Frontiers of Materials Science (v.6, #4)
The role of hyaluronic acid in biomineralization by Zhen-Hua Chen; Xiu-Li Ren; Hui-Hui Zhou; Xu-Dong Li (283-296).
Hyaluronic acid has been extensively investigated due to intrinsic properties of natural origin and strong ability to bind ions in water. Hyaluronic acid is an excellent crystal modifier because its abundant negatively charged carboxyl groups can bind the cations protruding from the crystal lattice. In this review, we mainly present the latest work focus on the role of hyaluronic acid in controlling the crystallization, breaking the symmetry of crystal, and the surface funtionalization of nanocrystals.
Keywords: hyaluronic acid; biomineralization; crystal growth; extracellular matrix; bone and cartilage repair
Effect of functional groups on the crystallization of ferric oxides/oxyhydroxides in suspension environment by Qiong Zhou; Olga Albert; Hua Deng; Xiao-Long Yu; Yang Cao; Jian-Bao Li; Xin Huang (297-303).
This paper investigated the effects of five kinds of Au surfaces terminated with and without functional groups on the crystallization of ferric oxides/oxyhydroxides in the suspension condition. Self-assembled monolayers (SAMs) were used to create hydroxyl (-OH), carboxyl (-COOH), amine (-NH2) and methyl (-CH3) functionalized surfaces, which proved to be of the same surface density. The immersion time of substrates in the Fe(OH)3 suspension was divided into two time portions. During the first period of 2 h, few ferric oxide/oxyhydroxide was deposited except that ɛ-Fe2O3 was detected on -NH2 surface. Crystallization for 10 h evidenced more kinds of iron compounds on the functional surfaces. Goethite and maghemite were noticed on four functional surfaces, and maghemite also grew on Au surface. Deposition of ɛ-Fe2O3 was found on -OH surface, while the growth of orthorhombic and hexagon FeOOH were indicated on -NH2 surface. Considering the wide existence of iron compounds in nature, our investigation is a precedent work to the study of iron biomineralization in the suspension area.
Keywords: biocrystallization; suspension; ferric oxide/oxyhydroxide; functional group
Supported La1−x Ce x MnO3 perovskite catalysts: preparation, characterization and catalytic performance in methane combustion by Ying Shao; Xiao-Fei Wang; Min Ao; Cai-Rong Gong; Guo-Liang Fan; Hai-Feng Chen (304-310).
A serials of La1−x Ce x MnO3 (x = 0, 0.2, 0.4, 0.6 and 0.8) catalysts have been prepared via a sol-gel process using citric acid as a chelating agent. The phase composition and morphology of the catalysts are characterized by XRD, SEM and TEM. La1−x Ce x MnO3/γ-Al2O3/cordierite catalyst has also been prepared by immersion process using cordierite honeycomb ceramic as carrier and γ-Al2O3 as support agents. The effect of Ce-doping on the structure of perovskite and catalytic property of methane combustion is explored. The results show that with the increase of Ce substitution, the crystal structure of perovskite changes from the tetragonal system to the orthorhombic system and when the x is equal to 0.2, the catalytic property in methane combustion is the best.
Keywords: perovskite; preparation; sol-gel; methane combustion
BiCoO3-doped (K0.475Na0.475Li0.05)(Nb0.8Ta0.2)O3 lead-free piezoelectric ceramics by Ke-Pi Chen; Zhe Zhang (311-318).
(1-x)(K0.475Na0.475Li0.05)(Nb0.8Ta0.2)O3-xBiCoO3 (KNLNT-BC) lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method. Effects of the BC content on the phase structure, microstructure and electrical properties of KNLNT-BC ceramics were investigated. XRD patterns reveal that all the ceramic samples are in the pure perovskite-type structure, and the phase structure changes from the tetragonal to pseudo-cubic phase with the increase of the BC content. After the substitution of BC, the grain size is significantly reduced and relaxer behaviors are induced. By adding a small amount of BC to KNLNTceramics, piezoelectric properties are improved, while further addition of BC makes the piezoelectric properties deteriorate markedly. The optimized electrical properties at x = 0.005 are as follows: d 33 = 194 pC/N, k p = 0.44.
Keywords: lead-free ceramic; potassium sodium niobate; BiCoO3 ; piezoelectric property
Bulk scale production of carbon nanofibers in an economical way by Ravindra Rajarao; Badekai Ramachandra Bhat (319-325).
An economical route for the scalable production of carbon nanofibers (CNFs) on a sodium chloride support has been developed. CNFs have been synthesized by chemical vapor deposition (CVD) method by using metal formate as catalyst precursors at 680°C. Products were characterized by SEM, TEM, Raman spectroscopy and XRD method. By thermal analysis, the purity of the as grown products and purified products were determined. This method avoids calcination and reduction process which was employed in commercial catalysts such as metal oxide or nitrate. The problems such as detrimental effect, environmental and even cost have been overcome by using sodium chloride as support. The yield of CNFs up to 7800 wt.% relative to the nickel catalyst has been achieved in the growth time of 15 min. The advantage of this synthesis technique is the simplicity and use of easily available low cost precursors.
Keywords: metal formate; carbon nanofiber (CNF); chemical vapor deposition (CVD); high yield; sodium chloride support; environmental friendly route
Enhanced mechanical properties of linear segmented shape memory poly(urethane-urea) by incorporating flexible PEG400 and rigid piperazine by Xiao-Yan Zhang; Yu-Fei Ma; Yong-Gang Li; Pin-Pin Wang; Yuan-Liang Wang; Yan-Feng Luo (326-337).
The goal of this study is to design and synthesize a linear segmented shape memory poly(urethane-urea) (SMPUU) that possesses near-body-temperature shape memory temperature (T tran) and enhanced mechanical properties by incorporating flexible poly(ethylene glycol) 400 (PEG400) to form poly(D,L-lactic acid)-based macrodiols (PDLLA-PEG400-PDLLA) and then rigid piperazine (PPZ) as a chain extender to form the desired SMPUUs (PEG400-PUU-PPZ). PEG400 increased M n while maintaining a lower T g of PDLLA-PEG400-PDLLA, which together with PPZ improved the mechanical properties of PEG400-PUU-PPZ. The obtained optimum SMPUU with enhanced mechanical properties (σ y = 24.28 MPa; ɛ f = 698%; U f = 181.5 MJ/m3) and a T g of 40.62°C exhibited sound shape memory properties as well, suggesting a promising SMPUU for in vivo biomedical applications.
Keywords: poly(urethane-urea); poly(D,L-lactic acid); poly(ethylene glycol); piperazine; shape memory property; mechanical property
Preparation and properties of poly HTBN-based urethane-urea/organo reactive montmorillonite nanocomposites by Zai-Feng Li; Yuan Wu; Fu-Tao Zhang; Yu-Yang Cao; Shou-Peng Wu; Ting Wang (338-346).
With ultrasonic assistant mixing way, an intercalated mixture of polyol/organo reactive montmorillonite (ORMMT) was pretreated. The prepolymer composed MMT clay was prepared by reaction of polyol/ORMMT mixture with toluene diisocyanate (TDI). The resultant prepolymer reacted with extender (DMTDA) and then the polyurethane-urea/organo reactive montmorillonite (PUU/ORMMT) nanocomposites were obtained. The structure, morphology and properties of PUU/ORMMT nanocomposites were characterized by FT-IR, TEM, AFM, strain-stress machine, TGA, and dynamic mechanical analysis (DMA). The results showed that when the OMMT content is 3%, the PUU/ORMMT nanocomposities performed super mechanical properties. Because of the presence of ORMMT, both T g of the soft segment and tanδ of the PUU increased, and the decomposition temperature for the first step and the second step increased respectively. TEM images showed that the organophilic MMT particles in the PUU composite exhibit a high degree of intercalation and exfoliation.
Keywords: polyurethane-urea (PUU); organo-MMT; morphology; dynamic mechanical analysis (DMA); nanocomposite
Preparation and properties of adjacency crosslinked polyurethane-urea elastomers by Yuan Wu; Yu-Yang Cao; Shou-Peng Wu; Zai-Feng Li (347-357).
Adjacency crosslinked polyurethane-urea (PUU) elastomers with different crosslinking density were prepared by using hydroxyl-terminated liquid butadiene-nitrile (HTBN), toluene diisocyanate (TDI) and chain extender 3,5-dimethyl thio-toluene diamine (DMTDA) as raw materials, dicumyl peroxide (DCP) as initiator, and N,N′-m-phenylene dimaleimide (HVA-2) as the crosslinking agent. The influences of the crosslinking density and temperature on the structure and properties of such elastomers were investigated. The crosslinking density of PUU elastomer was tested by the NMR method. It is found that when the content of HVA-2 is 1.5%, the mechanical properties of polyurethane elastomer achieve optimal performance. By testing thermal performance of PUU, compared with linear PUU, the thermal stability of the elastomers has a marked improvement. With the addition of HVA-2, the loss factor tanδ decreases. FT-IR spectral studies of PUU elastomer at various temperatures were performed. From this study, heat-resistance polyurethane could be prepared, and the properties of PUU at high temperature could be improved obviously.
Keywords: HTBN; PUU; crosslinking; HVA-2; thermal property; FT-IR
Tribological behavior of ultra-high molecular weight polyethylene in a hip joint simulator by N. Mohamad Raffi; D. Kanagarajan; V. Srinivasan (358-365).
In this paper effects of various injection molding parameters on tribological properties of ultra-high molecular weight polyethylene (UHMWPE) were investigated. The tribological properties like coefficient of friction and wear rate were obtained from the experimental results of hip simulator which was designed and fabricated in the laboratory. Bovine serum was used as a lubricant in this study. In addition, the hardness of the specimen was also investigated as well. The injection molding parameters that varied for this study are melt temperature, injection velocity and compaction time. The results show that contact loads and melt temperature were mostly influenced the tribological behavior of UHMWPE. A wear mechanism map was developed to study the dominant wear mechanism that influences the wear behavior of UHMWPE. SEM was employed to study the worn out morphologies of UHMWPE. The dominant wear mechanisms that are dominated through our study are ironing, scratching, ploughing, plastic deformation, and fatigue wear.
Keywords: UHMWPE; injection molding parameter; wear; tribological property; hip simulator
Annealing effect on structural and magnetic properties of Tb and Cr co-implanted AlGaN by Chun-Hai Yin; Chao Liu; Dong-Yan Tao; Yi-Ping Zeng (366-370).
Unintentionally doped AlGaN layers, which were co-implanted with 400 keV Tb+ ions and 200 keV Cr+ ions at doses of 1.5×1015 cm−2, have been rapid thermally annealed at 800°C and 900°C for 5 min in flowing N2. Compared with Tb implanted AlGaN sample, the Tb and Cr co-implanted sample reveals a larger magnetic signal. In this work, the annealing effect on the structural and magnetic properties of Tb and Cr co-implanted AlGaN thin films have been studied. XRD and Raman scattering results indicate that no second phase presents in the thin films and most of the implantation induced defects can be removed by post-implantation annealing. Superconducting quantum interference device (SQUID) measurements show clear room temperature ferromagnetic behavior and an increase in the saturation magnetization as a result of annealing. The saturation magnetization of the 900°C annealed sample is about 15 times higher than that of the 800°C annealed sample.
Keywords: diluted magnetic semiconductor (DMS); room temperature ferromagnetism; ion implantation; III-nitride thin film