Investigation of Thermophysical Properties of Zr-Based Metallic Glass-Polymer Composite

Composites based on Zr65Cu17.5Ni10Al7.5 metallic glass (MG) and polytetrafluoroethylene (PTFE) were prepared by ball milling. Different composites (30/70, 50/50 and 70/30) were produced. Samples for dynamic mechanical analysis and laser flash analysis were fabricated in the supercooled region of the metallic glass and viscous region of the polymer. Spark plasma sintering (SPS) was performed at the supercooled region for the metallic glass powder. Characteristics such as thermal, mechanical, and structural properties were studied. A formation of the Zr2Cu and Zr2Ni intermetallic was found in the metallic glass after SPS. A formation of the nanocrystalline Zr2Cu was found in composite samples. Dynamical mechanical analysis (DMA) was used to study the mechanical behavior of the material. It was concluded that the 70/30-MG/PTFE composite sample had better thermal conductivity than the other composite samples. The thermal conductivity of the metallic glass was the highest among the samples and it increased with the MG content in composites.

Numerical and Experimental Evaluation of Thermal Conductivity: An Application to Al-Sn Alloys

Evaluation of thermal conductivity of composite materials is extremely important to control material performance and stability in thermal applications as well as to study transport phenomena. In this paper, numerical simulation of effective thermal conductivity of Al-Sn miscibility gap alloys is validated with experimental results. Lattice Monte-Carlo (LMC) method is applied to two-phase and three-phase materials, allowing to estimate effective thermal conductivity from micrographs and individual phase properties. Numerical results are compared with literature data for cast Al-Sn alloys for the two-phase model and with a specifically produced powder metallurgy Al-10vol%Sn, tested using laser flash analysis, for a three-phase simulation. A good agreement between numerical and experimental data was observed. Moreover, LMC simulations confirmed the effect of phase morphology as well as actual phase composition on thermal conductivity of composite materials.

Effects of Anodizing Conditions on Thermal Properties of Al 20XX Alloys for Aircraft

Anodizing was applied to improve the heat dissipation performance of aluminum (Al) alloys, by forming an oxide layer, such that they could be employed in aerospace applications. The methods employed were hard sulfuric acid (high hardness), soft sulfuric acid (low hardness), boric-sulfuric mixed acid, tin-sulfuric mixed acid, and chromic acid solutions. Each process was completed under optimized conditions. The surface morphology was observed using field emission scanning electron microscopy (FE-SEM) and a digital camera. For the determination of thermal performance, Fourier transform infrared spectroscopy (FT-IR) was used to measure the emissivity at 50 °C, and laser flash analysis (LFA) was utilized to analyze the thermal diffusivity at room temperature to 300 °C. The radiative property of metals is often ignored because of their low emissivity, however, in this research, the emissivity of the metal oxides was found to be higher than that of bare metal series. This study improved the heat dissipation properties by oxidization of Al via the anodizing process.

Enhanced Thermal Conductivity of Silicone Composites Filled with Few-Layered Hexagonal Boron Nitride

In this study, we demonstrate the use of silicone/few-layered hexagonal boron nitride (FL-hBN) composites for heat dissipation applications. FL-hBN is synthesized via a green, facile, low-cost and scalable liquid exfoliation method using a jet cavitation process. The crystal structures, surface morphologies and specific surface areas of pristine h-BN and FL-hBN were characterized by XRD, SEM, TEM and AFM (atomic force microscopy). The results confirmed that FL-hBN with a thickness of ~4 nm was successfully obtained from the exfoliation process. In addition, we introduced both pristine h-BN and FL-hBN into silicone with different ratios to study their thermal properties. The results of the laser flash analysis indicate that the silicon/FL-hBN composite exhibited a higher thermal conductivity than that of the silicone/h-BN composite. With the optimal loading content of 30 wt.% FL-hBN content, the thermal conductivity of the composite could be enhanced to 230%, which is higher than that of silicone/h-BN (189%). These results indicate that jet cavitation is an effective and swift way to obtain few-layered hexagonal boron nitride that could effectively enhance the thermal conductivity of silicone composites.

High-Temperature Thermophysical Property Measurement of Proposed Gen3 CSP Containment Materials

The US Department of Energy (DOE) has sponsored an initiative to improve the thermal efficiency of Concentrating Solar Power (CSP) systems. To approach parity with conventional fossil fuel-based electricity generation, the operating temperature of the CSP power cycle must exceed 700°C with integrated thermal energy storage. The materials used to house this high-temperature heat transfer media must be thermally stable and corrosion resistant. However, the temperature-dependent thermophysical properties of commonly used containment materials (nickel alloys and alumina-based firebricks) are either not well known or poorly understood. In this report, the high-temperature thermal properties of thirteen (13) candidate containment materials proposed by the CSP community are tested using laser flash analysis and differential scanning calorimetry.

The Effect of a Secondary Process on the Analysis of Isothermal Crystallisation Kinetics by Differential Scanning Calorimetry

This paper demonstrates the application of a modified Avrami equation in the analysis of crystallisation curves obtained using differential scanning calorimetry (DSC). The model incorporates a square root of time dependence of the secondary process into the conventional Avrami equation and, although previously validated using laser flash analysis and infrared spectroscopy, is not currently transferable to DSC. Application of the model to calorimetric data required long-duration isotherms and a series of data treatments. Once implemented, the square root of time dependence of the secondary process was once again observed. After separation of the secondary process from the primary, a mechanistic n value of 3 was obtained for the primary process. Kinetic parameters obtained from the analysis were used in the model to regenerate the fractional crystallinity curves. Comparison of the model with experimental data generated R2 values in excess of 0.995. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was used as model polymer due to the prominent secondary crystallisation behaviour that this polymer is known to display.