Unlike metals and polymers, it is difficult to cast or mold ceramics owing to their high melting point and mechanical hardness properties. The most used conventional method for fabricating ceramics involves high-temperature firing of compacted raw powders and high pressures in some situations. This sintering method is, however, costly, complex, labor-intensive and does not guarantee precision manufacturing. In recent years, cold sintering using high pressures has been extensively studied as a more convenient alternative method for producing monolithic ceramics are relatively low temperatures. Cold sintering techniques are limited to regular geometries and unsuitable for mass production. Therefore, large-scale and low-temperature manufacturing of ceramic devices with flexible geometric designs remains an important challenge.
Additive manufacturing, also known as 3D printing, has been increasingly used in manufacturing various devices owing to its efficiency and flexibility. 3D printing has been identified as a promising candidate for the production of ceramic devices with complex geometries. Nevertheless, despite the significant research efforts, direct 3D printing of ceramic-based materials under ambient conditions with no posttreatment requirements is yet to be reported. From previous findings, this challenge can be solved by developing strategies capable of conveniently molding or casting ceramics under mild conditions like polymers or metals.
On this account, Dr. Hao Wang, Dr. Yan Bao, Dr. Zhengyi Mao, Mr. Jie Pan, Dr. Haidong Bian, Professor Zhengtao Xu, Professor Jian Lu and Professor Yang Yang Li from the City University of Hong Kong developed a new method for direct fabrication of gelatinous and monolithic ceramic objects from common salts under ambient conditions (ambient pressure and room temperature). First, a supervariate system was created by mixing precursor solutions of common salts. Next, the supervariate ceramic gels were dried under ambient conditions and converted into monolithic ceramic materials. Finally, the mechanical properties of the resulting ceramic objects were examined in detail. Their research work is currently published in the journal, Advanced Engineering Materials.
The researchers showed that the resulting monolithic ceramic materials exhibited excellent mechanical properties, including a high hardness value (1.2 GPa) and a significant reduction in the elastic modulus (26 GPa). Moreover, the ceramics dried under ambient conditions showed tolerance to high-temperature annealing (1500 °C). During the annealing process, it stayed intact and achieved a further improvement in the hardness (11.7 GPa) and elastic modulus (132 GPa). The reported approach holds promise for low-cost, easy and precision production of different ceramic devices for different applications. It also displayed possibilities for automatic mass production.
The successful manufacturing of monolithic ceramics was attributed to the generic mechanism that played a critical role in suppressing new surfaces during the fabrication process. This important mechanism was enabled by dissolving multiple ionic compounds in the precursor solutions. During solidification, the different ions offered great supervariate arrays of aggregating and bonding propensities, allowing the filling of the cracks and voids to remove the dangling bonds responsible for the formation of defects. The term “supervariate” refers to the components of the aggregating process as well as the crystallinity, properties and tenable phase behaviors associated with the ceramic products.
In a nutshell, City University of Hong Kong researchers demonstrated the successful manufacturing of gelatinous and monolithic ceramics with an excellent mechanical performance from multiple-ionic precursor solutions under ambient conditions. Moreover, they showed the effectiveness and efficiency of the supervariate strategy for casting or molding ceramics under ambient conditions like polymers or metals with great convenience to obtain the required mechanical performances and functionalities. In a statement to Advances in Engineering, the authors said that the versatility of the supervariate ceramics will broaden their applications and importance among materials scientists.
Figure credit: Advanced Engineering Materials, https://doi.org/10.1002/adem.202100866
Wang, H., Bao, Y., Mao, Z., Pan, J., Bian, H., Xu, Z., Lu, J., & Li, Y. (2021). Supervariate Ceramics: Gelatinous and Monolithic Ceramics Fabricated under Ambient Conditions. Advanced Engineering Materials, 23(12), 2100866.