Dianying Chen

Combustion synthesis of network silicon nitride porous ceramics

A porous silicon nitride ceramics, composed of a network interconnected β-Si3N4 rods, was prepared by using the combustion synthesis method. Si powder with more than 20 wt.% diluent α-Si3N4 was fully nitrided under high nitrogen pressure. The interconnected open porosity of the obtained combustion products was as high as 64.40%. In the combustion products, rod-like β-Si3N4 grains were formed to build up the network silicon nitride porous ceramics.

Preparation and growth mechanism of β-Si3N4 rod-like crystals by combustion synthesis

Abstract This paper presents the preparation of β-Si 3 N 4 rod-like crystals that have an average aspect ratio of ∼10 by combustion synthesis of the mixture of Si, α-Si 3 N 4 and Y 2 O 3 under 5 MPa nitrogen pressure. By using a quenching device, the growth morphology of β-Si 3 N 4 rod-like crystals was observed and it is concluded that the growth mechanisms result from the synergy of VLS (vapor–liquid–solid) and VS (vapor–solid).

The influence of PbZrO3/PbTiO3 ratio on diffuse phase transition of Pb(Zn1/3Nb2/3)O3-PbZrO3-PbTiO3 system near the morphotropic phase boundary

The diffuse phase transition of Pb(Zn1/3Nb2/3)O3–PbZrO3–PbTiO3 (PZN–PZ–PT) ternary solid solution near the rhombohedral/tetragonal morphotropic phase boundary (MPB) is reported in this paper for the first time. All compositions near MPB exhibit a relaxor behavior around dielectric permittivity peak. It is found that the extent of diffuse phase transition of PZN–PZ–PT increases with the increases of PbZrO3/PbTiO3 ratio.

Si3N4 rodlike crystal-reinforced MoSi2 matrix composites

Abstract A MoSi 2 -based composite reinforced with 20 vol.% Si 3 N 4 rodlike crystals was fabricated by Spark Plasma Sintering (SPS) process. The microstructure and mechanical properties of the composite were investigated. Relative densities of the monolithic material and composite were above 95%. No reactions between Si 3 N 4 and MoSi 2 were observed. The composite containing Si 3 N 4 rodlike crystal had higher hardness than monolithic MoSi 2 . The room-temperature flexural strength increased 60% compared to that of pure MoSi 2 . Especially the room-temperature fracture toughness of the composites was higher than that of MoSi 2 , from 3.6 MPa m 1/2 for MoSi 2 to 5.1 MPa m 1/2 for composites with 20 vol.% Si 3 N 4 , respectively. Besides, the yield strength at elevated temperature and the low-temperature oxidation resistance for 20 vol.% Si 3 N 4 –MoSi 2 composite exhibited considerable improvement over that of monolithic MoSi 2 . These results showed that Si 3 N 4 rodlike crystal is an effective reinforcement for MoSi 2 .

The effect of additives on the morphology of combustion synthesized rod-like β-Si3N4 crystals

Abstract This paper presents the results of synthesizing rod-like β-Si 3 N 4 crystals by combustion synthesis with (Y 2 O 3 +Al 2 O 3 ) or (Y 2 O 3 +MgO) as additives. The Mg-doping sample forms a more uniform and regular microstructure (∼10 μm) than that of the Al-doping sample(5–10 μm), while both additives had marked effects on the growth of rod-like β-Si 3 N 4 crystals compared with those without additives, for the viscosity of Mg-containing liquid phase is lower than that of Al-containing liquid phase.

Dispersion of PZN-PZT powder in organic media with chemically bonded dispersant

The dispersion of chemically bonded dispersant named di-isopropoxy titanium dioleate in the PZN-PZT powder with organic media was investigated through FT-IR technique and sediment test. The results showed that the dispersant exhibited a good dispersion in the PZN-PZT suspensions. The interaction mechanism between the dispersant and the powder particle surface was involved in the formation of a strongly chemical bond through the reaction of alkoxy groups on the dispersant molecule with the surface hydroxyl of the PZN-PZT powder. The dispersant concentration corresponding exactly to the monomolecule layer coverage onto the PZN-PZT particle surface was determined to be 0.25 wt%.

Spontaneous ferroelectric-relaxor transition of Pb(Zn1/3Nb2/3)O3-PbZrO3-PbTiO3 system near morphotropic phase boundary

Abstract The dielectric properties of Pb(Zn1/3Nb2/3)O3-PbZrO3-PbTiO3 (PZN-PZ-PT) system near morphotropic phase boundary (MPB) are studied in this paper. It is found that, for the samples with tetragonal symmetry, a spontaneous normal ferroelectric—relaxor phase transition exists in temperature lower than that of permittivity peak.