[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] A tungsten-copper duplex structure has received consideration for use as a divertor plate in a conceptual design of the Fusion-Experimental Reactor (FER). Thermal fatigue tests were performed on tungsten-copper brazed specimens using an argon-plasma jet as an energy source to heat the specimens. Two types of specimens were prepared: Smooth and slit specimens at the braze region. The specimens were examined in detail through visual and non-destructive inspections after 100 cycles were carried out. Detectable change was not observed at the braze region of the specimens. From numerical analyses, a high shearing stress is expected to occur at the root of the slit, which is more than twice that for a smooth specimen. The results indicate that detailed techniques for detecting flaws lying especially in the edge region of the joining interface should be incorporated into the failure assessment of a duplex structure. (orig.)

[en] Ni22Cr10A11.0Y/ZrO₂-25CeO₂-2.5Y₂O₃ and Ni22Cr10A11.0Y/ZrO₂-8Y₂O₃ duplex(bond+top) thermal barrier coatings were prepared using the air plasma spray process. Properties such as phase transformation in the ceramic top coating, bond coat oxidation and thermal barrier effect were investigated to compare ZrO₂-CeO₂-Y₂O₃ with ZrO₂-Y₂O₃ under the 1300 .deg. C high temperature thermal cycles. In condition of as-sprayed, both coatings showed 7∼11% porosity fraction and typical lamellar structures formed by continuous wetting of liquid droplets. In the ZrO₂-CeO₂-Y₂O₃ coating, the phase ratio of tetragonal to cubic was 75:25, and ZrO₂-Y₂O₃ coating had 100% untransformable tetragonal phase. There was no monoclinic phase in both coatings. However, the phase ratio of coatings was changed after 1300 deg. C thermal cycles. In the ZrO₂-CeO₂-Y₂O₃ coating, the ratio of tetragonal to cubic was changed to 88:12 and monoclinic phase was not detected, but in the ZrO₂-Y₂O₃ coating 10∼19% monoclinic phase had formed. The life of coatings was found to be strongly dependent upon the temperature of the bond coat experienced during exposure to peak temperature of 1300 .deg. C. When the bond coat experienced a temperature higher than 1100 .deg. C the campaign life of both TBC decreased drastically and this was related to the oxidation behaviour. A1₂O₃ was formed preferentially along the bond and top coat interface and the other oxides such as NiO and Ni(Cr,A1)₂O₄ spinel, which were believed to decrease the coating life by oxide growth stress, were formed rapidly at the top coat side of interface at temperature higher than 1100 .deg. C. The ZrO₂-CeO₂-Y₂O₃ coating was superior to ZrO₂-Y₂O₃ coating because there was no phase transformation from tetragonal to monoclinic(which induces volume expansion) and the effect of oxide growth stress was relatively small by better thermal insulation.(i.e, bond coat experienced a temperature lower than 1100 .deg. C for a given TBC thickness)

[en] Short note. 3 refs

[en] Thermal barrier coatings (TBCs) serve as thermal insulator in the hot region of an aircraft engine. Besides this, it also protects the underlying metal surface from the harsh corrosive and eroding environment. The associated lower thermal conductivity of TBC ceramic materials plays an important role in the improvement of thermal efficiency of the engine in term of increased combustion temperature and power. The thermal conductivity of the conventional yttria stabilized zirconia (YSZ) and three advanced ceramic materials with perovskite (CaZrO/sub 3/) and pyrochlore structure (La/sub 0.75/Nd/sub 0.25/)2Zr2O/sub 7/ & Nd/sub 2/Ce/sub 2/O/sub 7/) have been determined using differential scanning calorimetry (DSC). With thin metallic disk on the ceramic samples of different heights were heated / scanned using a standard DSC apparatus. The results were evaluated for the thermal conductivity measurement using well established procedure /calculations. The analyzed results were compared with that of other techniques given by other researchers and found to be in good agreement with an error of 10-15%. The result of coefficient of thermal expansion (CTE) that was measured using a dilatometer up to 1273°K has also given. (author)

[en] Recent emphasis on research in geologic isolation of nuclear wastes and geoenergy resource development has created a renewed demand for engineering thermophysical property data for rocks and other geologic materials at elevated pressures and temperatures. In contrast to fabricated engineering materials, with properties which can be specified, rocks used in engineering design are complex, naturally occurring materials having properties which must be characterized, rather than specified, for engineering studies. Much difficulty in measuring, reporting, and using thermophysical properties of rocks results from (1) rock inhomogeneity and anisotropy on both microscopic and macroscopic scales; (2) inclusion of pore fluids, such as water; and (3) measurement of laboratory properties under conditions quite different from those of in situ material. Because measurements on in situ materials are scarce, many analyses must depend on extrapolated values of uncertain accuracy. A survey of thermophysical property data available for geologic thermal transport studies indicates that caution must be taken to effectively match data abstracted from the literature with project objectives

[en] In this work, glass fiber felt (GFF) was prepared via wet beating method to explore the correlation between the physical properties (air permeability, thermal conductivity and acoustic property) and microstructure. The consequence presents that increasing the layers of GFF could enlarge the average pore size, but almost have no effect on air permeability. It also finds that the thermal insulation property and acoustic property could be enhanced via the increase layers of GFF. More the layers leads to a superior sound insulation property. This is because that layered structure can avoid thermal bridge to reduce thermal conductivity. Besides, the comparatively big mismatching among characteristic acoustic impedances (CAIs) of layered structure result in multi-reflection, which will causing the increasing of acoustic property. (paper)

[en] A simple graphite limiter has been designed for high heat load in a tokamak device. The thermal contact conductance αsub(c) was measured as the function of contacting pressure p, because αsub(c) is an important parameter for the graphite limiter design. Both experiments on small samples and full scale limiter assembly provided consistent data of αsub(c) = -- 0.1 W/cm².⁰C at p = 1 kgf/cm² (-- 0.1 MPa). This value is considered to be sufficiently large from the viewpoint of the limiter thermal design. Heat load test was performed on the simple graphite limiter by using electron beam. Two kinds of materials employed in the test were POCO graphite and SIC-6 graphite which has thermal expansion coefficient similar to that of SiC. The test results showed that both graphite materials had enough thermal shock resistance to the heat load q = -- 500 W/cm², t = 3 -- 20 s, and SiC coating on SIC-6 graphite had better behavior against thermal shock, comparing with TiC coating on POCO graphite. (author)

[en] Yttria-Stabilized Zirconia (8YSZ) coatings were deposited on silicon (100) substrates via r.f. magnetron sputtering. Crystal structure, Infrared (IR) absorption bands and microstructure of deposited thin films were determined by X-ray diffraction (XRD), Fourier Transformed Infrared Spectroscopy (FTIR), AFM and SEM, respectively. The thermal diffusivity of YSZ coatings onto silicon substrate was determined by the phase lag method of the photoacoustic signal for rear and frontal illuminations using a two beam photoacoustic cell [1, 2]. XRD results show the presence of a tetragonal phase with (101) and (112) orientations. On the other hand, FTIR spectra exhibit the 2Eu and F 1u modes as two broad bands in the frequency at 453 cm-1 and 468 cm-1, and 740 cm-1, corresponding to the tetragonal and monoclinic phases of ZrO2, respectively. The AFM images showed that the coatings is composed of spheroid and elongated grains; besides, a SEM micrograph showing a cross-sectional view of the samples evidenced a dense structure in the entire coatings. The effective thermal diffusivity was measured in the system Si/YSZ and also on the Si (100) substrate, from which a simple model of two layer systems [3, 4] was used to estimate the thermal diffusivity (?) of the YSZ coatings. Additionally, by specific heat measurements at constant pressure (cp ) using the DSC technique, and mass density ( ) calculations using the Archimedes and Aleksandrov's methods for both in bulk and film 8YSZ samples, the thermal conductivity (k) was obtained. The results were: ?= (0.0021±0.0002) and (0.0023±0.0002) cm2/s, = (4.7725±0.005)x103 and (5.883±0.005)x103 kg/m3, cp(427±14) J/kgK, and k = (0.43±0.06)and (0.57±0.06) W/mK for in bulk and film 8YSZ samples, respectively

[en] Plasma facing materials and components in future thermonuclear confinement experiments will be subjected to severe thermal loads. Thermal fatigue damage of materials and components originates in the tokamak specific, pulsed plasma operation. In addition thermal shock damage will be initiated by plasma disruptions or vertical displacement events (VDE). Due to the 14 MeV neutrons generated in the fusion process the material properties will degrade during irradiation. (author)