[en] In the temperature range investigated, tracer diffusion in powder compacts occurs by high diffusivity paths, composed of at least grain boundary and surface diffusion. It was shown that effective grain boundary diffusion coefficient increase with temperature for the same density of specimens and decrease with increasing density of specimens for the same temperature. Tracer diffusion is slowest in powder specimens pre-sintered at the highest diffusion annealing temperature, but for all specimens investigated, it is faster than grain boundary diffusion in massive specimens

[en] How long does it take to boil an egg? Theoretical prediction, based on a simple adaptation of the solution to the exact thermal diffusion equation for a sphere, is consistent with experiments. The experimental data are also used to estimate an average value for the thermal diffusivity of an egg

[en] The two main properties related to heat conduction are thermal conductivity (K) and thermal diffusivity (D). However, while the meaning of K is very well known, the role played by D is usually undervalued and misunderstood. In this paper we will try to clarify the meaning of thermal diffusivity, first in homogeneous materials and then in composite materials. In this latter case, we will find that sometimes the association of two good thermal diffusers gives a bad diffuser. Moreover, by properly choosing the constituents of the composites we can manufacture materials with thermal properties that are not found in nature

[en] This article deals with thermal diffusion vibration analysis in an unbounded medium including a spherical cavity. Multi single/dual-phase-lag models based upon the Green-Naghdi theory are obtained to discuss the thermoelastic diffusion of the spherical cavity. The surface of the cavity is traction and chemical potential free, not isolated, and subjected to a flux varying harmonically with time. A comparison of results is made, and the validity of results is acceptable. Benchmark outcomes are tabulated to aid other researchers in their future investigations. (author)

[en] Thermal properties of functional materials are closely linked to atomic dynamics, which may be described in terms of atomic vibrations and diffusion kinetics. We have used the techniques of neutron scattering, lattice dynamics and molecular-dynamics simulations to investigate the dynamics and related material properties in a variety of ionic solids especially with polyhedral network structures. The talk will seek to convey the challenges and current status in this important area with examples from some of our research on properties of important functional materials in which dynamics plays an essential role, namely, negative thermal expansion materials, ferroelectrics and fast ion conductors. We have identified characteristic phonon modes and diffusion pathways that provide a microscopic understanding of the underlying mechanisms associated with the functional properties. In addition, our recent study on water-ice in Ih phase solves an outstanding problem of identifying the anharmonic phonons leading to the anomalous thermal expansion at low temperature

[en] When the thermal diffusivity, χ, of a thin film on a substrate is measured by means of the mirage method, the photothermal deflection of the probe beam is determined by the heat radiation field contributed by the film and the substrate, heated by the pump beam. A two-dimensional algorithm is here presented in order to deduce the measure of the diffusivities of the film and the substrate in one set of mirage detection from the experimental data

[en] We investigate the influence of the grain size on the thermal diffusivity of pure Al₂O₃ ceramics by using mirage effect. Results show that the value of thermal diffusivity decreases with increasing grain size, when the grain size of the sample is smaller than 200 nm, and the value of that increases with increasing grain size when the grain size is larger than 200 nm. The detailed experiments, the results, analyses, discussions are presented in this paper

No abstract available

[en] Extensive advancement in the field of geotechnology, hypersonic transport mediums and design of new materials have attracted researchers to make in-depth study of thermoelastic materials considering diffusion and viscosity effects. Fractional calculus produces more rational results in such studies. In this view, considering two-temperature generalized visco-thermoelastic diffusion with fractional order theory of generalized thermoelasticity, a model is formulated in the context of Lord Shulman (LS) and Green Lindsay (GL) theories of thermoelasticity. The medium considered for study is thermoelastic plate which is kept traction free initially at uniform temperature and is isoconcentrated. The constitutive relations and governing equations are non-dimensionalized and transformed to ordinary differential equation using Laplace transformation with respect to time ‘t’ and Fourier transformation with respect to space variable ‘x’. Mechanical and thermal loads are applied on both surfaces of the plate. Solutions in transformed domain are obtained from resulting system of differential equations. Various quantities like stress, temperature field, mass concentration and chemical potential are obtained for copper material in physical domain by numerical inversion of Laplace and Fourier transforms. The numeric results of LS model are presented graphically. The outcome of this work underlines that disturbances in field quantities can be reduced by increasing two-temperature parameter or decreasing fractional order parameter. Also viscosity parameters have significant influence on field quantities. (author)

No abstract available