Fabrication And Characterization Of Porous Ceramics By Precursor Pyrolysis

Due to an unique combination of good thermal stability, oxidation resistance, thermal shock resistance, excellent resistance to chemical corrosion, and excellent filtration as well as adsorption and desorption abilities, porous ceramics have received considerable interest in recent years.This paper made four kinds of porous ceramics by different pore-forming theories: Low-temperature fabrication of porous SiC ceramics using precursor as binder, porous mullite ceramics from silicone resin (SR) and Al2O3 powders pyrolyzed together, and porous Si-O-C and SiO2 ceramics from SR pyrolyzed in different atmospheres. The effects of shaping pressure, precursorr content, mean particle size of filler, pore-forming agent and temperature rate on characterizations of as-fabricated porous ceramics were investigated. The structures and properties of as-fabricated porous ceramics were tested, and the reasons were analyzed.The processes, structures and properties of as-fabricated porous SiC ceramics were researched, which were fabricated with Polycarbosilane (PCS) and SR as binder. The results showed:With increasing of binder content, the characterizations of porous SiC ceramics separately using PCS and SR as binder had similar changing regulations, that was, the bulk density, average pore size and fracture strength increased, while the open porosity decreased; however, the effect of mean particle size of SiC powders was different. When binder content was low, the fracture strength of porous SiC ceramics using PCS as binder was higher, because the residual thermal stress had the main effect; when binder content increased, the ceramic yield of preceramic polymer became the dominant factor, so the fracture strength of porous SiC ceramics using SR as binder was highter. Porous mullite ceramics were fabricated by SR and Al2O3 powders pyrolysed together at a low temperature (1300℃). The results as following:The highest fracture strength of porous mullite ceramics arrived at 50MPa, the average pore size was smaller than 270nm, and the open porosity was below 50%. The characterizations of porous mullite ceramics were adjusted by adding pore-forming agent(C powders) in the starting mixtures, when the shaping pressure was 43MPa. When the filler was nmAl2O3 powders, with the increasing of nmC orμmC content, the open porosity and the average pore size of porous mullite ceramics increased, but the fracture strength decreased with fluctuation. When the filler wasμmAl2O3 powders, with the increasing of nmC content, the open porosity of porous mullite ceramics became higher, the aversge pore size kept 116nm after reaching it, and the fracture strength decreased with fluctuation; With the increasing ofμmC content, the average pore size became larger, the open porosity firstly decreased and then increased, while the fracture strength firstly increased and then decreased.Porous Si-O-C and SiO2 ceramics were fabricated by SR pyrolyzed in different atmospheres. The results came:The fracture strength of porous Si-O-C ceramics was high (the highest was 64.93MPa), the average pore size was between 1μm and 10μm, and the open porosity was between 27% and 42%. The effect of temperature rate on open porosity and fracture strength was little, while the average pore size changed largely. This meaned that higher temperature rate only made the pyrolysis of preceramic polymer faster, and had little effect on the pyrolyzed process.The as-fabricate porous SiO2 ceramics was mesoporous ceramics, and the average pore size was smaller than 30nm, while the pore size distribution was narrowly distributed between 9nm and 50nm. The open porosity was very high, which reached 80%.The researchment showed that the process of porous ceramics fabrication by precursor pyrolyzed is simple and easy controlled. The porous ceramics with high fracture strength can be made by it at a low temperature, the average pore size of which is nm orμm, while the open porosity is adjusted in a large range.