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Seoul, South Korea

The present invention relates to a method for preparing wholly aromatic polyimide resin with improved heat-resistance. In particular, the present invention provides a method for preparing polyimide resin having enhanced heat-resistance and superior mechanical properties, especially elongation rate and tensile strength at high temperature through liquid polymerization of two kinds of aromatic tetracarboxylic dianhydrides and aromatic diamine whose mixed ratio is properly regulated. Since the polyimide prepared according to the method of the present invention exhibits high heat-resistance and improved ensile strength and elongation rate at high temperature while maintaining intrinsic properties of polyimide, it can be used as a core heat-resistant material of semiconductor and aerospace fields where higher heat-resistance and mechanical properties are required.

The present invention relates to a method for preparing wholly aromatic polyimide powder with antistatic properties or electric conductivity. In particular, the present invention relates to a method for preparing wholly aromatic polyimide composite powder, comprising the steps of dissolving aromatic diamine in a phenolic polar organic solvent in which electrically conductive carbon black powder and multi-wall carbon nano-tube (MWCNT) powder are dispersed, adding aromatic tetracarboxylic dianhydride thereto, and polymerizing the resulting mixture. The wholly aromatic polyimide powder prepared according to the method of the present invention shows excellent antistatic properties or electric conductivity simultaneously with maintaining similar or equal heat-resistance and mechanical properties as compared to conventional polyimide resin.

Park D.Y.,Daelim Co. | Lee B.B.,Daelim Co.
Structural Engineering International: Journal of the International Association for Bridge and Structural Engineering (IABSE) | Year: 2012

The Second Dolsan Bridge has a total length of 464 m, consisting of a 230 m main span and two 117 m side spans. This is the first time that a cable-stayed bridge with a concrete edge girder has been built in Korea. The main criterion governing the design and construction of the bridge was the control of tensile stress and negative moment -in not only the edge girder but also the slab - due to the traffic load and the wet concrete load of the deck while under construction. It is necessary to exercise tight geometric control of the camber during construction and to carry out thorough checks to minimize cracking in the deck slab. For this reason, a continuous three-span floating deck system with intermediate piers and a form traveler (FT) supported by permanent stays were chosen. This floating system reduces the tensile stress on the pier table and eliminates the cost of constructing cross-beams on the pylons as well as the maintenance cost of the bearings. Using the FT supported by permanent stays, the tensile stress on top of the previous segment is significantly reduced during the pouring of the concrete. The intermediate piers, while preventing significant displacement and cracking due to the traffic load, also increased the stiffness of the side span and enabled the stay cables on the side span to behave as backstays. Thus, this structure represents a viable example of a cable-stayed bridge with concrete edge girders. Source

Kim J.,Daelim Co. | Suk J.,Daelim Co. | Nam D.,Daelim Co. | Ha K.,Daelim Co. | Choung Y.,Yonsei University
Desalination and Water Treatment | Year: 2013

The subject of this research was electron equivalent fluxes about the decomposition of pharmaceuticals (sulfamethazine and sulfathiazole) using an oxygen-based membrane biofilm reactor (MBfR). The influent concentrations in pharmaceuticals feed-medium were (in ppb): sulfamethazine (40) and sulfathiazole (85). The oxygen-based MBfR system consisted of two membrane modules connected to a recirculation loop. The main membrane module contained a bundle of 32 hydrophobic hollow-fiber membranes inside a polyvinyl-chloride pipe shell and the other module contained a single fiber used to take biofilm samples. Pure O2 was supplied to the inside of the hollow fibers through the manifold at the base, and the O2 pressure for both reactors was 13 kPa. (1 kPa = 0.0099 atm = 0.145 psi). HRT was 3 h. The decomposition ratio of pharmaceuticals (sulfamethazine and sulfathiazole) using oxygen-based MBfR was (%): sulfamethazine (77 ± 2) and sulfathiazole (87 ± 2). In all cases, nitrification was the largest provider of electrons, together accounted for at least 99.98% of the total electron flux. © 2013 Copyright Balaban Desalination Publications. Source

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