Showing papers in "Materials Chemistry and Physics in 1994"

Semiconductor wafer bonding: recent developments

Abstract: Recent advances in semiconductor wafer direct bonding science and technology are reviewed in terms of room-temperature contacting, interface energy, interface bubbles, interface charges, thinning one wafer of a bonded pair and properties of bonded structures. Although silicon wafer bonding (with or without surface oxide) and silicon-on-insulator preparation are the main topics, bonding of dissimilar materials is also discussed. Examples of wafer bonding applications for material and device integration are given.

Effect of temperature on the acidic dissolution of copper in the presence of amino acids

Abstract: The corrosion behaviour of a copper electrode in a 1 M HCl solution has been studied potentiokinetically at different temperatures ranging from 25 to 55 °C. The inhibition efficiency of four amino acids was then tested for three concentrations in the range 10 −5 –10 −3 M. The amino acids, in the presence of HCl solution, caused a shift, mainly in the anodic direction of the corrosion potential at low current densities as well as the linear part of the cathodic Tafel line. The protection efficiency of each amino acid was calculated for different temperatures and concentrations. The amino acids act as a corrosion inhibitor in HCl solution through adsorption on the copper surface. The kinetic results, operating through a compensation effect, could well account for the variation of the inhibiting capacities of the various amino acids. The results reported in this paper elucidate the effect of temperature and the molecular structure on the inhibition efficiency, α-alanine was the most efficient of the four amino acids for inhibiting the corrosion of copper in HCl solution. Thermodynamic parameters for adsorption of the amino acids are calculated.

Surface characterization of yttria-stabilized tetragonal ZrO2. Part 1. - Structural, morphological and surface hydration features

Abstract: The characterization of three microcystalline Y2O3-stabilized tetragonal zirconia (t-ZrO2) preparations was carried out by BET, XRD, HRTEM, and FTIR spectroscopy, and revealed that morphological and surface features of t-ZrO2 specimens depend, much more than in the case of the monoclinic modification (m-ZrO2), on the preparative history of the material. Preparations fired at T ⩽ 1000 K are mostly made up of coin-like particles terminating with the same crystal plane and present only one surface OH species, but after firing at higher temperatures crystal shape and morphology of the various preparations start changing appreciably and differing from one another. The morphological changes are also monitored by changes in the IR spectrum of the surface OH layer, which becomes quite similar to that of the microcrystalline m-ZrO2 phase. After firing at T ⩾ 1173 K, some of the t-ZrO2 preparations will generate to various extents (depending on the Y2O3 content and on the preparative procedure) an amorphous phase coating the particles. This modification can be monitored by appreciable changes in the IR spectrum of the surface OH layer.

Sol-gel processing of electrical and magnetic ceramics

Abstract: A review is given of the sol-gel processing of electrical and magnetic ceramics. Materials include, SnO2,In2O3, WO3, V2O5, VO2, ZrO2, ZnO, BaTiO3, YBa2Cu3O7−δ, Al2O3, 2MgO · 2Al2O3 · 5SiO2, SiO2. 3Al2O3 · 2SiO2, PbTiO3, Pb(Zr,Ti)O3, (Pb, La)(Zr,Ti)O3, LiNbO3, Pb(Mg 1 3 Nb 2 3 )O3, Pb(Zn 1 3 Nb 2 3 )O3, Pb(Sc 1 2 Ta 1 2 )O3, Fe2O3, (Bi,Y)3Fe5O12, and BaFe12O19. Details are reported for the synthesis routes and the fabrication of ceramic components, including conductors, resistors and insulators, and includes, electronic and ionic properties, varistors, thermistors, superconductors, dielectrics, ferroelectrics, magnetics, and microelectronic materials.

The martensitic transformation in Ti-rich TiNi shape memory alloys

Abstract: The martensitic ( Ms ) transformation temperatures and their ΔH values of Ti 51 Ni 49 and Ti 505 Ni 495 alloys are higher than those of equiatomic or Ni-rich TiNi alloys The Ti-rich TiNi alloys exhibit good shape recovery in spite of a great deal of second phase Ti 2 Ni or Ti 4 Ni 2 O existing around B2 grain boundaries The nearly identical transformation temperatures indicate that the absorbed oxygen in Ti-rich TiNi alloys may react with Ti 2 Ni particles, instead of the TiNi matrix, to form Ti 4 Ni 2 O Martensite stabilization can be induced by cold rolling at room temperature Thermal cycling can depress the transformation temperatures significantly, especially in the initial 20 cycles The R-phase transformation can be promoted by both cold rolling and thermal cycling in Ti-rich TiNi alloys due to introduced dislocations depressing the Ms temperature The strengthening effects of cold rolling and thermal cycling on the Ms temperature of Ti-rich TiNi alloys are found to follow the expression Ms = To — KΔσ y The K values are affected by different strengthening processes and related to the as-annealed transformation temperatures The higher the as-annealed Ms (or As ), the larger the K value

Ultrasonic attenuation of tellurite glasses

Abstract: Investigations are reported of the longitudinal ultrasonic attenuation in tellurite glasses containing molybdenum oxide of different concentrations by using the pulse echo technique at 2, 4, 6 and 10 MHz in the temperature range 120–300 K. The results showed the presence of a very well defined peak which shifts to higher temperature with increasing frequency, suggesting a kind of relaxation process. Activation energies and relaxation frequencies were calculated; the activation energy was found to increase from 0.11 to 0.139 eV with the increase of molybdenum oxide from 20 to 50 mol.%.

Elastic constants of semiconducting tellurite glasses

Abstract: The velocity of longitudinal and transverse ultrasonic waves in four different compositions of (MoO3)x (TeO2)1−x glass system (x = 0.2, 0.3, 0.45, 0.5) have been measured at room temperature using the pulse echo technique. The velocity data have been used to determine the elastic moduli, Debye temperature and Poisson's ratio for each composition. The results indicate that the elastic moduli depend upon the composition of the prepared glass.

A study of site occupation of eu3+ in me2y8(sio4)6o2 (me=mg, ca, sr)

Abstract: Alkaline earth (Mg, Ca, Sr) yttrium silicate oxyapatites doped with Eu 3+ show red luminescence with comparable intensity. In this system of phosphors, the Eu 3+ ions enter 4f sites and 6h sites simultaneously according to the fluorescence spectra, in which two 5 D 0 - 7 F 0 lines of Eu 3+ are observed. The assignment of 5 D 0 - 7 F 0 lines from Eu 3+ (4f) and Eu 3+ (6h), as well as their different properties has been discussed in the context.

Electrodeposition of aluminum in molten AlCl3-n-butylpyridinium chloride electrolyte

Abstract: Electrodeposition of aluminum was carried out by DC constant current and pulse current methods in the molten salt system AlCl 3 -BPC at 30 °C. The aluminum was unable to deposit from a basic AlCl 3 -BPC melt, whereas it could deposit from an acidic melt. The influence of electrodeposition conditions and the morphology of the layers were investigated by X-ray diffraction and scanning electron microscopy, respectively. The properties of electrodeposited layers varied with the electrolysis time, the current form, the electrolyte composition and the current density. The current density increased and smaller particle size and better adhesiveness of the electrodeposited layer were realized by pulse current compared to direct current.

Luminescence and nonlinear optical properties of perovskite-like niobates and titanates

Abstract: The luminescence and nonlinear optical properties of perovskite-like niobates and titanates are reported and discussed in relation with other perovskite-like compounds. It is found that the nonlinear optical properties of these compounds can be predicted rather reliably by considering both the structure and the luminescence properties.

Advanced metallization schemes for bonding of InP-based laser devices to CVD-diamond heatsinks

Abstract: Semiconductor devices, and in particular InP-based laser devices, are usually bonded on a mounting plate (called a submount or heatsink) or directly onto a package. This bonding assembly, which comprises the die-bonding metallic layers, the joint solder and the submount, serves the purpose of heat dissipator, mechanical support and electrical conductor. As such, the quality of both the bonding metallization and the submount are as important as the device die itself to assure the short- and long-term reliable operation of the electronic assembly. Due to its high thermal conductivity, diamond has been used as a very efficient thermal conductor and dissipator under electronic and photonic devices. This application has become even more attractive since the commercialization of the chemically vapor-deposited (CVD)-diamond, due to its lower cost and larger available surface area compared to natural diamond. Therefore it is only natural to use CVD-diamond as the material of choice for mass production of high-power InP-based laser diode submounts. The device is attached to the submount by a metallic bonding medium that contains a few layers, such as an adhesion layer (typically of titanium (Ti) adjacent to the submount), a barrier layer (typically of platinum (Pt)) and capped with hard solder (such as gold-tin (AuSn) eutectic alloy, which has a melting temperature of 278 °C). While offering optimum bonding conditions, the Ti/Pt/AuSn bonding system provides a high quality bond of the laser diode to the CVD-diamond submount. However, the extensive reaction of the AuSn solder with the Pt and Ti layers, even after short bonding periods of 5–10 s, may lead to mechanical deterioration of the bonded assembly, resulting in delamination of the metal and failure of the bond. This failure occurs mainly due to the thermodynamically reactive nature of the Pt-Sn couple, which reacts almost spontaneously even at room temperature. The reaction consumes the Pt layer and an appreciable amount of Sn, leading to the disappearance of the barrier layer and to dilution of Sn from the solder. The variation in the molten solder stoichiometry results in premature solidification of the solder through the bonding cycle after consumption of the entire Pt barrier layer, and dissolution of the Ti adhesion layer, as well. In order to maintain the good wetting performance of the AuSn solder to the Ti/Pt metals, but yet to improve the thermodynamic stability of the metallurgical bonding system, various other metals such as Ni, W, Cr and some of their alloys were evaluated as advanced alternatives to the Pt barrier layer. The quality of the evaluated metallurgical systems was judged upon wetting performance, thermodynamic stability and lack of premature freezing of the molten solder. The Ti/W/W(Ni 3 Sn 4 )/Ni 3 Sn 4 /Au multilayered structure was finally defined as the optimal and superior metallurgical scheme for the purpose of bonding laser chip to CVD-diamond submount. The time required until the first surface local freezing phenomenon was observed at the AuSn solder (with eutectic composition of 80 wt.% Au) on Ti/W/W(Ni 3 Sn 4 )/Ni 3 Sn 4 /Au structure while melted at 320 °C was 200 s, compared to 5–10 s at the Ti/Pt/Au/AuSn system. At the former system the solder was maintained melted at 320 °C for more than 1 h before it was completely frozen, which is much longer than the 30 s measured for the latter system. It was also observed that not only did the AuSn solder on the Ti/W/W(Ni 3 Sn 4 )/Ni 3 Sn 4 multilayer maintain its accurate stoichiometric composition through the entire bonding cycle, but it also provided excellent adhesion and integrity for the entire bonded assembly.

Synthesis of YAG:Cr phosphors by precipitation from aluminum and yttrium sulfate solutions

Abstract: Luminescent chromium doped yttrium aluminum garnet (YAG:Cr) powders were prepared using yttrium and aluminum (hydrous) oxide precursor particles produced by precipitation from aqueous sulfate solutions in urea. The rate of precipitation of yttrium hydrous oxide particles was observed to be slower than that of the aluminum hydrous oxide particles in the two component solution (yttrium plus aluminum sulfate). However, as single components the yttrium hydroxide nucleation occurred at a faster rate. The pH of the single aluminum and yttrium sulfate solution must be ≥ 2.9 and ≥ 5.5, respectively for precipitation to occur. Precipitation in a two component mixture is controlled by the acidic aluminum sulfate solution and homogeneous co-precipitation was not achieved. We have sped up the reaction by seeding a yttrium sulfate solution with aluminum hydroxide particles to promote rapid heterogenous nucleation of yttrium hydrous oxide. Heat treatment of the resulting precursor powders to 1200°C yielded YAG powders with some unreacted alumina and yttria.

XPS study on O(1s) and Fe(2p) for nanocrystalline composite oxide LaFeO3 with the perovskite structure

Abstract: The changes of the chemisorbed oxygen on the interface and surface of grains and the lattice oxygen in the bulk phase have been examined by the comparison of O(1s) spectra of several uncompacted and compacted materials LaFeO 3 under the static pressures of 0.5, 1.0 and 1.5 GPa at ambient temperature. The results indicate that the amount of the chemisorbed oxygen increases with the reduction in grain sizes, and it also changes with compacting pressures. When the diameters of grains reduce to be less than 15 nm, the ratio of the chemisorbed oxygen to lattice oxygen increases dramatically. It was found that the compacting pressures also make Fe(2p) spectra change, and there are pseudozero valent iron atoms in nanocrystalline LaFeO 3 . These results reflect the differences between nanocrystalline and conventional-crystal materials.

Sol-gel derived anatase TiO2: morphology and photoactivity

Abstract: High-surface area TiO 2 (anatase) was prepared by the sol-gel method and characterized by various instrumental and analytical methods, including X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, porosimetry, specific surface area measurements, scanning electron microscopy, and titration of surface hydroxyl groups. The specimen was tested for photodegradation of phenol and nitrophenols carried out in aqueous suspension at pH = 3; photoactivity was compared with that of commercially available anatase TiO 2 . Results are discussed in terms of porosity, surface area, and availability and population of surface OH groups, consequent upon the particular method used for preparation. The observed partial deactivation in time of gel-derived anatase was studied, and almost complete restoration of photoactivity after thermal treatment at 573 K for 3 hours was observed.

Synthesis and dielectric properties of lead magnesium niobate a review

Abstract: Lead-based relaxors are technologically important materials for multilayer ceramic capacitors and electro-optic devices. Typical of relaxor materials is lead magnesium niobate (PMN), which shows excellent dielectric properties. The commercial production of these materials, however, has suffered owing to the nonreproducibility that arises from evaporation of lead oxide during synthesis. This paper reviews the methods attempted for the fabrication of single-phase PMN. The salient features of these processes, with their chemical reactions, advantages and limitations, are described in the first section of this review. The second part of the article summarizes the factors that influence the dielectric properties. The article concludes with a brief discussion of the promising methods for large-scale production of PMN with acceptable dielectric behaviour.

Bioactive glass-ceramic: formation, characterization and bioactivity

Abstract: A new bioactive glass-ceramic with the nominal composition CaO (54.5), MgO (6.0), SiO2 (32.8), P2O5 (6.1) and CaF2 (0.6) (in wt.%) has been developed. Crystalline phases, termed akermanite, wollastonite and apatite, were found to precipitate simultaneously at temperatures between 930 and 1150 °C. No cracks appear in the glassceramic after crystallization. This new type of glass-ceramic demonstrates a flexural strength of 233 MPa and a fracture toughness of 2.95 MPa m 1 2 , which are higher than those of dense hydroxyapatite and other well-known bioactive materials. The glass-ceramic exhibits a high bioactivity in vitro. The occurrence and recombination of surface cracks in the material can be observed when it is immersed in a simulated bodily fluid (SBF) for sufficient periods, and this can be explained in terms of a self-healing mechanism. The mechanism of apatite formation onto the surface of the glass-ceramic is discussed.

Spectrothermal studies on the decomposition course of cobalt oxysalts Part II. Cobalt nitrate hexahydrate

Abstract: The thermal decomposition of cobalt oxalate dihydrate was thoroughly investigated in dynamic air or nitrogen. Thermal events occurring throughout the decomposition range (room temperature to 600 °C) were monitored by means of thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). These events were characterized on the bases of physicochemical analyses using X-ray diffractometry (XRD), infrared spectroscopy (IR) and scanning electron microscopy (SEM). Non-isothermal kinetic and thermodynamic parameters ( A , k , ΔE , ΔH , C p and ΔS ) were determined. The results obtained showed that the oxalate dehydrates in dynamic nitrogen atmosphere at slightly lower temperature (150 °C) than in air (160 °C), while the decomposition commenced at higher temperature in nitrogen (350 °C) than in air (270 °C). The product of decomposition in air was found to be Co 3 O 4 while in nitrogen, metallic cobalt was the final product. The decomposition process in nitrogen was endothermic in nature, while in air it occurred exothermically, which was attributed to an oxidative decomposition process involving atmospheric oxygen.

Wetting behavior between solder and electroless nickel deposits

Abstract: The present study investigated contact angles between electroless nickel deposits and 95Pb 5Sn and 63Sn 37Pb solders under vacuum. The contact angles generally decrease with respect to temperature rise and lowering in P contents of the deposit. Annealing on the electroless nickel deposits tended to enhance the wetability of the solder on the deposits. The variation in contact angle is accompanied by the formation of the intermetallic compounds Ni3Sn2 and Ni3Sn4 between solder and the electroless nickel deposits.

Dielectric constant dependence of Poole-Frenkel potential in tantalum oxide thin films

Abstract: A change of more than five orders of magnitude of leakage current density has been observed in tantalum oxide films with a dielectric constant ranging from 20 to 45. The films were deposited by a simple DC reactive sputtering technique. The measured leakage current density dependence on the film's dielectric constant can be explained by the Poole-Frenkel potential barrier model in which the barrier height is inversely proportional to the dielectric constant of the material. This intrinsic dielectric constant dependence of the trap barrier may give a limit on the lowest leakage current density that one can obtain in a high dielectric constant film.

Synthesis and structural characterization of nanocrystalline aluminium oxide

Abstract: Nanocrystalline alumina (Al 2 O 3 ) powder has been synthesized by the d.c. arc plasma method at atmospheric conditions using aluminium electrodes. Structural characterization by X-ray diffraction and transmission electron microscopy confirmed the ultrafine nature of the particulates. Investigation of the size distribution revealed a long-normal behaviour of the nanoparticles. Chemical analysis of the particulates was carried out using X-ray photoemission spectroscopy. The Al 2p core level spectrum revealed the presence of unreacted Al 0 , in addition to Al 3+ , suggesting a core of Al 0 surrounded by a layer of Al 2 O 3 as the particle structure.

Preparation of fine LaNiO3 powder from oxalate precursors via reactions in inverse microemulsions

Abstract: The inverse microemulsion technique has successfully been used to synthesize lanthanum and nickel oxalate particles, which could readily be processed to form a fine LaNiO 3 powder. Under appropriate conditions, the metal oxalate coprecipitates were microhomogeneously mixed in the form of spherical particles about 20 nm in diameter. When these coprecipitated lanthanum and nickel oxalate particles were clacined at 800 °C for 20 h, fine LaNiO 3 powder was obtained. This powder was found to have the formula LaNiO 2.82–2.90 .

Dielectric, thermal and pyroelectric properties of ferroelectric bismuth vanadate single crystals

Abstract: Single crystals of $Bi_2V0_{5.5}$ (BiV) which is n = 1 member of Aurivillius family of oxides, have been grown by slowly cooling the melts of the prereacted compound. The dielectric, pyroelectric and ferroelectric properties have been studied along the c - axis as a function of temperature of the first time. The ferroelectric Curie temperature (720 K) of these single crystals is confirmed by dielectric, pyroelectric, specific heat and hysteresis loop studies. The dielectric and specific heat data obtained well beyond 720 K confirm that BiV undergoes yet another crystallographic transition at 827 K. The pyroelectric figures of merit from the point of view of different applications have been calculated at 300 K by combining pyroelectric, dielectric and thermal properties.

Preparation of nepheline glass-ceramics and their application as dental porcelain

Abstract: The batch of starting glass was prepared from analytical-grade reagents. Crystallization of the nepheline glass system was investigated using differential thermal analysis, X-ray diffraction, transmission and scanning electron microscopy. The major crystalline phase was found to be nepheline, Na 2 O · A1 2 O 3 · 2SiO 2 . The Vickers microhardness of these materials is 640–660 MPa, and the thermal expansion coefficients are 12.1–16.6 × 10 −6 K −1 from 298 to 773 K. The nepheline glass-ceramic powders were coated on a NiCr alloy pattern. It was found that the failures of the composites usually occurred at the interface between the alloy and opaque layer.

Studies of physicochemical and surface properties of alumina modified with rare-earth oxides. I: Preparation, structure and thermal stability

Abstract: The effects of the kind and amount of certain lanthanide oxides (Ln = La, Ce, Pr, Nd and Sm) on the structure and thermal stability of transition aluminas have been investigated. Lanthanide oxide addition has been found to retard the transformation of γ-Al 2 O 3 to α-Al 2 O 3 and the associated sintering. The presence of lanthanide aluminate with the perovskite-type structure is responsible for the thermal stabilization of transition alumina.

The influence of Bi2O3 non-stoichiometry on the non-linear property of ZnO varistors

Abstract: Proper choice of the starting compounds for the additive oxides enhances the non-linearity coefficient $(\alpha)$ to 40-60. High or-values can be achieved by using $Bi_2O_3$ containing $Bi^{5+}$ and consequently higher oxygen content. $Bi_20_3$ prepared by various low temperature chemical routes are more effective in increasing the a values. Ceramics formulated from ZnO + oxygen - excess $Bi_20_3$ have $\alpha$ = 6 to 14, whereas in presence of the transition metal oxides, the same fomulations exhibit $\alpha$-values up to 60, with the sharp turn-on point on the current-voltage curves. The oxygen-excess behaviour of $Bi_20_3$ is related to its defect-fluorite structure, with the excess oxygen located at the vacant tetrahedral voids and are charge com- pensated by $Bi^{5+}$ ions. This is supported by X-ray diffraction, opticaf reflectance spectra and electron paramagnetic resonance data. The depletion layer is formed at the pre-sintering stage as a result of electron trapping by oxygen evolved from the additives being chemisorbed on ZnO particles. The depletion layer is stabilized on either sides of the grain boundary by the higher talent transition metal ions that are preserved through charge compensation by cation vacancies, after the sintering.

Nonstoichiometry-activity relationship in perovskite-like manganites

Abstract: High surface area LaMnO3+δ and La1−xBaxMnO3+δ catalysts were prepared through decomposition of citrate precursors. Thermogravimetric analyses of lanthanum manganite revealed the existence of a reversible non-stoichiometry dependent on thermal treatment conditions. When heated in air, a portion of the Mn4+ manganese cations underwent a reduction to Mn3+. During cooling reoxidation occurred, with the final Mn 3+ Mn 4+ ratio dependent on the cooling rate. Electrical conductivity measurements suggest that this ratio is close to unity for a cooling rate of 20 °C h−1. We have found that varying the cooling rate did not modify this ratio by more than 10%. The catalytic activity for the total oxidation of carbon monoxide was found to be independent of such a small variation in Mn 3+ Mn 4+ ratio. To obtain a large change in this ratio, barium was substituted for lanthanum. Reoxidation during cooling could only be observed for lower amounts of barium (x 0.5. Lastly, the catalytic activity was shown to vary with barium content, reaching a maximum for 0.2

Channeling implants in silicon crystals

Abstract: Boron and phosphorus channeling implants in silicon at medium and high energies are reviewed. A wide range of doses has been investigated from low doses (1012/cm2), where the radiation damage can be neglected, to high doses (1015/cm2) where the damage influences the depth distribution. At low doses the profile results from the superimposition of the channeled and of the random component. So the maximum penetration of the channeled particles along the different channels can be easily experimentally determined. The maximum penetration of ions and the extracted electronic stopping are reported for [100], [110] axial channeling and for implants in thick amorphous Si targets. Increasing the dose a third component is necessary to describe the dopant profile. This contribution is related to the fraction of dechanneled particles that depends on the number of displaced silicon atoms. In this case the profiles can be determined as a convolution of three gaussian curves. Channeling tails are present also for implants performed in a random equivalent direction. These tails can be reduced but cannot be avoided. Monte Carlo simulations, based on a simple treatment of the electronic energy loss within different channels, describe quite well the profiles at low doses. The lateral spread of channeled implants under the mask is quite small also at relatively high doses. This lateral spread has been studied by means of two dimensional spreading resistance and a comparison with random implant is presented. In channeling implants the radiation damage is also reduced and the amount of extended defects generated after thermal annealing is reduced too. All these effects are presented and discussed.

Hydrogen transport in ferritic stainless steel under elastic stress

Abstract: An electrochemical technique was used to study the effects of elastic stress on hydrogen permeation in AL 29-4-2 ferritic stainless steel. Tensile stress increased the permeability. The change in diffusivity induced by the stress was relatively inconsistent, but the activation energy consistently increased. The average partial molar volume of hydrogen deduced from the increased hydrogen flux at 40–60° C was 2.3 cm3 mol−1.

The structural effect on the kinetics of acid leaching refining of Fe-Si alloys

Abstract: The kinetics of refinement of Fe-Si alloys by acid leaching is affected by their structural state. Two different phase constitutions were studied to access this effect: an industrial alloy with a low Al Ca ratio and a laboratory-prepared alloy with a high Al content. The first contains silicon, FeSi 2 (tet.), FeSi 2 (orth.), beyond a quaternary phase Fe-Al-Si-Ca (Caalsifer), CaAi 2 Si 1.5 , CaSi 2 , Al-Fe-Si as minor phases. The precipitation of Al-Fe-Si phases is induced in the second by the high Al Ca ratio. In a previous study, leaching experiments by a two-step procedure have shown that Ca-Al-Si, Caalsifer and Al-Fe-Si phases are more soluble. The Cracking Shrinking Model (CSM) was applied to explain the behaviour of the industrial alloy. In the present study, it is shown that the same model applies to the kinetics of dissolution of the laboratory-prepared alloy and also, that an adequate control of Fe Al vs. Si Ca ratios may improve the attainable refining yield.

Nucleation in the pre-coalescence stages: universal kinetic laws

Abstract: This article is devoted to a detailed summary of recent results on the dynamic scaling of the cluster size distribution (CSD) and other universal kinetic laws in the pre-coalescence stages of nucleation and growth. A comprehensive presentation is given to the systematic approaches developed for elucidating the dynamic evolution of the CSD for sizes within the nucleation barrier layer (NBL) and beyond. In the pre-coalescence stages of nucleation and before the complete depletion of the monomer, the CSD for sizes within and beyond the NBL obey dynamic scaling relations. The dynamic scaling relations and their asymptotic limits are invariant to the size dependence of the cluster formation energy. For sizes beyond the NBL, the scaling relation of the CSD exhibits an asymptotic universal power law, the exponent of which depends only on the interphase interfacial atom transport mechanism. Comparison with limited available experimental data for sizes beyond the NBL confirms the predictions. The physical reasons behind the universal kinetic laws in the pre-coalescence stages of nucleation are outlined. The universal kinetic laws open a doorway to the systematic study of nucleation in condensed materials by providing a genera] novel foundation to guide the design of nucleation experiments and to elucidate fundamental mechanisms based on macroscopic observations of the cluster size distribution in the pre-coalescence stages of nucleation and growth.