Studio del comportamento meccanico di smalti porcellanati per substrati metallici

Composite porcelain enamels are inorganic coatings for metallic components based on a special ceramic-vitreous matrix in which specific additives are randomly dispersed. The ceramic-vitreous matrix is made by a mixture of various raw materials and elements and in particular it is based on boron-silicate glass added with metal oxides(1) of titanium, zinc, tin, zirconia, alumina, ecc. These additions are often used to improve and enhance some important performances such as corrosion(2) and wear resistance, mechanical strength, fracture toughness and also aesthetic functions. The coating process, called enamelling, depends on the nature of the surface, but also on the kind of the used porcelain enamel. For metal sheets coatings two industrial processes are actually used: one based on a wet porcelain enamel and another based on a dry-silicone porcelain enamel. During the firing process, that is performed at about 870°C in the case of a steel substrate, the enamel raw material melts and interacts with the metal substrate so enabling the formation of a continuous varying structure. The interface domain between the substrate and the external layer is made of a complex material system where the ceramic vitreous and the metal constituents are mixed. In particular four main regions can be identified, (i) the pure metal region, (ii) the region where the metal constituents are dominant compared with the ceramic vitreous components, (iii) the region where the ceramic vitreous constituents are dominant compared with the metal ones, and the fourth region (iv) composed by the pure ceramic vitreous material. It has also to be noticed the presence of metallic dendrites that hinder the substrate and the external layer passing through the interphase region. Each region of the final composite structure plays a specific role: the metal substrate has mainly the structural function, the interphase region and the embedded dendrites guarantee the adhesion of the external vitreous layer to the substrate and the external vitreous layer is characterized by an high tribological, corrosion and thermal shock resistance. Such material, due to its internal composition, functionalization and architecture can be considered as a functionally graded composite material. The knowledge of the mechanical, tribological and chemical behavior of such composites is not well established and the research is still in progress. In particular the mechanical performances data about the composite coating are not jet established. In the present work the Residual Stresses, the Young modulus and the First Crack Failure of the composite porcelain enamel coating are studied. Due to the differences of the porcelain composite enamel and steel thermal properties the enamelled steel sheets have residual stresses: compressive residual stress acts on the coating and tensile residual stress acts on the steel sheet. The residual stresses estimation has been performed by measuring the curvature of rectangular one-side coated specimens. The Young modulus and the First Crack Failure (FCF) of the coating have been estimated by four point bending tests (3-7) monitored by means of the Acoustic Emission (AE) technique(5,6). In particular the AE information has been used to identify, during the bending tests, the displacement domain over which no coating failure occurs (Free Failure Zone, FFZ). In the FFZ domain, the Young modulus has been estimated according to ASTM D6272-02. The FCF has been calculated as the ratio between the displacement at the first crack of the coating and the coating thickness on the cracked side. The mechanical performances of the tested coated specimens have also been related and discussed to respective microstructure and surface characteristics by double entry charts.

Anaerobic oxidation of ethanol over spinel mixed oxides: the first step in the steam-iron process for H2 production

The future hydrogen demand is expected to increase, both in existing industries (including upgrading of fossil fuels or ammonia production) and in new technologies, like fuel cells. Nowadays, hydrogen is obtained predominantly by steam reforming of methane, but it is well known that hydrocarbon based routes result in environmental problems and besides the market is dependent on the availability of this finite resource which is suffering of rapid depletion. Therefore, alternative processes using renewable sources like wind, solar energy and biomass, are now being considered for the production of hydrogen. One of those alternative methods is the so-called “steam-iron process” which consists in the reduction of a metal-oxide by hydrogen-containing feedstock, like ethanol for instance, and then the reduced material is reoxidized with water to produce “clean” hydrogen (water splitting). This kind of thermochemical cycles have been studied before but currently some important facts like the development of more active catalysts, the flexibility of the feedstock (including renewable bio-alcohols) and the fact that the purification of hydrogen could be avoided, have significantly increased the interest for this research topic. With the aim of increasing the understanding of the reactions that govern the steam-iron route to produce hydrogen, it is necessary to go into the molecular level. Spectroscopic methods are an important tool to extract information that could help in the development of more efficient materials and processes. In this research, ethanol was chosen as a reducing fuel and the main goal was to study its interaction with different catalysts having similar structure (spinels), to make a correlation with the composition and the mechanism of the anaerobic oxidation of the ethanol which is the first step of the steam-iron cycle. To accomplish this, diffuse reflectance spectroscopy (DRIFTS) was used to study the surface composition of the catalysts during the adsorption of ethanol and its transformation during the temperature program. Furthermore, mass spectrometry was used to monitor the desorbed products. The set of studied materials include Cu, Co and Ni ferrites which were also characterized by means of X-ray diffraction, surface area measurements, Raman spectroscopy, and temperature programmed reduction.

Development of a multi-species method by GC-coupling with inductively coupled plasma isotope dilution mass spectrometry for the simultaneous determination of alkylated lead, mercury and tin compounds

An accurate and sensitive species-specific GC-ICP-IDMS (gas chromatography inductively coupled plasma isotope dilution mass spectrometry) method for the determination of trimethyllead and a multi-species-specific GC-ICP-IDMS method for the simultaneous determination of trimethyllead, methylmercury, and butyltins in biological and environmental samples were developed. They allow the determination of corresponding elemental species down to the low ng g-1 range. The developed synthesis scheme for the formation of isotopically labeled Me3206Pb+ can be used for future production of this spike. The novel extraction technique, stir bar sorptive extraction (SBSE), was applied for the first time in connection with species-specific isotope dilution GC-ICP-MS for the determination of trimethyllead, methylmercury and butyltins. The results were compared with liquid-liquid extraction. The developed methods were validated by the analysis of certified reference materials. The liquid-liquid extraction GC-ICP-IDMS method was applied to seafood samples purchased from a supermarket. The methylated lead fraction in these samples, correlated to total lead, varied in a broad range of 0.01-7.6 %. On the contrary, the fraction of methylmercury is much higher, normally in the range of 80-98 %. The highest methylmercury content of up to 12 µg g-1 has been determined in shark samples, an animal which is at the end of the marine food chain, whereas in other seafood samples a MeHg+ content of less than 0.2 µg g-1 was found. Butyltin species could only be determined in samples, where anthropogenic contaminations must be assumed. This explains the observed broad variation of the butylated tin fraction in the range of <0.3-49 % in different seafood samples. Because all isotope-labelled spike compounds, except trimethyllead, are commercially available, the developed multi-species-specific GC-ICP-IDMS method has a high potential in future for routine analysis.

From polymer precursors to metal oxides

We report on a strategy to prepare metal oxides including binary oxide and mixed metal oxide (MMO) in form of nanometer-sized particles using polymer as precursor. Zinc oxide nanoparticles are prepared as an example. The obtained zinc polyacrylate precursor is amorphous as confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The conversion from polymer precursor to ZnO nanocrystals by thermal pyrolysis was investigated by means of XRD, thermogravimetric analysis (TGA) and electron microscopy. The as-synthesized ZnO consists of many individual particles with a diameter around 40 nm as shown by scanning electron microscopy (SEM). The photoluminescence (PL) and electron paramagnetic (EPR) properties of the material are investigated, too. Employing this method, ZnO nanocrystalline films are fabricated via pyrolysis of a zinc polyacrylate precursor film on solid substrate like silicon and quartz glass. The results of XRD, absorption spectra as well as TEM prove that both the ZnO nanopowder and film undergo same evolution process. Comparing the PL properties of films fabricated in different gas atmosphere, it is assigned that the blue emission of the ZnO films is due to crystal defect of zinc vacancy and green emission from oxygen vacancy. Two kinds of ZnO-based mixed metal oxide (Zn1-xMgxO and Zn1-xCoxO) particles with very precise stoichiometry are prepared by controlled pyrolysis of the corresponding polymer precursor at 550 oC. The MMO crystal particles are typically 20-50 nm in diameter. Doping of Mg in ZnO lattice causes shrinkage of lattice parameter c, while it remains unchanged with Co incorporation. Effects of bandgap engineering are seen in the Mg:ZnO system. The photoluminescence in the visible is enhanced by incorporation of magnesium on zinc lattice sites, while the emission is suppressed in the Co:ZnO system. Magnetic property of cobalt doped-ZnO is checked too and ferromagnetic ordering was not found in our samples. An alternative way to prepare zinc oxide nanoparticles is presented upon calcination of zinc-loaded polymer precursors, which is synthesized via inverse miniemulsion polymerization of the mixture of the acrylic acid and zinc nitrate. The as-prepared ZnO product is compared with that obtained from polymer-salt complex method. The obtained ZnO nanoparticles undergo surface modification via a phosphate modifier applying ultrasonication. The morphology of the modified particles is checked by SEM. And stability of the ZnO nanoparticles in aqueous dispersion is enhanced as indicated by the zeta-potential results.

Organokompatible Zinnoxid-Nanopartikel

In der vorliegenden Arbeit werden verschiedene Methoden der Synthese von Zinn(IV)oxid Nanopartikeln, deren Stabilisierung durch unterschiedliche Surfactants und der Einbau der Nanomaterialien in PMMA beschrieben und die erhaltenen Materialien charakterisiert. Die Darstellung der Zinnoxid Nanopartikel wurde über drei verschiedene Synthesewege durchgeführt: a) Polymeric Precursor Methode, b) Solvothermal-Synthese und c) säurekatalysierte Fällungsreaktion. Im Rahmen von a) konnte neben der thermodynamisch stabilen Phase von Zinn(IV)oxid ebenfalls die metastabile orthorhombische Phase synthetisiert werden. Durch eine Analyse der Pyrolysebedingungen konnte der Kristallisationsmechanismus des Zinnoxids ausgehend vom Precursor bis zur tetragonalen Phase des Zinn(IV)oxid diskutiert werden. Die Synthesemethoden b) und c) boten sich zur Darstellung von oberflächenmodifizierten Zinnoxid Nanopartikeln an. Als Surfactant benutzte man unter anderem Alkylphosphonsäuren, da eine hydrophobe Oberfläche die Dispersion in MMA ermöglichte. Abschließend wurde eine radikalische in situ-Polymerisation von MMA in Gegenwart von oberflächenmodifizierten Partikeln durchgeführt. Der erhaltene Verbundwerkstoff zeichnete sich durch eine erhöhte thermische Stabilität aufgrund weniger Strukturdefekte des Polymers aus. Durch eine Untersuchung des Polymerisationsmechanismus konnte die Wirkung der oberflächenmodifizierten Nanopartikel auf die Polymerisation veranschaulicht werden. Aufgrund der nicht homogenen Verteilung der Nanopartikel im Verbundwerkstoff konnte jedoch keine Charakterisierung der optischen Eigenschaften durchgeführt werden.

In-situ DRIFT/MS study of the conversion of ethanol on mixed Mg/Si oxides

Due to the high price of natural oil and harmful effects of its usage, as the increase in emission of greenhouse gases, the industry focused in searching of sustainable types of the raw materials for production of chemicals. Ethanol, produced by fermentation of sugars, is one of the more interesting renewable materials for chemical manufacturing. There are numerous applications for the conversion of ethanol into commodity chemicals. In particular, the production of 1,3-butadiene whose primary source is ethanol using multifunctional catalysts is attractive. With the 25% of world rubber manufacturers utilizing 1,3-butadiene, there is an exigent need for its sustainable production. In this research, the conversion of ethanol in one-step process to 1,3-butadiene was studied. According to the literature, the mechanisms which were proposed to explain the way ethanol transforms into butadiene require to have both acid and basic sites. But still, there are a lot of debate on this topic. Thus, the aim of this research work is a better understanding of the reaction pathways with all the possible intermediates and products which lead to the formation of butadiene from ethanol. The particular interests represent the catalysts, based on different ratio Mg/Si in comparison to bare magnesia and silica oxides, in order to identify a good combination of acid/basic sites for the adsorption and conversion of ethanol. Usage of spectroscopictechniques are important to extract information that could be helpful for understanding the processes on the molecular level. The diffuse reflectance infrared spectroscopy coupled to mass spectrometry (DRIFT-MS) was used to study the surface composition of the catalysts during the adsorption of ethanol and its transformation during the temperature program. Whereas, mass spectrometry was used to monitor the desorbed products. The set of studied materials include MgO, Mg/Si=0.1, Mg/Si=2, Mg/Si=3, Mg/Si=9 and SiO2 which were also characterized by means of surface area measurements.

Sintesi e caratterizzazione di nanoparticelle di ossido di stagno dopate

In the last years, new materials have been developed in the broad area of nanoscience. Among them, an emergent class characterized by excellent electrical conductivity properties as well as high optical transmittance in the visible region are TCOs (Transparent Conducting Oxides). Due to their versatile properties, they have found many applications in a lot of optoelectronic devices, such as solar cells, liquid crystal displays, touch-panel displays, gas sensors, to cite a few examples. Different research groups have studied and characterized the TCOs. In this context, a new synthetic method has been developed to produce FTO nanocrystals (Fluorine-doped Tin Oxide NCs) in Prof. Pinna’s lab at the Humboldt University in Berlin. FTO belongs to the TCO category, and they have been studied as a promising alternative to ITO NCs (Indium Tin Oxide) which represent the standard TCO material in terms of properties and performances. In this work, FTO NCs have been synthesized using the “benzyl alcohol route” (a non-aqueous sol-gel method) via microwave, which permits to produce FTO particles with good properties as revealed by the characterizations performed, employing a cheap, fast and clean method.

Tin (IV) oxide nanostructures: controlled synthesis, properties and applications in dye-sensitized solar cells

Für viele Anwendungen von Nanomaterialien sind maßgeschneiderte Produkte wün-schenswert, weswegen ein tiefgreifendes und genaues Wissen der Reaktionsabläufe, die zu diesen Produkten führen, unabdingbar ist. Um dies im Fall von SnO2 zu erreichen, behandelt diese Arbeit die kontrollierte Synthese und genaue Charakterisierung von Nanopartikeln von Zinn(IV) Oxid.

Glycerol oxidehydration to acrylic acid on complex mixed-metal oxides

The project of this Ph.D. thesis is based on a co-supervised collaboration between Università di Bologna, ALMA MATER STUDIORUM (Italy) and Instituto de Tecnología Química, Universitat Politècnica de València ITQ-UPV (Spain). This Ph.D. thesis is about the synthesis, characterization and catalytic testing of complex mixed-oxide catalysts mainly related to the family of Hexagonal Tungsten Bronzes (HTBs). These materials have been little explored as catalysts, although they have a great potential as multifunctional materials. Their peculiar acid properties can be coupled to other functionalities (e.g. redox sites) by isomorphous substitution of tungsten atoms with other transition metals such as vanadium, niobium and molybdenum. In this PhD thesis, it was demonstrated how it is possible to prepare substituted-HTBs by hydrothermal synthesis; these mixed-oxide were fully characterize by a number of physicochemical techniques such as XPS, HR-TEM, XAS etc. They were also used as catalysts for the one-pot glycerol oxidehydration to acrylic acid; this reaction might represent a viable chemical route to solve the important issue related to the co-production of glycerin along the biodiesel production chain. Acrylic acid yields as high as 51% were obtained and important structure-reactivity correlations were proved to govern the catalytic performance; only fine tuning of acid and redox properties as well as the in-framework presence of vanadium are fundamental to achieve noteworthy yields into the acid monomer. The overall results reported herein might represent an important contribution for future applications of HTBs in catalysis as well as a general guideline for a multifaceted approach for their physicochemical characterization.

Synthesis of novel ribose-based thioimidate n-oxides

This work is based on the study of new synthetic paths to obtain thioimidate N-oxides (TINOs) from D-ribose and to study their reactivity with the purpose to obtain ketonitrones. TINOs, aren’t well known molecules, but these enantiomerically pure backbones could be valuable intermediates in the synthesis of novel ketonitrones which are key intermediates in the synthesis of iminosugars. TINOs were discovered from the study of glucoraphanin, a particular glucosinolate, that unexpectedly cyclized into a TINO after desulfatation, by a spontaneous intramolecular Michael addition. The first part of this work was to synthetize the TINO 3 from D-ribose 1. The key step was the desilylative cyclisation of a suitably functionalized thiohydroximate 2. Based on precedent work developed in the laboratory, we could obtain the thiohydroximate from D-ribose. We then focused our studies on the cyclisation step trying to find the suitable substituents that could give the TINO in good yield by desilylative cyclisation. The second part of the project is to obtain ketonitrones 4 by palladiumcatalyzed coupling reaction.

Mechanism of action of tin-containing fluoride solutions as anti-erosive agents in dentine - an in vitro tin-uptake, tissue loss, and scanning electron microscopy study

Solutions containing tin and fluoride exhibit remarkable anti-erosive properties with tin ions as a major agent. To elucidate its mechanism of action in dentine, the tin uptake on and in the tissue was investigated and related to histological findings and substance loss. Samples were treated twice daily, each treatment lasting for 2 min, with fluoride solutions [pH 4.5; 1,500 parts per million (p.p.m.) F] containing 2,100, 1,400, or 400 p.p.m. Sn as SnCl(2). In experiments 1 and 2, samples were eroded with citric acid (pH 2.3) six times each day, each treatment lasting for 5 min; in experiment 2, the demineralized organic matrix was continuously digested by collagenase; in experiment 3, no erosive challenges were performed. Sample surfaces and cross-sections were investigated using energy dispersive X-ray spectroscopy, scanning electron microscopy, and profilometry. Surface retention of tin was found in almost all treatment groups and was highest in experiment 2. On cross-sections, tin was retained within the organic matrix; in mineralized areas, tin was found mainly within a depth of 10 mum. Test solutions inhibited substance loss significantly; in experiment 2, the effect was dose-dependent. Erosion inhibition seemed to depend mainly on the incorporation of tin in the mineralized dentine when the organic portion was preserved, but on surface precipitation when the organic portion was continuously digested.