The Effect of Weight Content or Density on the Burning Behavior of Some Cellulosic Specimens

The effect of different densities of various cellulosic specimens on their burning behavior has been of interest in this investigation. By using a vertical flammability tester, burning times of different unfinished cellulosic samples, such as white paper, straw paper, and cardboard, have been chosen and their flammability characteristics have been determined. The obtained figures for the consumed identical samples show that, by increasing their densities, their burning time and temperature of burning have been increased. However a decrease in the burning rate could rationally be attributed. Furthermore a decrease in the burning temperature proved a reasonable synonymy toward the decrease in the burning rate. In addition to this, burning rate is antithetical toward the density of the consumed specimens. A thermogravimetric analysis of a selected cellulosic material fortified our hypothesis; i.e., the thermal decomposition temperature differs from the burning temperature, whereas the latter temperature is merely dependent on the weight content or density of the samples.     

Facile route to prepare film of poly(3,4-ethylene dioxythiophene)-TiO2 nanohybrid for solar cell application

Composite using poly(3,4-ethylenedioxythiophene) (PEDOT) as electronic conducting polymer and nanocrystalline titanium dioxide (TiO₂) as host matrix were prepared by the template method. We applied an original in situ photopolymerization technique to synthesize PEDOT inside the TiO₂ pore and characterized the polymer and pore filling by different analysis (cyclic voltammetry, atomic force microscopy, spectroscopy and thermogravimetric measurements). Results were compared with those obtained on PEDOT films synthezised by monomer oxidization in the presence of FeCl₃. In situ generation of PEDOT by photopolymerization was observed to be higher and self-limiting after 22% filling of the mesoporous TiO₂ network. Hybrid materials were used to fabricate an indium-tin oxide/nano-crystalline TiO₂/PEDOT/Au device. The current-voltage characteristics indicate that a built-in electrical field has been created at the nano-crystalline TiO₂/PEDOT interface with energy conversion efficiency of 0.09% without dye.     

Wide characterisation to compare conventional and highly effective microwave purification and functionalization of multi-wall carbon nanotubes

Both microwave-assisted and conventional acidic treatments for the purification and functionalization of multi-wall carbon nanotubes were investigated. Impurities such as zeolite, catalyst particles and amorphous carbon were eliminated. In comparison to the harshness of the acidic treatment of a conventional technique, the microwave-assisted procedure makes it possible to obtain a material with a higher degree of purity (> 98%) and -COOH functionalization in a shorter time, at a lower temperature, with a smaller amount and lower concentration of acid, as well as without agitation. An extensive step-by-step characterization of the treated samples has shown that the microwave-assisted treatment has limited effects on the significant characteristics of the nanotubes.     

Effects of precursor evaporation temperature on the properties of the yttrium oxide thin films deposited by microwave electron cyclotron resonance plasma assisted metal organic chemical vapor deposition

Yttrium oxide thin films are deposited using indigenously developed metal organic precursor (2,2,6,6-tetra methyl-3,5-hepitane dionate) yttrium, commonly known as Y(thd)₃ (synthesized by ultrasound method). Microwave electron cyclotron resonance plasma assisted metal organic chemical vapor deposition process was used for these depositions. Depositions were carried out at a substrate temperature of 350 °C with argon to oxygen gas flow rates fixed to 1 sccm and 10 sccm respectively throughout the experiments. The precursor evaporation temperature (precursor temperature) was varied over a range of 170-275 °C keeping all other parameters constant. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and infrared spectroscopy. Thickness and refractive index of the coatings are measured by the spectroscopic ellipsometry. Hardness and elastic modulus of the films are measured by load depth sensing nanoindentation technique.C-Y₂O₃ phase is deposited at lower precursor temperature (170 °C). At higher temperature (220 °C) cubic yttrium oxide is deposited with yttrium hydroxide carbonate as a minor phase. When the temperature of the precursor increased (275 °C) further, hexagonal Y₂O₃ with some multiphase structure including body centered cubic yttria and yttrium silicate is observed in the deposited film. The properties of the films drastically change with these structural transitions. These changes in the film properties are correlated here with the precursor evaporation characteristics obtained at low pressures.     

PBT的湿热老化性能研究(二)

采用热失重方法评估PBT材料湿热老化过程中的变化。PBT材料失重2%时对应的温度,可以反映材料性能的变化。当失重2%温度降低超过10℃时,PBT材料的力学物性也会发生重大变化,下降超过一半。     

Study of ZnSe powder mass depleted in temperature field

Evaporative crystallization of nano-particles involves a complicated multiphase mass and heat transfer process that is dependent on the crystal size in a temperature field. It becomes more complicated for the crystallization of ZnSe powders using this method because of multiprocesses including sublimation, crystallization, and decomposition. This work reports our preliminary studies on the evaporation process to two different sizes of ZnSe powders. We investigated the influences of crystal size on mass depleted between 200 and 800 °C. On the basis of our experimental data, a model of mass depleted of ZnSe nano- and micro-powder was proposed.     

Dielectric characterization of concrete at high temperatures

For reliable modelling of microwave heating of concrete its complex permittivity has to be known precisely within the full range of working temperatures. Dielectric characterization of dry concrete cured with different water-to-cement (w/c) ratios and concrete samples from nuclear power plant constructions was performed during heating and cooling cycles from room temperature to 700 °C and back. On average, higher permittivity values are found for concretes cured with smaller w/c ratio (more dens and less porous) as compared to concretes cured with higher w/c ratio (lighter and more porous). Samples from nuclear power plant reveals a permittivity close to the concrete prepared with lowest w/c ratio. Permittivity change along increasing temperature correlates with moisture loss and thermal decomposition reactions. These reactions are irreversible that lead to a permittivity divergence in heating and cooling scenarios. The variations of concrete permittivity because of w/c ratio, water transport and decomposition reactions are discussed.