Heinz Vonmont

Regio-and stereoselective isomerization of hexabromocyclododecanes (HBCDs) : Kinetics and mechanism of γ-to α-HBCD isomerization

Hexabromocyclododecanes (HBCDs) are high production volume chemicals (>20000 ty(-1)) used as flame retardants for plastics and textiles. Lately, we reported on the stereoselective isomerization of beta-HBCDs. Herein we present insights into the mechanism and kinetics of (+)gamma- to (+)alpha- and of (-)gamma- to (-)alpha-HBCD isomerization. Only two of the six bromine atoms migrated, indicating that rearrangements of gamma- to alpha-HBCDs are regio- and stereoselective as well. The apparent first-order isomerization rate constants increased from 0.0013 to 0.0031 to 0.0070 min(-1) at 120, 130, and 140 degrees C, respectively, corresponding to half-lives of 540, 230, and 99 min. Thus, a thermal treatment of materials containing gamma-HBCDs at temperatures >100 degrees C may induce the formation of alpha-HBCDs and, hence, may alter the diastereomeric ratio of a HBCD mixture. The inversion of vicinal dibromides in like-configurations (RR/SS) prevailed, whereas unlike-configurations (RS/SR) were not affected. An intramolecular, stereoselective migration of neighboring bromine atoms via a four-center transition state would explain the observed stereoisomer pattern and first-order kinetics. Despite the fact that vicinal dibromides in HBCDs prefer synclinal (gauche) conformations, antiperiplanar (staggered) conformations are assumed to facilitate concerted 1.2-shifts of both bromine atoms. A conformation analysis revealed that under kinetic control, only those bromine atoms in the more flexible part of the molecules are migrating, whereas those in the conserved triple-turn motive were not affected. Thus, this structural motive, common to all alpha-, beta-, and gamma-HBCDs, is more rigid and less reactive than the flexible part, containing the reacting dibromides in like-configurations.

Laser-induced particulate as carrier of analytical information in LA-ICPMS direct solid microanalysis.

Laser ablation in combination with plasma spectrochemistry is an ideal technique for depth profiling analysis, based on signal profiles. However, signal profiles were found to be critically influenced by the characteristics of the ablated particles, especially their composition and size distribution, and consequently transport mechanism and plasma-assisted vaporization efficiency. Even for a refractory material like ceramic, relics of melting following laser irradiation were found, so that particles were non-stoichiometric as compared to the parent material. Estimates of transport efficiency showed that this is highly variable as a function of particle size. Large particles are likely to be lost in the sample chamber. Fine particles are prone to wall reaction, especially in Ar ambient. Variability in particle delivery to the ICP-MS was suspected to be the cause for an element-dependent analyte signal response. Fluctuation in particle vaporization degree as a consequence of plasma temperature instability was also responsible for element-dependent signal profile deviation. However, for a 10-fold higher mass load into the plasma, no direct fractionation effects were observed. Differential transport of chemically-differentiated analyte-carriers is suggested to be primary cause for element-dependent signal structure.

Spatially resolved quantitative profiling of compositionally graded perovskite layers using laser ablation-inductively coupled plasma mass spectrometry

Fuel cell cathodes can be constructed as a stack of perovskite layers whose composition gradually changes over a few hundreds of µm. They are prepared by sintering a mixture of two ceramic powders (Mn-perovskite and Co-perovskite), where the proportions of the mixture contributes to the chemical gradation. Laser ablation-ICP-MS permitted the determination of the proportions of Mn-perovskite and Co-perovskite, in several depth profiles. The set-up and the laser operating conditions were specifically optimised so that correct elemental concentration profiles could be acquired, without beam induced artefacts. Lateral resolution below 100 µm and a depth resolution of 0.1–0.2 µm were obtained. Quantification was carried out from the proportions of the mixture of perovskites and the elemental composition of the individual perovskites (i.e., a “weighted summation”). The composition of the powder was previously determined via digestion and ICP-MS. Comparison with semi-quantitative data from SEM-EDX showed that the developed method provided reliable responses. Analysis of the signal structure of the depth profiles was performed by means of signal convolution and numerical differentiation. The occurrence of differential bands in conjugate pairs could be assessed and used for a realistic description of the sample structure. The fluctuation of analyte concentrations at low level (<1 µm) suggests that further improvements in the sampling thickness might conflict with robust and powerful quantification. Therefore, the determined pulse-related depth resolution of 100–200 nm seems to be a good compromise between spatially resolved analysis and quantification capability. The rapidity, flexibility and detection power of LA-ICP-MS are advantages that integrate and extend the analytical capabilities of other well-established beam-assisted techniques (i.e., XPS, AES, SIMS, SNMS, GD-OES/MS, SEM-EDX) and permit critical control of the quality of the fabricated products.

Elektrofilterasche aus Müllverbrennungsanlagen

ZusammenfassungElektrofilterasche aus Müllverbrennungsanlagen ist auf Grund der hohen Belastung an Schwermetallen und organischen Giftstoffen ein Sondermüllprodukt. Solche Rückstände müssen entweder in Sondermülldeponien (z.B. Unterlage) abgelagert oder vor der Deponierung aufgearbeitet werden. Für die Aufarbeitung und speziell die Wertstoffgewinnung aus diesen Rückständen ist eine Kenntnis der chemischen Zusammensetzung und deren Schwankungsbreite von großer Bedeutung. Zu diesem Zweck wurde bei entsprechenden Behörden und Betreibern von Müllverbrennungsanlagen nach Analysedaten über die chemische Zusammensetzung von Elektrofilterasche angefragt. Die Resultate, ergänzt durch eigene Analysedaten, sind die Grundlage dieses Artikels.AbstractThe combustion of municipal solid waste leads to emissions containing high contents of heavy metals and organic pollutants. These residues, mainly collected by the electrostatic precipitator, have either to be deposited in special waste dumps or treated before being disposed in ordinary landfills. For the treatment or partial recycling of these residues the composition and the related variation are of primary importance. In this context a national inquiry for analysis data about fly ash composition was started. The results of this study, completed by own analytical results are presented in this paper.

Verglaste Filterstäube aus Müllverbrennungsanlagen

ZusammenfassungFeste Rückstände aus der physikalischen Rauchgasreinigung von Müllverbrennungsanlagen enthalten neben Al, Ca-Silikaten und Metalloxiden (Wertstoffen) auch hohe Gehalte an human- und ökotoxikologischen Schadstoffen, wie Alkalihalogenidsalzen, Schwermetallverbindungen und organischen Substanzen, z.B. PCDD, PCDF und PCB. Im Hinblick auf eine Weiterverwertung der oxidischen Wertstoffe, z.B. in Form von technischen Glasprodukten ist eine vollständige Zerstörung der organischen Giftstoffe und effektive Abtrennung der anorganischen Schadstoffe von den Wertstoffen erforderlich. Diese Ziele lassen sich nur mittels einer thermischen Behandlung erreichen. Detaillierte Untersuchungen an verglasten Filterstäuben aus Müllverbrennungsanlagen ergaben hinsichtlich der Stoffumsetzung, der chemischen Zusammensetzung und der Qualität der erhaltenen Glasphase durchweg positive Resultate.AbstractSolid waste residues from municipal solid waste incinerator flue gas cleaning systems basically consists of Al, Ca-silicates and metal oxides. At lower concentrations, environmentally harmful compounds such as alkali halide salts, heavy metals and traces of organic pollutants, e.g. PCDD, PCDF and PCB, are also present. For the reuse of the valuable materials (Al, Ca and metal oxides), an effective treatment technique for destroying the organic contaminants and separating the anorganic toxins from the non-toxic components has to be applied, which can only be achieved through thermal processing. Detailed investigations on vitrified electrostatic precipitator ash from municipal solid waste incinerator plants have shown promising results in regard to the mass balances, the chemical composition and the quality of the glass phase obtained.