Abstract: The near‐surface nucleation and crystallization behavior of Ag+ ion‐implanted lithia‐alumina‐silica glasses has been studied. For room‐temperature Ag implants, crystallization of the glass ceramic phase was prevented by dissolution of Ag precipitates and migration of Ag atoms at temperatures below that necessary for formation of the glass ceramic phase. Crystallization was demonstrated after low‐temperature or low‐dose‐rate implantations. Optical spectroscopy was used to monitor the size of colloidal Ag particles and to detect the presence of the crystalline phase. Rutherford backscattering spectroscopy (RBS) was used to obtain the depth distribution of Ag atoms in the glass and thus monitor Ag migration. For samples implanted at room temperature and at relatively high dose rates (∼1 μA/cm2), aggregation of the Ag atoms into colloids occurred during implantation and also during subsequent annealing to temperatures ?350 °C. The RBS spectra indicate some migration of the Ag to the surface at these temperatu...

Abstract: The maturation of calcium phosphate crystals formed by the conversion of spontaneously precipitated amorphous calcium phosphate (ACP) was studied in aqueous media at temperatures ranging from 20° to 37°. Reaction pH was kept at 7.4 with either Hepes buffer or by the pH-stat addition of base. Reaction kinetics were followed by monitoring solution calcium and total phosphate, and, in the pH-stat controlled reaction, by recording the amount of KOH needed to maintain pH. Reaction products were examined chemically and by X-ray diffraction and transmission electron microcopy. The first crystals to form deviated markedly from apatite in morphology, composition, structure, and solubility. They were extremely thin and flaky in appearance, had a low Ca/P molar ratio (1.4), contained an appreciable amount of acid phosphate (16%), and had an exceptionally largea-axis (10.5 A vs. 9.4 A for apatite). With maturation, the crystals became thicker but smaller in lateral dimensions, more apatitelike in structure and composition, and less soluble. However, this ripening of the crystals was accompanied by unusual inflections in the solution Ca and total PO4 curves, and, in the case of the pH-stat experiments, in the OH consumption profiles as well. These anomalous post-ACP solution changes suggest that a phase change had taken place during crystal maturation. Although the observed structural and compositional changes are not inconsistent with the perfection of an initially defective apatite, the changes in crystal morphology and the anomalous behavior of the reaction solution may more accurately reflect a conversion of the ACP first into an OCP-like crystalline phase which subsequently hydrolyzes into apatite.

Abstract: We have measured the effects of annealing in air on various properties of several amorphous alloys. Reported here are results on the changes in Curie temperature, in the physical dimensions of lengths of amorphous ribbon, and in the magnetic anisotropy. Increases in Curie temperature up to 35°C have been measured. All the alloys examined show a steady increase in T c on annealing at low temperatures, but some compositions show a smaller increase in T c on annealing near the crystallization temperature than on annealing at lower temperatures. There appear to be two competing mechanisms influencing T c . All the alloys examined show a clearly measurable decrease in length on annealing; we interpret this as an increase in bulk density. The kinetics of the annealing are similar to those of the stress relaxation. Finally, annealing experiments on the shape of 60 Hz hysteresis loops show a decrease in the anisotropy associated with non-uniform internal stresses, but in some cases also show the slow development of a fairly strong uniaxial anisotropy with its easy axis perpendicular to the ribbon axis. This uniaxial anisotropy is tentatively ascribed to the development of an oxide layer during annealing, which in turn produces a uniform compressive stress due to differential thermal contraction and therefore a stress-magnetostriction anisotropy. The changes in Curie temperature and in sample dimensions cannot be ascribed to oxidation. All the results described above are for annealing treatments that do not cause crystallization. The time for crystallization at various temperatures has been measured, and activation energies for crystallization derived.

Abstract: Oxidation rates of aluminum—1 to 14 pct magnesium melts in air, oxygen, flue gas, and carbon dioxide at temperatures from 600 to 1100°C were measured with an automatic recording balance. For most conditions, a protective amorphous film on the melt surface kept the oxidation rate low initially. After an interval that was shortened by increasing temperature or magnesium content, the film crystallized to magnesium oxide and magnesium aluminate, accompanied by a sudden increase in oxidation rate. Known as breakaway oxidation, this phenomenon could be produced by adding crystalline magnesium oxide or magnesium aluminate seed to melts protected with amorphous oxide. Flue gas or carbon dioxide in the atmosphere, sodium or beryllium in the alloy, or boron dusted on the surface delayed crystallization unless seed was added. Beryllium was the most effective. Flue gas from burning natural gas delayed breakaway oxidation of unseeded melts containing up to about 4 pct magnesium at normal melting furnace temperatures near 750°C. Slow melting of solid aluminum-magnesium alloy concentrated magnesium in the first liquid to melt, sharply decreasing the interval before breakaway oxidation after melting. Rapidly melting the solid increased the protective interval. Homogenizing the solid just below the melting range before rapid melting further extended the interval before the onset of breakaway oxidation.

Abstract: The thermal conductivity of a glassy PdSi alloy has been measured in the temperature range 0.1–30 K. The thermal conductivity contributed by the phonons has the same anomalous behavior as found for all non-metallic amorphous materials. Heat treatment increases the phonon thermal conductance by ∼50%, a change which does not appear to be related to partial crystallization.

Abstract: Binary mixtures of a linear polyester (poly(ϵ-caprolactone)) and a crystallizable monomer (trioxane) have been investigated by means of differential scanning calorimetry and optical and electron microscopy. The phase diagram indicates the existence of a eutectic at a temperature TmE = 314°K and for a polymer volume fraction ϕ2E = 0.70, values close to those predicated by the Flory–Huggins theory (using χ = 0.3). Microscopic studies reveal unusual morphologies: (1) In hypoeutectic mixtures, at room temperature, the solvent crystallizes as highly ramified or branched needles. When the remaining melt reaches the eutectic composition, transcrystallization of the polymer is induced by the epitaxial deposition (as established by electron diffraction) of polycaprolactone on the existing trioxane crystals, and leads to highly ordered structures. (2) In hypereutectic mixtures a predominantly spherulitic texture is observed. Blends of trioxane and several other linear polyesters are found to exhibit similar behavior.

Abstract: The structure of melt-spun nylon 6 filaments was studied using on-line x-ray diffraction and birefringence measurements. Measurements were also made on as-spun and treated filaments. On-line wide-angle x-ray scattering measurements indicated that crystallization did not occur on the nylon 6 spinline at spinning rates up to 1000 m/min when spinning was done into either ambient air of 60% relative humidity or into wet saturated air. The filaments did crystalline gradually on the bobbin to a paracrystalline pseudohexagonal (γ) form. The rate of crystallization was dependent on the molecular orientation developed in the spun filaments. Crystalline orientation factors based on hexagonal symmetry were computed as a function of take-up velocity for fibers which were conditioned 24 hr in air at 65% relative humidity. Annealing in air or treatment in water or 20% formic acid solution causes a transformation from the pseudohexagonal form to the α monoclinic form. The tangent modulus of elasticity and tensile strength of spun and conditioned filaments increase with increasing take-up velocity and spinline stress, while elongation to break decreases with these variables.

Abstract: We report the solid‐phase growth of epitaxial Si thin films by the heating of amorphous Si deposited onto atomically clean (100) Si substrates at room temperature. Epitaxial Si layers ranging in thickness from 1000 to 5000 A have been grown by heating the amorphous films in ultrahigh vacuum to temperatures of 500–600 °C. Good crystal quality of the layers grown by this method has been demonstrated by Rutherford backscattering and transmission electron microscopy.

Abstract: A laboratory continuous mixed-suspension, mixed-product-removal crystallizer was used to study the effects of temperature on the kinetics of crystallization of potassium nitrate. A differential refractometer was used to continuously monitor the supersaturation permitting the measurement of supersaturation levels of order 10−3Kg solute/Kg water. The nucleation rate exhibited an inverse relationship with temperature.

Abstract: The conversion of monoclinic selenium to trigonal selenium is studied by x‐ray diffraction, optical microscopy, and thermal analysis between 343 and 487 K. Below the melting temperature of the monoclinic crystal the process is topochemical, but not topotactic. The melting of the monoclinic crystals to the pure Se8‐ ring melt occurs at 413 K (with a heat of fusion of 2.8 kJ/mole Se, and an entropy of fusion of 6.8 J/K/mole Se). The nucleation of the trigonal phase in the monoclinic single crystal is athermal and occurs in crystalline register with the monomer, either through the nature of the nucleating defect or through epitaxy. The time for the appearance of the fixed temperature‐independent number of nuclei is governed by an activation energy of about 100 kJ/mole. The subsequent growth occurs by crystallization during polymerization in the direction of the macromolecular helix axis, independent of the host crystal. Above 360–380 K, the trigonal phase branches to spherulitic crystals with radial c‐axis orientation. The linear crystal growth is described over the whole analyzed temperature range by the same exponential (−1/T) rate law with an activation energy of 113 kJ/mole, which indicates that ring opening is the rate‐determining step.

Abstract: The microstructure and growth characteristics in the annealed amorphous alloy Ni40Fe40P14B6 were studied by transmission electron microscopy and X-ray diffraction. Samples were annealed for 2 h at 370°C to initiate crystallization. In the early stages of crystallization, the crystals were well separated and of a nearly rectangular section. The smaller crystals were of a high degree of perfection and were single phase. All crystals had a (Fe,Ni)3(P,B) type bct structure. The crystals consist of a collection of plates and spheroids about 100A across. The spatial orientation of the plates varies from region to region of the crystal indicating that the crystals are twinned. Dark field analysis showed that the plates consist of microtwins or faults. It is concluded that the plate and spheroid structure is caused by small differences in composition within the crystal. The crystallography, however, does not vary across the crystal. This suggests that the amorphous matrix is not chemically homogeneous.