Supervariate Ceramics: Gelatinous and Monolithic Ceramics Fabricated under Ambient Conditions

Significance 

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.

Supervariate Ceramics: Gelatinous and Monolithic Ceramics Fabricated under Ambient Conditions - Advances in Engineering

Figure credit: Advanced Engineering Materials, https://doi.org/10.1002/adem.202100866

About the author

Dr. Yang Yang Li is an associate professor at the Department of Materials Science and Engineering, City University of Hong Kong. She obtained her B.S. degree from Peking University, M.S. degree from National University of Singapore, and Ph.D degree from the University of California, San Diego.

Her research interest focuses on i) biomineralization and green processing of ceramics; ii) sensors, particularly surface-enhanced Raman spectroscopy (SERS) probes for food safety, environmental, and biomedical applications; iii) electrochemistry of materials for electrocatalysis and batteries.

About the author

Professor Jian LU 

Dip Ing, MSc, PhD (UTC), Habilitation (Sorbonne University (Pierre et Marie Curie)), Fellow SEM, Fellow HKAES, Fellow HKIS, Academician: National Academy of Technologies of France 

City University of Hong Kong

  • Chair Professor of Mechanical Engineering
  • Senior Fellow of Hong Kong Institute for Advanced Study
  • Director of Hong Kong Branch of National Precious Metals Material Engineering Research Center (since Dec 2015)
  • Director of Centre of Advanced Structural Materials (since Aug 2011)
  • Vice-President (Research and Technology) and Dean of Graduate Studies (15 Nov 2013 – 30 Nov 2020)
  • Dean of College of Science and Engineering (2010-14 Nov 2013)

His research interests are surface science and engineering, processing and mechanical properties of nanomaterials and advanced materials, experimental mechanics and residual stress. Prof. Jian Lu has published more than 460 journal papers including papers in Nature (cover story), Science, Science Advances, Nature Materials, Nature Communications, Materials Today, Advanced Materials, Physical Review Letters, Acta Materialia, Journal of the Mechanics and Physics of Solids. His publications have been cited more than 32,000 times. He is the inventor of more than 50 granted patents in USA, Europe and China with international extension.

He was awarded in 2006 the French Knight Order of National Merit (Chevalier de l’Ordre National du Mérite); and in 2017 the Knight of the National Order of the French Legion of Honour (Chevalier de la Legion D’honneur); In 2011, he was elected as an Academician of the National Academy of Technology of France. He was the recipient of the 12th Guanghua Engineering Science and Technology Award in 2018, which was regarded as “the most prestigious award for engineering and technology achievement in China”.

Reference

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 ConditionsAdvanced Engineering Materials, 23(12), 2100866.

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