Recycling Al-Si Alloy by Semisolid Material Dragged during Continuous-Casting Strip Processing

Recycled Al–Si (9.2%) alloy contaminated with Fe (0.3%), Pb (3.1%) and Sn (11.4 %) was cast and poured at 650 oC, approximately 50 oC above the liquidus line. A cooling slope was used to obtain a semisolid material that feeds a ceramic nozzle designed to function as a good contact area for solidification and improve the quality of strip casting. The internally cooled material rolls in soluble oil (1 oil / 9 water) at a rate of 0.2 l/s and works as a heat exchanger which drags the metallic slurry puddle generated at the roll surface at a speed of 0.12 m/s. This forms a metallic strip with a thickness of 2 mm and a width varying from approximately 45 mm to 60 mm. The cooling system of the rolls, combined with four springs placed at the housing screw, prevented adhering of the metallic strip during production at a pressure of approximately 450 N. Cracks were observed on the strip surfaces; however, these defects did not interrupt the continuous flow of the solidified strip during manufacturing. The strip’s poor surface quality could be related to the Pb and Sn contamination as well as cold cracks due to the low pouring temperature. Al-Si eutectics positioned at a grain boundary of α-Al globular structures, as well as the presence of a Sn phase, resulted in a metallic strip with a yield stress, maximum stress and elongation of 94.5 MPa, 100.2 MPa and 1.6%, respectively.

Investigation of the Quasi-Binary Phase Diagram FLiNaK-NdF3

The NdF3 solubility in molten eutectic FLiNaK, which is a conceivable medium for a molten salt reactor (MSR), was determined by the quasi-binary phase diagram FLiNaK-NdF3. The eutectic mixture FLiNaK was prepared by direct melting of components LiF, NaF and KF·HF. The acidic anhydrous salt (KF·HF) was used instead of the hygroscopic KF. The NdF3 was sintered by hydrofluorination of Nd2O3. The oxygen impurity in the prepared eutectic FLiNaK, determined by an oxygen analyzer LECO OH836, was 0.036 wt.%, whereas the NdF3 contained 0.04 wt.% of oxygen. A part of the FLiNaK-NdF3 quasi-binary phase diagram was obtained using two thermal analysis techniques: differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The FLiNaK-NdF3 phase diagram in the region of 0–30 mol.% NdF3 contains one eutectic at 2 mol.% NdF3 and 450 °C and two peritectic points: 8 mol.% NdF3 at 500 °C and 22 mol.% NdF3 at 575 °C. The region of the FLiNaK-NdF3 phase diagram below the liquidus line is rather complicated due to the complex structure of the multicomponent system in its molten state, as in its solid state. The NdF3 solubility in FLiNaK is about 5 mol.% at 490 °C and 29 mol.% at 700 °C; this means that the process of the MA transmutation in the MSR can be carried out in molten FLiNaK with a content of actinides as high as 15–20 mol.% in the temperature range of 550–650 °C.

MESOPHASE AND GLASS FORMATION IN BINARY SYSTEMS CEASIUM AND BARIUM ALKANOATESMESOPHASE AND GLASS FORMATION IN BINARY SYSTEMS CEASIUM AND BARIUM ALKANOATES

Phase equilibria in binary systems of individually non-mesomorphic components: propionates, isobutyrates, butyrates and valerates of cesium and barium at temperatures from 20 to 400 °C have been investigated by the me­thods of differential thermal analysis and polarization polythermal microscopy. In all systems, the formation of intermediate li­quid-crystalline solutions of smectic modification (type A) was established. The tempe­rature-concentration regions of the formation of ionic liquid crystals and glasses are determined. The studies carried out show that in binary systems of cesium and barium alkanoates interme­diate liquid-crystal solutions are generated due to the latent mesomorphism of the correspon­ding cesium alkanoate and due to the eutectic decrease in liquidus temperatures in the binary systems. The thermal stability of the induced mesophase in the case of systems of the consi­dered type is influenced by the following factors: the degree of ordering of the melt, which correlates with the length of the alkyl chain of the alkanoate anion, and a decrease in the temperatures of the liquidus line relative to the latent clearing temperature. The possible influence of compounds melting congruently or incongruently, formed in binary systems, should also be taken into account. Experimental data indicate the largest temperature-concentration range of the mesophase in the butyrate system, where there are the most favorable conditions for the implementation of intermediate li­quid crystal solutions. Such conditions are the lar­gest decrease in liquidus temperatures in a series of systems relative to the latent clearing point, as well as an additional increase in thermal stability due to the formation of a congruently melting compound of anisometric structure. In the case of the valerate system, a certain increase in anisotropy in comparison with the butyrate system is leveled by high liquidus temperatures; here is the narrowest region of existence of the intermediate mesophase due to its thermal destabilization.

Thermodynamic Assessment of Phase Equilibria in the SrO-Al2O3 System

Thermodynamic modeling of phase equilibria with the subsequent construction of the phase diagram of the SrO–Al2O3 system has been carried out. To calculate the activities of the oxide melt in the course of this work, we used the approximation of the theory of subregular ionic solutions, with the most optimal values of the energy parameters Q1112 = –104 349: Q1122 = –217 689; Q1222 = –104 436 J/mole. The results obtained for the liquidus line in this work are in good agreement with the literature experimental data. In the course of the calculation, the values of the equilibrium constants for the formation of strontium aluminates from the components of the oxide melt were estimated.

Partial-cluster model of viscosity of copper-aluminum melt

The adequacy of the developed partial-cluster viscosity model with respect to melts of metal alloys was verified using the well-studied copper-aluminum system, for which the state diagram and viscosity isotherms are known in a wide range of compositions. Based on the literature on the thermodynamics of mixing copper and aluminum melts, it was found that this shift is accompanied by heat generation due to the formation of intermetallic compounds in the melt. The destruction of these compounds requires appropriate heat consumption, therefore, it should be taken into account in the partial-cluster viscosity model as an additional thermal barrier to randomization. On this basis, a refined and more generalized form of the partial-cluster model with the expression of the randomization energy of the melt in the form of the algebraic sum of the randomization heat along the liquidus line and the heat of destruction of any intermetallic formations is proposed ΔHch = RTliq – ΔHmix. Application of the generalized partial-cluster model to copper-aluminum melts ensured the repetition of the extreme form of empirical isotherms, even with the appearance of excess viscosity in the calculated dependence. A more detailed analysis of the heat of mixing according to its covalent and metal components showed that the second of them is already randomized and only the covalent component should be taken into account, which should be randomized and should be included in the total randomization barrier in the form ΔHch = RTliq – ΔcovH. Taking this component into account allowed us to obtain a more adequate calculated dependence of the viscosity of the Cu – Al alloy at a temperature of 1100 оC with a correlation coefficient of 0.986, which can be considered as a priority result in the description of viscosity isotherms according to state diagrams. This result is due to the analytical determination of the fraction of clusters in the melt based on the distribution of clusters proposed by the authors according to the number of particles included in the framework of the concept of randomized particles developed by the authors, which is directly related to the Boltzmann’s distribution.

Numerical Modeling of Heat and Mass Transfer during Cryopreservation Using Interval Analysis

In the paper, the numerical analysis of heat and mass transfer proceeding in an axially symmetrical articular cartilage sample subjected to the cryopreservation process is presented. In particular, a two-dimensional (axially symmetrical) model with imprecisely defined parameters is considered. The base of the heat transfer model is given by the interval Fourier equation and supplemented by initial boundary conditions. The phenomenon of cryoprotectant transport (Me2SO) through the extracellular matrix is described by the interval mass transfer equation. The liquidus-tracking (LT) method is used to control the temperature, which avoids the formation of ice regardless of the cooling and warming rates. In the LT process, the temperature decreases/increases gradually during addition/removal of the cryoprotectant, and the articular cartilage remains on or above the liquidus line so that no ice forms, independent of the cooling/warming rate. The discussed problem is solved using the interval finite difference method with the rules of directed interval arithmetic. Examples of numerical computations are presented in the final part of the paper. The obtained results of the numerical simulation are compared with the experimental results, realized for deterministically defined parameters.

Casting of Clad Strip Consisting of Al-Sn Alloy and Pure Aluminum

Casting of clad strip consisting of Al-40%Sn-1%Cu alloy and 1050 pure aluminum from molten metals was attempted using an unequal diameter twin-roll caster equipped with a scraper. The liquidus line and solidus line of the Al-40% Sn-1% Cu alloy are 620 °C and 220 °C, respectively. The liquidus line and solidus line of the 1050 are 657 °C and 646 °C, respectively. Therefore, solidification temperatures of the two aluminum alloys are much different. When an Al-40%Sn-1%Cu solidification layer was bonded to a solidification layer of the 1050 alloy, the temperature of the 1050 solidification layer surface was higher than the solidus line of Al-40% Sn-1% Cu. However, the Al-40% Sn-1% Cu alloy could be bonded to the 1050 strip and a two-layer clad strip could be cast. The interface between the two strips was very clear. Electron Probe Microanalysis (EPMA) indicated that Sn in the Al-40% Sn-1% Cu alloy did not diffuse into the 1050 alloy. Tensile shear tests were conducted using the as cast clad strip, and no breakage occurred at the interface between the strips but only in the Al-40% Sn-1% Cu layer. This result confirmed that the two strips were strongly bonded at the interface.

Structural state and thermodynamic stability of Al–Cu alloys

It is known that processes occurring in binary system melts affect the crystallization process and the phase composition of alloys. To predict these processes, we should determine the region of thermodynamic stability of the melt. In this paper, the structural properties of hypoeutectic and hypereutectic alloys in Al–Cu system are studied depending on the heating temperature above the liquidus line and aftercooling rate. It is shown that overheating of Al–Cu melts to 150 K above the liquidus line and further cooling leads to complete suppression of the process of formation of primary aluminum crystals in hypoeutectic alloys and [Formula: see text] phase in hypereutectic alloys. For the first time, by accounting in Gibbs energy of binary Al–Cu alloy for the first degree approximation of high-temperature expansion of thermodynamic potential, the dependence of temperature of line of the melt thermodynamic stability on copper content in alloy is obtained.

Appearance and Disappearance of Quasi-Liquid Layers on Ice Crystals in the Presence of Nitric Acid Gas

The surfaces of ice crystals near the melting point are covered with thin liquid water layers, called quasi-liquid layers (QLLs), which play crucial roles in various chemical reactions in nature. So far, there have been many spectroscopic studies of such chemical reactions on ice surfaces, however, revealing the effects of atmospheric gases on ice surfaces remains an experimental challenge. In this study, we chose HNO3 as a model atmospheric gas, and directly observed the ice basal faces by advanced optical microscopy under partial pressure of HNO3 (~10−4 Pa), relevant to those found in the atmosphere. We found that droplets (HNO3-QLLs) appeared on ice surfaces at temperatures ranging from −0.9 to −0.2 °C with an increase in temperature, and that they disappeared at temperatures ranging from −0.6 to −1.3 °C with decreasing temperature. We also found that the size of the HNO3-QLLs decreased immediately after we started reducing the temperature. From the changes in size and the liquid–solid phase diagram of the HNO3-H2O binary system, we concluded that the HNO3-QLLs did not consist of pure water, but rather aqueous HNO3 solutions, and that the temperature and HNO3 concentration of the HNO3-QLLs also coincided with those along a liquidus line.

Forces generating crystallization differentiation, and the evolution of the melt composition on the example of plagioclase

Crystallization differentiation processes in the melt volume are investigated for albite-anorthite continuous solid solution series. It has shown that crystallization differentiation occurs in the isothermal melt volume due to hydrodynamic instability of the melt/solid particles system. The time of particle settling in a 10 cm thick melt layer is estimated for different particle sizes. In terrestrial conditions, the existence of large melt volumes with long lifetime is possible in the case of a long-lived heat source of high thermal power. This source is a mantle thermochemical plume with a mushroom-shaped head. The particle settling time is estimated for the melt layer thickness, i. e. plume head thickness equal to 10 km. A calculation technique is presented for composition of the melt remaining after settling of plagioclase particles. The results of calculations of changes in the melt composition due to crystallization differentiation at a temperature T = 1410 °C and a pressure P = 6,3 kbar are presented. For a melt whose composition corresponds to N 47,5 (weight percentage of anorthite is 47,5 %), the oxide content in the settled plagioclase, the composition of the melt in its intercrystalline spaces, and the residual melt composition are calculated. At constant temperature, the crystallization differentiation of the melt whose composition corresponds to plagioclase leads to the compositional changes in the initial melt. Calculations of the melt composition have shown that the melt is depleted in anorthite component owing to settling of plagioclase particles. The composition of plagioclase therewith shifts to the liquidus line, reaching its limit on this line