Micellization and morphological characterization of Ag-micelles prepared by poly(vinyl acetate)-silver nitrate in solvent/nonsolvent system

The inducing method for preparing Ag-micelle solution with the use of mixed solvent/nonsolvent, and the morphological characterization of the generated metal-micelles were investigated and reported in this paper. In this method, an Ag containing metal chelate polymer (MCP) raw solution was preprepared by dissolving poly(vinyl acetate) (PVAc)-silver nitrate (AgNO3) MCP in cone. formic acid, and a mixed solvent of HCOOH/H2O with specific water composition was then added to induce the micellization of the MCP chain. The critical water concentration (CWC) that was needed for inducing the formation of the Ag-micelles, and the water concentration at which the flocculation of the Ag-micelles occurred in micellar solution, were studied by measuring the transmittance of the dilute MCP solution; the results showed that a long-lasting MCP solution with stable micelles might be prepared by using a H2O/ HCOOH solvent of specific weight ratio 1:1.2. The effect of the AgNO3 concentration on the morphology of the Ag-micelles was also investigated by transmission electron microscopy (TEM). At AgNO3 concentration below 0.5 wt%, the Ag-micelles displayed a variety of core-shell structure; but as the AgNO3 concentration was increased to 1.0-2.0 wt%, micelles that had Ag-solid embedded in the micellar core were observed

Growth of intermetallic compounds in the Sn-9Zn/Cu joint

We have studied the microstructure of the Sn-9Zn/Cu joint in soldering at temperatures ranging from 230 degrees C to 270 degrees C to understand the growth of the mechanism of intermetallic compound (IMC) formation. At the interface between the Sn-9Zn solder and Cu, the results show a scallop-type epsilon-CuZn4 and a layer-type gamma-Cu5Zn8, which grow at the interface between the Sn-9Zn solder and Cu. The activation energy of scallop-type epsilon-CuZn4 is 31 kJ/mol, and the growth is controlled by ripening. The activation energy of layer-type gamma-Cu5Zn8 is 26 kJ/mol, and the growth is controlled by the diffusion of Cu and Zn. Furthermore, in the molten Sn-9Zn solder, the results show eta-CuZn grains formed in the molten Sn-9Zn solder at 230 degrees C. When the soldering temperature increases to 250 degrees C and 270 degrees C, the phase of IMCs is epsilon-CuZn4

Development of composite dielectrics with high specific capacitance and stable temperature characteristics

A new alternative of tailoring the dielectric characteristics of a BaTiO3-based ceramic is established in this study. The ceramic dielectrics were made by either two or three constituents having a composition of (Ba0.96Ca0.04)(Ti1.0-xZrxMn0.01)O-3 (BCTZ), where x ranges from 0 to 0.22, and sintered with Ni inner electrodes at 1300degreesC for 4 h in a reducing atmosphere. Both alternative stacking, i.e., layer-by-layer of different compositions, and bulk stacking configurations were prepared by screen-printing, resulting in a composite dielectric of different characteristics. It is obtained that the Curie temperature (T-c) of the BCTZ ceramics decreases with an increase of Zr in the dielectrics, i.e., -8degreesC per mole of Zr. In addition, the stacking configuration, the proportion and the number of constituents in the composite materials control the dielectric characteristics of the multilayer ceramic capacitors. On the basis of the principles outlined, a multilayer ceramic dielectric having k-value in excess of 8000 with the X7R specification (-55 similar to +125degreesC, +/-15%), which consists of two BCTZ ceramics with Curie temperatures of -20 and 100degreesC, was successfully developed. (C) 2002 Kluwer Academic Publishers

Dewetting Retardation on Ag/Cu Coated Light Emitting Diode Lead Frames During the Solder Immersion Process

The process of SnPb immersion in Ag/Cu coated light emitting diode lead frames (LED LFs) (alloy 42) was investigated. SnPb solder was found to cause dewetting of the LF substrate after 6 s of immersion. We believed that the dewetting of the SnPb solder could be attributed to spalling of the interfacial compound grains. The addition of a small amount of Ni to the molten SnPb solder (0.1 wt.%) retarded that spalling and helped to prevent dewetting. The mechanisms for spalling retardation by the addition of Ni additives are as follows: (1) the Ni additives slow down the reaction rate between the molten SnPb solder and the Ag/Cu plating layer; (2) the Ni additives participate in interfacial reactions to form (Cu,Ni)(6)Sn(5) ternary compounds, which are more stable than binary compounds and have a slower ripening process

Effect of surface pretreatments on the adherence of porcelain enamel to a type 316L stainless steel

Porcelain enameled 316L stainless steel with different surface pretreatments was produced by a slurry-fusion technique for evaluation of the enamel/steel adherence using an electrical conductivity meter. From the measured results, it is found that the adherence of the porcelain enamel to the steel depends on the roughness of the enamel-steel interface, which, in turn, is controlled by surface pretreatments of the steel substrates. The difference in the adherence of the enameled steel can be explained from an examination of the microstructure of enamel-steel interfaces by scanning electron microscopy. Good adherence is associated with those specimens that have a long enamel-steel interface contour, i.e., rough interfaces. In addition, X-ray diffraction analysis of the delaminated enamel fragments upon impact deformation reveals that failure of the enamel coatings in an oxidized steel occurred at the oxide-steel interface which is supposed to have strong chemical bonding, and that the oxide scales present before enameling are partially dissolved in the enamel during firing. The difference in the coefficients of thermal expansion among enamel, oxide, and steel is likely to play an important role in determining the failure mode of the enameled stainless steel. In summary, these results suggest that the adherence of the porcelain enamel to the 316L stainless steel is mainly controlled by a mechanism of mechanical interlocking. (C) 1999 Kluwer Academic Publishers

Study of Interfacial Reactions Between Sn(Cu) Solders and Ni-Co Alloy Layers

The interfacial reactions between electroplated Ni-yCo alloy layers and Sn(Cu) solders at 250 degrees C are studied. For pure Co layers, CoSn(3) is the only interfacial compound phase formed at the Sn(Cu)/Co interfaces regardless of the Cu concentration. Also, the addition of Cu to Sn(Cu) solders has no obvious influence on the CoSn(3) compound growth at the Sn(Cu)/Co interfaces. For Ni-63Co layers, (Co,Ni,Cu)Sn(3) is the only interfacial compound phase formed at the Sn(Cu)/Ni-63Co interfaces. Unlike in the pure Co layer cases, the Cu additives in the Sn(Cu) solders clearly suppress the growth rate of the interfacial (Co,Ni,Cu)Sn(3) compound layer. For Ni-20Co layers, the interfacial compound formation at the Sn(Cu)/Ni-20Co interfaces depends on the Cu content in the Sn(Cu) solders and the reflow time. In the case of high Cu content in the Sn(Cu) solders (Sn-0.7Cu and Sn-1.2Cu), an additional needle-like interfacial (Ni(x),Co(y),Cu(1-x-y))(3)Sn(4) phase forms above the continuous (Ni(x),Cu(y),Co(1-x-y))Sn(2) compound layer. The Ni content in the Ni-yCo layer can indeed reduce the interfacial compound formation at the Sn(Cu)/Ni-yCo interfaces. With pure Sn solders, the thickness of the compound layer monotonically decreases with the Ni content in the Ni-yCo layer. As for reactions with the Sn(Cu) solders, as the compound thickness decreases, the Ni content in the Ni-yCo layers increases

鍍膜技術於燃料電池水管理最佳化之應用

Proton exchange membrane fuel cells (PEMFC) have been regarded as a candidate forfuture power sources for transport, residential and portable applications, primarily due to theadvantageous characteristics of high power density, high energy-conversion, simplicity ofoperation and near-zero pollutant emission. Although many problems of PEMFC have beensolved, the water management inside the membrane electrode assembly (MEA) is still need tobe farther improved.The operation temperatures of PEMFC is limited at lower than 80℃, primarily due to theinsufficient water content of the anode causes the dry out phenomenon and decreases theproton conductivity. This study aims to utilize the coating technique to enhance the dispersiondegree and decrease the addition amount of hydrophilic materials, which could not easily tobe overcome via traditional ultrasonic technique. Furthermore, the coating technique is furtherused to investigate the feasibility of novel water management mechanism design and assistthe optimization of this new design. Experimentally, the X-ray diffraction meter, fieldemission scanning electron microscopy are used to analyze the microstructure andcomposition; cyclic voltammetry method is used to measure the utilization of catalyst;sessiledrop method is used to measure the hydrophilic property of membrane electrode assembly.Overall, this project is aimed to solve the problems of water management by introducingthe coating technique to increase the wettability of the membrane electrode assembly (MEA).Our research team has sound specialties and experiences in preparing nano-structure materialsand performing fuel-cell analyses over the years. We believe that the research outcomesobtained from this project shall have an essential impact on the fuel cell industry.質子交換膜燃料電池(PEMFC)由於具有高能量密度、高能量轉換效率、操作簡易及零污染等優點，被視為最有可能取代現有的化石燃料，作為未來運輸設施、家用設備及可攜式電子產品的能源供應型態之一。儘管國內外各單位對於燃料電池的投入，使燃料電池得以快速地發展，但膜電極內部的水管理依然需要進一步地改善。本計畫將焦點回歸至利用鍍膜技術突破先前單純利用超音波混成技術將水分子吸附劑添加於陽極觸媒層以及質子交換膜內部所產生的瓶頸，並利用鍍膜技術更進一步的對於燃料電池水分子吸附劑添加的結構進行改良與研究。質子交換膜由於在高溫(>80℃)操作時，會由於陽極端的水含量低於所需而開始產生破裂，同時降低質子導電度，因此限制質子交換膜燃料電池的操作溫度。為了維持一定的水含量，添加親水性物質於陽極觸媒層與質子交換膜中為目前研究的主要趨勢。但在之前計畫中所提出的超音波混成技術雖然可以從結果中得到明顯的效能提升，但由於親水性物質的分散與用量依然無法大量的降低。因此在本計畫中企圖以本實驗是原有的鍍膜技術應用於燃料電池膜電極水管理中，提高親水物質分散性與添加量，並同時利用鍍膜技術對於膜電極組水管理的整體架構進行嘗試與改良，使得水管理效能可以更上一層樓。在實驗過程中使用各種分析儀器如XRD、SEM、TEM 進行膜電極微結構成分分析；使用循環伏安法、粉體電阻儀、四點探針對其電性與化學催化性進行分析；利用應力分析儀器對質子交換膜的機械性質進行分析。本研究從提高質子交換膜燃料電池的操作溫度著手，希望經由對於膜電極本質特性的提升同時能更進一步突破之前優化質子交換膜燃料電池水管理時所遇到的瓶頸。整體而言，本研究團隊已有多年從事奈米材料製備與燃料電池電池研究的經驗，所提的研究方法亦能跳脫傳統單一製程模式，導入新穎而特殊之混成技術，相信透過本計劃的執行，必能提升薄膜電極組相關產業技術能量