The aim of the work was to explore the possibility of producing metallic composite phase change materials (C-PCMs) intended to be used as Latent Heat Thermal Energy Storage (LH-TES) systems, by exploiting the inverse microstructure in Miscibility Gap Alloys (MGAs). To this purpose, six different compositions based on Al-alloys were produced by casting, varying compositional and process parameters. The produced materials were composed by an Al-based matrix with a dispersed low melting Sn-rich phase that can store/release latent heat by its melting/solidification, while the matrix remains in solid state. Thermodynamic CALPHAD-based simulations were carried out to visualize the expected phases and properties, while FE Analyses were used to estimate the cooling rate experienced by the alloys during processing. Microstructural characterization was performed with both optical and FEG-SEM observations, while thermal characterization was performed with Differential Scanning Calorimetry and dilatometry tests. Results show in all the alloys a microstructure characterized by the active phase(s) embedded in the high-melting phases, resulting in a suitable structure for limiting the exudation of the Sn-rich phase. However, high complexity in terms of structures and morphology was found, combined with a wide range of diverse conformations through various compositions. Thermal response tests show promising enthalpies of fusion of the Sn-rich phase, from 20 to 40 J/g depending on the tin content, in the range of 200-230°C. Furthermore, the stability of this thermal response results to be consistent already after the first cycle; at the same time, alloys show the form stability after the first cycle. All these features together make this system very attractive for Thermal Energy Storage applications.
L’obiettivo del lavoro di tesi è stato quello di esplorare la possibilità di produrre materiali compositi metallici contenenti stagno (C-PCM) destinati ad essere utilizzati come sistemi di accumulo termico di energia (LH--TES) sfruttando il calore latente e la microstruttura inversa tipica delle leghe a lacuna di miscibilità (MGA). A questo proposito, sono state prodotte 6 diverse composizioni basate su leghe di alluminio mediante una tecnica di fusione, andando a variare parametri composizionali e di processo. Tutte le composizioni contenenti stagno presentano una matrice ricca in alluminio e una fase ricca in stagno, la quale può immagazzinare e rilasciare calore latente durante fusione e solidificazione. Simulazioni termodinamiche basate su CALPHAD sono state condotte per calcolare le fasi e le proprietà previste dai dati termodinamici, mentre analisi FE sono state utilizzate per stimare la velocità di raffreddamento sperimentate dalle leghe durante il processo. La caratterizzazione microstrutturale è stata eseguita con l’impiego di microscopio ottico e microscopio elettronico a scansione, mentre la caratterizzazione termica è stata effettuata con test DSC e dilatometria. I risultati mostrano una microstruttura inversa in tutte le leghe, con la fase attiva incorporata nelle fasi alto fondenti, risultando nel complesso una struttura adatta per limitare la fuoriuscita di stagno. Tuttavia, è stata riscontrata un'alta complessità in quanto a strutture e morfologia, unita ad un ampio spettro di diverse conformazioni al variare delle composizioni. Le analisi calorimetriche, invece, mostrano entalpie di fusione della fase attiva promettenti, da 20 a 40 J/g a seconda del contenuto di stagno, nell'intervallo di 200-230°C. Inoltre, la risposta termica risulta stabile già dopo il primo ciclo. Anche le analisi dilatometriche mostrano una tendenza marcata alla stabilizzazione del comportamento dal secondo ciclo in poi. L’insieme di questi risultati rendono questo sistema molto attraente per applicazioni di stoccaggio di energia termica.
Microstructural and thermo-mechanical characterization of Aluminium alloys with relevant Sn content
BETTEGA, ISAIA
2022/2023
Abstract
The aim of the work was to explore the possibility of producing metallic composite phase change materials (C-PCMs) intended to be used as Latent Heat Thermal Energy Storage (LH-TES) systems, by exploiting the inverse microstructure in Miscibility Gap Alloys (MGAs). To this purpose, six different compositions based on Al-alloys were produced by casting, varying compositional and process parameters. The produced materials were composed by an Al-based matrix with a dispersed low melting Sn-rich phase that can store/release latent heat by its melting/solidification, while the matrix remains in solid state. Thermodynamic CALPHAD-based simulations were carried out to visualize the expected phases and properties, while FE Analyses were used to estimate the cooling rate experienced by the alloys during processing. Microstructural characterization was performed with both optical and FEG-SEM observations, while thermal characterization was performed with Differential Scanning Calorimetry and dilatometry tests. Results show in all the alloys a microstructure characterized by the active phase(s) embedded in the high-melting phases, resulting in a suitable structure for limiting the exudation of the Sn-rich phase. However, high complexity in terms of structures and morphology was found, combined with a wide range of diverse conformations through various compositions. Thermal response tests show promising enthalpies of fusion of the Sn-rich phase, from 20 to 40 J/g depending on the tin content, in the range of 200-230°C. Furthermore, the stability of this thermal response results to be consistent already after the first cycle; at the same time, alloys show the form stability after the first cycle. All these features together make this system very attractive for Thermal Energy Storage applications.File | Dimensione | Formato | |
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2023_12_Bettega_Executive_Summary_02.pdf
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Descrizione: Executive Summary
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2023_12_Bettega_Tesi_01.pdf
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Descrizione: Tesi
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16.22 MB
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16.22 MB | Adobe PDF | Visualizza/Apri |
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https://hdl.handle.net/10589/215546