Grain Boundary Phase Analysis of Silicon Nitride by a Newly Developed 300kv Field-Emission Electron Microscope

1994 ◽  
Vol 346 ◽  
Author(s):  
Y. Bando ◽  
H. Suematsu ◽  
M. Mitomo
Keyword(s):  
Electron Microscope ◽  
Silicon Nitride ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Phase Analysis ◽  
Field Emission ◽  
Boundary Phase ◽  
Emission Electron ◽  
Triple Points

ABSTRACTThe grain boundary phase of silicon nitride containing additives Y2O3 and Nd2O3 has been studied by means of a newly developed 300kV field emission ATEM. The composition of the two-grain boundary phase of about 1 nm thick is successfully determined. It is then found that the compositions among the grain boundaries are not the same and the additives of Y2O3-Nd2O3 are poor in the two-grain boundary, while they are rich in the triple points.

Grain Boundary Microstructure of a Hot Isostatically Pressed Silicon Nitride

1997 ◽  
Vol 3 (S2) ◽  
pp. 731-732
Author(s):  
L. Fu ◽  
M. J. Hoffmann ◽  
X. Pan
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Chemical Composition ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Phase ◽  
Sintering Aids ◽  
Size And Morphology ◽  
Boundary Microstructure

Si3N4-based materials exhibit attractive mechanical properties for high-temperature applications. These properties are influenced strongly by the size and morphology of the grain boundaries and grain-boundary phase. An amorphous intergranular film (IGF) commonly exists at two grain junctions. The thickness of these IGFs sensitively depend on the chemical composition of the intergranular phase.In this work, our studies on the grain boundary microstructure of Si3N44 ceramics made by Hot Isostatically Pressing (HIPing).Si3N44 materials were densified by HIPing Si3N4 powders (UBE E-10) at 1950°C at 200 MPa for 1 hour, with sintering aids of either Y2O3 or Y2O3 + A12O3. Two materials were made: material A consisting of 2 wt% Y2O3; material B consisting of 5 wt% Y2O3 and 1 wt% A12O3. Both as-HIPed and oxided samples were investigated. TEM specimens were prepared by conventional procedures. The microstructure and chemical composition were studied on a JEOL 2000FX.

Characteristics and Application of Temperature-Field Emitters

1975 ◽  
Vol 33 ◽  
pp. 144-145
Author(s):  
N. Tamura ◽  
T. Goto ◽  
Y. Harada
Keyword(s):  
Temperature Field ◽  
Electron Microscope ◽  
Field Emission ◽  
Resolving Power ◽  
High Brightness ◽  
Field Emitters ◽  
Emission Electron ◽  
Sufficient Stability ◽  
Scanning Electron ◽  
Illuminating System

On account of its high brightness, the field emission electron source has the advantage that it provides the conventional electron microscope with highly coherent illuminating system and that it directly improves the, resolving power of the scanning electron microscope. The present authors have reported some results obtained with a 100 kV field emission electron microscope.It has been proven, furthermore, that the tungsten emitter as a temperature field emission source can be utilized with a sufficient stability under a modest vacuum of 10-8 ~ 10-9 Torr. The present paper is concerned with an extension of our study on the characteristics of the temperature field emitters.

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

Glassy grain-boundary phase crystallization of silicon nitride: Kinetics and phase development

1995 ◽  
Vol 14 (19) ◽  
pp. 1362-1365 ◽  
Author(s):  
G. Bernard-Granger ◽  
J. Crampon ◽  
R. Duclos ◽  
B. Cales
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Boundary Phase ◽  
Phase Development

GRAIN BOUNDARIES: PHASE TRANSITIONS AND CRITICAL PHENOMENA

1991 ◽  
Vol 05 (19) ◽  
pp. 2989-3028 ◽  
Author(s):  
E.I. RABKIN ◽  
L.S. SHVINDLERMAN ◽  
B.B. STRAUMAL
Keyword(s):  
Phase Transitions ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Critical Phenomena ◽  
External Surface ◽  
Theoretical Models ◽  
Boundary Structure ◽  
Boundary Phase ◽  
Recent Experimental Data ◽  
Grain Boundary Structure

Recent theories of grain boundary structure have been reviewed briefly. The possibility of existence of the same variety of phase transitions on grain boundaries as that on the crystal external surface has been demonstrated. Recent experimental data and theoretical models concerning grain boundary phase transitions are critically analysed. Grain boundary phase transitions connected with the formation of thin disordered layers on the boundary (prewetting, premelting) are particularly distinguished. Results of recent indirect experiments, which may be treated in terms of prewetting and premelting, have been reviewed. Experimentally observed critical phenomena in the vicinity of the prewetting transition on the tin-germanium interphase boundary have been discussed in terms of the critical exponents theory. Some ideas regarding directions of further research are presented.

Corrosion of Si3N4-Ceramics in Acids and Basics

2006 ◽  
Vol 45 ◽  
pp. 148-155 ◽  
Author(s):  
Jochen Schilm ◽  
Mathias Herrmann ◽  
G. Michael
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Corrosion Behavior ◽  
Aqueous Media ◽  
Structural Features ◽  
Boundary Phase ◽  
The Subject ◽  
Corrosion Mechanisms ◽  
Si3n4 Ceramics ◽  
Made In

The corrosion behavior of silicon nitride materials in aqueous media strongly depends on the composition and amount of the grain boundary. But there exist no systematic investigations of the relation between the corrosion behavior and the composition and amount of the grain-boundary phase. The subject of this study is based on the evaluation of the corrosion mechanisms of Si3N4 ceramics and YSiAlON glasses, both with defined and characterized compositions, in acidic and basic environments with different concentrations. Special effort has been made in describing the compositions of grain boundary phases in the sintered Si3N4 ceramics. A model to describe structural features of YSiAlON-glasses was developed which allows the correlation of the corrosion behavior of the ceramics and the glasses with their compositions. In combination with SEM and TEM investigations it became possible to give structural reasons for the different observed corrosion mechanisms.

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