Characteristics of the binary faceted eutectic: benzoic acid – salicylic acid system

The consistent symmetry relations computed from the heterogeneous nucleation data of the non‐ideal benzoic acid – salicylic acid eutectic system verifies the validity of nucleation theory. The kinetics of crystal growth from the molten state of the system follows the dislocation mechanism. Anomalous behaviour of both viscosity and activation energy for the eutectic melt confirms the essence of specific interactions animating molecular clusters rich in predominating eutectic phase. Micromorphology of the system obeys the Hunt‐Jackson model. The plot between a mechanical property and variable anisotropic growth velocity for the eutectic composite evidentially complies with the Weibull probability distribution curve. The curve is perused with two cut‐off points corresponding to a lower strength limit in the slow and fast growth regions and an upper strength limit in the moderate growth region. The latter aspect reveals the theoretical strength of the eutectic crystallites. The strength‐growth relationship explicated thereby is linear, optimum and linear respectively in the slow, moderate and fast growth regions of solidification. The moderate anisotropic growth (∼2.96 X 10^‐7m³s^‐1) is of greater interest by virtue of its attribute to unifying and organizing the crystallites parallel to each other in the growth direction. The eutectic composite material obtained by this process attains remarkable superiority in the mechanical properties over its isotropic growth in an ice bath (∼273 K), and its constituent phases. The co‐relation between excess thermodynamic functions indeed predicting the liquidus character and the microstructural parameters inevitably structuring the morphology is presented. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermodynamic and lamella models relationship for the eutectic system benzoic acid – cinnamic acid

The present investigation reveals the relationship between excess thermodynamic functions and the growth habits of the eutectic phases from the melt by continuous melt‐growth technique. Excess thermodynamic functions computed for different compositions of the benzoic acid – cinnamic acid eutectic system have been found consistent with the criteria of spontaneity and Planck formulation, and their reliability has been ascertained by the application of Guggenheim lattice theory. The results on the kinetics of anisotropic growth of the eutectic phases from the melt, evidentially evince the dislocation mechanism. Evidences have been obtained for a parabolic variation of mechanical strength with growth velocity of the eutectic material grown anisotropically from the melt at different intervals, which offer supporting complement to the dislocation mechanism governing the dependence of growth velocity on supercooling ΔT in the solidus – liquidus interface in a form : V = k(ΔT)². A moderate anisotropic growth region has been explored by unique results of strength properties and microscopic results as well, to growing a layer of lamellae in a unidirectional lamina. An anisotropic eutectic composite lamellae lamina developed by moderate growth velocity (7.3 × 10^‐8m³s^‐1), is of greater interest offering optimum hardness, approximately varying between three‐and eight fold average increase in different modes of the mechanical strength in comparison to its isotropic growth carried out in an ice‐bath (∼273K), and manifold superior to its constituent phases irrespective of the growth mode. The directional lamina of uniform microstructural parameter lamellae, indicates that there is a perfect lamella‐ matrix equilibrium for which excess thermodynamic functions do vanish. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solidification behavior and microstructural evolution of the Cr‐Nb eutectic alloy

A series of microstructures including fully coupled eutectic, both α‐Cr and β‐Cr₂Nb primary dendrites embedded in eutectic and only β‐Cr₂Nb primary dendrites plus eutectic were observed in the arc‐melted Cr‐Cr₂Nb eutectic alloy. By employing EPMA analysis performed at the eutectic regions, the eutectic composition of the Cr‐Cr₂Nb system was indicated to contain less than 18 at.%Nb. Based on the solidification phase selection involving phase competitive nucleation and growth, the α‐Cr phase was predicted to be the primary nucleating phase and the β‐Cr₂Nb the primary growing phase. Under large undercooling conditions, the solidification process was controlled by nucleation, which led to the formation of α‐Cr primary particles. With the decrease in undercooling, the solidification process developed into growth controlling, which caused the occurrence of β‐Cr₂Nb primary phase since the actual solidification path of the alloy lay within the hypereutectic region. The explanation was confirmed by the experimental composition analysis.     

Mode of solidification and strength properties for lead-tin binary system

Tensile strength and ductility of unidirectionally and randomly solidified Sn, Pb and Sn–Pb eutectic alloy are determined. Appreciable increase in the ductility from random to directional growth has been observed in case of Sn, Pb and Pb–Sn eutectic. Improvement in tensile strengths of pure metals and their eutectic composite by 15–20% and 15%, respectively, was evident in case of directionally solidified to randomly grown samples. The increase in tensile strength of the eutectic was 2–2.5 times to the strength of the pure metals. Tensile strength of directionally solidified Pb–Sn eutectic studied at different rates of solidification for constant temperature gradient was lower at higher and at lower rates of solidification than the value at medium rates of solidification.     

The preferential orientation of the directionally solidified Si–TaSi2 eutectic in situ composite

The Si–TaSi₂ eutectic in situ composite is a favorable field emission material due to relatively low work function, good electron conductivity, and three-dimensional array of Schottky junctions grown in the composite spontaneously. The preferential orientation during directional solidification is determined by the growth anisotropy. In order to obtain the preferential direction of the steady-state crystal growth, the transmission electron microscopy (TEM) is used for analysis. It is found that the preferential orientation of the Si-TaSi₂ eutectic in situ composite prepared by Czochralski (CZ) technique is [3 3¯ 2¯] Si∥[0 0 0 1] TaSi₂, (2 2 0)Si∥(2 2¯ 0 0) TaSi₂. Whereas the preferential orientation of the Si–TaSi₂ eutectic in situ composite prepared by electron beam floating zone melting (EBFZM) technique is [0 1¯ 1¯ ]] Si∥[0 0 0 1] TaSi₂,(0 1¯ 1) Si∥(0 1¯ 1 1)TaSi₂. The preferential directions of the Si-TaSi₂ eutectic in situ composites prepared by two kinds of crystal growth techniques are distinctly different from each other, which results from different solid–liquid interface temperatures on account of the different crystal growth conditions, e.g. different solidification rate, different temperature gradient, different solid–liquid interface curvature and different kinetic undercooling.     

Strength and microstructures of Benzoic Acid-Benzamide system

Pure end products in their binary eutectic of a benzoic acid-benzamide system, grownunidirectionally and randomly, exhibited marked anisotropy in their peculiar properties particularly if the growth is carried out in some periodic manner. Modulus of ruptures of eutectic composite and the constituent materials for both the growths have been determined. Directional-growth of the composite yields a bending strength quite larger than that can be obtained from an anomalous growth. Pure components also offer slighly greater strength in an ordered growth. Microphotographs of grown materials are related to the mode of crystallization of the materials.     

On the orientational relationship between eutectic α-Fe2Si5 and ϵ-FeSi

The undirectional solidification of the eutectic between α-Fe₂Si₅ and ?-FeSi was carried out. The temperature gradient at the liquid-solid interface was 70°C/cm. Microstructures of the aligned composite were fibrous and lamellar, for last and slow growth rates respectively. The growth direction of α and the preferred axial orientation relationships between α and ? were determined for both structures.     

A new approach of creating Au‐Sn solder bumps from electroplating

A homogeneous melting eutectic Au/Sn solder bump for laser chip application has been developed. The under‐bump metallization consists of a Ni wetting layer, a plating seed layer of Pt/Au/Ti multi‐layer scheme. The solder is electroplated as a sequence of Ni, Au and Sn layers. The bump can be exposed to multi‐step reflow cycles. The reflow of the solder as plated starts with a phase forming process in the solid state which results in an eutectic‐like phase and the near eutectic dand z phases. The dand z phases dissolve during the liquid state stage of the reflow at temperatures between 300 and 350 °C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

TEM analysis of the container effect of Au‐based catalyst droplets during vapour‐liquid‐solid growth of axial ZnTe/CdTe nanowires

Axial heterostructure nanowires (NWs) of ZnTe/CdTe were grown by vapour‐liquid‐solid growth realized in a molecular beam epitaxial chamber. By alternative supply of Zn or Cd and constant Te the heterostructure was generated. The liquid phase is provided by a Au‐based eutectic droplet which stays at the tip of the NW during the entire growth. For structural and chemical characterization by TEM the NWs were harvested from the substrate and transferred to a holey carbon film. The NWs exhibit an expansion of the diameter correlated with the interface region between ZnTe and CdTe. Idiomorphic growth of the CdTe is evident from electron diffraction experiments. The growth rate of CdTe appears to be smaller compared to that of ZnTe at the same temperature. Both, quantitative high‐resolution TEM and energy dispersive X‐ray spectroscopy line scans reveal a smeared ZnTe/CdTe interface along about 200 nm. The smearing is due to both, the liquid catalyst which buffers the supply of Cd instead of Zn at the liquid/solid interface and to the strain which is induced by the lattice mismatch. It forces the system to consume the remnant Zn for the NW growth in favour of Cd. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,crystal growth and properties of the charge transfer complex adduct of 2‐nitro aniline with picric acid – An organic non‐linear optical material

The organic NLO material 2‐nitro aniline and picric acid (2NAP) was synthesized, needle shaped single crystals of dimension 10 × 1 × 0.8 mm^‐3 were grown by slow evaporation solution growth technique from the saturated solution of the title compound in chloroform at ambient temperature. The material was characterized through elemental analysis, powder XRD, ¹H NMR, ¹³C NMR and FTIR techniques. The various planes of reflection have been identified from the XRD powder pattern. The formation of the charge transfer complex was confirmed by UV‐VIS spectroscopy. The thermal stability of the crystals was investigated using TG/DTA analyses techniques. The second harmonic generation (SHG) efficiency of the material was estimated using Nd: YAG laser as source. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ce3+∶GdLu2Al5O12/Al2O3共晶微结构及其发光性能

稀土共晶闪烁体是通过定向凝固晶体生长技术,将具有不同折射率的两相制备成具有射线探测功能的共晶材料,其中含有激活离子的闪烁体相的折射率高于基质相。在高能射线辐照下,闪烁体相将入射高能射线转换成荧光,然后,荧光在闪烁体相和基底相的界面以全反射的形式实现定向输出,从而有效提高辐射探测成像的空间分辨率。本工作采用微下降法成功生长得到φ3 mm×117.0 mm 的1.0%(原子数分数)Ce∶GdLu₂Al₅O₁₂/Al₂O₃闪烁共晶样品。通过切割抛光加工得到φ3 mm×2.0 mm的共晶薄片,并将该共晶薄片进行微观结构、能谱分析和荧光性能等表征和测试,结果表明所得到的共晶样品由Ce∶GdLuAG和Al₂O₃两晶相构成,微观结构呈现出“中国结”结构,并在生长方向呈现出一定的有序排列。荧光光谱测试表明该共晶材料存在Gd³⁺-Ce³⁺间的能量传递,具有典型的Ce³⁺辐射跃迁,其中双宽峰发射峰最强位于560 nm。此外,根据生长速率对共晶样品发射峰强、峰位以及荧光寿命影响,优化出最佳下拉生长速率为4.0 mm/min。     

Control of the phase composition and morphology of a Cu‐Sb eutectic alloy via liquid‐liquid structure transition

The current paper focuses on the solidification characteristics of a Cu‐Sb eutectic alloy in its different liquid states. Liquid alloy resistivity‐temperature patterns suggest an irreversible temperature‐induced liquid‐liquid structure transition (TI‐LLST), and a reversible TI‐LLST occurred during the heating‐cooling runs. A set of solidification experiments was conducted based on the results. The irreversible TI‐LLST caused an enhanced solidification undercooling, increased solidification rate, refined regular eutectic morphologies, and absence of a pre‐eutectic Cu₂Sb phase. The reversible TI‐LLST resulted in different phase compositions and eutectic structures. The mechanisms behind these transitions are also briefly discussed.     

Observation of the periodic fluctuant dendritic structure in an Al–38 wt% Cu hypereutectic alloy processed by ACRT-B method

The microstructure of periodic fluctuant dendritic θ in a matrix of +θ eutectic was obtained in an Al–38 wt% Cu alloy processed by ACRT-B method grown at growth velocities (V) ranging from 5 to 60 μm/s and crucible rotating in a trapezoidal way with maximum rotation rates (Ω_max) ranging from 100 to 400 rpm. Formation of this structure is explained by the influence of the periodical Ekman flow on the growth of dendritic θ during the spin-up and spin-down process. It was also observed that the +θ eutectic between the primary dendrites of θ (CuAl₂) is not periodic and fluctuant during ACRT-B process. This is quite different from our previous observation of periodic eutectic in Al–Cu eutectic processed by similar ACRT-B method.     

Contribution to the tin‐rich region of the Sn‐Zn‐Ti system

The tin‐rich region of the system Sn‐Zn‐Ti system has been studied by diffusion couples, differential scanning calorimetry and electron microprobe analyses. Ternary eutectic reaction occurs at 193.7°C near to the binary tin‐zinc eutectic point and titanium content less than 0.9 at.% Ti. Three ternary compounds with approximate formulae: Ti₈Sn₅Zn₂ to Ti₅Sn₃Zn, TiSn₄Zn₅ and Ti₂Sn₄Zn₃ have been observed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of diffusion couple technique for the determination of the Ti‐Bi‐Sn phase diagram

The system Ti‐Bi‐Sn has been investigated by solid/liquid diffusion couples at 500, 600, 700 and 800°C. A non‐negligible solubility of Sn into solid Bi is found. Diffusion layers of the recently revealed ternary compound Ti₃BiSn have been observed, thus its existence has been confirmed. Data about the homogeneity ranges of the binary end‐system compounds have been obtained. The assessed growth constants of the diffusion layers are comprised in the interval 10^‐12 –10^‐14 m².s^‐1. The phases participating in the hypothetical ternary eutectic reaction, probably are: (Bi), (Sn), Liquid and Ti₂Sn₃. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rapid crystallization and growth mechanisms of highly undercooled Ag–Cu–Ge ternary alloy

Crystallization from undercooled melt of Ag-33.4 wt% Cu-28.1 wt% Ge ternary alloy was carried out with glass fluxing method under different undercoolings and the nucleation and growth characteristics of the primary phase, two-phase eutectic, and ternary eutectic are investigated. It is found that both the solidification microstructures and the size of primary phase (Ge) and intermetallic compound η vary significantly with undercooling, whereas the ternary eutectic structure has no apparent variation. With the increase of undercooling, macrosegregation of primary (Ge) phase becomes weak and this phase experiences a “large block/strip→small particle” morphology transition. Moreover, the ((Ge)+η) two-phase eutectic can nucleate in preference to the primary (Ge) phase within a large undercooling regime. The intermetallic compound phase η grows competently with (Ge) phase and it can directly form alloy melt. The experimental results of the containerless processing by a 3 m drop tube indicate that in order to make the ternary eutectic nucleate in preference to the (Ge) primary phase and the ((Ge)+η) two-phase eutectic with the glass fluxing method, the undercooling should be at least larger than 195 K.     

Enhancement of solder properties of Sn‐9Zn lead‐free solder alloy

The eutectic alloy Sn‐9Zn was considered as a potential alternative to lead‐tin solder alloys when compared with other solders. In this paper, ternary, quaternary and penternary additions of the elements Bi, Cu and In were added to the eutectic alloy as a trial to improve its properties. The results showed that, the penternary alloy has properties superior to those of the binary, ternary and quaternary alloys. The alloy of composition Sn‐9Zn‐1Bi‐2Cu‐2In has the most suitable properties as a candidate alloy for lead‐free solder. It has a lower melting point, 186°C, which is very close to that of Sn‐37Pb solder, a lower value of electrical resistivity, 16.5 μΩ.cm, compared with that of Sn‐37Pb (17 μΩ.cm), higher value of the Young's modulus, 47 GPa, compared with 45 GPa of Sn‐37Pb and a higher value of the Vickers hardness, 191 MPa, compared with 129 MPa of Sn‐37Pb eutectic alloy. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A novel growth method for ZnAl2O4 single crystals

ZnAl₂O₄ is a well‐known wide band gap compound semiconductor (E_g=3.8eV), ceramic, opto‐mechanical, anti‐thermal coating in aero‐space vehicles and UV optoelectronic devices. A novel method for the growth of single crystals of a ternary oxide material was developed as a fruit of a long term work. Material to be grown as metal incorporated single crystal was taken as precursor and put into a bath containing acid as reaction speed up reagent (catalyst) as well as solvent with a metal foil as cation scavenger. Using this method, ZnAl₂O₄ crystals having hexagonal facets are prepared from a single optimized bath. Structural and compositional properties of crystals were studied using Philips, Xpert ‐ MPD: X‐ray diffractometer and Philips, ESEM‐TMP + EDAX. Thus technique was found to be a new low cost and advantageous method for growth of single crystals of ternary oxide a material. We hope that these data be helpful either as a scientific or technical basis in material processing. Dedicated to Prof. P. Ramasamy © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Solidification behaviour of eutectic and monotectic alloys: Succinonitrile - acenaphthene system

The phase diagram of succinonitrile-acenaphthene system, determined by the thaw-melt method, shows the formation of a eutectic at 0.99 mole fraction of succinonitrile and a monotectic at 0.35 mole fraction of succinonitrile with a large miscibility gap. The linear velocity of crystallization (v) of the pure components, eutectic and monotectic, studied at different undercooling (ΔT) by measuring the rate of movement of the growth front in a capillary, suggests that crystallization data obey the equation: v = u(ΔT)ⁿ where u and n are constants depending on the nature of solidification of the compounds. While the microstructural investigation of eutectic shows broken lamellar and eutectic dendrite-type morphologies that of monotectic exhibits fibrous and broken fibrous-type microstructures depending on the rate of solidification.     

Synthesis and characterization of a micro scale zinc oxide–PVA composite by ultrasound irradiation and the effect of composite on the crystal growth of zinc oxide

Micro scale zinc oxide-polyvinyl alcohol (ZnO–PVA) composite has been synthesized by ultrasound irradiation. The properties of the as-prepared ZnO–PVA composite material are characterized by X-ray diffraction (XRD), thermo gravimetric analysis (TGA), transmission electron microscopy (TEM), and diffuse reflection spectroscopy (DRS). A band gap of 3.25 eV is estimated from DRS measurements. The controlled crystal growth of zinc oxide has been studied by using the as-prepared micro scale ZnO–PVA composite as seeds for the crystal growth of ZnO.