Gradient-Hierarchic-Aligned Porosity SiOC Ceramics

Cekdar Vakifahmetoglu,Damla Zeydanli,Fernanda Dos Santos Ribeiro,Gian Domenico Soraru,Paulo Renato Orlandi Lasso,Murilo Daniel De Mello Innocentini

doi:10.1038/srep41049

Abstract

This work describes a simple technique to produce porous ceramics with aligned porosity having very high permeability and specific surface area. SiOC-based compositions were processed from blends of three types of preceramic polymer and a catalyst, followed by curing and pyrolysis. The heating applied from the bottom of molds promoted the nucleation, expansion and rising of gas bubbles, and the creation of a ceramic matrix with axially oriented channels interconnected by small round pores. The samples were analyzed by SEM, tomography, BET, water immersion porosimetry and permeation to gas flow. The resulting bodies presented levels of open porosity (69.9–83.4%), average channel diameter (0.59–1.25 mm) and permeability (0.56–3.83 × 10−9 m2) comparable to those of ceramic foams and honeycomb monoliths, but with specific surface area (4.8–121.9 m2/g) typical adsorbents, enabling these lotus-type ceramics to be advantageously used as catalytic supports and adsorption components in several environmental control applications.

Highlights

Porous materials, especially ceramics, have been successfully used in many technological processes such as insulation, filtration and purification and catalysis[1,2]
We present a facile technique, not requiring any freezing medium or specialized equipment apart from a simple hot-plate, to form hierarchically porous monolithic SiOC ceramics, having interconnected aligned porosity
It was observed that the pores at the bottom of the samples (Fig. 1(a and c)) were smaller compared to those at the top (Fig. 1(b and d)) causing an aligned and gradient porosity

Summary

Introduction

Especially ceramics, have been successfully used in many technological processes such as insulation (buildings, machines, etc.), filtration and purification (molten metals, gases, wastewater, etc.) and catalysis[1,2]. Following the same method, preceramic polymer blends were crosslinked in Teflon lined stainless steel autoclaves and pyrolyzed, resulting in samples with a unidirectional porosity reaching around 65%20 It is a simple process, such solidification. In order for a porous component to possess a wide range of desirable characteristics, such as rapid transport of fluids and gases, low pressure drop, high selectivity, fast uptake and release, etc., it should comprise a high specific surface area (SSA) together with interconnected cellular (micron range) framework, i.e. hierarchical porosity[4] In these aforementioned methods, the goal was merely to form aligned porosity materials, but the formation of components that facilitate tunable aligned porosity together with high surface area was never explored. Characterizations included evaluation of bulk and superficial properties and permeability to air flow

Methods

Results

Conclusion