Papers by Author: Ning Hui Wang

Abstract: Using Mg(NO₃)₂·6H₂O as raw materials, Mg(OH)₂ crystals were synthesized by a composite-hydroxide-mediated(CHM) method at 160-200 °C for 24 h. Hexagonal plates Mg(OH)₂ crystal were formed at high content of magnesium nitrate. The size of the plates increased to 5-15 μm while the content of magnesium nitrate was 30 mmol. The strength of (001) plane became stronger than (101) plane with the high content of magnesium nitrate, and this tendency became more obvious at high magnesium nitrate concentration. It is explained that the more Mg²⁺ ion fill the polar plane. The strength of (001) plane became stronger than (101) plane at high temperature. It can be explained Mg(OH)₂ crystal become more steady with more non-polar plane at high temperature, and the shape of the sample showed a change from irregular to cubic shape with heated temperature increase. It indicates that the Mg(OH)₂ crystal growth benefits from high temperature. It is conjectured that the connecting of the [Mg(OH)₆]⁴⁺ basic units with the common edges change into common vertex angle.

Abstract: The novelty of the current work lies in the simple synthesis of a new class of monodisperse, luminescent silica spheres produced upon calcination of hybrid amine-functionalized silica spheres which can known the role of ethylenediamine (en) on the morphology and luminescence properties of the resultant silica spheres.

Abstract: A novel synthesis route for the production of Sr3MgSi2O8:Eu2+,Dy3+ sub-micron quasisphere phosphor powder is reported. Both the host and activator cations were co-precipitated in water-ethanol mixed solutions and precipitation was performed with analytical grade ammonium citratetribasic. As the dispersion media, optimum concentration for PEG in the precursor solution is determined to be 0.08 g/mL. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and fluorescence spectrophotometer were employed to characterize the phosphor. The effect of the calcining temperature on the crystalline particle and luminescence properties of Sr3MgSi2O8:Eu2+,Dy3+ is systematically discussed. Sr3MgSi2O8:Eu2+,Dy3+ single phased quasi-sphere phosphor was achieved by calcining the asprecipitated precursor at 1100°C. Sr2SiO4 was identified as the intermediate phase during the calcination process. Despite the small particle size, the emission intensities were higher by the present method. However, the afterglow characteristic was not better than that prepared by solidstate reaction in the comparable condition.

Abstract: This paper presents a method for calculating the temperature field distributions for MgO single crystal furnace. Finite element method (FEM) had been used to carry out the temperature field distributions of MgO single crystal furnace in terms of its energy consumption. Then fuzzy model of the furnace was developed using adaptive neuro-fuzzy inference system (ANFIS), for carrying out its temperature field analysis. Performance was evaluated by comparing finite element model with fuzzy model and good correlation was achieved between them.

Abstract: High quality magnesium oxide (MgO) single crystals have been grown by an arc-fusion method. Due to the hostile environment for observing the process occurring in the inner zone of the furnace, direct measurements on the arcs by conventional diagnostic method are practically impossible. Moreover, it has been proved that the control of the temperature field of the whole system is crucial to grow high-purityMgO single crystals with large and super-large sizes. However, very few studies have been carried out to investigate the correlation between the thermal behavior and MgO single crystal growth in the furnace. In present study, a transient 3D finite element model has been developed to depict melt/crystal interface and to find out the determining factors that affect the crystal growth rate and the growth direction. It is shown that the model gave a good description of the bath shape which agrees well with that of the solidified MgO in experiments. By the transient analysis, the trend and time delay of the temperature variation on the shell were also predicted.

Abstract: In order to obtain ultra-smooth and damage free substrate surfaces for MgO single-crystal substrate with high polishing efficiency, an experimental investigation based on systemically designed polishing experiments are presented and discussed. Considering the structural characteristics and chemical properties of the MgO single crystal, the experiments use a polishing slurry containing SiO2 abrasives so that the process is performed under a combination of mechanical and chemical actions. The effects of the polishing process parameters, such as polishing pressure, rotational speed of polishing plate, and the flow rate and concentration of the polishing slurry, on the surface roughness and material removal rate (MRR) are analyzed. Finally, a recommendation is made for selecting the appropriate polishing parameters for MgO single crystal substrate, based on which a surface roughness of 0.3nm can be achieved on the MgO substrate in 20min of polishing time.