Abstract: New amorphous alloys exhibiting a wide supercooled liquid region before crystallization were found to form by melt spinning in wide composition ranges of LaAlM, MgYM and ZrAlM (M = Ni or Cu) systems consisting of the constituent elements with significantly different atomic sizes. The temperature span between glass transition temperature, Tg, and crystallization temperature, Tx, ΔTx ( = Tx − Tg) is > 50 K in the compositional ranges around La2AlM, Mg6Ln3M and Zr3AlM and the largest ΔTx reaches 126 K. The critical cooling rate for the glass formation, Rc, is as low as 87–115 K/s and Tg/Tm is > 0.6 in the composition range where ΔTx > 50 K. There is a clear tendency for Rc to decrease with an increase of ΔTx and Tg/Tm. The crystallization of the alloys with large ΔTx occurs through the simultaneous precipitation of several compounds. Based on these results, it is presumed that the large glass-forming ability for these alloys is due to a combined effect of the difficulty of long-range atomic redistribution required for the precipitation of the compounds, the rapid increase of viscosity with decreasing temperature and the large liquidus-solidus interfacial energy which originates from the optimally bonding and packing states resulting from large negative heat of mixing and large atomic size ratios.

Abstract: The crystallization behavior after partial or complete melting of the α phase of iPP is examined by combined differential scanning calorimetry (DSC) and optical microscopy: calorimetric results are directly correlated with corresponding morphologies of microtome sections of DSC samples. On partial melting at various temperatures (hereafter referred to as Ts) located in a narrow range (4°C) below and near Tm, the number of nuclei increases (as in classical self-nucleation experiments), by several orders of magnitude; on subsequent cooling, the crystallization peak is shifted by up to 25°C. After partial melting in the lower part of the Ts range and recrystallization, the polymers display a prominent morphology “memory effect” whereby a phantom pattern of the initial spherulite morphology is maintained. After partial melting in the upper part of the Ts range the initial morphology is erased and self-nucleation affects only the total number of nuclei. The present experimental procedures make it possible to define, under “standard” conditions, the crystallization range of the polymer and in particular, the maximum crystallization temperature achievable when “ideally” nucleated. © John Wiley & Sons, Inc.

Abstract: We have investigated the phase transformation mechanisms and the resulting microstructures of excimer laser‐induced crystallization of amorphous Si films on SiO2. It is shown that the process can be characterized into two major regimes, based on the dependence of the grain size and the melt duration as a function of the incident energy density. It is found that at the transition between the two regimes, exceedingly large grain‐sized polycrystalline films can be obtained. We call this the super lateral growth phenomenon, and propose a model based on liquid‐phase regrowth from the residual solid seeds when near‐complete melting of the Si film occurs.

Abstract: Structures using X-ray diffraction data collected to 1.5-A resolution have been determined for the protein ribonuclease-A at nine different temperatures ranging from 98 to 320 K. It is determined that the protein molecule expands slightly (0.4% per 100 K) with increasing temperature and that this expansion is linear. The expansion is due primarily to subtle repacking of the molecule, with exposed and mobile loop regions exhibiting the largest movements. Individual atomic Debye-Waller factors exhibit predominantly biphasic behavior, with a small positive slope at low temperatures and a larger positive slope at higher temperatures. The break in this curve occurs at a characteristic temperature of 180-200 K, perhaps indicative of fundamental changes in the dynamical structure of the surrounding protein solvent. The distribution of protein Debye-Waller factors is observed to broaden as well as shift to higher values as the temperature is increased.

Abstract: Bulky amorphous alloys in a cylindrical shape with diameters up to 16 mm were found to form by water quenching a Zr 65 Al 75 Ni 10 Cu 175 melt in a quartz tube The amorphous phase of this alloy has the widest temperature interval of supercooled liquid region before crystallization The glass transition temperature, crystallization temperature and Vickers hardness for the bulky amorphous alloy with a diameter of 16 mm are 625 K, 750 K and 465, respectively, being nearly the same as those for the corresponding melt-spun ribbon with a thickness of 30 μm The extremely large glass-forming ability is presumably due to a combination of significantly different atomic size ratios among the constituent elements and the necessity of redistribution of Al for the progress of crystallization

Abstract: Rock textures commonly preserve a record of the near-surface crystallization history of volcanic rocks. Under conditions of simple cooling without convection or mixing, textures will reflect sample cooling rate, the temperature at which crystallization was initiated, and the distribution of mineral phase precipitation across the crystallization interval. Compilation of plagioclase size and number density data on natural (dike, sill and lava lake) and experimental samples suggests that (1) growth and nucleation rates of plagioclase in natural basaltic samples are a predictable function of cooling rate, and (2) the observed crystallization rate dependence on cooling rate is similar to that observed in experiments initiated at subliquidus temperatures. Comparison of natural and experimental samples thus suggests that most basalts crystallize under conditions of heterogeneous nucleation, with the number density of preexisting nucleii partially controlling textural responses to cooling rate changes. Time scales of crystallization and cooling in magmatic systems are intimately linked through a balance between heat removal from the system and heat evolved through crystallization. Evaluation of textural data in the context of recent numerical models of crystallization in simple (one- and two-component systems) provides new insight into regularities in the crystallization behavior of basaltic magmas. For example, the rate of change in crystal size (and number density, as dictated by mass balance) has been used as a measure of the relative importance of time scales of crystallization and cooling in numerical models of crystallizing systems. In natural samples, plagioclase size scales with the length scale of cooling such that a logarithmic plot of grain size as a function of normalized distance across the dike has a slope that appears approximately independent of dike width (solidification time). Comparison with available textural data for other phenocryst phases suggests that the same may be true for pyroxene and magnetite crystallization, with each phase having a characteristic slope probably controlled by the thermodynamic properties of the crystallizing phase. Measured crystal size distributions are unimodal and show maximum frequencies in the smaller size classes; distributions broaden and the grain size at peak frequency increases with increasing crystallization times (decreasing cooling rates). In contrast, partially crystallized Makaopuhi lava lake samples have crystal size distributions that decrease exponentially with increasing crystal size. Measured size distributions in dikes can be explained by late stage modification of Makaopuhi-type distributions through loss of small crystals, possibly the consequence of growth without nucleation. Finally, this compilation of the textural response of basaltic magmas to changes in cooling rate suggests that empirical calibrations of crystallization rate dependence on cooling rate from natural samples provide a reasonable model for plagioclase crystallization in near-surface basaltic systems. Predicted growth rates will be slow and relatively constant (10-10–10-11 cm/s) for crystallization times expected in most shallow volcanic systems (<1000 years).

Abstract: X-ray scattering and surface tension measurements reveal the formation of a crystalline monolayer on the surface of liquid n-alkanes at about 3 \ifmmode^\circ\else\textdegree\fi{}C above the bulk solidification temperature. The molecules in the monolayer are hexagonally packed and oriented normal to the surface. The single solid monolayer persists down to the bulk solidification temperature, thus exhibiting a very limited partial wetting.

Abstract: A fabrication process polycrystalline silicon thin film transistors commences with the deposition of an ultra-thin nucleating-site forming layer onto the surface of an insulating substrate (e.g., 7059 glass). Next, an amorphous silicon film is deposited thereover and the combined films are annealed at temperatures that do not exceed 600° C. By patterning the deposition of the nucleating site forming material on the glass substrate, the subsequently deposited amorphous film can be selectively crystallized only in areas in contact with the nucleating-site forming material.

Abstract: The nucleating activity of different insoluble additives in the heterogeneous nucleation of organic and inorganic glass-forming melts is treated from a generalized thermodynamic standpoint. The activity of a nucleating catalyst is defined through the adhesion energy and calculated from the forces of cohesion in the substrate and in the overgrowing crystal. An estimate is also made of the relative contribution of structure mismatch to the bonding energy by evaluating the total energy of misfit dislocations at the deposit/substrate interface. This approach extends and specifies the limits of application of existing concepts of crystallographic matching and mismatching. By this generalized method, there is a possibility of predicting the nucleating activity of various crystallization cores in the induced crystallization of glass-forming melts by using data on the heat of sublimation (or the temperature of melting) of the respective nucleation catalyst or the value of its thermal expansion coefficient.

Abstract: The application of a high-pressure die casting technique to La-Al-TM (TM=Co, Ni, Cu) alloys was found to produce bulk amorphous alloys in cylinder and sheet forms. The maximum sample diameter (d,) for formation of an amorphous phase is 3 mm for La 55 Al 25 (Ni or Cu) 20 , 7 mm for La 55 Al 25 Ni 10 Cu 10 and above 9 mm for La 55 Al 25 Cu 10 Ni 5 Co 5 . There is a clear tendency for d, to increase with an increase in the temperature interval of a supercooled liquid region. The glass transition temperature (T g ), the crystallization temperature (T x ) and the heat of crystallization (ΔH x ) remain unchanged in the thickness range of 1 to 7 mm for the La 55 Al 25 Cu 10 Ni 10 alloy

Abstract: The structure and defects of fully syndiotactic polypropylene [sPP] in its dominant (t 2 g 2 ) 2 phase were studied using X-ray and electron diffraction and molecular modeling. In agreement with previous proposal from much less syndioperfect sPP (77%), it is found that the chains pack in a fully antichiral cell along both the a and b axes, which is thus doubled from its currentlyaccepted dimensions. Cell parameters are a= 1.45 nm, b= 1.12 nm, c= 0.14 nm, and space group Ibca. Crystallization at temperatures below ca. 130°C causes incorporation of packing defects along the b axis, which is simulated using molecular modeling

Abstract: With short term shearing at low degrees of supercooling a method has been developed by which nucleation during shearing can effectively be separated from the subsequent crystal growth, whi...

Abstract: The crystallization of alpha -Si:H into poly-Si using an excimer laser has been examined. The resulting microstructure was found to be stratified into a large-grain surface region, formed from the liquid phase, and a fine-grain underlying layer, thought to be formed by solid phase crystallization. The threshold beam energies for these sequential phase changes were identified from surface reflectance measurements after crystallization and the energies increased with diminishing hydrogen content of the material. The electrical characteristics of thin-film transistors made with material crystallized at energies close to the melt threshold could be correlated with the limited depth of large-grain material. For significantly higher beam energies, coplanar structures showed a severe degradation in leakage current due to lateral diffusion of phosphorus, across the channel from the source and drain regions. When this effect was avoided, thin-film transistors with field-effect mobilities up to 160 cm/sup 2//V-s and on/off current ratios up to 10/sup 8/ were obtained. >

Abstract: The stabilizing effects of various additives against inactivation of an enzyme (β-galactosidase from Aspergillus oryzae) during freeze-drying were studied, with a focus on their crystallinity. The crystalline morphology of mannitol and inositol in freeze-dried cakes depended on the solute concentrations before freezing and the freeze-drying method used. The additives in their amorphous state showed concentration-dependent stabilization of the enzyme, whereas additive crystallization during freeze-drying decreased their effects. Heat treatment before freeze-drying also caused crystallization and diminished the stabilizing effects. Noncovalent soluble aggregates were observed in the inactivated enzyme solution. These results show the importance of maintaining the amorphous state of additives used as stabilizing agents during freeze-drying.

Abstract: Crystallization of BaTiO[sub 3] from an X-ray amorphous, metal organic precursor was investigated by comparing samples heated in O[sub 2], air, argon, and CO[sub 2]. It is evident that an intermediate barium titanium oxycarbonate phase forms between 500 and 620C and that BaTiO[sub 3] forms directly by the endothermic decomposition of this phase between 635 and 700C. From thermodynamic calculations, thermal analysis, X-ray diffraction, and Raman spectroscopy, it is concluded that the intermediate oxycarbonate is a highly disordered, metastable, and weakly crystalline phase with a stoichiometry close to Ba[sub 2]Ti[sub 2]O[sub 5]Co[sub 3].

Abstract: Heating the solutions of the sodium salt of the monomers Ph(F)R 4 -X-Ph(OH)-X-Ph(F)R 4 (R= H, F; X= CO, C≡CPhSO 2 , C≡CPhCO) resulted in their polymerization yielding dendritic polymers with molecular weights M n in the range 7410-35500, highly soluble in common organic solvents and retaining more than 95% of their mass up to 500°C. T g 's were observed ranging from 135 to 231°C but there were no evidence for melting or crystallization

Abstract: Recent physical theories for the formation of the Earth suggest that about 4.5 b.y. ago the mantle of the Earth was partially or completely molten. Fractional crystallization of this hypothetical magma ocean would result in a strong chemical stratification of the Earth's mantle. Such a scenario is controversial from the geochemical point of view. However, it has been noted that the simple scenario of fractional crystallization could be avoidable in a convective magma ocean if crystals remain suspended. In this paper, the problem of suspension is developed with the help of an energetic approach: convection must do some work against gravitational settling. We distinguish three regimes of convective suspensions. Absolute or complete sedimentation occurs when the energy dissipation due to the settling exceeds the heat loss from the convective layer. This is possible only in large-scale systems like magma oceans and implies that cooling can proceed only together with sedimentation, crystallization, and a decrease in the liquidus temperature at a constant pressure. A regime of partial differentiation occurs when the energy dissipation due to the settling is less than the total heat loss but larger than the power which can be spent by convection on the crystal reentrainment process. The differentiation is not complete, and a competition between the rate of cooling, the rate of sedimentation, and the rate of turbulent diffusion determines the degree of differentiation. The third regime is an absolute suspension which could be sustained for an indefinitely long time. In this case, sedimentation starts only when the crystal fraction reaches the maximum packing value: when the viscosity of the magma rapidly increases. The power which can be spent by convection on reentrainment is equal to eαgd/cp of the total energy supply to the convective layer, where e 15 GPa) or 10^(−3) – 10^(−1) cm during crystallization of shallow layers, the first regime (“fractional crystallization”) is unavoidable. The estimates depend on various poorly constrained parameters and processes, such as heat flux, viscosity, thermodynamical disequilibrium and highly variable viscosity convection. For absolute suspension the crystal size must be at least e^(½) times less, or 10^(−3) – 10^(−1) cm and 10^(−4) – 10^(−2) cm, respectively, if e ∼ 0.01. The partial differentiation occurs in a narrow (one decade) range between these two regimes. The radius of about 1 cm must be considered as an absolute upper bound above which fractional differentiation is guaranteed. These estimates for the critical crystal size are orders of magnitude lower than suggested previously, and thus the problem of crystal sizes becomes a central one for magma oceans. A necessary condition for reentrainment is the existence of local mechanisms. The absence of such mechanisms to reentrain the particles from the bottom would mean that an absolute suspension is impossible even if the energetics allows it. Turbulence is considered as a possible important factor. A simple model of convection predicts a strong turbulence, provided the viscosity is less than 10^9 – 10^(10) P. Rotation reduces this critical viscosity to 10^5 – 10^8 P but this is still sufficiently large and is reached only near the maximum packing crystal fraction. Power law or Bingham rheology of partial melts can exclude any turbulence already at 20 – 30% of crystal fraction. We also show that the energetic criterion for the absolute suspension with e ∼ 1 coincides with the condition that the particle concentration gradient suppresses the turbulence.

Abstract: Disclosed are a gallium nitride type semiconductor device that has a single crystal of (Ga 1-x Al x ) 1-y In y N, which suppresses the occurrence of crystal defects and thus has very high crystallization and considerably excellent flatness, and a method of fabricating the same. The gallium nitride type semiconductor device comprises a silicon substrate, an intermediate layer consisting of a compound containing at least aluminum and nitrogen and formed on the silicon substrate, and a crystal layer of (Ga 1-x Al x ) 1-y In y N (0≦x≧1, 0≦y≦1, excluding the case of x=1 and y=0). According to the method of fabricating a gallium nitride base semiconductor device, a silicon single crystal substrate is kept at a temperature of 400° to 1300° C. and is held in the atmosphere where a metaloganic compound containing at least aluminum and a nitrogen-containing compound are present to form a thin intermediate layer containing at least aluminum and nitrogen on a part or the entirety of the surface of the single crystal substrate, and then at least one layer or multiple layers of a single crystal of (Ga 1-x Al x ).sub. 1-y In y N are formed on the intermediate layer.

Abstract: A method is disclosed for preparing a crystalline aluminosilicate zeolite from a reaction mixture containing only sufficient water so that the reaction mixture may be shaped if desired. In the method, the reaction mixture is heated at crystallization conditions and in the absence of an external liquid phase, so that excess liquid need not be removed from the crystallized material prior to drying the crystals.

Abstract: The kinetics during the induction period of polymer crystallization is studied by means of depolarized light scattering measurements. The spinodal decomposition during this period is shown to be caused by orientation fluctuations of polymer segments. Time evolution of these orientation fluctuations can be described by the spinodal decomposition kinetics in terms of transformation from the isotropic to nematic phase proposed by Doi et al.

Abstract: Chemical modification of proteins has been and continues to be an important biochemical tool for the study of protein structure and function. One such type of approach has been the reductive methylation of lysine residues. In order to address the consequences of such methylation on the crystallization and structural properties of a protein, the three-dimensional structure of hen egg white lysozyme in which all lysine residues have been alkylated has been determined and refined to a nominal resolution of 1.8 A and a crystallographic R factor of 17.3%. Crystals used in the investigation were grown from 1.5-1.8 M MgSO4 and 50 mM Tris at pH 8.0 and belonged to the space group P2(1)2(1)2(1) with unit cell dimensions of a = 30.6 A, b = 56.3 A, c = 73.2 A, and one molecule per asymmetric unit. It was not possible to grow crystals of the modified lysozyme under the conditions normally employed for the hen egg white protein. Overall, the three-dimensional structures of the native lysozyme and the modified protein are very similar with only two surface loops differing to any significant extent. Specifically, the positions of the alpha-carbons for these two forms of the protein, excluding the surface loops, superimpose with a root-mean-square value of 0.40 A. The magnitude of the structural changes observed between the modified an unmodified forms of lysozyme is similar to that seen when an identical protein structure is solved in two different crystalline lattices.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract: The in vitro five-stage surface reactions of two bioactive glass compositions, 45S5 and 52S4.6, and one bioinert glass, 60S3.8, exposed to three simulated body fluids (SBF) were analyzed using Fourier Transform infrared Spectroscopy (FTIR). There was little effect of SBF composition on ion exchange, silica hydrolysis, and silica polymerization (stages 1–3) of glass with silica content up to 52 wt%. However, calcium and phosphate ions in SBF accelerated the formation of an amorphous calcium-phosphate (a-CP) layer (stage 4), and crystallization (stage 5) of the hydroxycarbonate apatite (HCAp) layer. The magnesium ions had a retardation effect on the kinetics of stages 4 and 5, but little effect on stages 1–3. In SBF solutions which contained calcium and phosphate ions an amorphous calcium-phosphate (a-CaP) layer formed on even a 60S3.8 glass which was not bioactive in vivo. However, the a-CaP layer did not crystallize to form HCAp. Thus, there is a significant contribution from the ions present in the SBF solutions to the HCAP formation and crystallization of HCAp on bioactive glasses. Also, silanol repolymerization is necessary for rapid crystallization of HCAp. © 1993 John Wiley & Sons, Inc.