Advanced Materials Research Vol. 699

Abstract: Printed circuit boards (PCBs) and copper-clad laminate (CCLs) are the foundation of the electronic industry, and the core components of all kinds of electronic products. With the accelerated pace of information equipment replacement, waste PCBs and CCLs increase every year, and generated a lot of e-waste. Sweden Ronnskar smelter made an analysis on elements of the PCBs used in the personal computer, the results showed that the PCBs generally contain precious metals gold, silver and non-ferrous metals such as copper, wherein the mass fraction of copper is up to 26.8%, the mass concentration of gold and silver respectively reached 80 g/t and 3300 g/t, which much higher than the average gold grade and having high recycling value. Waste PCBs also contain heavy metals such as lead, cadmium, chromium, which have a great deal of harm to the environment and human body. This paper focuses on the physical and chemical properties of the electronic circuit board such as calorific value and moisture, on the content measurement and analysis of gold, copper and other precious metals so that the physical and chemical properties of the ingredients in waste PCBs and CCLs are determined from a qualitative and quantitative point of view, which is very important for looking for recyclable value of the waste PCBs and CCLs and for determining the best method of recycling them. The test results showed that the waste PCBs and CCLs had very high recycling value.

Abstract: We have developed a near-field scanning microwave microscopy (NSMM) system that contains a high-quality factor resonator, a sharp metallic probe tip, a 6-degree scanning stage and a vector network analyzer. By applying incident GHz microwaves through the probe tip over samples under test and measuring the magnitude and phase shift of the reflection parameter S11, we have precisely detected the ion concentration of electrolytes in a variety of fluidic systems which are sealed under a 50 μm thick dielectric cover. As expected, the measured magnitude of S11 monotonically increases with the ion concentration, but not linearly, and is sensitive to the tip-sample spacing. This technique offers a useful way for on-site, real-time monitoring of the changes in electrolyte fluids of limited volume in a sealed device. Further work is needed to reveal the exact correlation between the deflection magnitude and ion concentration.

Abstract: This paper describes application of carbon nanotube (CNT) gas sensor to chemical detection of sulfur hexafluoride (SF6) decomposition products generated by AC or DC corona discharge, aiming to develop a new diagnosis method of gas-insulated switchgear (GIS) filled with high pressure SF6 gas. Currently, most of GIS are designed and operated for conventional high voltage AC (HVAC) power transmission lines. Moreover, in recent years, the electrical power industry has shown a trend shifting from HVAC to high voltage DC power transmission, which has many advantages such as high power capacity and low power loss.This technological trend motivated us to explore and expand the application of CNT gas sensor to detection of SF6 decomposition products generated by AC and DC corona discharges. It was found that the CNT gas sensor exhibited significant response to AC and DC corona discharges and its dependency on the DC voltage polarity. In order to elucidate the mechanism of the polarity effect, SF6 decomposition products were analyzed by Fourier transform infrared spectroscopy as well as using a gas detection tube. Based on comparison between the polarity effects on the CNT sensor response and the decomposition products, a possible contribution of hydrogen fluoride to the CNT gas sensor response was suggested.

Abstract: Single-walled carbon nanotubes (SWCNTs) gas sensor has attracted a great deal of attention because of their remarkable properties. The sensor response is attribute to the semiconducting CNT whose electronic properties depend on its chirality. The authors have previously found that the sensor response increased by using separated semiconducting SWCNTs from a mixture with metallic one. Since the electronic structure (metallic or semiconducting) of CNTs is governed by their chirality, a chirality-selective fabrication of CNT gas sensor is essential to improve their performance. In this study, we proposed chirality-based separation of semiconducting SWCNTs by using spin-column chromatography. Pristine CNT suspension was separated into three fractions that had different chiralities of semiconducting SWCNTs. Separated semiconducting CNTs of each fraction were used for fabrication of three CNT gas sensors by dielectrophoresis. Comparison of these sensor responses to NO2 revealed that sensor response depended on the chirality.

Abstract: Aiming to guide the manufacture process of carbon fiber and obtain high properties productions, we propose a hybrid algorithm named father-keeping immune genetic algorithm based on back propagation neural network (FKIGA-BP) as a properties prediction model. The present study also compares it with BP neural network forecasting method. It shows better search precision and convergence efficiency. The prediction results are consistent with the practical experiment data.