Microstructural characterization of a SiC Whisker-Reinforced HIPped Reaction-Bonded Si3N4

1988 ◽  
Vol 120 ◽  
Author(s):  
S. C. Farmer ◽  
P. Pirouz ◽  
A. H. Heuer
Keyword(s):  
Grain Boundaries ◽  
Glassy Phase ◽  
Microstructural Characterization ◽  
Core Region ◽  
Sintering Aid ◽  
The Core ◽  
Composite Fabrication ◽  
The Matrix ◽  
Sic Whiskers

AbstractA SiC whisker reinforced HIPped RBSN material fabricated with a Y2O3 sintering aid was characterized using TEM. The matrix is > 90% β-Si3 N4 with a Y-Si-O-N glassy phase at the Si3 N4 grain boundaries and about the SiC whiskers. The SiC whisiers are heavily faulted and have a well defined core. Si3 N4 precipitates are observed in the core region after composite fabrication. A preliminary mechanism for the growth of the SiC whisker, based on the VLS mechanism is proposed.

AEM characterization of SiC fiber/AIN composites

1994 ◽  
Vol 52 ◽  
pp. 630-631
Author(s):  
K. Park ◽  
C. Sung
Keyword(s):  
Liquid Phase ◽  
Grain Boundaries ◽  
Creep Tests ◽  
Cross Sectional ◽  
Sintering Aid ◽  
Sic Fiber ◽  
Vacuum Atmosphere ◽  
The Matrix ◽  
Convergent Beam

SiC fiber (15 vol. %)/AlN composites were fabricated by hot pressing at 1650°C and 17.6 MPa using a 4Ca(OH)2·Al2O3 sintering aid under vacuum atmosphere. Creep tests for the composites were conducted at compressive stress of 50 MPa and at 1120°C for 48 hours under oxygen atmosphere. Cross-sectional TEM samples were analyzed using a Philips EM400T TEM and a Noran ultrathin window Micro-Z detector. Selected area diffraction (SAD), convergent beam electron diffraction (CBED), and energy dispersive X-ray spectroscopy (EDXS) were used to identify the microstructure and microchemistry of the matrix, fiber, and matrix/fiber interface of the composites.Generally, the AIN matrix contained a liquid phase at grain boundaries and a high density of dislocations within the grains (Fig. 1(a)). Most of the additives were present at the grain boundaries. Fig. 1(b) shows a SAD pattern from the liquid phase at the grain boundaries. The liquid phase was identified as Ca12Al14O33 with a cubic structure (a = 1.198 nm).

Microstructure of Polycrystalline MgO Penetrated by a Silicate Liquid

1996 ◽  
Vol 2 (3) ◽  
pp. 113-128 ◽  
Author(s):  
Sundar Ramamurthy ◽  
Michael P. Mallamaci ◽  
Catherine M. Zimmerman ◽  
C. Barry Carter ◽  
Peter R. Duncombe ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Glassy Phase ◽  
Silicate Liquid ◽  
Two Phase ◽  
The Matrix ◽  
Devitrification Process ◽  
Phase Mixture

Dense, polycrystalline MgO was infiltrated with monticellite (CaMgSiO4) liquid to study the penetration of liquid along the grain boundaries of MgO. Grain growth was found to be restricted with increasing amounts of liquid. The inter-granular regions were generally found to be comprised of a two-phase mixture: crystalline monticellite and a glassy phase rich in the impurities present in the starting MgO material. MgO grains act as seeding agents for the crystallization of monticellite. The location and composition of the glassy phase with respect to the MgO grains emphasizes the role of intergranular liquid during the devitrification process in “snowplowing” impurities present in the matrix.

Characterization of the SiCf/SiC Composite Fabricated by the Whisker Growing Assisted CVI Process

2005 ◽  
Vol 287 ◽  
pp. 200-205 ◽  
Author(s):  
Ji Yeon Park ◽  
S.M. Kang ◽  
Weon Ju Kim ◽  
Woo Seog Ryu
Keyword(s):  
Flexural Strength ◽  
Chemical Vapor ◽  
Pyrolytic Carbon ◽  
Chemical Vapor Infiltration ◽  
Interlayer Thickness ◽  
Filling Time ◽  
The Matrix ◽  
Sic Whiskers

To obtain a dense SiCf/SiC composite by the chemical vapor infiltration (CVI) process, whisker growing before matrix filling was applied, which is called the whisker growing assisted CVI process. The whisker growing and matrix filling processes were carried out using MTS (CH3SiCl3) and H2 as source and diluent gases, respectively. Tyranno-SATM was used as a reinforced substrate. Characterizations of SiC whisker grown during the in situ whisker growing process have been investigated. The weight gain rates with the matrix filling time and the density of composites was measured. The flexural strength with the thickness of the pyrolytic carbon (PyC) interlayers has been evaluated. b-SiC whiskers with many stacking faults were grown well in the Tyranno SATM fabrics. Tyranno-SA/SiC composite with a PyC interlayer thickness of 150 nm had a flexural strength of 610 MPa and the density of 2.71 g/cm3.

scholarly journals Characterization of rifampicin-resistant Mycobacterium tuberculosis in Taiwan

2003 ◽  
Vol 52 (3) ◽  
pp. 239-245 ◽  
Author(s):  
Hsing-Yu Hwang ◽  
Chung-Yu Chang ◽  
Lin-Li Chang ◽  
Shui-Feng Chang ◽  
Ya-Hui Chang ◽  
...  
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Core Region ◽  
Banding Patterns ◽  
The Core ◽  
Resistant Tuberculosis ◽  
Proportion Method ◽  
The Mean ◽  
Novel Alleles ◽  
The Relationship

Sixty-three rifampicin-resistant (Rifr) isolates of Mycobacterium tuberculosis from Kaohsiung, Taiwan, were analysed for mutations in the core region (69 bp, codons 511–533) of the rpoB gene. Some 84.1 % (53/63) of the resistant isolates showed mutations in this region, especially in codons 531 (41.5 %), 526 (18.9 %), 516 (15.1 %) and 533 (7.5 %). Five novel alleles of a total of 16 different types of mutations were identified in Rifr isolates. Ten Rifr isolates (15.9 %) exhibited no mutations in the core region of rpoB. Also, they did not show mutations in another 365 bp fragment (codons 99–220) of rpoB. The agar proportion method was used to determine the relationship between the degree of rifampicin resistance and alterations in the core region of rpoB. The results revealed that the mean MIC was 92.38 μg ml−1 for the 53 isolates with a mutation in the core region, whereas the mean MIC of the other 10 isolates without mutations was only 24.8 μg ml−1. This indicates that the isolates with mutations in the core region had higher levels of resistance than those without mutations in this region. IS6110 restriction fragment length polymorphism (RFLP) was used for typing of 55 Rifr M. tuberculosis isolates. Isolates contained two to 19 copies of IS6110, with sizes ranging from 600 to 16 000 bp. The majority (85 %) contained six to 16 copies. No strains lacking IS6110 were found. A total of 54 of 55 RFLP types were defined at the 90 % similarity level. The observation of varied IS6110-associated banding patterns indicates that an outbreak of drug-resistant tuberculosis did not occur in this area.

scholarly journals Microstructural evolution of a modified HP alloy: experimental and complementary computational study

2017 ◽  
pp. 5141-5145
Author(s):  
Sandra Simonetti ◽  
C. Lanz ◽  
G. Brizuela ◽  
A. Juan
Keyword(s):  
Computational Study ◽  
Microstructural Characterization ◽  
X Ray Diffraction ◽  
X Ray ◽  
Eutectic Carbides ◽  
The Matrix ◽  
Secondary Precipitates ◽  
M23c6 Carbides ◽  
Cast Condition

In this work is presented results of the microstructural characterization of austenitic stainless steel (HP series) modified with Nb, aged at temperatures of 750, 800, 850, 900 and 950oC in air at different times. Microstructural changes were analyzed using optical microscopy, scanning electron microscopy (SEM) equipped with (EDS), x-ray diffraction and Vickers hardness. In the as-cast condition, the microstructure consists of an austenitic matrix and eutectic carbides network, Cr, Nb-rich carbides. The Cr-rich carbides are M7C3 type, whereas, those rich in Nb are NbC. During aging, there is a second precipitation in the matrix of very fine needle form of M23C6 carbides, which leads to an increase in hardness. After that, the decreasing in hardness is associated with a coalescence phenomenon of the secondary precipitates. Computational modeling shows that M23C6 is lesser stable than M7C3 carbide.

scholarly journals Preparation and Microstructural Characterization of a High-Cr White Cast Iron Reinforced with WC Particles

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2596
Author(s):  
Aida B. Moreira ◽  
Laura M. M. Ribeiro ◽  
Pedro Lacerda ◽  
Ricardo O. Sousa ◽  
Ana M. P. Pinto ◽  
...  
Keyword(s):  
Cast Iron ◽  
Base Metal ◽  
White Cast Iron ◽  
Microstructural Characterization ◽  
Ex Situ ◽  
Matrix Composites ◽  
The Matrix ◽  
Eutectic Constituent ◽  
Cold Pressed

High-chromium white cast iron (WCI) specimens locally reinforced with WC–metal matrix composites were produced via an ex situ technique: powder mixtures of WC and Fe cold-pressed in a pre-form were inserted in the mold cavity before pouring the base metal. The microstructure of the resulting reinforcement is a matrix of martensite (α’) and austenite (γ) with WC particles evenly distributed and (Fe,W,Cr)6C carbides that are formed from the reaction between the molten metal and the inserted pre-form. The (Fe,W,Cr)6C precipitation leads to the hypoeutectic solidification of the matrix and the final microstructure consists of martensite, formed from primary austenite during cooling and eutectic constituent with (Fe,Cr)7C3 and (Fe,W,Cr)6C carbides. The presence of a reaction zone with 200 µm of thickness, between the base metal and the composite should guarantee a strong bonding between these two zones.

scholarly journals Structural and Computational Characterization of Disease-Related Mutations Involved in Protein-Protein Interfaces

2019 ◽  
Vol 20 (7) ◽  
pp. 1583 ◽  
Author(s):  
Dàmaris Navío ◽  
Mireia Rosell ◽  
Josu Aguirre ◽  
Xavier de la Cruz ◽  
Juan Fernández-Recio
Keyword(s):  
Protein Interactions ◽  
Computational Analysis ◽  
Molecular Level ◽  
Binding Free Energy ◽  
Evolutionary Conservation ◽  
Core Region ◽  
Protein Protein Interactions ◽  
The Core ◽  
Protein Interfaces

One of the known potential effects of disease-causing amino acid substitutions in proteins is to modulate protein-protein interactions (PPIs). To interpret such variants at the molecular level and to obtain useful information for prediction purposes, it is important to determine whether they are located at protein-protein interfaces, which are composed of two main regions, core and rim, with different evolutionary conservation and physicochemical properties. Here we have performed a structural, energetics and computational analysis of interactions between proteins hosting mutations related to diseases detected in newborn screening. Interface residues were classified as core or rim, showing that the core residues contribute the most to the binding free energy of the PPI. Disease-causing variants are more likely to occur at the interface core region rather than at the interface rim (p < 0.0001). In contrast, neutral variants are more often found at the interface rim or at the non-interacting surface rather than at the interface core region. We also found that arginine, tryptophan, and tyrosine are over-represented among mutated residues leading to disease. These results can enhance our understanding of disease at molecular level and thus contribute towards personalized medicine by helping clinicians to provide adequate diagnosis and treatments.

Structural characterization of the core region from the lipopolysaccharide of the haloalkaliphilic bacterium Halomonas alkaliantarctica strain CRSS

2010 ◽  
Vol 8 (23) ◽  
pp. 5404 ◽  
Author(s):  
Giuseppina Pieretti ◽  
Sara Carillo ◽  
Barbara Nicolaus ◽  
Annarita Poli ◽  
Rosa Lanzetta ◽  
...  
Keyword(s):  
Structural Characterization ◽  
Core Region ◽  
The Core
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