Amorphous Solid Phase Research Articles

On the nanocrystalline to glass transition during ball milling

Mechanical alloying performed by ball milling metallic powders leads to a nanocrystalline state and metastable phases such as supersaturated solid solutions and amorphous phases. The nanocrystalline state may act as a transition state for the crystal to glass transition. Assuming polymorphic (or partitionless) melting of a nanocrystalline supersaturated solid solution, it is found that a critical nanograin size for amorphization may be defined. This critical size depends on the concentration of the supersaturated solid solution. Application to the Zr based hexagonal solid solution Zr-Ni allows a quantitative evaluation of this effect. It is shown that for nanocrystalline size the classical T 0 curve is significantly lowered in temperature, yielding a polymorphous crystal to glass transition for smaller nickel concentration than for conventional crystalline sizes. Therefore, both supersaturation and grain refining to nanocrystalline dimensions work towards an easier amorphization by ball milling.

Solute Partitioning in a Calcium Carbonate‐Phosphoric Acid‐Water System

AbstractA range of Ca phosphates form in a time‐dependent process, when calcite interacts with a dilute orthophosphate solution. This study was conducted to ascertain the possible formation of a stable CaCO3‐PO4 compound on calcite surfaces and to characterize its precursors. The solution's ionic speciation provided evidence of the formation of a CaHCO3‐PO4 compound (CBP) with a stoichiometric Ca/P ratio of 3 and a solubility product, Ksp, of (Ca2+)3(HCO−3)3(PO3−4) = 10−28.36. This hypothesis was also supported by electron spectroscopy analyses of the surface layers of the final solid product and scanning electron microscopy (SEM). Prior to the CBP formation, either a compound with the same Ca/P ratio as dicalcium phosphate (DCP, CaHPO4) formed, or CBP was in quasi‐equilibrium at a Ca/P ratio of 1.5 to 2.3. Another possibility is that a poorly crystalline or amorphous Ca phosphate solid phase was formed. Finally, the newly formed CBP converted to hydroxyapatite (HAP, Ca5 (PO4)3OH).

Structural disorder in ion irradiated carbon materials

Abstract The effects of ion irradiation on carbon based materials are reviewed laying emphasis on the well known ability of carbon to have different kinds of bonding configuration with the surrounding atoms. It was found that two kinds of bonding configuration of the carbon atoms are allowed in solid amorphous carbon phases. These rearrange the four valence electrons of carbon into sp 2 (trigonal bond) and sp 3 (tetrahedral bond) hybridizations. Driving the trigonal carbon fraction ( x ), the physical and chemical nature of solid carbon materials can change in a dramatic way ranging from metallic ( x ≈ 100%) to insulating ( x ≈ 0%) through semiconductor properties. The amount of the tetrahedral (or trigonal) carbon atoms can be controlled by ion beam irradiation, using suitable conditions and/or introducing foreign species such as hydrogen or silicon by the implantation technique. In hydrogenated amorphous carbon (a-C:H) and hydrogenated amorphous silicon-carbon alloys (a-Si 1− x C x :H), the ion beam effects are able to produce stable and reproducible compounds, achieved by tuning the hydrogen (silicon) concentration with well defined equilibrium curves between the trigonal carbon fraction and hydrogen (silicon) content. Raman spectroscopy and temperature dependent conductivity experiments performed on these alloys suggest clustering effects in samples with high carbon content ( x ≈ 0.5) due to the strong binding energy of the CC double bond with respect to CSi and SiSi. Several models and theoretical studies such as the “random covalent network” (RCN) and molecular dynamics calculations have been used to fit the experimental results. It is shown that, while RCN models are highly inaccurate because of the clustering effects, molecular dynamics calculation data are very close to the experimental measured physical properties and confirm the ability of the trigonal carbon to cluster in graphite-like aggregate.

FTIR studies of sodium hyaluronate and its oligomers in the amorphous solid phase and in aqueous solution

FTIR studies of sodium hyaluronate and its oligomers in the amorphous solid phase and in aqueous solution

Amorphization of metals by ion implantation and ion mixing methods

In this paper, we present a review of the experimentally determined characteristics of solid-phase amorphization of metals and alloys under ion implantation and ion mixing conditions. For the first time we systematically consider the characteristic features and the thermodynamic, structural, and kinetic criteria for amorphization in different metallic systems, and we demonstrate the expediency of the following classification of alloys undergoing amorphization: “metal-metalloid” systems, intermetallics, heterophase alloys, alloys with high positive heat of mixing. We compare solid-phase amorphization under conditions of bombardment by beams of charged particles, thermal mixing of the alloy components, and mechanical alloying. We consider the phase and structural states preceding amorphization and the possibilities for predicting metallic systems which can undergo amorphization.

Formation of Ni80P20 solid solution phase under high pressure

A Ni-P solid-solution phase was obtained by quenching from the melt under a pressure of 4.5 GPa. It was considered as a metastable high-pressure phase. Metastable phases with the same composition as the melt, such as supersaturated solid solutions and amorphous phases, are easily prepared using a high pressure quenching method.

Formation of NI80P20solid solution phase under pressure

Abstract A Ni-P solid solution phase was obtained by quenching of melts under a pressure of 4.5 GPa. This was considered as a metastable high pressure phase. Despite the lack of thermodynamic parameters for Ni80, P20 alloy under pressure, the degree of undercooling, nucleation frequency and crystal growth velocity were calculated. We conclude that metastable phases with the same composition as the melting phase, such as supersaturated solid solution phase and amorphous phase, are easily prepared by high-pressure quenching.

Solid phase amorphization and crystallization in multilayer and bilayer Rh-Si thin films

Solid phase amorphization in multilayer structures consisting of alternating layers of crystalline Rh and amorphous Si thin films and in a bilayer structure consisting of a crystalline Rh thin film deposited on a [100] oriented single crystal Si wafer have been studied by in situ resistivity measurement and cross-sectional transmission electron microscopy. In both of the structures, amorphous alloys of Rh and Si form upon heating from 120 to 250 °C. The metastability of the amorphous alloy as measured by the crystallization temperature depends on the alloy composition and the initial layer thickness of Rh and Si. The amorphous alloy that has a composition close to that of RhSi is quite stable and has a crystallization temperature of around 450 °C. Its kinetics of solid state amorphization and crystallization have been measured and are discussed.

Stability and thermodynamic properties of supersaturated solid solution and amorphous phase formed by ball milling in the Zr- Al system

Zr100-xA1x (x ≤ 40) metastable alloys were synthesized by high- energy ball milling of elemental Zr and Al powders: supersaturated substitutional cph solid solution for x ≤ 15 and an amorphous phase for x ≥ 17.5. We performed a calorimetric study of the thermodynamics and kinetics of the metastable- to- equilibrium transformations of these phases. Their stability range (temperature/composition), as well as the apparent activation energies associated with the transformations, were determined. The transformation enthalpies were measured and used to determine the enthalpy of formation for these metastable phases. For both as- milled and relaxed amorphous phases, the measured enthalpy of crystallization is compared with those estimated for an undercooled liquid. Different amounts of retained entropy at the glass transition temperature were used to estimate the enthalpy loss upon undercooling due to the excess specific heat.

Solid State Amorphization in Silicide—Forming Systems

ABSTRACTSolid phase amorphization has been found to occur in all refractory metal and a number of rare—earth and platinum group metal thin film on silicon systems. For Ti/Si, Zr/Si, Hf/Si, V/Si, Nb/Si and Ta/Si systems, the growth of amorphous interlayer (a—interlayer) was found to follow a linear law in the initial stage. Si atom was found to be the dominant diffusing species in the solid phase amorphization in Ti/Si, Zr/Si and Hf/Si systems. For the Y/Si system, the stability of amorphous interlayer depends critically on the composition of the amorphous films.Auto–correlation function analysis was utilized to determine the structure of the amorphous interlayers. HRTEM in conjunction with the fast Fourier transform were applied to determine the first nucleated crystalline phase. Simultaneous presence of multiphases was observed to occur in a number of refractory metal/Si systems. Interesting electrical properties of amorphous interlayers were found for Ti/Si, Zr/Si and Hf/Si systems.

Amorphization induced by mechanical alloying and cold rolling

Solid state amorphous phase change is studied in the NiTi system. It is found that the crystalline to amorphous transition can be obtained by the mechanical alloying, or by annealing of the multilayers produced by mechanical alloying and/or cold rolling. Different products are found after the annealing of the multilayers. The activation energies and interdiffusion coefficients are obtained for the solid state amorphous reaction.

Molecular dynamics simulation of silica liquid and glass

A molecular dynamic computer simulation of the cooling of liquid silica to form an amorphous solid (glassy) phase was performed using the potential of Tsuneyuki, Tsukuda, Aoki, and Matsui, which was found to be consistent with the structure of several crystalline phases of silica. In the simulations, at low temperatures the atoms formed an almost perfect random tetrahedral network, and on subsequent annealing the material formed a perfect network, with each silicon having four oxygen neighbors and each oxygen having two silicon neighbors. The simulated material at low temperatures has a structure that is in close agreement with experimental neutron scattering measurements on amorphous silica. Several properties of the material were calculated and compared with experiment, and the nature of the ‘‘inherent structure’’ of the material as a function of temperature was investigated. The potential of Tsuneyuki et al. provides an excellent model for amorphous silica as well as crystalline silica.

Ti-Al Alloys Prepared by Ball Milling and Hot Isostatic Pressing

For the powder metallurgical production of Ti-Al alloys, elemental powder blends and prealloyed powders were mechanically alloyed in a planetary ball mill. Thereby metastable solid solutions or amorphous phases are formed depending on the overall composition and the milling conditions. The crystalline phases exhibit an extremely small crystallite size of about 10 - 30 nm. This favors the consolidation of the powders which was performed by hot isostatic pressing in the temperature range between 500 °C and 800 °C. The results show that fully dense Ti-48 at.% Al alloys can be obtained only for a temperature of 800 °C. The crystallite sizes increase during compaction, but remain below about 0.15 µm. This allows the preparation of test specimens to investigate the mechanical properties of Ti-Al alloys with submicron crystallite sizes.

Crystallization Process of Fe73.5Cu1Nb3Si13.5B9

ABSTRACTTo clarify the relation between high magnetic permeability and magnetic phases of Fe73.5Cu1Nb3Si13.5B9 ribbons, the process of precipitation was investigated by using the Xray diffraction, DTA, VSM and the Mössbauer spectra at various annealing temperatures. The volume fraction of each magnetic phase was estimated. The sample annealed at 853K which shows maximum permeability is composed of partially ordered Fe3Si(70%), Fe(B) solid solution(10%) and amorphous(20%) phases. The relative permeability of the sample annealed below 853K increases with increasing the volume fraction of both of the Fe3Si partially ordered and the Fe(B) solid solution phases. The relationship between tile permeability and the volume fraction is interpreted by the random anisotropy model.

About the amorphization criteria in aluminium-based alloys

A review is made of the various amorphization criteria and their ability to explain the metallic glass formation in aluminium-based alloys. X-ray analysis of various binary alloys melt spun at wheel speeds ranging from 20 m s −1 to 60 m s −1 provides the experimental basis. It is shown that these speeds are the lower limit for either glass formation or extended solid solution formation. A kinetic description shows that the easiest glass-forming composition is expected to be within the coupled growth region. In the case of aluminium-based binary alloys, the existence of extended solid solution and of intermetallic compounds with high aluminium content can inhibit amorphous formation. The role of third element is to increase the T g temperature or to modify solid solution formation, as illustrated by the addition of 3 at.% Zr, in an AlNi system. Finally, the link between static and dynamic criteria is underlined on a plot of the aluminium-based binary systems on a two structural parameters map, where the tendencies to form an extended solid solution, amorphous or quasicrystalline phase by rapid quenching from the melt are distinguished.

Raman spectroscopic study of dilute HOD in liquid H2O in the temperature range − 31.5 to 160 °C

We present Raman data for the OD stretch mode of 10 mol % HOD in H2O for the liquid phase from −31.5 to 160 °C. We find that an exact isosbestic does not hold, but rather the crossing of isotherms slowly but uniformly changes with temperature. We present an analysis based on Boltzmann statistics which gives evidence for a distribution of deuterium hydrogen bond strengths with minimum energy near the frequency (2440 cm−1) also found in the solid ice and amorphous solid phases. This analysis also gives evidence for a band of frequencies above 2630 cm−1 due to OD oscillators all at essentially the same high energy relative to the strongest hydrogen bonds, and we interpret this band as due to broken hydrogen bonds. This allows us to calculate hydrogen bond probabilities, and we find this probability increases with decreasing temperature and approaches a value equal to the four bonded percolation threshold near the singular temperature Ts ≂−45 °C for the anomalies of supercooled water. Peak frequency and full width at half-maximum of the OD stretch band are found to drop precipitously to the amorphous solid values as T→Ts implying the ultimate state of supercooled water is similar to the amorphous solid.

Response of intermetallic compounds to electron irradiation

Intermetallic alloys exhibit a wide spectrum of responses to electron irradiation at energies above the threshold energy for ballistic damage. All chemically ordered compounds will chemically disorder at low temperatures whereas disordered compounds will order at temperatures above approximately room temperature. Volume expansion of the material can be associated with the irradiation as well as mechanical softening. At low temperatures, an amorphous solid solution phase is often the end result of the irradiation process whereas at temperatures above room temperature (and below the crystallization temperature) irradiation leads to the crystallization of an amorphous phase. It has also been shown that the structural response to irradiation in these compounds may be anisotropic. The response to irradiation has been shown to be strongly influenced by several material properties and experimental conditions some of which are listed below.

Geochemistry of dissolved phosphate in the Sepik River and Estuary, Papua, New Guinea

The natural regulation of phosphate in the Sepik River and Estuary, Papua, New Guinea, was investigated by fitting field measurements to a chemical model. Results indicate that ferric iron and phosphate in the river and salinity to 12 ppt in the estuary are primarily influenced by equilibration with a discrete amorphous solid phase. Dissolved ferric iron is saturated with respect to amorphous ferric hydroxide in the river and most of the estuary. Dissolved phosphorus is equilibrated with amorphous ferric hydroxide-phosphorus solid solution in river waters and the low salinity third of the plume. A modest input of phosphate, believed driven by disequilibrium, was observed at mid-estuary. Input is roughly equivalent to removal and is thought to be limited by a paucity of phosphorus in the solid phase. Oceanic fluxes of phosphorus from major Pacific Islands may not be large despite disproportionately large sediment fluxes, if other watersheds contain reservoirs of solid phosphorus as small as the Sepik River.

Phase Dependence of the IR Spectra of Nitrobenzene

Abstract The IR spectra of nitrobenzene-d0 and -d5 were recorded in gas and liquid phases at 25°C and in amorphous solid phase at -170°C. The appearance of new bands and intensity changes going from liquid to solid phase spectrum, are interpreted in terms of molecular symmetry modifications. A normal coordinates analysis was performed and the potential energy distribution agrees well with previous assigments.

Al-20 mass%Ti混合粉末のメカニカルアロイング

Alloying processes, formation of amorphous phase and hardening of Al-20 mass% (12.4 at%)Ti mixed powders during mechanical alloying with an Attritor type of ball mill, have been investigated by means of optical, scanning and transmission electron microscopy, X ray analysis and hardness measurements.The mechanical alloying (MA) process detected consists of flake-forming, cold welding of the flaked powders, fracturing of the composite powders, formation of solid solution and amorphous phase. The amount of solute titanium in the composite powder after 493.2 ks MA was estimated to be about 17 mass% from the lattice parameter measurement and grain sizes of the matrix aluminum were in the range from about 20 to 60 nm. The amount of oxygen in mechanically alloyed powders increased with milling time, and dispersions of Al2O3 particles were observed by TEM. The spherorized composite powders with the average particle size of 0.6 μm after 2200 ks MA were amorphous. The amorphous particles showed halo patterns in electron diffraction and showed no grain boundary, no dislocation and few Al2O3 particles in TEM. A remarkable increase in hardness of the composite powders was explained in terms of solid solution hardening of titanium in aluminum, dispersion hardening of Al2O3 particles, work-hardening and hardening by grain refinement.