Colloidal processing: enabling complex shaped ceramics with unique multiscale structures

Abstract

Colloidal processing of fine ceramic powders enables the production of complex shaped ceramics with unique micro and macro structures which are not possible to produce via conventional dry processing routes. Because of this enhanced structural control and shaping capabilities, colloidal processing has been exploited to produce ceramic components with ever increasing complexity and functionalities. In this review, we revisit some of the research efforts on this topic to highlight its relevance and growing importance for the advanced manufacturing of functional ceramics. Selected examples of colloidal systems with increasing level of complexity are discussed to showcase the wide range of structures that can be generated through wet processing approaches. The historical development and background knowledge pertaining to colloids and surface interactions is first briefly reviewed. The major colloidal shape forming and additive manufacturing processes that utilize colloidal pastes and inks are then reviewed, highlighting the control of suspension rheology needed in these techniques. Next, methodologies that combine suspended particles with a pore‐forming phase are discussed as a means to produce porous ceramic materials. Further control over the interactions between anisotropic particles and their alignment in suspensions can be gained via externally applied fields (such as magnetic) to produce texturally aligned green bodies. This leads to bioinspired ceramics that can programmably morph into complex shaped objects upon sintering. Hierarchical porous structures with high mechanical efficiency are also shown as an example of the multiscale designs that can be generated through advanced colloidal processing. As drying of ceramic bodies is an inevitable consequence of wet colloidal processing, the current understanding of this critical processing step is reviewed. Finally, the gaps in knowledge in these fields are discussed to provide our perspective on where the field may support advances in ceramics in the future.

Multiscale Nanoparticle Assembly: From Particulate Precise Manufacturing to Colloidal Processing

“…[98] After removal of the template, the hollow copper capsules were processed into different shapes by using standard techniques like slip-casting. [3] The preparation of macroscopic aerogel monoliths and the processing of textured ceramics basically represent efforts of two typically separated communities, which use different methods, however with comparable goals. The density of the foam can be precisely controlled by the degree of compaction with a minimum density of as low as 7% relative to bulk copper.…”

“…[3,27] We restrict the discussion to recent examples, where specific efforts were undertaken to position and orient platelets as anisotropic building blocks within a macroscopic body. As this is an extremely broad field, the examples are structured according to the dimensionality of the building blocks and final assembled structures.…”

“…[3] Many of the fundamental problems faced in colloidal processing are also relevant in nanoparticle assembly. [3] Many of the fundamental problems faced in colloidal processing are also relevant in nanoparticle assembly.…”

Viscoelastic behaviors and drying kinetics of different aqueous gelcasting systems for large Nd: YAG laser ceramics rods

“…However, although the gelcasting technology has been developed for decades and it has unique advantages in the preparation of transparent ceramics, there are still some problems that have not been completely solved up to now . The transparent ceramics prepared by gelcasting were generally small round wafer or rectangular strip (about 10‐30 mm in diameter or length) .…”

Freeze casting for near‐net‐shaping of dense zirconium diboride ceramics

“…These will be converted into large pores or channels after freeze‐drying and sintering. Such microstructure is the aim when ice templating is used to produce porous materials, but it is undesirable for high strength, dense advanced ceramic component fabrication as is the aim of the present work. Increasing the concentration of solids in the suspension reduces the tendency of segregation of particles in front of the growing ice crystals.…”