Porous polymer derived ceramics

Porous ceramics, in particular cellular ceramics with open and closed porosity, are key enabling components in different demanding applications because of their favorable set of properties. The production of porous ceramics from preceramic polymers offers advantages in terms of simple processing methodology, low processing cost, and ease of control over porosity and other properties arising from the composition of the resultant ceramics. Therefore, a vast amount of research has been conducted, in the past decade, towards the fabrication and characterization of porous ceramics produced from different polymeric precursors, such as polysiloxane, polycarbosilane, polysilazane and borazine. The potential of polymer-derived-ceramics can only be fully achieved if the type of fabrication method used is tailored taking into account the specific application of interest. For brevity, this review deals specifically with the different processing strategies employed to obtain, from polymer precursors, ceramic foams, membranes, aerogels or porous ceramics for which porosity higher than 50 vol% has been deliberately introduced, including also components with high specific surface area or hierarchical porosity. The different processing strategies, such as replica, sacrificial template, direct foaming, etching, aerogel forming, fiber spinning and automated manufacturing, are explained and the published literature has been reviewed with particular concern for the critical issues that affect the pore size, the amount of porosity and strength of the ceramic components.