Hai Yun Jin

Fabrication and Properties of Machinable AlN-BN Ceramic Nanocomposites

The AlN/h-BN nanocomposite powders were synthesized through the reaction of AlN powder, boric acid (H3BO3) and urea (CO(NH2)2) in a nitrogen atmosphere, and the machinable AlN/BN ceramic nanocomposite s were fabricated by hot-pressing in N2 atmosphere. The existing and distribution of h-BN phase are revealed by X-ray diffraction (XRD), TEM and SEM. For the existing of weak interface between h-BN and AlN grains, the machinability of AlN/BN composites is improved obviously. For the finer microstructures, the mechanical properties and the machinability of the composites with micrometer sized AlN coated with nano-sized BN are better than the AlN/h-BN composite of mechanical mixing type.

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).

The Mechanical Properties of AlN/BN Laminated Ceramic Composites

AlN/BN laminated ceramic composites were fabricated using tape-casting and hot-pressing by optimizing the designs of the structure and geometry of AlN/BN laminated ceramic composites. The results showed that the fracture toughness and bending strength for AlN/BN laminated ceramics reached 9.1MPa.m1/2 and 378MPa respectively. The fracture toughness is two times higher than that of AlN monolithic ceramics. The excellent fracture toughness of AlN/BN laminated ceramics could be mainly attributed to crack deflection, delaminating, branching, parallel propagation and crack laminate pilling out at the AlN/BN weak interface.

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.

A Study on Reaction Bonded Ceramics Fabricated by Silicon Infiltration to B4C Preforms

Silicon was infiltrated into B4C preforms to fabricate B4C based composites ceramics at 1600 °C under vacuum circumstance. In this paper, silicon infiltration process was discussed by theoretical calculation. The volume expansion caused by reactions between silicon and boron carbide was about 89.1% from the calculation. In our study, the maximum density of B4C preform for the infiltration of silicon was about 1.5g/cm3 which was larger than theoretical result. The results of mechanical behavior showed that B4C based composites had excellent mechanical properties with a density lower than 2.6g/cm3, Vickers-hardness of this material was 27.2GPa, and this material showed a flexural strength of 349MPa and fracture toughness of 3.8 MPa*m1/2.

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.

Effect of Hexagonal BN on the Microstructure and Mechanical Properties of Pressureless Sintered Porous Si3N4 Ceramics

Porous silicon nitride ceramics with various amounts (25, 35, and 45 vol %) of hexagonal boron nitride (h-BN) were fabricated at 1800°C for 2h by the pressureless sintering process. With FESEM and TEM, the effects of h-BN on the microstructure and mechanical properties of Si3N4 ceramics were investigated. Results of the microstructure and mechanical properties of Si3N4/BN composites showed that the growth of the elongated β-Si3N4 were hindered by h-BN additive, which resulted in the decrease of fracture toughness of Si3N4/BN ceramics with increasing h-BN content. The morphologies of the fracture surfaces by FESEM revealed the fracture mode for Si3N4/BN composites to be intergranular. However, phase analysis by XRD indicated that the effect of h-BN on the α- to β- Si3N4 phase transformation of Si3N4/BN composites was negligible.

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.