Coalescence of Cu contacted nanoparticles with different heating rates: A molecular dynamics study

The coalescence, the initial stage of sintering, of two contacted Cu nanoparticles is investigated under different heating rates of 700, 350 and 233 K/ns. The nanoparticles coalesced rapidly at the initial stage when the temperature of the system is low. Then, the nanoparticles collided softly in an equilibrium period. After the system was increased to a high temperature, the shrinkage ratio, gyration radius and atoms’ diffusion started to change dramatically. The lower heating rate can result in smaller shrinkage ratio, larger gyration radius and diffusion of atoms. However, the growth of sintering neck is hardly influenced by the heating rate. The results provide a theoretical guidance for the fundamental understanding and potential application regarding nanoparticle sintering.

Effects of Ni Sheath on the Microstructure and Properties of BSCCO-2223 Tapes

Effects of Ni sheath on the microstructure, mechanical properties and bubbling phenomenon during heating process of BSCCO-2223 ceramic tapes have been investigated. Ni sheath gives Bi-2223 tapes a better ability to protect ceramic core from the damage of external force. Hardness of Ni sheath is double than that of Ag sheath reached to about 70 HV. Tensile strength of the Ni-sheathed Bi-2223 tapes is also enhanced by 80%. Harder Ni sheath is also beneficial to improve the texture of the tapes. However, serious bubbling phenomenon, which can reduce the transport property of tapes, will appear during heating process owing to the bad oxygen permeability of Ni. A lower heating rate (30°C/h) is a favorite to decrease the number and size of bubbles. In addition, Ni sheath can reduce the formation rate of Bi-2223 phase which implies that longer sintering time and higher cost of fabrication will be consumed.

A Comparative Analysis of the Kinetic Experiments in Polyethylene Pyrolysis

A review of literature has been conducted to survey the kinetic data of low-density polyethylene (LDPE) pyrolysis. The review reveals large variations in the reported global kinetic parameters. The cause of variation has been identified to be the difference in the experimental techniques, including thermogravimetric analysis (TGA) and non-TGA methods. Even within the nonisothermal TGA data, large variations have been observed at heating rate of 20 K/min, while the variations are insignificant at lower heating rate regimes (2–10 K/min), indicating the influence of heat/mass transfer resistance controlling the kinetics. Detailed analysis revealed that most of the current techniques are unable to capture all the relevant data necessary for estimating the kinetic parameters of the aforementioned process. The outcome of this review work thrusts the need for a better experimental technique to estimate the kinetic parameters of complex reactions, such as polymer pyrolysis.

Reaction Sintering of Mg2Si Intermetallic Compound by Microwave Irradiation

In order to reduce the oxidizing and volatilizing caused by Mg element in the traditional methods for synthesizing Mg2Si compounds, solid state phase reaction at low temperature was introduced by microwave field. XRD was used to characterize the powders. At the same time, the influences of parameters during the synthesis processing were discussed. The results suggest that the heating profile is also dependent on the initial green density and higher green density provides lower heating rate while power setting are fixed and the oxidation of Mg can be rest rained by changing microwave heating programs. It was found that high purity Mg2Si intermetallic compound can be obtained with excessive content of 8at% Mg from the stoichiometric Mg2Si, 853K and 30min

Preparation of Fully Biodegradable Poly(L-lactide) and Poly(ethylene succinate) Blend and its Crystallization Property

Both poly(L-lactide) (PLLA) and poly(ethylene succinate) (PES) are biodegradable synthetic aliphatic polyesters with excellent biocompatibility. They are semicrystalline thermoplastic polymers processed by most conventional processing methods. In view of their complementary properties, blending PLLA with PES becomes a promising approach to improve the properties of PLLA without compromising its biodegradability. In the present work, fully biodegradable PLLA/PES blend(the weight ratio 90/10) was melt-blended in stainless steel chamber. The crystallization morphology was investigated using a polarized optical microscope (POM), showing more clear spherulites with typical crosslink extinction patterns and faster crystallization rate of PLLA in blend at the lower heating rate. It clearly showed that the addition of PES largely increased the crystallization rate of PLLA and improved the crystallinity of PLLA in blends.

Effect of Heating Rate on Sintered Microstructure of W-Cu Nanocomposite Powder Produced Using W-CuO Mixture

The sintered microstructure homogeneity of W-15wt%Cu nanocomposite powders prepared from W-CuO mixture was investigated. The increment of heating rate considerably affected the homogeneity of sintered microstructure. In case of the higher heating rate, the microstructure was more homogeneous than that of the lower heating rate by reason of Cu- exudation during heating-up process.

Temperature selection and thermoregulation in the Moorish gecko, Tarentola mauritanica

Temperature selection in a thermal gradient and the physiological responses to heat exposure were studied in the Moorish gecko, Tarentola mauritanica, from Crete. In association with previous indications that the Moorish gecko has a bimodal activity pattern, we found a bimodal temperature selection with modes at 27-28 and 30-32°C. In this respect, it resembles the closely related Israeli gecko, Ptyodactylus guttatus. However, Tarentola is more susceptible to heat exposure and has a moderate thermoregulatory capacity compared to P. guttatus and this is probably related to its reaching more northern latitudes than Ptyodactylus. During heat exposure (up to 40°C) oxygen consumption increased significantly and was not sustained by the moderate increase (Q10 = 1.44) in heart frequency. We found a significantly lower heating rate than cooling rate in Tarentola. This is in accord with allometric predictions for its low body mass and might stem from the high mass-specific evaporative water loss and from the relatively small increment in heart rate during heat exposure which may adaptively retard heat gain from the environment and maximize its activity periods.

"Scan" behaviour in Podarcis muralis: the use of vantage points by an actively foraging lizard

Two adult Podarcis muralis whose normal movements incorporated the flat top of a wall, frequently paused so that they were looking outwards from an edge ("scan" posture), especially during longer (≥9 s) periods immobile. Investigations of the posture on raised wooden platforms in outdoor enclosures, using two juvenile lizards, showed that (1) lizards spent significantly more time on platforms than would be expected from random movement, and this was not because wood is a favoured substrate for basking; (2) lizards which were immobile on platforms spent significantly more time at edges than would be expected by chance; (3) body orientations at 67.5-112.5° to the edge were the most frequent and these were maintained for significantly longer periods than the remaining orientations; exceptions were from 0800-0900 h when orientation was often parallel to the edge facing the sun and from 1200-1300 h with only a thin strip of shade at 45°, into which the lizards fitted themselves. Lizards basking in the laboratory beneath a tungsten bulb at the edge of a raised platform adopted outward-facing orientations when the platform height was ≥6 mm. When presented with a choice between basking more effectively (i.e. rapid heating rate) or adopting the "scan" posture at an edge with a lower heating rate or with no heating, they opted for the former. Podarcis sicula, P. filfolensis, Lacerta viridis and L. vivipara all showed an excess of outward-facing orientations when the basking bulbs were place near edges of platforms, but Psammodromus hispanicus did not. Only the two Podarcis species, however, spent more time on raised platforms than would be expected by chance when basking was possible at many sites in an arena.