Materials Science Forum Vols. 544-545

Abstract: For the investigation of high aspect ratio structures with Atomic Force Microscope (AFM), the cantilevers with very sharp and long tips are useful. Electron beam induced deposited(EBID) tips can be simply fabricated by aligning the electron beam directly down the vertical axis of Si cantilever and then irradiating a single spot on the cantilever for a proper time in the dominant atmosphere of residual gases generated by the oil of the diffusion pump of the Scanning Electron Microscope (SEM). However, the EBID tips cannot grow over 1&m in the residual gas atmosphere since there is a little carbon source. We could enhance the height of tips by dipping the cantilever into the organic solvents, drying it in the vacuum chamber and irradiating electron beam on it. With this process, we could acquire the tip whose base diameter is 180nm and effective length is 3.18&m. In addition, we observed that the growth behaviors of the tips are different in accordance with the species of the solvents and we will discuss the effects of the organic solvents on the growth of the tips.

Abstract: In order to give machinability to hard and brittle AlN ceramics, the homogeneous dispersion of fine BN particles into AlN matrix was investigated. The AlN/BN nanocomposite was fabricated by hot-pressing AlN-BN composite powder, which was prepared by reducing and heating AlN particles containing a mixture of boric acid, urea and carbon. The nanocomposite containing 20 vol.% BN showed high strength, machinability and relatively high thermal conductivity.

Abstract: Various polymer-based scaffolds reinforced by the hydroxyapatite (HAp) for bone tissue engineering were successfully synthesized by in-situ co-precipitation method. The influence of HAp in composite scaffolds on the pore morphology, microstructure, and mechanical properties was investigated. The polymer-based scaffolds appeared to be macroporous and an interconnected open pore microstructure with pore size around 200 μm. The pore structure of the composite scaffolds was not much changed by the presence of HAp but the pore size of the composite scaffolds decreased with adding the HAp. The compressive modulus and yield strength of the polymer-based scaffolds improved by the presence of HAp.

Abstract: Artificial graphite generally manufactured by carbonization sintering of shape-body of Kneaded mixture using granular cokes as filler and pitch as binder, going through pitch impregnation process if necessary and finally applying graphitization heat treatment. The effect of thermal oxidation with air or CO2 atmosphere on IG-11 graphite samples was investigated. The results show a localized oxidation process which progressively reveals the large coke particles with increasing overall weight loss in air. The surface of graphite was peel off which was not changed the specific gravity after air oxidation. However, the specific gravity of graphite continuously decreased by CO2 oxidation. Decreasing of specific gravity in the CO2 oxidation was because that CO2 gas ingress the surface to interior. The pore shape after the CO2 oxidation showed the longneck beakers.

Abstract: Carbon nanotubes and nanofibers were synthesized at 400-800°C by a typical CVD method using SiO2, Al2O3, or MgO supported Ni or Co catalyst, and acetylene as feedstock. The effects of temperature, substrates and catalyst on the yield and structure of carbon nanotubes and nanofibers were investigated in detail. The experimental results showed that Ni based catalysts tended to form carbon nanofibers with “herringbone” structure, though for Ni/Al2O3 catalyst, the products at 800°C changed to a structure like carbon nanotube. Co based catalysts tended to form carbon nanotubes.

Abstract: CdS was synthesized by solvothermal reaction of CdCl2.2.5H2O and (NH2)2CS in ammonia solution at 200 oC for 10 h. XRD, TEM and SAED show that the products are nanocrystalline CdS. The phase is 100 % hexagonal (hcp) in pure water, gradually transformed into cubic with the increase of NH3 concentration, and 100 % cubic in 25 % NH3 solution. By using FTIR, no solvents were detected in the products. Raman analysis revealed the presence of 1LO (longitudinal optical) and 2LO phonon peaks at 297.0 and 597.1 cm-1 for CdS (hcp), and 295.9 and 596.9 cm-1 for CdS (cubic), respectively. Strong peaks of the photoluminescent (PL) spectra were detected at 450 nm for hcp, and 519 nm for cubic.

Abstract: Nano-hydroxyapatite/polyamide66/chitosan composite (n-HA/PA66/CS) was prepared by a co-precipitation method and porous scaffolds from n-HA/PA66/CS composite were prepared by means of porogen–leaching method and were characterized by SEM, IR, XRD and universal mechanical testing machine. IR and XRD analyses showed that some chemical bonds existed between n-HA and polymers. Furthermore, macroporous structure of the scaffolds and mechanical strength were tested with a changed ratio of porogens (PVP/NaCl). When the ratio of PVP and NaCl is1: 6, the scaffold processed highly porosity and the pores were interconnected. The compressive strength of the scaffold, can meet the requirement of tissue regeneration.

Abstract: Nanosized α-aluminum oxides have been prepared by hydrolysis of aluminum alkoxides using a sol-gel procedure. The Na(AOT) as a surface active agent was added into the alumina precursor solution to investigate the influence on size and morphology of alumina particles. The product phase was mainly boehmite with mean particle size of 20~30 nm. The crystal phases and morphology of the alumina nanoparticles were analyzed by X-ray diffractometry and by transmission electron microscopy, respectively. The TEM observations revealed that α-Al2O3 with about 80 nm spherical and hexagonal shapes was formed after calcination at 1200oC. The TG/DSC analyses were also done to determine the phase changes of alumina precursors from room temperature to 1200oC.

Abstract: A novel nano-hydroxyapatite/chitosan (n-HA/CS) composite scaffold with high porosity was developed by a new method of emulsion-foaming/freeze-drying process and was characterized by means of infrared spectroscopy (IR), scanning electronic microscopy (SEM) and universal material testing machine. In addition, the porosity and density of the scaffold were also calculated. IR result shows that the characteristic absorption peaks belonging to both CS and HA are present in their composite, and the slight band-shifts and peak-decrease suggest that some interactions have taken place between the two phases of CS and n-HA in the composite. SEM photo displays that, with the dosage increase of Tween-80, the prepared scaffold shows highly porous and interconnected structure, in which macropores and micropores coexist. The calculated data demonstrate that the porosity of the scaffold is proportional to the content of the emulsifier, while the compressive strength is inversely. When 15wt% emulsifier used, the porosity of the scaffold can be up to 90% and the density is 0.453g/cm3, while the corresponding compressive strength is about 2.4MPa. The newly developed n-HA/CS composite scaffolds may serve as a good 3-D substrate for cell attachment and migration in bone tissue engineering.

Abstract: Scaffold in bone tissue engineering must have a three-dimensional (3-D) interconnected porous structure acting as a template for bone tissue regeneration, and material fabricating the scaffold must be biocompatible and can provide structural support during bone growth and remodeling at the same time. In this paper, a method of phase separation and particle leaching combined (PS/PL) was used to prepare porous scaffold of nano-hydroxyapatite and polyamide6 (n-HA/PA6) composite. The results show that the scaffold prepared by PS/PL has not only interconnected macropores of 100~300 μm, but also micropores on the walls of macropores, and PS/PL scaffold is more interconnective in compare with phase separation (PS) scaffold. When the porosity of the scaffold is about 79%, its compressive strongth is about 3.27 MPa, that is similar to the human cancellous bone(2~10MPa). Ethanol has some effect on hydrogen bonds, but fabricating method will not change the chemical component of the composite. The porous scaffold is prospect for bone tissue engineering.