The features of firing aluminitride substrates, characterized by a high temperature of more than 1800 0С and the presence of a reducing environment, are described. It is shown that the high quality of substrates in parallelism, thermal conductivity, and other properties can be achieved, along with the establishment of optimal firing modes, using a special design of a capsule based on boron nitride, which is a container that consists of a body - a box of rectangular cross section, bottom and plane-parallel dividing plates with supports. To create a local (inside the capsule) clean recovery medium, thorn-groove interlocks between the body and the bottom are provided, filled with a heat-resistant inert powder.
In the present work we have studied an extension of the classical thermal rectification, arising in certain cases from the contact of two dissimilar bulk materials with different temperature dependence of the thermal conductivity, to the Si-Ge system when boundary scattering effects are taken into account. Moreover, the directionality of the in-plane heat flow in a Si plate can be achieved by tuning the thickness and the impurity concentration along the cross section of the plate. We have designed several potential structures with this function in mind and discussed the physics behind.
ABSTRACTTemperature variations of the thermopower (TEP) of acceptor graphite intercalation compounds (GIC) are very different from that of pristine graphite. At low temperatures the TEP increases monotonically with T, then levels off above 150 K. This behavior is ascribed to the phonon drag effect. In the region where the TEP is nearly constant, phonon relaxation is mainly controlled by the Rayleigh scattering due to point defects or impurities. This process leads to T-independent phonon drag TEP. The importance of Rayleigh scattering is due to the large cross section diameter of the Fermi surface in GIC. At low temperatures where the boundary scattering becomes important, the TEP is proportional to T3 . Detailed calculations are carried out by solving the phonon-carrier coupled Boltzmann equation.
In this paper, the stochastic parameters of the effective thermal conductivity of multilayer composites are considered. The examined specimens of composites were built with a different number of layers and each had a different saturation density of a composite matrix with fibers. For each case of laminate built with a prescribed number of layers and assumed saturation density, 10,000 tests of its effective thermal conductivity were carried out using numerical experiments. It was assumed that the fibers located in each layer were rectilinear, had a circular cross-section and that they could take random positions in their repeatable volume elements (RVEs). In view of the mentioned assumptions, the heat flux passing throughout a cross-section of a composite sample, perpendicular to the fibers’ direction, was considered. The probability density functions were fitted to the obtained data and then the chosen stochastic parameters of the effective thermal conductivity coefficients were determined.
Stochastic Thermal Properties of Laminates Filled with Long Fibers