Corrosion of metals is an issue that aff ects many industries including oil, chemical, car and aerospace, pharmaceutical and medical industries. In addition, the prevention of oxidation is essential in organic as well as conventional solid-state applications, as it allows a far greater range of materials to be utilized and combined. A common approach used for preventing oxidation or corrosion of an item is to apply protective or barrier layers to mechanically isolate it from the environment. This approach is known as passive corrosion protection. Despite being just one-atom-thick, graphene (G) and hexagonal boron nitride (hBN) have high impermeability and they are also inert to most chemicals. For these reasons, they have been studied as eff ective barrier layers. However, graphene and hBN present some di fferences among which the most well known regards the electronic properties: graphene is a semimetal whereas hBN is a wide-bandgap insulator. Thus, graphene and hBN coatings behave in a signi cantly di fferent way. Among the several techniques developed for the production of graphene and hBN layer, chemical vapor deposition (CVD) is emerged as ideal process for large-scale applications. In this work, CVD growth of graphene and hBN on copper has been optimized to achieve a good quality monolayers in order to test their performance protecting the underneath metal against oxidation and wet corrosion. The CVD-grown coatings has been investigated by optical and scanning electron microscopy (SEM) and Raman analysis. Optical analysis and SEM allowed the visualization of the morphology of the surface and Raman analysis proved the quality of the monolayers. In a comparative study, we probe in real time the oxidation of both graphene-coated and hBN-coated copper samples, subjected to two representative oxidative scenarios (acute short term, and mild long-term). While Raman spectroscopy is the technique chosen for the real-time investigation, X-ray photoemission spectroscopy and X-ray induced Auger electron spectroscopy are used to establish the degree of oxidation of the samples before and after the oxidation experiments. The inhibition-corrosion performance of graphene and hBN were further investigated electrochemically in Na2SO4 solution (0.1M). The potentiodynamic scan was used to fi nd the corrosion penetration rate and the interpretation of the electrochemical impedance spectroscopy data is aided by analogy to equivalent circuits involving simple components such as resistors and capacitors. Our findings point out the diff erent protective behavior of graphene and hBN, showing that they both excel in diff erent oxidative situations. For prolonged protection, hBN coatings will eventually outperform G-ones, even if the intrinsic quality of G-layer is higher than that of the hBN. Regarding the wet corrosion study, the results show good protective properties for both graphene and hBN, highlighting a superior performance of the latter one.
La corrosione dei metalli è un problema che a ffligge molte industrie tra cui le petrolchimiche, chimiche, automobilistiche e aerospaziale, farmaceutiche e mediche. Inoltre, la prevenzione dell'ossidazione è essenziale nelle applicazioni a stato solido, in quanto permette a una maggior quantit à di materiali di poter essere utilizzati e combinati insieme. Un comune approccio usato per prevenire l'ossidazione o la corrosione di un substrato è quello di applicare una barriera protettiva per isolarlo meccanicamente dall'ambiente. Questo approccio è noto come protezione passiva dalla corrosione. Nonostante siano solo formati da un singolo strato di atomi, grafene (G) e nitruro di boro esagonale (hBN) sono impermeabili e sono inoltre inerti alla maggior parte di specie chimiche. Per queste ragioni, sono entrambi studiati come rivestimenti per diverse applicazioni. Grafene ed hBN hanno molte propriet à simili ma anche alcune diff erenze, tra cui la pi ù nota riguarda le propriet à elettroniche: il grafene è un semimetallo mentre hBN è un isoltante con un ampio band gap. Perci ò, i rivestimenti di grafene ed hBN si comportano in modo molto di fferente. Molte tecniche sono state sviluppate per la produzione di grafene ed hBN, in particolare la deposizione chimica da vapore (CVD) spicca come processo ideale per applicazioni su larga scala. In questo lavoro la crescita di grafene ed hBN su substrati di rame tramite CVD è stata ottimizzata in modo da ottenere dei monolayer di buona qualit à per poi testare le loro performance nel proteggere il metallo sottostante contro la corrosione e l'ossidazione. I rivestimenti prodotti tramite CVD sono stati studiati con microscopio ottico ed a scansione elettronica (SEM) e con microscopia Raman. Le analisi con microscopio ottico e SEM permettono di visualizzare la morfologia della super ficie e le analisi Raman provano la qualità dei monolayers. In uno studio comparativo, abbiamo investigato in tempo reale l'ossidazione dei campioni di rame rivestiti di grafene ed hBN in due diff erenti condizioni: la prima maggiormente ossidante per un breve tempo e la seconda scarsamente ossidante per lungo tempo. Mentre la spettroscopia Raman è stata la tecnica scelta per lo studio in tempo reale, la spettroscopia fotoelettronica a raggi X (XPS) e la spettroscopia a elettroni Auger sono state usate per determinare il grado di ossidazione dei campioni prima e dopo gli esperimenti. Successivamente la capacit à di grafene ed hBN di inibire la corrosione è stata investigata elettrochimicamente in una soluzione di Na2SO4 (0.1M). La tecnica di potentiodynamic scan e stata usata per trovare il rateo di corrosione. I dati ottenuti dalla spettroscopia a impedenza elettrochimica sono stati interpretati tramite dei circuiti equivalenti che includono dei semplici componenti come resistori e capacitori. I risultati dello studio sull'ossidazione puntualizzano il diverso comportamento protettivo di grafene ed hBN e mostrano che la visione semplicistica di un rivestimento migliore dell'altro è troppo severa; entrambi eccellono in di fferenti condizioni. Per tempi prolungati i rivestimenti di hBN possono superare quelli in grafene, anche se la qualit à intrinsica del grafene è maggiore di quella dell'hBN. Anche lo studio condotto sulla corrosione mostra che entrambi i rivestimenti sono e fficaci, specialmente il nitruro di boro esagonale.
Comparative study of CVD-grown graphene and boron nitride as protective coatings for copper against oxidation and corrosion
GALBIATI, MIRIAM
2015/2016
Abstract
Corrosion of metals is an issue that aff ects many industries including oil, chemical, car and aerospace, pharmaceutical and medical industries. In addition, the prevention of oxidation is essential in organic as well as conventional solid-state applications, as it allows a far greater range of materials to be utilized and combined. A common approach used for preventing oxidation or corrosion of an item is to apply protective or barrier layers to mechanically isolate it from the environment. This approach is known as passive corrosion protection. Despite being just one-atom-thick, graphene (G) and hexagonal boron nitride (hBN) have high impermeability and they are also inert to most chemicals. For these reasons, they have been studied as eff ective barrier layers. However, graphene and hBN present some di fferences among which the most well known regards the electronic properties: graphene is a semimetal whereas hBN is a wide-bandgap insulator. Thus, graphene and hBN coatings behave in a signi cantly di fferent way. Among the several techniques developed for the production of graphene and hBN layer, chemical vapor deposition (CVD) is emerged as ideal process for large-scale applications. In this work, CVD growth of graphene and hBN on copper has been optimized to achieve a good quality monolayers in order to test their performance protecting the underneath metal against oxidation and wet corrosion. The CVD-grown coatings has been investigated by optical and scanning electron microscopy (SEM) and Raman analysis. Optical analysis and SEM allowed the visualization of the morphology of the surface and Raman analysis proved the quality of the monolayers. In a comparative study, we probe in real time the oxidation of both graphene-coated and hBN-coated copper samples, subjected to two representative oxidative scenarios (acute short term, and mild long-term). While Raman spectroscopy is the technique chosen for the real-time investigation, X-ray photoemission spectroscopy and X-ray induced Auger electron spectroscopy are used to establish the degree of oxidation of the samples before and after the oxidation experiments. The inhibition-corrosion performance of graphene and hBN were further investigated electrochemically in Na2SO4 solution (0.1M). The potentiodynamic scan was used to fi nd the corrosion penetration rate and the interpretation of the electrochemical impedance spectroscopy data is aided by analogy to equivalent circuits involving simple components such as resistors and capacitors. Our findings point out the diff erent protective behavior of graphene and hBN, showing that they both excel in diff erent oxidative situations. For prolonged protection, hBN coatings will eventually outperform G-ones, even if the intrinsic quality of G-layer is higher than that of the hBN. Regarding the wet corrosion study, the results show good protective properties for both graphene and hBN, highlighting a superior performance of the latter one.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/131907