Frontiers of Materials Science in China

Carbon nanotubes (CNT) have a unique structure and feature. In the present study, cell proliferation was performed on the scaffolds of single-walled CNTs (SWCNT), multiwalled CNTs (MWCNT), and on graphite, one of the representative isomorphs of pure carbon, for the sake of comparison. Scanning electron microscopy observation of the growth of osteoblast-like cells (Saos2) cultured on CNTs showed the morphology fully developed for the whole direction, which is different from that extended to one direction on the usual scaffold. Numerous filopodia were grown from cell edge, extended far long and combined with the CNT meshwork. CNTs showed the affinity for collagen and proteins. Proliferated cell numbers are largest on SWCNTs, followed by MWCNTs, and are very low on graphite. This is in good agreement with the sequence in the results of the adsorbed amount of proteins and expression of alkaline phosphatase activity for these scaffolds. The adsorption of proteins would be one of the most influential factors to make a contrast difference in cell attachment and proliferation between graphite and CNTs, both of which are isomorphs of carbon and composed of similar graphene sheet crystal structure. In addition, the nanosize meshwork structure with large porosity is another property responsible for the excellent cell adhesion and growth on CNTs. CNTs could be the favorable materials for biomedical applications.

In this work, a pH/temperature responsive hydrogel (PMEA) from N-acryloylglycine methyl ester (NAGME), N-acryloylglycine ethyl ester (NAGEE), and acrylic acid (AAc) was synthesized by free radical polymerization. The swelling behaviors and drug release properties of hydrogels were systematically investigated at different temperature, pH, and AAc content. It was found that the hydrogel PMEA demonstrated pH and temperature responsive nature. The caffeine-release behaviors showed that only 49.1% caffeine was released from PMEA in pH 2.70 phosphate buffer solution (PBS) after 500 minutes, whereas more than 93.9% caffeine was gradually diffused into the medium in pH 7.49 PBS over the same time interval. In addition, the caffeine release was much higher at 37°C than that at 14°C in deionized water. As seen from the results, the PMEA seems to be a potential drug carrier with pH-temperature responsiveness.

Cold rolled dual phase steels with low C and Si addition were investigated in terms of combination of composition and processing in order to improve mechanical properties and workability including welding and galvanizing. Mo and Cr could be used as alloying elements to partially replace C and Si to assure enough hardening ability of the steels and also give solute-hardening. Mo addition is more effective than Cr addition in terms of obtaining the required volume fraction of martensite and mechanical strength. The ferrite grain was effectively refined by addition of Nb microalloying, which gives optimized mechanical properties. The experimental results show that it is possible to obtain the required mechanical properties of high grade 800 MPa dual phase steel, i.e., tensile strength > 780 MPa, elongation > 15%, and yield/tensile strength ratio < 0.6 in the condition of low carbon (C < 0.11 wt.%) and low silicon design (Si < 0.05 wt.%) through adequate combination of composition and processing.

ZrB2 is a combined bonding compound composed of strong covalent bonds which make it difficult to sinter and densify. Thus, rare earth or other metal elements are usually used to be sintering additives to improve its sintering properties. To forecast properties of ZrB2 solid solutions with addition of lanthanum, their valence electron structure (VES) was calculated by using the empirical electron theory (EET) of solids and molecules, and the effect of lanthanum with various proportion on the VES and properties of ZrB2 ceramics has been studied. The results show that with the increase of the lanthanum addition content, the hybridization steps of Zr and B atoms of ZrB2 solid solutions are still A16 and 5, respectively. The hybridization step of lanthanum is always A1. The covalent electron numbers and bonding energy of the strongest bonds of the ZrB2 matrix decrease with the lanthanum addition content increase. These suggest that the addition of lanthanum will improve the fracture toughness and decrease the hardness, crystal cohesive energy and melting point of ZrB2. In a word, its sintering properties are improved, and its densities are increased.

A nano-scaled graphite oxide (GO) was prepared with a micro-layer structure for intercalation. Graphite-intercalated SnO2 was obtained at temperatures lower than 100°C. The morphology, microstructure, crystalline phases and thermal property of this intercalative composite were studied by atomic force microscopy (AFM), field-emission scanning electron microscopy (FE-SEM), X-ray diffractometry (XRD) and differential scanning calorimetry-thermogravimetry (DSC-TG) doped with a proper amount of graphite-intercalated composites (GITs), GIT-SnO2 composite was obtained after heat treatment. This combined gas sensor reveals low resistance and high sensitivity to butane between 200°C and 300°C.

The luminescence lifetime of the 0.01 mol.%-0.1 mol.% Er3+- and 0–20 mol.% Y3+-codoped Al2O3 powders prepared at a sintering temperature of 900°C in a non-aqueous sol-gel method has been investigated to explore the enhanced mechanism of photoluminescence properties of the Er3+-doped Al2O3 by Y3+ codoping. For the 0.1 mol.% Er3+-Y3+-codoped Al2O3 powders, the measured lifetime of Er3+ gradually increases with increasing Y3+ concentration. Consequently, codoping with 20 mol.% Y3+ leads to an increase in the measured lifetime from 3.5 to 5.8 ms. By comparing the measured lifetime for different Er3+ concentrations in the Al2O3 powders, the radiative lifetime of both the Er3+-doped and the Er3+-Y3+-codoped Al2O3 powders is estimated to be about 7.5 ms. Infrared absorption spectra indicate that Y3+ codoping does not change the-OH content in the Er3+-Y3+-codoped Al2O3 powders. The prolonged luminescence lifetime of the 4I13/2 level of Er3+ in Er3+-doped Al2O3 powders by Y3+ codoping is ascribed to the decrease in the energy transfer rate between the Er3+ ions and the Er3+ and -OH, respectively, due to the suppressed interaction between Er3+ ions.

In this study, the effects of variable parameters on arc shape and depth of penetration in twin-wire indirect arc gas shielded welding were investigated. The variation of arc shape caused by changes of the parameters was recorded by a high-speed camera, and the depths of penetration of specimen were measured after bead welding by an optical microscope. Experiments indicated that proper parameters give birth to a concentrated and compressed welding arc, which would increase the depth of penetration as the incensement of the arc force. Several principal parameters including the distance of twin wires intersecting point to base metal, the included angle, and the content of shielding gas were determined. The arc turned more concentrated and the depth of penetration increased obviously as the welding current increased, the arc turned brighter while unobvious change of penetration occurred as the arc voltage increased, and the deepest penetration was obtained when the welding speed was 10.5 mm/s.

Titanium dioxide (TiO2), with its large band gap, has attracted much attention due to its excellent photocatalytic activity. TiO2 ball-shaped nano-particles were deposited on silicon substrates by a thermal oxidation approach. With an increase in the annealing temperature the surface morphology and the structure of TiO2 remained stable, exhibiting good heat stability; meanwhile, the hydrogen production rate also increased. The femtosecond pump-probe spectroscopic study showed that the lifetime of carriers of the samples as- deposited and post-annealed at different temperatures were longer than 20 ps.