Additive manufacturing (AM) of ceramic materials has attracted tremendous attention in recent years, due to its potential to fabricate suitable advanced ceramic structures for various engineering applications. Robocasting, a subset of ceramic AM, is an ideal technique for constructing fine and dense ceramic structures with geometrically complex morphology. With the freedom and convenience to deposit various materials within any 3D spatial position, ceramic robocasting opens up unlimited opportunities, which are otherwise hardly attainable from other AM techniques. Here, a summary of the recent progress on the fabrication of single and multi-ceramic structures by robocasting is provided, as well as the prospects of achieving shapeable ceramic structures. The current challenges in ceramic robocasting and an outlook on its development, especially toward the fabrication of self-shaping ceramic structures, are also discussed.

Ceramic Robocasting: Recent Achievements, Potential, and Future Developments.

3D printing is a competitive manufacturing technology, which has opened up new possibilities for the fabrication of complex ceramic structures and customised parts. Extrusion-based technologies, also known as direct ink writing (DIW) or robocasting, are amongst the most used for ceramic materials. In them, the rheological properties of the ink play a crucial role, determining both the extrudability of the paste and the shape fidelity of the printed parts. However, comprehensive rheological studies of printable ceramic inks are scarce and may be difficult to understand for non-specialists. The aim of this review is to provide an overview of the main types of ceramic ink formulations developed for DIW and a detailed description of the more relevant rheological tests for assessing the printability of ceramic pastes. Moreover, the key rheological parameters are identified and linked to printability aspects, including the values reported in the literature for different ink compositions.

Rheological characterisation of ceramic inks for 3D direct ink writing: A review

Along with vast research on the additive manufacturing (AM) of polymeric and metallic materials, three-dimensional (3D) manufacturing of ceramic materials is now the modern trend. Among all the additive manufacturing techniques, Direct Ink Writing (DIW) permits the ease of design and rapid manufacturing of ceramic-based materials in complicated geometries. This paper presents an outline of the contributions and tasks in the fabrication 3D ceramic parts by the DIW technique. The current state-of-the-art manufacturing of various ceramics such as alumina, zirconia, and their composites through Direct Ink Writing (DIW) is described in detail. Moreover, this review paper aims at the innovations in the DIW approach of ceramic materials and introduces the progression of the DIW for the manufacturing of ceramics. Most importantly, the DIW technique has been explained in detail with illustrations. The prospects and challenges related to the DIW technique are also underscored.

Direct ink writing (DIW) of structural and functional ceramics: Recent achievements and future challenges

In recent years, additive manufacturing (AM) has emerged as a type of efficient manufacturing technology for building ceramic prototypes with increased dimensional accuracy, improved time efficiency, and reduced cost A wealth of research works have been conducted to uncover the underlying formation mechanism of zirconia ceramic parts manufactured by AM processes and to improve the performance of the parts In spite of the achievements, there are still some unresolved issues, such as porosity, cracks, coffee staining, which impede the adoption of AM processes for zirconia part manufacturing This paper aims to review the recent research efforts on zirconia ceramic manufactured using AM techniques The existing works are mainly categorized in terms of the different AM preparation methods and the applications More importantly, the challenges and opportunities related to AM of zirconia products are discussed As such, this review provides not only a comprehensive survey of the existing research, but also an insightful discussion regarding the potential research in the future Innovations are expected to be stimulated for many critical industrial applications

Additive manufacturing of zirconia ceramics: a state-of-the-art review

Due to the special crystal structures and electron configurations, high-entropy alloys (HEAs) are expected to have favorable activities for electrocatalytic reactions. In this paper, a set of oxygen evolution reaction (OER) criteria are applied for the HEA-based electrocatalyst design. Specifically, FeNiMnCrCu HEA is predicted to have a better OER performance than the baseline FeCoNiCrAI HEA. To demonstrate this design approach, both FeNiMnCrCu and FeCoNiCrAI samples are prepared and tested. Their crystal structures and electrocatalytic performance are examined. This paper demonstrates the potential of using finely tuned HEAs for OER applications.

Electrocatalytic activity of high-entropy alloys toward oxygen evolution reaction

Advanced ceramic materials with complex design have become inseparable from the current engineering applications. Due to the limitation of traditional ceramic processing, ceramic additive manufacturing (AM) which allows high degree of fabrication freedom has gained significant research interest. Among these AM techniques, low-cost robocasting technique is often considered to fabricate complex ceramic components. In this work, aqueous ceramic suspension comprising of commercial nano-sized yttria-stabilized zirconia (YSZ) powder has been developed for robocasting purpose. Both fully and partially stabilized YSZ green bodies with complex morphologies were successfully printed in ambient conditions using relatively low-solid-content ceramic suspensions ( 94% of the theoretical density despite its high linear shrinkage (up to 33%). The microstructure analysis indicated that dense fully and partially stabilized YSZ with grain size as small as 1.40 ± 0.53 and 0.38 ± 0.10 μm can be obtained, respectively. The sintered partially stabilized YSZ solid and porous mesh samples (porosity of macro-pores >45%) exhibited hardness up to 13.29 GPa and flexural strengths up to 242.8 ± 11.4 and 57.3 ± 5.2 MPa, respectively. The aqueous-based ceramic suspension was also demonstrated to be suitable for the fabrication of large YSZ parts with good repeatability.

Robocasting of dense yttria-stabilized zirconia structures

A non-precious metal catalytic system of Fe-doped Ta2O5 is developed by pulsed laser deposition toward efficient oxygen evolution reaction (OER). The optimal Fe concentration is determined to be 5 at.%for optimized OER activity via a series of electrochemical characterizations. The 5 at.% Fe-doped Ta2O5 nanolayer possesses a low onset overpotential of 0.22 V, an overpotential of 0.38 V at 10 mA/cm2 and a Tafel slope of 54 mV/dec. Comprehensive first-principles calculations attribute the enhanced OER activity to the substitutional FeTa dopants, which generate a new active OER site on surface and simultaneously accelerate electron transfer over oxygens.

Aihong Liu

Papers

Robocasting of dense yttria-stabilized zirconia structures

Economical Fe-doped Ta2O5 electrocatalyst toward efficient oxygen evolution: a combined experimental and first-principles study