Jun-Hong Zhao

Influence of pressures on the crystallization process of an amorphous Fe73.5Cu1Nb3Si13.5B9 alloy

Amorphous Fe73.5Cu1Nb3Si13.5B9 alloys, prepared by a melt-spinning technique, were annealed at a temperature of 823 K under pressures in the range of 1–5 GPa and ambient pressure. The high pressure experiments were carried out in a belt-type pressure apparatus. The microstructure of the annealed alloys has been investigated by x-ray diffraction, electron diffraction, and transmission electron microscopy. Experimental results show that the initial crystalline phase in these annealed alloys is α-Fe solid solution (named as α-Fe phase below), and high pressure has a great influence on the crystallization process of the α-Fe phase. The grain size of the α-Fe phase decreases with the increase of pressure (P). The volume fraction of the α-Fe phase increases with increasing the pressure as the pressure is below 2 GPa, and then decreases (P>2 GPa). The mechanism for the effects of the high pressure on the crystallization process of amorphous Fe73.5Cu1Nb3Si13.5B9 alloy and latent applications of high-pressure anne...

Intense short-wavelength photoluminescence from thermal SiO2 films co-implanted with Si and C ions

Intense short-wavelength photoluminescence (PL) observed at room temperature from thermal SiO2 films co-implanted with Si and C is reported. A flat Si profile was first implanted, followed by 1100 °C annealing for 60 min. C ions were subsequently used to be implanted into the same depth region. PL was observed from the as-implanted samples with and without annealing. The PL intensity increases with annealing temperature. Comparing the PL spectra and the PL dynamics of the C-implanted, annealed, Si-implanted (CIASI) SiO2 films with those from Si- and C-implanted SiO2 films suggests that the interaction of Si and C in SiO2 films plays an important role in the luminescence in CIASI SiO2 films.

Elemental and Sr–Nd–Pb isotopic geochemistry of Mesozoic mafic intrusions in southern Fujian Province, SE China: implications for lithospheric mantle evolution

Cretaceous mafic dykes in Fujian province, SE China provide an opportunity to examine the nature of their mantle source and the secular evolution of the Mesozoic lithospheric mantle beneath SE China. The mafic rocks have SiO 2 ranging from 47.42 to 55.40 wt %, Al 2 O 3 from 14.0 wt % to 20.4 wt %, CaO from 4.09 to 11.7 wt % and total alkaline (K 2 O+Na 2 O) from 2.15 wt % to 6.59 wt %. Two types are recognized based on their REE and primitive mantle-normalized trace element patterns. Type-A is the dominant Mesozoic mafic rock type in SE China and is characterized by enrichment of light rare earth elements (LREE) ((La/Yb)n = 2.85–19.0) and arc-like trace element geochemistry. Type-P has relatively flat REE patterns ((La/Yb)n = 1.68–3.43) and primitive mantle-like trace element patterns except for enrichment of Rb, Ba and Pb. Type-A samples show EMII signatures on the Sr-Nd isotopic diagram, whereas type-P rocks have high initial 143 Nd/ 144 Nd ratios (0.5126–0.5128) relative to the type-A rocks ( 143 Nd/ 144 Nd = 0.5124–0.5127). The type-A rocks have 207 Pb/ 204 Pb ranging from 15.47 to 15.67 and 206 Pb/ 204 Pb from 18.26 to 18.52. All the type-A rocks show a negative correlation between 143 Nd/ 144 Nd and 206 Pb/ 204 Pb ratios and a positive relationship between 87 Sr/ 86 Sr and 206 Pb/ 204 Pb ratios, indicating mixing of a depleted mantle source and an EMII component. Geochemical modelling shows that the parental magmas were formed by 5–15 % partial melting of a spinel lherzolite, and contaminated by less than 1 % melt derived from subducted sediment. The type-P magmas were derived from a mantle source unmodified by subduction components. The wide distribution of type-A dykes in SE China suggests that subduction-modified lithospheric mantle was extensive beneath the Cathaysia Block. Geochemical differences between Mesozoic and Cenozoic mafic rocks indicate that lithospheric thinning beneath SE China occurred in two episodes: firstly by heterogeneous modification by subducted components in early Mesozoic times, and later by chemical–mechanical erosion related to convective upwelling of the asthenosphere during Cenozoic times.

K-Ar Dating, Geochemical, and Sr-Nd-Pb Isotopic Systematics of Late Mesozoic Mafic Dikes, Southern Jiangxi Province, Southeast China: Petrogenesis and Tectonic Implications

A geochemical and isotopic study was carried out on late Mesozoic mafic dikes in southern Jiangxi Province in order to clarify their petrogenesis and explore tectonic implications. K-Ar dating results show that these mafic dikes intruded during Jurassic to Late Cretaceous (147-79 Ma) time. Dominantly sub-alkaline in composition, these dikes share several geochemical features: they are significantly enriched in large-ion lithophile element (LILE, e.g., Rb, Ba, Sr) and slightly enriched in light rare-earth elements (LREE), and are variably depleted in high-field-strength elements (HFSE, e. g., Nb, Ta, Ti). However, mafic dikes intruded in the Late Jurassic to Early Cretaceous (147-139 Ma) are also characterized by weaker Nb and Ta negative anomalies compared with dikes intruded in the mid-Late Cretaceous (118-78 Ma). Age-corrected Sr-Nd isotopic ratios show relatively wide ranges for (87Sr/86Sr)I from 0.7042 to 0.7130, and -10.8 to +5.9 for εNd(T). 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios for these dikes range from 17.819 to 18.400, 15.472 to 15.730, and 37.711 to 38.787, respectively. Geological, geochemical, and isotopic evidence suggests that the mafic dikes in southern Jiangxi Province were not significantly affected by crustal contamination. We consider them to have originated from dominantly EM-2 type lithospheric mantle ± minor asthenospheric mantle (MORB or DMM). The geochemical and Sr-Nd-Pb isotopic characteristics of basalts and mafic dikes, together with geochemical and isotopic data from granitoids, volcanic rocks, and rift basins in Southeast China suggest that this region was dominated by a lithospheric extensional tectonic regime in the late Mesozoic. This study, integrated with published geochemical and isotopic data for upper Mesozoic and Cenozoic basaltic rocks, allows us to postulate that lithospheric thinning in Southeast China continued until the end of Late Cretaceous time, and was accompanied by a shift in the mantle sources of basaltic rocks.

Geochemistry, Petrogenesis, and Tectonic Significance of Mesozoic Mafic Dikes, Fujian Province, Southeastern China

Major- and trace-element data for Mesozoic mafic dikes from Fujian Province, Southeast China, provide insights into the nature of their mantle source and evolution of the lithospheric mantle beneath the Cathaysian block. These dikes are alkali to subalkali in composition, and are characterized by high Al2O3 (14.0-20.4 wt%) and moderate CaO (4.09-12.7 wt%) compared to Cenozoic basalts in the same region. In primitive mantle-normalized plots, they are enriched in LREE and LILE, and depleted in HFSE (Nb and Ta), with positive Pb and negative Ti anomalies. They are divided into two types, based on their REE contents: type 1 had low total REE (53.8-145.5 ppm) with relatively flat chondrite-normalized patterns [(La/Yb)n=1.68-4.65], whereas type 2 has much higher total REE (63-247 ppm) with LREE enrichment [(La/Yb)n = 4.63-19]. Zr/Y ratios show a good correlation with Y in the type 1 dikes, but not in the type 2 varieties. Rocks in both groups experienced modest crustal contamination. All have slightly higher Pb isotopic ratios than the associated Cenozoic basalts, suggesting that the Mesozoic dikes were derived from a mantle source that had been modified by subducted materials (fluid + sediment). Type 1 dikes are believed to have been derived from garnet-spinel lherzolite, whereas type 2 dikes were probably derived from spinelor spinel-plagioclase lherzolite. Both mantle sources were compositionally heterogeneous and they experienced different degrees of depletion. Asthenospheric upwelling provides a possible mechanism for lithosphere thinning and extension, leading to emplacement of the dikes.

Ordering of the crystalline phase α-Fe(Si) in annealed Fe73.5Cu1Nb3Si13.5B9 alloy

The ordering of the crystalline phase alpha-Fe(Si) in annealed Fe73.5Cu1Nb3Si13.5B9 alloy has been investigated in detail in this paper using XRD technology. The alpha-Fe(Si) phase in the Fe73.5Cu1Nb3Si13.5B9 alloy annealed at 490 degrees C for I h has been found to consist of a DO3 order region with the shape of a sphere and a disordered region. The size of the DO3 order region and the degree of order of the alpha-Fe(Si) phase increase with increasing annealing temperature. All regions in the alpha-Fe(Si) rain almost have the DO3 structure as the annealing temperature increases to 590 degrees C, The shape of the DO3 order region of the alpha-Fe(Si) phase in the Fe73.5Cu1Nb3Si13.5B9 alloy annealed at 550 degrees C changes from spheroid for 20 min into spherical for 60 min

Different luminescent properties of C+-implanted SiO2 films grown by thermal oxidation and PECVD

Abstract Room temperature photoluminescence (PL) from C+-implanted SiO2 films grown by thermal oxidation and PECVD is reported. There are great differences in the luminescent properties, which are shown by PL spectra, PL excitation (PLE) spectra, and the PL dynamics. The structural analysis of the C+-implanted SiO2 films are taken by FTIR, Raman, and HRTEM. The differences in light emission are attributed to the structural characteristics of SiO2 films before and after C ion implantation.

The effects of high pressure on carbon nitride—in situ measurements of micro photoluminescence and infrared spectra

The effects of high pressure up to 24 GPa on carbon nitride were studied using in situ micro photoluminescence (PL) and infrared (IR) absorption measurements at room temperature. The experiments indicate pressure-induced PL quenching with pressure increasing from 0 to 7 GPa, but the PL remains unchanged from 7 to 24 GPa. The PL results display the pressure effect of PL enhancement after release of pressure to ambient atmosphere. The IR absorption bands broaden toward low frequency after release of pressure. These may be explained by using the PL model of undistorted sp2 clusters, which, as PL centers, undergo distortion under pressure and pressure-induced local atomic rearrangement in the sample.

Electron field emission from nitrogen-containing diamond-like carbon films deposited by filtered arc deposition

Abstract In this paper, electron field emission properties and fluorescent displays of 300 nm thick nitrogen-containing diamond-like carbon (DLC:N) films are reported. The films were deposited on to highly n -doped Si (111) substrates by filtered arc deposition (FAD) with different N 2 partial pressures (0.01, 0.05, 0.1 Pa) in the deposition chamber. Their electron field emission properties were studied using a simple diode structure. It was shown that the DLC:N film possessed enhanced field emission properties when a N 2 pressure of 0.05 Pa was used. Emission current of 0.1 μA was detected under the electric field of 8.1 V/μm. An emission current density of 0.204 mA/cm 2 was obtained under 17.8 V/μm.

Evaluation of effective mass transport coefficients through comparison of solidification on the ground and on board a satellite

Mass transport caused by buoyancy convection in front of the solid–liquid interface was evaluated in terms of measurements of primary dendritic spacing combining with separation of the effective (or integral) mass transport coefficient DL. It was shown that DL in normal gravity (1g) condition was 1.64 times as high as that in microgravity (μg) condition at the cooling rate (v) of 0.056 K/s for Pd40Ni40P20 alloy. The higher DL value is due to the contribution of buoyancy convection on the ground.