Advanced Materials Research Vols. 299-300

Abstract: Porous NiTi alloys were prepared by powder metallurgy method using NH₄HCO₃ as space-holder. The effect of sintering temperature on pore characteristic, phase composition and compressive property of porous NiTi alloys was studied by XRD, SEM, EDS and a universal testing machine. The results show with the increase of sintering temperature the porosity of porous NiTi alloys first increases and then decreases, but the content of NiTi phase, compressive strength and modulous of sintered products continuously increase. When sintered at 980°C for 2h, the porous NiTi alloys have higher porosity of 53.6%, better compressive strength of 173.7MPa and elastic modulous of 4.2GPa. The phases of sinter products are mainly composed by TiNi, Ti₂Ni, and TiNi₃ phases.

Abstract: Fe_xCo_1-x alloys were prepared by low temperature hydrothermal method. The influence of Fe content on static magnetic and microwave absorbing properties was studied. XRD results show that Fe_xCo_1-x alloys are single-phased body-centered cubic (BCC) structure for both 70% and 80% Fe content. The lattice constant of the alloys increases with increasing Fe content. The coercivity decreases with the increase of Fe content. The composites with high resistivity were prepared by homogeneously mixing Fe_xCo_1-x alloy nanoparticles and paraffin wax, and their microwave absorption properties were studied.

Abstract: SiO₂ optical fiber preform, the parent material in manufacturing optical fiber, plays an important role in the properties of optical fiber. In this paper, SiO₂ dry gel was prepared by Sol-Gel method. According to this method, the gel was formed by hydrolyzing tetraethyl orthosilicate(TEOS) with hydrochloric acid and ammonia water, and the SiO₂ dry gel was obtained by heat treatment of the gel at different temperature. The structure of the dry gel as prepared was characterized by X-ray Diffraction(XRD), Fourier Transform Infrared Spectroscopy(FT-IR) and Scanning electron microscope(SEM). As a result, amorphous structure is proved. Meanwhile, microscopic cracks are found to be decreased by adding formamide and increased when the heat-treatment temperature is above 75°C.

Abstract: The phosphors YAG doped with Ce³⁺ was prepared by low-temperature combustion method. Utilizing the prepared YAG powders as raw material and Li₂O-CaO-ZnO-Y₂O₃-Al₂O₃-SiO₂ glass powder as sintering additive, YAG:Ce³⁺ ceramics were sintered at 1400-1550°C for 10h in vacuum. The sinter-ability of the YAG ceramics was studied by measuring the linear shrinkage rate. The phase, microstructure and photoluminescence properties of the YAG: Ce3⁺ powders and ceramics were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) analysis. The results show that the sinter-ability properties of YAG:Ce³⁺ ceramics was mainly associated with sintering temperature and contents of glass sintering additive; the best result was achieved when the sample was sintered at 1500°C and doped sintering additive of 1%.

Abstract: Based on the density functional theory, the structure of pure ZnO, N doped, and Ga-N/Ga-2N co-doped wurtzite ZnO was calculated by using first-principle plane wave ultrasoft pseudopotential method. Electronic structures of these ZnO-based doping syetems were studied. The calculations of band structure, total density of states, and partial density of states show that Ga-2N donor/acceptor co-doped ZnO is easier to implement the p-type ZnO than other cases.

Abstract: Lithium zinc silicate (LZS) glasses containing Li₂O–ZnO–SiO₂–Na₂O–B₂O₃–BaO–P₂O₅ with different BaO/(BaO+ZnO) ratios were prepared by conventional melt and quench technique and subsequently converted into glass-ceramics. The effect of BaO/(BaO+ZnO) ratio on various thermo-physical properties was investigated by changing the ratio from 0 to 0.226. The crystalline phases were characterized by X-ray diffraction technique on the composite glass-ceramics, including Li₃Zn_0.5SiO₄, Li₂OZnSiO₄ and cristobalite phase. The thermal expansion coefficient (TEC) in the temperature range 70–400 oC increased from 107 × 10^-7 to 141 ×10^-7 / oC. The increase in expansion coefficient was associated with the formation of different phases which in turn influenced the rigidity/bonding in the glass-ceramics. The microstructure was analyzed by scanning electron microscopy (SEM), and the grain size became bigger after the addition of BaO.

Abstract: Magnesium apatite (MA, (Ca₉Mg)(PO₄)₆(OH)₂) and Hydroxyapatite (HA) coatings were synthesized on Ti6Al4V substrates by a sol-gel dip coating method. Glucose and bovine serum albumin (BSA) were added to the standard simulated body fluid (SBF) separately to form organic-containing simulated body fluids. MA and HA coatings were immersed in standard and organic modified SBF for time periods of 4, 7, 14, 21 and 28 days at 37±1°C. The surface dissolution and deposition behavior of the coatings after soaking were examined with Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The results show that glucose in SBF has no apparent effect on the deposition of new apatite from the solution. BSA in SBF shows retardation effect on the deposition of apatite by forming a protein dominant globular layer. This layer inhibits the further deposition of apatite from SBF solution.

Abstract: In this paper, Nb-doped BaTiO₃-(Na_0.5Bi_0.5)TiO₃ (BBNT-Nb) based PTCR ceramic material has been prepared using high purity Nb₂O₅, Bi₂O₃, Na₂CO_3, TiO₂ and BaTiO₃ powders as starting materials, and its structural and electrical properties are investigated. The results indicated that the Nb₂O₅ dopant is helpful not only to promote the formation of tetragonal BBNT structure without any second phase, but also to decrease the room-temperature resistivity. For the 0.10at% Nb-doped BBNT material with BNT content 35mol%, the properties of room-temperature resistance of 10⁴Ω·cm, temperature coefficient (α_k) of 6.3%/°C, PTCR anomaly lg(R_max/Rmin) of 3.6 and Curie temperature (Tc) of 193°C are obtained.

Abstract: The Sn-Co/C composites as novel anode materials for lithium-ion batteries were prepared by solid-state sintering. The influences of carbon black content in Sn-Co/C composite on material structures and the electrochemical properties were investigated. Structure analyses show that carbon black mainly is physically mixed with CoSn phase and could inhibit the growth of grain of CoSn phase, avoid the formation of large particles and increase the specific surface area obviously. Electrochemical analyses show that the refinement of grain size or particle size could contribute to improve the discharge capacity and cycle performance, but the increasing of specific surface area could reduce the charge-discharge efficiency. When carbon black content is 6 wt.%, the discharge capacity reach its maximum, which is 275 mAh/g, the initial charge-discharge efficiency is 52.8% and the retention of discharge capacity is 72.8% after 30 cycles.

Abstract: The crystal structure, microstructure, Curie temperature and magnetocaloric properties of (Mn_1-xFe_x)₅Sn₃ (x=0.1~0.5) alloys were studied in this paper. The alloys were prepared by powder metallurgy method with magnetic pressing and magnetic sintering. All samples crystallize in the hexagonal InNi₂-type structure with space group P6₃/mmc. The lattice parameter, cell volumes of the (Mn_1-xFe_x)₅Sn₃ decrease with increasing x, while the Curie temperature of these alloys increases almost linearly with increasing x. All samples exhibit a moderate magnetocaloric effect, and the curves of magnetic entropy change are flat in a wide temperature range, which is suitable for the Ericsson cycle.