Calorimetric study and thermodynamic description of Ga-Ge-Li liquid alloys

This publication contains the thermodynamic results received by the drop calorimetry method. The experiments were conducted for four different cross sections, at the temperature of 1080 K. The investigated alloys were as follows: (Ga_0.75Li_0.25)_1-xGe_x, (Ge_0.50Li_0.50)_1-xGa_x, (Ga_0.50Li_0.50)_1-xGe_x, (Ga_0.25Li_0.75)_1-xGe_x. The mixing enthalpy changes measured for all four cross sections of the Ga-Ge-Li system are characterized by negative deviations from the ideal solutions. The Muggianu model with the ternary interaction parameters was applied to elaborate the experimental data of the mixing enthalpy change with the use of the optimized thermodynamic parameters of the binary systems available in the literature.     

(C_2H)_2M_n(M=Cu、Ag、Au;n=1-4)团簇的密度泛函理论研究

采用密度泛函理论的B3LYP和PBEIPBE方法,对(C_2H)_2M_n(M=Cu、Ag、Au;n=1-4)团簇的结构和性质进行了研究。结果表明:(C_2H)_2M_n(M=Cu、Ag、Au;n=1-4)簇的最稳定结构都是在C_2HM_n(M=Cu、Ag、Au;n=1-4)簇最稳定结构的基础上,又与C_2H自由基相互作用的结果。NBO计算结果表明:银与2个C_2H自由基的相互作用弱于铜和金。(C_2H)_2M_n(M=Cu、Ag、Au;n=1-4)簇最稳定结构的相互作用能均为负值,表明形成的团簇较稳定,并且出现了奇-偶振荡效应(n=1-4),含偶数个IB原子的团簇比含奇数个IB原子的团簇稳定。红外分析表明:(C_2H)_2M_n(M=Cu、Ag、Au;n=1-4)团簇中C_2H自由基的C≡C和C-H键的伸缩振动都发生了红移,随着团簇尺寸的增加(n=1-4),也出现了奇-偶振荡效应。     

An optimal method to calculate the viscosity of simple liquid ternary alloys from the measured binary data

An optimal method to calculate the viscosity of simple liquid ternary alloys from the measured binary data is investigated in this paper. In order to find a relationship which describes the ternary viscosity data from binary data most adequately, a comparison was made between three different approaches tested on the example of the Au–Ag–Cu system. The optimal method turned out to be the extension of the Redlich–Kister polynomial to excess viscosity without any ternary term. This optimal method was applied further on the Fe–Ni–Co system. The estimation of viscosities for liquid Fe–Ni–Co alloys was done in different sections with molar ratio of two components equal to 1:1, 1:3 and 3:1. A diagram showing iso-viscosity lines was constructed at the investigated temperature of 1873 K.     

Sensor properties and surface characterization of the metal-deposited SPR optical fiber sensors with Au,Ag, Cu,and Al

Metal-deposited optical fiber sensors with Cu and Al with a film thickness of 45 nm based on surface plasmon resonance (SPR) were fabricated for the first time. The response curves and the properties of these sensors were investigated with a comparison of those of the sensors with Au and Ag. The reflection properties of thin films of Au, Ag, Cu, and Al due to the SPR phenomenon were also measured and considered. The metal-deposited SPR optical fiber sensors with Au, Ag, and Cu have high sensitivities and good responses. Though the sensor with Al shows a lower sensitivity, it has a wider response range in the refractivity. The response curve of the sensor with Au calculated from SPR theoretical equations agreed well with that obtained by the experiment. However, the response curves of the sensors with Ag, Cu, and Al have the effects of the surface oxide layers. The surface characterization of these metal films by X-ray photoelectron spectroscopy (XPS) showed the presence of oxide layers on the films of Ag, Cu, and Al. A very thin (about 0.3 nm) oxide layer is present on Ag, while thick (about 2 nm) oxide layers are present on Cu and Al.     

The oxidation of ethanol on Cu(110) and Ag(110) catalysts

The oxidation of ethanol was studied on Cu(110) and Ag(110) single crystals by temperature programmed reaction spectroscopy. The single crystal surfaces were preoxidized with ¹⁸O₂, and deuterated ethanol, CH₃CH₂OD, was used to distinguish the hydroxyl hydrogen from the ethyl hydrogens. The ability of both surfaces to dissociatively chemisorb ethanol was greatly enhanced by surface oxygen. CH₃CH₂OD was selectively oxidized upon adsorption at 180 K to adsorbed CH₃CH₂O and D₂¹⁸O. The Ag(110) surface was more active than the Cu(110) surface for the dehydrogenation of ethoxide to acetaldehyde and hydrogen. The recombination of surface hydrogen with ethoxide to yield CH₃CH₂OH was also observed. Following high exposures of ethanol the surface intermediate CH₃CH₂OD₂ was produced upon adsorption at 180 K from the interaction of two CH₃CH₂OD molecules, and this surface complex subsequently decomposed to C₂H₄, D₂O and hydrogen. The present results for the oxidation of ethanol are compared to the previous investigations of methanol oxidation on Cu(110) and Ag(110).     

Different ways to find the thermodynamic functions describing the formation of binary alloys: part 1 comparison between models and experimental data

The thermodynamic functions describing the formation of binary alloys are known for only a small part of all the systems. Models are in many cases the only way to find thermodynamic data. Two models, MIEDEMA's on the one hand and BENNETT's and WATSON's on the other hand are compared with new experimental data to characterize their accuracy and reliability, in regard of the experimental difficulties.     

Limitations of a regular associated solution approximation in describing the thermodynamic behaviour of complex liquid alloys

The validity of the regular associated solution (RAS) model for describing the thermodynamic properties of complex liquid alloys has been analysed by applying it to the Cu-In system. The presence of Cu₃In as the associated species in equilibrium with the free atoms in the liquid state was assumed. Liquid copper-indium alloys exhibit a very complex thermodynamic behaviour where the deviations from ideality of activities and integral enthalpy of mixing vary from positive to strongly negative and the properties are strongly temperature dependent. It is seen that a regular solution type interaction among species is insufficient to model the thermodynamic properties of liquid Cu-In alloys and the temperature dependence of interaction energies among the species has to be taken into account. A modified associated solution model incorporating volume effects and temperature dependence of interaction energies could successfully describe the thermodynamic properties of liquid Cu-In alloys.     

The thermodynamic analysis of Guinier–Preston zones in aged supersaturated Al–Cu alloys

Being the structural cause of hardening, Guinier–Preston (GP) zones in many alloys still attract much interest. The expression of energy for GP zones in the Al–Cu alloy is established by combining the essential Gibbs energy with the interfacial energy and the strain energy. Based on the equilibrium between GP zones and the surrounding matrix, a quantitative analysis on the sizes, concentrations, aging temperatures and their relationships can be predicted. The size and the concentration of GP zones calculated with defined composition and aging temperature accord with the experimental results well.     

Assessment of the aluminum-rich corner of the Al–Cu–Mg–(Ag) phase diagram

The thermodynamic expressions for the phases found in the aluminum-rich corner of the Al–Cu–Mg–(Ag) system were evaluated and refined to develop a self-consistent database. Microstructural characterization and thermal analysis aided in revising published thermodynamic data for the Al–Cu–Mg and Al–Cu–Mg–Ag systems. To represent the presence of silver an additional interaction energy term was formulated for the S phase, which was completed with the help of ab initio calculations that predicted silver substitution for aluminum within the phase.     

Experimental and thermodynamic study of tantalum-containing iron-based alloys reinforced by carbides: Part I — Case of (Fe,Cr)-based ferritic steels

Experiments and thermodynamic calculations were performed on three iron-based alloys containing 30 wt% of chromium and 3 to 6 wt% of tantalum. Solidus temperatures, natures, and surface fractions of all phases present after an exposure for 50 h at 1000, 1100, and 1200  ^°C, were determined for each alloy. These results were compared to values calculated using Thermo-Calc. Two alloys display solidus temperatures above 1400  ^°C, while all the liquidus temperatures are higher than 1500  ^°C. Tantalum carbides are present with high fractions, compared to similar Co-based and Ni-based alloys. Their observation and quantification using electron microscopy micrographs and image analysis may lead one to overestimate the surface fractions of TaC. Calculations of carbide fractions from the chemical composition of the matrix is to be preferred. A precipitation of coarse chromium carbides may occur for 1100 and 1200  ^°C.     

Long-term stability of Ag and Cu thin films on glass, LTCC and alumina substrates

Silver (Ag) and copper (Cu) are regarded as advanced material for metallization systems in microelectronic devices because of their high electrical conductivity and enhanced electromigration resistance. Typically, organic circuit boards as well as ceramic and glass–ceramic substrates use galvanic deposited Cu films or screen-printed metallization for this purpose. When applying the latter approach, however, the lateral resolution in the μm-region being required e.g. for novel high frequency applications can not be guaranteed. Hence, sputter deposition is envisaged for the realization of thin film metallization systems. The reliability of 300?nm thick Cu and Ag thin films is comparatively investigated under accelerated aging conditions, utilizing a test structure which consists of parallel lines stressed with current densities up to 2.5?×?10^6?A?cm^?2 at temperatures up to 300°C on Si/SiO₂, glass, LTCC (low temperature co-fired ceramics) and alumina substrates. To detect the degradation via the temporal characteristics of the current signal a constant voltage is applied according to the overall resistance of the test structure. Knowing the mean time to failure (MTF) and the activation energy at elevated temperatures conclusions on the migration mechanism can be drawn. Whereas on LTCC substrates the activation energy E_a is about 0.75?eV for both Ag and Cu thin films, the higher activation energies of about E_a?~?1?eV measured for Cu on glass and alumina indicate a suppression of back diffusion especially at enhanced temperature levels. This effect is predominantly caused by a stable oxide layer which is formed at high temperatures and which acts as passivation layer. Therefore, the overall electromigration resistance is lower compared to Ag.     

Assessment of atomic mobilities of Al and Cu in fcc Al–Cu alloys

Based on various kinds of experimental diffusivities and thermodynamic parameters available in the literature, the atomic mobilities of Al and Cu in face-centered cubic (fcc) Al–Cu alloys have been assessed as a function of temperature and composition by means of DIffusion Controlled TRAnsformation (DICTRA) software package. Comprehensive comparisons between the calculated and measured diffusivities show that most of the experimental data can be well reproduced by the presently obtained atomic mobilities. In addition, the atomic mobilities obtained in the present work can also reasonably predict the concentration profiles for a variety of diffusion couples in fcc Al–Cu alloys including the one prepared in the present work.     

银金钯铂组成对三元金属团簇结构的影响

纳米合金团簇的结构研究为具有特殊的光、电、磁和催化材料设计奠定了重要的理论依据。优化了含有Ag、Au、Pd和Pt原子的三元金属团簇稳定结构,并分析了不同类型原子组成对三元团簇结构的影响。采用Gupta势函数描述由这4种金属原子构成的相同类型原子间及异种类型原子间相互作用。使用自适应免疫优化算法优化Ag26、Au26、Pd26、Pt26团簇以及Ag10AunPd16-n、Ag10AunPt16-n、Ag10PdnPt16-n与Au10PdnPt16-n(n=0-16)金属团簇稳定结构。并通过势能量二阶有限差分值分析这些团簇结构的相对稳定性。     

Adhesive properties study on the interfaces of AlN and metal of Pd,Ag and Cu

AlN is used as high power LED package material because of its excellent thermal conductivity. But its poor adhesive with metal is not compatible with the later processing sequence. The properties of the bonding between the deposited palladium,silver,copper and the clean Al-terminated (0001) surface of wurtzite AlN are investigated by using the density-functional theory. The results show that the sites of deposited metal atoms on N site are more stable than that on Al site. Relaxations are found at all the s...     

Low temperature transient liquid phase bonding of Au/Sn and Cu/Sn electroplated material systems for MEMS wafer-level packaging

This paper presents the development of a low temperature transient liquid phase bonding process for 8″ wafer-level packaging of micro-electro-mechanical systems. Cu/Sn and Au/Sn material systems have been investigated under varying bonding temperatures from 240 to 280 °C and different dwell times from 8 to 30 min. The used bond frame had a width of 80 μm and lateral dimensions of 1.5 mm × 1.55 mm. The sealing frame of the cap wafer consisted of Au and Cu, respectively, and Sn. The MEMS wafer only holds the parent metal of Au or Cu. High quality bonds were confirmed by shear tests, cleavage analysis, polished cross-section analysis using optical and electron microscope, energy dispersive X-ray spectroscopy and pressure cocker test. The samples showed high shear strength (>80 MPa), nearly perfect bond regions and no main failure mode in the cleavage analyses. Non-corroded Cu test structures confirmed the hermeticity.     

A thermodynamic model of the Z-phase Cr(V, Nb)N

Precipitation of large Z-phase particles, Cr(V, Nb)N, replacing fine MX carbonitrides, Nb(C, N) or V(N, C), has recently been identified as a major cause for premature breakdown in long-term creep strength of a number of new 9%–12% Cr martensitic steels, especially the high Cr variants.

A thermodynamic model of the Z-phase has been developed based on the regular solution model. The model predicts Z-phase to be stable and to fully replace the MX particles in most of the new 9%–12% Cr steels, which is in good agreement with experimental observations.

The rate of precipitation of Z-phase is a crucial factor for the long-term creep stability of these steels. Driving force calculations with the model allow estimates of the influence of the individual alloying elements on the rate of Z-phase precipitation, and can thus contribute useful information for alloy design to delay and retard Z-phase precipitation.

According to these calculations, particularly Cr has a strong accelerating effect on Z-phase precipitation.     

Comparison of electrocardiographic data (P waves): test of a shape-based approach

We tested a method for comparing ECG signals (P waves), in a sample of 10 normal males. In each subject, sets of 219 body surface ECGs were simultaneously recorded during tidal respiration. Only beats at end expiration and peak inspiration were considered. The beats of each group were subdivided into two subgroups of the same size (about 30 beats) and separately averaged. The two averaged beats at end expiration, assumed to be equal, were compared in order to estimate the noise variance (sigma2), i.e., the lowest value of variance at which the beats were statistically similar (P less than 0.05). At the same value of sigma2, the beat at end expiration significantly differed from that at peak inspiration. By considering the individual leads, significant differences were found in more than 50% of the 219 ECGs, in specific thoracic areas. The data indicated that the method can reveal differences between P waves occurring during tidal respiration and provide information on the topographical distribution of the differences.     

Experimental and thermodynamic study of the high temperature microstructure of tantalum containing nickel-based alloys

Experiments and thermodynamic calculations were performed on three nickel-based alloys containing chromium, carbon and tantalum. Solidus and liquidus temperatures, and natures and surface fractions of the carbides after exposure for 100 h at 1000, 1100 and 1200 ^∘C were determined for each alloy. These results are compared with calculated results, using a thermodynamic database. Good agreement was generally found for the solidus temperatures but less good agreement for the liquidus ones. For alloys containing chromium carbides alone, carbide fractions and matrix compositions correspond to calculation results. But the presence of tantalum carbides in the third alloy was not predicted by calculations.