Metal zirconium phosphate macroporous monoliths: Versatile synthesis, thermal expansion and mechanical properties

•Macroporous metal zirconium phosphate monoliths are synthesized.•Glycerol ensures homogeneous distribution of metal salt in the gel skeleton.•Polycrystalline monolith with hierarchically porous structure was obtained.•Ultralow thermal expansion was observed due to the presence of nanoscale porosity.

A versatile synthetic method has been developed for the fabrication of metal zirconium phosphate (MZP) macroporous monoliths via a sol–gel process accompanied by phase separation. More than 30 kinds of MZP monolithic polycrystalline monoliths with co-continuous macroporous structure have been synthesized by simply adding the target metal salt in the starting solution with optimized compositions. Glycerol, due to its high boiling point, plays the key role as the solvent to prevent metal salt from recrystallization, allowing a homogeneous distribution of metal salts over the polymerizing zirconium phosphate network. Hierarchically porous polycrystalline strontium zirconium phosphate (SrZrP) monolith has been obtained when the dried gel was calcined at 1000 °C. Very low thermal expansion (coefficient of thermal expansion (CTE) as 1.4 × 10−6 K−1) over a wide temperature range (38 °C–1000 °C) together with good mechanical properties (flexural modulus as 8.0 GPa from 3 point bending test and Young's modulus as 1.9 GPa from uniaxial compression test) has been demonstrated, while high porosity (43%) due to the presence of macropores reduces bulk density. As compared with dense ceramics of the same composition, the CTE value is lower and can be attributed to the presence of nanometer-sized small pores, which absorbs the anisotropic thermal expansion of each crystallite in the macropore skeletons at elevated temperatures.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide