Influence Of Melting Conditions Research Articles

Influence of melt preparing technology on the structure of cast aluminum-silicon alloy

Influence of melting conditions on the structure of AL30 alloy has been studied. To this end, the temperature dependences of physical properties of liquid alloy has been investigated. In is shown, that the formation of the microhomogeneous and the equilibrium alloy structure during melting process leads to significant decreasing of amounts of eutectic silicon. However, the amounts of primary α-aluminum solid solution and intermetallic compounds with dendritic form are increasing. Such treatment leads to decreasing of size of primary α-aluminum solid solution particles. On the base of experiments the physical model of aluminum-silicon alloy solidification was proposed.

Influence of melting conditions on the thermal behaviour of poly( l-lactic acid)

Abstract The influence of melting temperature and time on the thermal behaviour of poly( l -lactic acid) (PLLA) was studied with differential scanning calorimetry (DSC). Different melting conditions were investigated at temperature ranging from 200 to 210 °C, and for time from 2 to 20 min. For lower-molecular-weight PLLA, a single exothermic peak could be observed at cooling rate of 2 °C/min, after melted at different conditions. The obtained peak temperature and degrees of crystallinity dramatically increased with an increase of melting temperature or time. During subsequent heating scans, double melting peaks could be observed, which were significantly affected by prior melting conditions. The degradation of this material in the melt and the melt/re-crystallization mechanism might be responsible for the observations above. Apart from double melting, double cold crystallization peaks were observed during heating traces for this material after fast cooling (20 °C/min) from the melt. Prior melting conditions could significantly influence the cold crystallization behaviour. The competition between the crystallization from the nuclei remained after cooling, and that from spontaneous nucleation might be responsible for the appearance of double peaks. Additionally, the influence of melting conditions on the thermal behaviour of PLLA was dependent on the initial molecular weight.

Cr(III) in gahnite-containing transparent glass-ceramics: Influence of melting conditions and heat treatment on crystallization and spectroscopic properties

Abstract Transparent glass ceramics with Cr(III) were obtained by different thermal treatment of glass with composition (mol%) 73.6 SiO2,11.8 Al2O3, 4.2 Li2O, 7.0 ZnO, 1.6 TiO2, 1.5 ZrO2, 0.3 As2O3, 0.024 Cr2O3, melted under various conditions. Parallel measurements of X-ray diffraction, optical and EPR spectra reveal the different formation ofgahnite from precursor glass or petalite-like phase.

Influence of melting conditions on the quality of baddeleyite-corundum refractories

On etudie la qualite de refractaires d'alumine-zircone electrofondus en fonction des conditions de fusion (oxydante ou reductrice). La fusion oxydante donne les meilleurs resultats

Kinetics of polymer crystallization from the melt (calorimetric approach)

AbstractCrystallization kinetics for 12 polymers including polyolefins, polyesters, polyurethanes, polysiloxanes was measured by the evolution of heat in a modified Calvet‐type calorimeter over wide temperature ranges. The results are analyzed in terms of the Avrami equation and a comparison between calorimetric and dilatometric results is carried out. It is concluded that, although in the majority of cases experimental results do not obey the Avrami equation, for some polymers the agreement is rather good. The Avrami parameter obtained, however, depends on the experimental technique. Possible reasons for this disagreement are discussed. Analysis of the calorimetric crystallization rate in the vicinity of the melting point by using the kinetic theory of crystallization shows that the growth is controlled by surface (two‐dimentional) nucleation. Energy parameters for the crystallites were determined and it is shown that the surface energy of the crystallites depends on the molecular structure of the polymer. Temperature dependence of the calorimetric crystallization rate of the polymers for which crystallization rates could be determined above and below the maximum rate are analyzed using a kinetic equation with common approximations for the transport term. The influence of melting conditions on the crystallization rate was studied. The results indicate heterogeneous nucleation in the polymer melt. It is concluded that this may be due both to impurities and to high regularity of macromolecules in the polymer melt.