Thermophysical properties of NP2 brand nickel

The heat capacity and the thermal diffusivity of NP2 brand nickel were investigated in the temperature interval 296–1000…1375 K of the solid-state, including the region of the magnetic phase transformation. Measurements were carried out on samples from one initial ingot by laser flash technique and method of differential scanning calorimetry using LFA-427 and DSC 404 F1 setups, respectively. The thermal conductivity was calculated based on the measured thermophysical properties. The estimated errors of the obtained results were 2–4%, 3–5%, and 2–3% for thermal diffusivity, thermal conductivity, and heat capacity, respectively. For investigated thermophysical properties the fitting equations and the reference table have been received.

Effect of Substrate Holder Design on Stress and Uniformity of Large-Area Polycrystalline Diamond Films Grown by Microwave Plasma-Assisted CVD

In this work, the substrate holders of three principal geometries (flat, pocket, and pedestal) were designed based on E-field simulations. They were fabricated and then tested in microwave plasma-assisted chemical vapor deposition process with the purpose of the homogeneous growth of 100-μm-thick, low-stress polycrystalline diamond film over 2-inch Si substrates with a thickness of 0.35 mm. The effectiveness of each holder design was estimated by the criteria of the PCD film quality, its homogeneity, stress, and the curvature of the resulting “diamond-on-Si” plates. The structure and phase composition of the synthesized samples were studied with scanning electron microscopy and Raman spectroscopy, the curvature was measured using white light interferometry, and the thermal conductivity was measured using the laser flash technique. The proposed pedestal design of the substrate holder could reduce the stress of the thick PCD film down to 1.1–1.4 GPa, which resulted in an extremely low value of displacement for the resulting “diamond-on-Si” plate of Δh = 50 μm. The obtained results may be used for the improvement of already existing, and the design of the novel-type, MPCVD reactors aimed at the growth of large-area thick homogeneous PCD layers and plates for electronic applications.

Effect of radiative heat loss on thermal diffusivity evaluated using normalized logarithmic method in laser flash technique

The laser flash technique is a standard method to measure the thermal diffusivity of solid samples especially at high temperatures. To understand the reliability of thermal diffusivity evaluation at high temperature for solid samples with low-thermal-diffusivity values, we analyzed the effect of radiative heat loss using the logarithmic method. The results revealed that when the Biot number was 0.1, the deviation from the input thermal diffusivity value was approximately −1.6%. In addition, when an aluminum silicate (AS) sample was heated to 1,273 K, the maximum deviation was approximately −0.35%. In contrast, the difference between the input value and the thermal diffusivity evaluated by the halftime method when AS was heated to 1,273 K was approximately 2.38%. Thus, since the effect of radiative heat loss was found to be negligible, it is concluded that the normalized logarithmic method should be very useful for the thermal diffusivity analysis of low-thermal-diffusivity solid samples at high temperature.

Experimental study of the transport properties of Nd-Fe-B and Sm-Co magnets

The article adduces new reliable experimental data on the thermal conductivity and the thermal diffusivity of hard magnetic materials of brands N35M, N35H, N35SH, as well as YX18, YX24 and YXG22, YXG30 with main components represented by the crystalline phases of Nd2Fe14B, SmCo5 and Sm2Co17 type, respectively. The temperature range from 293 to 773…1273 K has been investigated by laser flash technique with an error of 3—4%. The reference tables of the thermal diffusivity and thermal conductivity coefficients have been developed. The character of the thermal diffusivity changes near the Curie point has been determined. The critical indices and the critical amplitudes have been defined.

THERMAL DIFFUSIVITY STUDIES OF ZnO-CuO AT HIGH TEMPERATURES

An n-type semiconducting oxide such as Zinc Oxide (ZnO) has been exploited for their well-known gas sensing properties. Previous studies on these applications have mainly focused on electrical properties. Only limited reports were available on thermophysical properties of ZnO-based ceramics gas sensor. Therefore in this work, we report on the thermal diffusivity of Zinc Oxide-Copper Oxide (ZnO-CuO) ceramic composites by solid-state method using a laser flash technique. Thermal diffusivity of samples was measured at temperatures between 27 °C to 400 °C. The role of CuO was observed to enhance the thermal diffusivity of ZnO system with respect to the temperatures. ZnO-CuO samples played a significant role in improvement of thermal diffusivity value at temperature of 200 °C and above. Subsequently, sample of higher thermal diffusivity will exhibit lower initialization time for gas sensor to activate. Hence, the enhanced thermal diffusivity suggested that ZnO-CuO composite samples hold a promising possibility in gas sensor application.