correlation to defects in the final products as well as changes of parameters during the steelmaking process. The computational methods used were multivariate (MVA) data analysis and the rule-based methods “decision trees” and “neural nets”. The project was carried out in close cooperation with Outokumpu Stainless Avesta and the Royal Institute of Technology (KTH). PDA – OES data from sheet samples with and without surface defects were processed by all three methods, all showing statistically significant and consistent correlation. The formation of surface defects is positively correlated to the number of “medium” to “large” inclusions of the classes AlCaMg and AlCa i.e. mixed oxides of these elements. The second part of the research was an evaluation of variations in inclusion characteristics in different process stages using synthetic slags. A large number of samples were collected from experimental trials with two types of synthetic slags, and the conventional process without slag addition for reference. The samples were taken in the ladle furnace at three stages, and in the tundish in connection with the final test sample before casting. PDA – OES data from these samples were evaluated with MVA and decision tree methods. The results showed that the different process stages can be identified from the PDA-OES data with rather good certainty. No significant difference between the use of synthetic slags and the conventional process was detected. In the course of the evaluation work, it was also found that the computational statistics methods must be used with caution. The reason is that data due to “statistical noise” can be identified as significant, giving misleading results. Further work to reduce this problem will be necessary.
|
|
| 6. |
|
|
| 7. |
- Bengtson, Arne
(author)
-
LIBS compared with conventional plasma optical emission techniques for the analysis of metals – A review of applications and analytical performance
- 2017
-
In: Spectrochimica Acta Part B - Atomic Spectroscopy. - : Elsevier BV. - 0584-8547 .- 1873-3565. ; 134, s. 123-132
-
Journal article (peer-reviewed)abstract
- This review is focused on a comparison of LIBS with the two most common plasma Optical Emission Spectroscopy (OES) techniques for analysis of metals; spark OES and glow discharge (GD) OES. It is shown that these two techniques have only minor differences in analytical performance. An important part of the paper reviews a direct comparison of the analytical figures of merit for bulk analysis of steels using spark and LIBS sources. The comparison was carried out using one instrument with interchangeable sources, eliminating differences related to the optical system and detectors. It was found that the spark provides slightly better analytical figures of merit. The spark analysis is considerably faster, the simple design of the spark stand has enabled complete automation, both properties of great importance in the metallurgical industry for routine analysis. The analysis of non-metallic inclusions (NMI) with spark and LIBS is presented, in the case of the spark this has become known as Pulse Distribution Analysis (PDA). A very significant difference between the techniques is that the electrical spark typically evaporates ~ 100 times more material than a single laser pulse, resulting in complete evaporation of an NMI present in the evaporated metal. The major advantage of LIBS is that it is localised with very good lateral resolution. The major advantages of spark is that it is much faster (can be done simultaneous with the bulk analysis) and easier to quantify. Compositional Depth Profiling (CDP) is compared for GD-OES and LIBS. It is shown that for applications where GD-OES is well suited, e.g. coated metallic sheet, GD-OES still performs slightly better than LIBS. Similar to the case of NMI analysis, the major advantage of LIBS is the great lateral resolution. This allows elemental surface mapping, as well as CDP of very small areas on μm scale. One further advantage of LIBS is that samples of almost any material, shape and size can be analysed, whereas GD-OES has only limited capabilities for non-flat and small samples. A general conclusion of this review is that LIBS is not likely to replace spark and GD-OES in the foreseeable future, for applications where these techniques are well suited. On the other hand several new applications, particularly in the field of on-line monitoring of industrial processes, are making great inroads for LIBS in the metallurgical and manufacturing industries.
|
|
| 8. |
- Bengtson, Arne, et al.
(author)
-
Optical Emission – Pulse Distribution Analysis (PDA/OES) for applications to Aluminium alloys
- 2012
-
Reports (peer-reviewed)abstract
- The technique PDA/OES is briefly reviewed. It is based on detection of the signals from individual sparks in OES analysis, which usually comprises a few thousand sparks in each burn. Sparks hitting inclusions/particles of characteristic elemental composition give rise to “outliers” of higher intensity for “marker” elements characteristic of the particle type. The outliers are extracted by statistical analysis, and processed by the software to identify and quantify the particles. PDA/OES is used mainly in the steel industry, where the main interest is to detect and analyse non-metallic inclusions (NMI). In this work, PDA/OES has been tested for applicability to aluminium alloys. In this case the main interest is metallic particles, but there are also some types of NMI’s of interest. It was found that PDA functions in the same way as in steels, but there are several factors limiting the applicability. Firstly, the smallest detectable particles are about 1 μm diameter, and the particle number density should not exceed about 20000/mm3 for PDA to detect then as individual particles. In aluminium, many particles (precipitates) of interest are much smaller and present in much higher number densities. Secondly, the elements present in the metallic particles also exist as dissolved in the surrounding metal, giving a high and noisy background which limits the possibility to detect signals from the particles as outliers. These constraints has limited the applicability to metallic particles in the several μm range, using Fe as the “marker” element. However, for certain types of NMI it is likely that very small particles down to 1 μm can be detected. The experimental work has shown that the scanning spark technique OPA can provide additional useful analytical information. Macroscopic segregation at the mm – several cm ranges can rapidly be investigated in two dimensions. In combination with PDA, macroscopic “clusters” of particles can be mapped.The spark optical emission techniques PDA/OES and Original Position Analysis (OPA) have been investigated for application to aluminium alloys. PDA/OES has been optimised for detection and quantification of metallic particles in the several µm range with. The OPA technique has been evaluated for rapid determination of macroscopic segregation.
|
|
| 9. |
- Bengtson, Annika, et al.
(author)
-
Phylogeny and evolution of the South African genus Metalasia (Asteraceae-Gnaphalieae) inferred from molecular and morphological data
- 2014
-
In: Botanical journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4074 .- 1095-8339. ; 174:2, s. 173-198
-
Journal article (peer-reviewed)abstract
- Metalasia is a genus in tribe Gnaphalieae (Asteraceae), endemic to South Africa and with its main distribution in the Cape Floristic Region. The genus comprises 57 species and, with a number of closely related genera, it constitutes the Metalasia clade'. A species-level phylogenetic analysis is presented, based on DNA sequences from two nuclear (internal and external transcribed spacer: ITS, ETS) and two plastid (psbA-trnH, trnL-trnF) regions together with morphological data. Analyses combining molecular and morphological data attempt not only to resolve species interrelationships, but also to detect patterns in character evolution. Phylogenetic analyses corroborate our earlier study and demonstrate that Metalasia is formed of two equally sized, well-supported sister groups, one of which is characterized by papillose cypselas. The results differ greatly from earlier hypotheses based on morphology alone, as few morphological characters support the phylogenetic patterns obtained. The two clades of Metalasia do, however, appear to differ in distribution, corresponding to the different rainfall regimes of South Africa. Analyses show a few taxa to be problematic; one example is the widely distributed M.densa which appears to be an intricate species complex.
|
|
| 10. |
- Bengtson, Annika, et al.
(author)
-
PHYLOGENY AND GENERIC DELIMITATION OF THE METALASIA CLADE (ASTERACEAE-GNAPHALIEAE)
- 2011
-
In: International journal of plant sciences. - : University of Chicago Press. - 1058-5893 .- 1537-5315. ; 172:8, s. 1067-1075
-
Journal article (peer-reviewed)abstract
- The Metalasia clade, which consists of the genus Metalasia and a number of much smaller satellite genera, is a South African group in the tribe Gnaphalieae (Asteraceae). This study scrutinizes the phylogenetic relationships of the Metalasia clade by means of chloroplast (trnL-trnF, psbA-trnH) and nuclear (external transcribed spacer, internal transcribed spacer) sequence data. The Metalasia clade is confirmed to be a monophyletic group, and the phylogenetic positions of the included genera are determined. The genus Metalasia may be monophyletic if the monotypic Planea is included, but the node has very poor support and further studies are needed. The Metalasia species fall into two well-supported groups, distinguishing the members of Karis's Metalasia densa group from the others. Lachnospermum is shown to be monophyletic and is placed as a possible sister group to Metalasia. Phaenocoma is placed as sister to the branch consisting of Metalasia and Lachnospermum. Calotesta, Hydroidea, and Atrichantha form a clade, with the monotypic Dolichothrix as their sister group.
|
|
