DIFFUSION-CONTROLLED DISSOLUTION OF ZIRCONIUM IN MOLTEN URANIUM WITH MONOTONICALLY INCREASING TEMPERATURE

ABSTRACTThe leaching mechanisms of simulated low-level radioactive waste forms are being determined as support for development of an accelerated leach test. Two approaches are being used: (1) comparison of leaching data with results of a model that describes diffusion from a finite cylinder, and (2) observation of the leaching process at temperatures between 20°C and 65°C. To provide results that can be used for modeling, leaching at elevated temperatures must change neither the leaching mechanism nor the structural controls of leaching such as the porosity. Releases of 137Cs, 85Sr, calcium, sodium and potassium from portland cement containing sodium sulfate, as a simulated evaporator sludge, have been determined under a variety of experimental conditions. Data from the leach tests were compared to model results for diffusion from the finite cylinder. While most leaching appears to be diffusion controlled, notable exceptions occur. For all samples, activation energies ranging between 6 and 11 Kcal/mole have been calculated from the relationship of the effective diffusion coefficient to increasing temperature, close to the expected value of 5 Kcal/mole for diffusion.

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What Determines the Peak-Temperature in Binary Ni3Al?

MRS Proceedings ◽

10.1557/proc-364-689 ◽

1994 ◽

Vol 364 ◽

Cited By ~ 1

Author(s):

C. Rentenberger Karnthaler ◽

H.P. Karnthaler

Keyword(s):

Maximum Stress ◽

Dynamic Recovery ◽

Al Alloys ◽

Shear Stresses ◽

Compression Axis ◽

Pronounced Change ◽

Diffusion Controlled ◽

Ordered Alloys ◽

Multiple Cross ◽

Increasing Temperature

AbstractIn Ni3Al alloys the yield stress increases with increasing temperature up to a maximum stress, reached at the temperature TP. Below TP glide occurs on primary octahedral planes whereas above TP glide on primary cube planes is dominating. Therefore this change of glide planes was considered to determine TP.TEM investigations were carried out to study the mechanisms that control TP in Ni3Al specimens with [001] compression axis. In this case no shear stresses are acting on any of the cube glide systems. The TEM results show a pronounced change of the dislocation structure on the {111} glide planes below and above the peak. The breakdown of the barriers (locked screw dipoles) starts when the diffusion is high enough to facilitate their annihilation. The dynamic recovery of the locked screws occurs by multiple cross-slip via octahedral planes. It is proposed that, in this and other ordered alloys, the value of TP is diffusion controlled.

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Microstructural Evolution during Sintering of the P/M Blended Elemental Ti-5Al-2.5Fe Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.498-499.55 ◽

2005 ◽

Vol 498-499 ◽

pp. 55-60 ◽

Cited By ~ 2

Author(s):

Rodrigo P. Siqueira ◽

Hugo Ricardo Zschommler Sandim ◽

Vinicius André Rodrigues Henriques ◽

J.F.C. Lins

Keyword(s):

Microstructural Evolution ◽

Cost Effective ◽

X Ray Diffraction ◽

Blended Elemental ◽

Surgical Implants ◽

Diffusion Controlled ◽

Effective Option ◽

Temperature Homogenization ◽

Increasing Temperature ◽

Cold Pressed

The alpha-beta Ti-5%Al-2.5Fe (wt-%) alloy was developed as a cost-effective option to replace the traditional Ti-6%Al-4%V alloy in the manufacture of surgical implants because of its larger biocompatibility (V-free alloy). Samples of this alloy were prepared using the blended elemental (BE) technique. The isochronal sintering of the cold pressed compacts was carried out at 700, 1000, and 1400°C in vacuum. In this work, the preliminary results of the behavior of elementary powders during sintering and the corresponding microstructural evolution are shown. The alloy was characterized by means of scanning electron microscopy (SEM) in the backscattered mode, X-ray diffraction (XRD), energy-dispersive spectrometry (EDS), and density measurements. The results indicate that the homogenization of the alloy is diffusion-controlled. Non-equilibrium Ti-Al phases as well as Fe-Al compounds were identified in samples sintered at lower temperatures (700oC). With increasing temperature, homogenization of the alloy takes place and a structure consisting of coarse plate-like alpha and intergranular beta is present.

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Effects of Temperature and Grain Size on Diffusivity of Aluminium: Electromigration Experiment and Molecular Dynamic Simulation

Journal of Physics Condensed Matter ◽

10.1088/1361-648x/ac4b7f ◽

2022 ◽

Author(s):

Zhen Cui ◽

Yaqian Zhang ◽

Dong Hu ◽

Sten Vollebregt ◽

Jiajie Fan ◽

...

Keyword(s):

Grain Size ◽

Molecular Dynamic ◽

Effective Diffusivity ◽

Md Simulations ◽

Atomic Diffusion ◽

Polycrystalline Aluminum ◽

Metallic Material ◽

Self Diffusion ◽

Diffusion Controlled ◽

Increasing Temperature

Abstract Understanding the atomic diffusion features in metallic material is significant to explain the diffusion-controlled physical processes. In this paper, using electromigration experiments and molecular dynamic (MD) simulations, we investigate the effects of grain size and temperature on the self-diffusion of polycrystalline aluminum (Al). The mass transport due to electromigration are accelerated by increasing temperature and decreasing grain size. Magnitudes of effective diffusivity (Deff) and grain boundary diffusivity (DGBs) are experimentally determined, in which the Deff changes as a function of grain size and temperature, but DGBs is independent of the grain size, only affected by the temperature. Moreover, MD simulations of atomic diffusion in polycrystalline Al demonstrate those observations from experiments. Based on MD results, the Arrhenius equation of DGBs and empirical formula of the thickness of grain boundaries at various temperatures are obtained. In total, Deff and DGBs obtained in the present study agree with literature results, and a comprehensive result of diffusivities related to the grain size is presented.

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Influence of time, pH, temperature, organic matter and exchangeable cations on the adsorption of oxamyl on illites and kaolinites

The Journal of Agricultural Science ◽

10.1017/s0021859600028562 ◽

1980 ◽

Vol 94 (3) ◽

pp. 557-563 ◽

Cited By ~ 3

Author(s):

O. P. Bansal ◽

Vijay Bansal

Keyword(s):

Molecular Structure ◽

Organic Matter ◽

Order Reaction ◽

Exchangeable Cations ◽

Exchangeable Cation ◽

First Order ◽

Diffusion Controlled ◽

Acid And Base ◽

Controlled Adsorption ◽

Increasing Temperature

SummaryThe adsorption of oxamyl under various conditions of time, pH, temperature, organic matter and exchangeable cations on illites and kaolinites was examined. The first order reaction indicated diffusion-controlled adsorption, maximum adsorption occurring at pH 6–5 which is near the pK value of oxamyl. Exchangeable cation in the order Na > H > Ca, organic matterand increasing temperature decreased adsorption. Adsorption isotherms and the molecular structure of oxamyl point to a reaction mechanism for oxamyl association with acid- and base-saturatedclays which involve either protonation or co-ordination of exchangeable clay cations to the carbonyl of the amide structure.

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Growth Kinetics of IMC Formed between Sn-3.5Ag-0.75Cu BGA Solder and Electroless Ni-P/Cu Substrate by Solid-State Isothermal Aging

Materials Science Forum ◽

10.4028/www.scientific.net/msf.449-452.893 ◽

2004 ◽

Vol 449-452 ◽

pp. 893-896 ◽

Cited By ~ 1

Author(s):

Jeong Won Yoon ◽

Chang Bae Lee ◽

Seung Boo Jung

Keyword(s):

Solid State ◽

Growth Kinetics ◽

Isothermal Aging ◽

Ball Grid Array ◽

Cu Substrate ◽

Diffusion Controlled ◽

Increasing Temperature ◽

Electroless Ni ◽

Kinetics Of ◽

Deposit Layer

The growth kinetics of intermetallic compound (IMC) layers formed between Sn-3.5Ag-0.75Cu BGA (ball grid array) solder and electroless Ni-P/Cu substrate by solid state isothermal aging were examined at temperatures between 70 and 170°C for 0 to 100 days. In the solder joints between the solder ball and electroless Ni-P/Cu pads, the IMC layer was (Cu,Ni)6Sn5. Also, a P-rich Ni layer formed at the interface between (Cu,Ni)6Sn5 and original Ni-P deposit layer because of the phosphorous accumulation. These IMC layer thicknesses increased linearly with the square root of aging time and the growth was faster for higher aging temperatures. On the contrary, the shear strength decreased with the increasing temperature and time. The growth of IMC layer was mainly controlled by diffusion-controlled mechanism over the temperature range studied. The apparent activation energy calculated for the growth of the (Cu,Ni)6Sn5 IMC was 69.75 kJ/mol.

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The Effect of Strain Rate on the Yield Behavior of Iron-Based Lro Alloys at Elevated Temperatures

MRS Proceedings ◽

10.1557/proc-81-235 ◽

1986 ◽

Vol 81 ◽

Author(s):

H. T. Lin ◽

R. C. Wilcox ◽

B. A. Chin

Keyword(s):

Yield Strength ◽

Strain Rate ◽

Temperature Dependence ◽

Elevated Temperatures ◽

Positive Temperature ◽

Yield Behavior ◽

Sem And Tem ◽

Diffusion Controlled ◽

Iron Based ◽

Increasing Temperature

AbstractThe sensitivity of iron-based LRO alloys to strain rate at elevated temperatures was investigated. The tensile results indicate that the iron-based LRO alloys exhibit a positive temperature dependence of yield behavior, but are insensitive to variations in strain rate between 10-5 and 100 sec-1. These observations, along with SEM and TEM results, suggest that previous proposed diffusion-controlled mechanisms are not responsible for the increase in yield strength with increasing temperature.

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ELEMENTARY ACTS OF PHOTOREACTIONS OF 2,6-DIPHENYL-1,4-BENZOQUINONE IN VARIOUS SOLVENTS

IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA ◽

10.6060/ivkkt201962fp.5756 ◽

2018 ◽

Vol 62 (1) ◽

pp. 26-30

Author(s):

Dmitriy N. Gurulev ◽

Lyubov V. Palatkina ◽

Natalia A. Kuznetsova ◽

Vladimir I. Porkhun

Keyword(s):

Exchange Process ◽

Nmr Spectrum ◽

Meta Position ◽

Semiquinone Radicals ◽

Diffusion Controlled ◽

Order Of Magnitude ◽

Diffusion Rate Constant ◽

Wide Line ◽

The Stability ◽

Increasing Temperature

In order to determine the effect of the polarity of solvents on the reactivity and the course of the reactions of semihinone radicals, their complexes, this study of 2,6-diphenyl-1,4-benzoquinone, (class of substituted benzoquinones) and its dimer D was carried out. It was found that in the NMR spectrum of the dimer solution, with increasing temperature, the lines widen, and there is one wide line close to the chemical shift to the protons of the meta-groups of quinone. The NMR spectrum of a solution D in deuterochloroform at low temperatures contains lines corresponding to the aromatic part of the protons in the meta position, respectively (7.05 M.d, 6.89 M.d.). That is, the exchange process between the non-equivalent parts of the diamagnetic dimer molecule of the preceding dissociation takes place with the constant of the velocity k-1, coinciding in order of the inverse spin-spin relaxation time. The value of k-1 increases by more than an order of magnitude with the increasing polarity of the solvent. This effect is due to the stronger solvent solvation of the activated complex in the transition state compared to the molecule. The reaction of dimerization of semiquinone radicals is diffusion-controlled, since the values of ∆H1≠ in all solvents differ from the activation energy of viscosity by no more than 1 kcal/M and the values of the velocity constant in 5-8 times differ from the diffusion rate constant calculated by Debye. The solvation of radicals leads to a decrease in the diffusion coefficients of radicals and, possibly, to the shielding of the reaction center, which causes a decrease in k1. With the decrease of the constant in the specified number of solvents, the stability of the radical increases, which is manifested in a symbiotic increase in the equilibrium constant K. The reason for the increase of the direct constant k1 in solvents with high permittivity is explained.

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Reduction kinetics of lead-rich slag with carbon in the temperature range of 1073 to 1473K

Journal of Mining and Metallurgy Section B Metallurgy ◽

10.2298/jmmb120823012h ◽

2013 ◽

Vol 49 (2) ◽

pp. 201-206 ◽

Cited By ~ 1

Author(s):

X. Hou ◽

K.C. Chou ◽

B. Zhao

Keyword(s):

Activation Energy ◽

Reaction Rate ◽

Graphite Crucible ◽

Reduction Reaction ◽

Synthetic Slag ◽

Reduction Kinetics ◽

Temperature Range ◽

Diffusion Controlled ◽

The Difference ◽

Increasing Temperature

Extensive experiments have been carried out on the reduction of lead-rich slag in graphite crucible at temperature range of 1073 to 1473K. The reduction kinetics was also compared between industrial sinters and synthetic slags. The extent of reduction was measured by the volume of CO-CO2 gas produced at a given temperature and time. It was found that, at a given temperature, the reaction rate between the slag and carbon was initially fast and then slow as the extent of the reaction increases. Only limited reaction between slag and carbon occurred at temperatures below 1173K. At temperatures above 1173K, the reaction rate increased significantly with increasing temperature. The reduction reaction was found to be mainly liquid-solid reaction, which was chemically controlled at initial stage and diffusion controlled at later stage. The apparent activation energy was calculated to be 83.8 kJ/mol at chemically controlled stage and 224.9 kJ/mol at diffusion controlled stage for reduction of industrial sinter. For the synthetic slag, the reaction activation energy was 102.9 kJ/mol at chemically controlled stage and 259.4 kJ/mol at diffusion controlled stage. The difference of the activation energy between industrial sinter and synthetic slag can be explained by the difference in their CaO/SiO2 ratios.

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A TEM investigation of a hyper-eutectic lead-tin alloy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010010487x ◽

1988 ◽

Vol 46 ◽

pp. 562-563

Author(s):

John A. Sutliff

Keyword(s):

Volume Diffusion ◽

Eutectic Mixture ◽

Precipitation Reaction ◽

Directionally Solidified ◽

X Ray Diffraction ◽

X Ray ◽

Transmission Electron ◽

Diffusion Controlled ◽

Discontinuous Precipitation Reaction ◽

Controlled Precipitation

Near-eutectic Pb-Sn alloys are important solders used by the electronics industry. In these solders, the eutectic mixture, which solidifies last, is the important microstructural consituent. The orientation relation (OR) between the eutectic phases has previously been determined for directionally solidified (DS) eutectic alloys using x-ray diffraction or electron chanelling techniques. In the present investigation the microstructure of a conventionally cast, hyper-eutectic Pb-Sn alloy was examined by transmission electron microscopy (TEM) and the OR between the eutectic phases was determined by electron diffraction. Precipitates of Sn in Pb were also observed and the OR determined. The same OR was found in both the eutectic and precipitation reacted materials. While the precipitation of Sn in Pb was previously shown to occur by a discontinuous precipitation reaction,3 the present work confirms a recent finding that volume diffusion controlled precipitation can also occur.Samples that are representative of the solder's cast microstructure are difficult to prepare for TEM because the alloy is multiphase and the phases are soft.

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