Diffusion Coefficients of Interest for the Simulation of Heat Treatment in Rare-Earth Transition Metal Magnets

2012 ◽  
Vol 727-728 ◽  
pp. 163-168 ◽  
Author(s):  
Marcos Flavio de Campos
Keyword(s):  
Experimental Data ◽  
Heat Treatment ◽  
Activation Energy ◽  
Rare Earth ◽  
Transition Metal ◽  
Impurity Atom ◽  
Diffusion Coefficients ◽  
Arrhenius Equation ◽  
Atom Diffusion ◽  
Essential Input

In the case of the modeling of sintering and heat treatments, the diffusion coefficients are an essential input. However, experimental data in the literature about diffusion coefficients for rare-earth transition metal intermetallics is scarce. In this study, the available data concerning diffusion coefficients relevant for rare-earth transition metal magnets are reviewed and commented. Some empirical rules are discussed, for example the activation energy is affected by the size of the diffusing impurity atom. Diffusion coefficients for Dy, Nd and Fe into Nd2Fe14B are given according an Arrhenius equation D=D0exp (-Q/RT). For Dy diffusion into Nd2Fe14B, Q 315 kJ/mol and D08 . 10-4m2/s.

Viscosity Of Molten Rare Earth Metal Trichlorides I. Cecl3, Ndcl3, Smcl3, Dycl3 And Ercl3

2003 ◽  
Vol 58 (7-8) ◽  
pp. 457-463 ◽  
Author(s):  
A. Potapov ◽  
V. Khokhlov ◽  
Y. Satoa
Keyword(s):  
Activation Energy ◽  
Rare Earth ◽  
Viscous Flow ◽  
Rare Earth Metal ◽  
Dynamic Viscosity ◽  
Kinematic Viscosity ◽  
Arrhenius Equation ◽  
Earth Metal ◽  
Capillary Viscometer ◽  
Density Data

The kinematic viscosity of molten CeCl3, NdCl3, SmCl3, DyCl3 and ErCl3 has been measured by using a capillary viscometer. The dynamic viscosity was computed by using density data taken from the literature. The viscosity increases with going from CeCl3 to ErCl3. The activation energy of the viscous flow, calculated by the Arrhenius equation, rises in the same order.

scholarly journals Ternary interdiffusion coefficients in α2-phase Ti3Al/Nb system

2012 ◽  
Vol 48 (2) ◽  
pp. 283-290 ◽  
Author(s):  
W. Wang ◽  
B. Yuan ◽  
C. Zhou
Keyword(s):  
Activation Energy ◽  
Ternary System ◽  
Diffusion Coefficients ◽  
Theoretical Basis ◽  
Single Phase ◽  
Arrhenius Equation ◽  
Diffusion Activation Energy ◽  
Α2 Phase ◽  
Interdiffusion Coefficients ◽  
Diffusion Activation

The ?2 single phase interdiffusion in Ti3Al-Nb ternary system was studied at temperatures of 1323, 1373 and 1423 K. The interdiffusion coefficients were calculated by the method of Dayananda. The average ternary interdiffusion coeffcients were determined in the mid of the diffusion zone, and the trace diffusion coefficients can be estimitaed in the limit cX?0. The obtained main interdiffusion coeffcients is little smaller than privious reported and the diffusion activation energy of Nb calculated by the trace diffusion coefficients is 299.29 kJmol-1 accoding to the Arrhenius equation. These results can provide a theoretical basis for the mechanisms of Nb improving the oxidation resistance of Ti3Al.

Infrared absorption spectroscopy of hydrogen and deuterium in CaO and SrO crystals

1989 ◽  
Vol 4 (1) ◽  
pp. 224-231 ◽  
Author(s):  
J. L. Park ◽  
R. González
Keyword(s):  
Activation Energy ◽  
Diffusion Coefficient ◽  
Absorption Spectra ◽  
Infrared Absorption ◽  
Diffusion Coefficients ◽  
Elevated Temperatures ◽  
Arrhenius Equation ◽  
Lithium Concentration ◽  
Infrared Absorption Spectroscopy ◽  
Infrared Absorption Spectra

Infrared absorption spectra have been used to characterize OH− and OD− ions at the surface and the bulk of undoped CaO, lithium doped CaO, and SrO crystals. Diffusion of deuterons from D2O vapor into these crystals was performed at elevated temperatures. Diffusion coefficients were obtained to be D (CaO) = 3 ⊠ 10−6 cm2/sec at 1773 K and D (SrO) = 4 ⊠ 10−7 cm2/sec at 1523 K. For the doped CaO crystal with lithium concentration of 310 ppm, the diffusion coefficient was measured to be D (CaO:Li) = 4 ⊠ 10−7 cm2/sec at 1473 K and the activation energy in the Arrhenius equation was estimated to be 1.7 eV.

Hydrogen diffusion and effect of grain size on hydrogenation kinetics in magnesium hydrides

2008 ◽  
Vol 23 (2) ◽  
pp. 336-340 ◽  
Author(s):  
X. Yao ◽  
Z.H. Zhu ◽  
H.M. Cheng ◽  
G.Q. Lu
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Grain Size ◽  
Diffusion Coefficients ◽  
Hydrogen Diffusion ◽  
Metal Hydrides ◽  
Grain Size Effect ◽  
Temperature Dependent ◽  
Hydrogenation Kinetics ◽  
Work First

Hydrogenation and dehydrogenation of metal hydrides are of great interest because of their potential in on-board applications for hydrogen vehicles. This paper aims to study hydrogen diffusion in metal hydrides, which is generally considered to be a controlling factor of hydrogenation/dehydrogenation. The present work first calculated temperature-dependent hydrogen diffusion coefficients by a theoretical model incorporated with experimental data in a Mg-based system and accordingly the activation energy. The grain size effect on diffusion in nanoscale was also investigated.

Optimizing the Heat Treatment of Rare Earth-Transition Metal Sintered Magnets

2010 ◽  
Vol 660-661 ◽  
pp. 290-295 ◽  
Author(s):  
Marcos Flavio de Campos ◽  
José Adilson de Castro
Keyword(s):  
Heat Treatment ◽  
Rare Earth ◽  
Transition Metal ◽  
Transition Metals ◽  
Finite Volume Method ◽  
Phase Diagrams ◽  
Cooling Rate ◽  
Slow Cooling ◽  
Annealing Temperatures ◽  
Volume Method

Rare earth transition metals magnets, as for example SmCo5, NdFeB and Sm(CoCuFeZr)z magnets are, very often, submitted to a post-sintering heat treatment where the coercivity increases. In many cases, a slow cooling between the sintering and the annealing temperatures is applied. To optimize the time and cooling rate of heat treatment, it was developed a model using the finite volume method. This model takes into account the diffusivities of the different atom species and also the boundaries of phase diagrams.

Note: Color development rate in dulce de leche

1995 ◽  
Vol 1 (2-3) ◽  
pp. 137-140 ◽  
Author(s):  
M.S. Pauletti ◽  
E. Castelao ◽  
N. Sabbag ◽  
Y S. Costa
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Formation Process ◽  
Arrhenius Equation ◽  
Development Rate ◽  
Sensorial Analysis ◽  
Color Formation ◽  
Color Development ◽  
Global Rate ◽  
Different Temperatures

The time necessary to obtain the characteristic dulce de leche color at different temperatures was studied. Samples were held at constant temperature until they reached a standard prescribed color. Sensorial analysis of the final color of the samples was performed in order to detect any difference. Results showed that color among samples was not significantly different (p = 0.95). Arrhenius equation was used to correlate the kinetics results. Variance analysis showed a very good correlation of experimental data (r2 = 0.98). The apparent activation energy values for both studied systems were similar (13.88–14.45 kcal mol–1) but somewhat smaller than those given by other authors for similar systems. The global rate constant value of color formation process at any temperature was slightly larger when the protein/carbohydrate ratio was higher.

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