Interface Reaction and Atomic Transport During COSi2 Film Formation

1992 ◽  
Vol 260 ◽  
Author(s):  
Z. G. Xiao ◽  
J. W. Honeycutt ◽  
G. A. Rozgonyi
Keyword(s):  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Film Formation ◽  
Microstructural Analysis ◽  
Interface Reaction ◽  
Lattice Diffusion ◽  
Atomic Transport ◽  
Transmission Electron ◽  
Boundary Diffusion Coefficient ◽  
Short Annealing

ABSTRACTThe formation process of COSi2 films grown from Co deposited on a Si single crystal was investigated as a function of very short annealing times by transmission electron microscopy and x-ray diffraction. Information on the interfacial reactions and atomic transport phenomena was obtained from a microstructural analysis of the CoxSiy layers formed. It was demonstrated that Co is the dominant diffusion species during COSi2 formation. Co atoms are generated at the COSi2/COSi2 interface via the reaction 2CoSi=CoSi2+Co and diffuse to the COSi2/Si interface, where they react with Si by Co+2Si=CoSi2. Direct microscopic evidence indicates that diffusivity of Co atoms along a COSi2 grain boundary greatly exceeds that through the COSi2 lattice. The grain boundary diffusion coefficient is estimated to be up to 100 times larger than the lattice diffusion coefficient. On this basis the influence of grain size on COSi2 film formation is discussed.

Characterization of the Penetration Mechanisms of Water into Polycrystalline UO2

2010 ◽  
Vol 1265 ◽  
Author(s):  
Ilaria Marchetti ◽  
Fabio Belloni ◽  
Jerome Himbert ◽  
Paul Carbol ◽  
Thomas Fanghänel
Keyword(s):  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Spent Nuclear Fuel ◽  
Secondary Ion Mass Spectrometry ◽  
Depth Profiling ◽  
Water Diffusion ◽  
Lattice Diffusion ◽  
Boundary Diffusion Coefficient ◽  
Key Issues ◽  
Boundary Width

AbstractFollowing containment failure in the scenario of geological disposal of spent nuclear fuel, the penetration rate of groundwater into the UO2 matrix could cause a rapid increase of the fraction of inventory becoming available for prompt dissolution. In this respect, oxygen and water diffusion mechanisms are key issues to investigate. In this work, secondary-ion-mass-spectrometry (SIMS) depth profiling has been applied to characterize a polycrystalline UO2 pellet exposed to 18O-labelled water at room temperature. 18O depth profiling up to 25 μm beneath the pellet surface clearly indicates a combination of oxygen diffusion into the UO2 lattice and water diffusion along grain boundaries, behaving as high diffusivity paths. The lattice diffusion coefficient of oxygen, DL, and the quantity δDB – product of the grain boundary width, δ, and the grain boundary diffusion coefficient of water, DB – have been measured, resulting in DL = (2.5 ± 0.1) × 10-24 m2 s-1 and δDB = (7.5 ± 0.3) × 10-24 m3 s-1.

Pressure, temperature, water content, and oxygen fugacity dependence of the Mg grain-boundary diffusion coefficient in forsterite

2018 ◽  
Vol 103 (9) ◽  
pp. 1354-1361 ◽  
Author(s):  
Hongzhan Fei ◽  
Sanae Koizumi ◽  
Naoya Sakamoto ◽  
Minako Hashiguchi ◽  
Hisayoshi Yurimoto ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Water Content ◽  
Oxygen Fugacity ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Boundary Diffusion Coefficient ◽  
Temperature Water

scholarly journals Phenomenological analysis of densification mechanism during spark plasma sintering of MgAl2O4

2009 ◽  
Vol 24 (6) ◽  
pp. 2011-2020 ◽  
Author(s):  
Guillaume Bernard-Granger ◽  
Nassira Benameur ◽  
Ahmed Addad ◽  
Mats Nygren ◽  
Christian Guizard ◽  
...  
Keyword(s):  
Spark Plasma Sintering ◽  
Interface Reaction ◽  
Grain Boundary Sliding ◽  
Lattice Diffusion ◽  
Densification Rate ◽  
Densification Mechanism ◽  
Plasma Sintering ◽  
Transmission Electron ◽  
In Series ◽  
Spark Plasma

Spark plasma sintering (SPS) of MgAl2O4 powder was investigated at temperatures between 1200 and 1300 °C. A significant grain growth was observed during densification. The densification rate always exhibits at least one strong minimum, and resumes after an incubation period. Transmission electron microscopy investigations performed on sintered samples never revealed extensive dislocation activity in the elemental grains. The densification mechanism involved during SPS was determined by anisothermal (investigation of the heating stage of a SPS run) and isothermal methods (investigation at given soak temperatures). Grain-boundary sliding, accommodated by an in-series {interface-reaction/lattice diffusion of the O2− anions} mechanism controlled by the interface-reaction step, governs densification. The zero-densification-rate period, detected for all soak temperatures, arise from the difficulty of annealing vacancies, necessary for the densification to proceed. The detection of atomic ledges at grain boundaries and the modification of the stoichiometry of spinel during SPS could be related to the difficulty to anneal vacancies at temperature soaks.

Grain-boundary diffusion coefficient in α-Al2O3 from spark plasma sintering tests: Evidence of collective motion of charge disconnections

2018 ◽  
Vol 44 (15) ◽  
pp. 19044-19048 ◽  
Author(s):  
Yoshihiro Tamura ◽  
Eugenio Zapata-Solvas ◽  
Bibi Malmal Moshtaghioun ◽  
Diego Gómez-García ◽  
Arturo Domínguez-Rodríguez
Keyword(s):  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Spark Plasma Sintering ◽  
Boundary Diffusion ◽  
Collective Motion ◽  
Grain Boundary Diffusion ◽  
Plasma Sintering ◽  
Boundary Diffusion Coefficient ◽  
Spark Plasma ◽  
Α Al2o3

Correlation of steady-state creep and changing microstructure in polycrystalline SiC sintered with powder derived via gaseous reactants in an are plasma

1988 ◽  
Vol 3 (5) ◽  
pp. 1021-1030 ◽  
Author(s):  
R. D. Nixon ◽  
J. B. Posthill ◽  
R. F. Davis ◽  
H. R. Baumgartner ◽  
B. R. Rossing
Keyword(s):  
Grain Boundary ◽  
Boundary Diffusion ◽  
Grain Boundary Sliding ◽  
Lattice Diffusion ◽  
Steady State Creep ◽  
Dislocation Glide ◽  
Creep Mechanisms ◽  
Transmission Electron ◽  
Dislocation Movement ◽  
Boundary Sliding

The mechanisms of steady-slate creep in compression in a sintered SiC produced via sintering of β-SiC powders derived from gaseous reactants in a plasma are have been determined from (1) kinetic data within the ranges of temperature and constant stress of 1770–2020 K and 17–208 MPa, respectively, and (2) the results of transmission electron microscopy (TEM) and other microbeam characterization techniques. The stress exponent was 2.06 ± 0.04; the values of activation energy were 913 ± 13 and 630 ± 14 kJ/mol above and below, respectively, a knee of ∼∼ 1920 K. Gliding dislocations and B4C precipitates, which developed within the grains during creep, and their interaction were the dominant microstructural features of the crept material. Apparent nonmechanical pinning of the dislocations at the precipitates indicated that the latter attracted the dislocations rather than acting as classical obstacles to dislocation movement. A synthesis of this information leads to the conclusion that the controlling creep mechanisms in this SiC were grain boundary sliding accommodated by grain boundary diffusion at T < 1920 K and lattice diffusion at T > 1920 K. The parallel mechanism of dislocation glide also contributed to the total strain.

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