Fabrication And Mechanical Strengthening Research Of Low-cost Inorganic Ceramic Membranes

In past decades, inorganic ceramic membranes have been receiving more and moreattention for environment and energy applications due to their unique advantages such as hightemperature resistance, good chemical stability, easy to clean and renew. However, due totheir higher cost compared with polymeric counterparts, the further practical applications ofceramic membranes are hindered. Accordingly, we started this research with the aims ofreducing the raw material cost, simplifying the preparation technology, lowering the sinteringtemperature, and focused on fabrication and characterization of the low-cost porous mulliteceramic membrane and the dense ceria-based thick membrane for solid oxide full cells(SOFCs) electrolytes. Specific research contents could be described as follows.(1) Low-cost solid wastes (fly ash and nature bauxite) were used as raw materials, V2O5and AlF3as additives to fabricate porous mullite membrane supports by causing the growth ofmullite crystals with various morphologies via an in situ reaction sintering. The effects ofadditive contents and sintering temperature on the open porosity, dynamic sintering,microstructure and phase evolution of the membrane supports were investigatedsystematically by characterization methods including thermal dilatometric measurement，XRD, SEM, et al. It indicated that the addition of V2O5and AlF3could effectively lower themullitization temperature and promote the anisotropic growth of mullite crystals. Afteroptimization, the membrane support with3wt.%V2O5and4wt.%AlF3(A4V3) additionsintered at1300°C exhibited an open porosity as high as~50%, the secondary mullitizationcompleted with a high mullite phase content of86.75%.(2) Comparison study of pore size, gas permeation, mechanical properties and thecomposition of mullite whiskers of A4V3and A0V0were preformed via pore size distribution,biaxial flexural strength and SEM. It showed that A4V3sintered at1300°C possessedmechanical strength of69.8±7.2MPa. When be given the same level of biaxial flexuralstrength, A4V3always showed higher open porosity than A0V0. Possible mechanicalstrengthening mechanism was further discussed based on the fracture surfaces of themembrane supports. The fabricated membrane support A4V3featured an interlockingmicrostructure composed of anisotropically grown Al2O3-rich mullite whiskers with an aspectratio of18.2±3.6at1300°C.(3) Nano-sized Ce0.79Gd0.2Cu0.01O2-(CGCO) and Ce0.80Gd0.2O2-(CGO) powders weresynthesized via a facile PVA-assisted combustion method. Full densification temperature can be achieved at much lower temperature (950°C) with minor CuO doping (1mol%, CGCO) ascompared with CGO (1400°C), meanwhile, mechanical strength can be enhanced with CuOco-doping. The CGCO sintered at1100°C possesses high relative density of98.80%andbiaxial flexural strength of302±35MPa, which is higher than those of CGO sintered at1400°C (96.43%,250±39MPa). A tentative microstructural analysis indicates that thisstrength enhancement can be attributed to the formation of stronger CuO-rich grainboundaries during sintering as a consequence of the slight modification in grain boundarychemistry, resulting in a change in fracture mode from partial to completetransgranule-dominant.