Thermodynamic assessment of MCl–YCl3 (M=Na,K, Rb,Cs) systems

Thermodynamic properties and phase diagrams of the MCl–YCl₃ (M=Na, K, Rb, Cs) systems were reassessed by using the CALPHAD method with the latest phase diagram data. A two-sublattice ionic solution model (M⁺)_P(Cl⁻, ${\mathrm{YCL}}_6^{3-}$, YCl₃)_Q reflecting the ionic behavior of the components was adopted to describe the liquid phase in the systems. A new set of optimized model parameters was found, and the calculated phase diagrams and enthalpies of mixing have good agreement with experimental data. The calculated liquidus near to YCl₃ side agrees much better with experimental data compared with previous work. In consideration of high and low temperature modifications as well as stability of intermediate compounds, Gibbs energies of formation of these compounds evaluated in the present work are more reasonable.     

Experimental and theoretical analysis of the operation of a natural gas cogeneration system using a polymer exchange membrane fuel cell

This paper reports experimental and numerical results of an investigation of five identical cogeneration systems using PEM (Polymer Exchange Membrane) fuel cells and running on natural gas. The natural gas is reformed locally to produce hydrogen. The accuracy of numerical results is validated by comparison with experimental data and the system performances are analysed in terms of electrical, thermal and total efficiencies. It appears that the energetic performances are low, particularly at low current. Simple solutions for enhancing the system electrical performances by modifying control laws are proposed.     

Induction plasma synthesis of fullerenes and nanotubes using carbon black–nickel particles

The existence of fullerenes (as allotropes of carbon) was established in the mid-1980s and during the last 15–18 years, systematic efforts have been devoted to improve the methods of their synthesis, including plasma-based system methods. The work presented here is focused on the investigation of fullerenes synthesis, using a radio frequency plasma reactor. The main objectives were to explore the use of induction plasma technology for the synthesis in-continuo of carbon fullerenes and to predict their formation conditions through conduct of theoretical studies. Thus, a thermodynamic study was carried out to predict the equilibrium composition of fullerenes produced at several combinations of operating conditions. Additionally, a statistical factorial design experiment, employing four factors at two levels, was also developed, in order to study the influence of the system’s operating parameters on the eventual C₆₀ fullerene yield. The results obtained showed that the reactor pressure, the electrical power and the raw material feed rates all have an important effect on the synthesis of fullerenes. The highest C₆₀ concentration in the products was found to be about 7.7 wt.%. Various other carbon nanostructures, such as nanotubes and nano-onions, were also successfully produced.     

Harnessing the Melting Peculiarities of Ultra‐High Molecular Weight Polyethylene Fibers for the Processing of Compacted Fiber Composites

Summary: Compacted fiber composites offer unique properties due to their lack of an extraneous matrix. The conditions of processing ultra‐high molecular weight polyethylene (UHMWPE) fibers were simulated in a heated pressure cell. In situ X‐ray diffraction measurements were used to follow the relevant transitions and the changes in the degree of crystallinity during melting and crystallization. The results strongly support the suggestion that the hexagonal crystal phase, in which the chain conformation is extremely mobile on the segmental level, constitutes the physical basis of compaction technologies for processing UHMWPE fibers into a single‐polymer composite. This report suggests that using a pseudo‐phase diagram outlining the occurrence of different phases during slow heating and the degree of crystallinity can provide valuable insight into the technological parameters relevant for optimal processing conditions.

Degree of crystallinity as a function of pressure and temperature in a region relevant to compaction processes.     

Phase diagrams for oil/methanol/ether mixtures

One-phase transmethylations of vegetable oils with methanol to form methyl esters occur considerably faster than conventional two-phase reactions. Addition of simple ethers is an efficient method for producing a single phase. Ternary phase diagrams have been determined at 23°C for oil/methanol/ether mixtures; these are useful when applying the one-phase method across a wide range of conditions. Soybean, canola, palm, and coconut oils were used in combination with five ethers, namely, tetrahydrofuran (THF), 1,4-dioxane (DO), diethyl ether (DE), diisopropyl ether (DI), andtert-butyl methyl ether (TBM). All five ethers can produce miscibility for all methanol/oil compositions. The ether/methanol volumetric ratios required for miscibility at a methanol/soybean or canola oil volumetric ratio of 0.20 (5.4 molar ratio) at 23°C are: THF, 1.15; DO, 1.60; DE, 1.38 DI, 1.57; and TBM, 1.57. For THF, this results in one-phase mixtures that contain 65 vol% oil. Soybean and canola oil form identical diagrams. Palm oil requires slightly less ether at the lower methanol concentrations, but coconut oil requires considerably less across the whole concentration range. Acid-catalyzed reactions, when performed at the boiling point of the most volatile component, require less ether than predicted from the diagrams.     

The role of calcium ions and lignosulphonate plasticiser in the hydration of cement

Experiments involving equilibrium dialysis, conductivity, X-ray diffraction analysis (XRD), differential thermal analysis (DTA) and isothermal titration calorimetry (ITC) have been carried out to investigate the role of calcium ions and polymeric plasticisers in cement/admixture hydration. Results from a study of lignosulphonic acid, sodium salt, acetate as a plasticiser shows that a plasticiser has dual role; one mainly as a kinetic inhibitor (poison) in cement hydration mechanism and the other as a dispersant. Evidence of a weak Ca²⁺ binding to lignosulphonate sulphonic moieties was found at low ionic strengths of 0.1 M using ITC. No evidence of formal Ca²⁺ binding to lignosulphonate sulphonic acid moieties was found using equilibrium dialysis at higher ionic strength of 1 M (ionic strengths of 0.4 M are typically found in Portland cement pore solution), as is often suggested in cement/admixture literature.     

Improving the performance of an active carbon-nitrogen adsorption cryocooler by thermal regeneration

Thermodynamic analysis was done on single and two stage active carbon nitrogen adsorption cryocoolers to study the effect of thermal regeneration on the performance. Heat regeneration within compressors operating in the same temperature range is considered. From the analysis done on 80 K cooler and 117.5 K cooler, it is found that dramatic efficiency improvement is possible with the use of compressor heat regeneration techniques.     

The Calcia–Zirconia Phase Diagram Revisited: Stability of the Ordered Phases φ1 and φ2

Single crystals of CaO-stabilized ZrO₂ containing between 15.3 and 18.9 mol% CaO were heat-treated for 5000 h at 1200°C to study the stability of the ordered defect-fluorite phase, CaZr₄O₉ (φ₁). Subsequent TEM analysis of the equiaxed φ₁ domains in samples richer than approximately 18 mol% in CaO showed a random distribution of φ₁ variants, with no preferred interfacial habit planes. A critical review of the literature, combined with the new data, supports the Stubican-Hellmann-Hannon version of the phase diagram in the region 15 to 26 mol% CaO and 1000° to 1400°C and strongly suggests that φ₁ is a stable phase in the ZrO₂-CaO systems.     

Effect of hydrocarbons precursors on the formation of carbon nanotubes in chemical vapor deposition

High-temperature decomposition of hydrocarbons may lead to the formation of carbon deposits. However in our present studies, we found that the morphology of carbon deposits over MgO supported Fe catalyst during chemical vapor deposition (CVD) process was closely related to the thermodynamic properties and chemical structures of hydrocarbon precursors. Six kinds of hydrocarbons (methane, hexane, cyclohexane, benzene, naphthalene and anthracene) were used as carbon precursors in this study. Methane which has a pretty simple composition and is more chemically stable was favorable for the formation of high-purity single walled carbon nanotubes (SWNTs). For high-molecular weight hydrocarbons, it was found that the chemical structures rather than thermodynamic properties of carbon precursors would play an important role in nanotube formation. Specifically, the CVD processes of aromatic molecules such as benzene, naphthalene and anthracene inclined to the growth of SWNTs. While the cases of aliphatic and cyclic hydrocarbon molecules seemed a little more complicated. Based on different pyrolytic behaviors of carbon precursors and formation mechanism of SWNTs and multi-walled carbon nanotubes (MWNTs), a possible explanation of the difference in CVD products was also proposed.     

Relationship between Transformation Temperature and Time-Temperature-Transformation Curves of Tetragonal-to-Monoclinic Martensitic Transformation in Zirconia-Yttria System

The tetragonal → monoclinic ( t → m ) martensitic phase transformation in ZrO₂–0.5–4 mol% Y₂O₃ proceeds during isothermal aging at various temperatures from 350 to 800 K; i.e., the transformation increases sigmoidally with aging time. The time-temperature-transformation ( T - T - T ) curves show a typical C shape, with very high rate for lower Y₂O₃-content specimens, and the rate decreases with higher Y₂O₃ content. The transformation temperature ( M _s) of the t → m transformation obtained from dilatation curves during the cooling stage coincides well with C curves above the nose temperature. The t → m transformation should occur isothermally, as suggested by a nucleation and growth mode.