Dr. Maxim Sokol
Department of Materials Science and Engineering
Drexel University, Philadelphia, PA (USA)
Nanoceramics and nanostructured ceramics are attracting growing interest, thanks to advances in the synthesis of nanocrystalline ceramic powder and development of new processing methods. They exhibit unique mechanical, and surface characteristics such as superplasticity, machinability, strength, hardness, and bioactivity due to the fine grain size, abundant grain boundaries, and controllable crystallinity. In order to fully exploit their exceptional properties, a deep understanding of the materials’ behavior across length scales is necessary. In fact, knowing how the nanoscale structure influences the bulk properties enables the design of high-performance materials. An important aspect is the ability to tailor the desired nanostructured features in the sintered ceramic, a challenging issue requiring a careful control of all stages of manufacturing, from powder synthesis to densification.
This presentation is divided into two parts. In the first part of the talk, a unique fabrication process termed high-pressure spark plasma sintering (HPSPS) that enables consolidation of fully dense nanostructured ceramics along with an in-depth microstructural examination of fully dense magnesium aluminate spinel (MAS) with average grain sizes below 30 nm will be presented. Furthermore, an abnormal mechanical behavior of the nanostructured oxide ceramics, known as Inverse Hall-Patch will be discussed in detail.
In the second part, the MAX phases, a nanolayered, hexagonal, early transition-metal carbides and nitrides and their 2D derivatives known as MXene (pronounced “maxenes”) will be introduced. MXenes have shown promise in a wide range of applications, such as energy storage, catalysis, EMI shielding, among many others. However, MXene oxidation in aqueous colloidal suspensions when stored in water at ambient conditions remains a challenge. Recently, we showed that the edges of MXene flakes are positively charged. This insight opened a new avenue to selectively functionalize the edges differently from the faces to vary both surfaces. Our results show that by simply capping the edges of individual MXene flakes with polyanions, it is possible to significantly reduce their propensity for oxidation even when held in aerated water for weeks. This discovery finally makes long-term storage of MXenes possible which can make its industrial scale processing viable.