Coupled Diffusion Equation Solutions To Ag/Ge (L 11) And Cs/Si (100) Interactions

1993 ◽  
Vol 317 ◽  
Author(s):  
J. A. Venables ◽  
R. Persaud ◽  
F. L. Metcalfe ◽  
R. H. Milne ◽  
M. Azim
Keyword(s):  
Diffusion Coefficients ◽  
Room Temperature ◽  
Secondary Electron ◽  
Effective Diffusion ◽  
Coupled Diffusion ◽  
Effective Diffusion Coefficients ◽  
Comparison With Experiment ◽  
Surface Phases ◽  
Electron Imaging ◽  
And Diffusion

ABSTRACTSurface diffusion has been studied in the Ag/Ge (111) and Cs/Si (100) systems using UHV-SEM based techniques, biassed secondary electron imaging (b-SEI), Micro-AES and RHEED. Ag and Cs were deposited through a mask of holes held close to the substrate at room temperature, and annealed at higher temperatures Ta. Under certain conditions, the Ag and Cs patches split into two distinct regions with different sub-Monolayer (ML) coverages θ, observable using b-SEI; the sensitivity for Cs/Si (100) is below 0.5% ML. These patch widths were measured as f(ø,Ta,t), and effective diffusion coefficients extracted. Both systems were modelled using coupled diffusion equations, involving adatoms in two different surface phases. Comparison with experiment yields activation energies for adsorption (Ea) and diffusion (Ed).

Some Comparisons of Ag Deposits on Ge and Si(111)

1992 ◽  
Vol 280 ◽  
Author(s):  
F. L. Metcalfe ◽  
J. A. Venables
Keyword(s):  
Crystal Growth ◽  
Surface Diffusion ◽  
Secondary Electron ◽  
Diffusion Length ◽  
Effective Diffusion ◽  
Rate Equations ◽  
Kinetic Rate ◽  
Annealing Conditions ◽  
Electron Imaging

ABSTRACTCrystal growth and surface diffusion have been studied in the Ag/Ge(lll) system using UHV-SEM based techniques, biassed secondary electron imaging (b-SEI), micro-AES and RHEED. Ag was deposited through and past a mask of holes held close to the substrate at 300<Td< 775K. Under certain conditions, the Ag patches were observed to split into two regions corresponding to the √3×√3R30° (hereafter √3) and a lower coverage 4×4 structure, each of which were easily observable using b-SEI. These patch widths were measured as a function of Td, and of annealing times at temperatures Ta, and effective diffusion coefficents extracted. The diffusion length of adatoms over the 4×4 structure is larger than that over the √3 structure. These observations are modelled using kinetic rate equations, and the results are compared with previous studies of Ag/Si(111). We find that energies characterising processes on top of the √3 layers of both systems are very similar, but that processes involved in the formation of the layers are quite different. The coverage of the √3 Ag/Ge(111) layer is close to 1 ML for all Td studied, unlike √3 Ag/Si(111). where it depends on deposition and annealing conditions.

Effective Diffusion Coefficients and Thermal Stability of the Structure of Metallic Glass Fe48Co32P14B6

2020 ◽  
Vol 62 (12) ◽  
pp. 2258-2265 ◽  
Author(s):  
S. V. Vasiliev ◽  
V. I. Parfenii ◽  
E. A. Pershina ◽  
A. S. Aronin ◽  
O. V. Kovalenko ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Metallic Glass ◽  
Diffusion Coefficients ◽  
Effective Diffusion ◽  
Effective Diffusion Coefficients ◽  
Thermal Stability Of

scholarly journals Modeling and thermodynamic properties of ‘bacaba’ pulp drying

2019 ◽  
Vol 23 (9) ◽  
pp. 702-708 ◽  
Author(s):  
Maria F. de Morais ◽  
José R. O. dos Santos ◽  
Marisângela P. dos Santos ◽  
Dyego da C. Santos ◽  
Tiago N. da Costa ◽  
...  
Keyword(s):  
Activation Energy ◽  
Thermodynamic Properties ◽  
Diffusion Coefficients ◽  
Effective Diffusion ◽  
Thermal Conditions ◽  
Drying Process ◽  
Experimental Conditions ◽  
Effective Diffusion Coefficients ◽  
Drying Rates ◽  
Increasing Temperature

ABSTRACT This study aimed to dry ‘bacaba’ (Oenocarpus bacaba Mart.) pulp under different thermal conditions, fit different mathematical models to the dehydration curves, and calculate the diffusion coefficients, activation energy and thermodynamic properties of the process. ‘Bacaba’ fruits were meshed to obtain the pulp, which was dried at temperatures of 40, 50 and 60 °C and with thickness of 1.0 cm. Increase in drying temperature reduced the dehydration times, as well as the equilibrium moisture contents, and drying rates of 0.65, 1.04 and 1.25 kg kg min-1 were recorded at the beginning of the process for temperatures of 40, 50 and 60 °C, respectively. The Midilli’s equation was selected as the most appropriate to predict the drying phenomenon, showing the highest R2, lowest values of mean square deviation (MSD) and χ2 under most thermal conditions, and random distribution of residuals under all experimental conditions. The effective diffusion coefficients increased with increasing temperature, with magnitudes of the order of 10-9 m2 s-1, being satisfactorily described by the Arrhenius equation, which showed activation energy (Ea) of 37.01 kJ mol-1. The drying process was characterized as endergonic, in which enthalpy (ΔH) and entropy (ΔS) reduced with the increment of temperature, while Gibbs free energy (ΔG) was increased.

Measurement of effective diffusion coefficients in dairy powders by confocal microscopy and sorption kinetic profiles

2019 ◽  
Vol 20 ◽  
pp. 100108 ◽  
Author(s):  
Valentyn Maidannyk ◽  
Eva Lutjes ◽  
Sharon Montgomery ◽  
Noel McCarthy ◽  
Mark A.E. Auty
Keyword(s):  
Confocal Microscopy ◽  
Diffusion Coefficients ◽  
Effective Diffusion ◽  
Sorption Kinetic ◽  
Effective Diffusion Coefficients ◽  
Dairy Powders
Sign in / Sign up

Export Citation Format

Share Document