Multicomponent metal-organic frameworks (MOFs) comprise multiple, structurally diverse linkers fixed into an ordered lattice by metal ions or clusters as secondary building units (SBUs). Here, we show how multicomponent MOFs are ideal platforms for engineering materials with high levels of vacancy defects. First, a new type of quaternary MOF that is built up from two neutral, linear ditopic linkers, a 3-fold-symmetric carboxylate ligand, and a dinuclear paddlewheel SBU was synthesized. This MOF, named MUF-32 (MUF = Massey University Framework), is constructed from dabco, 4,4′-bipyridyl (bipy), 4,4′,4″-nitrilotrisbenzoate (ntb), and zinc(II), and it adopts an ith-d topology. The zinc(II) ions and ntb ligand define an underlying [Zn2(ntb)4/3] sublattice (with pto topology) that is "load bearing" and maintains the structural integrity of the framework. On the other hand, the dabco and bipy ligands are "decorative", and high levels of vacancy defects can be introduced by their partial omission or removal. These defects can be generated by direct synthesis or by postsynthetic modification. The framework structure, crystallinity, and porosity are maintained even when vacancy levels of 80% are reached. Defect healing is possible by introducing free ligands in a solvent-assisted process to restore pristine MUF-32. Computational analysis reveals that the mechanical instability of the [Zn2(ntb)4/3] sublattice sets an upper limit on defect levels in this material. Multicomponent Metal-Organic Frameworks as Defect-Tolerant Materials Seok J. Lee, [a] Celine Doussot, [a] Anthony Baux, [a] Lujia Liu, [a] Geoffrey B. Jameson, [a] Christopher Richardson, [b] Joshua J. Pak, [c] Fabien Trousselet, [d] Francois-Xavier Coudert, [d] Supporting Information PlaceholderABSTRACT: Multicomponent metal-organic frameworks (MOFs) comprise multiple, structurally-diverse linkers fixed into an ordered lattice by metal ions or clusters as secondary building units (SBUs). Here, we show how multicomponent MOFs are ideal platforms for engineering materials with high levels of vacancy defects. First, a new type of quaternary MOF that is built up from two neutral, linear ditopic linkers, a threefold-symmetric carboxylate ligand, and a dinuclear paddlewheel SBU was synthesized. This MOF, named MUF-32 (MUF = Massey University Framework), is constructed from dabco, 4,4'-bipyridyl (bipy), 4,4',4''-nitrilotrisbenzoate (ntb) and zinc(II), and it adopts an ith-d topology. The zinc(III) ions and ntb ligand define an underlying [Zn 2 (ntb) 4/3 ] sublattice (with pto topology) that is 'load bearing' and maintains the structural integrity of the framework. On the other hand, the dabco and bipy ligands are 'decorative' and high levels of vacancy defects can be introduced by their omission. These defects can be generated by direct synthesis or by postsynthetic modification. The framework structure, crystallinity and porosity are maintained even when vacancy levels of 80% are reached. Defect healing is possible by introducing free ligands in a s...

Open porosity cellular SiC-based ceramics have a great potential for energy conversion, e.g. as solar receivers. In spite of their tolerance to damage, structural applications at high temperature remain limited due to high production costs or inappropriate properties. The objective of this work was to investigate an original route for the manufacturing of porous SiC ceramics based on 3D printing and chemical vapor infiltration/deposition (CVI/CVD). After binder jetting 3D-printing, the green α-SiC porous structures were reinforced by CVI/CVD of SiC using CH3SiCl3/H2. The multiscale structure of the SiC porous specimens was carefully examined as well as the elemental and phase content at the microscale. The oxidation and thermal shock resistance of the porous SiC structures and model specimens were also studied, as well as the thermal and mechanical properties. The pure and dense CVI/CVD-SiC coating considerably improves the mechanical strength, oxidation resistance and thermal diffusivity of the material.

We present here an original route for the manufacturing of SiC ceramics based on 3D printing, polymer impregnation and pyrolysis and chemical vapor deposition (CVD). The green porous elastomer structures were first prepared by fused deposition modeling (FDM) 3Dprinting with a composite polyvinyl alcohol/elastomer wire and soaking in water, then impregnated with an allylhydridopolycarbosilane preceramic polymer. After crosslinking and pyrolysis, the polymer-derived ceramics were reinforced by CVD of SiC using CH3SiCl3/H2 as precursor. The multiscale structure of the SiC porous specimens was examined by X-ray tomography and scanning electron microscopy analyses. Their oxidation resistance was also studied. The pure and dense CVD-SiC coating considerably improves the oxidation resistance.

A process combining the pyrolysis of a lignocellulosic structure and reactive gas treatments has been developed to prepare porous TiC-SiC ceramics for solar receivers. The natural micro-porosity of balsa was complemented by a high open macro-porosity by laser cutting a periodical arrangement of parallel channels. The lignocellulosic structure was first pyrolysed into carbon. This reactive carbon material was then converted into TiC by Reactive Chemical Vapor Deposition (RCVD) using TiCl4/H2. After controlling the absence of cracks due to volume changes, the TiC structure was finally infiltrated by the Chemical Vapor Infiltration (CVI) of SiC using CH3SiCl3/H2. The density, porous structure, elemental and phase compositions, oxidation behavior and crushing strength were assessed after pyrolysis, RCVD and CVI. The SiC CVI coating significantly improves the compressive strength, the oxidation resistance and the thermal properties. The SiC layer is no longer fully protective at high temperature but the mechanical properties remain reasonably high.