High Melting Point Phase Research Articles

06/01663 Screening of high melting point phase change materials (PCM) in solar thermal concentrating technology based on CLFR: Hoshi, A. et al. Solar Energy, 2005, 79, (3), 332–339

06/01663 Screening of high melting point phase change materials (PCM) in solar thermal concentrating technology based on CLFR: Hoshi, A. et al. Solar Energy, 2005, 79, (3), 332–339

Screening of high melting point phase change materials (PCM) in solar thermal concentrating technology based on CLFR

We have investigated the suitability of high melting point phase change materials for use in new, large scale solar thermal electricity plants. Candidate materials for latent heat thermal energy storage are identified and their operating parameters modeled and analysed. The mathematical characteristics of charging and discharging these storage materials are discussed. Several high melting point, high conductivity materials are shown to be suitable and advantageous for use with solar thermal electricity plants, such as Sydney University’s novel, low cost CLFR and MTSA collector systems, as well as existing parabolic trough and tower technologies.

Numerical and Experimental Investigations of Melting and Solidification Processes of High Melting Point PCM in a Cylindrical Enclosure

In the present work, a computational model is developed to investigate and predict the thermal performance of high melting point phase change material during its melting and solidification processes within a cylindrical enclosure. In this model the phases are assumed to be homogeneous and a source term, S, arises from melting or solidification process is considered as a function of the latent heat of fusion and the liquid phase fraction. The numerical model is verified with a test problem and an experiment is performed to assess the validity of the assumptions of it and an agreement between experimental and computational results is achieved. The findings show that utilizing of PCMs of high melting points is a promising technique especially in space applications.

Structure and composition of built-up layers on coated tools during turning of Ca-treated steel

Built-up layers formed on CVD coated cutting tools during turning of Ca-treated steel were investigated. The built-up layers were analysed using scanning electron microscopy and transmission electron microscopy (TEM) in combination with energy dispersive X-ray spectroscopy, electron diffraction, energy-filtered TEM and high resolution TEM. This is the first paper where the inclusion layer is studied and analysed using TEM. The structure and composition of the inclusion layer is reported in detail and compared with the inclusion population in the workpiece material. The part of the inclusion layer that was subjected to the highest temperature during cutting was crystalline, and is composed of round sulphide grains (Ca 0.85Mn 0.15S) and deformed elongated aluminate grains (CaO·6Al 2O 3). These are the high-melting point phases of the inclusions present in the steel and it appeared that only these compounds can contribute to the formation of the solid built-up layer.

In situ sputter deposition discharge diagnostics for tailoring ceramic film growth

Reactive sputter deposition is widely used for growing technologically important ceramic films, including high melting point phases near room temperature, metastable phases, and nanoscale layered structures with controlled interfaces. Film properties are governed by kinetic processes at each electrode and in the gas phase. A knowledge of the reacting species and reaction paths is essential for reproducible growth of desired ceramic phases and structures. Obtaining this knowledge is the first critical step in developing transferrable processes. In this article, we briefly describe reactive sputter deposition of oxides and nitrides from metal and ceramic targets, and identify important chemical features of the process. Production of activated gas species by plasma volume collisions between ground state reactive gas molecules and rare gas atoms in low-lying metastable energy states is discussed. We then review mass and optical spectrometric methods for real-time monitoring of nonelectronic species in the discharge, and using many examples, show how the information obtained from in situ diagnostics gives insight into the chemistry of ceramic film growth.

Inoculation mechanism of rare earth–Mg alloy in molten cast iron

The dissolution region of RE–Mg (RE=rare earth) alloy in the reaction chambers of in-mould inoculated castings was studied by scanning electron microscopy and on electron microprobe. The dissolution region of the inoculant was divided into 7 zones according to its microstructure. The RE–Mg alloy is composed of Mg2Si, a Mg2Si–Si eutectic, FeSi, RE–Mg–Si and other silicides. The dissolution of the alloy is a process in which the low melting point phases such as Mg2Si, a Mg2Si–Si eutectic and RE–Mg–Si dissolve first, and the high melting point phases such as FeSi and FeSi2 dissolve later. In addition, some intermediate products form during the dissolution process. This causes a concentration gradient of Mg and RE in the melt which results in a transition of the graphite morphology from normal spheroid to open nodule, vermicular and flake graphite. The dissolution of the FeSi phase in the melt forms local sites of high silicon concentration which promote the nucleation and growth of the graphite. © 1998 Chapman & Hall

Diffusion soldering

Diffusion soldering is a hybrid of diffusion bonding and soldering. The principle of the process is to run a minute volume of solder into a joint between components that are pressed together and to solidify the solder by conversion to high melting point phases through isothermal reaction with the substrates. Thereafter the joint will not remelt unless heated to the temperature at which the high melting point phases melt. Tin can be used to make diffusion soldered joints between components of pure gold.The objctive of the present study was to evaluate tin as a diffusion solder for joining items of 18 carat golds, representative of alloys widely used in the fabrication of jewellery. The permissible range of the process parameters have been identified and a process specification has been developed. Joints can be made by heating to 450°C, which is substantially lower than the temperature needed for brazing of jewellery using conventional carat filler alloys. The resulting joints are colour matched and have mechanical properties that are likely to be adequate for jewellery applications. Diffusion soldering with tin has also been applied successfully to join 22 carat jewellery and the new jewellery alloy of 990 gold.

Structural Study of the Two Phases of Tetrakis(methylseleno)tetrathiafulvalene (TSeC1–TTF)

Abstract The crystal structure of the low-melting point phase (L-phase) of a single component organic semiconductor, TSeC1–TTF, is determined and compared with that of the high-melting point phase (H-phase). The intracolumnar overlap mode and the calculated intermolecular overlap integrals are slightly larger in the L-phase, to which is ascribed the low resistivity of the L-phase. The L-phase, however, does not have two-dimensional networks of intercolumnar Se···Se contacts, which exist in the H-phase. This may be associated with the difference of the melting points.

Effect of interfacial energies on heterogeneous nucleation

From experimental evidence it has previously been shown that heterogeneous nucleation is non-reciprocal and therefore that the balance of interfacial energies is a controlling factor. If σNL > σNS + σSL the nucleus S can grow from the liquid L on the substrate N. When nucleation takes place the contact angle θ is small and there is epitaxy between the nucleant and the nucleus that reduces the σNS to very low values so that, as a first approximation, heterogeneous nucleation can be expected when σNL > σSL. Interfacial energies σSL are roughly proportional to the melting point, and high melting point phases usually nucleate lower melting phases. The contrary may happen if the low melting phase has a low symmetry crystal. Nucleation can take place on high index faces of this crystal because, although its average σNL is lower than the σSL of a higher melting point, high symmetry crystal, the σNL of its high index faces may be higher than the σSL.MST/845

Effect of interfacial energies on heterogeneous nucleation

Abstract From experimental evidence it has previously been shown that heterogeneous nucleation is non-reciprocal and therefore that the balance of interfacial energies is a controlling factor. If σNL > σNS + σSL the nucleus S can grow from the liquid L on the substrate N. When nucleation takes place the contact angle θ is small and there is epitaxy between the nucleant and the nucleus that reduces the σNS to very low values so that, as a first approximation, heterogeneous nucleation can be expected when σNL > σSL. Interfacial energies σSL are roughly proportional to the melting point, and high melting point phases usually nucleate lower melting phases. The contrary may happen if the low melting phase has a low symmetry crystal. Nucleation can take place on high index faces of this crystal because, although its average σNL is lower than the σSL of a higher melting point, high symmetry crystal, the σNL of its high index faces may be higher than the σSL.MST/845