Frontiers of Materials Science (v.2, #1)

A review: Hot topics on magnesium technology in China by Zhen-hua Chen; Ji-hua Chen (1-8).
Magnesium alloys have wide applications in automobiles, aerospace and so on due to many advantages, while a number of undesirable properties including poor corrosion resistance, inferior creep resistance and bad plastic processing ability have hindered their applications. Creep-resistant magnesium alloy design, plastic processing of magnesium alloys and rapid solidification processing of magnesium alloys have become the hot topics in magnesium technology. Other than these, surface modification as well as laser beam welding are also involved. The research progress and development in magnesium technology in China are reviewed in the paper.
Keywords: magnesium alloy; creep resistance; plastic processing; rapid solidification

We prepared surface-modified TiO2 nanoparticle (21 nm)/polypropylene nanocomposites using a twinscrew extruder and an injection molding machine. The TEM (transmission electron microscopy) and SEM (scanning electron microscopy) images showed homogeneous dispersion of nano-TiO2 at 1 vol.% filler content and weak nanoparticle matrix interfacial adhesion. It was found that the essential work of fracture (EWF) approach, usually characterizing fracture toughness of ductile materials, was no longer applicable to the nanocomposite samples because of the extreme crack blunting and tearing processes observed in the EWF tests. As an alternative approach, the specific essential work-related yield was used for assessment of the plane-strain toughness, as suggested in the literature. The results indicated that the addition of 1 vol.% nano-TiO2 did not toughen the polypropylene (PP) matrix at all. On the other hand, it was observed from the EWF tensile curves that the nanoparticles enhanced the ductility of the PP matrix greatly, the reason of which was probably ascribed to the high level of molecular orientation of the injection molded samples, as revealed by the polarized optical microscopy (POM). Because of the highly ductile behavior induced by the nanoparticles, the fracture energy achieved two-to three-fold increase, depending on the ligament lengths of the samples. The difference between the toughness and ductility of nanocomposites was discussed.
Keywords: fracture; toughness; ductility; nanocomposites; nanoparticles; polypropylene (PP)

Magnetic and optical properties of polycarbonate/Fe nanocomposites by Ya Shi; Zheng-cao Li; Chun-hua Xu; Wei Miao; Yu-quan Wang; Zheng-jun Zhang (16-19).
The magnetic and optical properties of polycarbonate (PC)/Fe nanocomposite films prepared by a solution blended process and the role of Fe additives are investigated. The saturation magnetization of the PC/Fe nanocomposites depends on the weight of Fe nanoparticles. Meanwhile, an increase of photoluminescence (PL) intensity with decreasing Fe additives is interpreted. The optical band gap corresponds to the increase of PL elements. The transmittance of the films increases with reduced Fe, and the PL peak energy of PC/Fe composites is also correlated to the weight ratio.
Keywords: polycarbonate (PC); Fe; nanocomposite; magnetic property; optical property

The role of hydroxyl and atomic oxygen in multiwall carbon nanotube growth by Qiang Chen; Ya-bo Fu; Chun-mei Zhang; Yue-fei Zhang; Li-zheng Yang (20-25).
Multiwall carbon nanotubes (CNTs) were grown by the plasma-enhanced chemical vapor deposition (PECVD) method in downstream on the p-Si (100) substrate. Besides precursors, methane as the carbon source and hydrogen as the ablation, oxygen or H2O was alternatively inlet into the reactive chamber at the pressure of 0.05 MPa. Given characterizations of the tube structure and tube mass weight, the role of radical atomic O, hydroxyl and perhydroxyl in multiwall CNT growth was explored. In addition to a small amount of O2 (∼0.67%) or H2O (∼0.1%), it was found that a high quantity of pure nanotubes can be grown in the downstream. However, no nanotube could be formed or even the carbon matrix generated when the concentration of O2 or H2O exceeded a proper value in the mixture. The mechanism of multiwall CNT growth controlled by active radicals was explored in this paper.
Keywords: nanotubes; plasma enhanced chemical vapor deposition (PECVD); water; hydroxyl; mechanism

Self-assembly of truxene derivatives investigated by STM by Xiao-bo Mao; Zhun Ma; Yan-lian Yang; Sheng-bin Lei; Chen Wang; Wei Huang (26-30).
Truxene and its derivatives were synthesized, and their assembly structures were studied by scanning tunneling microscopy (STM) technique. Parallelogram-shaped dimers with different contrast can be resolved for two-dimensional assembly of truxene molecules. Moreover, the side-chain-effect is introduced into the system to tune and control the assembling structures of the truxene for one of the two truxene derivatives, hexatetradecyltruxene (truxene-C14) with six C14 side chains, showing stripe assembling structures with different contrast. While for the other one, 2,7,12-tertriazine-5,5′,10,10′,15,15′-hexatetradecyltruxene (tertriazine-truxene-C14) form the intermolecular multi-hydrogen bonds. Hydrogen bond interaction influences the molecular orientation and conformation of these two-dimensional supramolecular architectures. These results demonstrate the role of hydrogen bonds in molecular assembly formations and what is more, would be beneficial for understanding and fine tuning of the assembling of truxene-related opto-electronic materials.
Keywords: self-assembly; truxene derivatives; scanning tunneling microscopy (STM)

Preparation and photoluminescence of ZnO with nanostructure by hollow-cathode discharge by Xin-chao Bian; Chun-qing Huo; Yue-fei Zhang; Qiang Chen (31-36).
Without the use of a metal catalyst in the process, ZnO with nanostructures was successfully prepared on Si (100) substrate by simple chemical vapor-deposition method. In our work, Ar was used as the plasma forming gas, O2 was the reactive gas and metal zinc powder (99.99% purity) vaporized by cylinder hollow-cathode discharge (HCD) acted as the zinc source. The crystal structures of the as-synthesized ZnO nanostructures were characterized by X-ray diffraction (XRD); the ZnO sample growing on the wall of the crucible showed a ‘comb-like’ nanostructure, while the other one at the bottom of the crucible showed a ‘rod-like’ structure, which can be attributed to the difference of the oxygen content. The measurement on the photoluminescence (PL) performance of the ZnO nanostructures was carried out at room temperature. The results indicated that the ‘comb-shape’ ZnO nanomaterial possessed a remarkably strong ultraviolet emission peak centered at 388 nm, while ZnO nanorods, except better ultraviolet emission, also had relatively strong blue-green emission ranging from 470 to 600 nm due to the existence of oxygen vacancies. The growth mechanism of ZnO with nanostructures is also discussed in this paper.
Keywords: cylinder hollow-cathode discharge (HCD); ZnO with nanostructure; chemical vapor-deposition method

Effects of oxygen on multiwall carbon nanotubes growth by PECVD by Chun-mei Zhang; Ya-bo Fu; Qiang Chen; Yue-fei Zhang (37-41).
Multiwall carbon nanotubes (MWCNTs) were grown by dielectric barrier discharge (DBD)-type plasma enhanced chemical vapor deposition (PECVD) method in downstream. The temperature was 973 K and the compositions of gases were methane, hydrogen and oxygen in the total pressure of 0.05 MPa. The effect of O2 concentration in the mixture on the configuration of carbon nanotubes (CNTs) was investigated in detail. Results from scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that CNTs grown in CH4/H2 (38.6%/61.4%, volume) mixture have many defects and contained disordered graphitic materials. With the addition of appropriate amount of O2 (∼0.67%), high-purity CNTs could be obtained. However, no CNT, even no carbon matrix existed under the condition of an excessive oxygen concentration (>1.0%, volume) in the mixture. In order to understand the role of O2 during CNTs growth, optical emission spectroscopy (OES) was in-situ employed and the results predicted that the improvement of CNTs quality in O2 addition was attributed to the effect of OH oxidation from the reaction of atomic oxygen with hydrogen in the plasma.
Keywords: carbon nanotube (CNT); plasma enhanced chemical vapor deposition (PECVD); atomic oxygen; hydroxyl

Oxygen-ion diffusion and electrical conduction of La2Mo2−2x Fe x O9−δ systems by Chun Li; Qian-feng Fang; Xian-ping Wang; Guo-guang Zhang (42-47).
Based on the novel oxygen ion conductor La2Mo2O9, a series of Fe-doped samples of La2Mo2−x Fe x O9−δ (x = 0, 0.025, 0.05, 0.1) was prepared by conventional solid-state reaction method. The structure, phase transition, oxygen ion diffusion and electrical conductivity were studied with X-ray diffraction (XRD), differential scanning calorimeter (DSC), direct current (dc) resistivity, and dielectric relaxation (DR) measurements. One DR peak associated with the short-distance diffusion of oxygen vacancies was observed in both temperature and frequency spectra. The activation energy for oxygen ion diffusion in Fe-doped La2Mo2O9 samples was smaller than that in un-doped samples. Fe doping can increase the ionic conductivity of La2Mo2−x Fe x O9−δ samples as well as the ionic transference number in the temperature range from 680°C to 400°C in comparison with the un-doped samples, although the electronic conductivity slightly increases. It is found that because of the small solubility of Fe2O3 in La2Mo2O9 (<5%), Fe doping cannot suppress the phase transition that occurred around 570°C, but 2.5% K doping at La site at the same time (e.g. in sample La1.95K0.05Mo1.95Fe0.05O9−δ ) can completely suppress this phase transition and increase conductivity at lower temperatures.
Keywords: oxide-ion conductor; La2Mo2O9 ; dielectric relaxation (DR); phase transition

Study of bipolar pulsed plasma electrolytic carbonitriding on nanostructure of compound layer for a gamma Ti-Al alloy by Mahmood Aliofkhazraei; Alireza Sabour Rouhaghdam; Mohsen Roohzendeh (48-54).
The surface hardening of a gamma Ti-Al alloy by using bipolar pulsed nanocrystalline plasma electrolytic carbonitriding has been studied in this investigation. Coating process was performed on a triethanolaminebased electrolyte by a cooling bath. The nanostructure of the obtained compound layer was examined with the figure analysis of the scanning electron microscopy (SEM) nanographs. The effects of the process variables, i.e., frequency, temperature of the electrolyte, applied voltage and treatment time, have been experimentally studied. Statistical methods were used to achieve the optimum size of the nanocrystals. Finally, the contribution percentage of the effective factors of the pulsed current was revealed, and the confirmation run showed the validity of the obtained results.
Keywords: bipolar; nanocrystalline; nanostructure; pulsed nanocrystalline plasma electrolytic carbonitriding

The high-intensity pulsed ion beam (HIPIB) technique is developed to treat metallic and ceramic surfaces to improve materials performance. The processing is based on the beam-material interactions: remelting and/or ablation of a top layer on the irradiated surfaces (extreme surface heating effect); subsequently, the molten states may be frozen at an ultra-fast re-solidification rate after termination of the ion beam pulse. Surface smoothing and reconstruction of titanium alloys and ZrO2-Y2O3 coatings have been observed as one of the typical outcome under high-intensity pulsed ion beam irradiation. It is demonstrated that the changes in surface morphology may significantly contribute to the improvements of overall performance of the materials.
Keywords: high-intensity pulsed ion beam (HIPIB); surface remelting; surface smoothing; titanium alloys; ceramic coatings

The effects of hydrogen on electrochemical behavior and susceptibility of stress corrosion cracking (SCC) of pure copper were studied. SCC susceptibility of pure copper in a 1 M NaNO2 solution was increased by pre-charged hydrogen. The effect of hydrogen on the susceptibility is more obvious in the low stress region due to the longer fracture time, which resulted in a longer time for more hydrogen to diffuse toward the crack tip. Synergistic effects of hydrogen and stress on corrosion and SCC processes were discussed. The results showed that an interaction between stress and hydrogen at the crack tip could increase the anodic dissolution rate remarkably.
Keywords: stress corrosion cracking (SCC); hydrogen effect; pure copper

The electron beam could be controlled by magnetic field for fast deflection, in which way multi-beam could be produced by deflection technique. The multi-beams run simultaneously for material processing with different heat input and positions. Therefore, it is possible to adjust the thermal effects and optimize the process. In this paper, the generation of multi-beams in electron beam welding (EBW) was investigated, and the processes of EBW with multi-beams were also investigated by both the numerical simulation methods, i.e., finite element analysis (FEA), and the experiments. The result shows that the residual stress of EBW could be minimized by using the multiple beam technique, and at the same time the welding deformation could also be reduced with the optimized parameters.
Keywords: electron beam welding (EBW); finite element analysis (FEA); multiple beam technique; residual stress; deformation

The spheroidizing heat treatment is normally required prior to the cold forming in GCr15 steel in order to improve its machinability. In the conventional spheroidizing process, very long annealing time, generally more than 10 h, is needed to assure proper spheroidizing. It results in low productivity, high cost, and especially high energy consumption. Therefore, the possibility of directly spheroidizing during hot deformation in GCr15 steel is preliminarily explored. The effect of hot deformation parameters on the final microstructure and hardness is investigated systematically in order to develop a directly spheroidizing technology. Experimental results illustrate that low deformation temperature and slow cooling rate is the favorite in directly softening and/or spheroidizing during hot deformation, which allows the properties of asrolled GCr15 to be applicable for post-machining without requirement of prior annealing.
Keywords: directly softening or/and spheroidizing; hot deformation; ferrite transformation; divorce eutectoid transformation (DET)

By using self-made vibrating wavelike sloping plate (VWSP) setup, the process of preparing semisolid billets of light alloys by semi-continuous casting and thixo-forging process were studied. Semisolid billets with fine spherical or rosette grains were prepared by the proposed process, and the solidified shell on the sloping plate surface can be effectively avoided. During the casting process, due to metal flow and vibrating, burst nucleation in the whole melt and dendrite fracture take place, which causes the formation of fine spherical microstructures. Casting temperature, vibrating amplitude, sloping plate length and sloping angle are the main factors influencing the alloy microstructure. Under the current experimental conditions, the proper casting temperature ranges of 660°C–680°C, the amplitude value smaller than 2 mm and the proper sloping angle ranges of 40°–60° are suggested. When the reheating temperature is 575°C and the holding time is 60 min for AZ91D alloy, and 597°C and 90 min for Al-6Si-2Mg (wt.%) alloy, the semisolid forging process can be successfully implemented. Thixo-forming products of such two alloys are fine with smooth appearance, good microstructures and properties.
Keywords: wavelike; sloping plate; vibrating; semisolid; semi-continuous casting; forming

Bioactive and biodegradable polyurethanes (BDPUs) have drawn much attention in recent years. As part of the research program to search for novel prepolymers for BDPUs, a study was carried out on the synthesis and characterization of triblock copolymers comprising poly(tetrahydrofuran) as a central block and poly(γ-benzyl L-glutamate)s as outer blocks.A new macroinitiator terminated with phenylalanine was first prepared from the condensation of a distal hydroxy poly(tetrahydrofuran) with N-tert-butoxycarbonyl L-phenylalanine in the presence of dicyclohexylcarbodiimide, followed by removing the protecting group. Then, it was employed to initiate the ring-opening polymerization of γ-benzyl L-glutamate N-carboxyanhydride in varying feeding ratios to give rise to the targeted triblock copolymers.The length of the outer poly(γ-benzyl L-glutamate) blocks was well tailored by varying the monomers to macroinitiator feeding ratio. All the triblock copolymers exhibited a nearly symmetrical and unimodal molecular weight distribution while only one distinct glass transition temperature was evidenced from −10°C to 25°C.
Keywords: γ-benzyl L-glutamate N-carboxyanhydride (BLG-NCA); phenylalanine end-capped macroinitiator; poly(tetrahydrofuran) (PTHF); ring-opening polymerization (ROP); triblock polypeptide copolymer

This study is focused on the ability of apatite formation on the surface of nano-hydroxyapatite (HA)/chitosan (CH) composite in simulated body fluid (SBF) in vitro. At first, natural nano-HA was prepared according to a wet-balling method and the composite was prepared by combining the natural nano-hydroxyapatite and chitosan, and then in vitro biomineralization test of natural nano-HA/CH composite was carried out in standard SBF. Subsequently, the quantity of the weight of the particles formed on the composite surface in SBF was measured by analytical balance, and the morphology change on the surface of the composite was observed by a scanning electron microscope (SEM). Lastly, a Fourier transform infrared spectroscope (FTIR) was used to investigate the chemical components of the particles formed on the natural nano-HA/CH composite surface in SBF. The result of quantity assessment shows that the weight of the composite increased with the increase of soaking time. The SEM image shows that the particles were gradually formed on natural nano-HA/CH composite surface, and the FTIR spectrum of the particles on composite surface confirms that these particles were carbonate apatite. This study indicates that the nano-HA/CH composite has a good ability for apatite formation in SBF, which predicts the bone-inducing ability of natural nano-HA/CH composite in vivo.
Keywords: natural nano-hydroxyapatite (HA); chitosan (CH); composite; bio-mineralization

In the present paper, porous hydroxyapatite (HA) microspheres were fabricated using gelatin as a pore-forming agent by spray-drying method. The mean particle size of the microspheres is about 7 μm and the surface area is about 53.4 m2/g. The experimental results showed that the porosity of the prepared microspheres is higher and the pores are more interconnected compared with the microspheres obtained without any additives.
Keywords: hydroxyapatite (HA); porous microspheres; spray drying; characterization

The bulk catalyst effect of dibutyltin dilaurate (DBTDL) on the reaction of NCO respectively with OH and NH2 was investigated in detail. The results showed that DBTDL had specific catalyst effect on the reaction of NCO with OH and no measurable effect on the reaction of NCO with NH2. In situ Fourier transform infrared spectroscopy (FTIR) used in the reaction injection molding (RIM) process showed that with increasing the concentration of DBTDL, the formation rate of the soft segment became fast, and the order degree of urea carbonyls became worse. Meanwhile, more arrange manners of urea carbonyl were present. The bands at 1653, 1647 and 1637 cm−1 were able to be detected at the low conversion. No hydrogen-bonded urea carbonyl available in the spectra at the beginning. The tensile-stress behavior showed that, with the increase of the DBTDL content, the interaction between polar groups became weak, while the virtual crosslinks also became weak. Although the break stress (d), 300‰δ and the hardness of elastomers decreased obviously, however, the tear strength, associated with the morphology of polyurethane-urea (PUU), showed the maximum when the DBTDL content was 2.63‰.
Keywords: catalyst; polyurethane-urea (PUU); kinetics; morphology; mechanical properties; reaction injection molding (RIM)

Preparation of H-oleoyl-carboxymethyl-chitosan and the function as a coagulation agent for residual oil in aqueous system by Gang-zheng Sun; Xi-guang Chen; Yan-yan Li; Bo Zheng; Zheng-hui Gong; Jian-jun Sun; Heng Chen; Jie Li; Wen-xing Lin (105-112).
In this study, H-form oleoyl-carboxymethyl-chitosan (H-O-CMCS) was prepared as a coagulation agent to clean up the residual oil from the waste-water of oil extraction (WWOE). The Fourier transform infrared (FTIR) spectra confirmed the formation of an amide linkage between amino groups of carboxymethyl chitosan (CMCS) and carboxyl groups of oleic acid. The adsorption capacities of four absorbents (H-O-CMCS, chitosan, activated carbon and polyaluminium chloride (PAC)) for the residual oil were investigated. Compared with chitosan, activated carbon and PAC, H-O-CMCS was more effective in removing the residual oil from WWOE, which could successfully wash up almost 99% of residual oil from WWOE at the dosage of 0.2 g/L, the mixing time of 3 min, 500 rpm, and a broader range of pH (the system temperature ⩽ 45°C). In similar conditions, comparatively, chitosan, activated carbon and PAC could wash 90%, 82% and 92% of residual oil from WWOE, respectively.
Keywords: H-oleoyl-carboxymethyl-chitosan (H-O-CMCS); residual oil; adsorption

The properties of hydrophobically associating copolymer P(acrylamide (AM)/2-phenoxylethylacrylate (POEA)), composed of acrylamide and a small amount of POEA (⩽1.0 mol.%) as hydrophobe, were investigated in aqueous solution under various conditions. The results showed that the solution properties were strongly affected by the microstructure of copolymer. The copolymers (BP series) with hydrophobic microblocky structure exhibited large viscosity enhancement due to the intermolecular hydrophobic association, while that did not occur for the random copolymers (RP series). The hydrophobic association thickening behaviors were also remarkably dependent on the number and length of the hydrophobic block in polymer chain. Nonlinear viscosity relationship was found as increasing hydrophobe content and SMR (surfactant/hydrophobic monomer molar ratio), and a maximum appeared at the middle position as a result of the competitive effect between inter- and intra- molecular hydrophobic associations. Solution properties were further studied as a function of the polymer concentration, salinity, temperature and shear rate. The block copolymers show high salt tolerance and shear thinning as well as recovery after shear.
Keywords: water-soluble polymers; copolymer P(acrylamide/2-phenoxylethylacrylate); solution properties; viscosity