Additive Manufacturing of Ceramics. Printing Beyond the Binder

This research project focuses on the production of ceramics via Additive Manufacturing (AM) techniques, with particular focus on extrusion-based technologies. The main advantage of AM is the ability to produce cellular structures with high complexity and controlled porosity, allowing to manufacture light but efficient stretch-dominated structures. The inspiration comes from nature: bone architectures are a great example, consisting of thin, solid skins attached to highly porous, cellular cores. Very few commercially available AM systems are suited for ceramic materials, and most of them use ceramic powders as feedstock. Residual pores and cracks are very hard to avoid and result in low strength, poor reliability and loss of unique material properties such as glass optical transparency. AM technologies employing polymers are at a much more advanced stage of development. The goal has been to exploit such advances and to provide alternatives to the ceramic powder-binder approaches. Three different material families were explored: preceramic polymers, geopolymers, and glass. The same preceramic polymer, a commercial polysilsesquioxane, was employed as a non sacrificial, reactive binder to develop inks for stereolithography (SL) and direct ink writing (DIW). The first technology allowed for production of dense, crack-free SiOC micro-components with strut size down to ~200 μm and optimal surface quality. No shape limitations were experienced, but porous structures or small dense parts are the best options in order to avoid residual pores and cracks. The second approach was employed for the fabrication of complex biosilicate scaffolds for tissue engineering with a rod diameter of 350 µm and unsupported struts. The preceramic polymer had the double role of source of silica and rheology modifier. Ceramic matrix composites (CMCs) were also fabricated; the preceramic polymer developed the ceramic matrix (SiOC) upon pyrolysis in inert atmosphere, whereas reinforcement was given by chopped carbon fibers. Geopolymer components with controlled porosity were designed and produced first by negative replica of PLA sacrificial templates and then by DIW. Highly porous ceramic components with features of ~800 μm and unsupported parts with very limited sagging were produced with the latter approach. A novel extrusion-based AM approach was finally developed for the production of objects starting from molten glass. The system processed glass from the molten state to annealed components of complex, digitally designed forms. Objects possessing draft angles and tight radii were fabricated. Within the design space it was possible to print with high precision and accuracy; parts showed a strong adhesion between layers, and high transparency through the layers

Porous Geopolymer Components

Geopolymers are based on an inorganic 3D network of alumino-silicate units usually synthesized through reaction of alumino-silicate powders in presence of a silicate alkaline solution. The rheological characteristics of the reactive mixtures and the fact that these systems can consolidate at low or even room temperature, together with their intrinsic micro- and meso-porosity and mechanical properties, are the reason why they are considered for a wide range of applications, such as construction materials, thermal insulation, filters, adsorbers and so on. Open cell alkali or acid-based geopolymer foams were produced by direct foaming using different fabrication approaches. Potassium-based foams with a porosity up to 85 vol% were obtained from metakaolin, potassium silicate and potassium hydroxide, while metakaolin and phosphoric acid were used to fabricate foams containing an aluminum phosphate crystal phase already after synthesis at room temperature, and a total porosity of ~80 vol%. The strength of the foams depended on the porosity of the components as well as the heat treatment temperature. Components with designed, non-stochastic porosity were also produced by additive manufacturing, specifically Direct Ink Writing. Paste with suitable pseudo-plastic rheology were developed and we fabricated components with overhangs and spanning features, including highly porous 3D lattices

3D printed geopolymeric lattices: Effect of different filler materials on mechanical properties

Our group developed mixtures based on geopolymer for additive manufacturing of porous components via direct ink writing (DIW). We optimized the rheological properties in order to obtain suitable inks for the production of highly porous lattices. It should be noted that, as geopolymer mixtures are subjected to ongoing poly-condensation reactions, their viscosity changes with time in what can be seen as a 4D printing process. Different materials were added to the mixture, such as glass and plastic fibers, as well as fillers like sand, to produce innovative 3D printed geopolymeric composites. The influence of these materials on the mechanical properties was evaluated

Methods and apparatus for additive manufacturing of glass

In illustrative implementations of this invention, a crucible kiln heats glass such that the glass becomes or remains molten. A nozzle extrudes the molten glass while one or more actuators actuate movements of the nozzle, a build platform or both. A computer controls these movements such that the extruded molten glass is selectively deposited to form a 3D glass object. The selective deposition of molten glass occurs inside an annealing kiln. The annealing kiln anneals the glass after it is extruded. In some cases, the actuators actuate the crucible kiln and nozzle to move in horizontal x, y directions and actuate the build platform to move in a z-direction. In some cases, fluid flows through a cavity or tubes adjacent to the nozzle tip, in order to cool the nozzle tip and thereby reduce the amount of glass that sticks to the nozzle tip

Biodiesel Processing Using Sodium and Potassium Geopolymer Powders as Heterogeneous Catalysts

This work investigates the catalytic activity of geopolymers produced using two different alkali components (sodium or potassium) and four treatment temperatures (110 to 700 \ub0C) for the methyl transesterification of soybean oil. The geopolymers were prepared with metakaolin as an aluminosilicate source and alkaline activating solutions containing either sodium or potassium in the same molar oxide proportions. The potassium-based formulation displayed a higher specific surface area and lower average pore size (28.64-62.54 m\ub2/g; 9 nm) than the sodium formulation (6.34-32.62 m\ub2/g; 17 nm). The reduction in specific surface area (SSA) after the heat treatment was more severe for the sodium formulation due to the higher thermal shrinkage. The catalytic activity of the geopolymer powders was compared under the same reactional conditions (70-75 \ub0C, 150% methanol excess, 4 h reaction) and same weight amounts (3% to oil). The differences in performance were attributed to the influences of sodium and potassium on the geopolymerization process and to the accessibility of the reactants to the catalytic sites. The Na-based geopolymers performed better, with FAME contents in the biodiesel phase of 85.1% and 89.9% for samples treated at 500 and 300 \ub0C, respectively. These results are competitive in comparison with most heterogeneous base catalysts reported in the literature, considering the very mild conditions of temperature, excess methanol and catalyst amount and the short time spent in reactions

Additive Manufacturing of Optically Transparent Glass

We present a fully functional material extrusion printer for optically transparent glass. The printer is composed of scalable modular elements able to operate at the high temperatures required to process glass from a molten state to an annealed product. We demonstrate a process enabling the construction of 3D parts as described by computer-aided design models. Processing parameters such as temperature, which control glass viscosity, and flow rate, layer height, and feed rate can thus be adjusted to tailor printing to the desired component, its shape, and its properties. We explored, defined, and hard-coded geometric constraints and coiling patterns as well as the integration of various colors into the current controllable process, contributing to a new design and manufacturing space. We report on performed characterization of the printed materials executed to determine their morphological, mechanical, and optical properties. Printed parts demonstrated strong adhesion between layers and satisfying optical clarity. This molten glass 3D printer demonstrates the production of parts that are highly repeatable, enable light transmission, and resemble the visual and mechanical performance of glass constructs that are conventionally obtained. Utilizing the optical nature of glass, complex caustic patterns were created by projecting light through the printed objects. The 3D-printed glass objects described here can thus be extended to implementations across scales and functional domains including product and architectural design. This research lies at the intersection of design, engineering, science, and art, representing a highly interdisciplinary approach.Massachusetts Institute of Technology. Department of Mechanical EngineeringGlass Art Society (Technology Advancing Glass Grant

Rapid SARS-CoV-2 intra-host and within-household emergence of novel haplotypes

In February 2020, the municipality of Vo’, a small town near Padua (Italy) was quarantined due to the first coronavirus disease 19 (COVID-19)-related death detected in Italy. To investigate the viral prevalence and clinical features, the entire population was swab tested in two sequential surveys. Here we report the analysis of 87 viral genomes, which revealed that the unique ancestor haplotype introduced in Vo’ belongs to lineage B, carrying the mutations G11083T and G26144T. The viral sequences allowed us to investigate the viral evolution while being transmitted within and across households and the effectiveness of the non-pharmaceutical interventions implemented in Vo’. We report, for the first time, evidence that novel viral haplotypes can naturally arise intra-host within an interval as short as two weeks, in approximately 30% of the infected individuals, regardless of symptom severity or immune system deficiencies. Moreover, both phylogenetic and minimum spanning network analyses converge on the hypothesis that the viral sequences evolved from a unique common ancestor haplotype that was carried by an index case. The lockdown extinguished both the viral spread and the emergence of new variant

Additive Manufacturing of Ceramics. Printing Beyond the Binder

This research project focuses on the production of ceramics via Additive Manufacturing (AM) techniques, with particular focus on extrusion-based technologies. The main advantage of AM is the ability to produce cellular structures with high complexity and controlled porosity, allowing to manufacture light but efficient stretch-dominated structures. The inspiration comes from nature: bone architectures are a great example, consisting of thin, solid skins attached to highly porous, cellular cores. Very few commercially available AM systems are suited for ceramic materials, and most of them use ceramic powders as feedstock. Residual pores and cracks are very hard to avoid and result in low strength, poor reliability and loss of unique material properties such as glass optical transparency. AM technologies employing polymers are at a much more advanced stage of development. The goal has been to exploit such advances and to provide alternatives to the ceramic powder-binder approaches. Three different material families were explored: preceramic polymers, geopolymers, and glass. The same preceramic polymer, a commercial polysilsesquioxane, was employed as a non sacrificial, reactive binder to develop inks for stereolithography (SL) and direct ink writing (DIW). The first technology allowed for production of dense, crack-free SiOC micro-components with strut size down to ~200 μm and optimal surface quality. No shape limitations were experienced, but porous structures or small dense parts are the best options in order to avoid residual pores and cracks. The second approach was employed for the fabrication of complex biosilicate scaffolds for tissue engineering with a rod diameter of 350 µm and unsupported struts. The preceramic polymer had the double role of source of silica and rheology modifier. Ceramic matrix composites (CMCs) were also fabricated; the preceramic polymer developed the ceramic matrix (SiOC) upon pyrolysis in inert atmosphere, whereas reinforcement was given by chopped carbon fibers. Geopolymer components with controlled porosity were designed and produced first by negative replica of PLA sacrificial templates and then by DIW. Highly porous ceramic components with features of ~800 μm and unsupported parts with very limited sagging were produced with the latter approach. A novel extrusion-based AM approach was finally developed for the production of objects starting from molten glass. The system processed glass from the molten state to annealed components of complex, digitally designed forms. Objects possessing draft angles and tight radii were fabricated. Within the design space it was possible to print with high precision and accuracy; parts showed a strong adhesion between layers, and high transparency through the layers.Questo progetto di ricerca riguarda la produzione di ceramici tramite tecniche di manifattura additiva (AM), con particolare focus su tecnologie estrusive. Il principale vantaggio dell’AM è la possibilità di produrre strutture cellulari ad elevata complessità e porosità controllata, consentendo di produrre reticoli stretch-dominated leggeri ma efficienti. L’ispirazione è offerta dalla natura: le strutture ossee sono un ottimo esempio, in quanto si compongono di un involucro esterno, denso e sottile, e di un cuore a struttura cellulare altamente porosa. I sistemi di AM disponibili in commercio per la produzione di componenti ceramici sono molto pochi, e la maggior parte di essi utilizza polveri ceramiche. È molto difficile evitare porosità residua e cricche, e di conseguenza si ottengono oggetti dalla resistenza limitata e privi delle peculiarità di alcuni materiali, come ad esempio la trasparenza del vetro. Le tecnologie di AM che utilizzano polimeri sono ad uno stadio di sviluppo molto più avanzato. L’obiettivo è di sfruttare tale vantaggio e di fornire alternative agli approcci polvere-legante. Sono stati esplorati tre diversi materiali: polimeri preceramici, geopolimeri, e vetro. Un unico polimero preceramico, un polisilsesquiossano commerciale, è stato utilizzato come legante reattivo, non sacrificale per lo sviluppo di inchiostri per stereolitografia (SL) e direct ink writing (DIW). La prima tecnologia ha consentito di produrre micro-componenti in SiOC densi e privi di cricche, con una dimensione dei pilastri fino a ~200 μm e ottima qualità superficiale. Non ci sono state limitazioni di forma, anche se strutture porose o oggetti densi di piccole dimensioni sono da preferire per evitare porosità residua e cricche. Il secondo approccio ha portato alla fabbricazione di scaffold bioceramici per ingegneria tissutale con filamenti di diametro 350 µm e parti non supportate. Il polimero preceramico ha il doppio ruolo di fonte di silice e di modificatore reologico. Sono stati prodotti anche compositi a matrice ceramica (CMCs); il polimero preceramico sviluppa la matrice (SiOC) tramite pirolisi in atmosfera inerte, mentre il rinforzo è dato da fibre di carbonio macinate. Componenti in geopolimero a porosità controllata sono stati progettati e prodotti prima tramite replica negativa di template sacrificali in PLA, e poi via DIW. Il secondo approccio ha portato alla produzione di reticoli ceramici con filamenti di ~800 μm e parti non supportate con deflessione molto limitata. È stato sviluppato infine un innovativo processo estrusivo a partire da vetro fuso. Un unico sistema è in grado di lavorare il vetro dallo stato fuso fino alla ricottura di componenti complessi progettati digitalmente. Sono stati realizzati oggetti comprendenti sporgenze di diversa entità e piccoli raggi di curvatura. All’interno dello spazio di progettazione è stato possibile stampare con elevata precisione e accuratezza; le parti stampate mostrano una forte adesione tra gli strati e un’elevata trasparenza attraverso di essi

Lenti fotocromiche per ottica adattiva

L'elaborato descrive la caratterizzazione di un materiale fotocromico e il suo utilizzo per la progettazione e la realizzazione di un dispositivo di ottica adattiva in grado di variare la propria lunghezza focale; si riportano inoltre i risultati dei test effettuati per la valutazione della risoluzione del sistema realizzat