Barbara Novosel

Air-stable monodispersed Mo6S3I6 nanowires

We report on the properties of a new air-stable nanowire material with the chemical formula Mo6S3I6 .T he distinguishing features of the material are rapid one-step synthesis, easy isolation and controllable dispersion into small-diameter wire bundles. Elemental analysis, x-ray diffraction, thermogravimetry, differential thermal analysis, Raman scattering and electron microscopy were used to characterize the material.

Preparation of reactive metal powders by thermal decomposition of hydrazidocarbonates

This procedure for metal powder preparation involves a combination of decomposition and reduction processes. The large mass loss through evolution of gaseous products leaves agglomerates of a fine-grained three-dimensional network of metal particle 0.2 to 1 μm in size.ZusammenfassungDas beschriebene Verfahren zur Metallpulverherstellung beinhaltet eine Kombination von Zersetzungs-und Reduktionsprozessen. Der gro\e Masseverlust bei der Freisetzung von gasförmigen Produkten hinterläβt Agglomerate eines feinkornigen dreidimensionalen Netzwerkes aus Metallpartikeln der Grö\e 0.2 bis 1 m.

Study of the drying zirconia gel-precipitates using thermal analysis

Thermoanalytical techniques (TG, DTG, DTA and EGA) can be helpful in studying gel compositions and relating the chemical history and the role of the precipitant to the chemical properties of gels. The objective of our work was to determine the influence of the initial conditions in the reaction mixture on the product characteristics. Zirconia gels were prepared by the gelprecipitation method by the hydrolysis of zirconium tetrachloride dissolved in methanol. The substitution of water by methanol was chosen in order to obtain a reaction medium in which better control of the hydrolysis and condensation reactions of the zirconium precursor were achieved and thus also better control of the final properties of the dried zirconia gel-precipitates could be obtained. The nature of the hydrated zirconia gels obtained during the gelation process is strongly influenced by the conditions of the reaction mixture, e.g. concentration of the zirconium precursor, the mixing rate and particularly by the amount of water added. To distinguish between various types of water in the gel-precipitates, the furnace atmosphere and the partial water pressure were altered appropriately. It was shown that initial zirconium to water molar ratio has a significant effect on the properties of the final products. It was assumed that, according to the preparation conditions, three different types of water are present in the formed zirconia gel-precipitates. Modification of the dehydration processes of zirconia gel-precipitates enables control of the final microstructural and surface properties of the dried gels which are suitable for further catalysts support as well as mixed oxide preparation.

Thermal properties and reactivity determination of micro- and submicrometer nickel powders

Monodispersed fine metal nickel powders of uniform shape and high purity are increasingly required for specific uses in many technological areas, especially in the preparation of electronic materials such as the manufacture of conductive inks and pastes and the formation of catalysts. Metallic nickel powders were prepared in ethylene glycol by the reduction of a nickel solution. Hydrazine was used as a reducing agent. Metal powders were characterized by chemical analysis, scanning electron microscopy (SEM), thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). Particle size distributions were determined using laser light scattering. The reactivity and purity of these fine nickel powders were tested by repeated oxidation and reduction of nickel powders in oxidative and reductive atmospheres.

Determination of mechanism of thermal decomposition of Mg, Ca and Zn hydrazidocarbonates by evolved gas analysis

Hydrazo-carbonates are complex compounds and products of the reactions between solutions of metal ion and solutions of hydrazido-carbonic acid. The decomposition of Mg(N2H3COO)2. 2H2O, Ca(N2H3COO)2·H2O and Zn(N2H3COO)2 in inert atmosphere were studied. By classical thermoanalytical methods and data on the composition of the intermediates and final products the mechanisms of the thermal decomposition could not be resolved therefore also evolved gas analysis was used (EGA). The first step of thermal decomposition of Ca and Mg hydrazidocarbonates is dehydration. With the heating the decomposition of the hydrazido-carbonates proceeds under evolution of the ammonia, carbon monoxide and/or nitrogen and carbon dioxide giving as the intermediates for calcium and magnesium compounds the corresponding carbonates oxides as the final products. The zinc compound decomposes to the oxide, ZnO but also zinc cyanamide was detected during to the thermal treatment.ZusammenfassungHydrazocarbonate sind Komplexverbindungen und Reaktionsprodukte der Reaktion zwischen Lösungen von Metallionen und Lösungen von Hydrazidocarbonsäure. Es wird die Zersetzung von Mg(N2H3COO)22H2O, Ca(N2H3COO)·2H2O und Zn(N2H3COO)2 in inerter Atmosphäre untersucht. Anhand klassicher thermoanalytischer Methoden und Daten über die Zusammensetzung von Zwischen- und Endprodukten konnte kein Mechanismus für die thermischer Zersetzung gefunden werden, weshalb auch eine Analyse der freigesetzten Gase (EGA) durchgeführt wurde. Der erste Schritt der thermischen Zersetzung von Ca- und Mg-Hydrazidocarbonaten ist die Dehydratation. Bei Erhitzen erfolgt die Zersetzung von Hydrazidocarbonaten unter Freisetzung von Ammoniak, Kohlenmonoxid und/oder Stickstoff und Kohlendioxid als Zwischenprodukt für Calcium- und Magnesiumverbindungen, wobei die entsprechenden Carbonatoxide als Endprodukte entstehen. Die Zinkverbindung zerfällt in das Oxid ZnO, aber auch Zinkcyanamid kann beim Erhitzen beobachtet werden.

Thermal behavior of the products isolated in uranium compound-hydrazine systems

Products obtained via precipitation from the reactions of uranium compounds with hydrazine were characterized by thermal analysis and other methods. Precipitates of uranium oxides were isolated from the reactions with hydrazine at 60 and 100°C. Upon heating in an inert atmosphere, the samples underwent dehydration, accompanied by decomposition of the hydrazine. Hydrazine and its decomposition products, ammonia and hydrogen, partially reduced the uranium(VI) to uranium(IV) oxide. The products obtained by precipitation at 60°C were stable in air. In contrast, the products obtained on reduction at 100°C exhibited pronounced sensitivity toward oxidation by air.ZusammenfassungAus Uranverbindungen mit Hydrazin gefällte Produkte werden mittels Thermoanalyse und anderen Methoden beschrieben.Niederschläge von Uranoxiden wurden aus der Reaktion mit hydrazin bei 60 und 100°C isoliert. Bei Erhitzen in inerter Atmosphäre werden die Proben unter gleichzeitiger Zersetzung des hydrazins dehydratiert. Hydrazin und seine Zersetzungsprodukte Ammoniak un Wasserstoff reduzieren Uran(VI)-oxide teilweise zu Uran(IV)-oxiden. Die beim Fällen bei 60°C erhaltenen Produkte sind an Luft stabil. Im Gegensatz dazu besitzen die bei der Reduktion bei 100°C erhaltenen Produkte gegenüber der Oxydation an Luft eine gesteigerte Empfindlichkeit.