Preparation and properties of a low-cost porous ceramic support from low-grade palygorskite clay and silicon-carbide with vanadium pentoxide additives

Alow-cost porous ceramic support was prepared from low-grade palygorskite clay(LPGS) and silicon carbide(SiC)with vanadium pentoxide(V_(2) O_(5)) additives by a dry-press forming method and sintering.The effects of SiC-LPGS ratio,pressing pressure,carbon powder pore-forming agent and V_(2) O_(5) sintering additives on the microstructure and performance of the supports were investigated.The addition of an appropriate amount of SiC to the LPGS can prevent excessive shrinkage of the support during sintering,and increase the mechanical strength and open porosity of the supports.The presence of SiC(34.4%) led to increases in the open porosity and mechanical strength of 40.43% ± 0.21% and(17.76 ± 0.51) MPa,respectively,after sintering at 700℃ for 3 h.Because of its low melting point,V_(2) O_(5) can melt to liquid during sintering,which increases the mechanical strength of the supports and retains the porosity.Certainly,this can also encourage efficient use of the LPGS and avoid wasting resources.

Electrochemical Properties of Tubular SOFC Based on a Porous Ceramic Support Fabricated by Phase-Inversion Method

In this work, a tubular ceramic-supported solid oxide fuel cell （SOFC） was successfully fabricated by a low cost and simple process involving phase-inversion, brush coating and co-sintering. Properties in- cluding sintering behavior, microstructure of the tubular support as well as the electrochemical properties of single cell were investigated. The results show that a porous tubular support with finger-like pores and macrovoids was obtained after phase-inversion process. The tubular support is proved to be gaspermeable after sintering at 1400 ℃ with shrinkage of about 34%. The maximum power density of single tubular SOFC is 100 mW/cm2 and 122 mW/cm2 at 850 ℃ when fed with wet methane and hydrogen, respectively. The current collection, thickness of electrolyte and gas permeability of tubular support should account for the large total resistance. The present tubular design could be expected to deliver a higher voltage for longer support with several segmented-in-series cell stacks.

Cordierite Ceramics Prepared from Poor Quality Kaolin for Electric Heater Supports: Sintering Process, Phase Transformation, Microstructure Evolution and Properties

To efficiently utilize the kaolin, an economical way of preparing cordierite ceramic with high performance for electric heater supports was put forward. In this study, sintering process, phase transformation, microstructure evolutions were systematically studied by heating microscope, X-ray diffraction, scanning electronic microscope and thermal analysis. Properties（physical properties, electrical properties and coefficient of thermal expansion（CTE）） were tested for comprehensive performance evaluation. The results showed that the utilization of poor quality kaolin broadened the firing range of cordierite ceramic which was from 1 200 to 1 380 ℃. Microstructure becomes loose with increasing of the pore size, which had significant influence on bending strength and electrical properties. High content of K2 O in poor quality kaolin was the reason for liquid phase generation in sintering process, which further leads to microstructural changes. The cordierite ceramic sintered at 1 320 ℃ had the properties as follows： CTE of 1.98×10^（-6） ℃^（-1）（500 ℃）, bending strength of 90 MPa, apparent porosity of 15.1%, dielectric constant of 7.5（100 Hz）, and volume resistivity of 1.05×109 Ω·cm（100 Hz）. The comprehensive properties are very suitable for use as electric heater supports.

A reverse particle grading strategy for design and fabrication of porous SiC ceramic supports with improved strength

Porous ceramics usually require high mechanical strength and maximized porosity simultaneously,while for conventional particle grading strategies,it is highly challenging to meet both demands.To this end,a reverse particle grading strategy was developed based on the linear packing model by unusually introducing coarse particles(d50=16μm)into a fine particle(d50=5μm)matrix.Following the extrusion and sintering process,tubular porous SiC ceramic supports with improved mechanical strength were successfully fabricated.The effects of coarse particles on the rheological properties of the ceramic paste and the macroscopic properties and microstructure of the SiC supports were systematically investigated.With an increase in the content of coarse SiC particles to 30 wt%,the pressure generated during extrusion decreased from 5.5±0.2 to 1.3±0.1 MPa.Notably,the bending strength of the tubular supports increased from 36.6±5.6 to 49.1±4.5 MPa when 20 wt%coarse powder was incorporated.The notably improved mechanical strength was attributed to the distribution of coarse particles that prolonged the route of crack deflection.Additionally,the optimized tubular supports had an average pore size of 1.2±0.1μm,an open porosity of 45.1%±1.6%,and a water permeability of 7163±150 L/(m2·h·bar)as well as good alkali and acid corrosion resistance.Significantly,the strategy was proven to be feasible for the scale-up fabrication of 19-channel SiC tubular porous ceramic supports.