An experimental and theoretical study of the glass-forming region of the Mg-Cu-Sn system

The amorphization of Mg-Cu-Sn alloys with various compositions has been studied using the melt-spinning technique, with particular emphasis on the magnesium-rich corner of the ternary phase diagram. The results have been interpreted in terms of Miedema's theory, which highlights competition between the amorphous phase and crystalline solid solutions. Competition by ordered intermetallic compounds has also to be considered in order to explain the restricted amorphization region found in these experiments.CONICET career research worker.     

砷化镓单晶中微晶和非晶的形成机制

利用高分辨电子显微镜对0.0049N和0.049N荷载Vickers压痕锈发砷化镓单晶的相转变进行了观察和研究,结果表明,在大小压痕作用下分别发生了单晶向和微晶的转变,微晶的结构由小于10nm,取向各异的纳米晶和非晶组成,在完全非晶化的结构中存在少量由几个原子组成的原子簇,在非晶和晶体的交界区能观察到许多晶体缺陷以及沿这些缺陷产生的晶格扭曲和非晶相岛,对这种非晶化现象提出了两种可能的诱发机制,高压力诱导非晶化和剪切诱导非晶化。     

Formulation of tablets containing an ‘in-process’ amorphized active pharmaceutical ingredient

The aim of this work was a preliminary study of the “in-process” amorphization of clopidogrel hydrogensulfate (CLP) as model drug during the production of tablets as dosage form. A solvent method was used for amorphization and the crystalline phase of CLP was detected by differential scanning calorimetry; the physical parameters of fresh and stored tablets were investigated. For the amorphous form, Aerosil 200 was selected as crystallization inhibitor as the most suitable of eight auxiliary agents. The optimum composition of the product for amorphization in the scaling-up process (100-fold) was 7 parts of CLP to 3 parts of Aerosil 200. In this scaled-up product, the amorphous CLP was fixed on the surface of microcrystalline cellulose. The tablet form further stabilized the amorphous form. Finally, the steps of an “in-process” amorphization are given as a protocol, which can promote stabilization of an amorphized active pharmaceutical ingredient.     

Formulation of tablets containing an 'in-process' amorphized active pharmaceutical ingredient

The aim of this work was a preliminary study of the "in-process" amorphization of clopidogrel hydrogensulfate (CLP) as model drug during the production of tablets as dosage form. A solvent method was used for amorphization and the crystalline phase of CLP was detected by differential scanning calorimetry; the physical parameters of fresh and stored tablets were investigated. For the amorphous form, Aerosil 200 was selected as crystallization inhibitor as the most suitable of eight auxiliary agents. The optimum composition of the product for amorphization in the scaling-up process (100-fold) was 7 parts of CLP to 3 parts of Aerosil 200. In this scaled-up product, the amorphous CLP was fixed on the surface of microcrystalline cellulose. The tablet form further stabilized the amorphous form. Finally, the steps of an "in-process" amorphization are given as a protocol, which can promote stabilization of an amorphized active pharmaceutical ingredient.     

非晶化程度对不同成分Mg-Ni非晶合金电极充放电容量的影响

研究了球磨过程中的非晶化程度对不同成分Mg-Ni非晶合金电化学吸放氢性能的影响。研究结果表明,随着合金成分的不同,非晶化程度的影响不同。当Ni含量低于50％(原子分数)时,合金粉末中的非晶相所占比例越高,即非晶化程度越高时,合金电极的放电容量越大;而当Ni含量高于50％(原子分数)时,非晶合金中存在少量游离态的Ni相,可提高电极的放电量。分析认为这与Ni相的存在改善了合金的吸放氢动力学性能有关。     

Amorphous phase growth by isothermal annealing-induced interdiffusion reactions in mechanically deformed Ni/Ti multilayered composites

The growth of amorphous phase and the formation of competing intermetallic compounds in mechanically deformed Ni/Ti multilayered composites have been investigated by X-ray diffraction, scanning electron microscopy, transmission electron micrography, and magnetic measurement. Experimental observations in the Ni/Ti system have been performed, supporting a transient nucleation model for solid-state amorphization. The amorphous layers in the Ni/Ti multilayered composites continue to grow until they have attained a temperature-dependent critical thickness or a temperature-dependent critical annealing time. The relationships between the critical amorphous layer thickness and temperature, between the critical annealing time and temperature, and between the annealing conditions (temperature, time) and amorphization transformation, have been deduced and compared with the experimental results. The quantitative relationships can give a direction for the bulk amorphization in the Ni/Ti multilayered composites.     

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.     

Crystallization and amorphization studies of a Ge(2)Sb(2.3)Te(5) thin-film sample under pulsed laser irradiation

We present the results of crystallization and amorphization studies on a thin-film sample of Ge(2)Sb(2.3)Te(5), encapsulated in a quadrilayer stack as in the media of phase-change optical disk data storage. The study was conducted on a two-laser static tester in which one laser, operating in pulsed mode, writes either amorphous marks on a crystalline film or crystalline marks on an amorphous film. The second laser, operating at low power in the cw mode, simultaneously monitors the progress of mark formation in terms of the variations of reflectivity both during the write pulse and in the subsequent cooling period. In addition to investigating some of the expected features associated with crystallization and amorphization, we noted certain curious phenomena during the mark-formation process. For example, at low-power pulsed illumination, which is insufficient to trigger the phase transition, there is a slight change in the reflectivity of the sample. This is believed to be caused by a reversible change in the complex refractive index of the Ge(2)Sb(2.3)Te(5) film in the course of heating above the ambient temperature. We also observed that the mark-formation process may continue for as long as 1 mus beyond the end of the write laser pulse. This effect is especially pronounced during amorphous mark formation under high-power, long-pulse illumination.     

Solid-state amorphization behaviour in Ni/Zr multilayers with oxygen contamination

The solid-state amorphization by the interdiffusion reaction in sputter-deposited Ni-Zr multilayer films with oxygen contamination has been investigated by differential scanning calorimetry and X-ray diffractometry. Through X-ray photoelectron spectroscopy analysis, it was found that the multilayer films were contaminated with oxygen during deposition in a low-vacuum system (10^–5 torr), and the concentration was modulated having the maximum in zirconium-rich regions. The kinetics of amorphization reactions has been examined by non-isothermal and isothermal annealing. Oxygen introduced into the sample during sample preparation and annealing treatments appears to affect the kinetics of the amorphization reaction associated with variation of the activation energy for interdiffusion in the amorphous layer and a critical thickness of the amorphous layer. The origins of abnormal behaviour in forming intermetallic compound as well as amorphous phase, are discussed in the context of the oxygen incorporation.     

干摩擦应变诱导板条马氏体固态非晶化的能量分析及其模型

使用定点离子束切割制样(FIB)并根据透射电镜(TEM)表征，分析了板条马氏体钢干摩擦层内部板条马氏体协调塑性变形、演变为纳米层片结构并发生非晶化的全过程。结果表明，高密度位错缠结和缺陷集中是纳米层片结构的典型特征，这种结构产生的界面在高应变驱动下发生非晶化。这些非晶产物，为进一步细化磨屑和形成表面自润滑层提供结构条件。基于上述实验结果并结合摩擦学和材料学理论建立了干摩擦过程中的非晶化形核模型，计算了发生非晶化的热力条件和能量壁垒。结果表明，根据经典形核理论和晶体向非晶转变的吉布斯自由能壁垒计算公式所建立的干摩擦非晶化形核能量模型，可用于计算发生非晶化必需的临界位错密度值。根据对应的计算结果，可控制摩擦条件用干摩擦应变诱导板条马氏体的固态非晶化。     

Investigation of crystallization and amorphization dynamics of phase-change thin films by subnanosecond laser pulses

We report experimental results on amorphization and crystallization dynamics of reversible phase-change (PC) thin-film samples, GeSbTe and GeBiTe, for optical disk data storage. The investigation was conducted with subnanosecond laser pulses using a pump-and-probe configuration. Amorphization of the crystalline films could be achieved with a single subnanosecond laser pulse; the amorphization dynamics follow closely the temperature kinetics induced in the irradiated spot. As for crystallization of the samples initially in the amorphous state, a single subnanosecond pulse was found to be insufficient to fully crystallize the irradiated spot, but we could crystallize the PC film (in the area under the focused spot) by applying multiple short pulses. Our multipulse studies reveal that the GeSbTe crystallization is dominated by the growth of nuclei whose initial formation is slow but, once formed, their subsequent growth (under a sequence of subnanosecond pulses) happens quickly. In the case of GeBiTe samples, the crystalline nuclei appear to be present in the material initially, as they grow immediately upon illumination with laser pulses. Whereas our amorphous GeSbTe samples required approximately 200 pulses for full crystallization, for the GeBiTe samples approximately 15 pulses sufficed.     

Increasing the dissolution rate of a low-solubility drug through a crystalline-amorphous transition: a case study with indomethacin [correction of indomethicin

The purpose of this research is to further the understanding of the crystalline to amorphous phase transition (amorphization) that occurs when some crystalline drugs are dry blended with porous adsorbents. Indomethacin (IMC) and three grades of silica gel (SGs) were used in the study. Amorphization of crystalline IMC occurs rapidly during dry mixing with SG and was independent of mixing intensity and time. Extent of amorphization increases with lower ratios of IMC:SG and with decreased IMC and SG particle size. Blocking H-bonding silanol groups on SG by chemical modification reduced the extent of amorphization. IMC-SG mixtures showed improved dissolution rates over crystalline IMC, the improvement being directly related to the extent of amorphization. To preserve the improved dissolution rate, mixtures should be protected from moisture and heat. This approach holds promise as a mean of improving the dissolution rate of sparingly soluble drugs such as IMC.     

冷轧 Ni/Ti 多层中的固态非晶化反应——Ⅱ.恒速升温退火处理(英文)

通过重复冷轧 Ni/Ti 包覆粉末制备出 Ni/Ti 多层。使用 XRD,SEM,TEM,DSC 和磁性分析方法研究了该多层由恒速升温退火导致的固态非晶化反应。恒速升温退火时多层中首先形成非晶相,当非晶相层厚超过一临界值后,元素间将通过互扩散形成金属间化合物 Ni_3Ti 和 NiTi,最后已形成的非晶相晶化成金属间化合物 Ni_3Ti 和 Ti_2Ni。首次利用扩散控制的层长大机制和瞬时形核模型,计算了恒速升温退火处理时多层中非晶层长大厚度和金属间化合物的形成温度。     

Substantial diffusion of Zr during solid-state amorphization in Ni/Zr multilayers

To examine the proposed model that amorphization is achieved by the motion of one species only, Ni/Zr multilayers have been prepared by sputter deposition at a pressure of 1 Pa. The as-deposited specimen shows the planar and sharp interface between Ni and Zr layers. The amorphous phase is clearly observed at the residual Ni layers and around the void edge in the Zr layer from the cross-sectional TEM images of the samples annealed at 300 C for 1 h. Composition analysis verifies that considerable Zr diffusion occurs through the grain boundary in the Ni layer during the annealing. The activation energy for amorphization is determined to be 1.17 eV per atom through a Kissinger-type analysis. This paper clearly shows the formation of amorphous NiZr alloys when Zr diffusion is comparable to Ni diffusion.     

High-resolution imaging of ion-implantation damage and mechanism of amortization in semiconductors

We have investigated the atomic structures of displacement cascades and amorphous-crystalline interfaces in silicon, ion implanted at 4 K, using high-resolution electron microscopy. The nature of the cascades and the process of amorphization are shown to be strong functions of ion-implantation and substrate variables. At 4 K the specific damage energy density for the crystalline to amorphous phase transition in silicon has been determined to be 12 eV/atom. The details of atomic structures of amorphous silicon and amorphous-crystalline interfaces are presented. The calculations of the mean free path between collisions and the energy deposited per atom are found to be consistent with experimental observations on amorphization of silicon.     

Laser-induced amorphization and crystallization on Se80Te20−xPbx thin films

Thin films of glassy alloys of a-Se₈₀Te_20−xPb_x (x=2, 6 and 10) was crystallized in a specially designed sample holder under a vacuum of 10⁻² Pa. The amorphous and crystallized films were induced by pulse laser (wavelength: 337.1 nm, frequency: 10 Hz, pulse duration: 4 ns and pulse energy: 0.963 mJ). After laser irradiation on amorphous and crystalline films: optical band gaps were measured. Crystallization and amorphization of chalcogenide films is accompanied by the change in the optical band gap. The change in optical energy gap could be determined by identification of the transformed phase. This change in the optical band gap may be due to the increase in the grain size and the reduction in the disorder of the system.     

The structure of shock and interphase layers for a heat conducting Maxwellian rate-type approach to solid–solid phase transitions

We consider a thermoelastic model for phase transforming materials which can adequately describe the evolution with respect to the temperature of the hysteresis loop both in compression and tension tests. The specificity of this model is that the Grüneisen coefficient changes its sign. The model is augmented by considering a dissipative mechanism governed by a Maxwellian rate-type constitutive equation that can describe stress relaxation phenomena toward equilibrium between phases. Existence and uniqueness of traveling wave solutions are investigated. One derives that the admissibility condition induced by the Maxwellian rate-type approach, coupled or not with Fourier heat conduction law is related to the chord criterion with respect to the Hugoniot locus. We investigate the structure of profile layers, and we focus on their thermodynamic properties. The influence of the exothermic or endothermic character of phase transitions on the inner structure of interphase layers is captured. A phenomenon of temperature overshoot/undershoot with respect to the front state temperature and Hugoniot back state temperature inside an interphase layer is revealed.     

Structural Modification of Al_(6)5Cu_(16.5)Ti_(18.5) Amorphous Powder through Annealing and Post Milling:Improving Thermal Stability

To improve thermal stability of the Al65Cu16.5Ti18.5 amorphous powder,structural modification of the amorphous powder was performed through annealing and post milling.Annealing above the crystallization temperature(Tx) not only induced nanoscale intermetallics to precipitate in the amorphous powder,but also increased Cu atomic percentage within the residual amorphous phase.Post milling induced the amorphization of the nanocrystal intermetallics and the formation of Cu9Al4 from the residual amorphous phase.Thus,a mixed structure consisting of amorphous phase and Cu9Al4 was obtained in the powder after annealing and post milling(the APMed powder).The phase constituent in the APMed powder did not change during the post annealing,which exhibited significantly improved thermal stability in comparison with the as-milled amorphous powder.     

Solution of adiabatic and nonadiabatic combustion problems using step-function reaction models

We consider the use of step-functions to model Arrhenius reaction terms for traveling wave solutions to combustion problems. We develop a methodology by which the Arrhenius reaction rate term is replaced by a suitably normalized step-function. The resulting model introduces interior interfaces and allows the conservation equations for energy and species to be solved explicitly within the subdomains bounded by the interfaces. The problem can then be reduced to a small number of nonlinear algebraic equations governing appropriate interface conditions. We apply this methodology to a variety of single-reaction problems and show that the resulting solutions agree with those obtained by the well-known front δ-function) approximations for large Zeldovich numbers. We then consider multiple reaction problems, specifically problems involving two independent reactions and problems involving sequential reactions. For these problems we compare the results with simpler front models as well as with Arrhenius kinetics. We show that the step-function models are generally superior to the front models where available and agree, both qualitatively and with reasonable quantitative accuracy, with solutions obtained via full Arrhenius kinetics.     

Solid state amorphization transformation in the mechanically alloyed Fe27.9Nb2.2B69.9 powders

Mössbauer spectrometry and Rietveld analysis of X-ray diffraction patterns were used to follow the solid state amorphization transformation during the milling process of the Fe_27.9Nb_2.2B_69.9 powders. The reaction between elemental Fe, Nb and B powders leads to the formation of the Nb(B) and Fe(B) solid solutions after 1 and 10 h of milling, respectively. A mixture of α-Fe, Nb(B) and highly disordered Fe(Nb, B) solid solution is found after 25 h of milling. An amorphous structure is obtained on further milling time (100 h). From the Mössbauer spectrometry results, it is observed that the total mixing of the elemental powders, at the atomic level, is achieved after 50 h of milling and a stationary state corresponding to a full paramagnetic amorphous phase is reached after 100 h of milling. The amorphization process can be described by an Avrami parameter close to n = 1.