Tubular ceramic structures from polymer precursors with controlled porosity, strength, and permeability characteristics

Abstract

A processing technique for the preparation of porous, silicon carbonitride-based ceramics in tubular geometry derived from a liquid polysilazane precursor is presented. After casting of polysilazane/polymer-microbead dispersions, cross-linking, and subsequent pyrolytic conversion and selective removal of polymer templates, specimens with an inner and outer diameter of 6 and 10 mm, respectively, and a length of up to 65 mm were obtained. Porosity was controlled by sacrificial template content and reached values up to 48% after pyrolytic conversion, at average pore opening radii of 1¯m. The tubular specimens exhibited diametral compression strengths (C-ring test) between 24 « 6 and 36 « 4 MPa. Darcian permeability constants of up to 1.7·10 ¹14 m 2 were found by gas permeability testing. The results demonstrate that this methodology facilitates the straightforward generation of complex-shaped porous specimens, further allowing for a control of strength and permeability in a specific range. Potential applications for the tubular, porous structures developed can be anticipated in the fields of separation or catalysis.

Porosity control in silicon nitride‐based support materials toward enhanced gas permeability

“…The gas permeability of samples was determined at room temperature using sintered tubular specimens, following a methodology reported previously 19,21 . Filtered compressed air was used as fluid.…”

“…24 The gas permeability of samples was determined at room temperature using sintered tubular specimens, following a methodology reported previously. 19,21 Filtered compressed air was used as fluid. The stationary permeating flow Q through the tube wall was determined at varying differential pressures Δp between feed and permeate, with Δp in the range between 0.…”

“…The majority of reports on the shaping of porous Si 3 N 4 materials have been focused on relatively simple geometries, involving pressing or casting techniques. However, a tubular geometry, which can also be obtained in a straightforward manner by casting processes, 19 is generally preferred for prospective applications as support material by facilitating an increased surface‐to‐volume ratio compared to planar configurations 20 . In a previous publication, we reported on the methodological development of a slip‐casting procedure suitable for the preparation of hollow‐tube shaped porous Si 3 N 4 , achieving permeability values of up to 9 ⋅ 10 −16 m 2 at porosities in the range between 32 and 41% 21 …”

Development of Inkjet Printable Formulations Based on Polyorganosilazane and Divinylbenzene

“…In addition, they contain hydrogen as a side group [36]. Polyorganosilazanes can be formulated with initiators, catalysts, or fillers to form processable matrix composites that can be fabricated by casting [37,38], coating [4,39], or additive manufacturing [18,[40][41][42][43]. Crosslinking is usually carried out thermally [44,45] or photochemically [46] after processing to reduce the loss of low-molecular-weight components and consequently leading to a high ceramic yield after pyrolysis at high temperature [47].…”

Open‐Porous Silicon Nitride‐Based Ceramics in Tubular Geometry Obtained by Slip‐Casting and Gelcasting

“…Generally, for prospective applications as support material for membranes or catalysts, a tubular configuration is preferred, resulting in an increased surface-to-volume ratio compared to planar setups. [5,17] The objective of this work is the implementation of two distinct colloidal processing strategies -slip-casting and gelcasting -in combination with partial sintering for generating porous Si 3 N 4 ceramics in tubular configuration. Properties relevant for their prospective use as support structures, including porosity, pore size, and permeability of porous Si 3 N 4 specimens, are evaluated with respect to sintering temperature and processing route chosen in order to gain insights on the selection of adequate preparation conditions to achieve desired combinations of pore morphology and permeating flux.…”