Nai Kui Gao

Fabrication of Aluminum Superhydrophobic Surface with Facile Chemical Etching Method

Superhydrophobic surfaces have attracted much interest for its potential applications. In this study, the superhydrophobic aluminum surfaces were fabricated by method of chemical etching. Aluminum surfaces were firstly chemically etched by hydrochloric acid, and modified with stearic acid. The relationship between the etching time and the surface hydrophobicity was investigated. The contact angle and the sliding angle were tested, the results showed that with increasing etching time, the contact angle experienced a rise and then decrease, while the sliding angle dropped first and then started to climb. A maximum value of 152 degrees for the contact angle and a minimum value of 3 degrees for the sliding angle were obtained with etching time of 1 minute. The results indicated an ideal superhydrophobic property of the aluminum surfaces.

Preparation and Dielectric Properties of Alumina Filled Epoxy Nano-Composite

The reported enhancement in dielectric properties obtained for polymer nano-composite seemed to be very encouraging. To further understand the dielectric behavior of epoxy nano-composite, aluminum oxide (Al2O3) nano-particles were incorporated into bisphenol A epoxy resin, and the dependence of nano-particle content and the dielectric properties was investigated in this study. Results showed that, when nano-particle contents was no more than 10phr, relative permittivity (εr) decreased to be lower than that of monolithic epoxy, and the minimum value appeared in 4phr nano-particle filled composite. The minimum value of tan delta (tanδ) appeared in 6phr nano-particle filled composite. DC volume resistivity (ρv) increased due to the introduction of nano-particles when the filler content is very small (about 2phr).

Dispersion and Impact Strength of Epoxy Resin/Nano-Al2O3 Composites

This paper focuses on the influence of nano-Al2O3 surface state and composite process on the dispersion of nano-Al2O3 filler. Toughening was performed to epoxy resin by nano-Al2O3, and the effect of impact property of epoxy resin/nano-Al2O3 composites was studied. The results showed that coupling agent treatment and high-speed shear dispersion can improve many properties of the composites. With nano-Al2O3 content increasing, the impact strength of the composites increased at first and then decreased. The maximum appears when the nano-Al2O3 content reached 3wt. %, no matter with or without the coupling agent treatment, which is 87.4% and 78.6% higher than that of monolithic epoxy resin respectively. The coupling agent treatment of nano-Al2O3 helped to improve the impact strength of the composites.

Effect of Degassing Treatment on the Crystalline Morphology of XLPE Insulation Used for 110kV XLPE Cable

Cross-linked polyethylene (XLPE) is a main kind of insulation materials, used in medium and high voltage power cable. High voltage XLPE cable production mainly adopts peroxide crosslinking method, and the performance of XLPE cable will be affected by decomposing by-products of crosslinking agent (DCP, dicumyl peroxide).In this paper, the XLPE cable was degassed with different times. The XLPE samples were analyzed by infrared spectrum analysis, DSC analysis and electron microscopy, and the influences of degassing on XLPE crystalline morphology were analyzed. The results showed that the crystal structure of XLPE in the cable was affected by degassing treatment. With the degassing treatment time went on, the by-products kept releasing. The content of by-products in 110kV XLPE cable decreased obviously in 2-7 days’ degassing treatment, and changed slowly after 7 days’. The growth and perfection of the original crystal in XLPE material were obtained, and the new small grains were formed in the material.

Study on Microstructure and Impact Strength of Nano-SiO2 Toughened Epoxy Resin Composites

In this paper, composites with different contents of epoxy resin/nano-SiO2 were fabricated, the influence of compounding process on nano-SiO2 dispersion was studied, the microstructure and the relationship between impact strength and nano-SiO2 content were investigated. The results showed that the distribution of nano-SiO2 particles in the composites could be improved efficiently using high-speed shearing dispersion method. To composites with or without the coupling agent treatment, the impact strength grew with increasing nano-SiO2 content, and increase to a maximum value when nano-SiO2 content was 3wt.%. The maximum value was 75.4%, and 45.5% higher than that of monolithic epoxy resin respectively. With the nano-SiO2 content increased continually, the impact strength of composite materials decreased. The coupling agent treatment of nano-SiO2 administered to improve the impact strength of the composites.

Microstructure and Flexural Property of CaCO3 Whisker Reinforced Epoxy Composite Material

Reinforcement was performed to epoxy resin by CaCO3 whisker, and the effect of flexural property of CaCO3 whisker reinforced composite materials was studied. The microstructures of the composite materials were observed by SEM. The results showed that the flexural strength of the composites increased with increasing CaCO3 whisker content, and the flexural strength reached to the maximum value when CaCO3 whisker content was about 15wt.%, and the maximum value was about 11% higher than that of pure epoxy resin. But, the strength would drop sharply with the excessive CaCO3 whisker.

Research on Water Content and Physicochemical Properties of Insulating Materials for Water-Soaked XLPE Cable

The buried environment of cross-linked polyethylene (XPLE) cable is relatively severe, and some ones are even immersed in water directly. In this paper, an XLPE cable was soaked in foul water to simulate the cable’s actual water area environment, lasting for three years. The water content in the insulation layers of water-soaked cable was measured by infrared spectrometer and moisture analyzer, and the crystal morphology and physicochemical properties of the insulation layers were investigated by differential Scanning Calorimeter (DSC), scanning electron microscopy (SEM) and tensile testing technology. The results showed that a small amount of water did enter into the cable insulation owing to the increasing of hydroxyl (-OH) content, and followed being verified by moisture analyzer. The degree of crystallinity of water-soaked cable insulating material is also increased, and the mechanical properties were deteriorated.

Electric Field Simulation of Typical Defects in the Epoxy/Paper Composites Insulated Tubular Bus

Many failures had occurred in operation of insulated tubular bus because of the poor product quality, and its primary reason was that some defects were led into the insulation system in the production, then the local electric field would increase and then result in partial discharge, which could accelerate the aging and even breakdown of the materials. In this research, a 1/4 three-dimensional model was established according to the actual structure of insulated tubular bus, and the simulation results obtained from static electric field and quasi-static electric field were compared. Besides, the electric field distribution of insulated tubular bus with typical defects was simulated based on ANSYS software. These three defects were air void, moisture and damage of semi-conducting layer. The simulation results showed that the electric field distribution of insulated tubular bus with typical defects was more suitable with quasi-static electric field simulating. The maximum electric field value was different with different defects, and dependent on the location and size of defects.

Analysis of Physical and Chemical Properties of XLPE Insulation for Long Term Running Cable

High temperature caused by copper core would have a certain impact on the performance of XLPE insulation during the long running process of the cable. In this paper, the XLPE/PVC cable running for 17years was investigated by using thermal analysis, microstructure analysis, mechanical property analysis and dielectric properties analysis. The influences of long-term operation for the physical and chemical properties of cable insulation are analyzed by the performance of the insulation material. DSC results indicated that position of shoulder peak would characterize the thermal history of material and express the crystal size distribution of XLPE indirectly. Mechanical property test results showed that effect of long term high temperature would decrease the elongation at break and breaking strength of XLPE. SEM results showed that the effect of long term high temperature increased the average size of crystal and the distribution of the crystal became concentrated, meanwhile it verified the relevant conclusion of DSC.

Influence of the Morphology of Alumina Filler on Electrical and Thermal Properties of Epoxy Resin Composites

Epoxy resin composites filled with alumina (Al2O3) particles of different morphology and content were fabricated by vacuum casting method. Electric and thermal properties of the composites were tested at room temperature to investigate the influence of Al2O3 morphology on epoxy resin composites. Electrical tests demonstrated that, volume resistivity of epoxy resin composites filled with spherical Al2O3 was bigger than with spherical-like Al2O3, relative permittivity and dielectric loss of epoxy resin composites increased with increasing of Al2O3 content, the effect on dielectric properties of spherical-like Al2O3, which had larger specific surface areas, was larger than spherical Al2O3 for the same content of filler. Thermal conductivity tests proved that, at the same content, thermal conductivity of epoxy resin composites filled with spherical-like Al2O3 was higher than with spherical Al2O3. According to the Agari model, spherical-like Al2O3 particles were easier to form conducting pathways in epoxy resin composites than spherical Al2O3 particles, considering their matte edges.