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Paper des Monats
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Clear evidence of the effects caused by hydrogen, introduced in different forms in an analytical glow discharge source (GDS) operated with argon, is presented for the different matrix elements copper, stainless steel, titanium, aluminium and silicon. When hydrogen is present even in small quantities in argon, not only are there significant changes in the emission line intensities of most elements (analyte and plasma species), but also new spectral features, such as emission bands of new compounds (hydrides of sputtered sample constituents) and a continuous background in the range ~220440 nm. Moreover, the discharge current (the dependent parameter in our experiments) decreases with increasing hydrogen concentration. Different modes of hydrogen introduction, externally in gaseous form or sputtered as a sample constituent, cause very similar effects in terms of discharge current, line intensity (of analyte and plasma gas) and emission continua, which implies similar changes in the discharge processes in the two cases. The excitation of the hydrogen continuum appears to quench the population of the argon metastables (11.55 and 11.72 eV) and, consequently, other elementary processes in the plasma in which the argon metastables take part, but to a different extent for each analyte.
The influence of hydrogen contained in a sample or otherwise introduced into a glow discharge source (GDS) is here extensively experimentally presented for the case of copper as a sample by means of the addition of small quantities of molecular hydrogen (<1% relative partial pressure) to the argon carrier gas. The progressive addition of molecular hydrogen causes different intensity changes particular to the individual lines of different species such as atomic (Cu I) and ionic (Cu II) copper, and also atomic (Ar I) and ionic (Ar II) argon. Some interesting features of the emission spectrum of hydrogen such as its line, band and even continuum spectrum are observed. It was also found that the depth resolution becomes worse even at very low concentrations of hydrogen.
Pre-treatment and electroplating of especially low alloyed high tensile strength steel components (such as those used in the aircraft industry) can be followed by a delayed hydrogen-induced fracture known as hydrogen embrittlement. As estimated by the fracture behavior, atomic hydrogen being evolved during the coating process and penetrating into the base metals is mainly trapped close to the interface base metal-coating. During a baking procedure after plating the atomic hydrogen can be removed from the traps and effuse through the coating as well as being more homogeneously distributed in the bulk of the base metal, both reducing the risk of embrittlement. Up to now there has been no analytical proof. Now investigations using GD-OES show that the hydrogen distribution in the coating, at the interface and within the bulk material, can be directly measured. The results give an improved knowledge and enable to work out process parameters and test procedures for coating techniques to be more effective to avoid hydrogen embrittlement.