Pore Structure Control Of Phosphate Bonded Si₃N₄ Porous Ceramics And The Chemical Combining Mechanism

porous ceramic is a new-type structure ceramic material, it has superior compositive performances of the mechanics, thermal and dielectric and was widely used in chemical industry, energy, electronics, aerospace, environmental protection, etc. Owing to excellent dielectric properties ofα-Si3N4, the study of a-Si3N4 porous ceramics as wave-transparent materials in aerospace field has pay close attention. To prepare a-Si3N4 porous ceramics with high porosity and high strength, this paper adopts the method of phosphate as binder and adding the pore-forming agent, uses low-temperature pressureless sintering technique, and obtainsa-Si3N4 porous ceramic materials with high porosity, controllable pore structure and excellent mechanics and dielectric properties. Analyse chemical combining mechanism through the bending strength of different phosphate bonding Si3N4.Fabricate high porosity ZrPiO7 bonded Si3N4 porous ceramic by an pressureless sintering process and adding naphthalene and starch as pore-forming agent which were excluded before or after ZrPiO7 generating temprature respectively. Analy the effect of the pore-forming agent and sintered temprature on pore structure by researching porosity, skrinkage, phase structure and microstructure. The results show that ZrP2O7 bonded Si3N4 porous ceramic materials has the porosity 30-70%, and pore structure with near-zero shrinkage by adding starch and naphthalene powder as pore-forming agent. Pore-forming agent can effectively improve porosity range and control the pore structure, and the effect of sintered temprature on pore structure is not obvious.In this paper, high porosity ZrP2O7 bonded Si3N4 porous ceramic was prepared by adding pore-forming agent, the effect of pore structure on bending strength and dielectric properties were studied. The results show that the bending strength of ZrP2O7 bonded Si3N4 porous ceramic materials is about 10～100MPa, dielectric constant is 2.3～4.5, porosity and pore size has significant effects on the properties of materials, the bending strength and the dielectric constant reduce with the porosity and pore size increases.The diffirent phosphate bonded Si3N4 porous ceramic was fabricated by using diffirent phosphate of reactive product Al2O3, ZrO2, SiO2 and HPO4 as binder. The relation of phase, microstructure, porosity, mechanical properties and phosphate content were researched, and the chemical combining mechanism was analysed. The results show that the phosphate and Si3N4 are bonded through reticulate structurephoaphate which was formed by chemical reaction of oxide and HPO4, the combining strength of different material mainly was influenced by the crystal structure and polymerization degree of phosphate.