ChemInform Abstract: Formation and Morphology of 2H-SiC Whiskers by the Decomposition of Silicon Nitride.

ChemInform ◽  
1990 ◽  
Vol 21 (28) ◽  
Author(s):  
J. LI ◽  
G. PENG ◽  
S. CHEN ◽  
Z. CHEN ◽  
J. WU
Keyword(s):  
Silicon Nitride ◽  
Sic Whiskers

Formation of SiC whiskers from silicon nitride

1992 ◽  
Vol 27 (10) ◽  
pp. 2726-2730 ◽  
Author(s):  
R. V. Krishna Rao ◽  
M. M. Godkhindi
Keyword(s):  
Silicon Nitride ◽  
Sic Whiskers

Oxidation Resistance and Mechanical Enhancement of Ferro-Silicon Nitride on Silica Sol Bonded SiC Castable

2018 ◽  
Vol 768 ◽  
pp. 286-290
Author(s):  
Ding Chen ◽  
Hua Zhi Gu ◽  
Ao Huang
Keyword(s):  
Silicon Nitride ◽  
Oxidation Resistance ◽  
Oxidation Rate ◽  
Microstructural Analysis ◽  
Isothermal Oxidation ◽  
Silica Sol ◽  
Damage Resistance ◽  
Sic Whiskers ◽  
Stress Damage ◽  
Ferro Silicon

Silica sol bonded SiC castable have obvious advantages of slag resistance and thermal stress damage resistance. However, they are not widely used due to their weak oxidation resistance at high temperature. Ferro-silicon nitride is added to improve the oxidation resistance of SiC castable. The efficiency of SiC castable in the presence of different contents of ferro-silicon nitride was evaluated through sintered properties, isothermal oxidation behaviors and microstructural analysis. The results show that sample with 5wt% ferro-silicon nitride possessed good mechanical behavior after heat treatment due to its acceleration for the formation of SiC whiskers. At 1500 °C, Isothermal oxdation curve indicated that the oxidation progress performed two-stage model controlled by chemical reaction at the earlier period and diffusion at the later period. Sample with 5wt% ferro-silicon nitride present faster oxidation rate (kc) at the earlier stage versus the contrast sample (0.025 mg·cm-2·min-1 vs 0.087 mg·cm-2·min-1), and slower oxidation rate (kd) at the later stage (0.145 mg·cm-2·min-1 vs 0.137 mg·cm-2·min-1). After 470 min isothermal oxidation test, the weigh gain of sample with 0 wt% ferro-silicon nitride exceeded the sample with 5wt% ferro-silicon nitride.

Whisker Orientation Measurements in Injection Molded Si3N4-SiC Composites

1988 ◽  
Author(s):  
J. T. Neil ◽  
D. A. Norris
Keyword(s):  
Fracture Toughness ◽  
Composite Material ◽  
Silicon Nitride ◽  
Aspect Ratio ◽  
Injection Molding ◽  
Hot Isostatic Pressing ◽  
Sem Micrographs ◽  
Sic Whiskers ◽  
Injection Molded ◽  
Sic Composites

Hot pressed composites of Si3N4 containing 30% SiC whiskers have shown substantial improvements in strength and fracture toughness relative to monolithic silicon nitride. Injection molded samples made of this composite material distorted in a systematic manner during densification by hot isostatic pressing. Whisker orientation and aspect ratio measurements based on digitized SEM micrographs were used to evaluate microstructure with respect to injection molding direction. Results show definite orientation of whiskers during injection molding which can be related to the observed densification distortion.

Formation and Morphology of 2H-SiC Whiskers by the Decomposition of Silicon Nitride

1990 ◽  
Vol 73 (4) ◽  
pp. 919-922 ◽  
Author(s):  
Jian-bao Li ◽  
Gang Peng ◽  
Shao-rong Chen ◽  
Zhen-gang Chen ◽  
Jian-guang Wu
Keyword(s):  
Silicon Nitride ◽  
Sic Whiskers

Tribological Properties of SiC Whisker Containing Silicon Nitride Composite

1988 ◽  
Vol 110 (3) ◽  
pp. 434-438 ◽  
Author(s):  
H. Ishigaki ◽  
R. Nagata ◽  
M. Iwasa ◽  
N. Tamari ◽  
I. Kondo
Keyword(s):  
Silicon Carbide ◽  
Silicon Nitride ◽  
Wear Rate ◽  
Block Type ◽  
Hot Press ◽  
Sliding Speed ◽  
Wear Characteristics ◽  
Silicon Carbide Whiskers ◽  
Sic Whiskers ◽  
Hot Press Sintering

The friction and wear characteristics of SiC whisker containing composite silicon nitride were studied. Silicon nitride powder which contains densification aids of Y2O3 and La2O3 was mixed with silicon carbide whiskers (10, 20, and 30 wt percent) and then hot-pressed at a temperature of 1800° C. Wear experiments were carried out with a ring on block type apparatus at the sliding conditions of the sliding speed of 314 mm/sec and the load of 5 N and experimental results showed that the SiC whisker had an evident effect to reduce the wear rate of silicon nitride blocks. Silicon carbide whiskers are not dispersed isotropically, but they are oriented to the direction which is perpendicular to the pressure of hot-press sintering. Therefore, wear characteristics of the composite ceramics are anisotropic. The effect of SiC whisker on wear rate of silicon nitride is larger for the surface which is perpendicular to the direction of pressure of hot-press sintering that than that for the surface which is parallel to the pressure. Although SiC whiskers have no evident effect on friction coefficient of silicon nitride at the above sliding condition, even small contents of SiC whiskers, such as 10 wt percent, reduce considerably the coefficient of friction and show similar frictional characteristics to that of monolithic silicon carbide at the lower sliding speed of 10 mm/min.

Grain boundaries in silicon nitride

1993 ◽  
Vol 51 ◽  
pp. 920-921 ◽  
Author(s):  
K Das Chowdhury ◽  
R. W. Carpenter ◽  
W. Braue
Keyword(s):  
Silicon Nitride ◽  
Grain Boundaries ◽  
Spatial Resolution ◽  
Powder Particle ◽  
High Spatial Resolution ◽  
Particle Surface ◽  
Sintering Aids ◽  
Very High Spatial Resolution ◽  
Sic Whiskers ◽  
Very High

Research on whisker/matrix interfaces and matrix grain boundaries in Si3N4 and Al2O3 composites reinforced with SiC whiskers by HREM imaging have shown that disordered layers exists in these regions. The disordered interfacial regions are often considered amorphous layers, particularly when they are thicker than ∼1nm. They appear to be discontinuous in the whisker/matrix interfaces and continuous in matrix grain boundaries. Thin amorphous layers in composites and conventionally synthesized ceramics, particularly those based on Si3N4, are expected to contain oxygen from sintering aids and powder particle surface impurities. In this paper we report the results of an investigation of silicon nitride matrix grain boundaries in Si3N4/SiC(w) composites (CMC) and polycrystalline CVD silicon nitride, using very high spatial resolution position resolved EELS and HREM imaging. Interfaces between SiC and silicon nitride in CMC materials have been discussed elsewhere.The CMC's were prepared by pressing and presintering Toyo-Soda α-silicon nitride (TS10) powder with 5.5 wt% Yttria and 1.1 wt% Alumina as sintering aids and 20 vol% β-SiC Huber whiskers at 1500°C in 0.1MPa Argon.

Lattice Imaging of Grain Boundaries in Ceramics

1977 ◽  
Vol 35 ◽  
pp. 114-115
Author(s):  
D. R. Clarke ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundaries ◽  
High Temperature Strength ◽  
Current Interest ◽  
Lattice Imaging ◽  
Special Significance ◽  
Structural Applications ◽  
Refractory Ceramics

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

TEM Studies of Grain Boundary Films in Si3N4 Ceramics

1991 ◽  
Vol 49 ◽  
pp. 930-931
Author(s):  
H.-J. Kleebe ◽  
J.S. Vetrano ◽  
J. Bruley ◽  
M. Rühle
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Hot Isostatic Pressing ◽  
Amorphous Film ◽  
Liquid Phase Sintering ◽  
Second Phase ◽  
High Temperature Mechanical Properties ◽  
Triple Points ◽  
Boundary Films

It is expected that silicon nitride based ceramics will be used as high-temperature structural components. Though much progress has been made in both processing techniques and microstructural control, the mechanical properties required have not yet been achieved. It is thought that the high-temperature mechanical properties of Si3N4 are limited largely by the secondary glassy phases present at triple points. These are due to various oxide additives used to promote liquid-phase sintering. Therefore, many attempts have been performed to crystallize these second phase glassy pockets in order to improve high temperature properties. In addition to the glassy or crystallized second phases at triple points a thin amorphous film exists at two-grain junctions. This thin film is found even in silicon nitride formed by hot isostatic pressing (HIPing) without additives. It has been proposed by Clarke that an amorphous film can exist at two-grain junctions with an equilibrium thickness.

Electron Microscopy of Silicon Nitride-Based Ceramics

1991 ◽  
Vol 49 ◽  
pp. 926-927
Author(s):  
Gareth Thomas
Keyword(s):  
Electron Microscopy ◽  
High Temperature ◽  
Silicon Nitride ◽  
World Wide ◽  
Sintering Temperature ◽  
Liquid Phase Sintering ◽  
High Temperature Strength ◽  
Sintering Additives ◽  
Glass Forming ◽  
Dense Product

Silicon nitride and silicon nitride based-ceramics are now well known for their potential as hightemperature structural materials, e.g. in engines. However, as is the case for many ceramics, in order to produce a dense product, sintering additives are utilized which allow liquid-phase sintering to occur; but upon cooling from the sintering temperature residual intergranular phases are formed which can be deleterious to high-temperature strength and oxidation resistance, especially if these phases are nonviscous glasses. Many oxide sintering additives have been utilized in processing attempts world-wide to produce dense creep resistant components using Si3N4 but the problem of controlling intergranular phases requires an understanding of the glass forming and subsequent glass-crystalline transformations that can occur at the grain boundaries.

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