• Title/Summary/Keyword: Physical and chemical reactions

Search Result 161, Processing Time 0.022 seconds

Synthesis and Physical Property of Multi-Functional Siloxane Protective Coating Materials Applicable for Electronic Components

  • Kim, Cheol Hyun;Cho, Hyeon Mo;Lee, Myong Euy
    • Bulletin of the Korean Chemical Society
    • /
    • v.35 no.6
    • /
    • pp.1665-1669
    • /
    • 2014
  • Four multialkoxy-functionalized siloxane base-polymers (BP-1~4) were synthesized through either hydrosilylation or condensation reactions in order to prepare multi-networked siloxane polymers having appropriate physical properties for protective coating in fabrications of electronics. Formulations of 4 base-polymers gave coating materials A and B. Product A showed well-controlled flowing and leveling properties, and product A-2 was successfully applied to protective insulating coating for junction areas of connectors and chips in PDP controller. Tack free time, extrusion rate, dielectric breakdown voltage, hardness, thermal stability, water resistance and flame resistance of products A and B were examined.

Synthesis, Structural Characterization, and Catalytic Activity of Flower Like ZnO Nanostructures

  • Ramachandran, K.;Kumar, G. Gnana;Kim, Ae Rhan;Yoo, Dong Jin
    • Bulletin of the Korean Chemical Society
    • /
    • v.35 no.4
    • /
    • pp.1091-1097
    • /
    • 2014
  • Tageteserecta flower like zinc oxide nanostructures composed of hexagonal nanorods were synthesized via sonochemical method at room temperature. The synthesized nanomaterials exhibited wurtzite hexagonal phase structure with the single crystalline nature. The diameter of the individual nanorods that constitute the flower shaped zinc oxide structures is in the range of 120-160 nm. The sonication time effectively determined the morphological properties of the prepared materials. The catalytic activity of prepared zinc oxide nanostructures towards N-formylation reactions were evaluated without any surface modification and the nanostructures exhibited good reaction yield with the prompt recyclability behavior.

Peptide Synthesis with Polymer Bound Active Ester. I. Rapid Synthesis of Peptides Using Polymer Bound 1-Phenyl-3-methyl-4-oximinopyrazole

  • Lee, Ki-Wha;Lee, Yoon-Sik
    • Bulletin of the Korean Chemical Society
    • /
    • v.10 no.4
    • /
    • pp.331-335
    • /
    • 1989
  • Polymer bound 1-phenyl-3-methyl-4-oximinopyrazoles were prepared through a series of chemical modifications of Merrifield's resin (chloromethylpolystyrene-$1{\%}$ DVB-copolymer). Several polymer active esters of N-blocked amino acids were prepared from the polymer bound 1-phenyl-3-methyl-4-oximinopyrazoles. Polymer bound active esters were found to be highly reactive in N-acylation reaction. The resins were tested for the preparation of several dipeptides. The peptides were obtained in high yields within 10 minutes and the progress of the reactions could be easily followed up by the color change of the resin. The resulting peptides were characterized by NMR and other physical methods.

The Importance of Essential-Oils in the Green Synthesis of Silver Nanoparticles

  • Barzinjy, Azeez Abdullah
    • Journal of the Korean Chemical Society
    • /
    • v.66 no.4
    • /
    • pp.284-297
    • /
    • 2022
  • The antibacterial activity of metallic nanoparticles (NPs), especially silver (Ag), has been investigated during the course of time in various chemical reactions for antibiotics free agents. Green synthesis of metallic NPs using either microorganisms or plant-extracts has appeared as a simple and replacement to chemical and physical methods. The synthesizing of these NPs through ecofriendly methods signifies an exceedingly applicable approach for offering economical, preferring scalability and possessing negligible ecological influences. Essential-oils are among the subordinate metabolites of plants and their antibacterial anti-inflammatory characteristics have been investigated widely and are commonly attained from the aromatic plants. The usage of essential-oils as reducing agents in biosynthesizing of Ag NPs bring together the interaction of a vital antibacterial agent that simplify the nucleation and growth process within the NPs formation. This review article is offering a progressive process of Ag NPs synthesis using essential oils along with proposing the most applicable formation mechanisms and their antibacterial activities.

NUMERICAL FLOW FIELD ANALYSIS OF AN ARCJET THRUSTER (Arcjet Thruster 유동의 전산해석)

  • Shin, Jae-Ryul;Choi, Jeong-Yeol
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2006.10a
    • /
    • pp.101-105
    • /
    • 2006
  • The computational fluid dynamic analysis has been conducted for the thermo-chemical flow field in an arcjet thruster with mono-propellant Hydrazine (N2H4) as a working fluid. The Reynolds Averaged Navier-Stokes (RANS) equations are modified to analyze compressible flows with the thermal radiation and electric field. The Maxwell equation, which is loosely coupled with the fluid dynamic equations through the Ohm heating and Lorentz forces, is adopted to analyze the electric field induced by the electric arc. The chemical reactions of Hydrazine were assumed to be infinitely fast due to the high temperature field inside the arcjet thruster. The chemical and the thermal radiation models for the nitrogen-hydrogen mixture and optically thick media respectively, were incorporated with the fluid dynamic equations. The results show that performance indices of the arcjet thruster with 1kW arc heating are improved by amount of 180% in thrust and 200% in specific impulse more than frozen flow. In addition to thermo-physical process inside the arcjet thruster is understood from the flow field results.

  • PDF

The Effect of HCl on the NOx Reduction in $H_2/HCl/Air$ Premixed Flame ($H_2/HCl/Air$ 예혼합 화염에서 NOx 저감을 위한 HCl의 효과)

  • Lee, Ki-Yong;Kwon, Young-Suk;Sin, Sung-Su
    • Proceedings of the KSME Conference
    • /
    • 2003.04a
    • /
    • pp.2180-2185
    • /
    • 2003
  • Numerical simulations of freely propagating flames burning $H_2/HCl/Air$ mixtures are performed at atmospheric pressure in order to understand the effect of HCl on the NOx reduction. A chemical kinetic mechanism is developed, which involves 26 gas-phase species and 99 reactions. Under several equivalence ratios the flame speeds are calculated and compared with those obtained from the experiments, the results of which is in good agreement. As HCl is added into $H_2/Air$ flame as additive, its chemical effect causes the reduction of radicals (H, OH, and O), and then the decrease of the net rate of NO production. It is found that the chemical effect of additive has much more influence on the reduction of EINO than its physical effect.

  • PDF

A Thermo chemical Study of Arcjet Thruster Flow Field

  • J-R. Shin;S. Oh;Park, J-Y
    • Proceedings of the Korean Society of Propulsion Engineers Conference
    • /
    • 2004.03a
    • /
    • pp.257-261
    • /
    • 2004
  • Computational fluid dynamics analysis was carried out for thermo-chemical flow field in Arcjet thruster with mono-propellant Hydrazine ($N_2$H$_4$) as a working fluid. The theoretical formulation is based on the Reynolds Averaged Navier-Stokes equations for compressible flows with thermal radiation. The electric potential field governed by Maxwell equation is loosely coupled with the fluid dynamics equations through the Ohm heating and Lorentz force. Chemical reactions were assumed being infinitely fast due to the high temperature field inside the arcjet thruster. An equilibrium chemistry module for nitrogen-hydrogen mixture and a thermal radiation module for optically thin media were incorporated with the fluid dynamics code. Thermo-physical process inside the arcjet thruster was understood from the flow field results and the performance prediction shows that the thrust force is increased by amount of 3 times with 0.6KW arc heating.

  • PDF

Palladium-based Electrical and Optical Hydrogen Gas Sensors

  • Jinwoo, Lee;Minah, Seo
    • Journal of Sensor Science and Technology
    • /
    • v.31 no.6
    • /
    • pp.397-402
    • /
    • 2022
  • In this short review, we explore the recent progress in metal-based gas-sensing techniques. The strong interaction between the metal films and hydrogen gas can be considered to play a considerably important role in the gas-sensing technique. The physical and chemical reactions in Pd-Pd hydride systems were studied in terms of the phase transition and lattice expansion of the metals. Two types of represented detection, electrical and optical, were introduced and discussed along with their advantages.

Recent Advances and Trends in Filters for Highly Selective Metal Oxide Gas Sensors (산화물 반도체형 가스센서의 선택성 향상을 위한 필터 연구 동향 및 전략)

  • Seong-Yong Jeong
    • Journal of Sensor Science and Technology
    • /
    • v.33 no.1
    • /
    • pp.48-55
    • /
    • 2024
  • Metal-oxide-based semiconductor gas sensors are widely used because of their advantages, such as high response and simple sensing mechanism. Recently, with the rapid progress in sensor networks, computing power, and microsystem technology, sensor applications are expanding to various fields, such as food quality control, environmental monitoring, healthcare, and artificial olfaction. Therefore, the development of highly selective gas sensors is crucial for practical applications. This article reviews the developments in novel sensor design consisting of sensing films and physical and chemical filters for highly selective gas sensing. Unlike conventional sensors, the sensor structures with filters can separate the sensing and catalytic reactions into independent processes, enabling selective and sensitive gas sensing. The main objectives of this study are directed at introducing the role of various filters in gas-sensing reactions and promising sensor applications. The highly selective gas sensors combined with a functional filter can open new pathways toward the advancement of high-performance gas sensors and electronic noses.

The Influence of Carbonation on Physical and Chemical Property in Mortar (모르터의 물리.화학적 특성에 미치는 중성화의 영향)

  • 문소현;소승영;소양섭
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • 1995.10a
    • /
    • pp.30-34
    • /
    • 1995
  • There are carbonatiion, salt attack, freezing & thawing and alkali-aggregate reactions as the cautions of durability lowering of concret structure. Generally, these cautions complicatedly lower the durability of structure and among these cautions the most serious problem is salt attack and carbonation. This study is intending to get the carbonation phenominon, that among cement calcium hydroxides change into calcium carbonate by responding to carbon mitrogen in the air.

  • PDF