The copper sulfide coating on polyacrylonitrile with a chelating agent of ethylenediaminetetraacetic acid by an electroless deposition method and its EMI shielding effectiveness

In this study, a copper sulfide layer was instantaneously coated on the polyacrylonitrile (PAN) by an electroless plating method with the reduction agents NaHSO₃ and Na₂S₂O₃·5H₂O and a chelating agent (ethylenediaminetetraacetic acid, EDTA). A variety of concentrations of EDTA was added to obtain the anchoring effect and chelating effect in the electroless plating bath. The mechanism of the Cu_{x(x = 1, 2)}S growth and the electromagnetic interference shielding effectiveness (EMI SE) of the composite were studied. It was found that the vinyl acetate was residual in PAN substrate would be purged due to the swelling effect by EDTA solution. Then, the anchoring effect occurred due to the hydrogen bonding between the pits of PAN substrate and the chelating agent. Consequently, the copper sulfide layer deposited successfully by the electroless plating reacted upon EDTA. The swelling degree (S_d) was proposed and evaluated from the FTIR spectra. The relationship between swelling degree of the PAN composite and EDTA concentration (C) is expressed as follows: S_d = 0.13 + 0.90 × e^(?15.15C). On the other hand, the FESEM micrograph showed that the average thickness of copper sulfide increased from 76 to 383 nm when the concentration of EDTA increased from 0.00 to 0.20M. For this reason, the EMI SE of the composites increased from 10–12 dB to 20–23 dB. The GIA‐XRD and laser Raman analysis indicated that the deposited layer consisted of CuS and Cu₂S. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

SUPERSATURATION, INDUCTION PERIOD, AND METASTABLE ZONE WIDTH OF CaCl2—Na2C03—HCl SYSTEM

The supersaturation, induction period, and mctastablc zone width ofan aqueous supersaturated solution of CaC₂—Na₂C0₃—HCl system are studied in the present paper. The supersaturation is varied and predicted within a reasonable accuracy when a specified amount of HCl(_aq) is added into the aqueous supersaturated CaC₂—Na₂C0₃—HCl solution. It is found that the decrease of solution supersaturation at low pH is caused mainly by the decrease of carbonate ions. Then, the induction periods are estimated by using the coagulation theory and they can be expressed as a function of supersaturation alone, which results from different values of reagent concentration and pH. Finally, the theoretical metastable zone widths based on arbitrary induction periods are obtained. Meanwhile, the induction periods are measured at various levels of reagent concentration and solution pH by applying the conductivity method. Accordingly, the metastable zone widths are determined experimentally and compared with the theoretical results. It is concluded that the present method is an useful tool for determining the metastable zone width of aqueous supersaturated CaC₂—Na₂C0₃—HCl solution.     

Use of flexible micro-temperature sensor to determine temperature in situ and to simulate a proton exchange membrane fuel cell

In this work, a micro-temperature sensor on a 40 μm flexible stainless-steel substrate was fabricated using micro-electro-mechanical systems (MEMS). Embedding a micro-temperature sensor in a proton exchange membrane fuel cell (PEMFC) to monitor temperature will not damage the sensor during the experimental process. This investigation is the first to develop a micro-temperature sensor that can be placed anywhere between the membrane electrode assembly (MEA) and the flow-channel plate inside a PEMFC. The simulated temperature is consistent with the experimentally determined temperature. The performance curve is also consistent with experimental results, revealing the accuracy of the simulation and the effectiveness of monitoring temperature inside a PEMFC.     

Synthesis and trans-ureation of N,N’-diphenyl-4,4′-methylenediphenylene biscarbamate with diamines: a non-isocyanate route (NIR) to polyureas

A non-isocyanate route (NIR) of making polyureas of high molecular weight has been found through trans-ureation of N,N’-diphenyl-4,4′-methylenediphenylene biscarbamate (4,4′-DP-MDC) with a variety of diamines and mixed diamines. The preparation of 4,4′-DP-MDC was achieved readily by carbonylation of 4,4′-methylenedianiline (4,4′-MDA) with diphenyl carbonate (DPC) using organic acids as catalysts. It was found that the highest yield (99%) of pure 4,4′-DP-MDC can be isolated in a toluene solution under mild conditions co-catalyzed by benzoic acid and tertiary amine. Trans-ureation of 4,4′-DP-MDC with aliphatic amines indicated that the process is a highly solvent dependent process and was found to be extremely facile in dimethyl sulfoxide (DMSO) at 80 °C and in tetramethylene sulfone (TMS) at 140 °C in absence of any catalyst. Particularly, the most effective polymerization process was developed using tetramethylene sulfone (TMS) as the solvent under reduced pressure for concurrently distilling off phenol from the reaction mixture during the polymerization in a shifting equilibrium towards polyurea. However, this solvent-assisted trans-ureation was found to be in-efficient when N,N’-dimethyl-4,4′-methylenediphenylene biscarbamate (4,4′-DM-MDC) was used in a similar condition for comparison. Thus, an efficient green-chemistry process has been developed based on 4,4′-DP-MDC in making urea prepolymers, urea elastomers and urea plastics all in excellent yields without using reactive methylenediphenylene diisocyanate (MDI) or any catalysts in the trans-ureation polymerizations.     

Quantitative study of shrinkage and warpage behavior for microcellular and conventional injection molding

This research investigated the effects of processing conditions on the shrinkage and warpage (S&W) behavior of a box‐shaped, polypropylene part using conventional and microcellular injection molding. Two sets of 2^6‐1 fractional factorial design of experiments (DOE) were employed to perform the experiments and proper statistical theory was used to analyze the data. After the injection molding process reached steady state, molded samples were collected and measured using an optical coordinate measuring machine (OCMM), which had been evaluated using a proper R&R (repeatability and reproducibility) measurement study. By analyzing the statistically significant main and two‐factor interaction effects, the results show that the supercritical fluid (SCF) content (nitrogen in this case, in terms of SCF dosage time) and the injection speed affect the S&W of microcellular injection molded parts the most, whereas pack/hold pressure and pack/hold time have the most significant effect on the S&W of conventional injection molded parts. Also, this study quantitatively showed that, within the processing range studied, a reduction in the S&W could be achieved with the microcellular injection molding process. POLYM. ENG. SCI., 45:1408–1418, 2005. © 2005 Society of Plastics Engineers     

Adaptive Neuro-Fuzzy Inference System Modeling of MRR and WIWNU in CMP Process With Sparse Experimental Data

Availability of only limited or sparse experimental data impedes the ability of current models of chemical mechanical planarization (CMP) to accurately capture and predict the underlying complex chemomechanical interactions. Modeling approaches that can effectively interpret such data are therefore necessary. In this paper, a new approach to predict the material removal rate (MRR) and within wafer nonuniformity (WIWNU) in CMP of silicon wafers using sparse-data sets is presented. The approach involves utilization of an adaptive neuro-fuzzy inference system (ANFIS) based on subtractive clustering (SC) of the input parameter space. Linear statistical models were used to assess the relative significance of process input parameters and their interactions. Substantial improvements in predicting CMP behaviors under sparse-data conditions can be achieved from fine-tuning membership functions of statistically less significant input parameters. The approach was also found to perform better than alternative neural network (NN) and neuro-fuzzy modeling methods for capturing the complex relationships that connect the machine and material parameters in CMP with MRR and WIWNU, as well as for predicting MRR and WIWNU in CMP.     

A heuristic for nesting problems of irregular shapes

Layout has a close relationship with product cost in the vein of how to most efficiently cut product patterns from raw materials. This is the so-called “nesting problem”, which occurs frequently in sheet metal and furniture industries, wherein material utilization needs to be maximized. In this paper, a quick location and movement (QLM) algorithm is proposed to solve the situation of irregular shapes nested on multiple irregular sheets. This approach includes two major parts: it first approximates irregular shapes to a polygon with the use of a cluster of straight lines, and second, it arranges the approximated shapes one-by-one with the proposed step-by-step rule. Finally, this study investigates and compares examples presented by other authors. The results show that the QLM algorithm takes less time to calculate a layout and the material utilization efficiency is higher compared to other methods.     

Ignition of carbon nanotubes using a photoflash

When fluffy carbon nanotubes (CNTs) are subjected to a photoflash, there is a rapid increase in temperature to over 475 °C within 0.03 s. This is attributed to absorption of the light by the CNTs, which results in the generation of an acoustic wave and oxidation of the CNTs. Ignition is due to the exposure of the flammable catalytic particles embedded in CNTs to air. The appearance of sub-micrometer iron oxide particles in the samples indicates that the oxidized iron nanoparticles formed due to flash exposure may agglomerate or fuse depending on the amount of iron catalysts and CNT fluff temperature which is increased due to flash absorption.