Inkjet printing is a versatile manufacturing method with applications beyond its traditional application in graphics and text printing, particularly in structural and functional materials. This thesis aims to enhance the understanding of DOD inkjet printing processes by investigating the behaviour of solvent mixtures and nanoparticle suspensions to identify the key parameters affecting drop ejection, drying and stacking processes. Drop ejection and flight were investigated with two modes of inkjet printheads, using a range of fluids formulated from solvent mixtures and characterised by the dimensionless Z number. The printable range was found to be 1.17 smaller or equal to Z smaller or equal to 36.76 for a 10 pl (21.5 micro metre diameter) shear-mode Dimatix printhead. However, with an 80 micro metre diameter squeeze-mode MicroFab printhead, the range was found to be narrower with 4.02 smaller or equal to Z smaller or equal to 16.2. However, both printheads were found to show a printable range of Weber number with 0.4 <We <20. Weber number is determined by the drop velocity and hence the actuating pulse. When designing inks for future printing work, not only the fluid properties, but also the pulse voltages need to be considered. The drop stacking and solidification processes of drops containing nano ZrO2 particles were investigated to enhance the understanding of drop drying and drop/drop interactions. In-situ synchrotron X-ray radiography provides a promising method to track the time-evolved solid segregation within printed drops during drying. Both the initial contact angle and substrate temperature during printing strongly influence the drying process and the final dried deposit shape. The drops were first pinned and then there was a slight sliding of the three-phase contact line. Drops were deformed by the stacking of overprinted drops when printed on Kapton tapes and silicon wafer surfaces, but not on glass slides due to the small contact angle of water on glass slides. Crack-like defects were found at the edge of the final dried stacking structures. The coffee stain effects within a single inkjet printed droplet and the 3D structures before and after sintering were investigated to find out the influence of ink properties, printing parameters and substrate temperature on inkjet printed structures. It was found coffee staining was more obvious at high substrate temperatures. When adding 25 vol% ethylene glycol (EG) or 5 wt% polyethylene glycol (PEG), the coffee stain effect is reduced or eliminated under room temperature drying. X-ray tomography has been demonstrated as a valuable tool for the characterization of 3D printed objects and defects that form during their manufacture. Defects were characterised as microvoids or large-scale crack-like defects. The majority of the microvoids revealed are associated with mechanisms and processes within a single drop, e.g. segregation during dryings such as the formation of coffee stains or coffee rings. The size or distribution of microvoids can be controlled by changing the ink formulation, with higher PEG content inks showing lower concentrations of microvoids.

Nous avons étudié in situ et en temps réel la structure de grains du silicium multi-cristallin issue de la solidification dirigée en utilisant l’imagerie X synchrotron. La radiographie X permet de suivre l’évolution de l’interface solide/liquide et de caractériser sa dynamique et sa morphologie. La topographie X nous donne des informations sur la structure de grains formée, les contraintes et les défauts issus de la solidification. Nous avons montré l’importance la préparation de l’état initial de la solidification en particulier pour les expériences de reprise sur germe. L’analyse de la morphologie de l’interface solide/liquide nous a permis de caractériser la surfusion cinétique du front de solidification, de comprendre l’évolution des sillons de joints de grains et d’analyser les mécanismes de compétition de grains ainsi que de révéler l’impact des impuretés sur la structure de grains formée à l’issue de la solidification. Le phénomène de maclage a aussi été observé dans nos expériences et nous avons démontré que les macles dans le silicium multi-cristallin peuvent être des macles de croissance. Deux types de macles ont été identifiés et le phénomène de compétition de grains en présence de macles étudié. / We studied in situ and real-time the grain structure of multi-crystalline silicon from directional solidification using synchrotron X-ray imaging techniques. X-ray Radiography gives information on the evolution, dynamics and morphology of the solid/liquid interface. X- ray Topography gives more information on the grain structure, strains and defects that occur during solidification step. We showed the importance of the preparation of the initial stage of solidification in particular in the experiments where solidification is initiated from seed. The analysis of the solid/liquid interface morphology allowed us to characterize the kinetic undercooling of the solidification front, to understand the evolution of the grains boundary grooves and to analyze the mechanisms of grain competition and also to reveal the impurities impact on the grain structure formed at the end of the solidification. We also observed twinning phenomenon in our experiments and we demonstrated that twins in multi-crystalline silicon can be growth twins. Two kinds of silicon twins have been identified and the grain competition phenomenon with twins studied.