Advanced Materials Research Vols. 236-238

Abstract: Surface with micro-porous layer can enhance the boiling heat transfer efficiency of tube. The novel nucleate boiling tubes were manufactured by sinter-bonding metal particles on the outside surface. Two conventional bare tube reboilers were revamped with the novel tubes. Industrial application revealed that the revamps effectively increased the heat duty of reboilers with small heat transfer area and reduced heat transfer temperature difference across the heat exchanger. Porous surface tube was beneficial to heat transfer and operating cost.

Abstract: The corrosion behavior of Al-RE coating in copper accelerated acetic acid salt spray test (CASS) was studied by electrochemical impedance spectroscopy (EIS). Typical EIS spectral changes were clearly observed during the CASS process. The EIS was shown to be a very useful tool for studying corrosion resistance mechanism. Scanning electron microscope and X-ray energy dispersive spectroscopy were used to analyze the microstructure of Al-RE coatings before and after CASS test. The results revealed that the corrosion behavior of Al-RE coating could be divided into two different stages. In the first stage of CASS, there were two capacitive impedance semicircles in the complex plane plots. The high frequency semicircle responded to barrier layer, the low frequency semicircle responded to the electrochemical reaction of Al-RE coating. In the second stage of CASS, porous layer began to influence the electrochemical behavior.

Abstract: In this paper a novel strategy that aimed to coordinate the hydrolysis rates of different silanes was used to prepare PMOs. Attribute to the organic precursor released from the CH₂Cl₂ phase, the hydrolytic process of organosilane was obviously changed in the water-surfactant system. Consequently, the hydrolysis rates of different silanes do well match in a macroscopic level. These PMO materials were characterized by TEM and powder XRD. All the results indicated that large organic functionalized PMO materials with highly ordered hexagonal mesostructure and high loading of organic species were successfully prepared, while the ²⁹Si MAS NMR experiment proved the organic species had been incorporated into the framework.

Abstract: A numerical approach was used to investigate the flow characteristics around a butterfly valve with the diameter of 2108 mm by the commercial computational fluid dynamics (CFD) code FLUENT6.3. The simulation was carried out to predict flow field structure, flow resistance coefficient, hydrodynamics torque and so on, when the large diameter butterfly valve operated at various opening degrees. The three-dimensional simulation results shown that there are vortexes presented near valve back region as the opening degree smaller than 40 degree; the flow resistance coefficient reduces rapidly with the increasing of opening degree and the resistance coefficient is quite small as the angle larger than 50 degree; the hydrodynamic torque reduces with the increasing of opening degree and the hydrodynamic torque is smaller than 20% of maximum torque; the torque ratio and the pressure drop ratio are reduce with the increasing of opening degree, the pressure drop ratio reduces rapidly as the opening degree is smaller than 50 degree.

Abstract: Carbon nanofibers synthesis from the flame is a new method. The method needs simple laboratory equipments and normal atmosphere pressure. The experimental system is introduced. Carbon source is the carbon monoxide and the nitric acid nickel is served as catalyst. The carbon nanofibers were characterized by scanning electron microscope and transmission electron microscope. Carbon nanofibers with less impurity were captured successfully in the flame. The diameter of carbon nanofibers was approximate from one to two hundred nanometers, and its length was dozens of microns. The growth process and mechanism of carbon nanofiber from the flame is very complicated. The influence of catalyst can reveal the growth mechanism of carbon nanofiber. This study aims to examine the catalyst formation condition for carbon nanofibers in pyrolysis flame and to characterize the morphology. Carbon nanofibers with less impurity can be prepared when the diameter of catalyst in is between twenty and thirty nanometers. The catalyst particle size can determine the morphology of carbon nanofibers.

Abstract: Nitrogen-doped zinc oxide (N-doped ZnO) nanocrystallites were synthesized via improved one-step combustion technique by using citric acid as additive. Scan electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to determine the grain size, shape, degree of nitrogen incorporation and nature of the resultant oxynitride chemical bonding. The catalytic performance of N-doped ZnO on the thermal decomposition of ammonium perchlorate (AP) was investigated by DSC-TG technique. The results show that the as-synthesized N-doped ZnO has uniform crystallite size about 20-30nm in diameter and 1.25%wt nitrogen incorporation, which forms into NO bonding region in ZnO crystal lattice. The nitrogen doping is accountable for the significant increase in catalytic activity on the thermal decomposition of AP versus the commercial nanometer ZnO and the thermal decomposition peak shifts 133°C downward when the content of N-doped ZnO in AP is 3%wt.

Abstract: High-purity and homogeneous powders of CeB₆ with nanometer size were prepared by combustion synthesis and subsequent acid- leaching. The effects of reactant ratio on the phase and morphology of the combustion product were discussed. The combustion product and leached product were analyzed by XRD, SEM and EDS. The results indicate that the combustion product consists of CeB₆, MgO and Mg₃B₂O₆. The combustion products are denser and less layered when the Mg content and KClO₃ content increase. The content of CeB₆ in the combustion product could be enhanced with increasing the excessive content of Mg. The purity of CeB₆ is higher than 99.0% and its particles are smaller than 150nm.

Abstract: Cu₃V₂O₈ powder was prepared by the liquid phase precipitation method and characterized using XRD , SEM and BET. The photocatalytic decolorization of methyl orange in Cu₃V₂O₈ powder suspension was investigated using 20w UV light as light source．The result shows that the the liquid-phase precipitation method is a simple and effective method for Cu₃V₂O₈ powder preparation. It was found that the sample prepared with the n(V)/n(Cu)moral ratio be 2/3, pH=7 and calcinated under 750°C for 4 hours was pure triclinc Cu₃V₂O₈ phase.

Abstract: The precursor of yttria was prepared by yttrium nitrate and ammonium oxalate in water solution. Pyrolysis behavior of the precursor and the characterization of yttria phase transformation were studied through thermoanalysis. The grain growth kinetic behavior of yttria nanopowders was investigated by the X-ray powder diffraction (XRD) result of the powders obtained through roasting the precursor. Pattern of the yttria powders and agglomeration of its grain were measured by means of SEM and laser particle size analysis methods. The results suggested that cubic crystal phase yttria could be obtained by sample calcination for 1 h under 823 K. When the precursor was calcined under conditions of temperature ranging from 823 K to 1173 K, yttria grain ranging 7 nm ~ 16 nm could be obtained ,with grain growth exponent of n< 0.2 . In addition , an significant increase in grain-growth-rate constant was observed as the temperature went up. The higher temperature, the faster growth. Grain growth activation energy was different in low-temperature and high-temperature fields. The activation energy was 77.42 kJ•mol^-1 when the temperature was lower than 965 K, and became 524.36 kJ•mol^-1 when the temperature was higher than 965 K. Yttria powders is highly dispersed whose agglomerates sized about 400 nm after being dispered in deionezed water.

Abstract: The crystal zinc borate (Zn₃B₆O₁₂·3.5H₂O) nano-strips and nano-flakes were successfully prepared by a wet method using boric acid (H₃BO₃) and Zn(NO₃)₂·H₂O as raw materials in situ aqueous solution, and triethanolamine as the modifying agent. The nano/microstructures and morphologies of the as-obtained samples were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometer (EDS) and thermogravimetric analysis (TGA). It had been found that the as-prepared materials displayed nanostrips with average length from 100 to 200nm and the thicknesses about 30nm as well as nanoflakes with diameter about 4μm and thickness about several nanometers morphology.