Effects of Molecular Structure on the Physical,Chemical, and Electrical Properties of Ester-Based Transformer Insulating Liquids

This article presents the experimental studies carried out on the environmental friendly polyol ester insulating liquids to investigate the effect of molecular structure on the physical, chemical, and electrical properties. Six different polyol esters that can be produced from the transesterification of various methyl esters with neopentylglycol/trimethylolpropane alcohols were synthesized and compared with those of refined, bleached, and deodorized palm oil (RBDPO) and mineral transformer oil. The finding suggests that the physical properties like fire point, pour point, and viscosity are very much affected by the molecular weight and molecular composition of the polyol esters. The electrical properties are also highly influenced by the molecular structure-related characteristics, such as the polarity, dipole polarization, carbon chain length, and degree of branching. The results confirm the findings of previous studies that the polyol esters and RBDPO have more polarity and dipole polarization compared to mineral oil. The experimental evidence showed that the newly synthesized insulating liquids have favorable thermal and electrical properties, thus suggesting that the insulating liquids have the potential to replace conventional insulating liquids to provide a more sustainable power system in the future.     

Lubrication properties of trimethylolpropane esters based on palm oil and palm kernel oils

Due to the global drive towards biodegradable products, trimethylolpropane [2‐ethyl‐2‐(hydroxymethyl)‐1, 3‐propanediol] (TMP) esters based on palm and palm kernel oils were synthesized, their lubrication properties evaluated, and their potential as base stock for biodegradable lubricants assessed. Two types of TMP esters were considered: palm kernel (PKOTE) and palm oil (PPOTE) TMP esters, derived from palm oil and palm kernel methyl esters, respectively. Lubrication properties such as viscosity, viscosity index (VI) and pour point (PP) were determined according to methods of the American Society for Testing and Materials. Wear and friction properties were evaluated using a four‐ball test machine, while oxidative stability was studied with the Penn State Micro‐oxidation thin‐film test. High VI ranges between 170 to 200 were recorded for these base stocks. PP were relatively high, between 4 to —1 °C, but were improved to at least —33 °C in high oleic palm oil TMP esters. The effects of chemical structure and impurities on wear properties and oxidative stability were also studied. The presence of methyl esters was found to improve wear, but hydroxyl groups in mono‐ and diesters had negative effects at high concentrations. Differences in chemical structures of PKOTE and PPOTE were shown to affect friction and wear results. Both base fluids exhibit oxidative stability comparable to other high oleic base fluids.     

Synthesis and characterization of poly(hydroxamic acid) chelating resin from poly(methyl acrylate)‐grafted sago starch

A new chelating ion‐exchange resin containing the hydroxamic acid functional group was synthesized from poly(methyl acrylate) (PMA)‐grafted sago starch. The PMA grafted copolymer was obtained by a free‐radical initiating process in which ceric ammonium nitrate was used as an initiator. Conversion of the ester groups of the PMA‐grafted copolymer into hydroxamic acid was carried out by treatment of an ester with hydroxylamine in an alkaline solution. The characterization of the poly(hydroxamic acid) chelating resin was performed by FTIR spectroscopy, TG, and DSC analyses. The hydroxamic acid functional group was identified by infrared spectroscopy. The chelating behavior of the prepared resin toward some metal ions was investigated using a batch technique. The binding capacities of copper, iron, chromium, and nickel were excellent and the copper capacity was maximum (3.46 mmol g⁻¹) at pH 6. The rate of exchange of the copper ion was very fast that is, t_1/2 < 5 min. It was also observed that the metal ion‐sorption capacities of the resin were pH‐dependent and its selectivity toward the metal ions used is in the following order: Cu²⁺ > Fe³⁺ > Cr³⁺ > Ni²⁺ > Co²⁺ > Zn²⁺ > Cd²⁺ > As³⁺ > Pb²⁺. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1256–1264, 2001     

Solid‐phase extraction of lead and copper on a polyhydroxybutyrate‐b‐polydimethyl siloxane (PHB‐b‐PDMS) block copolymer disc and flame atomic absorption spectrometric determination of them in water and food samples

A separation and preconcentration procedure based on solid‐phase extraction of Cu(II) and Pb(II) as their Sudan III chelates on polyhydroxybutyrate‐b‐polydimethyl siloxane (PHB‐b‐PDMS) block copolymer disc has been established. Various analytical parameters including pH, amount of Sudan III, eluent type and volume, sample volume, flow rates were optimised. The effects of concomitant ions on the retentions of the analyte ions on PHB‐b‐PDMS disc were also examined. The detection limits for Cu(II) and Pb(II) were found to be 2.3 and 4.9 μgL^?1, respectively. Preconcentration factor was found to be sixty. Relative standard deviation was found to be 5%. The accuracy of the method was confirmed by analysing certified reference materials (TMDA 54.4 fortified lake water and NIST 1515 Apple leaves). Optimised method was applied to determine the analyte ions in various water and food samples from Turkey.     

Different ligand based monodispersed Pt nanoparticles decorated with rGO as highly active and reusable catalysts for the methanol oxidation

Addressed herein, a highly effective and monodisperse Pt/L@rGO nanocatalysts were successfully synthesized by using different types of ligands (pentylamine, Pt/PA@rGO and tripentylamine, Pt/TPA@rGO) and the impact of ligand on catalytic activity of the prepared nanomaterials have been examined for methanol oxidation. An easy and facile ultrasonication method was applied to produce highly efficient, monodispersed and durable (Pt) NPs dispersed on reduced graphene oxides (rGO). The structure morphology, composition and properties of Pt/L@rGO NPs were characterized by using different techniques such as ICP-OES, XPS, TEM, HRTEM, and XRD methods. A different ligand based monodisperse Pt (0) nanocatalysts have been compared with each other and commercial catalysts in terms of catalytic performance, life-time and reusability of catalyst for methanol oxidation reaction in THF at room temperature. All experimental results demonstrate the highly stable and reusable rGO furnished Pt (0) nanomaterials and their excellent catalytic performance in the methanol oxidation reactions at room temperature.     

A new ideal evaporative freezing cycle

A new ideal evaporative freezing cycle for freezing of water is proposed and analyzed by using the conservation of energy and the conservation of mass principles. The proposed cycle utilizes low temperature heat sources such as solar energy, geothermal energy, and waste heat, and consists of a freezing chamber, an air-to-air heat exchanger, a desiccant chamber, an air-to-water heat exchanger, and a fan through which air circulates at atmospheric pressure. The operating principles of the cycle is based on the fact that as dry air picks up moisture from water, the water vapor absorbs heat primarily from the remaining body of the water, and thus the water is cooled and frozen. It is shown that the proposed system can produce 28.4 g ice/kg dry air circulated at most and have a thermal coefficient of performance up to 0.47. The proposed evaporative freezing cycle offers a viable alternative to the conventional refrigeration methods and provides refrigeration by using the inexpensive source of thermal energy source. Also, various aspects of the cycle proposed is discussed.     

西伯利亚白刺果实红色素提取工艺的研究

本实验研究了从西们利亚自刺果实中提取红色素的工艺条件和色素的理化性质.结果表明:西伯利亚白刺果实红色素的最大吸收波长为346nm:将西伯利亚白刺果实在30 ℃烘干,粉碎,按料液比(m/V)1:10、提取温度40℃、pH3、浓度75%乙醇溶液浸提2h,可得红色素;西伯利亚白刺果实红色素对酸、碱、光、热、食品添加剂和金属离子性质稳定.     

The Relationship Between Contact Resistance and Contact Force on Au-Coated Carbon Nanotube Surfaces Under Low Force Conditions

Carbon nanotube (CNT)-coated surfaces are investigated to determine the electrical contact performance under low force conditions. The surfaces under investigation are vertically aligned multiwalled CNTs formed on a silicon substrate and coated with an Au film. These planar surfaces are mated with a hemispherical Au plated probe mounted in a nanoindentation apparatus. The maximum contact force used is 1 mN. The contact resistance of these surfaces is investigated as a function of the applied force and is also studied under repeated loading cycles. The surfaces are compared with a reference Au-Au contact under the same experimental conditions and the results compared to established contact theory. The results show that the vertically aligned multiwalled CNT surface provides a stable contact resistance. This paper shows the potential for the application of CNT surfaces as an interface in low force electrical contact applications.     

Performance of synthetic storm technique in estimating fade dynamics in equatorial Malaysia

In this paper, the synthetic storm technique (SST) is applied to 1‐minute rainfall rate collected from a rain gauge to predict the fade dynamics of the signal in an earth‐to‐satellite link in an equatorial climate location without the needs of satellite beacon measurements. The obtained results are compared with the statistics calculated from measured rain attenuation and with the ITU recommendation model. As for fade duration, a good agreement with measurements has been found together with a significant improvement in terms of prediction errors with respect to the ITU‐R model. Synthetic storm technique is also able to predict fade slope statistics fairly well and has equivalent performance of ITU‐R model.