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As new generation mediums for high-performance cooling and thermal management, appropriate candidates for the liquid metal should have a low enough melting point, small viscosity, high thermal conductivity, and large heat capacity. Meanwhile, it must not be poisonous and caustic. The most important prerequisite is that the working liquid metal needs to remain in liquid state when its cooling role is being performed under an appropriate temperature range for computer chips, which is generally below 100°C. It is commonly held that a metal appears as a rigid block. With this impression in mind, the fact is often ignored that those alloys with extremely low melting points, several degrees centigrade above zero, actually stay in the liquid state around room temperature. Among the various liquid metals, it can be found that liquid gallium or its alloys can serve as a perfect candidate for the heat transfer medium in a wide variety of devices and systems. Unfortunately, there have been limited efforts to apply such liquid metals to cool high-power electronic components, especially computer chips, until around 2002 [1].

An in-depth analysis of the thermal properties of liquid metals, such as gallium, strongly suggests that they are well suited for the cooling of computer chips owing to their low melting point. In fact, gallium can generally be kept in a liquid state at a temperature much lower than the room temperature due to its large sub-cooling point. It turns out to be an important merit for gallium-based alloys to be used as the cooling fluid. The low melting point and very low vapor pressure of such a liquid metal make it easy to handle, and its high thermal conductivity guarantees excellent cooling performance. Further, the low kinetic viscosity of liquid metal improves its capability for heat removal, especially at the liquid–solid interface and enhances its attractiveness as a new-generation coolant. The normal (dynamic) viscosity of gallium is about 1.5 times that of water, which means that it can be pumped through small channels with relative ease. The surface tension of liquid metals is much higher than that of water, which makes them immune to the presence of small cracks or channels in case of an imperfect seal, which would be a serious leakage for water as a cooling fluid. Besides, liquid metals are non-toxic and relatively cheap. The two principal advantages lie in their superior thermophysical properties of absorbing heat away from a hot chip and the ability to pump these electrically conductive liquids efficiently with silent, vibration-free, non-moving, magnetofluid-dynamic (MFD) pumps. All these compelling properties warrant their future applications in chip cooling technology.

This chapter is dedicated to illustrate the typical liquid metal medium and related properties regarding advanced cooling. Unlike most of the conventional cooling fluids [2], a liquid metal offers tremendous opportunities for the coming society.

Synthesis of aluminum nitride (AlN) whiskers by reduction-nitridation of alumina-calcia compounds and their chemical properties were investigated. Five kinds of the oxide compounds (CaA₁₂O₁₉, CaAl₄O₇, CaAl₂O₄, Ca₁₂Al₁₄O₃₃, Ca₃Al₂O₆) which were prepared by firing at 1300°C for 240 min in air, were fired at 1800 to 1900°C for 60 to 240 min in a nitrogen (N₂) atmosphere. Transparent AlN whiskers were deposited on the inner surface of carbon crucible in the specimens of CaA₁₂O₁₉, CaAl₄O₇ and CaAl₂O₄. However, no whisker was produced in the specimens of Ca₁₂Al₁₄O₃₃ and Ca₃Al₂O₆. Both diameter and length of the whiskers produced in this study increased with increasing CaO content in the oxide compounds. Since the system in this study includes no iron and/or other metals at the tip of the whiskers, the growth mechanism is thought to be vapor-solid (VS). Transparency of AlN whiskers was maintained after exposing in air for 6 months, and no weight gain was observed through oxidation in air. The whiskers had such a stability in air that extreme low oxidation rates were observed, obeying the parabolic law. The activation energies were 109 kJ/mol at 900-1000°C and 237 kJ/mol at 1000-1200°C, respectively.

In recent years, the study of microbial fuel cell raises social attention, because it both can degrade organic pollution and produce electricity. So far, the researchers have studied a variety of material about microbial fuel cell and investigated its feasibility of being substrate to transition of microbial fuel cell. The substrate of the microbial fuel cell will cause significant influence to the coulomb efficiency and various types of bottom species lead to different production performance. The increasing of the utilization rate of electricity production benefit from the rapid development of science and technology even the embedded exploration of microbial fuel cell by researcher, so as to alleviate the existing energy crisis, although the lower supply of its current and power. This review introduces the various reaction substrate and its biochemical characteristics, sources, production performance, the research status and application.