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Over the past few decades, the research field of nanomaterials (NMs) has developed rapidly because of the unique electrical, optical, magnetic, and catalytic properties of these materials. Among the various methods available today for NM synthesis, techniques for plasma generation in liquid are relatively new. Various types of plasma such as arc discharge and glow discharge can be applied to produce metal, alloy, oxide, inorganic, carbonaceous, and composite NMs. Many experimental setups have been reported, in which various parameters such as the liquid, electrode material, electrode configuration, and electric power source are varied. By examining the various electrode configurations and power sources available in the literature, this review classifies all available plasma in liquid setups into four main groups: (i) gas discharge between an electrode and the electrolyte surface, (ii) direct discharge between two electrodes, (iii) contact discharge between an electrode and the surface of surrounding electrolyte, and (iv) radio frequency and microwave plasma in liquid. After discussion of the techniques, NMs of metal, alloy, oxide, silicon, carbon, and composite produced by techniques for plasma generation in liquid are presented, where the source materials, reaction media, and electrode configurations are discussed in detail.

Latent heat storage using alloys as phase change materials (PCMs) is an attractive option for high-temperature thermal energy storage. Encapsulation of these PCMs is essential for their successful use. However, so far, technology for producing microencapsulated PCMs (MEPCMs) that can be used above 500°C has not been established. Therefore, in this study, we developed Al-Si alloy microsphere MEPCMs covered by α-Al2O3 shells. The MEPCM was prepared in two steps: (1) the formation of an AlOOH shell on the PCM particles using a boehmite treatment, and (2) heat-oxidation treatment in an O2 atmosphere to form a stable α-Al2O3 shell. The MEPCM presented a melting point of 573°C and latent heat of 247 J g−1. The cycling performance showed good durability. These results indicated the possibility of using MEPCM at high temperatures. The MEPCM developed in this study has great promise in future energy and chemical processes, such as exergy recuperation and process intensification.

Table 2. Thermophysical properties of proposed PCM candidates-sugar alcohol, molten salt, and metallicwith phase-changing point over 100°C.from steelworks 2) has more enthalpy at lower temperature but more exergy at a higher temperature over 100°C. Table 3 lists frequently selected keywords from the collected papers. Papers on LHS and PCM frequently used general keywords such as "phase-change material", "PCM", "thermal energy storage", and "latent heat". Apart from these, interestingly, "solar energy" was also frequently used; these papers dealt with PCMs that can store solar energy through melting for various utilities. Keywords such as "phase-change composites", "thermal conductivity", "shape-stabilized" should be noteworthy in that these are related to general problems encountered during the use of PCMs, that is, capsulation and low thermal conductivity. Recent Advancements in LHS Technology PCM CapsulesGenerally, because LHS mainly utilizes the phase change between solid and liquid, the encapsulation of the PCM is necessary to avoid the leakage of a liquid PCM. In addition, Regin et al. 70) noted the functions and requirements of PCM containment: (i) meeting the requirements of strength, flexibility, corrosion resistance, and thermal stability; (ii) acting as a barrier to protect the PCM from harmful interactions with the environment; (iii) providing a sufficient surface for heat transfer, and (iv) providing structural stability and easy handling. PCM capsules are classified into macroand microcapsules.Macrocapsules are the most conventional PCM capsules, and many papers have reported various shell materials such as metal and plastics, and various shapes such as spherical [71][72][73][74][75] and cylindrical. 72,[76][77][78] In contrast, micro-encapsulation of PCM has recently attracted considerable attention [79][80][81][82][83][84][85] because it reduces the reactivity of the PCMs with the outside environment, increases the heat transfer area of the PCMs, and enables the core material to withstand frequent changes in the volume of the storage material during phase change. Table 4 lists trends in manufacturing methods for PCM capsules. Many papers have reported the production of various microcapsules, and the manufacturing methods, core PCM materials, shell materials, thermophysical properties, and capsule sizes of the same have been studied. Micro-interfacial polymerization, 80) in-situ polycondensation, [81][82][83][84][85] and complex coacervation 79) are the most popular microen- ISIJ International, Vol. 50 (2010), No. 9 79,80) 1232© 2010 ISIJ proposed the encapsulation of spherical metal PCMs such as Cu and Pb with an electroplated Ni layer to recover industrial hightemperature waste heat such as combustion offgas. The PCM spherical capsule with Ni coverage provided hybrid functions of both heat storage and catalysis. Nickel worked well as a catalyst of the gas phase reaction CH 4 ϩH 2 Oϭ 3H 2 ϩCO at 1000°C.In summary, the encapsulation of low-temperature PCMs is a state-of-the-art technology; in p...