Ex situ X-­Ray absorption study of Li-­rich layered cathode material Li[Li0.2Mn0.56Ni0.16Co0.08]O2

The Li-rich layered transition metal oxides (LLOs) Li2MnO3-LiMO2 (M=Mn, Co, Ni, etc.) have drawn considerable attention as cathode materials for rechargeable lithium batteries. They generate large reversible capacities but the fundamental reaction mechanism and structural perturbations during cycling remain controversial. In the present thesis, ex situ X-ray absorption spectroscopy (XAS) measurements were performed on Li[Li0.2Mn0.56Ni0.16Co0.08]O2 at different stage of charge during electrochemical oxidation/reduction. K-edge spectra of Co, Mn and Ni were recorded through a voltage range of 3.7-4.8V vs. Li/Li+, which consist of X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Oxidation states during initial charge were discussed based on values from literature as well as XANES analysis. Information about bond distance, coordination number as well as corresponding Debye-Waller factor were extracted from Gnxas analysis of raw data in the EXAFS region. The possibility of oxygen participation in the initial charge was discussed. Co and Ni prove to take part in the oxidation/reduction process while Mn remain in the tetravalent state. The cathode material appears to retain good structural short-range order during charge-discharge. A resemblance of the pristine sample and sample 4 was discovered which was firstly reported for similar compounds.

Bioremediation of PAHs - Limitations and soultions

Introduction 1.1 Occurrence of polycyclic aromatic hydrocarbons (PAH) in the environment Worldwide industrial and agricultural developments have released a large number of natural and synthetic hazardous compounds into the environment due to careless waste disposal, illegal waste dumping and accidental spills. As a result, there are numerous sites in the world that require cleanup of soils and groundwater. Polycyclic aromatic hydrocarbons (PAHs) are one of the major groups of these contaminants (Da Silva et al., 2003). PAHs constitute a diverse class of organic compounds consisting of two or more aromatic rings with various structural configurations (Prabhu and Phale, 2003). Being a derivative of benzene, PAHs are thermodynamically stable. In addition, these chemicals tend to adhere to particle surfaces, such as soils, because of their low water solubility and strong hydrophobicity, and this results in greater persistence under natural conditions. This persistence coupled with their potential carcinogenicity makes PAHs problematic environmental contaminants (Cerniglia, 1992; Sutherland, 1992). PAHs are widely found in high concentrations at many industrial sites, particularly those associated with petroleum, gas production and wood preserving industries (Wilson and Jones, 1993). 1.2 Remediation technologies Conventional techniques used for the remediation of soil polluted with organic contaminants include excavation of the contaminated soil and disposal to a landfill or capping - containment - of the contaminated areas of a site. These methods have some drawbacks. The first method simply moves the contamination elsewhere and may create significant risks in the excavation, handling and transport of hazardous material. Additionally, it is very difficult and increasingly expensive to find new landfill sites for the final disposal of the material. The cap and containment method is only an interim solution since the contamination remains on site, requiring monitoring and maintenance of the isolation barriers long into the future, with all the associated costs and potential liability. A better approach than these traditional methods is to completely destroy the pollutants, if possible, or transform them into harmless substances. Some technologies that have been used are high-temperature incineration and various types of chemical decomposition (for example, base-catalyzed dechlorination, UV oxidation). However, these methods have significant disadvantages, principally their technological complexity, high cost , and the lack of public acceptance. Bioremediation, on the contrast, is a promising option for the complete removal and destruction of contaminants. 1.3 Bioremediation of PAH contaminated soil & groundwater Bioremediation is the use of living organisms, primarily microorganisms, to degrade or detoxify hazardous wastes into harmless substances such as carbon dioxide, water and cell biomass Most PAHs are biodegradable unter natural conditions (Da Silva et al., 2003; Meysami and Baheri, 2003) and bioremediation for cleanup of PAH wastes has been extensively studied at both laboratory and commercial levels- It has been implemented at a number of contaminated sites, including the cleanup of the Exxon Valdez oil spill in Prince William Sound, Alaska in 1989, the Mega Borg spill off the Texas coast in 1990 and the Burgan Oil Field, Kuwait in 1994 (Purwaningsih, 2002). Different strategies for PAH bioremediation, such as in situ , ex situ or on site bioremediation were developed in recent years. In situ bioremediation is a technique that is applied to soil and groundwater at the site without removing the contaminated soil or groundwater, based on the provision of optimum conditions for microbiological contaminant breakdown.. Ex situ bioremediation of PAHs, on the other hand, is a technique applied to soil and groundwater which has been removed from the site via excavation (soil) or pumping (water). Hazardous contaminants are converted in controlled bioreactors into harmless compounds in an efficient manner. 1.4 Bioavailability of PAH in the subsurface Frequently, PAH contamination in the environment is occurs as contaminants that are sorbed onto soilparticles rather than in phase (NAPL, non aqueous phase liquids). It is known that the biodegradation rate of most PAHs sorbed onto soil is far lower than rates measured in solution cultures of microorganisms with pure solid pollutants (Alexander and Scow, 1989; Hamaker, 1972). It is generally believed that only that fraction of PAHs dissolved in the solution can be metabolized by microorganisms in soil. The amount of contaminant that can be readily taken up and degraded by microorganisms is defined as bioavailability (Bosma et al., 1997; Maier, 2000). Two phenomena have been suggested to cause the low bioavailability of PAHs in soil (Danielsson, 2000). The first one is strong adsorption of the contaminants to the soil constituents which then leads to very slow release rates of contaminants to the aqueous phase. Sorption is often well correlated with soil organic matter content (Means, 1980) and significantly reduces biodegradation (Manilal and Alexander, 1991). The second phenomenon is slow mass transfer of pollutants, such as pore diffusion in the soil aggregates or diffusion in the organic matter in the soil. The complex set of these physical, chemical and biological processes is schematically illustrated in Figure 1. As shown in Figure 1, biodegradation processes are taking place in the soil solution while diffusion processes occur in the narrow pores in and between soil aggregates (Danielsson, 2000). Seemingly contradictory studies can be found in the literature that indicate the rate and final extent of metabolism may be either lower or higher for sorbed PAHs by soil than those for pure PAHs (Van Loosdrecht et al., 1990). These contrasting results demonstrate that the bioavailability of organic contaminants sorbed onto soil is far from being well understood. Besides bioavailability, there are several other factors influencing the rate and extent of biodegradation of PAHs in soil including microbial population characteristics, physical and chemical properties of PAHs and environmental factors (temperature, moisture, pH, degree of contamination). Figure 1: Schematic diagram showing possible rate-limiting processes during bioremediation of hydrophobic organic contaminants in a contaminated soil-water system (not to scale) (Danielsson, 2000). 1.5 Increasing the bioavailability of PAH in soil Attempts to improve the biodegradation of PAHs in soil by increasing their bioavailability include the use of surfactants , solvents or solubility enhancers.. However, introduction of synthetic surfactant may result in the addition of one more pollutant. (Wang and Brusseau, 1993).A study conducted by Mulder et al. showed that the introduction of hydropropyl-ß-cyclodextrin (HPCD), a well-known PAH solubility enhancer, significantly increased the solubilization of PAHs although it did not improve the biodegradation rate of PAHs (Mulder et al., 1998), indicating that further research is required in order to develop a feasible and efficient remediation method. Enhancing the extent of PAHs mass transfer from the soil phase to the liquid might prove an efficient and environmentally low-risk alternative way of addressing the problem of slow PAH biodegradation in soil.

Produzione di compositi a matrice di alluminio con rinforzo particellare nanometrico

Le leghe di alluminio da fonderia rivestono un ruolo fondamentale in ambito industriale e in particolare il settore dei trasporti ha notevolmente incrementato il loro impiego per la realizzazione di componenti strutturali. Al fine di aumentare ulteriormente la resistenza specifica, tali leghe possono essere impiegate come matrici per lo sviluppo di compositi (Metal Matrix Composites, MMCs), le cui fasi di rinforzo possono avere diversa composizione, forma e dimensione. In particolare, nel caso di rinforzo particellare, più le particelle sono piccole e finemente disperse nella matrice, più elevato può essere l’incremento delle prestazioni meccaniche. In quest’ottica, la ricerca ha portato allo sviluppo dapprima di compositi caratterizzati da un rinforzo micrometrico e, in anni recenti, si sta concentrando sul rinforzo nanometrico (Metal Matrix Nano Composites, MMNCs). I nano-compositi possono essere ottenuti attraverso metodologie differenti: tecniche in situ, in cui il rinforzo viene generato all’interno della matrice attraverso opportune reazioni chimiche, e tecniche ex situ, in cui i dispersoidi vengono inseriti nella matrice fusa, una volta già formati. Sebbene l’incremento prestazionale ottenibile da tali materiali sia stato dimostrato, è necessario far fronte ad alcune problematiche connesse a ciascuna tecnologia produttiva quali, ad esempio, il controllo dei parametri di processo, per quanto riguarda le tecniche in situ, e l’ottenimento di una efficace dispersione delle nano-particelle all’interno della matrice, nel caso delle metodologie ex-situ. Lo scopo della presente attività di tesi è lo studio di fattibilità, basato anche su un’ampia indagine bibliografica, e l’implementazione di metodologie produttive, su scala di laboratorio, volte allo sviluppo di MMNCs a matrice in lega di alluminio (A356, Al-Si-Mg). L’interesse è stato posto in primo luogo sul processo in situ di gas bubbling, mirato all’ottenimento di rinforzo d’allumina, indotto dalla reazione tra matrice metallica e gas ossidante (in questo caso aria secca industriale). In secondo luogo, dal punto di vista delle tecniche ex situ, è stato approfondito l’aspetto della dispersione delle particelle di rinforzo nel fuso, prestando particolare attenzione alla tecnica di trattamento ultrasonico del metallo.

Studio e sviluppo di tecniche per la produzione di nanocompositi a matrice di alluminio

Foundry aluminum alloys play a fundamental role in several industrial fields, as they are employed in the production of several components in a wide range of applications. Moreover, these alloys can be employed as matrix for the development of Metal Matrix Composites (MMC), whose reinforcing phases may have different composition, shape and dimension. Ceramic particle reinforced MMCs are particular interesting due to their isotropic properties and their high temperature resistance. For this kind of composites, usually, decreasing the size of the reinforcing phase leads to the increase of mechanical properties. For this reason, in the last 30 years, the research has developed micro-reinforced composites at first, characterized by low ductility, and more recently nano-reinforced ones (the so called metal matrix nanocomposite, MMNCs). The nanocomposites can be obtained through several production routes: they can be divided in in-situ techniques, where the reinforcing phase is generated during the composite production through appropriate chemical reactions, and ex situ techniques, where ceramic dispersoids are added to the matrix once already formed. The enhancement in mechanical properties of MMNCs is proved by several studies; nevertheless, it is necessary to address some issues related to each processing route, as the control of process parameters and the effort to obtain an effective dispersion of the nanoparticles in the matrix, which sometimes actually restrict the use of these materials at industrial level. In this work of thesis, a feasibility study and implementation of production processes for Aluminum and AlSi7Mg based-MMNCs was conducted. The attention was focused on the in-situ process of gas bubbling, with the aim to obtain an aluminum oxide reinforcing phase, generated by the chemical reaction between the molten matrix and industrial dry air injected in the melt. Moreover, for what concerns the ex-situ techniques, stir casting process was studied and applied to introduce alumina nanoparticles in the same matrix alloys. The obtained samples were characterized through optical and electronic microscopy, then by micro-hardness tests, in order to evaluate possible improvements in mechanical properties of the materials.

Studio delle criticità e della messa in sicurezza di un ex sito di cava ripristinato con fanghi di cartiera

Questo elaborato ha come obiettivo quello di analizzare, inquadrandolo anche da un punto di vista tecnologico, un trattamento innovativo di bioremediation in situ realizzato in una ex-area di cava, nella quale, in seguito al ripristino ambientale mediante fanghi di cartiera, si è verificato un fenomeno di degradazione anaerobica del materiale tombato che ha portato alla produzione di una ingente quantità di biogas e alla sua successiva migrazione verso abitazioni limitrofe.