Abstract
Nowadays, the O?-sialon ceramics are synthesized by the reaction of Si3N4, SiO2 and Al2O3. However, it is difficult to achieve the single phase materials. Here, we have successfully developed porous single phase O?-sialon ceramics by pre-oxidation combined with gas-pressure sintering method. The effects of ?-Si3N4 powder on the microstructure, phase evolution, mechanical property were investigated. The result illustrated that the main crystal phase of the porous ceramics was composed of the single O?-sialon phase. The pores were well distributed and generated from the decomposition of Si2N2O. The elongated O?-sialon grains were found and formed around pore walls. Additionally, the addition of ?-Si3N4 powder was beneficial for improving the bending strength because of the reduction of porosity and pore size. The porous O?-sialon ceramics with uniform pores obtained the excellent bending strength when the ?-Si3N4 powder was 6 wt%.
Highlights
In terms of structural materials, generally, pore always is considered as a defect which significantly degrades mechanical properties [1,2,3]
Most of the scholars devoted to investigating porous α-SiAlON, β-SiAlON and multiphase sialon ceramics [17,18,19], which mainly intended to pursue mechanical properties and dielectric property as well as thermal conductivity
This indicated that pre-oxidation combined with gaspressure sintering method was a good approach to fabricate porous ceramics
Summary
In terms of structural materials, generally, pore always is considered as a defect which significantly degrades mechanical properties [1,2,3]. The porous O’-sialon ceramics are fabricated by pre-oxidation combined with gas-pressure sintering. Afterwards, these green bodies were subjected to oxidation at 1200 oC with 10 oC/min heating rate for a dwell time of 0.5 h in a muffle furnace These pre-oxidation samples were immersed in a powder bed included of Si3N4 and BN within a graphite crucible, while Si3N4: BN weight ratio was defined at 1:1 and sintered in a furnace (Highmulti-5000, Fujidempa Co. Ltd, Osaka, Japan) at 1750 oC for 2 h with a heating rate of 5 oC/min under a nitrogen pressure of 3 MPa. The Archimedes principle was carried out to calculate the porosity for sintered samples, in which deionized water was regarded as an immersing medium. Six samples were utilized to test, from which the average value of the bending strength was calculated
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