A phenomenological theory of polycomponent interactions in non-ideal mixtures. Application to NH3/H2O and other working pairsInteractions entre les composants de mélanges non-idéaux : théorie et application au fluide actif NH3 / H2O et à d'autres fluides actifs

The paper proposes an original linear phenomenological theory (Ph T) of evolution physical mono-, bi- and particular polycomponent gas–liquid interactions with non-ideal mixture. The expressions of the phenomenological factors (entropy source, force, coefficient and coupled heat and mass transfer currents) are deduced. The theory is particularized to the NH₃/H₂O and other gas–liquid systems used in the thermal absorption technology. The work's conclusions are listed next. The paper raises the problem of ammonia bubble absorption which is difficult to answer with current theory of interface mass transfer and absorption as a surface phenomenon. The heat and mass transfer at the gas–liquid interface is governed by the thermodynamic force, which applies also to solid–liquid, solid–gas, or liquid–liquid, gas–gas type interactions and continuous or discontinuous media. The paper mentions a postulate referring to the force behavior approaching an ideal point, previously formulated by the author. According to its consequence, the mass and heat currents suffer an ideal point approaching (i.p.a.) effect, not mentioned so far in the specialized literature, consisting in a continuous increase of their absolute value by several percent (for a pure component), to several hundred times (for a binary system) when the interacting system approaches an ideal state, as compared to the values of states which are far from the same ideal point. In this way, “far from equilibrium” becomes synonymous to “low interaction”. The classic assessment of the interface mass transfer by analogy with heat transfer lacks basic physics. The (Ph T) satisfactorily explains the problem of ammonia bubble absorption. Absorption is a mass phenomenon, not a surface one. An intensive way of improving absorption is emphasized, which seeks to promote the i.p.a. effect appearance rather than the extensive way currently used, based on increasing gas–liquid interaction area. To this extent, the bubble absorber is hereby proposed for efficient absorption. The i.p.a. effect existence offers an additional chance for a satisfactory explanation of the Marangoni effect.     

Optimization of annealing temperature for YBa2Cu3O7 thin films post-annealed at a low oxygen partial pressure

Post-annealing of YBa₂Cu₃O₇ (YBCO) thin films is usually performed at 850–900°C in atmospheric-pressure oxygen. In this study, coevaporated YBCO films on LaAlO₃ were post-annealed in an oxygen partial pressure of 29 Pa at temperatures in the range 700–825°C. Zero resistance transition temperatures were 89–90 K. Both d.c. (room-temperature resistance and critical-current density) and a.c. parameters (extracted from eddy-current response measurements at 25 MHz) were monitored. The optimum temperature is close to 750°C, which is on the YBCO thermodynamic stability line at this low oxygen partial pressure.     

Corrosion resistance of AlN–SiC–TiB2 composite in air

The oxidation kinetics of AlN–SiC–TiB₂ composite in air has been investigated in terms of a theoretical analysis associated with the experiment data. The effects of temperature and temperature heating rate on the oxidation reaction have been discussed by using the “characteristic oxidation time”. The results show that the calculated results by our model can give a good agreement with the experimental data. From this study it is shown that, the “characteristic oxidation time” is a very useful parameter for comparing the property of oxidation resistance for different composites.     

Wettability and reactivity between B4C and molten Zr55Cu30Al10Ni5 metallic glass alloy

The isothermal wetting and spreading behaviors of molten Zr₅₅Cu₃₀Al₁₀Ni₅ metallic glass alloy on B₄C substrates were studied using a modified sessile drop method at 1133–1253 K in a high vacuum. A distinct reaction layer consisting of ZrB₂ and ZrC_x was produced at the interface and displayed good wettability with the molten alloy. The entire spreading kinetics could be characterized by four representative stages: (i) an initial rapid spreading presumably driven by adsorption of the active Zr atoms at the solid–liquid interface, (ii) a quasi-linear and (iii) a linear spreading stage controlled by the chemical reaction between Zr and B₄C in both cases, and (iv) an approach-to-equilibrium stage with precipitation of crystals in the liquid. An increase in temperature promotes the wetting and reaction. In view of the reasonable wettability and reactivity, there is a potential for preparing Zr-base bulk metallic glass matrix composites reinforced by in situ ZrC–ZrB₂ hybrid ceramic particulates using B₄C as a reaction agent by way of an infiltration synthesis technique.     

Wetting induced by near-surface Ti-enrichment in the CaF2/In–Ti and CaF2/Cu–Ti systems

This paper is concerned with the wetting of CaF₂ by liquid Cu and In and with the effect of Ti additions to the melt. According to thermodynamic analysis and to the experimental observations, the significantly decreased contact angle following the addition of Ti to the molten metals is not due to the formation of interfacial fluoride phases, in contrast to previously reported results. Ab initio density functional calculations indicate that preferential Ti adsorption takes place at the near CaF₂ surface. It is suggested that the presence of a Ti-enriched liquid, adjacent to the substrate, gives rise, by means of heterogeneous nucleation, to the formation of a thin intermetallic compound layer that stands behind the experimentally observed enhanced wetting. The suggested wetting mechanism is supported by the notable correlation that has been observed between the temperature dependence of the contact angle and the temperature domains, associated with the presence of intermetallic compounds in both Me–Ti (Me = Cu, In) binary systems.     

Interface interaction in the B4C/(Fe–B–C) system

The wetting behavior in the B₄C/(Fe–C–B) system was investigated in order to clarify the role of Fe additions on the sinterability of B₄C. Iron and its alloys with C and B react with the boron carbide substrate and form a reaction zone consisting of a fine mixture of FeB and graphite. The apparent contact angles are relatively low for the alloys with a moderate concentration of the boron and carbon and allow liquid phase sintering to occur in the B₄C–Fe mixtures. A dilatometric study of the sintering kinetics confirms that liquid phase sintering actually takes place and leads to improved mass transfer. A thermodynamic analysis of the ternary Fe–B–C system allows accounting for the experimental observations.     

Current progress in ternary LREBa2Cu3Oy materials and their application

The J_c and H_irr values at 77 K of ternary light-rare-earth compounds, LREBa₂Cu₃O_y “LRE-123”, are usually high enough to serve in various applications. Several sources of vortex pinning can be in these composites tailored to fit the needs of the particular application. The list comprises LRE/Ba solid solution, oxygen vacancies, large particles of secondary phases, twin planes, nanoscale lamellas, etc. By means of the latter defects one can achieve a very high irreversibility field. Refinement of secondary phase particles and the optimal choice of their amount enhance the electromagnetic performance in a broad temperature range, up vicinity of T_c, allowing levitation at liquid oxygen, 90.2 K. An optimum content of MoO₃ doubles the self-field super-current at 77 K, H||c-axis. Altogether, the pinning tailoring in ternary LRE-123 materials provides a flexible and reliable way to fit the electromagnetic performance with the needs of sophisticated high-temperature and high-magnetic-field applications.     

Spreading of liquid lead droplets on metallic iron covered by silicon oxide particles or films

As well known, the spreading of a liquid metal droplet on a solid metal is very sensitive to the presence of chemical heterogeneities on the solid metal. In this study, wetting experiments with liquid lead on heterogeneous surfaces composed of iron and silicon oxide particles or films were performed using the dispensed drop technique. High purity iron and binary iron–silicon substrates with different silicon contents were studied. Before the wetting experiments, the substrates are annealed at 850 °C in a N₂–H₂ atmosphere in order to reduce iron oxides and to form silicon oxide particles or films on the surface. The liquid lead droplet is then released onto the metallic substrate partly or wholly covered by the oxides. The spreading of the liquid metal droplet strongly depends on the surface area fraction covered by the oxides.     

Interface phenomena in the Y2O3/(Al–Cu) system

Wetting behavior and the interface reaction in the Y₂O₃/(Cu–Al) system were investigated at 1423 K. A contact angle of about 130° was measured in the Y₂O₃/Cu system. Aluminum addition to copper improves wetting and the transition from non-wetting to wetting (θ ≤ 90°) was observed for the alloy with 50 at.% Al. The microstructure examination of the interface indicates that Al reacts with yttria, yttrium dissolves in the melt and a crater of AlYO₃ is formed at the substrate. The interface interaction in the Y₂O₃/(Cu–Al) system is in a good agreement with the results of a thermodynamic analysis in the Y–Al–Cu–O system. The crater depth and the macroscopic final contact angles are correlated with the Y and Al activities in the melt.     

Investigations of Bi substitution in NdBa2Cu3Oy

Attempts to substitute Bi for Nd in orthorhombic NdBa₂Cu₃O _y , prepared in air or oxygen at about 950°C led instead to formation of Ba₂NdBiO₆, a new cubic compound witha=0.8703 nm. The possibility was then explored of preparing superconducting (Nd_1–x Bi _x )Ba₂Cu₃O _y , by first forming the tetragonal phase at 880–950°C in nitrogen or argon followed by reheating in oxygen or air at 250–500°C in order to insert the additional oxygen required to yield the orthorhombic form while avoiding oxidation of Bi³⁺ to Bi⁵⁺. X-ray diffraction studies, electrical conductivity measurements, and thermogravimetric analysis of products indicate that Bi does not enter the NdBa₂Cu₃O _y , lattice in either the tetragonal or the orthorhombic phase. Ba₂NdBiO₆ clearly forms on reheating in oxygen or air even at low temperatures, and evidence is presented that a poorly crystallized oxygen-deficient form of this compound is already present prior to the reheating.     

Interfaces Between Two or Three Coexisting Fluid Phases in the System Methane–Perfluoromethane: Calculations with the Born–Green–Yvon Equation

Wetting is studied for the binary mixture methane–perfluoromethane (CH₄–CF₄) with the Born–Green–Yvon (BGY) equation in the attractive mean field approximation (AMFA). The general phase behavior is consistent with the AMFA equation of state. Close to a three-phase equilibrium L₁L₂ V, perfect wetting of the interface L₁ V by the second liquid phase L₂ occurs. Liquid–vapor and liquid–liquid interfaces in the vincinity of the three-phase equilibrium are calculated with the BGY equation, and the surface tension is estimated from the density profiles. The results are compared to previous investigations of wetting in fluid systems, especially the theory of Cahn.     

Wetting behavior of liquid Fe–C–Ti alloys on sapphire

Wetting behavior in the (Fe–C–Ti)/sapphire system was studied at 1823 K. The wetting angle between sapphire and Fe–C alloys is higher than 90° (93° and 105° for the alloys with 1.4 and 3.6 at.% C, respectively). The presence of Ti improves the wetting of the iron–carbon alloys, especially for the alloys with carbon content of 3.6 at.%. The addition of 5 at.% Ti to Fe–3.6 at.% C provides a contact angle of about 30°, while the same addition to Fe–1.4 at.% C decreases the wetting angle to 70° only. It was established that the wetting in the systems is controlled by the formation of a titanium oxicarbide layer at the interface, which composition and thickness depend on C and Ti contents in the melt. The experimental observations are well accounted for by a thermodynamic analysis of the Fe–Ti–Al–O–C system.     

Nature of intrinsic and impure luminescence of MAlP2O7 crystals

The results of the photoluminescence (PL) investigation of pure and chromium-doped MAlP₂O₇ (M = Na, K, Cs) compounds are presented. The spectra of the intrinsic luminescence of MAlP₂O₇ crystals consist of a separated UV band at a peak position near 330 nm and a complex wide band which covers the region of visible light up to 750 nm at excitation by VUV synchrotron radiation. The “red” band in 600–1000 nm diapason appears in the PL spectra of crystals doped with chromium ions. The effect of the temperature on the structure, the peak positions and intensities of the luminescence bands was studied. An assumption about the nature of the intrinsic PL was made. The “red” luminescence was considered as a result of the ⁴Т₂ → ⁴А₂ radiation transitions in the impurity Cr³⁺ ions located in the intermediate crystal field.     

Surface activated bonding of LCP/Cu for electronic packaging

A lamination technique for liquid crystal polymer (LCP)/Cu was developed for high speed and high performance printed circuit boards (PCB). This approach was accomplished by using a modified surface activated bonding (SAB) process to achieve enhanced adhesion and a smooth interface. Systematic investigation of peel strength of four categories of samples, namely “as bonded”, “annealed”, “Cu-deposited”, and “Cu-deposited and annealed” showed highest peel strength in the “Cu-deposited and annealed” sample. Significant improvements in adhesion were observed in the samples cleaned with argon-radio frequency (Ar-rf) plasma (“as bonded” samples) followed by Cu deposition on LCP, which were heated after bonding in low vacuum pressure at 240∘C (about 70–75 times higher than that of “as bonded”). XPS analyses on peeled surfaces of the “Cu-deposited and annealed” sample reveal bulk fracture in the LCP. Threefold lower loss in conduction of SAB processed laminate than that of conventional heat laminate was most likely due to smooth interface of the SAB processed laminate (surface roughness was ninefold lower than that of conventional heat laminate). A plausible adhesion mechanism of Cu/LCP might be due to bonding of Cu adhesion sites to plasma induced dangling sites of LCP surface, and thermal reconstruction of Cu deposited layers.     

Simulation of ternary ammonia–water–salt absorption refrigeration cyclesSimulation des cycles frigorifiques à absorption à ammoniac / eau / sel

This paper proposes a new working fluid for refrigeration cycles utilizing low temperature heat sources. The proposed working fluid consists of the ammonia–water working fluid mixture and a salt. The salt is used to aid the removal of ammonia from the liquid solution. This effect is a manifestation of the well known “salting-out” effect. While the addition of salt improves the generator performance, it also has a detrimental effect on the absorber. The overall effects on the performance of three absorption cycles using the NH₃–H₂O–NaOH working fluid have been investigated using computer simulations. The results indicated that salting out can lower the generator operating temperature while simultaneously improving the cycle performance. Furthermore, limiting the salt to the generator suggests potential for further improvement in cycle performance.     

In situ observation of Ag–Cu–Ti liquid alloy/solid oxide interfaces

In situ investigation methods are a very interesting means for understanding high-temperature interface processes. A method of direct observation of the interactions between transparent materials (Al₂O₃, SiO₂, CaF₂) and metal melts was elaborated. For the Ag–36.65 at.%Cu–8.15 at.%Ti/sapphire system, the formation of a dark compound at the interface was observed to occur at high temperature. This result does not confirm the conclusion of a neutron spectroscopy study which indicated that titanium oxides form at the interface only during solidification of the alloy. Interactions of the same alloy with SiO₂ and CaF₂ were also considered.     

Elaboration, microstructure and reactivity of Cr3C2 powders of different morphology

Cr₃C₂ powders have been prepared by heat-treatment of metastable chromium oxides of controlled morphology in H₂---CH₄ atmosphere. Starting with these highly reactive oxides allows formation of Cr₃C₂ at 700 °C. The reaction is pseudomorphic and different grain shapes (needles, rods, spheres and polyhedra) have been obtained. The size distribution is narrow and the grain size is generally of the order of a few tens of micrometers, but the “spheres” are in fact made up of aggregates of small platelets about 1.5 μm wide and 0.7 μm thick. The oxidation in air of the carbides was studied by thermal analyses (TGA, DTG and DSC) and was found to proceed in four steps in the 250–700 °C range. The differences observed between the carbides are related to their morphology and texture.     

Microstructural characterization of α2 + B2 titanium aluminide intermetallic (Super-α2) using transmission electron microscopy

Dislocation structures in as-received and plastically deformed commercial α₂ + B2 and homogeneous ordered B2 intermetallic titanium aluminide alloys (“super-α₂”) were characterized with transmission electron microscopy. Thin foils prepared by twin-jet electropolishing and ion beam thinning were found to yield different deformation structures. Electropolished foils were found to contain lath-like bands of dislocation loops with Burgers' vectors (b) in the B2 phase that were actually thinning artifacts. Dislocations in lightly deformed ion-beam-thinned foils appeared to be predominantly screw dislocations with