Applied Mechanics and Materials Vols. 217-219

Abstract: Nano-zirconia (Nano-ZrO2) has good natural color, high strength, high toughness, high chemical stability, excellent corrosion resistance and resistant to chemical attack and microbial erosion particularly, which is one of the biocompatible inert materials and is widely used in biology, medicine and other fields. There are cubic (c-ZrO2), tetragonal (t-ZrO2) and monoclinic (m-ZrO2) phase three different crystal structures of zirconia (ZrO2) in normal atmosphere and different temperatures. In the three different crystal structures, t-ZrO2 has the best performance for ceramic dental materials. However, ZrO2 is usually in the form of m-ZrO2 at room temperature. So to study the synthesis and stabilization methods at room temperature of nano-t-ZrO2 is very important in scientific significance and application prospects.

Abstract: Silicon nitride nanoceramics were fabricated by hot press sintering two kinds of Si₃N₄ nano-sized powders. The effect of starting powders on microstructure, mechanical properties and thermal shock resistance were investigated. The microstructure of sintered materials consists of spherical grains and the addition of α–Si₃N₄ to starting powders does not affect the grain morphology. The flexural strength, fracture toughness and thermal shock resistance increase with the increase in amount of α–Si₃N₄ starting powders, and the maximum mechanical properties are obtained when the amount of α–Si3N4 powders is 40wt.%. The hardness values decrease with the increase of α–Si₃N₄ amount.

Abstract: Nano nickel oxide (NiO) particles were synthesized by a homogeneous precipitation method using NiCl2 as starting material and CO(NH2)2 as precipitant. Proper amount of NP-10 and appropriate organic solvent were added in the preparation process as dispersant. The chemical composition and properties were characterized by means of transmission electron microscope, X-ray diffractometer, and thermo gravimetry-differential thermal analyzer. The effects of reactant ratio, reaction temperature, reaction time, surfactant concentration, organic modifier concentration, agglomeration temperature as well as other reaction conditions on the appearances, size and dispersity degree of nano particles were investigated. The experiment results show that homogenous nano NiO particles were obtained by reacting nickel oxide and urea with a weight ration of 1:5 for 6 h at 80°C, then calcining for 2 h at 300°C. Adding surfactant NP-10 and organic solvent butanol to reaction system increases the dispersity and decreases the particle size of nano nickel oxide.

Abstract: Ultrafine silicon dioxide were modified by -NH2-teminated poly(amido-amine) (PAMAM) dendrimers to improve their dispersibility in the coatings. The modification mechanism was studied through density functional theory (DFT) in the gas phase. Virous initial configurations of ion bound to PAMAM were established to investigate the structures and the energetics of the complexes. Two stable conformers are found: types A ( is bound to the amine site) and C ( is bound to the amide site). Types A and C indicate the chemical bond formation of Si-N and Si-O, respectively.

Abstract: Magnetite nanoparticles with an average particle size ranging from 4.2 to 34.2 nm were synthesized by thermal decomposition of iron(II) acetate with and without a reducing agent. While in the presence of reducing agent, magnetite nanopartices with an average size of 4.2 nm and 12.6 nm were synthesized by varying the amounts of the surfactants. While in the absence of the reducing agent, magnetite nanoparticles with an average size of 26.4 nm and 34.2 nm were prepared.

Abstract: Pineapple leaf fiber (PALF) was pretreated by sodium hydroxide, and hydrolyzed by sulfuric acid to obtained nano-cellulose (NC). The SEM showed that size of NC is 30-50nm. Bis[3-(triethoxysilyl)propyl]tetrasulfide (Si-69) was employed to sueface modificate the NC. The results of characterization of particle size, zeta potential, FTIR and contact angle illuminated that particle size of surface modified NC was smaller than NC and zeta potential of -75.8mV was lower than NC’s. The hydrophobicity of surface modifiedNC has been improved.

Abstract: Three series of PES/SiO₂ composites, containing 0.5-7 wt% nano-sized SiO₂ with different specific surface area, were prepared by solution blending. The resulting composites exhibit the higher glass transition temperature (Tg) than that of pure PES. The Tg of composite showed a maximum increment of 24.0 °C by the addition of 7 wt% A300. The trade name of A300 is Aerosil 300. It is one of the fumed silica nanoparticles products of Degussa. The decomposition temperatures (Td) of composites were always higher than that of pure PES and showed a maximum increment of 37.0 °C by the addition of 3 wt% A300. The oxygen transmission rate of composites are always lower than that of pure PES and decreases with increasing SiO₂ content to 1 wt% and then increases to 7 wt%. The composite with 1 wt% A300 exhibits a maximum decrement percentage of 46 %. The Tg, Td, and oxygen barrier property are as a function of the SiO₂ content and size. The finer SiO₂ are more effective in increasing the Tg, Td and oxygen barrier property.

Abstract: Nono-sized organic bentonite (OMMT) was synthesized through intercalation modification process with organic phosphorus flame retardant (Cyagard RF-1) and quaternary ammonium salt (CTAB). Composite materials of polybutylene terephthalate (PBT)/OMMT, Polyamide-6 (PA6)/OMMT was prepared by a double screw extrusion. The flame retardancy and mechanical properties of these materials were characterized. Nano-sized OMMT has large interlayer spacings and good dispersion after modification. In compared with PBT and PA6, composite materials of PBT/OMMT and PA6/OMMT had high tensile strength, bending strength and notched impact strength, while their elongation decreased after addition of nano-sized OMMT, the limiting oxygen index ( LOI ) and UL94 vertical combustion of OBT/OMMT and PA6/OMMT composite materials with dosage of 3 wt% OMMT decreased slightly, in comparison with these composite metarials containing constant amounts of flame retardant.

Abstract: Targeting at the brittleness of cured epoxy (EP), functionalized CNTs were integrated into the thermoset to make high-performance CNTs/EP nano-composites.In this investigation, polymaleic acid modified CNTs with a high surface grafting ratio (PMA-CNTs)was prepared through the plasma induced grafting technique , then further functionalized with amino groups to yield A-PMA-CNTs, which were then incorporated into epoxy matrix. Characterization of mechanical properties and heat resistance of the A-PMA-CNTs/EP nanocomposites indicates that A-PMA-CNTs can significantly strengthen and toughen the epoxy resin, with an increased glass transition temperature.

Abstract: The thermomechanical treatment of a 2A12 aluminum alloy was researched and the influence of deformation ratio above recrystallization temperature on microstructure and hardness was analyzed emphatically. The result reveals that when the deformation ratio is low at first, the hardness of specimen decreased because the effect of recrystallization softening overwhelms the effect of deformation strengthening. However, hardness increased with increasing deformation ratio. In addition, the microstructure became more homogeneous and grains were refined obviously by metallography microscope observation with increasing deformation ratio. The second phase precipitates dispersedly to strengthen the alloy.