Superparamagnetic Silicon Carbonitride Ceramic Fibers Through In Situ Generation of Iron Silicide Nanoparticles During Pyrolysis of an Iron-Modified Polysilazane

Encapsulating Nickel-Iron Alloy Nanoparticles in a Polysilazane-Derived Microporous Si-C-O-N-Based Support to Stimulate Superior OER Activity

The in situ confinement of nickel (Ni)-iron (Fe) nanoparticles (NPs) in a polymer-derived microporous silicon carboxynitride (Si-C-O-N)-based support is investigated to stimulate superior oxygen evolution reaction (OER) activity in an alkaline media. Firstly, we consider a commercial polysilazane (PSZ) and Ni and Fe chlorides to be mixed in N,N-dimethylformamide (DMF) and deliver after overnight solvent reflux a series of Ni-Fe : organosilicon coordination polymers. The latter are then heat-treated at 500 °C in flowing argon to form the title compounds. By considering a Ni : Fe ratio of 1.5, face centred cubic (fcc) NixFey alloy NPs with a size of 15-30 nm are in situ generated in a porous Si-C-O-N-based matrix displaying a specific surface area (SSA) as high as 237 m2 ⋅ g-1. Hence, encapsulated NPs are rendered accessible to promote electrocatalytic water oxidation. An OER overpotential as low as 315 mV at 10 mA ⋅ cm-2 is measured. This high catalytic performance (considering that the metal mass loading is as low as 0.24 mg cm-2) is rather stable as observed after an activation step; thus, validating our synthesis approach. This is clearly attributed to both the strong NP-matrix interaction and the confinement effect of the matrix as highlighted through post mortem microscopy observations.

SiCNFe Ceramics as Soft Magnetic Material for MEMS Magnetic Devices: A Mössbauer Study

Polymer-derived SiCNFe ceramics is a prospective material that can be used as soft magnets in MEMS magnetic applications. The optimal synthesis process and low-cost appropriate microfabrication should be developed for best result. Homogeneous and uniform magnetic material is required for developing such MEMS devices. Therefore, the knowledge of exact composition of SiCNFe ceramics is very important for the microfabrication of magnetic MEMS devices. The Mössbauer spectrum of SiCN ceramics, doped with Fe (III) ions, and annealed at 1100 °C, was investigated at room temperature to accurately establish the phase composition of Fe-containing magnetic nanoparticles, which were formed in this material at pyrolysis and which determine their magnetic properties. The analysis of Mössbauer data shows the formation of several Fe-containing magnetic nanoparticles in SiCN/Fe ceramics, such as α-Fe, Fe_xSi_yC_z, traces of Fe-N and paramagnetic Fe³⁺ with octahedral oxygen environment. The presence of iron nitride and paramagnetic Fe³⁺ ions shows that the pyrolysis process was not completed in SiCNFe ceramics annealed at 1100 °C. These new observations confirm the formation of different Fe-containing nanoparticles with complex composition in SiCNFe ceramic composite.

Advances in the Synthesis of Preceramic Polymers for the Formation of Silicon-Based and Ultrahigh-Temperature Non-Oxide Ceramics

Preceramic polymers (PCPs) are a group of specialty macromolecules that serve as precursors for generating inorganics, including ceramic carbides, nitrides, and borides. PCPs represent interesting synthetic challenges for chemists due to the elements incorporated into their structure. This group of polymers is also of interest to engineers as PCPs enable the processing of polymer-derived ceramic products including high-performance ceramic fibers and composites. These finished ceramic materials are of growing significance for applications that experience extreme operating environments (e.g., aerospace propulsion and high-speed atmospheric flight). This Review provides an overview of advances in the synthesis and postpolymerization modification of macromolecules forming nonoxide ceramics. These PCPs include polycarbosilanes, polysilanes, polysilazanes, and precursors for ultrahigh-temperature ceramics. Following our review of PCP synthetic chemistry, we provide examples of the application and processing of these polymers, including their use in fiber spinning, composite fabrication, and additive manufacturing. The principal objective of this Review is to provide a resource that bridges the disciplines of synthetic chemistry and ceramic engineering while providing both insights and inspiration for future collaborative work that will ultimately drive the PCP field forward.