Crystalline morphologies of poly(e-caprolactone) (PCL) and deuterated polycarbonate (d-PC) blends were studied by small-angle neutron and X-ray scattering (SANS and SAXS). Measurements were conducted at both room temperature and temperatures above the melting point (60 °C) of PCL. Due to the different contrast between the phases for neutrons and X-rays, SANS exhibited a monotonic drop in intensity with increasing scattering angle while SAXS showed lamellar (peak) scattering. A two-correlation length model provided an excellent fit for the SANS data over the entire composition range. This model reproduced not only the shape but also the absolute magnitude of the scattering curves. The long range correlation length (~10s A) and the short range correlation length (-10 A) derived from this model are inferred to be associated with the crystalline PC domain and the local cluster in the amorphous phase (possibly resulting from crystallization-induced phase separation), respectively. Both the long range correlation length obtained from SANS and the long period measured from SAXS showed identical composition dependence. This further supports the applicability of the two-correlation length model and our interpretation.
The phase equilibria of the quinary system Na + +K + + Cl -+ CO 3 2-+ B 4 O 7 2-+ H 2 O was studied at T ) 298.15 K by the isothermal dissolution equilibrium method. The solubility and physicochemical properties (density, viscosity, refractive index, conductivity, and pH value) of the equilibrium solutions were determined. A phase diagram and physicochemical properties-composition diagrams were plotted on the basis of the solubility data. The isothermal solubility diagram of the quinary system (saturated with KCl) consists of 14 univariant curves, 7 invariant points, and 8 crystallization regions corresponding to NaCl, Na 2 B 4 O 7 ‚10H 2 O, K 2 B 4 O 7 ‚4H 2 O, Na 2 CO 3 ‚10H 2 O, Na 2 CO 3 ‚7H 2 O, Na 2 CO 3 ‚H 2 O, NaKCO 3 ‚6H 2 O, and K 2 CO 3 ‚1.5H 2 O, respectively. Pitzer's theory was adapted for theoretically describing relations of the high-concentration multicomponent systems in the study. Using Harvie's chemical equations, which are based on Pitzer's theory, the solubility of the quinary system at T ) 298.15 K was calculated. The calculated values agree with the measured ones, with a deviation of less than 9.59%.
Abstract:The possibilities of different phase transitions to cBN with Li 3 N as catalyst at high temperature and high pressure (1600-2200 K, 4.8-6.0 GPa) are analyzed, in the framework of the second law of thermodynamics. The Gibbs free energy (∆G) of three reactions which may happen in the Li 3 N-BN system: hBN + Li 3 N→Li 3 BN 2 , hBN→cBN, and Li 3 BN 2 →cBN + Li 3 N, is calculated, with the influence of high temperature and high pressure on volume included. We show that ∆G of hBN + Li 3 N→Li 3 BN 2 and hBN→cBN are between −35~−10 KJ·mol , respectively. However, ∆G of Li 3 BN 2 →cBN + Li 3 N can be positive or negative. The area formed by the positive data is a V-shaped area, which covers the most part of the cBN growing V-shaped area. It confirms that Li 3 BN 2 is stable in the P-T area of cBN synthesis, and cBN is probably transformed directly from hBN. Analysis suggests that Li 3 BN 2 promotes the transition from hBN to cBN.
Abstract:The nucleation of cubic boron nitride (cBN) single crystals synthesized with lithium nitride (Li3N) as a catalyst under high pressure and high temperature (HPHT) was analyzed. Many nanometer-sized cubic boron nitride nuclei formed in the near surface layer, as detected by high resolution transmission electron microscopy. Based on the experiment results, the transformation kinetics is described by a nucleation and growth process in the thermodynamic stability region of cBN. A theoretical description is developed based on the heterogeneous nucleation and layer growth mechanism, and the relevant parameters are estimated and discussed. The critical crystal radius, r*, increases with the temperature under constant pressure; the change with temperature more pronounced at lower pressure (such as 4.5 GPa). The crystal growth velocity increased with the temperature, and it is parabolic with temperature under certain pressure. These results are consistent with experimental data.
In this paper, cubic boron nitride (cBN) single crystals are synthesized with lithium nitride (Li 3 N) as catalyst under high pressure and high temperature (HPHT). A lot of nanometer-sized cubic boron nitride nucleuses are found in the near surface layer of cBN crystals by high resolution transmission electron microscopy examinations. Based on the experiment results, the transformation kinetics is described by a nucleation and growth process in the thermodynamic stability region of cBN. The theoretical description is based on the heterogeneous nucleation and layer growth mechanism, and the relevant parameters are estimated and discussed. The results show that critical crystal radius, r * , is increasing with the elevated temperature under the same pressure, and temperature is the main influence on it under lower pressure. At the same time, the results show that crystal growth velocity has different changing tendency with different pressure under proper synthesized scope. The effect of the catalyst is suggested to lower the activation enthalpy for nucleation. These results are well consistent with experimental data.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.