Interfacial Energy Difference Research Articles

Effect of lattice disregistry variation on the late stage phase transformation behavior of precipitates in NiAlMo alloys

A variety of experimental techniques have been applied to examine how compositional variations in lattice disregistry (δ) affect the coarsening kinetics and particle morphology evolution of γ′ particles in several Ni-Al-Mo alloys. Mo segregates to and increases the lattice parameter of the γ matrix in two phase Ni-base Al alloys. Therefore, controlled ternary additions of Mo to dilute, binary Ni-Al alloys permits variation of the lattice parameter disregistry between the Ni-base solid solution and the Ni 3Al ordered precipitates. Compositions were selected to maintain an approximately constant 10% volume fraction of the second phase. The coarsening rate of the γ′ phase is observed to decrease with decreasing lattice disregistry and decreasing Al Mo ratio. The implications of this observation are discussed with reference to differences in solid solubility, diffusivity and interfacial energy. The γ′ particle shape in low coherency strain alloys is observed to be spherical and independent of particle size. In an alloy exhibiting appreciable δ and coherency strain, the γ′ particles evolve from randomly distributed spheres to sharply aligned cubes and rods as particle size increases. There is also an increase in δ with aging time in this alloy. Compression creep of [100] single crystals at 750°C did not affect the shape of particles in the low coherency strain alloys while in a higher disregistry alloy, a highly oriented array of plates grew with long edges perpendicular to the applied stress direction. These findings are discussed with regard to stress and thermodynamic considerations.

Crystallization kinetics of 1,4‐trans‐polyisoprene, 2. Polymer‐diluent mixtures

AbstractFour mixtures of 1,4‐trans‐polyisoprene with methyl oleate (vol. fraction of polymer: 0,696 to 0,092) were prepared, and a dilatometric study of the crystallization kinetics was carried out in a convenient temperature range. The polymer was found to crystallize in the form of its high melting polymorph. The amount of secondary crystallization was less compared to that observed earlier for undiluted polymer. Formation of crystalline phase was found to be more difficult. In the absence of nucleation and growth data, the actual differences in interfacial energies required for nucleation and growth could not be estimated quantitatively, however, the experimental results indicate that compared to the bulk system, the energy requirements for the primary nucleation act in case of mixtures are higher. The interfacial energy σ′e (calculated after neglecting the transport term) was in the range 2309–2356 cal/mol for all the mixtures and showed appreciable variation with change in polymer concentration. A molecular interpretation of the possible mechanism operating in the crystallization of mixtures is given.

Spherulite nucleation in blends of isotactic polypropylene with high-density polyethylene

Primary nucleation of spherulites in blends of isotactic polypropylene (iPP) with high-density polyethylene (HDPE) has been investigated by means of differential scanning calorimetry and optical microscopy. The number of iPP nuclei in blends crystallized isothermally at temperatures greater than 127°C decreases with increasing HDPE concentration to a much greater extent than follows from the decreasing amount of iPP, whereas in blends crystallized below 127°C this number increases strongly. The shapes of the spherulite size distributions indicate that athermal (heterogeneous) nucleation is disturbed. Experiments with nucleating agents demonstrate that heterogeneous nuclei migrate acrossinterphase boundaries from iPP melt to HDPE melt during mixing due to the difference in interfacial energy between the nuclei and the molten components of the blend. At temperatures below 127°C the HDPE crystals growing in the blend cause additional heterogeneous nucleation of iPP spherulites. This nucleating activity of HDPE crystals is responsible for the increase in nucleation density of the blend in spite of migration.

高温での結晶化現象のその場観察法による研究

An in-situ observation method has been developed to observe growth or dissolution processes of crystals at <1800 K, with as high visibility as in air, and under precisely controlled conditions. The method has been applied to silicate systems. Out of varieties of interesting phenomena, observations on metastable nucleation, which often takes place in complex component systems, are selected for this article. It is shown in a variety of silicate systems that a thermodynamically less stable phase can nucleate and grow steadily prior to the nucleation of the stable phase. This metastable nucleation is interpreted in terms of competition between the difference of interfacial energy between a crystal and a solution, which is evaluated by the number of unsaturated dangling bonds at the crystal surface, and chemical potential of the solution, which is evaluated from the solubility curve determined by this method.

Spherulite growth in isotactic polypropylene‐based blends: Energy and morphological considerations

AbstractThe kinetics of isothermal crystallization of polymer blends in which the matrix is a crystallizable polymer is considered. It is shown that depending on the difference in interfacial energies the inclusions are rejected or engulfed by the growing spherulite. Other factors influencing rejection, engulfing, and/or deformation of dispersed particles of the second polymer are the viscosity of the melt, the spherulite growth rate, and the size of dispersed particles. If the difference in interfacial energies is positive, then rejection or engulfing requires additional work to be done by the crystallization front. This dissipation of energy decreases the spherulite growth rate. It is estimated that the rejection of the second component is the most important phenomenon in the crystallization of blends. The spherulite growth rate of isotactic polypropylene in blends with low‐density polyethylene and several elastomers was studied as a function of crystallization temperature and concentration. The comparison of growth rate data with morphological changes occuring during crystallization of blends studied shows very good agreement with the theoretical predictions based on energetics considerations.

Spherulite nucleation in polypropylene blends with low density polyethylene

Primary nucleation of spherulites in blends of isotactic polypropylene (iPP) with low density polyethylene (LDPE) was investigated by means of differential scanning calorimetry and optical microscopy. The number of iPP spherulites in the blend decreases with increasing LDPE concentration to a much greater extent than follows from the decreasing amount of iPP. The shapes of spherulite size distributions indicate that athermal (heterogeneous) primary nucleation is inhibited. The density of primary nucleation in the blends decreases strongly with increasing mixing time. The same effect was observed in the blends with the nucleating agent which was added to iPP or LDPE. These experiments demonstrate that heterogenoeus nuclei migrate across interphase boundaries from the iPP melt to the LDPE melt during the mixing process. It is suggested that the interfacial energy difference between the nuclei and the molten components of the blend is responsible for the migration of nuclei.

多結晶雪の発生機構

To clarify the formation mechanism of snow polycrystals, which have the misorientation of c-axis at 70.5°, the possibility of formation of a cubic ice nucleus (diamond structure) is discussed on the basis of the homogeneous nucleation theory for supercooled water formed in the phase of supersaturated vapour. From the difference of specific interfacial energy between a hexagonal ice and a cubic ice, it follows that a critical cubic nucleus has a smaller activation energy than a critical hexagonal nucleus below a critical temperature ; namely, Ostwald's step rule (Stufenregel) holds for a change from cubic ice to hexagonal ice below a critical temperature.

Electron microscopy of nucleation and growth of indium and tin films

Abstract The results of measurements of island density and grain size variations as a function of film thickness and substrate temperature of vapour-deposited indium and tin films are given. It was observed that the nucleation and growth characteristics of indium and tin films are different even when the substrate temperatures are in the same ratio of their melting points. These differences are ascribed to the differences in interfacial surface energy, nucleation barrier, and critical thickness. The saturation density of indium was found to be 2 × 1011 cm−2 at 85°C while that of tin was 4 × 1011 cm−2 at 130°c. Island density curves systematically illustrate the occurrence of primary, secondary, and tertiary nucleation. This feature is also apparent from transmission and scanning electron micrographs of films deposited at 130°c. The presence of broad peaks in island density curves and dips in average grain size curves is due to the formation and growth of secondary nucleated islands. The spherical shape of...

L'interface cristal˗bain fondu

The main purpose ol this paper is to underline the fundamental structural as well as interfacial energy differences existing between the crystal-melt interface and other interfaces such as crystal-vapour, liquid-vapour and crystal I-crystal II. After a short review of the existing theories of liquids and melting process, an approach towards understanding the crystal-melt interfacial structure based on the Bernal random-liquid model is suggested. Finally, some preliminary experimental results on the measurement of contact angle and adhesion energy between the densest crystal plane and the melt for close packed metals are presented.

The reflexion of X-rays from the ‘anti-phase nuclei’ of AuCu 3 . II

A simplified method of calculating the diffraction patterns of crystals showing mistake broadening is outlined, and used to correct three results published by Wilson in 1943. Wilson’s model 3 (mistakes on {110} planes) is extended in the light of probable differences of the energy of interfaces between domains of different types. The apparent particle sizes obtained, when differences in interfacial energy are ignored, are: formistakes on { 100 } planes 3 N 1 2 / 2 ( h + k + l ) δ ; formistakes on { 110 } planes 3 ( 2 N ) 1 2 / 4 ( 2 h + k ) δ ; formistakes on { 111 } planes 3 ( 3 N ) 1 2 / 8 h δ if h ≥ k + l , 3 ( 3 N ) 1 2 / 4 ( h + k + l ) δ if h &lt; k + l ; where δ is the probability of a mistake per unit length, h, k, l are the positive values of the indices of reflexion arranged in the order h ≥ k ≥ 1, and N = h 2 + k 2 + l 2 . When differences in interfacial energy are taken into account the apparent particle size for mistakes on {100} planes becomes 2 N 1 2 / { 2 ( h + k + l − u ) δ ′ + ( h + k + l + u ) δ ′ ′ } , where u is the impaired index, and that for mistakes on {110} planes becomes ( 2 N ) 1 2 / { 4 h δ ′ + 2 ( h + k ) δ ′ ′ } when ( 2 N ) 1 2 / { 2 ( h + k ) δ ′ + ( 3 h + k ) δ ′ ′ } when k or l is the unpaired index. All {111} interfaces have the same energy in AuCu 3 , so the expressions for mistakes on {111} planes are not altered.