Use Of Diffusion Data Research Articles

Si and O diffusion in olivine and implications for characterizing plastic flow in the mantle

The relationship between diffusion of individual species and creep of silicates is unclear and has long been debated, factually anchored by the central observation that the activation energies for creep are higher than the activation energy for diffusion of any species. There have been numerous attempts to explain this difference. New advances in experimental technology enable us to demonstrate that this difference does not exist and was an artefact of the limited experimental resolution of earlier studies – the activation energies of creep and diffusion of Si in olivine are identical, 530 kJ/mol. This allows the creep mechanism in olivine to be understood as one of simple climb (consistent with microstructural observations) and opens possibilities of estimating, understanding and predicting the (much simplified) creep behavior of diverse silicates under a wide range of P‐T‐X conditions through the use of diffusion data–measured or computed.

The development and use of the diffusion scattering coefficients in room modeling software: The effect of diffuse reflections on reverberation time

In the last 20 years, much progress has been made in the measurement and characterization of sound diffusing surfaces. This presentation describes how this research might improve the accuracy of computer based geometric room modeling. To model diffuse reflections, one needs to know the scattering distribution and the portion of scattered energy that is diffusely reflected. AES Working Group SC-04-02 recently published an information document AES-4id-2001, which describes a measurement procedure to determine the polar balloons from scattering surfaces. This allows programmers to use actual measured or calculated distributions instead of Lamberts law, which applies to incoherent optical diffusion. ISO WG 25 is currently addressing a measurement procedure to determine the random incidence scattering coefficient. This scattering coefficient is used directly in geometrical modeling programs. The two measurement procedures will be contrasted. It will then be demonstrated by example how the use of diffusion data can affect the predicted reverberation time.

Experimental study of hydrogen bonding by mutual diffusion

N. Chen and T. C. Chan, Chem. Commun., 1997, 719 DOI: 10.1039/A608147I

An Alternate Interpretation of Polymer/Solvent Jump Size Units for Free-Volume Diffusion Models

Polystyrene/toluene mutual-diffusion coefficients have been measured as a function of temperature in the limit of infinite solvent dilution. The solvent to polymer jump size unit ratio (ξ) was determined from the Vrentas−Duda free-volume diffusion model for polymer self-diffusion and is in excellent agreement with values evaluated from solvent self- and binary mutual-diffusion coefficient data. Comparison of the free-volume model to a version of the Kirkwood−Riseman theory, modified for diffusion at infinite dilution under non-ϑ conditions, suggests that ξ follows the temperature dependence of the root-mean-squared end-to-end distance of the polystyrene and can be estimated without the use of diffusion data. This result establishes an explicit theoretical coupling between thermodynamic interactions, Brownian dynamics, and free-volume theory.

Reactions and phase relations in the Ti [sbnd]Al [sbnd]O system

Reactions between titanium and alumina were studied experimentally for Al 2O 3 substrates with a titanium-based coating and for planar Ti Al 2O 3 diffusion couples in the temperature range between 800 and 1100°C. Isothermal sections through the phase diagram were determined by using these results as well as by investigating equilibrated alloys. These experimental sections agree with those calculated from thermodynamic data. The morphology and layer thickness of the observed reactions zones have been explained on the basis of these phase relations, making use of diffusion data from binary systems Ti O and Ti Al. The important role of the initial Ti thickness on the type of reaction products has been demonstrated.

Tracer diffusion in polyatomic liquids

New tracer diffusion data are reported. These plus other recently published work provide a wide range of solute (monatomic and polyatomic species) size and solvent molecular type. A hard sphere model, making use of diffusion data from computer simulations on hard sphere fluid, predicts fairly well the diffusivities for the solutes in nonpolar solvents of compact molecules. The model fails for solvents of normal alcohols (except methanol) and of noncompact molecules. Stokes’ law is re-examined and found to be invalid except for solute molecules large compared to solvent molecules. The oft-quoted validity of Stokes’ law for self-diffusion is shown to be an accident of conditions under which the law is usually applied. Further verified is a recently published correlation formula relating tracer diffusivity, solvent viscosity, and particle size.