Amorphous and crystalline oxides on aluminium

In order to study the transition from amorphous to crystalline aluminium oxides, high purity aluminium was oxidized in dried oxygen of atmospheric pressure at 673 and 913 K. The morphology of the oxide layers produced was investigated by optical microscopy methods (phase and interference contrast) and scanning and transmission electron microscopy. The crystallinity was determined using electron (micro)diffraction methods. The existence of a hitherto undescribed transition aluminium oxide was established. Interface coarsening resulting from the formation of “tops” and “depressions” or “dimples”, as consequences of vacancy creation and injection in the substrate surface layers, was quantified by Auger depth profiling. The X-ray photoelectron spectroscopy technique revealed differences in the coordination of the aluminium cation between the amorphous and crystalline oxides.     

Crystallization behavior of Ge-doped eutectic Sb70Te30 films in optical disks

We report laser-induced crystallization behavior of binary Sb-Te and ternary Ge-doped eutectic Sb70Te30 thin film samples in a typical quadrilayer stack as used in phase-change optical disk data storage. Several experiments have been conducted on a two-laser static tester in which one laser operating in pulse mode writes crystalline marks on amorphous film or amorphous marks on crystalline film, while the second laser operating at low-power cw mode simultaneously monitors the progress of the crystalline or amorphous mark formation in real time in terms of the reflectivity variation. The results of this study show that the crystallization kinetics of this class of film is strongly growth dominant, which is significantly different from the crystallization kinetics of stochiometric Ge-Sb-Te compositions. In Sb-Te and Ge-doped eutectic Sb70Te30 thin-film samples, the crystallization behavior of the two forms of amorphous states, namely, as-deposited amorphous state and melt-quenched amorphous state, remains approximately same. We have also presented experiments showing the effect of the variation of the Sb/Te ratio and Ge doping on the crystallization behavior of these films.     

Rapid solidification of zirconium-based alloys

Zr based metal-metal binary and ternary alloys can be obtained in the amorphous state in very wide composition ranges. Several eutectic reactions and intermetallic compounds are present in these alloy systems which provide opportunities for examining the validity of different theories on glass formation. The amorphous phases in these alloys decompose by a variety of crystallization mechanisms. Instances of polymorphic, primary and eutectic crystallization have been encountered in these glasses. Zr-based metallic glasses possess excellent corrosion resistance and mechanical properties. In several studies their properties have been compared with that of their crystalline counterparts and interesting differences have emerged. In the solute lean Zr-based alloys very large freezing ranges are available for studying the liquid to solid transformation. It has been possible to study the formation of some of the low temperature phases directly from the liquid. This paper describes some of the aforementationed studies carried out on Zr-based amorphous and crystalline alloys.     

Transmission electron microscopy study on the growth of zinc oxide crystals under hydrothermal conditions

ZnO crystals were grown in the presence of ZnO nanorod seeds under hydrothermal conditions while the same location on the ZnO nanorod was repeatedly observed by transmission electron microscopy. The surface of the ZnO seed crystal was covered with an amorphous layer during the early stages of crystallization (0.5-1.5 h). This amorphous layer was subsequently transformed into nanocrystals after 3.0 h. Finally, after 5.0 h, ZnO seeds suddenly grew preferentially in the [001] direction. These results suggest that the formation process of an amorphous ZnO layer on the surface of the seed crystals and its subsequent crystallization plays an important role in the induction of further crystal growth of ZnO nanorods.     

Al-Zn-Ce非晶合金的相选择与组织结构演化

本文研究了具有典型分解特征的Al-Zn-Ce非晶合金的形成和晶化过程，探讨了各种相的生成顺序。XRD和DSC测试结果表明强烈的化合物短程序有利于Al-Zn-Ce非晶合金的形成。在Al-Zn-Ce非晶合金的晶化过程中存在复杂的相选择行为，多种相的竞争形核和有限生长使其具有复杂的结构特点。同时，结果也表明冷速对该体系非晶的形成有很大影响。     

Behavior of GeSbTeBi phase-change optical recording media under subnanosecond pulsed laser irradiation

We investigated the variations in reflectivity during the phase transition between amorphous and crystalline states of a Bi-doped GeTe-Sb2Te3 pseudobinary compound film with subnanosecond laser pulses, using a pump-and-probe technique. We also used a two-laser static tester to estimate the onset time of crystallization under 2.0-micros pulse excitation. Experimental results indicate that the formation of a melt-quenched amorphous mark is completed in approximately 1 ns, but that crystalline mark formation on an as-deposited amorphous region requires several hundred nanoseconds. Simple arguments based on heat diffusion are used to explain the time scale of amorphization and the threshold for creation of a burned-out hole in the phase-change film.     

Untersuchung von Schmelz‐ und Rekristallisationsprozessen sowie Riss‐, Oxid‐ und Porenbildung beim Schweißen

Investigation of melting and re‐crystallization processes and of crack, oxide and pore formation during welding In the paper some known investigation methods of the primary re‐crystallization and of the structure of the crystallization front are discussed. All these methods have disadvantages, in some cases they cause a limited validity or are expensive. The presented new method is based on the micrographic recording of the melting and solidifying metal surfaces. The method overcomes the above‐mentioned disadvantages. It is able to investigate in the welding seams not only the primary re‐crystallization processes but also the secondary ones including the formation of cracks and pores and the appearance of non‐metallic inclusions like oxides. The facilities of the method are demonstrated on some examples of use.     

沉淀剂对La_2Zr_2O_7制备过程的影响

分别采用氨水和草酸铵作沉淀剂,通过化学共沉淀法制备了单相La2Zr2O7粉末。利用DSC-TGA和XRD等方法对LZ前驱体的煅烧分解过程、产物物相进行了分析和表征。结果表明:氢氧化物前驱体在400~750°C分解得到无定型的复合氧化物,800℃保温2.5h即完成相转变形成单相组分的La2Zr2O7;而草酸盐前驱体在400~650°C草酸盐发生分解得到无定型氧化镧、氧化锆的混合物;700°C以后,La(OH)3的分解、无定型氧化物晶化得到六方结构氧化镧与单斜相氧化锆、Zr4+扩散到La2O3晶界生成La2Zr2O7等三个反应同时进行。获得单相组分La2Zr2O7的煅烧条件至少要1450℃,保温2.5h。草酸盐前驱体中镧和锆两种成分局部的分布不均匀是造成其处理温度比氨水法要高的直接原因。     

机械合金化法制备Co-Zr非晶软磁合金粉末的研究

研究了Co-Zr二元相图上4个共晶点成分配方Co90Zr10、Co53Zr47、Co35Zr65和Co21Zr79在球磨条件下的非晶态合金形成能力。分析结果表明,4种配方在一定的球磨时间内都能形成非晶态合金,其中非晶形成能力最强的为Co35Zr65。球磨时间对非晶的形成有重要影响,球磨时间过长,使形成的非晶态合金粉体反而向晶体转化。     

Formation of amorphous and nanocrystalline phases in high velocity oxy-fuel thermally sprayed a Fe–Cr–Si–B–Mn alloy

High velocity oxy-fuel (HVOF) thermal spray was used to deposit a Fe–Cr–Si–B alloy coating onto stainless steel (1Cr18Ni9Ti) substrate. Microstructures of the powder and the coating were investigated by X-ray diffraction (XRD), scanning election microscopy (SEM), transmission election microscopy (TEM) and differential scanning calorimeter (DSC). The coating had layered morphologies due to the deposition and solidification of successive molten or half-molten splats. The microstructures of the coating consisted of a Fe–Cr-rich matrix and several kinds of borides. The Fe–Cr-rich matrix contained both amorphous phase and nanocrystalline grains with a size of 10–50 nm. The crystallization temperature of the amorphous phase was about 605 °C. The formation of the amorphous phase was attributed to the high cooling rates of molten droplets and the proper powder compositions by effective addition of Cr, Mn, Si and B. The nanocrystalline grains could result from crystallization in amorphous region or interface of the amorphous phase and borides by homogeneous and heterogeneous nucleation.     

Isothermal and Dynamic Microcalorimetry for Quantifying the Crystallization of an Amorphous Drug during Interactive Powder Mixing

ABSTRACT

This study reports the crystallization of amorphous nifedipine during an interactive mixing process quantified by using isothermal and dynamic microcalorimetry. Interactive mixtures of amorphous nifedipine and uniform glass beads were prepared by mixing in a Turbula® mixer. The difference in the extent of crystallization of amorphous nifedipine during mixing was characterized by the time it took for the crystallization of a known amount of amorphous nifedipine in isothermal calorimetry and the change in the height of the crystallization peak at 65°C in dynamic calorimetry. It was found that both isothermal and dynamic microcalorimetry are useful techniques for quantifying the physical transition of amorphous nifedipine during interactive mixing. The rate and extent of crystallization of amorphous nifedipine depended on both mixing time and speed, but mixing time played a more dominant role because the transformation of amorphous to crystalline nifedipine was greater after 3180 revolutions (9.7%) than after 405 revolutions (0.9%) at 27 rpm. The same trend was observed at 109 rpm, but the percentage of crystalline nifedipine after 3180 revolutions was only 5.2%. This meant that an increase in mixing time rather than speed increased the rate of amorphous to crystalline transformation. The greatest cause for crystal transformation during interactive mixing was the presence of crystal seeds of the thermodynamically stable nifedipine Modification I because the amount of amorphous to crystalline transformation increased from 2.6% for a completely amorphous mixture to 6.6% for a 92:8 mixture of amorphous and crystalline nifedipine when mixed for 30 minutes at 106 rpm.     

Properties of anodic oxides grown on a hafnium–tantalum–titanium thin film library

A ternary thin film combinatorial materials library of the valve metal system Hf–Ta–Ti obtained by co-sputtering was studied. The microstructural and crystallographic analysis of the obtained compositions revealed a crystalline and textured surface, with the exception of compositions with Ta concentration above 48 at.% which are amorphous and show a flat surface. Electrochemical anodization of the composition spread thin films was used for analysing the growth of the mixed surface oxides. Oxide formation factors, obtained from the potentiodynamic anodization curves, as well as the dielectric constants and electrical resistances, obtained from electrochemical impedance spectroscopy, were mapped along two dimensions of the library using a scanning droplet cell microscope. The semiconducting properties of the anodic oxides were mapped using Mott–Schottky analysis. The degree of oxide mixing was analysed qualitatively using x-ray photoelectron spectroscopy depth profiling. A quantitative analysis of the surface oxides was performed and correlated to the as-deposited metal thin film compositions. In the concurrent transport of the three metal cations during oxide growth a clear speed order of Ti > Hf > Ta was proven.     

Isothermal and Dynamic Microcalorimetry for Quantifying the Crystallization of an Amorphous Drug during Interactive Powder Mixing

This study reports the crystallization of amorphous nifedipine during an interactive mixing process quantified by using isothermal and dynamic microcalorimetry. Interactive mixtures of amorphous nifedipine and uniform glass beads were prepared by mixing in a Turbula® mixer. The difference in the extent of crystallization of amorphous nifedipine during mixing was characterized by the time it took for the crystallization of a known amount of amorphous nifedipine in isothermal calorimetry and the change in the height of the crystallization peak at 65°C in dynamic calorimetry. It was found that both isothermal and dynamic microcalorimetry are useful techniques for quantifying the physical transition of amorphous nifedipine during interactive mixing. The rate and extent of crystallization of amorphous nifedipine depended on both mixing time and speed, but mixing time played a more dominant role because the transformation of amorphous to crystalline nifedipine was greater after 3180 revolutions (9.7%) than after 405 revolutions (0.9%) at 27 rpm. The same trend was observed at 109 rpm, but the percentage of crystalline nifedipine after 3180 revolutions was only 5.2%. This meant that an increase in mixing time rather than speed increased the rate of amorphous to crystalline transformation. The greatest cause for crystal transformation during interactive mixing was the presence of crystal seeds of the thermodynamically stable nifedipine Modification I because the amount of amorphous to crystalline transformation increased from 2.6% for a completely amorphous mixture to 6.6% for a 92:8 mixture of amorphous and crystalline nifedipine when mixed for 30 minutes at 106 rpm.     

Laser pulse crystallization of Pd-Si metallic glasses

A novel method of laser pulse crystallization (LPC) capable of revealing and quantifying crystallization in amorphous ribbons is presented. It is used to study the morphology of crystallization and, indirectly, surface crystallization (SC) of Pd-Si amorphous alloys in the composition range Pd₇₇Si₂₃-Pd₈₅Si₁₅. The laser-induced, frozen-in fronts of crystallization are studied by optical metallography and X-ray diffraction. The shapes of these fronts are determined by the initial degree of SC, which depends on alloy compositions, their thermal history and/or the surface of the ribbon being analysed. SC is inactive in alloys of eutectic composition (Pd₈₅Si₁₅) and is most pronounced for compositions near the border to the amorphous region on the silicon-rich side (Pd₇₇Si₂₃). For as-quenched ribbons, a stronger tendency to SC exists on the shiny surface of the ribbon. Low-temperature furnace annealing as well as room temperature ageing over a period of 2 years equalizes the degree of SC on both surfaces. The X-ray diffraction patterns taken from the regions containing frozen-in fronts of crystallization only reveal the presence of metastable phase II, independently of composition and/or thermal history of the given sample.     

Metal-induced crystallization of amorphous Si thin films assisted by atomic layer deposition of nickel oxide layers

Atomic layer deposition (ALD) of nickel oxide was applied to the nickel-induced crystallization of amorphous Si thin films. The nickel-induced crystallization was monitored as a function of annealing temperature and time using Raman spectroscopy. Since Raman spectroscopy allows for the numerical quantification of structural components, the incubation time and the crystallization rates were estimated as functions of the annealing temperature. The spatial locations of a nickel-based species, probably NiSi2, were investigated using X-ray photoelectron spectrometry. The formed NiSi2 seeds appeared to accelerate the crystallization kinetics in amorphous Si thin films deposited onto glass substrates. The ramifications of the atomic layer deposition are discussed with regard to large-panel displays, with special emphasis on the sophisticated control of the catalytic elements, especially nickel.     

Formation of amorphous anodic oxide films of controlled composition on aluminium alloys

Binary, non-equilibrium Al-29at%Nb, Al-44at%Ta, Al-19at%Ti, Al-25at%Ti and Al-32at%Zr alloys were prepared by magnetron sputtering and subsequently anodized at high Faradaic efficiency to grow barrier-type anodic films. Examination in the transmission electron microscope revealed amorphous anodic films of relatively uniform compositions across the film thicknesses, except for a layer of relatively pure alumina, of about 5% of the film thickness, present at the film/electrolyte interface of the Al-Ta alloy. The film compositions, from Rutherford backscattering spectroscopy, indicate that the alloy constituents are oxidized in their alloy proportions to form films comprising intimately mixed units of the various oxides, namely alumina, niobia, titania, tantala and zirconia. The films grow by co-operative transport of metal and oxygen ions under the electric field with formation of film material by both migration of metal ions outwards and of oxygen, and possibly hydroxyl, ions inwards. The average migration rates of Al³⁺, Nb⁵⁺, Ti⁴⁺ and Zr⁴⁺ ions are similar, to within 10%, but Ta⁵⁺ ions migrate more slowly than Al³⁺ ions. The results of the study show that a wide range of compositions of amorphous oxide films can be readily formed by anodic oxidation of appropriate alloys, including compositions containing units of normally crystalline anodic oxides, namely TiO₂ and ZrO₂.     

Thermal destruction of polymer-salt compositions containingd-metals in the form of oxygen-bearing anions

The behavior of polymer-salt compositions consisting of water-soluble nonionogenic polymers and salts containingd-metal-oxygen anions was studied in the range 20-700°C by thermal analysis, conductometry, optical microscopy, x-ray diffraction, and dilatometry. The salts used were ammonium heptamolybdate, ammonium B-paratungstate, and ammonium metavanActate and the polymers were poly(vinyl alcohol), polyvinylpyrrolidone, and methyl cellulose. The films prepared by drying the precursor compositions were found to retain, during heating, the polymer-salt molecular complexes formed at room temperature. The mechanism of the thermal destruction of the salts in the polymer-salt films was shown to differ from that in pure salts because, in the films, mutual stabilization of the polymer and salt took place. In the polymer-salt compositions, oxides were formed directly from amorphous precursors, without formation of intermediates, characteristic of the decomposition of pure salts. The oxides thus prepared consisted of fine particles and exhibited photochromic effect due to partial reduction of metal ions.     

Investigation of the crystallization of amorphous Si by imaging ellipsometry

We report results on a study of the formation of polycrystalline Si by thermally annealing amorphous Si films. The crystallization of amorphous Si is of increasing interest not only from a basic-physics point of view but also for its wide application in the semiconductor device area. The amorphous Si was deposited on a glass substrate coated with buffer layers and a small amount of Ni to stimulate crystallization. The process was followed with a spatial resolution of 3 microm using an imaging ellipsometer. Imaging ellipsometry constructs sample images from the differences in dielectric functions in different regions. In particular, we can easily detect the polycrystalline Si domains in an amorphous matrix. Results are shown as three-dimensional plots. These are then analyzed to show that the interfaces between domains are not abrupt, and that crystallization within the polycrystalline Si regions is not complete. The fundamental crystallization mechanism is the radial expansion of Ni-seeded needles, forming macroscopic disk-like domains.     

Amorphous nickel-iron oxides/carbon nanohybrids for an efficient and durable oxygen evolution reaction

Highly efficient and durable water oxidation electrocatalysts are critically important in a wide range of clean energy technologies,including water electrolyzers and rechargeable metal-air batteries.Here,we report a novel sonochemical approach to synthesize amorphous nickel-iron oxides/carbon nanohybrids with tunable compositions for the oxygen evolution reaction (OER).The sonochemically synthesized amorphous electrocatalysts with optimal composition exhibit a low overpotential of 290 mV at 10 mA·cm-2 and a Tafel slope of 31 mV·decade-1 in a 0.1 M KOH electrolyte,outperforming the benchmark RuO2 catalyst.Meanwhile,these nanohybrids are also highly stable and remain amorphous even after prolonged cycling.In addition to amorphism,sonochemistry endows as-prepared nickel-iron oxides/carbon nanohybrids with a simultaneously formed carbon scaffold and internal Ni(0),which can enhance the stability and activity for the OER.This work demonstrates that sonochemistry is a unique method for synthesizing amorphous metal oxides toward an efficient and durable OER.     

Phase separation in blends of oligo (caprolactone glycol)-based polyurethane with poly(vinyl chloride)

The structure of o!igo (caprolactone glycol)-based polyurethane-poly(vinyl chloride) (PVC) blends obtained from tetrahydrofuran solution was studied by X-ray diffraction and electron microscopy. The system is characterized by a oornp!ex phase diagram with two types of equilibria: (1) crystal-liquid equilibrium in the region of blend compositions up to 40 wt% PVC; (2) liquid-liquid equilibrium in the region of man compositions. The crystallization kinetics of oligo(caprolactone) polyurethane blocks from an initially compatible amorphous blend was investigated. Small-angle X-ray cattering (SAXS) studies provide evidence that the amorphous component (PVC) is incorporated in the interlamellar crystalline regions of the compositions. The amorphous blends are characterized by the presence of modulated structures at two scale levels, this being explained as e result of the process in which the bulk samples were obtained from a three-component polymer-polymer-solvent system.