Zur analytischen Verwendung von S-Methylisothiuroniumsulfat bei der Mercaptanbestimmung

Zusammenfassung Zur Vermeidung der Schwierigkeiten, die bei der Eichung in der polarographischen Mercaptananalyse auftreten, wurde ein Verfahren ausgearbeitet, das für die Bestimmung der Summe von Methyl- und Äthylmercaptan den Gebrauch von S-Methylisothiuroniumsulfat [(S-MIT)₂SO₄] und seine alkalische Zersetzung zu Methylmercaptan unmittelbar vor Gebrauch in der polarographischen Zelle vorschlägt. Untersuchungen über die Bestän-digkeit wäßriger Lösungen von (S-MIT)₂SO₄ ergaben, daß 0,001 M Lösungen bis zu pH 3 über 134 Tage unveränderlich sind. Das beständige und völlig geruchlose (S-MIT)₂SO₄ kann direkt als Urtitersubstanz für Methylmercaptan eingewogen werden. — Durch ac-Polarographie konnten Eichkurven bis zu einem Gehalt von 3 · 10^–6 Mol CH₃SH/l aufgestellt werden.Weiterhin wurde die Eignung des (S-MIT)₂SO₄ als Titrationsmittel zur amperometrischen Bestimmung des Quecksilbers im Mikrogramm-Bereich mit der vibrierenden Platinelektrode gezeigt. Die indirekte Anwendung dieser Methode erlaubt eine schnelle Bestimmung von Mercaptanen und Sulfid im Mikrogramm-Bereich (durchschnittlicher relativer Fehler 5%). Durch die Fällung der entsprechenden Quecksilbersalze sind durch Luftoxydation entstehende Verluste dieser Verbindungen zu vermeiden. Die Methode wurde angewendet zur Gehaltsbestimmung von Sulfideichlösungen und zur H₂S-Bestimmung in Gasen.

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Summary A procedure has been worked out for the improvement of the calibration in polarographic mercaptan analysis. For calibration in the determination of the sum of methyl- and ethylmercaptan use is made of the alkaline decomposition of S-methylisothiuronium sulphate [(S-MIT)₂SO₄] to methylmercaptan immediately before use in the polarographic cell. The stability of aqueous solutions of (S-MIT)₂SO₄ has been examined at different pH-values over 134 days and it has been shown that 0.001 M solutions are stable up to pH 3. The stable and odourless substance can be directly weighed as a primary standard for methylmercaptan. By a c-polarography calibration curves were obtained up to a concentration of 3×10^–6 Mole of CH₃SH/l.Furthermore it is shown that (S-MIT)₂SO₄ can be employed as titrant for the amperometric determination of mercury in the g range using the vibrating Pt electrode. By indirect application of this method mercaptans and sulphide can be determined quickly and exactly with an average relative error of 5%. The method was applied to the determination of the content of sulphide standard solutions and of hydrogen sulphide in gases.

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Diese Arbeit wurde im Rahmen, einer Vertragsforschung mit dem VEB Leuria-Werke Walter Ulbricht durchgeführt. Wir danken dem Werk für die Bereitstellung von Mitteln.     

Laser interference metallurgy: A new method for periodic surface microstructure design on multilayered metallic thin films

Methods for micro- and nanostructuring are essential for functionalization of materials surfaces. In particular, photon-assisted methods for synthesis of functional surfaces have been intensively investigated in the last years. In this study, a new method for surface modification and production of long-range order periodical structures called “laser interference metallurgy” is explored. A metallic thin film sample consisting of three layers composed of Fe, Cu and Al (from top to bottom) on a glass substrate was irradiated with an interference pattern using a Nd:YAG laser (wavelength of 355 nm, 10 ns of pulse duration). For the interference pattern, a configuration producing a line-type energy distribution was chosen. The laser fluence was high enough to melt the aluminium and copper layers at the interference maxima but the iron layer remained in the solid state. Thus, diffusive and convective exchange occurred between aluminium and copper at the energy maxima positions leading to periodical alloy formation with a long-range order. Because it remained in solid state, the iron layer at the top acted as a protective layer effectively preventing removal of the molten layers. The interaction of the different layers was characterized using FIB, TEM and EDX in STEM mode.     

A new type of nano-sized silicon/carbon composite electrode for reversible lithium insertion

A new type of nano-sized silicon/carbon composite was developed. It shows superior electrochemical cycling properties as negative electrode material for possible use in lithium-ion batteries with respect to high reversible and low irreversible capacity, and low fading.     

Effect of pressure on the Curie temperature of PdFe,PdCo, PtFe and PtCo alloys

The Curie temperatures of $\text{Pd}$Fe, $\text{Pd}$Co, $\text{Pt}$Fe and $\text{Pt}$Co alloys with Fe or Co concentrations between 1 and 10 at. % have been measured by thermal scanning of the ⁵⁷Fe Mössbauer resonance under pressures up to 170 kbar. Systematically, the largest (positive) values of the logarithmic derivative, dlnT_e/dlnV, are found in the most dilute alloys. The data are compared with models, which relate the variation of T_c under pressure to changes in the impurity spin-conduction electron coupling parameter, J_i, and to changes of the pure host metal susceptibility, χ_h. The discrepancies between the experimental data and these models are discussed.