S. Zhu

Low-temperature high-pressure preparation of transparent nanocrystalline MgAl2O4 ceramics

Transparent MgAl2O4 spinel nanoceramics have been sintered at relatively low-temperature (500-700 degrees C) under high pressure (2-5 GPa) using a hydrostatic press with high-temperature-calcined nanopowders. The morphology, nanostructure, optical property, and density of ceramics were analyzed by scanning electron microscopy, transmission electron microscopy, UV-VIS-IR transmission spectrum, and Archimedes draining method. The average grain size (< 100 nm for all samples sintered) depends on the sintering pressure and temperature. The nanoceramics are highly transparent even though their relative densities are all less than 99%, due to the low or negligible light scattering from the nanosized grains and pores. (c) 2006 American Institute of Physics.

Optical properties of metallic nanoparticles in Ni-ion-implanted α-Al2O3 single crystals

64 keV Ni ion implantation was performed at room temperature up to a dose of 1×1017 cm−2 in α-Al2O3 single crystals. The charge states, structure, and optical properties of metallic embedded Ni nanoparticles were studied by using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy, and optical spectroscopy, respectively. XPS analysis showed that implanted Ni ions are mainly in charge state of metallic Ni0. Nanoparticles distributed from the surface to 30 nm below the surface were observed in a high-angle annular dark-field image. The size of nanoparticles ranges from 1 to 5 nm in diameter. A high-resolution electron microscopy image indicated the Ni-implanted area had been entirely amorphized. A new broad absorption band centered at 400 nm appeared in the optical absorption spectrum of the as-implanted crystal, due to surface plasma resonance of Ni nanoparticles. We did not find any emission band in the as-implanted sample under a Xe lamp excitation wavelength of 250–430 nm in a spect...

Optical and magnetic properties of Ni nanoparticles in rutile formed by Ni ion implantation

Crystalline Ni nanoparticles in the near surface of TiO2 (rutile) have been synthesized by Ni ion beam implantation at room temperature to a fluence of 1×1017∕cm2. Transmission electron microscopy, optical absorption spectroscopy, and a superconducting quantum interference device magnetometer have been utilized to characterize the nanostructure, optical and magnetic properties of Ni particles in TiO2. Crystalline Ni nanoparticles with dimensions ranging 3–20 nm formed in the near surface of rutile, which caused a broad absorption band from 700 nm in the optical absorption spectrum. Magnetic measurement indicated that the coercive force of Ni nanoparticles was about 210 Oe at 10 K. The superparamagnetism of the nanoparticles was observed above blocking temperature T=85K.

Design of TiNi alloy two-way shape memory coil extension spring

Abstract This work presents a study of the development of the two-way shape memory effect (TWSME) by themomechanical training and its degradation due to working cycles in a shape memory alloys (SMAs) spring. A TWSME extension spring that could extend upon heating and contract upon cooling was obtained by constrained annealing and thermomechanical training. A stable TWSME recovery rate can reach 60–70% after training for 200 cycles. The investigation showed that constrained annealing temperature and the thermomechanical training procedure had a great effect on the TWSME. After 1000 working cycles, the TWSME recovery rate still maintained at 45% stably. The effect of the thermomechanical training on transformation characters was also investigated by differential scanning calorimetry (DSC). The inverse martensitic transformation temperatures increased and martensitic transformation temperatures decreased with increasing thermomechanical training cycles, which was attributed to the dislocations introduced into the TiNi shape memory alloys.

Photoluminescence of SnO2 nanoparticles embedded in Al2O3

Tetragonal Sn nanoparticles of ∼15 nm diameter are produced in Al2O3 by direct Sn implantation at room temperature. After thermal annealing at 1000 ◦ C in oxygen, the implantation-induced amorphous region recrystallized and the Sn nanoparticles turned into SnO2 nanoparticles with an average diameter of ∼30 nm as revealed by transmission electron microscopy. While no absorption and photoluminescence (PL) are observed from the metallic Sn nanoparticles, SnO2 nanoparticles exhibit an absorption edge at ∼280 nm and three emission bands at 410 nm, 520 nm and 700 nm, respectively. In addition to the previously reported blue and green emission from SnO2 nanostructures, a red PL band was observed due to the unique surface state of SnO2 nanoparticles embedded in Al2O3 substrate fabricated by ion implantation.

Formation of single-layered Au nanoparticles in Au ion implanted TiO2 and SrTiO3

Abstract Two-dimensionally (2D) ordered arrangements of Au micro-discs formed on the surfaces of TiO2 and SrTiO3 after “patterned” ion implantation. Cross-sectional TEM revealed that the Au micro-discs consisted of Au nanoparticles with a very narrow depth distribution (single-layered) and a narrow size range (2–6 and 3–5 nm in the implanted TiO2 and SrTiO3, respectively). They are located in the near surface layer surrounded by an amorphized matrix.

Two-way shape memory effect of TiNi alloy coil extension springs

A two-way shape memory effect (TWSME) spring that could elongate upon heating and contract upon cooling was obtained by constrained annealing and thermo-mechanical training. The effect of heat treatment and thermomechanical training on the TWSME and the effect of training on the transformation temperatures had been studied by elongation-temperature, electrical resistance measurements and differential scanning calorimetry (DSC). The TWSME recovery rate of extension spring increases with increasing the training cycles and increases to a saturation value. The inverse martensitic and martensitic temperatures decreased with increasing thermo-mechanical training cycles

Surface characterization of a Ti–2Al–2.5Zr alloy by nitrogen ion implantation

Abstract The structural mechanisms of the hardening of a Ti–2Al–2.5Zr alloy by 75 keV nitrogen ion implantation with doses of 3×10 17 and 8×10 17 N/cm 2 is investigated. The surface characterization of samples was studied by XPS, XRD and Vickers hardness tests. The results of XPS and XRD analysis show that TiN is formed in the surface region. Nitrogen implantation increases the surface hardness up to 340 and 260% for doses of 8×10 17 and 3×10 17 N/cm 2 , respectively, due to formation of TiN and irradiation-enhanced hardening.

Influence of electron irradiation on the martensitic transformation of a binary TiNi shape memory alloy

Abstract TiNi shape memory alloy samples annealed at 673 K for 1 h were irradiated within R-phase by 1.7-MeV electrons with different doses. The two-step martensitic transformation temperatures were measured by differential scanning calorimeter. The results indicated that the temperature M s of the onset of R-phase-to-martensite transformation decreased with increasing electron dose. The electron irradiation had a slight effect on the other transformation temperatures. The second lifetime of positrons determined by positron annihilation technology were lowered with increment of the irradiated dose. Relaxation of the elastic stress fields around the Ti 3 Ni 4 precipitates was the cause of the observed change of the transformation characteristics because of the migration and accumulation of irradiation-induced point defects.

Optical properties and structure characterization of sapphire after Ni ion implantation and annealing

Implantation of 64keV Ni ions to sapphire was conducted at room temperature to 1×1017ions∕cm2 with a current density of 5 or 10μA∕cm2. Metallic Ni nanoparticles were formed with the 5μA∕cm2 ion current and the NiAl2O4 compound was formed with the 10μA∕cm2 ion current. The crystals implanted with both current densities were annealed isochronally for 1h at temperatures up to 1000°C in steps of 100°C in an ambient atmosphere. Optical absorption spectroscopy, x-ray diffraction, transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy have been utilized to characterize the samples. The surface plasmon resonance (SPR) absorption band peaked at 400nm due to the Ni nanoparticles shifted toward the longer wavelength gradually with the annealing temperature increasing from 400to700°C. The SPR absorption band disappeared after the annealing temperature reached 800°C. NiO nanoparticles were formed at the expense of Ni nanoparticles with an increasing annealing temperature. The TEM analyses reveale...