Non-equilibrium Crystallization Research Articles

Low-temperature nanodoping of protonated LiNbO3 crystals by univalent ions

In the nanocomposite model developed here, crystals are treated as subordinate aggregate of pro- ton-selected structural elements, their blocks, and proton-containing quantum sublattices with preferred transport effects separating them. The formation of stratified reversible hexagonal structures is accompanied with protonation and formation of a dense network of H-bonds ensuring the nanocomposite properties. Nanodoping with H+ ions occurs during processing of crystals and glasses in melts as well as in aqueous solutions of Ag, Tl, Rb, and Cs salts. The isotope exchange H+ ↔ D+ and ion exchange H+ ↔ M+ lead to nanodoping of protonated materials with D+ and M+ ions. This is manifested especially clearly in Li-depleted nonequilibrium LiNbO3 and LiTaO3 crystals. Low-temperature proton-ion nanodoping over superlattices is a basically new approach to analysis of the structure and properties of extremely nonequilibrium materials.

Formation and stability of E93-type phases in the Ni-Nb alloy system studied by X-ray and neutron diffraction

By analyzing the phase states formed in Ni60-30Nb40-70 alloys under melt quenching and amorphous alloy crystallization, some researchers have revealed the formation of two E93-type phases (η′ and η″) with different crystal-lattice periods: 1.120 ± 0.001 and 1.164 ± 0.002 nm, respectively. To obtain more accurate information on the structure of these phases and explain the reasons of their formation during the non-equilibrium crystallization of a supercooled melt and an amorphous alloy, X-ray and neutron diffraction methods, as well as crystal-chemical criteria from the formation and stability theory for intermediate phases and metal glasses in transition-metal systems, are used. It is experimentally demonstrated that the η′ and η″ phases belong to different structural types, namely, Fe6W6C and Ti2Ni, respectively. The formation of the phases mentioned above is correlated with the corresponding crystal-chemical parameters: the size factor and the electron concentration.

C-10: High-speed video imaging of ice crystal formation in cells, tissues and droplets

Attempts to elucidate the causes of cryoinjury have benefited from nearly two centuries of microscopic observation of cell and tissue response during exposure to cold temperatures. However, the mechanisms of intracellular ice formation, a phenomenon that is strongly associated with irreversible cell damage, remains poorly understood: even in suspended, isolated cells, it has not been possible to obtain experimental evidence that conclusively supports or contradicts any of the competing hypotheses of intracellular ice formation (viz., the surface-catalyzed nucleation model, pore theory, or membrane rupture hypothesis). In part, this lack of progress has been due to the limited temporal resolution of conventional cryomicroscopy technology. Until recently, image acquisition rates in video cryomicroscopy studies have typically not exceeded 30 frames per second (fps), yielding a temporal resolution of 33 ms. Because the transformation of cell water to ice is completed in approximately 1 ms or less during rapid-cooling experiments, intracellular ice formation events cannot usually be detected using conventional video-micrography. As a result, cryomicroscopists have relied on the observation of cytoplasmic opacity changes as a proxy for intracellular freezing, an approach that can cause significant errors in estimates of intracellular ice formation kinetics. To detect the initial appearance and growth of ice crystals inside supercooled cells, and to quantify the phase transformation kinetics, it is necessary to use high-speed video cryomicroscopy to acquire micrographs at sub-millisecond resolution. In particular, to accurately measure intracellular ice formation kinetics in rapidly cooled somatic cells, image acquisition rates in the range 10 3 –10 4 fps are required, whereas shutter speeds should be faster than ∼0.1 ms to prevent motion blur. We have implemented such a high-speed imaging cryomicroscopy system, and have successfully used it to visualize non-equilibrium ice crystal formation and growth inside cells, tissue constructs, and microscale water droplets.

Kinetic approach to modeling the freezing porous media: Application to the food freezing

A new kinetic approach and general model for the processes of heat and mass (moisture) transfer in porous media under phase transition conditions is developed. It is assumed that the water crystallization process occurs according to non-instantaneous kinetics. As is shown in the study, this approach gives a possibility to describe the real process more completely and to reflect the main regularities of the phenomenon.Since the problem is significantly nonlinear the numerical method for the solution is applied. For the technological process of meat freezing, the phase front propagation and also temperature, moisture and ice distributions are obtained. It is shown that the thermal and moisture fields are homogeneous and therefore for considered initial data the freezing process is optimal from the view point of minimization of the energy consumption. The results of modeling are in a good agreement with experimental investigations, the discrepancy between them does not exceed 4.5%. The analysis indicates that simulation of the phase transition zone as an infinitely thin front in freezing process, which is an approach incorporated in most theoretical models, is not suitable for the non-equilibrium water crystallization processes and, thereby, conforms the validity of the kinetic approach.

Fabrication of W-Cu alloy via combustion synthesis infiltration under an ultra-gravity field

Tungsten copper alloy with a tungsten concentrate of 70 vol% was prepared by self-propagating high-temperature synthesis in an ultra-gravity field. The phase structures and components of the W-Cu alloy fabricated via this approach were the same as those via traditional sintering methods. The temperature and stress distributions during this process were simulated using a new scheme of the finite element method. The results indicated that nonequilibrium crystallization conditions can be created for combustion synthesis infiltration in an ultra-gravity field by the rapid infiltration of the liquid copper product into the tungsten compact at high temperature and low viscosity. The cooling rate can be above 100,000 K/s and high stresses in tungsten (~5 GPa) and copper (~2.6 GPa) were developed, which passivates the tungsten particle surface, resulting in easy sintering and densifying the W-Cu alloy. The reliability of the simulation was verified through temperature measurement and investigation of the microstructure. The W-Cu composite-formation mechanism was also analyzed and discussed with the simulation results.

Nonequilibrium crystallization of alloys in the naphthalene-dibenzyl system

Precrystallization supercooling states ΔTL− in the naphthalene-dibenzyl system are investigated via thermal analysis to determine the metastable area of the supercooling state under normal conditions of crystallization. Autonomous supercooling is observed and the enthalpy of crystallization relative to the liquidus and solidus temperature is found. It is established that ΔTL−falls smoothly as the concentration of the second component rises and reaches its lowest point with an eutectic alloy. The data on supercooling states and enthalpy are used to calculate different parameters of alloy crystallization in the system under study.

Highly efficient chiral resolution of DL-arginine by cocrystal formation followed by recrystallization under preferential-enrichment conditions.

An excellent chiral symmetry-breaking spontaneous enantiomeric resolution phenomenon, denoted preferential enrichment, was observed on recrystallization of the 1:1 cocrystal of dl-arginine and fumaric acid, which is classified as a racemic compound crystal with a high eutectic ee value (>95 %), under non-equilibrium crystallization conditions. On the basis of temperature-controlled video microscopy and in situ time-resolved solid-state (13) C NMR spectroscopic studies on the crystallization process, a new mechanism of phase transition that can induce preferential enrichment is proposed.

Microscopic X-Ray-Spectral and Thermal Analyses of an Alloy of the Al – Li – Mg System with Additives of Zirconium and Scandium

A commercial homogenized ingot from alloy 1421 of the Al – Li – Mg – Sc – Zr system is studied. The elemental composition of the phases is determined. Thermograms are obtained for melting and crystallization of the alloy. The temperature ranges and the succession of formation of phases in nonequilibrium crystallization of alloy 1421 are determined.

Improvement in ductility of high strength polycrystalline Ni-rich Ni3Al alloy produced by EB-PVD

A 300μm Ni-rich Ni3Al sheet was produced by electron beam physical vapor deposition (EB-PVD) and followed by different heat treatments to obtain fine γ′/γ two-phase structures with large elongation. Tensile testing was performed at room-temperature, and the corresponding mechanisms were investigated in detail. Results indicated that the as-deposited Ni3Al alloy exhibited non-equilibrium directional columnar crystal, and transited to equiaxed crystal with uniformly distributed tough γ phase after heat treatment. Meanwhile, the fracture mechanism transited from brittleness to a mixture of ductility and brittleness modes. With an appropriate heat treatment, high strength (ultimate tensile strength obtained 828MPa) and high ductility (elongation obtained 14.6%) Ni3Al alloy has been achieved, which was due to the mesh network microstructure. A series of transmission electron microscope (TEM) characterizations confirmed that the increasing flow stress of Ni3Al alloy was attributed to the cubical secondary γ′ phase precipitates (25–50nm) within the γ phase. This work provides a potential strategy for repairing the worn tip of single crystal engine blades using Ni-rich Ni3Al alloy by EB-PVD.

Influence of the nonequilibrium crystallization on the phase composition of the Al-Mo-Ti alloy

The phase composition, microstructure, and crystal structure of the AMT TU-48-4-366 (Technical Specifications) foundry alloy (which is used as the alloying material when smelting titanium alloys) are investigated by X-ray phase analysis, electron probe microanalysis, and microscopy. Lattice parameters of ɛ, p, and δ phases are calculated and their elemental composition is revealed. No formation of the Mo3Al refractory phase (tm = 2150°C) is observed during the primary crystallization of the Al-Mo-Ti foundry alloy in nonequilibrium conditions. Its presence in the refractory phase in the foundry alloy is caused by secondary crystallization processes, during which an ultradispersed mixture of Mo3Al + Mo3Al8 + TiMoAl6 phases is formed at temperatures 1311 and 1314°C. The ultradispersed silicon-containing σ phase with the Mo2.4Ti2.1Si0.8Al4.7 average composition, which was formed in nonequilibrium crystallization conditions, is revealed. Parameters and interplanar distances of its lattice are determined. It is established that the largest nonuniformity by molybdenum in peritectics of primary crystals occurs at a high crystallization rate, i.e., in the lower part of the Al-Mo-Ti ingot.

Diffusion versus Cocrystallization of Very Long Polymer Chains at Interfaces: Experimental Study of Sintering of UHMWPE Nascent Powder

Ultrahigh-molecular-weight polyethylene (UHMWPE) has been processed by means of sintering of a nascent powder. Particular attention was paid to the precompaction of the powder just below the melting point (Tm) under vacuum. The particle welding was subsequently carried out under pressure at various temperatures above Tm for various durations. Tensile drawing experiments performed on sintered samples either at room temperature or above Tm were specifically aimed at discriminating the role of chain interdiffusion through the particle interfaces from that of cocrystallization in the mechanism of particle welding. It turned out that efficient welding occurred within a very short time. One of the novel results of the work is the much weaker influence of sintering time as compared with temperature, giving evidence that chain interdiffusion is not governed by a reptation process. The entropy-driven melting explosion over distances much larger than the chain length between entanglements is suggested to be the main mechanism of the fast chain re-entanglement and particle welding in the present case of a nascent powder consisting of nonequilibrium chain-disentangled crystals. Another major aspect of this study is the demonstration of the huge cocrystallization efficiency in the interface consolidation in the solid state that significantly hides the kinetics of chain intertwining occurring in the melt.

038 What determines the temperature of ice crystallization?

Predicting the temperature and extent of ice freezing in aqueous solutions is crucial for areas as diverse as cryobiology, the prediction of climate and materials design. It has long been recognized that the thermodynamics of liquid water controls temperature and kinetics of ice crystallization. Parameterizations of the freezing temperatures in terms of the water activity of the solution have been successfully established, but the fundamental origin of the thermodynamic control of the non-equilibrium crystallization of ice has remained elusive. In this talk I will present a microscopic foundation, based on large scale molecular simulations and theoretical arguments, for the relationship between thermodynamics of the liquid and ice crystallization temperature in pure water and solutions, discuss the structure of the ice that forms (whether it is actually cubic ice), the structure of the water glass, and the evolution of the formation of ice on cooling of the liquid and rewarming of the glass. Some of the results to be discussed can be read in the following articles: 1. Moore, E. B. & Molinero, V. Structural transformation in supercooled water controls the crystallization rate of ice. Nature 479, 506–508 (2011). 2. Moore, E. B. & Molinero, V. Ice crystallization in water’s ‘no-man’s land’. J Chem Phys 132, 244504 (2010). 3. Moore, E. B. & Molinero, V. Is it cubic? Ice crystallization from deeply supercooled water. Phys Chem Chem Phys 13, 20008–20016 (2011). 4. Bullock, G. & Molinero, V. Low-density liquid water is the mother of ice: on the relation between mesostructure, thermodynamics and ice crystallization in solutions. Faraday Discussions, 2013, DOI: 10.1039/C3FD00085K http://pubs.rsc.org/en/content/articlelanding/2013/FD/C3FD00085K . Source of funding: None declared. Conflict of interest: None declared. valeria.molinero@utah.edu

Syntheses of Tabular Cobalt Ferrite Crystal Using Non-Equilibrium Crystallization Conditions

Cobalt ferrite CoFe2O4tabular crystals were synthesized via two-step coprecipitation using non-equilibrium crystallization conditions by supplying a solution of CoCl26H2O and FeCl36H2O and a solution containing NaOH at a later crystallization stage. Mean particle size of ~16.5 nm CoFe2O4primary particles synthesized by coprecipitation showed non-oriented structure. Effect of heat treatment temperature on the microstructures of the final CoFe2O4crystal was examined, orderly arranged plate-like tabular CoFe2O4crystals were formed under calcination at 800 °C. Magnetic hyspersis loops measured at 300 and 5 K indicated the anisotropy in the tabular crystals.

A new way of phase identification, of AgGaGeS4∙nGeS2 crystals

The phase identification of AgGaGeS4·nGeS2 (n=0–4) crystals grown by vertical Bridgman–Stockbarger technique was carried out to find the boundary value n between a homogeneous solid solution and its mixture with GeS2. To obtain reliable results, the conventional methods of X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) were completed by less common vapor pressure measurement in a closed volume and precise density measurements, which are very sensitive to the detection of small amounts of crystalline and glassy GeS2 and heterogeneous state of the crystals. The boundary value n=1.5 at 1045 K and the coexistence of the solid solution AgGaGeS4·1.5GeS2 with the β-GeS2 phase for n>1.5 was found. Glassy GeS2 (~2 mol%) was revealed by vapor pressure measurement and XRD studies in all the crystals. This is discussed in terms of the supersaturated solid solution decomposition upon temperature decreasing and the microphase separation of overcooled melt near the melting point under non-equilibrium crystallization. For the first time, the p–T dependence for glassy GeS2 was measured by the vapor pressure measurements.

Intracrystallite liquation in ternary alloys-solid solutions

The nonequilibrium crystallization in ternary alloys—solid solutions of the A-B-C model system and actual Cu-Ni-Mn system—are calculated according to the Petrov-Scheil model. It is shown that the temperature at which the distribution coefficient of the medium-melting component is 1 and the temperature at which the content of this component in the isolated solid phase is maximal are different for intracrystallite liquation in both cases. The conditions are formulated under which the parameters of the intracrystallite liquation should be compared with the characteristics of the dendritic liquation.

Phase Formation during Nonequilibrium Crystallization of Al–Mg–Si System Alloys

Nonequilibrium crystallization of alloys of the Al–Mg–Si system, and also their structure and phase composition in a cast condition are studied. Thermal analysis is used to establish phase transformation temperature ranges, occurring during nonequilibrium crystallization of industrial aluminum alloys AD31 and AD33. x-Ray microanalysis is used to determine metastable phase composition in the alloys in a cast condition.

Specific mass increment and nonequilibrium crystal growth

Unsteady nonequilibrium crystallization of ammonium chloride from an aqueous solution resulting in the formation of irregular, so-called seaweed, structures is experimentally investigated. It is shown that specific increment of mass for the coexisting structures (or parts thereof) is the same and changes with time (t) according to the power law a/t−b, where the factor a=1.87±0.09 and the factor b is determined by the system relaxation time. The normalization of the power law to the total time of structure growth allows obtaining a universal law that describes the specific mass increment with time for both seaweed and dendrite structures (including the non-coexisting ones).

Petrology, geochemistry, and geochronology of the Chah-Bazargan gabbroic intrusions in the south Sanandaj–Sirjan zone, Neyriz, Iran

The Chah-Bazargan gabbroic intrusions are located in the south of Sanandaj–Sirjan zone. Precise U–Pb zircon SHRIMP ages of the intrusions show magmatic ages of 170.5 ± 1.9 Ma. These intrusions consist primarily of gabbros, interspersed with lenticular bodies of anorthosite, troctolite, clinopyroxenite, and wehrlite. The lenticular bodies show gradational or sharp boundaries with the gabbros. In the gradational boundaries, gabbros are mineralogically transformed into anorthosites, wehrlites, and/or clinopyroxenites. On the other hand, where the boundaries are sharp, the mineral assemblages change abruptly. There is no obvious deformation in the intrusions. Hence, the changes in mineral compositions are interpreted as the result of crystallization processes, such as fractionation in the magma chamber. Rock types with sharp boundaries show abrupt chemical changes, but the changes exhibit the same patterns of increasing and decreasing elements, especially of rare earth elements, as the gradational boundaries. Therefore, it is possible that all parts of the intrusions were formed from the same parental magma. Parts showing signs of nonequilibrium crystallization, such as cumulate features and sub-solidification, underwent fracturing and were interspersed throughout the magma chamber by late injection pulses or mechanical movements under mush conditions. The geological and age data show that the intrusions were formed from an Al-, Sr-, Fe-enriched and K-, Nb-depleted tholeiitic magma. The magma resulted from the partial melting of a metasomatized spinel demonstrated by negative Nb, P, Hf, and Ti, and positive Ba, Sr, and U anomalies typical of subduction-related magmas.

Phase diagram of the Cu-Ni-Mn system

Part of the phase diagram of the Cu-Ni-Mn system from 0 to 20% Ni and from 30 to 50% Mn is refined with the help of a theoretical analysis and based on the experimental data. It is shown that the assumption that a line exists in the Cu-Ni-Mn ternary system along which the alloys with a zero crystallization range are arranged is erroneous. Only the alloys in the Cu-Mn and Ni-Mn binary systems have a zero crystallization range. The primary assumption that it is impossible to represent the nonequilibrium crystallization by Petrov-Scheil in the absence of a minimum line in the Cu-Ni-Mn system was not confirmed because previous studies were performed for a model system in which a convex liquidus line was present in the polythermal section connecting the minima in binary systems. In this study it is shown that this line is concaved towards lowering the temperature.

Investigating crystallization processes while brazing copper by copper-phosphorus brazing alloy with the purpose of controlling the structure of the brased seam

The possibility of predicting the structure of a brazed seam is considered. The brazing temperature is selected as the main method of influence since the composition of the liquid brazing alloy in the seam for eutectic systems will be determined by the line of the liquidus of the phase diagram of the “brazing alloy-brazed material” system. The influence of nonequilibrium crystallization conditions on the structure of the brazed seam is established. It is found that it is insignificant for the Cu-P system due to a small variation in the phosphorus solubility in the solid phase during crystallization. A simple formula for determining the thickness of the brazed seam is suggested. The results of calculations are confirmed by the experiments of brazing copper by the copper-phosphorus brazing alloy. It is shown that it is possible to obtain any eutectic content in the brazing alloy seam and, consequently, vary the strength properties of the seam.