Semiconducting metal oxide nanocrystals are an important class of materials that have versatile applications because of their useful properties and high stability. Here, we developed a simple route to synthesize nanocrystals (NCs) of copper oxides such as Cu2O and CuO using a hot-soap method, and applied them to H2S sensing. Cu2O NCs were synthesized by simply heating a copper precursor in oleylamine in the presence of diol at 160 °C under an Ar flow. X-ray diffractometry (XRD), dynamic light scattering (DLS), and transmission electron microscopy (TEM) results indicated the formation of monodispersed Cu2O NCs having approximately 5 nm in crystallite size and 12 nm in colloidal size. The conversion of the Cu2O NCs to CuO NCs was undertaken by straightforward air oxidation at room temperature, as confirmed by XRD and UV-vis analyses. A thin film Cu2O NC sensor fabricated by spin coating showed responses to H2S in dilute concentrations (1–8 ppm) at 50–150 °C, but the stability was poor because of the formation of metallic Cu2S in a H2S atmosphere. We found that Pd loading improved the stability of the sensor response. The Pd-loaded Cu2O NC sensor exhibited reproducible responses to H2S at 200 °C. Based on the gas sensing mechanism, it is suggested that Pd loading facilitates the reaction of adsorbed oxygen with H2S and suppresses the irreversible formation of Cu2S.

Three Mg single crystalline round-bar specimens with different crystal orientations were subjected to uniaxial tension-compression fatigue tests, and crystal orientation dependence on fatigue fracture behavior was investigated. Loading directions of AD, BC and EF specimens were [11 20], [1 100] and [0001] respectively. Results show that, at stress amplitude (• a ) greater than or equal to 60 MPa, fatigue life of BC specimen was longest, while that of EF specimen was shortest. Under stress amplitude of 20 MPa, crystal orientation dependence on fatigue lives was not confirmed. Our study suggests that fatigue life in Mg single crystals show a high degree of dependence on crystal orientation and stress.

No abstract

It is well known that magnesium (Mg) shows anisotropic fatigue behavior. However, the fatigue mechanisms have yet to be elucidated. The relationships between crystal orientations and crack initiation behavior in Mg single crystals were investigated by uniaxial tension-compression fatigue tests. Three types of round-bar specimens were prepared. The lording direction of AD, BC and EF specimen were [110], [100] and [0001], respectively. Fatigue tests were carried out with the stress ratio R=-1 and the frequency of 10Hz at room temperature in laboratory air. At stress amplitude (σa) over 40 MPa, fatigue lives of BC specimen and EF specimen were the longest and shortest. However, at σa =20 MPa, the fatigue life of all specimens were almost the same. It was found that fatigue lives of Mg single crystals strongly depend on crystal orientations and stress.

Three Mg single crystalline round bar specimens with different crystal orientations were subjected to uniaxial tension com pression fatigue tests, and the crystal orientation dependence on fatigue fracture behavior was investigated. The loading direction of AD, BC and EF specimens was 1120 , 1100 and 0001 respectively. At stress amplitude σ a over 60 MPa, fatigue life of BC specimen was longest and fatigue life of EF specimen was shortest. When the stress amplitude was 20 MPa, fatigue lives of all specimens were almost the same. Our study suggested that fatigue life in Mg single crystals show high dependence of crystal ori entation and stress.