Abstract: Measurements during pulsed laser irradiation indicate that amorphous Si melts at a temperature 200 \ifmmode\pm\else\textpm\fi{} 50 K below the crystalline value. Below energy densities required to melt the amorphous layer fully, the data are interpreted in terms of an explosive crystallization. The initial liquid layer solidifies to form coarse-grained polycrystalline Si. A thin, self-propagating liquid layer travels through the remaining amorphous Si at a velocity of 10-20 m/s, producing fine-grained polycrystalline Si.

Abstract: An equation expressing the volume fraction,x, of crystals precipitating in a glass heated at a constant rate, α, was derived. When crystal particles grow m-dimensionally,x is expressed as In [- ln(1 -x)] = -n (nα - 1.052mE/RT + Constant whereE is the activation energy for crystal growth andn is a numerical factor depending on the nucleation process. When the nuclei formed during the heating at the constant rate,α, are dominant,n is equal tom + 1, and when the nuclei formed in the previous heat-treatment before thermal analysis run are dominant,n is equal tom. The validity and usefulness of this equation was ascertained by applying it to a Li2O·2SiO2 glass. A method for determining the values ofn andm from DSC curves was proposed and it was concluded that the modified Ozawa-type plot is very useful and convenient to obtain the activation energy for crystal growth.

Abstract: Cristallisation et changements microstructuraux du PEO dans ces melanges par spectroscopie IR et calorimetrie differentielle

Abstract: An important development in the understanding of the fluid dynamics of convection has been the recognition that heatand mass-transfer processes in multicomponent systems are often fundamentally different to those in the more familiar one-component systems. In a system containing two or more properties that have different molecular diffusivities and opposing effects on the vertical density gradient, a wide range of novel and complex convective phenomena can occur. In the last few years fluid dynamicists and geologists have recognized that such convection, known by the general term of double­ diff usive convection, can occur in magmas and in other fluids of geophysical interest. The implications of this form of convection are far-reaching and are likely to revolutionize our perceptions of many geophysical processes. Theoretical and experimental analyses of double-diffusive convection were first developed in relation to the oceans, specifically with a view to explaining several different kinds of layering (Huppert & Turner 198 1a). It is also apparent that double-diffusive convection is likely to occur in many other systems of geophysical interest. Much attention has been given in particular to the notion that double-diffusive convection can play an important role in the differentiation of magmas. Some of the most

Abstract: In the form of a droplet emulsion, a number of liquid metals and alloys have been undercooled by substantial amounts (0.3–0.4 T m ) before crystallization. For example, pure Hg, In, Sn, and Bi can be undercooled by 90°C, 110°C, 187°C and 227°C respectively. Differential scanning calorimetry has been applied to determine the heat capacity difference, ∪Cp, between the undercooled liquid and crystalline solid. With decreasing temperature an increasing value of ∪Cp is observed which implies a reduction in configurational entropy of the liquid. In addition the heat capacity measurements allow for the determination of the free energy and the onset of the hypercooled regime which are useful in the evaluation of the crystallization kinetics.

Abstract: Crystallization at the margin of a quiet cooling magma has been studied numerically, taking into account the kinetics of crystallization. The variables are the latent heat value, the growth and nucleation functions, the initial magma temperature, and the thermal contrast between magma and country rock. We have investigated a wide range of values for these parameters corresponding to natural conditions. We show that after a highly transient stage, crystallization tends toward an equilibrium between heat production (latent heat release) and heat loss. Given the small diffusivity of country rocks, latent heat release is the main factor controlling the temperature evolution. In order to minimize the latent heat release, crystallization occurs at a temperature where nucleation is small. This can be close to either the liquidus or the solidus, depending on the initial conditions. The main process controlling crystallization is nucleation and not crystal growth. Nucleation occurs as a series of sharp pulses followed by longer periods of crystal growth. The nucleation pulses give birth to thermal oscillations. These oscillations can be sustained if the interior magma temperature is above the liquidus independently of the heat loss mechanism. We show that the phenomenon occurs on the scale of a few centimeters which corresponds to the inch-scale layering of many ultrabasic complexes. The model allows us to calculate crystal sizes which are in good agreement with geological observations. The crucial parameters which determine crystal size variations near the margins of igneous bodies are the initial thermal conditions as well as the nucleation and growth functions. In the main cooling regime close to the liquidus, significant size variations can be created by small thermal disturbances.

Abstract: The dependence of the order in the orientation of the chains in the crystalline structure on the crystallization temperature is described for the α-form of isotactic polypropylene.

Abstract: The pH of the solution from which the gel is precipitated determines the calcined zirconia crystal phase. Monoclinic zirconia is produced from materials precipitated in the 6.5 to 10.4 pH range; the tetragonal precursor is obtained for the 3 to 4 or 13 to 14 pH range. The calcination atmosphere, temperature history during calcination, and the presence of alkali do not appear to play a dominant role in determining the zirconia phase composition.

Abstract: The devitrification of glass from the BaF 2 LaF 3 ZrF 3 AlF 3 quaternary system is studied as a function of sample size and heating rate by differential scanning calorimetry. Results are analyzed in terms of a theory of non-isothermal crystallization kinetics similar to that of Matusita and Sakka but modified to allow for diffusion controlled growth of the crystallites.

Abstract: The enthalpies of formation were measured in the intermetallic compounds ZrNi5, Zr2Ni7, Zr7Ni10, ZrNi, and Zr2Ni, and the amorphous Zr1−xNix alloys with x=0.25, 0.35, and 0.65 by means of a solution calorimeter based on liquid aluminium. For the amorphous system Zr1−xNix, the concentration dependence of the crystallization enthalpy was studied by means of differential scanning calorimetry on 12 different compositions. The concentration dependence of the formation enthalpy of the crystalline materials was analyzed in terms of Miedema’s model. The enthalpy effects observed in some of the amorphous alloys point to the occurrence of compositional short‐range ordering.

Abstract: Individual powder particles of a droplet-processed and rapidly solidified 303 stainless steel are characterized in terms of microstructure and composition variations within the solidification structure using scanning transmission electron microscopy (STEM). Fcc is found to be the crystallization phase in powder particles larger than about 70 micron diameter, and bcc is the crystallization phase in the smaller powder particles. An important difference in partitioning behavior between these two crystal structures of this alloy is found in that solute elements are more completely trapped in the bcc structures. Massive solidification of bcc structures is found to produce supersaturated solid solutions which are retained to ambient temperatures in the smallest powder particles. Calculated liquid-to-crystal nucleation temperatures for fcc and bcc show a tendency for bcc nucleation at the large liquid supercoolings which are likely to occur in smaller droplets. The importance of small droplet sizes in rapid solidification processes is stressed.

Abstract: Reaction centers (RCs), integral membrane proteins that mediate the conversion of light into chemical energy, were crystallized by two different vapor diffusion techniques. In one method, small amphipathic molecules (1,2,3-heptanetriol and triethylammonium phosphate) were added to the RCs that had been solubilized in detergent. In the second method, crystallization occurred near the phase boundaries of a two-phase system created by the addition of polyethylene glycol and NaCl to RCs in octyl beta-D-glucoside. Several different crystal forms were obtained; two were analyzed by x-ray diffraction. One was monoclinic (space group P2) with beta = 105 degrees, and a = 70 A, b = 105 A, and c = 85 A, two RCs per unit cell, and one RC per asymmetric unit; the crystal diffracted to 3.5 A at 17 degrees C. The other crystal form was orthorhombic (space group C222) with a = 185 A, b = 170 A, and c = 105 A, with eight RCs per unit cell and one RC per asymmetric unit. Reversible light-induced EPR signals of the primary donor (bacteriochlorophyll dimer) showed that the RCs in the crystal were fully active. From the angular dependence of the EPR signal the molecular g anisotropy of the bacteriochlorophyll dimer was deduced to be g perpendicular - g parallel = (64 +/- 3) X 10(-5). Linear dichroism measurements were performed on the monoclinic crystal. The two bands at 535 and 544 nm assigned to the Qx transitions of the bacteriopheophytins were resolved and preliminary orientations of some of the pigments were obtained.

Abstract: Although europium speciation in silicate melts partly reflects prevailing oxygen fugacities, melt composition and structure play the major role in determining Eu2+/ Eu3+ ratios and europium partitioning into mineral phases Experimental evidence by different investigators on the magnitude of the compositional effect on Eu2+/Eu3+ provides consistent results only if account is taken of the oxygen buffer system employed in the experiments The medium-dependent reduction of europium can be understood in terms of the preferential stabilization of Eu2+ by a strong aluminosilicate complex in the melt phase, and to a much lesser degree by metasilicate complexes The stability of these complexes increases as the field strength of the associated cation species decreases Hence Eu2+-aluminosilicate complexes are preferentially stabilized relative to trivalent lanthanides in melts of appropriate composition and their presence minimizes the enthalpy of the melt The influence of these complexes is particularly pronounced in melts with a high feldspathic component and a strongly polymerized structure Their petrogenetic influence is best documented through the behaviour of europium relative to the other lanthanides during “anhydrous” anatexis in high-grade metamorphic terrains and in the anomalous europium partition coefficients of phenocryst phases which formed during the crystallization of highly silicic magmas

Abstract: When outer membranes from Neurospora crassa mitochondria are treated with low levels of phospholipase A2 under continuous dialysis, two-dimensional crystalline arrays of the pore protein component of these membranes are formed.

Abstract: The gels in the binary and ternary systems: SiO 2 B 2 O 3 , SiO 2 P 2 O 5 , SiO 2 B 2 O 3 P 2 O 5 ; were prepared by hydrolysis and polydensation of metalorganic compounds. The gelling times vary with the molar percentage of SiO 2 . The solvent was evacuated under hypercritical conditions in an autoclave in order to obtain aerogels free of cracks. The monolithicity of the aerogels is influenced by the method of preparation of the alcogels. The crystallization of BPO 4 was observed in the ternary system only. These materials can be converted into glasses by heat treatment. The structural evolution was followed by means of infrared spectroscopy and textural evolution by dilatometric measurements.

Abstract: Geochemical and field data for the Cordillera Paine (CP) pluton of southern Chile, indicate that differentiation took place by closed system in situ fractional crystallization. Minor, local and irregular separation of liquids from crystals led to the formation of evolved granites and aplites which are encountered mostly at the plutons roof and margins. Chemical trends show strong depletions of Sr, Ba, Mg less intense depletions of Ca, La, Ce, Nd, Fe, Ti, Al and enrichment of Nb, Y, Th, Rb and Si with differentiation. Pronounced crystal zoning of Ca, Sr and Ba in plagioclase, Ba in orthoclase and LREE, Y and Th in allanite closely correspond to the whole rock chemical variation. The crystal zoning data suggest that surface equilibrium only was maintained for the zoned elements during crystallization. Thus, continuous separation of liquids from crystals was not necessary to generate the kind highly evolved differentiates whose character reflects fractional crystallization. The schedule of liquid-crystal separation affects mainly the location, degree of dispersion and relative abundance of the differentiates. The homogeneity of the CP pluton and the intense crystal zoning suggest that crystal-liquid separation was inefficient, and that whole rock compositions approach liquid compositions. Assumption of a closed system during crystallization allows estimation of mineral/melt partition coefficients (K d s) using crystal core and whole rock compositions. Crystal zoning and whole rock chemical trends are consistent with models constructed using the K d s thus obtained along with modal abundances from petrographic estimates.

Abstract: Reduction of ethyl 4,4,4-trichloro- and 4,4,4-trifluoro-3-oxobutanoate by fermenting baker's yeast (Saccharomyces cerevisiae) on a preparative scale (20–50 g in ca. 3 1 of H2O) gave 70–80% yields of the trichloro- [(−)-(S)-1a] and trifluoro-hydroxyesters [(+)-(R)2a] of ca. 85 and 45% ee, respectively. Both, (−)-1a and (+)-2a could be obtained in > 98% ee by subsequent crystallization (of(−)-1, (+)-2a or the 3,5-dinitrobenzoate (+)-2b. The absolute configuration of both hydroxyesters was determined (a) by chemical correlation ((−)-1a), (b) from the melting diagrams and mixed melting points (differential-scanning calorimetry Fig. 1) of the dinitrobenzoates of the CF3-derivative (+)-2a and its CH3-analogue 8, and c) by X-ray analysis of the ester 2f from (+)-2a and (−)-camphanoyl chloride (Fig. 2 and 3).

Abstract: PURPOSE:To obviate the generation of crystallization and solvent crack in a charge transfer layer in the stage of manufacturing said layer and to maintain excellent mechanical strength and electrophotographic characteristic for a long period of time by using a specific arom. polycarbonate resin as a binder polymer of the charge transfer layer. CONSTITUTION:The arom. polycarbonate resin expressed by the formula is used as the binder polymer of the charge transfer layer. In the formula, X, X' denote a hydrogen atom, halogen atom or methyl group and R denotes a hydrogen atom, halogen atom, hydroxyl group, carboxyl group, acetyl group or alkyl group of 1-4C. The crystallization resistance of the charge transfer with a solvent is thus improved and the generation of the solvent crack by the solvent in the stage of coating the upper layer is obviated. As compared with the photosensitive body in which ordinary polycarbonate of bisphenol is used for the charge transfer layer, the excellent electrical characteristic exactly equal to the electrical characteristic of such photosensitive body is obtd.

Abstract: The primary crystalline phase developed in glass-ceramics in the system PbO-BaO-TiO2-B2O3 was investigated. X-ray diffraction and dilatometry were used to identify the primary phase as essentially pure PbTiO3. Peak shifts observed in X-ray diffraction patterns resulted from lattice strain due to crystal clamping, and not from (Pb, Ba) TiO3 solid solution formation. Lattice strain was found to increase as the glass-transition temperature of the residual glass increased above the Curie temperature of PbTiO3.

Abstract: The crystallization kinetics, viscosity, and temperature coefficient of expansion of amorphous As2Se3 were investigated. The crystallization kinetics of As2Se3 are characterized under isothermal conditions for undercoolings ranging from 37°C to 122°C using thermal analysis techniques. The crystallization kinetics can be accurately described by the Johnson-Mehl-Avrami transformation equation. At least at the lower observed temperatures As2Se3 exhibits an increasing nucleation rate with respect to time. Microscopic examination of partially crystallized specimens reveals constant isothermal growth rates with respect to time and a spherulitic growth habitat for the crystalline phase. All spherulites nucleated at free surfaces. The individual As2Se3 crystallites in the spherulites have a plate-like growth morphology at temperatures well below the crystalline melting point. At temperatures approaching the crystalline melting point the crystallites assume a rod-like growth morphology. The activation energy for the crystal growth rate was determined to be 1.6 eV by direct observation. A model for the crystallization kinetics consistent with the data is suggested which yields an activation energy of 2.7 eV for secondary nucleation within the spherulites for 240°C The viscosity of As2Se3 in the pure and doped states (1 at.% Ag) was measured in the glass transition region. Utilizing these data for pure As2Se3 and the high temperature data of previous investigators the interpolated activation energy for viscous flow in the temperature region of rapid crystallization was determined to be 2.7 eV. The linear temperature coefficient of expansion was determined to be 1.55 × 10−5/°C for T

Abstract: An equation is derived for evaluating the kinetic parameters of a transformation from variable temperature DSC or DTA, taking account of the variation in the reaction rate constant with time and temperature. Kinetic parameters for the crystallization of a ZrF4-BaF2-LaF3 glass are calculated using this equation.

Abstract: The effect of ionizing radiation on the melting behavior of high-density and low-density polyethylene was examined with data obtained by differential scanning calorimetry. Melting temperatures and fusion endotherms were obtained after absorbed doses of gamma radiation up to 3 MGy. The changes in melting temperatures and heat of fusion for the first and second meltings are related to the radiation chemistry of polyethylene. The changes in the first melting temperature are caused by radiation-induced links that decrease the melt entropy and increase the flod surface free-energy-per-unit area of chain-folded polyethylene crystals. These effects are dependent on the lamellar thickness distribution and on the types of links formed (intramolecular or intermolecular). The changes in melting temperature and heat of fusion obtained in the second melting are related to the inhibition of crystallization caused by the presence of radiation-induced links.