Preparation of C/C composites by the chemical vapor infiltration (CVI) of propane pyrolysis

The preparation of C/C composites by the chemical vapor infiltration (CVI) of the pyrolysis carbon from propane was studied. Pyrolysis carbon was deposited at 30 torr and at temperatures between 1,173 and 1,233 K. The rate of carbon deposition increased slightly with time. The main gas products in the exit gas were methane, ethylene, and acetylene. The fraction of ethylene decreased and that of acetylene increased with the reaction temperature and the propane concentration. The produced propyl radicals reacted further at a high temperature and at a high propane concentration. These trends were similar to those of the reported data. Changes of the shapes of deposited carbon in the pores of preform were confirmed with SEM photos. The mathematical modeling of the system with the deposition rate constant from the reference estimated experimental data well.     

Water sustainability: A systems engineering approach to restoration of eutrophic Lakes

We address restoration of eutrophic lakes and reservoirs through the formulation of dynamic optimization problems subject to complex PDAE systems representing biogeochemical processes in the water bodies. The model includes phytoplankton, zooplankton, fish, nutrients, DO, particulate and dissolved carbon dynamics. The PDAE has been transformed into an ordinary differential algebraic equation system by spatial discretization into two water layers. An optimal control problem for the implementation of three different restoration techniques and their combinations has been formulated within a control vector parameterization approach. Numerical results for the different problems provide optimal profiles for tributary deviation flowrate through a nearby wetland, aeration rates and fish removal rates, as restoration strategies.     

Characteristics of nanosized Bi-based glass powders prepared by flame spray pyrolysis as transparent dielectric layer material

Bi-based glass powders with particle size of 34 nm were prepared by high-temperature flame spray pyrolysis. The glass transition temperature (T_g) of the powders was 442 °C. Dielectric layers fired at temperatures of 480 and 500 °C contained voids, while those fired at temperatures above 540 °C had clean surfaces and no voids. The dielectric layers sintered at temperatures of 560 and 580 °C had transmittances of 70% in the visible range. Further, it was observed that the dielectric layers formed from the nanosized glass powders obtained from spray solutions containing excess boron had higher transmittances (80% in the visible range at a sintering temperature of 580 °C) than the layers formed from spray solutions containing stoichiometric amounts of boron.     

Optimal multi-floor plant layout with consideration of safety distance based on mathematical programming and modified consequence analysis

A general mathematical programming formulation which also considers safety factors is presented for solving the multi-floor plant layout problem. In the presence of a risk of physical explosion, the safety distance must be considered to generate more reasonable and safe layouts. The proposed method determines detailed multi-floor process plant layouts using mixed integer linear programming (MILP). To consider the safety distance, a consequence analysis is adopted for calculating an equipment physical explosion probit. As the TNT equivalency method is used, more realistic estimations of equipment damage are possible, generating safer plant layouts. The objective function minimizes the layout cost (total plant area, floor construction costs and connection costs) and explosion damage costs for the multi-floor problem. Two illustrative examples are presented to demonstrate the applicability of the proposed method.     

Flame retardancy and mechanical properties of polyamide 6 with melamine polyphosphate and ionic liquid surfactant‐treated montmorillonite

The mechanical properties and inflammability of polyamide 6 (PA6) nanocomposites incorporated with Montmorillonite organoclay (MMT) modified with thermal stable ionic liquid surfactants were investigated. The compatibility between ionic liquid‐treated MMT and PA6 matrix was improved and the intercalation morphology was achieved, which resulted in the increaseof tensile modulus. However, the addition of organo‐MMTs alone did not improve the inflammability of the PA6 nanocomposite, because of strong melt‐dripping behavior of PA6 matrix. Addition of auxiliary melamine polyphosphate (MPP) intumescent flame retardant to the nanocomposite prevented the melt dripping and enhanced inflammability performance. The enhanced inflammability of PA6/organoclay/MPP nanocomposites was attributed to the synergistic effect between imidazolium or phosphonium organo‐MMTs and intumescent flame retardant MPP. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40648.     

Polymerization by phase transfer catalysis

Poly(amide-carbonate)s and poly(amide-thiocarbonate)s derived from the diphenol-amides N-(2,6-dichloro-4-nitrophenyl)-2,2-bis(hydroxyphenyl)-propylamide (I), N-(2,6-dichloro-4-nitrophenyl)-3,3-bis(hydroxyphenyl)-butylamide (II), and N-(2,6-dichloro-4-nitrophenyl)-4,4-bis(hydroxyphenyl)-pentylamide (III), and phosgene or thiophosgene, have been synthesized under phase transfer conditions using several quaternary ammonium salts as phase transfer catalysts. Benzyltriethylammonium chloride (BTEAC) was effective in practically all cases due the hydrophilicity of this catalysts. Received: 21 February 1997/Revised: 28 April 1997/Accepted: 30 April 1997     

Improved electrical conductivity of a non-covalently dispersed graphene–carbon nanotube film by chemical p-type doping

Using a high-pressure air spray we developed a method to deposit electrically-conducting thin films consisting of non-covalently dispersed graphene and carbon nanotubes. The graphene–carbon nanotube film was immersed in a nitric acid and followed by exposure to fuming nitric acid. The acid treatment induced an increased concentration of atomic nitrogen on the graphene basal plane and carbon nanotube sidewall. This result indicates chemical p-type doping of the graphene oxide–carbon nanotube film. After the two acid treatments, the spray coated graphene oxide–carbon nanotube films on a glass substrate exhibit a low sheet resistance of 171 Ω/sq, and a high transmittance of 84% at a wavelength of 550 nm.     

Chromatographic analysis of ceramide III ofSaccharomyces cerevisiae

Ceramide was prepared by the cultivation ofSaccharomyces cerevisiae from cell extracts by solvent exfraction and analyzed by NP-HPLC using a UV detector. The mobile phase was composed of hexane, methanol, and IPA. From the experimental conditions, the composition of mobile phase was 72/5/23 (hexane/IPA/methanol, vol%). Quantitative analysis of ceramide was performed. Based on the analytical conditions, the effect of cultivation temperature for the production of ceramide was investigated and the optimum cultivation temperature was found to be 35°C. This paper is dedicated to Dr. Youn Yong Lee on the occasion of his retirement from Korea Institute of Science and Technology.     

Crystallization and dissolution behavior of l(+) calcium and zinc lactate in ethanol-water solvent

Crystallization and dissolution behavior of L(+) calcium and zinc lactate in 50% ethanol-water solution was studied. The effects of stirring, standing, ultrasonic wave, and temperature on the crystallization of L(+) calcium and zinc lactate were evaluated. It was found that standing had a positive effect on crystallization of L(+) calcium and zinc lactate, while stirring promoted dissolution of crystallized particles and resulted in high residual concentration in mother liquor. The application of ultrasonic wave did not influence much on crystallization process. L(+) calcium and zinc lactate crystallized easily at 5 ‡C; however, complete crystallization took more than 72 hours. These two salts dissolved rapidly and reached equilibrium within 1 hour.