Papers by Keyword: Gas Phase

Abstract: Kinetics of the siderite ore roasting in the air, helium and hydrogen flows has been studied in a gasometrical unit with continuous mass variation logging. We have derived the expression for determination of an apparent degree of calcination and identified its dependence on the size of the prill, the heat treatment duration, and gas-phase composition. Using a generalized chemical kinetics equation, we have obtained a formula for calculation of the decomposition period for siderite ore samples. It has been found that calcination rate increases with the temperature rise, irrespective of the sample size and atmospheric composition. Calcination process has been studied at low temperatures. We have demonstrated that it is feasible to describe the process of siderite ore thermal dissociation by a first-order kinetics equation. We have obtained the expression to calculate the duration of this process depending on different parameters. Using a generalized chemical kinetics equation, we have obtained a formula for checking the expressions that describe the experimental data. We have studied kinetics of the reduction of roasted ore samples at various temperatures using different sizes of the samples. The obtained results have been applied for optimization of the design values and operating conditions of the siderite ore roasting in shaft furnaces. These will also be used for designing a shaft furnace consisting of a calcination zone, reduction zone (metallization zone) and metallized product cooling zone, which will increase iron content in the end-product to 65-70%.

Abstract: In this research core-shell Cu@Si nanoparticles were obtained through evaporation of elemental precursors by a high-powered electron beam. The structures of the particles were investigated in order to elucidate their mechanisms of formation. The thermal stability of the particles was studied with the help of molecular dynamics calculations. The parameters of the thermal stability of the composite nanoparticles Cu@Si with different size were determined. It was concluded that with the temperature increasing the diffusion of copper atoms on the surface begins, leading to a reversal of the structure and the formation of particles having a particle type Si@Cu.

Abstract: Using the self-made experimental device, when MSW RDF was incinerated at temperature of 500°C ~900°C for 60min, Hg almost evaporated into the gas phase. With the increase of incineration temperature, concentration of 6 kinds of heavy metals in the gas phase increased and in the solid phase reduced significantly. The addition of 5% chlorine can make the concentration in gas phase of 8 kinds of heavy metal increased and heavy metal content of Zn, Cu, Pb, Cd, Hg in the solid phase decreased sharply. When the content of organic chlorine increased to a certain extent, no-volatile heavy metals such as Ni, Cr, concentration in the gas phase increased by about 30%. Compared with adding 5% PVC, the difference of adding 10% PVC is not significant. For Pb, Zn, concentrations in the gas phase increased and in the solid phase decreased slightly with water increasing, but effects on Cu were smaller, while on Hg, Cd, Ni, Cr, almost no effects.

Abstract: Presence of atmospheric PAHs in urban and suburban region (Beijing, China) was studied in April and July 2011. Forty-four pairs of gas and particle (TSP) phase samples were collected every six day by high volume (Hi-Vol) air samplers at four sampling sites, and determined separately by GC/MS based on USEPA Method TO-13A. Average total concentration (gas + particles) of PAHs (T-PAHs) was 135.1±49.0 ng/m3 and 181.2±40.9 ng/m3 in April and July, respectively. Gas phase PAHs (G-PAHs) was the major fraction, comprising 63–92% of T-PAHs. Lighter (2-, 3-, 4-ring) and heavier (5-,6-ring) PAHs were found predominantly in gas and particle phase, respectively. 2- to 6- ring PAHs contributed 10%, 53%, 26%, 7% and 4% of T-PAHs, respectively. Five major PAHs, naphthalene (NAP), fluorene (FLU), PHE, fluoranthene (FLA), and pyrene (PYR) contributed 70 – 90% of T-PAHs. G-PAHs increased significantly while PAHs in particle phase (P-PAHs) decreased from April to July. Volatilization from soil and more emission from power generation increase might explain the increase of G-PAHs, and the washout of P-PAHs along with particles might explain the decrease of P-PAHs. Given particulate organic carbon (OC) and elemental carbon (EC) being well correlated, P-PAHs was moderately correlated with OC and EC, suggesting that there were other mechanisms contributing to P-PAHs different from those of OC/EC. Significant correlation between P-PAHs with SO2 and NO2 suggested coal combustion and automobile exhaust to be contamination contributors.

Abstract: This paper introduces the fabrication method of a kind of gas phase phosphorus heavily-doped float zone (FZ) silicon, including thermal field design (electromagnetic copper coil with double water cooling system). This method solves the problems during the pulling process of heavily-doped FZ silicon crystal of phosphorus doped. The gas phase phosphorus heavily-doped FZ silicon crystal using this methods with low oxygen content (less than 0.2ppma),low radial resistivity variation (less than 10%), low resistivity (the minimum of 0.002 ohm.cm), and is good to meet the transient voltage suppressor (TVS) for silicon substrate material requirements.

Abstract: A two-phase model is proposed for describing the dynamics of a fluidized bed reactor used for polypropylene production. In the proposed model, the fluidized bed is divided into an emulsion phase and bubble phase where the bubble phase flow pattern is assumed to be plug flow and the emulsion phase is considered to be perfectly mixed. Similar previous models consider the reaction in the emulsion phase only. In this work the contribution of reaction in the bubble phase is considered and its effect on the overall polypropylene production is investigated. The kinetic model combined with hydrodynamic model in order to develop a comprehensive model for gas-phase propylene copolymerization reactor. Simulation profiles of the proposed model were compared with those of well mixed model for the emulsion phase temperature. The simulated temperature profile showed a lower rate of change compared to the previously reported models due to lower polymerization rate. Model simulation showed that about 13% of the produced polymer comes from the bubble phase and this considerable amount of polymerization in the bubbles should not be neglected in any modeling attempt.

Abstract: The well known wet chemical treatments of the silicon surface and its native oxidation in air cause a high density of interface states, which predominantly originate from dangling bonds strained bonds or from bonds, between adsorbates and silicon surface atoms. Therefore, a number of wet-chemical treatments have been developed for ultraclean processing in order to produce chemically and electronically passivated surfaces [1]. The saturation of dangling bonds by hydrogen removes the surface states and replaces them by adsorbate-induced states, which influence the surface band-bending [2]. The first thermal hydrogen desorption peak from a hydrogen passivated Si surface in vacuum or inert gas ambient can be detected at around 380°C [3,4]. Simultaneously the combination of the hydrogen atoms of neighboring dihydrides generates a pair of dangling bonds. At around 480-500°C dangling bonds are generated on the silicon surface by desorption of the remaining hydrogen [5]. At that moment the silicon surface becomes extremely reactive.

Abstract: Nanoporous-carbon (NPC) is compared directly to commonly-used polymers as a gassorbing coating material on surface acoustic wave (SAW) microsensor devices. The sensing capability of these materials is measured for volatile organic compounds (VOCs), toxic-industrial chemicals (TICs), and a chemical warfare agents (CWA) simulant. All of the coatings reversibly sorb and desorb the volatile VOC and TIC compounds, however, NPC outperforms the polymers over the range of analyte concentrations studied, especially at the lowest levels, by multiple ordersof- magnitude. Conversely, NPC has good retention properties for the semi-volatile CWA simulant tested, which while detrimental for use on a reversible SAW device, infers that NPC may be wellsuited as a preconcentrator coating for such analytes. NPC is a highly-disordered low-density carbon containing both nanopores and increased interplanar spacing between graphene sheet fragments, self-assembles using pulsed laser deposition, has no residual-stress at room temperature, is stable to 600 °C, and is chemically-inert in harsh environments. It has superior chemical and aging properties compared to the conventional polymer films used in microsensor devices.

Abstract: For long time it is known that protons in aqueous solutions have a detrimental effect on metallic materials. Relatively recently, it has also been observed in aqueous solution that the pitting corrosion resistance of Cr, stainless steel 304 and 310 decreases and the anodic dissolution rate increases due to the presence of hydrogen in the metal. In gas phase a high oxidation rate has been observed for hydrogen containing Cr and Fe. Hydrogen in the substrate can also enhance the oxidation of Fe in SS 316 and As in GaAs. All these results suggest enhanced dissolution in aqueous solution and enhanced oxide growth at the oxide/gas interface in gas phase oxidation due to hydrogen promoted outward-transport of substrate components. A possible mechanism for such out-transport is an increased metal ion diffusivity in the metal-oxide due to a high abundance of metal ion vacancies generated by hydrogen. In contrast to all the above examples, also positive effects of hydrogen have been identified under certain conditions. In an attempt to understand both the negative and the positive effects the concept of a beneficial, balanced oxide growth is used. In this concept a certain amount of hydrogen can be beneficial in the oxidation by improving the balance between oxygen-ion and metalion transport, leading to more dense and protective oxides. Depending on the temperature, H2 in air is considered as either a sink or a source for hydrogen in materials.

Abstract: In this study the vapour phase surface graft polymerization of acrylonitrile (AN) onto poly(ethylene terephthalate) (PET) film was conducted with benzoyl peroxide (BPO) as an initiator. Effects of reaction time and quantity of BPO on the polymerization were investigated. With the prolongation of reaction time, the graft polymerization took place rapidly at first, then slowed down, and leveled off. With the increase of BPO, the graft yield increased, then remained unchanged, and lastly began to decrease. The surface topography structure of the grafted PET film was observed by SEM. Grafted PET film was characterised by FTIR spectra, SEM photographs and contact angle measurement.