Papers by Author: De An Yang

Abstract: The thick-film metallization of AlN has received considerable attention because of its potential applications in electronic packaging. Here we reported on the thick film metallization of AlN by reactive binders. The metallization paste of Ag was prepared with organic vehicle of castor oil, ethyl cellulose and beta-terpineol and reactive binders of TiB2 and Co3O4. The control of the paste viscosity was discussed by changing the dispersant content. Meanwhile effects of the components and sintering process on the thick film properties were investigated. The properties of metallization film were analyzed with XRD, SEM and electrical test. The adhesion strength and the electrical resistance of the film were 12.7MPa and 5.3mΩ/□ respectively when the paste composition of Ag, TiB2, Co3O4 and the organic vehicle was 72.8%, 1.5%, 0.7% and 25% and the film was sintered in air at 850°C for 15 minutes.

Abstract: In this paper, the sol-gel process was used to synthesize a glass binder in thick-film paste for aluminum nitride (AlN) metallization. Some major factors that influenced the sol-gel process including PH value, quantity of water were discussed in detail. The xerogel was analyzed by means of TG-DSC in order to determine its optimum heat treatment process. Meanwhile, the sintering behavior of silver/glass composite thick film had been studied by varying the glass content. The results show that a glass powder of a low melting point and chemically compatible with AlN substrate can be obtained by sol-gel method when the composition (wt %) is CaO (40), B2O3 (15), SiO2 (35), BaO (10). During sintering, the glass becomes liquid and largely affects the microstructure development and square resistance of the thick film. When the glass content is optimum (10wt %), the film adhesion strength achieves maximum and the square resistance has a relatively low value.

Abstract: β-tricalcium phosphate (β-TCP) added with certain amounts of β-calcium pyrophosphate (β-CPP) was prepared. Degradation behavior of β-TCP/β-CPP ceramic was tested by soaking in Tris solution for 20d. The morphologies of composites before and after degradation were observed by SEM. The weight loss was tested after soaking in immersion solution. The results showed that the β-TCP/β-CPP ceramic had great potential as a biodegradable bone substitute.

Abstract: The β-TCP granules with the range of diameter from 314μm to 800μm were prepared. The β-TCP/HAP composite bioceramics were prepared by dipping β-TCP discs made from the granules in HAP sol. The component and morphology of the ceramics were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The compressive strength of specimens was tested by Testometric M350-20KN. The results show that the samples can be calcined at 1150°C without phase transformation of β-TCP to α-TCP by doping the β-TCP with 1wt% MgO. And the compressive strength of the composite ceramics reaches 24MPa.

Abstract: CaSO4/β-TCP composite powders were prepared by mixing CaSO4 and β-TCP. The CaSO4 /β-TCP (VS: VP) values were varied from 3:2 to 0:1. The composites were sintered at different temperatures. Tris was used to evaluate degradation behavior of the composites. The morphologies of composites before and after degradation were studied by SEM. The results show that degradation was increased with the increasing of VS: VP and decreased with the increasing of sintered temperatures.

Abstract: Calcium phosphate cement (CPC) is a kind of promising materials used in dental and orthopeadic restoration. Nowadays, CPC is of special interest due to its self-setting behavior when mixed with an aqueous liquid phase. In this study, α-tricalcium phosphate (α-TCP) and tetracalcium phosphate (TeCP) were served as the solid component of the cement, and the liquid component was consisted of sodium phosphate dibasic dedocahydrate (SPDD, Na2HPO4·12H2O), and/or citric acid. The cement’s properties as compressive strength and porosity were measured. The effects of preparing conditions, such as liquid-to-powder ratio (L/P) and liquid composition, on compressive strength of calcium phosphate were investigated. The results show that the compressive strength increases with the decreasing of pH value. There is a premium L/P in which the compressive strength gains its maxim. The compressive strength reached 21.69 MPa at the condition of L/P = 0.30mL/g and pH =5.

Abstract: Gypsum powders and calcium phosphate/gypsum powders were synthesized by wet method. The influences of the pH and temperature on the morphology of the gypsum crystal were studied by light microscopy. The effects of the initial calcium/phosphorus molar ratio and the pH of the solution on the microstructure and phase composition of the calcium phosphate/gypsum composite powders were studied by scanning electron microscopy and X-ray diffractometry. The results show that both temperature and pH value had influence on the crystal shape of gypsum and the pH value was the predominant parameter for the particle shape and phase composition of the composite powders.

Abstract: Al2O3 ceramic fillers were incorporated into polyetheretherketone (PEEK) to improve the mechanical property in order to suit its aerospace application. To get the high performance composite, it is important to control the dispersion of the nano-Al2O3 among the PEEK matrix. As a pre-fabrication process, the dispersion behaviors of the nano-Al2O3 particles in the liquid medium were studied. Thestability of suspensions was characterized by zeta potential, sediment volume, viscosity and TEM analysis. The mechanism of dispersing nano-Al2O3 aqueous suspension has been investigated including single-electronic stabilization, steric stabilization, and electrostatic stabilization. The highly dispersed and stabilized nano-Al2O3 aqueous suspensions were obtained at acidic condition (pH=3) with PEG-400 and tri-ammonium citrate (TAC).

Abstract: Sr(NO3)2, Fe(NO3)3 and citric acid (the mole ratio was 1:1:2) were mixed in water to form sol. Alumina substrate, which had been treated by ultrasonic cleaner, were dipped in the sol and pulled out, and the coating film was heated for 1h at 900oC. Through seventeen times treatment, SrFeO3-d thin film was coated on the alumina substrate. The remainder sol was dried and heated at 400oC, 800oC, 900oC for 2 h. The thin films and the powders were characterized by XRD. The morphologies of thin films were observed by SEM. The results showed that SrFeO3-δ was formed at 900oC on alumina substrate and the grain size was 100 ~ 200 nm. The oxygen sensitivity was measured in the temperature range of 377 ~ 577oC under different oxygen partial pressures. SrFeO3-δ thin film showed p-type conduction. The response time was less than 2 min when being exposed to a change from N2 to 0.466% O2 at 377oC.