Insights into the Microstructural Evolution Occurring during Pyrolysis of Metal-Modified Ceramers Studied through Selective SiO2 Removal.

Aitana Tamayo,Fausto Rubio,Juan Rubio,Mᵃ Angeles Rodriguez

doi:10.3390/ma14123276

Aitana Tamayo, Fausto Rubio + Show 2 more

Open Access

https://doi.org/10.3390/ma14123276

Copy DOI

Abstract

Silicon oxycarbide ceramers containing 5% aluminum, zirconium, and cobalt with respect to the total Si amount are prepared from a commercial polysiloxane and molecular precursors and pyrolyzed at temperatures ranging from 500 to 1000 °C. HF etching is carried out to partially digest the silica phase, thus revealing structural characteristics of the materials, which depend upon the incorporated heteroatom. From the structural and textural characterization, it was deduced that when Al enters into the ceramer structure, the crosslinking degree is increased, leading to lower carbon domain size and carbon incorporation as well. On the contrary, the substitution by Zr induced a phase-separated SiO2-ZrO2 network with some degree of mesoporosity even at high pyrolysis temperatures. Co, however, forms small carbidic crystallites, which strongly modifies the carbonaceous phase in such a way that even when it is added in a small amount and in combination with other heteroatoms, this transient metal dominates the structural characteristics of the ceramer material. This systematic study of the ceramer compounds allows the identification of the ultimate properties of the polymer-derived ceramic composites.

Highlights

The partial conversion of polysiloxane precursors into hybrid materials with high specific surface areas, tunable pore size distributions, and adjustable surface characteristics has been widely studied over the past years
At the early stages of research in polymers and hybrid materials for nanostructured ceramics, much effort was made on the modification of a silicon-based gel by aluminum and boron [2,3,4]
It is known that during pyrolysis, Al is able to form the AlOx Cy at a relatively low temperature through the reaction of the Al(OH)3 particles, which are dispersed within the ceramer network with the free carbon, decreasing the amount of free carbon and the observed decrease in the O/C ratio at temperatures beyond 800 ◦ C [2]

Summary

Introduction

The partial conversion of polysiloxane precursors into hybrid materials (ceramers) with high specific surface areas, tunable pore size distributions, and adjustable surface characteristics has been widely studied over the past years. The chemical and physical properties can be modified by using different heteroatoms, leading to the production of completely new materials with high purity and homogeneous distribution of the constituent phases. Bonding the heteroatoms to the hybrid precursor before crosslinking as well as the use of coordination compounds are the most explored methodologies for the preparation of metal-modified polymer-derived ceramics and ceramers [1]. At the early stages of research in polymers and hybrid materials for nanostructured ceramics, much effort was made on the modification of a silicon-based gel by aluminum and boron [2,3,4]

Objectives

Methods

Results

Discussion

Conclusion