Solid State Phenomena Vols. 121-123

Abstract: In this work, tricalcium phosphate [TCP, β-Ca3(PO4)2]/titania composite were prepared with different ratio of 75/25, 50/50 and 25/75 (HA/TiO2, wt %). The TiO2 and hydroxyapatite (HA) powders, as starting materials, were synthesized by precipitation and hydrothermal methods, respectively. The sintered bodies of β-TCP/TiO2 composite were prepared by hot pressing at pressure of 30 MPa and temperature of 800-1000 oC for 30 min under the pressure of 30 MPa in N2 atmosphere. During the sintering process, hydroxyapatite was decomposed to β-TCP and CaTiO3 at elevated temperature because TiO2 could accelerate the decomposition of hydroxyapatite. The hot-pressed composite with 98% of sintered density, showed high value of 1080 Hv in hardness, compared with the pure hydroxyapatite (600 Hv) before immersion in distilled water. Increasing sintering temperature led densification of the composite with moderately uniform microstructures. As increasing the amount of TiO2, the surface of the composite was less damaged or dissolved.

Abstract: The effect of Ca/P ratio on surface dissolution of hydroxyapatite [Ca10(PO4)6(OH)2, HA] in distilled water was investigated. The stoichiometric HA powder and desired Ca/P ratio achieved by adding either Ca3(PO4)2 for a Ca/P ratio of 1.62 or CaO for a Ca/P ratio of 1.72 were used as starting materials. Dense HA ceramics were obtained by sintering at 1200 oC for 2 h in air with under moisture protection. The sintered specimens were then placed into 40 ml of pH 7.4 distilled water. After immersing for certain period of time at 37 oC, crystal structure, weight loss and microstructure of the specimens were investigated. As increasing the immersion time, circular cavities similar to that normally attributed to osteoclast resorption lacunae were observed. As a result, it was found that the dissolution of HA along the grain boundary and subsequently microstructural disintegration was more distinct in 1.62 and 1.72 samples compared to pure HA.

Abstract: Various techniques in conventional transmission electron microscopy (CTEM) and scanning transmission electron microscopy (STEM) are applied to characterize comprehensively the microstructures of the nano-composite materials, including Cu2O quantum dots deposited on multiwall carbon nanotubes (CNTs) and Fe particles encapsulated in carbon nanohorns (CNHs) as two studying cases.

Abstract: 14-GHz electron cyclotron resonance ion source at the Heavy Ion Research Facility National Laboratory in Lanzhou has been used to investigate x-rays from the interaction of slow highly charged Ar17+and Ar16+ions for different energies with Be, Al, Ni, Mo and Au surfaces. Interaction of Ar17+ and Ar16+ ions with Metallic Surfaces for a wide range of energies has been studied by measuring the resulting x-ray emission. The characteristic features of the x-ray spectra have been explained.

Abstract: L-shell x-ray spectra of Mo surface induced by Xe28+ were measured with a Si(Li) detector. The x-ray intensity was found increased rapidly with the kinetic energy of the incident ions. The relation of x-ray intensity with kinetic energy of the projectile is discussed. There is a turning point of the intensity to the kinetic energy, and the explanation is given.

Abstract: We show that the intercalating of alkali atoms with adequate concentration can transform a metallic single-walled carbon nanotube (SWCNT) into a semiconductor tube or a semiconductor SWCNT into a semiconductor tube with different band gaps due to a unique feature of the band structures in SWCNTs. Results of Li2C60 in the (5,0) tube, Li2C112 in the (4,2) tube and K2C112 in the (7,0) tube show that this transition mechanism is quite general.

Abstract: Suspended gold nanowires can be made atomically thin with as many as five atoms, showing extremely large Au-Au bond distances. Using tools derived from Density Functional Theory (DFT) we study many questions posed by the experiments. First we use realistic molecular dynamics simulation to study the mechanisms of formation, evolution and breaking of these atomically thin Au nanowires under stress. We show how defects induce the formation one-atom chains that can grow as long as five-atoms before breaking. Results are in excellent agreement with experiments, except for the resulting shorter bond distances. In order to address this question, we use ab initio electronic structure calculations to show that the exceedingly large Au-Au interatomic distances experimentally obtained could be the effect of impurities. We studied the effect of single impurities H, B, C, N, O, S and small molecules as H2 on the nanowire's electronic and structural properties, in particular how they affect the maximum Au-Au bond length.

Abstract: The compressive deformation of metallic glass Cu was studied under uniformly distributed strains with different rates at 1 K temperature using molecular dynamics simulations. The interaction between atoms in the system adopts the embedded atom method (EAM) reported by Mishin. We found that MG Cu is an elastic/perfect plastic material and the Young modulus is about 50 Gpa with strain rates from 0.1ns-1 to 10 ns-1. At low strain rates the sample deforms inhomogeneously and the amorphous phase transforms continuously to a crystalline phase. It was observed that the nucleation, growth and mergence processes of crystalline are induced by stress. At high strain rates the system passes through plastic deformations homogeneously and keeps the amorphous structure. The higher flow stress occurs at higher strain with the strain rate increasing. The stress effect is an important factor that induces MG crystallization just like temperature effect. The relationship between characteristic nucleation rate and strain rate determines the different deformation mechanism of MG.

Abstract: Three armchair single-walled carbon nanotubes (SWCNTs) (7, 7), (12, 12), (17, 17) and three zigzag SWCNTs (12, 0), (16, 0), (20, 0) are investigated in this paper, using the molecular dynamic (MD) method with the second-generation Tersoff-Brenner (TB) potential. The Poisson’s ratio of these nanotubes under tensile and compressive loading is obtained. The effect of the strain and size on the Poisson’s ratio of nanotubes is analyzed systematically, from the viewpoints of the structure and the averaged atomic potential energy of nanotubes. The results show that the Poisson’s ratio of nanotubes decreases as the strain increases. The Poisson’s ratios of nanotubes of larger chiral angle decrease more quickly. For nanotubes of the same chiral angle, the larger the diameters of nanotubes are, the larger their Poisson’s ratios become. Moreover, the Poisson’s ratios of nanotubes of larger diameter are more approaching.