Novel B4C supports for ceramic membrane filtration

Abstract

Novel complex-shaped porous B₄C supports were fabricated for use in ceramic membrane filtration applications, the processing of which is described in detail. Firstly, an extrudable ceramic paste was formulated and homogenised, containing a high content of B₄C of super-coarse and ultrafine grades, plus water as liquid medium and various organic additives as thickener, binder, plasticiser, and lubricant. Secondly, tubular honeycomb parts (i.e., cylinders of ∼26 mm outer diameter with 30 inner channels of 3 mm diameter each) were extruded at ∼25 bar and dried in air at 120 °C for 24 h, resulting in robust green B₄C membrane supports without macro- or micro-defects. Thirdly, suitable debinding conditions were identified by thermogravimetry of the paste and its components, and the dry membrane supports were debinded at 700 °C for 1.5 h in high vacuum (<0.1 Pa) confirming that they retain their shape with minimal isotropic shrinkage (∼0.13–0.15 %). And fourthly, the debinded membrane supports were pressureless sintered at 2000 °C for 3 h in inert atmosphere undergoing only an additional 1 % isotropic shrinkage, resulting in B₄C membrane supports with low apparent density (∼0.89(1) g/cm³), high porosity (∼38–39 %), open interconnected micrometre pores (in the range ∼0.5–16 μm, and d₅₀∼1.5 μm), and low skeletal density (∼2.455(1) g/cm³). Importantly, their only partial densification makes them both sufficiently strong mechanically (∼68(2) MPa compressive strength) and highly permeable to water (∼13131(418) l/(m²·h·bar) permeability at ∼1.3 bar). These attributes, together with the intrinsic lightness and durability of B₄C ceramics, make these novel supports in principle very appealing for ceramic membrane filtration and other applications.