Abstract: The effect of different sintering additives on the high temperature oxidation and corrosion
behaviour of Si3N4 ceramics is investigated. A corrosion furnace was set up which allows testing of
ceramic discs at test temperatures upto 1500°C. It was possible to conduct tests under ambient oxygen
conditions, or with increased water vapour as well as testing with corrosive gases such as HCl or SO2.
Si3N4 was prepared with MgO, Al2O3, Y2O3 and Al2O3+Y2O3 sintering additives. These discs were
subjected to different oxidation and corrosion test conditions at temperatures of 1200°C and 1500°C for
upto 128 h. The effects that the different corrosion enviroments have on the corrosion resistance of the
Si3N4 materials are presented.
Abstract: Rod-like α-sialon was synthesized successfully using pure SiO2 and AlN as the starting
materials, carbon black as reductant, CaF2 and Y2O3 as addition agent by carbothermal
reduction-nitridation. The effects of reaction temperature (1450°C, 1500°C, 1600°C and 1700°C) and
additive (Li2CO3, CaF2, Y2O3 and Y2O3+CaF2) on phases and microstructure of the final products were
studied by XRD and SEM. The results showed that α-sialon was synthesized by carbothermal
reduction-nitridation at 1700°C for 3 hours. The morphology of the synthesized α-sialon was rod-like.
Abstract: Nd-doped α-SiAlON starting composition (Nd0.33Si9.38Al2.62O1.62N14.38) was prepared by gas
pressure sintering at 1825°C for 3 hrs. In order to explore the effect of post heat treatment on the developments
of elongated α-SiAlON grains, sample was heat treated at 1800°C for 4-12 hrs. It was found that
post heat treatments promoted formation of the elongated α-SiAlON grains. The controlling mechanism
of grain growth was determined via plotting on a graph the growth in width/length versus time graphics
using Image Analysis method. Different growth rates were found between the length and width direction
of the α-SiAlON crystals, resulting in anisotropic grain growth in the microstructural development.
Abstract: Slurry pumps are used to transport the liquid fluids with solid particles in the industries. The
materials of flow passage in a slurry pump are subjected to severe damage due to abrasive erosion. This
paper compares the abrasive erosion for an engineering ceramics i.e. hot pressed Si3N4 ceramics and a
high chrome cast iron i.e. Cr26 by laboratory test and industrial operation. The results indicate that the
erosion rate of Cr26 is much larger than that of hot pressed Si3N4 ceramics under the same test conditions.
That indicates that the engineering ceramics is a promising alternation of the expensive material such as
Cr26 in the application of slurry pumps. It is noted that the erosion pattern such as scale ripple has the
similar features for both materials, even the hardness of hot pressed Si3N4 ceramics is much higher than
Cr26. Further, the scale ripple is suspected to be originated from the relatively weak grain boundary and
enhanced by cavitation.
Abstract: In this paper, highly porous Si3N4 ceramics with high strength, homogeneous microstructure
were fabricated by introducing a proper amount of nanometer carbon in the Si3N4 slurry by gel-casting.
Scanning electron microscopy, X-ray diffraction, Archimedes water-displacement method and
three-point bending tests were employed to analyze the microstructures and mechanical properties of the
sintered bodies. It was shown by the XRD analysis that SiC particles were formed in the sintered bodies.
The pillar β- Si3N4 morphology, homogeneous microstructure and the SiC particles as a reinforcement
phase are the contributing factors for high porosity and good mechanical behavior.
Abstract: Toray T300 PAN-based carbon fibers were surface oxidized in air at 300, 400 and 500 °C. The
composition of surface was determined by X-ray photoelectron spectrometry (XPS), and the
monofilaments of original carbon fiber and surface oxidized carbon fibers were tensile tested at room
temperature. Three-dimensional carbon fiber reinforced BN-Si3N4 matrix composites were prepared by
precursor infiltration and pyrolysis using a hybrid precursor mixed by borazine and perhydropolysilazane.
With the increase of the oxidation temperature, the content of size on the surface of fiber reduces, and the
tensile strength of carbon fiber declines. Carbon fiber oxidized at 400 °C has a 93% residual strength and
the fiber oxidized at 500 °C is seriously decayed. The composite reinforced by original carbon fibers
exhibits excellent mechanical properties, including high flexural strength (182.3 MPa) and good
toughness; while the composite reinforced by 400 °C oxidized carbon fibers is weak (only 102.4 MPa)
and brittle. The distinct difference of mechanical properties between the two composite is attributed to the
change of the interfaces between carbon fibers and nitride matrices.
Abstract: In order to investigate the effect of sintering temperature on the microstructure and densification
process of Y-SiAlON ceramics, by hot pressing at 1750°, 1800°, 1850° and 1900°C for 1 h, respectively,
Y-α-SiAlON (m=1.2, n=1.2 according to formula Mm/3Si12-(m+n)Alm+nOnN16-n) was fabricated from
α-Si3N4, AlN, Al2O3 and Y2O3 starting powers. The results showed that α-SiAlON phase is formed in all
sintered specimens, and during Y-SiAlON sintering, all the samples begin to quickly shrink at 1550°C,
and the shrinkage is finished at 1750°C, which indicate that 1550 ~ 1750 °C is very important for the
densification process of Y-α-SiAlON ceramics, and 1750 °C is necessary for the Y-SiAlON densification.
Higher sintering temperature contributes to α-SiAlON grain development and the SiAlON ceramics
Abstract: Multi-step hot pressing sintering was adopted to prepare Y-SiAlON (Y0.4Si9.6Al2.4O1.2N14.8) at
1950°C for 60 min under 25 Mpa in nitrogen atmosphere, and the microstructure was studied. The phase
assemblages, microstructures and densification of the sintered samples were discussed in detail. In order
to contrast to multi-step sintering, one step sintering also was adopted. The results reveal that single-phase
α-SiAlON with elongated grain pattern is formed in the multi-step sintering specimens, because of
holding at low temperature in multi-step sintering is helpful to reduce the kinetics of crystal growth, the
mount of elongated grain in multi-step sintering samples is more than that of in one step sintering ones.
Abstract: Single phase Sialon was synthesized successfully from fly ash by carbothermal reductionnitridation
reaction in this paper. The effects of synthesizing temperature (1200°C, 1300°C, 1400°C
and 1450°C) and carbon content (stoichiometric content, exceeding 10%, 50% and 100%) on the final
production were studied by XRD and SEM. Synthesis mechanism of β-Sialon was also analysized.
The results indicated that single phase β-Sialon with z=3 was obtained using fly ash as raw materials
and carbon black of stoichiometric content as reducer by carbothermal reduction- nitridation reaction
in flow nitrogen at 1450°C for 3h. Temperature and content of carbon had significant effect on the
synthesis of β-Sialon.
Abstract: The Si-B-O-N microwave-transparent materials were prepared by gas pressure sintering
(GPS).The effect of BN and nano-SiO2 contents on the mechanical and dielectric properties of the
composites was studied. The microstructural characteristic and reinforced mechanism of the composites
were also investigated. The results showed that a series of Si-B-O-N wave-transparent materials could be
obtained by controlling the contents of raw materials and technological parameter. The bending strength
of composites is from 74.7MPa to 174.83MPa, the dielectric constant is from 3.5 to 4.2 and the tangent of
loss angle is from 0.5×10-3 to 4.5×10-3.