Jun Liu

Effect of surface treatment on unalloyed titanium implants : Spectroscopic analyses

Surgical implant finishing and sterilization procedures were investigated to determine surface characteristics of unalloyed titanium (Ti). All specimens initially were cleaned with phosphoric acid and divided into five groups for comparisons of different surface treatments (C = cleaned as above, no further treatment; CP = C and passivated in nitric acid; CPS = CP and dry-heat sterilized; CPSS = CPS and resterilized; CS = C and dry-heat sterilized). Auger (AES), X-ray photoelectron (XPS), and Raman spectroscopic methods were used to examine surface compositions. The surface oxides formed by all treatments primarily were TiO2, with some Ti2O3 and possibly TiO. Significant concentrations of carbonaceous substances also were observed. The cleaning procedure alone resulted in residual phosphorus, primarily as phosphate groups along with some hydrogen phosphates. A higher percentage of physisorbed water appeared to be associated with the phosphorus. Passivation (with HNO3) alone removed phosphorus from the surface; specimens sterilized without prior passivation showed the thickest oxide and phosphorus profiles, suggesting that passivation alters the oxide characteristics either directly by altering the oxide structure or indirectly by removing moieties that alter the oxide. Raman spectroscopy showed no crystalline order in the oxide. Carbon, oxygen, phosphorus, and nitrogen presence were found to correlate with previously determined surface energy.

SM:YAG OPTICAL PRESSURE SENSOR TO 180 GPA:CALIBRATION AND STRUCTURAL DISORDER

We report ultrahigh pressure calibration and fluorescence intensity measurements of Sm:YAG to 180 GPa in a diamond anvil cell at room temperature. Several fluorescence emission bands excited by argon ion laser were followed with increasing pressure and it was observed that Y4 band was the most intense in the pressure regime of 100–180 GPa. The Y4 band is calibrated against the R band of ruby to 180 GPa. Irreversible changes in the line intensities above 100 GPa were observed in Sm:YAG and quenched to ambient pressure. Linewidths of the fluorescence bands of the quenched phase indicate structural disorder. In contrast to ruby pressure sensor, the Y4 emission band of Sm:YAG is easily detectable at ultrahigh pressures.

Photoluminescence and x‐ray‐diffraction studies on Sm‐doped yttrium aluminum garnet to ultrahigh pressures of 338 GPa

We report photoluminescence and x‐ray‐diffraction studies on Sm‐doped yttrium aluminum garnet (YAG) to ultrahigh pressures of 338 GPa in a diamond‐anvil cell at room temperature. Photoluminescence spectra from Sm:YAG could be clearly identified with increasing pressures to 304 GPa. The rapidly shifting fluorescence from diamond anvil obscures the Sm:YAG emission spectra above 300 GPa. We provide the shift of the Y4 emission band of Sm:YAG to 304 GPa and give its pressure coefficients as referenced to the ruby standard to 180 GPa and platinum standard to 304 GPa. We present possible structural disorder mechanisms in Sm:YAG above 100 GPa which give rise to the line broadening and changes in intensities of various photoluminescence bands. The application of Sm:YAG as an optical pressure sensor in the ultrahigh‐pressure regime is also discussed.

Fluorescence emission from high purity synthetic diamond anvil to 370 GPa

We report laser excited fluorescence in high purity synthetic diamond anvil to pressures of 370 GPa in a diamond anvil cell device. The nitrogen impurity level in this diamond is extremely low, and it allows us to study the stress effects on the optical transitions in diamond without interference from impurities. Pressure in the diamond anvil cell was measured by x‐ray diffraction using the platinum standard. Pressure dependence of the fluorescence peak was measured between 270 and 370 GPa in the visible spectral range. The variation of excitation laser wavelength shows clear cutoff in the excitation threshold in the 514–633 nm range at 370 GPa.

Pressure dependence of the fluorescence spectra of the Sm: doped YAG to 73 GPa

Abstract The pressure dependence of the fluorescence spectra of the Sm-doped YAG optical pressure sensor is studied against the ruby in the diamond anvil cell up to 73 GPa. The Y2 band fluorescence excited by a 514.5 nm laser shows a linear pressure dependence of 0.32 ± 0.01 nm/GPa to 73 GPa. The relative intensity of the Y2 sub-band compared to the Y1 shows a significant increase with increasing pressure. At high pressures, the overall integrated intensity of the Y band increases by an order of magnitude which is in contrast to the ruby R1 line whose intensity decreases under identical conditions. X-ray diffraction studies show that the cubic phase of the YAG crystal is stable to 69 GPa and the volume compression is 17.9%. The increase in the fluorescence intensity of the Sm:YAG with increasing pressure has practical applications in the ultra high pressure/high temperature research.

Pressure-induced amorphization in gadolinium scandium gallium garnet by x-ray diffraction and spectroscopic studies

We report the first example of amorphization of garnets at high pressure and ambient temperature. Synchrotron x-ray diffraction and fluorescence spectroscopy at high pressure were performed on polycrystalline gadolinium scandium gallium garnet (GSGG) doped with and . X-ray diffraction measurements reveal a loss of long-range order beginning at GPa. This is followed by a change in local environment for dopants at 70 GPa as indicated by the loss of fluorescence emission. The amorphous phase is retained at ambient conditions, after decompression. We present possible mechanisms for these two distinct transformations in GSGG.

Phase transformation in Mo - Ru alloy induced by laser heating at high pressures

Phase transformations in the Mo - Ru alloy system were investigated at high pressures and high temperatures in a laser-heated diamond anvil cell. The room temperature compression of Mo - 20 at% Ru alloy to 67 GPa revealed that the BCC phase is stable to the highest pressure. Laser heating at high pressures performed without an insulating medium resulted in the formation of phase. However, controlled laser heating to 2200 K at 20 GPa with KCl insulating medium showed that the BCC phase transforms into a mixture of BCC and sigma phases. The present phase-stability data are discussed within the context of the rigid-band model and electron transfer under high pressures in transition metal systems.