Effect of the doping method on the sintering characteristics of Gadolinium-doped Ceria

Ce0.8Gd0.2O2-d (GDC) is considered one of the most promising electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC). The reduction of the sintering temperature is one of the most important challenge for the production of fully dense electrolyte. The sintering behaviour of a ceramic body is strongly related to the morphological characteristics of the initial powders and can be affected by the presence of a sintering aid. The latter can be added to the main phase using several methods, ball milling and precipitation being the most generally used. The paper aims to study the influence of the doping method and of the morphology of the dopant on the sintering characteristics of GDC. GDC powders with different specific surface area were doped with 3mol% CuO via ball milling and via nitrate salt and their sintering process followed by dilatometric measurements. The results indicate that the sintering is strongly dependent on the ratio between the specific surface area of pure GDC and CuO. Moreover, the morphology of the dopant greatly affects the sintering rate. Unexpectedly, ball milling was found to be the most effective doping method for CuO-doped GDC leading to a dense electrolyte at temperature as low as 900?

Semicelle SOFC: studio e produzione di elettroliti con processi a basso impatto ambientale

Le celle a combustibile ad ossido solido (SOFC) sono dei sistemi elettrochimici in grado di trasformare direttamente l’energia chimica di un combustibile (generalmente H2) e di un comburente (O2) in energia elettrica, senza l’intervento intermedio di un ciclo termico. Le SOFCs rappresentano un sistema energetico pulito, efficiente e sicuro, tuttavia questa tecnologia presenta costi di produzione ancora elevati e necessita di un maggiore sviluppo. L’argomento della presente tesi si colloca nell’ambito dello studio e realizzazione di materiali per l’elettrolita di SOFCs ed il contributo scientifico che si propone di fornire trova spazio nella necessità di migliorare la sinterizzazione di tali materiali e nell’ottimizzazione dei processi di formatura per produzioni facilmente scalabili a livello industriale con costo contenuto ed ecocompatibili. L’approccio di ricerca adottato è stato quello di approfondire le conoscenze relative ad un ossido di cerio drogato con gadolinio (GDC), scelto come elettrolita, cercando di comprendere su quali parametri intervenire per promuovere la densificazione ed ottimizzare il seguente processo di formatura. La ricerca si è articolata nei seguenti punti: a) Studio del processo di sinterizzazione in relazione alle caratteristiche morfologiche delle polveri di GDC pura ed esaminando l’influenza dell’ossido di rame, aggiunto come drogante, sul comportamento in sinterizzazione e microstruttura finale. I risultati indicano che il processo di sinterizzazione è enormemente influenzato dalla presenza del CuO, dalla sua morfologia e dalla procedura usata per il drogaggio b) Realizzazione di un inchiostro serigrafico a base di GDC in matrice acquosa da depositare su anodi in verde. La serigrafia rappresenta un’importante tecnica di formatura, facilmente adattabile ad una produzione industriale, con cui è possibile ottenere film di GDC densi. L’ottimizzazione dei processi in matrice acquosa porta un enorme contributo per la diminuzione dei costi di produzione e per la realizzazione di un processo maggiormente ecocompatibile. Questo obiettivo è stato raggiunto con la corretta scelta e caratterizzazione di tutti gli additivi di formatura c) Assemblaggio della semicella SOFC anodo supportante e relativo trattamento in co-firing. La messa a punto di un idoneo ciclo di burn out degli organici ha contribuito a preservare l’integrità ed omogeneità dei film depositati che dopo sinterizzazione risultano perfettamente densi e privi di cricche

Densification behaviour of screen printed Gadolinia doped Ceria films: effect of CuO

The effect of CuO on the densification of a Gadolinia doped Ceria (Ce0.8Gd0.2O2-d, GDC) deposited by screen printing on a GDC/NiO anode produced by tape casting was considered aiming to a complete co-firing of the anode-electrolyte half cell. A comparative study on a CuO-doped and undoped GDC revealed that the effect of CuO is strongly dependent on the thickness of the deposited layer and can lower of more than 100?C the temperature of co-firing of the anode-electrolyte half-cell. Chemical analysis did not reveal traces of CuO on the sintered GDC layer indicating that the oxide should evaporate from the electrolyte layer during sintering not affecting in this way its electrochemical propertie

Zeolite Catalysts for Phenol Benzoylation with Benzoic Acid: Exploring the Synthesis of Hydroxybenzophenones

In this paper, we report on the reaction of phenol benzoylation with benzoic acid, which was carried out in the absence of solvent. The aim of this reaction is the synthesis of hydroxybenzophenones, which are important intermediates for the chemical industry. H-beta zeolites offered superior performance compared to H-Y, with a remarkably high conversion of phenol and high yields to the desired compounds, when using a stoichiometric amount of benzoic acid. It was found that the reaction mechanism did not include the intramolecular Fries rearrangement of the primary product phenyl benzoate, but indeed, the bimolecular reaction between phenyl benzoate and phenol mainly contributed to the formation of hydroxybenzophenones. The product distribution was greatly affected by the presence of Lewis-type acid sites in H-beta; it was suggested that the interaction between the aromatic ring and the electrophilic Al3+ species led to the preferred formation of o-hydroxybenzophenone, because of the decreased charge density on the C atom at the para position of the phenolic ring. H-Y zeolites were efficient than H-beta in phenyl benzoate transformation into hydroxybenzophenones

Zeolite catalysts for phenol benzoylation with benzoic acid: Exploring the synthesis of hydroxybenzophenones

In this paper, we report on the reaction of phenol benzoylation with benzoic acid, which was carried out in the absence of solvent. The aim of this reaction is the synthesis of hydroxybenzophenones, which are important intermediates for the chemical industry. H-beta zeolites offered superior performance compared to H-Y, with a remarkably high conversion of phenol and high yields to the desired compounds, when using a stoichiometric amount of benzoic acid. It was found that the reaction mechanism did not include the intramolecular Fries rearrangement of the primary product phenyl benzoate, but indeed, the bimolecular reaction between phenyl benzoate and phenol mainly contributed to the formation of hydroxybenzophenones. The product distribution was greatly affected by the presence of Lewis-type acid sites in H-beta; it was suggested that the interaction between the aromatic ring and the electrophilic Al3+ species led to the preferred formation of o-hydroxybenzophenone, because of the decreased charge density on the C atom at the para position of the phenolic ring. H-Y zeolites were efficient than H-beta in phenyl benzoate transformation into hydroxybenzophenones

Histological and Chemical Analysis of Heavy Metals in Kidney and Gills of <i>Boops boops</i>: Melanomacrophages Centers and Rodlet Cells as Environmental Biomarkers

Industrialization has resulted in a massive increase in garbage output, which is frequently discharged or stored in waterways like rivers and seas. Due to their toxicity, durability, bioaccumulation, and biomagnification, heavy metals (such as mercury, cadmium, and lead) have been identified as strong biological poisons. Their presence in the aquatic environment has the potential to affect water quality parameters and aquatic life in general. Teleosts’ histopathology provides a sensitive indicator of pollutant-induced stress, because their organs have a central role in the transformation of different active chemical compounds in the aquatic environment. In particular, the gills, kidneys, and liver are placed at the center of toxicological studies. The purpose of this study is to examine the morphological changes caused by heavy metals in the kidney and gills of Boops boops, with a focus on melanomacrophages centers (MMCs) and rodlet cells (RCs) as environmental biomarkers, using histological and histochemical stainings (hematoxylin/eosin, Van Gieson trichrome, Periodic Acid Schiff reaction, and Alcian Blue/PAS 2.5), and immunoperoxidase methods. Our findings show an increase of MMCs and RCs linked to higher exposure to heavy metals, confirming the role of these aggregates and cells as reliable biomarkers of potential aquatic environmental changes reflected in fish fauna. The cytological study of RCs and MMCs could be important in gaining a better understanding of the complicated immune systems of teleosts