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11.
The authors describe the processes that are integral to the production of diamond polycrystals and provide characterization of precursor materials. The methods of producing diamond-based polycrystalline and composite materials are outlined, and the factors that have an influence on the composition and properties of such materials are analyzed. Some new approaches to the production of diamond-based superhard materials of various functionalities are discussed. 相似文献
12.
TiO2 supported on SiO2 surface is effective on the recovery of photocatalyst, morphological control, and coating on the substrate. Furthermore,
it shows much higher photocatalytic activity than pure TiO2. The silica support is quite influential on the surface properties of TiO2 supported on SiO2. The enhanced photocatalytic activity of TiO2–SiO2 could be explained by the effects of surface area, adsorption, band-gap energy and local structure. However, it is difficult
to say which one is the most important factor responsible for the photocatalytic property of TiO2–SiO2. For example, the reduction of particle size could effect on both of the surface area and band-gap energy. And, Ti–O–Si bonds
could modify the band-gap energy and local structure. Therefore, the photocatalytic properties of TiO2–SiO2 should be expressed by sum of many factors such as surface area, adsorption, band-gap energy and local structure. 相似文献
13.
Sang-Sun Park Seon-Mi Eom Masakazu Anpo Dong-Ho Seo Yukwon Jeon Yong-gun Shul 《Korean Journal of Chemical Engineering》2011,28(5):1196-1199
Titanium dioxide (TiO2) nanotube arrays are grown in a mixed electrolyte by anodizing process. The anodic nanotubes for N-doping were calcinated
at 773 K in a tube furnace with a mixture of NH3 and Ar gas. The photocatalytic activity of N-doped TiO2 nanotubes was carried out in a water-splitting reaction under UV and visible light irradiation. Various characterization
techniques (Scanning electron microscopy, X-ray diffractometry, X-ray photo-electron spectroscopy, etc.) are used to study
the surface morphology, phase of structure, and binding energy. 相似文献
14.
Jei-Kwon?MoonEmail author Chong-Hun?Jung Eil-Hee?Lee Hyung-Tae?Kim Yong-Gun?Shul 《Korean Journal of Chemical Engineering》2002,19(5):838-842
A PAN-4A composite ion exchanger containing about 80% 4A powder was prepared to remove strontium and cesium ions from acidic
solution. The SEM image of the fracture of composite bead showed that zeolite 4A powder was dispersed homogenously and the
pores were well formed. The mean pore size of composite bead was 0.14 μm and its porosity was about 74%, which is much higher
in comparison with the existing inorganic adsorbent beads. The acid and radiation stability tests showed that PAN-4A was stable
against acid solution higher than pH 2 and radiation dose less than 1.89×108 rad, respectively. Ion exchange tests showed that the PAN-4A was selective for Sr ion. The distribution coefficients of PAN-4A
for Sr and Cs ions at pH 2 were 2×104 mL/g and 280 mL/g, respectively. The ion exchange capacities (qs) of PAN-4A for Sr and Cs ions at pH 2, which are modeled by Dubinin-Polanyi equation, were 3.92 meq/g and 2.47 meq/g, respectively. 相似文献
15.
Sang Soo Lee Hyun Jong Kim Kyung Taek Jung Hak Soo Kim Yong Gun Shul 《Korean Journal of Chemical Engineering》2001,18(6):914-918
Iron or tungsten-doped nano TiO2 were successfully synthesized from TiCl4. All of the samples showed anatase phase of TiO2. For the iron-doped TiO2, Iron ion was well dispersed in the TiO2 lattice. However, tungsten-doped TiO2 formed 12-tungstate with anatase TiO2. As the concentration of tungsten increased, 12-tungstate disappeared. The photocatalytic oxidation of acetaldehyde was evaluated to examine the photocatalytic characteristics of metal-doped TiO2. Because of the surface containing metal oxide or metal precursors at high concentration metal ion, increasing the concentration of W or Fe ion decreased the reactivity. The reaction rate was drastically increased after 300 °C heat treatment. Furthermore, the photocatalytic activity of iron- or tungsten-doped TiO2 was higher than that of synthesized pure TiO2 and commercial TiO2. 相似文献
16.
Dongho Seo Sangsun Park Yukwon Jeon Sung-Won Choi Yong-Gun Shul 《Korean Journal of Chemical Engineering》2010,27(1):104-109
The durability of PEMFCs is one of the most important issues for application in automotive vehicles with a repeated start-up
and shut-down system. The understanding of degradation phenomena such as causes, mechanisms and influence of working condition
is essential to improving the performance and lifetime of PEMFC. We conducted on/off cyclic operation in a single cell configuration
with ultra purity nitrogen gas to investigate the physical degradation of membrane electrode assembly (MEA). After on/off
cycle operation for 100,000 cycles under different humid condition, the characteristics of the MEAs were examined by in situ
and ex situ analyses techniques. The physical degradation of MEA by on/off cycling led to a change in the membrane-electrode
interfacial structure, which is mainly attributed to the loss of cell performance. 相似文献
17.
Min-Soo Hyun Sang-Kyung Kim Byungrock Lee Donghyun Peck Yonggun Shul Doohwan Jung 《Catalysis Today》2008,132(1-4):138-145
PtRu/C catalysts were prepared using an aqueous co-impregnation method with NaBH4 as a reducing agent. In order to investigate the effect of the reducing agent concentration, metal ions were reduced in different NaBH4 concentrations for which the molar ratios of NaBH4 to metal ions were controlled to 1, 2, 5, 15, 50, and 250. The electrochemical properties were studied by cyclic voltammetry in a 0.5 M H2SO4 solution. The surface compositions and oxidation states of the catalysts were observed by X-ray photoelectron spectroscopy (XPS). According to the X-ray diffraction (XRD) results, Pt (fcc) peak shifts were observed and crystal sizes were calculated. The electro-catalytic activities of the prepared catalysts for methanol electro-oxidation were estimated using linear sweep voltammetry. Unit cell tests were carried out to compare the direct methanol fuel cell performances. The NaBH4 concentration was found to affect the dispersion and the surface composition of the prepared PtRu particles. Optimum molar ratios of NaBH4 to metal ions were 5 and 15 for methanol electro-oxidation. 相似文献
18.
Hydrogen peroxide oxidizes n-hexane, n-heptane, and n-octane at 50°C in the presence titanium silicalite TS-1 as a catalyst, forming isomeric mixtures of ketones and alcohols. Admixtures of organic acids, alcohols, benzene, and ethylbenzene sharply change the ratio of position isomers. For example, the normalized ratio is C(4): C(3): C(2) = 0.44: 1.0: 0.47 for n-heptane oxidation in the absence of additives, but it becomes 0.52: 1.0: 1.00 in the presence of benzyl alcohol and the addition of ethylbenzene changes it to 0.16: 1.0: 0.94. 相似文献
19.
A mathematical model for the calculation of the resistivity of oxide glasses as a function of their composition and temperature has been developed by the experimental statistical method. The root-meansquare deviation of the calculated values of log ρ [Ω cm] from the experimental data is equal to ±0.65. The model has been recommended to use in the design of electrically insulating silicate and borosilicate glasses and related coatings. 相似文献
20.