323,639 research outputs found
Thermophysical Properties of Fe-Si and Cu-Pb Melts and Their Effects on Solidification Related Processes
No full textAmong thermophysical properties, the surface/interfacial tension, viscosity, and density/molar volume of liquid alloys are the key properties for the modelling of microstructural evolution during solidification. Therefore, only reliable input data can yield accurate predictions preventing the error propagation in numerical simulations of solidification related processes. To this aim, the thermophysical properties of the Fe-Si and Cu-Pb systems were analysed and the connections with the peculiarities of their mixing behaviours are highlighted. Due to experimental difficulties related to reactivity of metallic melts at high temperatures, the measured data are often unreliable or even lacking. The application of containerless processing techniques either leads to a significant improvement of the accuracy or makes the measurement possible at all. On the other side, accurate model predicted property values could be used to compensate for the missing data; otherwise, the experimental data are useful for the validation of theoretical models. The choice of models is particularly important for the surface, transport, and structural properties of liquid alloys representing the two limiting cases of mixing, i.e., ordered and phase separating alloy systems
Diffusion-driven instabilities in the BT-GN oscillatory carbonylation reaction network
No full text\ua9 2024 Author(s).This study explores the role of diffusion in creating instabilities in the Bruk Temkin-Gorodsky Novakovic (BT-GN) oscillatory carbonylation reaction network. Stoichiometric network analysis and numerical methods revealed the presence of two destabilizing feedback cycles responsible for these instabilities. Analysis of a spatially uniform system showed that the saddle-node bifurcation can be simulated within the reaction network. The introduction of diffusion results in two types of instabilities: one occurs when a spatially uniform system is already unstable, leading to a reaction-diffusion front; and another involves diffusion-driven instabilities where introducing diffusion destabilizes a stable spatially uniform system. Slower PdI2 diffusion plays a key role in inducing these instabilities. Equations describing conditions for the emergence of the instabilities in both cases were derived
Hegel on Second Nature in Ethical Life
No full textWhat does it take to be subjectively free in an objectively rational social order? In this book Andreja Novakovic offers a fresh interpretation of Hegel&apos;s account of ethical life by focusing on his concept of habit or &apos;second nature&apos;. Novakovic addresses two central and difficult issues facing any interpretation of his Philosophy of Right: why Hegel thinks that it is is better to relate unreflectively to the laws of ethical life, and which forms of reflection, especially critical reflection, remain available within ethical life. Her interpretation draws on numerous parts of Hegel&apos;s system, particularly on his &apos;Anthropology&apos; and his Phenomenology of Spirit, and also explores connections between his account and those of other philosophers. Her aim is to argue that Hegel has a compelling conception of the ordinary ethical standpoint which takes seriously both the virtues and the perils of reflection.</jats:p
Oscillations in the concentration of phenylacetylene and its carbonylation products
No full textThe oscillatory nature of the palladium catalysed phenylacetylene oxidative carbonylation (PCPOC) reaction was first reported by Temkin and colleagues1-4. It was demonstrated that the PCPOC reaction in a catalytic system (PdI2, KI, O2, NaOAc in methanol) exhibits oscillations in redox potential, pH and the rate of CO/O2 gas mixture consumption. Later on, Novakovic and colleagues5-8 investigated the characteristics of the PCPOC reaction and carried out this reaction in a calorimeter for the first time. They reported simultaneous oscillations in pH and rate of heat evolution (Qr)5, the influence of oscillations on product selectivity as well as the dynamics of product formation6 and the influence of the reaction temperature on the period and amplitude of oscillations7. In addition, the products resulting from this reaction have been reported.8 To make use of all observations the reaction mechanism responsible for the oscillations needs to be understood. In this quest, the reaction network responsible for the initial reactions of PdI2 in this system were studied.9 Subsequently, the role of water in this oscillatory system, as well as the importance of the order of reactant addition and its effect on product formation have been reported.10 This recent study enabled the proposal of a prospective theory to describe the oscillatory behaviour. In this work the existence of oscillatory behaviour in the concentration of phenylacetylene and carbonylation products (E-3-phenylacrylic acid methyl ester, Z-2-phenylbut-2-enedioic acid dimethyl ester, E-2-phenylbut-2-enedioic acid dimethyl ester, 5,5-dimethoxy-3-phenylfuran-2(5H)-one and 3-phenylfuran-2,5-dione) is uncovered. The amplitude of the oscillations in phenylacetylene was as high as 34% relative to the initial amount of phenylacetylene added to the system. 1. A.V. Malashkevich, L.G. Bruk and O.N. Temkin, J. Phys. Chem. A, 1997, 101 (51), 9825-9827; 2. S.N. Gorodskii, A.N. Zakharov, A.V. Kulik, L.G. Bruk and O.N. Temkin, Kinet. Cat., 2001, 42 (2), 251-263; 3. S.N. Gorodskii, E.S. Kalenova, L.G. Bruk and O.N. Temkin, Russ. Chem. Bull., 2003, 52 (7), 1524-1543; 4. O.N. Temkin and L.G. Bruk, Kinet. Cat., 2003, 44 (5), 601-617; 5. K. Novakovic, C. Grosjean, S.K. Scott, A. Whiting, M.J. Willis and A.R. Wright, Chem. Phys. Lett., 2007, 435, 142–147; 6. K. Novakovic, C. Grosjean, S.K. Scott, A. Whiting, M.J. Willis and A.R. Wright, Phys. Chem. Chem. Phys., 2008, 10, 749-753; 7. K. Novakovic, A. Mukherjee, M. Willis, A. Wright and S. Scott, Phys. Chem. Chem. Phys., 2009, 11, 9044-9049; 8. C. Grosjean, K. Novakovic, S.K. Scott, A. Whiting, M.J. Willis and A.R. Wright, J. Mol. Cat. A, 2008, 284, 33-39; 9. K. Novakovic, J. Parker, Int. J. Chem. Eng, 2011; 10. K. Novakovic, J. Parker, Submitted
Design of Composites by Infiltration Process: A Case Study of Liquid Ir-Si Alloy/SiC Systems
No full textThe design of processing routes involving the presence of the liquid phase is mainly associated with the knowledge of its surface and transport properties. Despite this need, due to experimental difficulties related to high temperature measurements of metallic melts, for many alloy systems neither thermodynamic nor thermophysical properties data are available. A good example of a system lacking these datasets is the Ir-Si system, although over the last fifty years, the structures and properties of its solid phases have been widely investigated. To compensate the missing data, the Gibbs free energy of mixing of the Ir-Si liquid phase was calculated combining the model predicted values for the enthalpy and entropy of mixing using Miedema's model and the free volume theory, respectively. Subsequently, in the framework of statistical mechanics and thermodynamics, the surface properties were calculated using the quasi-chemical approximation (QCA) for the regular solution, while to obtain the viscosity, the Moelwyn-Hughes (MH) and Terzieff models were applied. Subsequently, the predicted values of the abovementioned thermophysical properties were used to model the non-reactive infiltration isotherm of Ir-Si (eutectic)/SiC system
Au-Ge based alloys for novel High-T Lead Free Solder materials - Fundamentals and applications(
No full textLow melting Au based alloys offer a combination of high corrosion and creep resistance as well as good electrical and thermal conductivity, and they support the capability for fluxless soldering. Despite their high price, Au alloys are of special interest for high temperature solder applications where these characteristics are essential, e.g. special MEMS devices, sensors exposed to aggressive media, biomedical applications or in space technology. The alloying system Au-Ge is characterized by a deep eutectic point with a melting temperature of 360°C, but information on the use of eutectic Au-Ge as solder material is very limited. In this work, the results of a group project within the European COST Action MP0602 "High Temperature Lead Free Solders" on the feasibility of Au-Ge based alloys as high-temperature lead free solder will be summarized. Beside the thermodynamic assessment of a number of important alloying systems (Cu-Ge, Ge-Ni, Au-Ge-Sb, Au-Ge-Si, Au-Ge-Sn) wetting and soldering tests using eutectic Au-Ge alloy and Cu and Ni substrates were performed. Sound joints with a high strength could be produced
Experimental Thermodynamics and Surface Properties of Ag-Cu-Ge Solder/Braze Alloys
No full textAg-based alloys have industrial importance in relation to their use as high-temperature solders in jewellery or braze alloys for thermoelectric modules. Good wetting properties and a tarnish-resistance of Ag-Ge and Ag-Cu-Ge alloys together with appropriate mechanical properties make them good candidates for bonding sterling silver (Ag-7.5Cu, in wt.%). The melting temperature and the heat of melting of Ag-Cu, Ag-Ge and Ag-Cu-Ge eutectic alloys have been measured by differential scanning calorimetry. From a technological point of view, particular attention should be paid to the surface tension, a key property of the joining processes. The aim of this study is to correlate the thermodynamic properties of the Ag-Cu-Ge system and its subsystems with their surface properties and to compare the model predicted property values to the data available in the literature
Micro-bioreactor arrays for controlling cellular environments: Design principles for human embryonic stem cell applications
No full textWe discuss the utilization of micro-bioreactor arrays for controlling cellular environments in studies of factors that regulate the differentiation of human embryonic stem cells. To this end, we have designed a simple and practical system that couples a microfluidic platform with an array of micro-bioreactors, and has the size of a microscope slide [E. Figallo, C. Cannizzaro, S. Gerecht, J.A. Burdick, R. Langer, N. Elvassore, G. Vunjak-Novakovic, Lab Chip 7 (2007) 710-719]. The system allows quantitative studies of cells cultured in monolayers or encapsulated in three-dimensional hydrogels. We review the operating requirements for studies of human embryonic stem cells (hESCs) under steady-state and dynamic conditions, and the related control of the mass transport and hydrodynamic shear. We describe the design and fabrication of the individual bioreactor components, and the criteria for selecting the bioreactor configuration and operating parameters, based on the analysis of the characteristic times and scales of reaction, convection and diffusion. To illustrate the utility of the bioreactor, we present a "case study" of hESC cultivation with detailed experimental methods and representative biological readouts. (C) 2008 Elsevier Inc. All rights reserved
New Insights into Phase Equilibria of the Sb-Sn System
No full textA new experimental investigation of the Sb-Sn phase diagram has been performed. Special attention was focused on the phase equilibria within SbSn-Sb3Sn4 composition range. Phase equilibria have been investigated by DSC measurements combined with a thorough optical and electronic microscopy examination with a special attention to the SbSn-Sb3Sn4 phase transformation. Both DSC and metallographic results have been critically evaluated and debated. The presence of two peritectic reactions L + Sb3Sn4 ⇌ (βSn) at 243 ± 1 °C and L + (Sb) ⇌ (SbSn) at 420 ± 1 °C have been confirmed. The invariant reaction at 321 ± 1 °C has been observed and an additional small effect at about 330-340 °C was systematically recorded. These results have been extensively discussed
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