The role of EM studies on the development of ceramic composites

1992 ◽  
Vol 50 (1) ◽  
pp. 150-151
Author(s):  
K.B. Alexander ◽  
H. T. Lin ◽  
P. F. Becher
Keyword(s):  
Silicon Nitride ◽  
Liquid Phase ◽  
Mechanical Response ◽  
Imaging Techniques ◽  
Growth Conditions ◽  
Ceramic Composites ◽  
Liquid Phase Composition ◽  
Electron Imaging

Advances in the development of ceramics and ceramic composites rely on an understanding of the mechanisms which contribute to the formation of desired microstructural features or control the mechanical response of the material. For example, in silicon nitride, careful control of the liquid phase composition and growth conditions permits the development of elongated grains which provide in-situ reinforcement of the material. Electron microscopy studies have aided in understanding the solution-reprecipitation process which controls the growth of silicon nitride as well as the role of the liquid phase on this process. The composition and thickness of the residual glass phase at the grain boundaries and triple points are important for both the toughening and creep response of the material and can only be realistically analyzed by high resolution analytical and electron imaging techniques.

In situ Mineralization of Hydroxyapatite for a Molecular Control of Mechanical Responses in Hydroxyapatite-Polymer Composites for Bone Replacement

2001 ◽  
Vol 711 ◽  
Author(s):  
Kalpana Katti ◽  
Praveen Gujjula ◽  
Arunprakash Ayyarsamy ◽  
Timothy Arens
Keyword(s):  
Polymer Composites ◽  
Polyacrylic Acid ◽  
Mechanical Response ◽  
Ex Situ ◽  
Molecular Control ◽  
Mechanical Responses ◽  
Initial Stage ◽  
Ir Spectroscopic

ABSTRACTIn situ mineralization of hydroxyapatite (HAP) and the role of organics in initial nucleation and growth of HAP is critical for the resulting nano and microstructure of HAP. In situ mineralization of hydroxyapatite (HAP) in the presence of Ca binding polymers such as polyacrylic acid has shown some promise towards improvement of mechanical response of uniaxial compressed HAP/polymer composites to loading. This work represents fundamental studies on the nature of in situ HAP precipitation on resulting microstructure of the composite and bulk mechanical properties. Specifically, an experimental study, evaluating the role of initial stage mineralization of HAP on bulk mechanical responses is conducted. Fourier transform infrared (FT-IR) spectroscopic (with micro attenuated total reflectance) techniques are utilized to evaluate the association of polymer (polyacrylic acid) with HAP during mineralization of HAP. In situ HAP exhibits a faster mineralization as compared to the ex situ mineralization samples, This improved kinetics is responsible for altering the resulting micro and nanostructure of the HAP/polymer composite. Small spectral changes are detected in the absorbance spectra of in situ HAP as compared to ex situ samples. Changes in mechanical response to loading included improvement in strain-to-failure and resulting toughness characteristics of the in situ composite. The control and development of molecular-level associations of polymer with HAP is suggested to be critical for the resulting macro properties. Our results may have significant implications for design of nanocomposites for biomedical applications.

Properties of In Situ Reinforced Silicon Nitride Ceramics

1991 ◽  
Vol 251 ◽  
Author(s):  
C.-W. Li ◽  
J. Yamanis ◽  
P.J. Whalen ◽  
C.J. Gasdaska ◽  
C.P. Ballard
Keyword(s):  
High Temperature ◽  
Silicon Nitride ◽  
Metastable Phase ◽  
Abrasive Particle ◽  
Ceramic Matrix Composites ◽  
Ceramic Composites ◽  
High Fracture Toughness ◽  
High Temperature Strength ◽  
Nitride Ceramics

ABSTRACTIn situ reinforced (ISR) silicon nitride ceramics have been developed to have microstructures that mimic the best whisker containing ceramic matrix composites. Large, interlocking needle-like grains of beta silicon nitride can be produced throughout these materials to create an isotropic, high-temperature ceramic with high fracture toughness (˜9 MPa√m), good high-temperature strength (4 Pt MOR = 750 MPa at 25°C and 500 MPa at 1375°C), high Weibull modulus (m >20), and low creep at high temperature. Since these materials do not rely on transforming metastable phase inclusions as a toughening mechanism, their fracture resistance is virtually insensitive to temperature. The high crack growth resistance of these ceramics also yields a material which is extremely defect tolerant. Residual MOR strengths of 300–400 MPa are typical after multiple 50-kg Vicker's indentations of the sample tensile surface. After abrasive particle impact, the biaxial strengths of the in situ reinforced ceramics are typically more than twice that of traditional, fine-grained silicon nitrides.Unlike ceramic composites toughened using whisker additives, the in situ reinforcement approach to silicon nitride development does not require the use of complicated whisker dispersion techniques for green processing, nor is shape-limiting hot pressing required for densification during sintering.

Importance of chemistry in high-tech ceramics design

2002 ◽  
Vol 74 (11) ◽  
pp. 2137-2144 ◽  
Author(s):  
P. Šajgalík
Keyword(s):  
Fracture Toughness ◽  
Silicon Carbide ◽  
Silicon Nitride ◽  
Liquid Phase ◽  
Grain Boundary ◽  
Ceramic Materials ◽  
High Tech ◽  
Polycrystalline Ceramics ◽  
Sintered Silicon

This paper deals with the role of chemistry in the design of high-tech ceramic materials. Grain boundary composition of polycrystalline ceramics dictates the hardness fracture toughness and creep resistance of liquid-phase sintered silicon nitride and silicon carbide materials.

Influence of Microstructure on Mechanical Response of Silicon Nitride Ceramic Composites in Nano-, Micro- and Macro-Volume of Material

2009 ◽  
Vol 409 ◽  
pp. 346-349
Author(s):  
Olga Shikimaka ◽  
Daria Grabco ◽  
Katalin Balázsi ◽  
Z. Danitsa ◽  
I. Mirgorodscaia ◽  
...  
Keyword(s):  
Silicon Nitride ◽  
Mechanical Response ◽  
Multiwall Carbon Nanotubes ◽  
Ceramic Composites ◽  
General Tendency ◽  
High Fracture ◽  
Silicon Nitride Ceramic ◽  
Nitride Ceramics ◽  
Hardness Increase ◽  
Dynamic Nanoindentation

The peculiarities of contact-induced deformation in nano-, micro- and macroscopic scale of silicon nitride ceramic composites have been studied by using quasistatic macro- and microindentation techniques, dynamic nanoindentation technique and microstructure investigations. The addition of multiwall carbon nanotubes (MWCNTs) to the ceramic matrix showed the modification of microstructure leading to the modification of mechanical behavior of material: increase of fracture toughness along with the decrease of hardness. The general tendency of hardness increase with decrease of deformation volume was observed for silicon nitride ceramics, as well as, a high fracture resistance in micro- and nano-deformed volumes of material.

Backscattered Electron Imaging for Embedded Subtle Defects in 32nm Processes

2010 ◽  
Author(s):  
Z. G. Song ◽  
H. S. Song ◽  
J. Yu ◽  
T. Su
Keyword(s):  
Imaging Techniques ◽  
Plasma Etch ◽  
Cross Sectional ◽  
Transmission Electron ◽  
Complementary Approach ◽  
Backscattered Electron ◽  
Electron Imaging ◽  
Z Contrast ◽  
Electron Energy Loss

Abstract Although the overall spatial resolution of backscattered electron (BSE) imaging suffers in comparison to secondary electron (SE) imaging, its superior sensitivity to atomic number (Z) contrast and ability to image through overlying insulation levels can provide a complementary approach for imaging subtle buried defects. BSE enables the localization and imaging of embedded defects through overlying insulator levels without the risk of compromising them with reactive ion etch (RIE) or plasma etch exposure or by anisotropic wet chemical delayering process steps. Once the embedded defect is localized with BSE in situ, subsequent imaging by cross sectional Transmission Electron Microscopy (XTEM) combined with elemental analysis by energy dispersive X-Ray analysis (EDX) or electron energy loss spectroscopy (EELs) can be performed without the risk of introducing artifacts. In this work, BSE imaging was successfully employed to image embedded subtle defects in 32nm node technologies through overlying insulator films not possible with conventional SE imaging techniques.

Microstructure and Microchemistry of Interfaces in Structural Ceramic Composites

1996 ◽  
Vol 458 ◽  
Author(s):  
K. B. Alexander ◽  
P. F. Becher ◽  
P. M. Rice ◽  
D. Braski ◽  
E. Y. Sun
Keyword(s):  
Silicon Nitride ◽  
High Resolution Electron Microscopy ◽  
Ceramic Composites ◽  
Silicon Nitride Ceramic ◽  
Resolution Electron ◽  
Phase Chemistry ◽  
Electron Energy Loss ◽  
Ceramic Interfaces ◽  
Composite Interfaces

ABSTRACTThe performance of reinforced ceramics, particularly the toughness and creep resistance, is often determined by the nature of the interface between the reinforcement and the ceramic matrix. Specially-designed experiments to investigate the role of the interfacial characteristics on toughening mechanisms and crack propagation in reinforced (silicon carbide whisker reinforced alumina) and self-reinforced (silicon nitride) ceramic composites will be described. In the whisker-reinforced composites, the interfacial topography and chemistry were of primary importance, whereas in the silicon nitride materials the formation of interfacial phases and glassy-phase chemistry influenced the interfacial debonding process. The composite interfaces were characterized by high resolution electron microscopy and high spatial resolution microchemical analysis, including energy-dispersive X-ray and electron energy loss spectroscopy. Results from energy-filtered images from ceramic interfaces will also be shown.

scholarly journals Role of Intraoperative Frozen Section Diagnosis in the Management of Patients with CNS Lesions: Evaluation of 60 Consecutive Intraoperative Frozen Sections from 1991 to 1993

2020 ◽  
Vol 1 (1) ◽  
Author(s):  
Seyed Mirsattari ◽  
Fraser W. Saunders
Keyword(s):  
Frozen Section ◽  
Imaging Techniques ◽  
Frozen Sections ◽  
Tissue Samples ◽  
Tissue Sections ◽  
Intraoperative Management ◽  
Clinical Diagnoses ◽  
Cns Lesions

To determine the role of intraoperative frozen sections (FSs) in the management of patients with central nervous system (CNS) lesions, 60 consecutive intraoperative clinical diagnoses of CNS lesions were presented and compared with concomitantly obtained FS diagnoses. Clinical diagnoses were established byhistory, physical examination, imaging techniques, and gross appearance of the abnormal tissue in situ. Tissue samples were obtained intraoperatively and processed for FS diagnoses. The findings of the FS diagnoses were reported to the operating room and compared with the clinical diagnoses. The remainingbiopsy samples were used to prepare paraffin-embedded tissue sections from which the definitive diagnoses were made. Comparison of the clinical and FS diagnoses, using paraffin-embedded tissue as the true diagnosis, shows that FS diagnosis has a limited contribution to intraoperative patient management by the neurosurgeon. The rate of diagnostic failures between the two techniques was very similar; clinical diagnoses and FSs were misinterpreted in 12 and 11 of the 60 cases, respectively. Compared to a clinical diagnosis, the intraoperative FS technique provided no significant improvement in diagnosis and management; it altered the intraoperative management of the patients in 2 of 60 cases.

Liquid Phase Sintering Behavior of Amorphous Nano-Sized Silicon Nitride Powders

2007 ◽  
Vol 336-338 ◽  
pp. 1069-1071 ◽  
Author(s):  
H.B. Li ◽  
Jun Ting Luo ◽  
Kai Feng Zhang
Keyword(s):  
Grain Size ◽  
Silicon Nitride ◽  
Liquid Phase ◽  
Sintering Temperature ◽  
Liquid Phase Sintering ◽  
Sintering Behavior ◽  
Average Grain Size ◽  
Sintering Method ◽  
Amorphous Si3n4

The amorphous nano-sized silicon nitride powders were sintered by liquid phase sintering method. Si3N4-Si2N2O composites were in-situ fabricated. The Si2N2O phase was generated by an in-situ reaction 2Si3N4(s)+1.5O2(g)=3Si2N2O(s)+N2(g). The content of Si2N2O phase up to 60% was obtained at a sintering temperature of 1650°C and reduced when the sintering temperature increased or decreased, which indicates that the reaction is reversible. The mass loss, relative density and average grain size increase with increasing of sintering temperature. The average grain size is less than 500nm when the sintering temperature is below 1700°C. During the sintering procedure, there is a complex crystallization and phase transition: amorphous Si3N4 → equiaxial α-Si3N4→ equiaxial β-Si3N4 → rod-likeSi2N2O → needle-like β-Si3N4. Small round-shaped β-Si3N4 particles are entrapped in the Si2N2O grains and a high density of staking faults are situated in the middle of Si2N2O grains at a sintering temperature of 1650°C.

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