Growth of The Mo5SiB2 Phase in A Mo5Si3/Mo2B Diffusion Couple

2000 ◽  
Vol 646 ◽  
Author(s):  
Sungtae Kim ◽  
R. Sakidja ◽  
Z. F. Dong ◽  
J. H. Perepezko ◽  
Yeon Wook Kim
Keyword(s):  
Diffusion Couple ◽  
Leading Edge ◽  
Growth Direction ◽  
Diffusion Couples ◽  
Microstructural Stability ◽  
Phase Development ◽  
Phase Sequence ◽  
Kinetics Of ◽  
Very High

ABSTRACTThe high melting temperature and oxidation resistance of the Mo5SiB2 (T2) phase and multiphase microstructures incorporating the T2 phase in the Mo-Si-B system have motivated further studies for applications in very high temperature environments. Since the long term microstructural stability is determined by diffusional processes, diffusion couples consisting of binary boride and silicide phases have been examined in order to evaluate the kinetics of T2 phase development and the relative diffusivities controlling the kinetics. Long term annealing (500 hrs) of the Mo5Si3/Mo2B diffusion couple yields the phase sequence of Mo5Si3/Mo3Si/T2/Mo2B at 1600°C. This indicates that the T2 phase initiates and grows from the Mo2B side to a thickness of about 32μm and the Mo3Si phase initiates and grows from the Mo5Si3 side to a thickness of about 15μm. Other annealing treatments allow for an analysis of the diffusion kinetics based upon the layer thickening and composition profile measurements. To identify the crystallographic growth direction of T2 on Mo2B, a wedge shaped TEM sample with very thin leading edge was prepared. Microstructure images indicate that the growth mode of the T2 phase is columnar. There is a clear tendency for the growth of T2 to be approximately normal to c-axis.

Phase Stability in Processing and Microstructure Control in High Temperature Mo-Si-B Alloys

2000 ◽  
Vol 646 ◽  
Author(s):  
J.H. Perepezko ◽  
R. Sakidja ◽  
S. Kim
Keyword(s):  
Phase Stability ◽  
Direct Access ◽  
Precipitation Reaction ◽  
Microstructural Stability ◽  
Two Phase ◽  
Solubility Behavior ◽  
Alternate Routes ◽  
Kinetics Of

ABSTRACTFor applications at ultrahigh temperatures the multiphase microstructural options that can be developed in the Mo-Si-B system have demonstrated an effective and attractive balance of essential characteristics. The coexistence of the high melting point (>2100°C) ternary intermetallic Mo5SiB2 (T2) phase with Mo provides a useful option for in-situ toughening. A further enhancement is available from a precipitation reaction of Mo within the T2 phase that develops due to the temperature dependence of the solubility behavior of the T2 phase. However, direct access to Mo+T2 microstructures is not possible in ingot castings due to solidification segregation reactions that yield nonequilibrium boride and silicide phases with sluggish dissolution. Alternate routes involving rapid solidification of powders are effective in suppressing the segregation induced phases. The processing and microstructure options can also be augmented by selected refractory metal substitutional alloying, such as the incorporation of Nb, that alters the solubility of the T2 phase and the relative phase stability to yield solidification of two phase refractory solid solution + T2 structures directly. The observed alloying trends highlight the role of atomic size in influencing the relative stability of the T2 phase. A key component of the overall microstructural control and long term microstructural stability is determined by the kinetics of diffusional processes. The analysis of selected diffusion couples involving binary boride and silicide phases has been used to assess the relative diffusivities in the T2 phase and coexisting phases over the range of solubility and to provide a basis for the examination of the kinetics of reactions involved in coatings and oxidation.

An Assessment of Layer Development at the Fuel/Cladding Interface During Irradiation of Metallic SFR Fuel Elements

2008 ◽  
Vol 1125 ◽  
Author(s):  
Dennis D. Keiser ◽  
James I. Cole
Keyword(s):  
Fission Product ◽  
Diffusion Couple ◽  
Chemical Interaction ◽  
Fission Products ◽  
Nuclear Fuels ◽  
Diffusion Couples ◽  
Fuel Cladding ◽  
Metallic Fuel ◽  
Phase Development ◽  
Metallic Nuclear Fuels

ABSTRACTTo investigate fuel cladding chemical interaction in irradiated metallic nuclear fuels, diffusion couple experiments have been performed using prototypic metallic fuel alloys with additions of noble metal and lanthanide fission product components mated against stainless steel claddings. The developed interdiffusion zones have been characterized using SEM/EDS/WDS to determine the development of phases and the interdiffusion behavior of specific fuel, cladding, and fission product components. The formed diffusion structures have been compared to actual interaction zones that form in irradiated metallic SFR fuels. This paper discusses how the structures compare between the diffusion couple-generated interdiffusion zones and those that develop in irradiated metallic nuclear fuels. It was found that similarities exist between the phase development and interdiffusion behavior in the annealed diffusion couples and the irradiated fuels. Nd, Mo, and Ru, which were added to a fuel alloy to represent fission products that are present in irradiated metallic nuclear fuels, were found to exhibit interdiffusion behavior in annealed diffusion couples that was similar to what has been observed in actual irradiated metallic fuels. This was also true for the original fuel components U, Pu, and Zr, along with the cladding constituent Fe, Ni, and Cr.

Growth of AlN bulk crystals from the vapor phase

2001 ◽  
Vol 693 ◽  
Author(s):  
Raoul Schlesser ◽  
Rafael Dalmau ◽  
Rositza Yakimova ◽  
Zlatko Sitar
Keyword(s):  
Single Crystals ◽  
Vapor Phase ◽  
Growth Direction ◽  
Nitrogen Atmosphere ◽  
Bulk Crystals ◽  
Seeded Growth ◽  
Long Term Stability ◽  
Dislocation Densities ◽  
Very High

AbstractAlN single crystals were grown by two different vapor phase processes: by vaporization of metallic Al in a nitrogen atmosphere, or by sublimation of an AlN source. Growth experiments were carried out under quasi-stagnant flow conditions, with typical flow rates of 100 sccm at reactor pressures ranging from 300 to 700 Torr. Growth temperatures ranged from 1800 to 2300°C. In Al vaporization experiments, the crystal shape and fastest growth direction was found to strongly depend on the growth temperature: at relatively low temperatures (1800-1900°C) long needles were grown, temperatures around 1900-2000°C yielded twinned platelets, while c-platelets were formed at temperatures above 2100°C. These c-plates grew at a rate of 5 mm/hr in the c-plane. When using AlN as a source material, growth rates were considerably slower, however, long-term stability of the Al flux was greatly improved. Seeded growth was demonstrated under these conditions. All grown single crystals were transparent and virtually colorless. Analytical results indicated very high crystalline quality and dislocation densities lower than 104cm-3.

TiAl3 Formation in the Titanium-Aluminum Diffusion Couple

2012 ◽  
Vol 322 ◽  
pp. 185-194 ◽  
Author(s):  
Mostafa Mirjalili ◽  
Mansour Soltanieh ◽  
Kiyotaka Matsuura ◽  
Munekazu Ohno
Keyword(s):  
Diffusion Couple ◽  
Intermetallic Layer ◽  
Pure Titanium ◽  
Diffusion Couples ◽  
Scattered Electron ◽  
Aluminum Sheets ◽  
Titanium Aluminum ◽  
Electron Imaging ◽  
Kinetics Of ◽  
Rich Side

Pure titanium and aluminum sheets were used to prepare titanium-aluminum diffusion couples. The diffusion couples were heated to temperatures 550, 575, 600, 625, 640, 650 and 700°C. SEM observations of the titanium-aluminum interface and EPMA results revealed that a TiAl3 intermetallic layer has formed and thickened between the layers. Grain boundaries of the TiAl3 compound, which were revealed by back-scattered electron imaging, indicated a size distribution across the layer. Finer grains which were located close to the titanium showed that TiAl3 has nucleated at the Ti-TiAl3 interface. Thus, the former grains which had formed close to the aluminum-rich side have grown and coarsened during annealing at high temperatures. Grain coarsening of TiAl3 decreased the kinetics of the layer thickening.

Kinetic Features of Solid-State Reactive Diffusion between Au and Sn-Base Solder

2007 ◽  
Vol 539-543 ◽  
pp. 2473-2478 ◽  
Author(s):  
M. Kajihara ◽  
T. Takenaka
Keyword(s):  
Solid State ◽  
Diffusion Couple ◽  
Diffusion Bonding ◽  
Experimental Results ◽  
Reactive Diffusion ◽  
Diffusion Couples ◽  
Kinetics Of ◽  
Bonding Technique ◽  
Kinetic Features

The kinetics of the solid-state reactive diffusion between Au and Sn was experimentally observed using Sn/Au/Sn diffusion couples prepared by a diffusion bonding technique. The diffusion couples were isothermally annealed at a temperature of T = 453 K. Due to annealing, AuSn, AuSn2 and AuSn4 compound layers are formed at the interface in the diffusion couple. The experimental results were used to evaluate quantitatively the effect of Ni on the growth of the Au–Sn compounds. The evaluation indicates that the addition of Ni into Sn between 1 and 5 mass% accelerates the growth of the Au–Sn compounds at T = 433–473 K.

Microstructural characterization of a rapidly solidified Al-Fe-V-Si alloy for elevated temperature applications

1988 ◽  
Vol 46 ◽  
pp. 550-551
Author(s):  
R. E. Franck ◽  
J. A. Hawk ◽  
G. J. Shiflet
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Grain Growth ◽  
Volume Fraction ◽  
Microstructural Characterization ◽  
Second Phase ◽  
Microstructural Stability ◽  
Elevated Temperature Strength ◽  
Temperature Applications

Rapid solidification processing (RSP) is one method of producing high strength aluminum alloys for elevated temperature applications. Allied-Signal, Inc. has produced an Al-12.4 Fe-1.2 V-2.3 Si (composition in wt pct) alloy which possesses good microstructural stability up to 425°C. This alloy contains a high volume fraction (37 v/o) of fine nearly spherical, α-Al12(Fe, V)3Si dispersoids. The improved elevated temperature strength and stability of this alloy is due to the slower dispersoid coarsening rate of the silicide particles. Additionally, the high v/o of second phase particles should inhibit recrystallization and grain growth, and thus reduce any loss in strength due to long term, high temperature annealing.The focus of this research is to investigate microstructural changes induced by long term, high temperature static annealing heat-treatments. Annealing treatments for up to 1000 hours were carried out on this alloy at 500°C, 550°C and 600°C. Particle coarsening and/or recrystallization and grain growth would be accelerated in these temperature regimes.

Comparative Labelling and Biokinetic Studies of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn)

1977 ◽  
Vol 16 (01) ◽  
pp. 30-35 ◽  
Author(s):  
N. Agha ◽  
R. B. R. Persson
Keyword(s):  
Complex Formation ◽  
Significant Influence ◽  
Room Temperature ◽  
Ph Value ◽  
Maximum Activity ◽  
Reduction Step ◽  
Labelling Yield ◽  
Different Temperatures ◽  
Kinetics Of

SummaryGelchromatography column scanning has been used to study the fractions of 99mTc-pertechnetate, 99mTcchelate and reduced hydrolyzed 99mTc in preparations of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn). The labelling yield of 99mTc-EDTA(Sn) chelate was as high as 90—95% when 100 μmol EDTA · H4 and 0.5 (Amol SnCl2 was incubated with 10 ml 99mTceluate for 30—60 min at room temperature. The study of the influence of the pH-value on the fraction of 99mTc-EDTA shows that pH 2.8—2.9 gave the best labelling yield. In a comparative study of the labelling kinetics of 99mTc-EDTA(Sn) and 99mTc- DTPA(Sn) at different temperatures (7, 22 and 37°C), no significant influence on the reduction step was found. The rate constant for complex formation, however, increased more rapidly with increased temperature for 99mTc-DTPA(Sn). At room temperature only a few minutes was required to achieve a high labelling yield with 99mTc-DTPA(Sn) whereas about 60 min was required for 99mTc-EDTA(Sn). Comparative biokinetic studies in rabbits showed that the maximum activity in kidneys is achieved after 12 min with 99mTc-EDTA(Sn) but already after 6 min with 99mTc-DTPA(Sn). The long-term disappearance of 99mTc-DTPA(Sn) from the kidneys is about five times faster than that for 99mTc-EDTA(Sn).

SATELLITE DATA FOR INVESTIGATION OF RECENT STATE AND PROCESSES IN THE SIVASH BAY

2017 ◽  
Author(s):  
Ekaterina Shchurova ◽  
Ekaterina Shchurova ◽  
Rimma Stanichnaya ◽  
Rimma Stanichnaya ◽  
Sergey Stanichny ◽  
...  
Keyword(s):  
Satellite Data ◽  
Water Exchange ◽  
High Salinity ◽  
Meteorological Data ◽  
Sea Surface ◽  
Azov Sea ◽  
Seasonal Wind ◽  
Ice Regime ◽  
Very High

Sivash bay is the shallow-water lagoon of the Azov Sea. Restricted water exchange and high evaporation form Sivash as the basin with very high salinity. This factor leads to different from the Azov Sea thermal and ice regimes of Sivash. Maine aim of the study presented to investigate recent state and changes of the characteristics and processes in the basin using satellite data. Landsat scanners TM, ETM+, OLI, TIRS together with MODIS and AVHRR were used. Additionally NOMADS NOAA and MERRA meteorological data were analyzed. The next topics are discussed in the work: 1. Changes of the sea surface temperature, ice regime and relation with salinity. 2. Coastal line transformation – long term and seasonal, wind impact. 3. Manifestation of the Azov waters intrusions through the Arabat spit, preferable wind conditions.

The effect of heterotrophic yield on the assessment of the correction factor for anoxic growth

1996 ◽  
Vol 34 (5-6) ◽  
pp. 67-74 ◽  
Author(s):  
D. Orhon ◽  
S. Sözen ◽  
N. Artan
Keyword(s):  
Correction Factor ◽  
Domestic Sewage ◽  
Yield Coefficient ◽  
Heterotrophic Growth ◽  
Metabolic Processes ◽  
Anoxic Conditions ◽  
Industrial Wastewaters ◽  
Systems Modelling ◽  
Kinetics Of ◽  
Very High

For single-sludge denitrification systems, modelling of anoxic reactors currently uses the kinetics of aerobic heterotrophic growth together with a correction factor for anoxic conditions. This coefficient is computed on the basis of respirometric measurements with the assumption that the heterotrophic yield remains the same under aerobic and anoxic coditions. The paper provides the conceptual proof that the yield coefficient is significantly lower for the anoxic growth on the basis of the energetics of the related metabolic processes. This is used for the interpretation of the very high values for the correction factor experimentally determined for a number of industrial wastewaters. A default value for the anoxic heterotrophic yield coefficient is calculated for domestic sewage and compatible wastewaters and proposed for similar evaluations.

Positive Emotions

2009 ◽  
pp. 12-24 ◽  
Author(s):  
Michael A. Cohn ◽  
Barbara L. Fredrickson
Keyword(s):  
Positive Emotions ◽  
Well Being ◽  
Life Outcomes ◽  
Short Term ◽  
Future Success ◽  
Broaden And Build Theory ◽  
Mental And Physical Health ◽  
Very High ◽  
Future Growth

Positive emotions include pleasant or desirable situational responses, ranging from interest and contentment to love and joy, but are distinct from pleasurable sensation and undifferentiated positive affect. These emotions are markers of people's overall well-being or happiness, but they also enhance future growth and success. This has been demonstrated in work, school, relationships, mental and physical health, and longevity. The broaden-and-build theory of positive emotions suggests that all positive emotions lead to broadened repertoires of thoughts and actions and that broadening helps build resources that contribute to future success. Unlike negative emotions, which are adapted to provide a rapid response to a focal threat, positive emotions occur in safe or controllable situations and lead more diffusely to seeking new resources or consolidating gains. These resources outlast the temporary emotional state and contribute to later success and survival. This chapter discusses the nature of positive emotions both as evolutionary adaptations to build resources and as appraisals of a situation as desirable or rich in resources. We discuss the methodological challenges of evoking positive emotions for study both in the lab and in the field and issues in observing both short-term (“broaden”) and long-term (“build”) effects. We then review the evidence that positive emotions broaden perception, attention, motivation, reasoning, and social cognition and ways in which these may be linked to positive emotions' effects on important life outcomes. We also discuss and contextualize evidence that positive emotions may be detrimental at very high levels or in certain situations. We close by discussing ways in which positive emotions theory can be harnessed by both basic and applied positive psychology research.

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