Friction and wear of diamond-containing polyimide composites in water and air

Polyimide-based composites containing fine diamond powder were fabricated using spark plasma sintering. The based material was polyimide (PI) containing a small amount of polytetrafluoroethylene (PTFE). Two types of diamond powder were used: one synthesized by statically high pressure, i.e., high-pressure diamond (HD), and the other synthesized by shock compression, i.e., shock-compression diamond (SD). We evaluated their tribological properties using a reciprocating friction tester in water and air using an Al₂O₃ mating ball. Adding HD to the polyimide-PTFE-based material decreased the composite's friction in water, but the effect of this addition in air was negligible. The specific wear rate of composites with different HD content was similar to that of the based material alone in water, while the wear of composites decreased with the addition of diamond in air. The effect of diamond powder size on friction and wear of composites was generally low in both water and air. The addition of SD decreased the friction coefficient of composites, but SD content only negligibly affected the friction in water and air. The specific wear rate was minimal at SD content of 5 vol.%, when diamond content was varied. Wear was almost independent of diamond powder size. SD reduced composite friction and wear better than HD; regardless of environment, its friction coefficient was less than 0.1 and the specific wear rate was in the level of 10⁻⁷ mm³/N m in both water and air.     

High-temperature tribological properties of strontium sulfate films formed on zirconia-alumina, alumina and silicon nitride substrates

In our present study, Al₂O₃, (ZrO₂–3 mol% Y₂O₃)–39.6 mass% Al₂O₃ and Si₃N₄ substrates coated with SrSO₄ and SrSO₄–10 mass% Ag films were prepared, and the friction and wear properties of these specimens were investigated using a reciprocating ball-on-disk tribometer in the temperature range from room temperature to 1073 K in air. It was clarified that (ZrO₂–3 mol% Y₂O₃)–39.6 mass% Al₂O₃ substrates coated with chemically precipitated SrSO₄ particles and the substrates coated with SrSO₄–10 mass% Ag films prepared by mechanically grinding and annealing at 1073 K for 3.6 ks exhibited low friction coefficients and low wear rates at all the testing temperatures. In addition, the average friction coefficients of Si₃N₄ substrates were reduced above 673 K by coating with chemically precipitated SrSO₄ particles.     

Effects of boundary conditions on the end-of-life treatment of LCD TVs

Differences in legislation and markets for recycled materials result in the national implementation of distinct end-of-life treatment strategies. This paper presents a comparative analysis of the boundary conditions in Belgium and Japan that cause the adoption of diverse treatment strategies for the rapidly increasing number of end-of-life flat screen TVs. In addition, both treatment strategies are evaluated from an ecological and economic perspective and opportunities for improvement are identified.     

Anodic Pt dissolution in concentrated trifluoromethanesulfonic acid

We investigated the anodic Pt dissolution in concentrated trifluoromethanesulfonic acid (TFMSA). The dependence of the Pt dissolution rate on the TFMSA concentration was first measured from the weight difference of a Pt-flag electrode before and after successive potential cycles. From this measurement, the Pt dissolution rate in 10 mol dm^?3 TFMSA is found to be over 40 times greater than those in 1 and 4 mol dm^?3 TFMSA. Next, the anodic Pt dissolution was assessed in 10 mol dm^?3 TFMSA by a potential step technique using a Pt dual microelectrode having generator and collector electrodes. The obtained result shows that the anodic Pt dissolution in 10 mol dm^?3 TFMSA occurs when the Pt generator electrode potential is stepped from 0.25 to 1.0–2.0 V vs. Ag/Ag₂SO₄. Furthermore, the absolute steady-state current-based coulomb charges obtained at the generator (|Q_G|) and collector (|Q_C|) reflect the anodic Pt dissolution and the reduction of the dissolved Pt, respectively. The magnitude of |Q_G| and |Q_C| linearly increase when the generator potential shifts from 1.0 to 2.0 V vs. Ag/Ag₂SO₄. The absolute ratio, |Q_C/Q_G|, also gradually increases according to the shift in the generator electrode potential. These results demonstrate that the anodic Pt dissolution in 10 mol dm^?3 TFMSA occurs at ≥1.0 V vs. Ag/Ag₂SO₄ and that the ratio of the anodic Pt dissolution per total reaction charges increases according to the positive shift of the Pt electrode potential.     

Depletion- and enhancement-mode modulation-doped field-effecttransistors for ultrahigh-speed applications: an electrochemicalfabrication technology

This paper is devoted to an electrochemical-etching-based technology for fabricating high-performance MODFETs for high-speed applications. The electrochemical etching in the gate openings is induced by the exposure of the Ni surface metal on the ohmic electrodes; it results in very slender gate-recess grooves, which are desirable for high-speed MODFETs because of the resulting achievable small gate-to-channel separation and low parasitic resistance. The technology is easy to implement, and is effective for enhancing the aspect ratio. Good control of aspect ratio is essential for achieving excellent device performance and limiting deleterious short channel effects. Successful vertical scaling, together with minimization of gate length by well-established electron-beam lithography using fullerene-incorporated electron-beam resist, leads to the realization of both optimal D- and E-mode MODFET's with ultrahigh extrinsic transconductance values and current gain cut-off frequencies. Fully passivated 0.07-μm D-MODFET's with 2.25 S/mm extrinsic transconductance and current gain cut-off frequency exceeding 300 GHz have been successful fabricated. In addition, 0.03 μm E-MODFETs with 2 S/mm transconductance and 300 GHz current gain cut-off frequency have been demonstrated. This electrochemical-etching-based technology provides both high-performance D- and E-MODFET's and, therefore, opens up the possibility to achieve ultrahigh-speed ICs based on DCFL configurations     

Highly c-axis oriented AlN layers grown on c-plane sapphire substrates by radio-frequency sputter epitaxy at 1080 °C

Aluminum nitride (AlN) single-crystalline layers were grown on c-plane sapphire substrates by radio-frequency magnetron sputter epitaxy using N₂/Ar mixture ambient gas and 5-N grade Al target. The crystalline structures of the AlN layers depending on substrate temperature and N₂ composition ratio in ambient gas, were predominantly studied. The crystalline quality of the AlN layer was improved by elevating substrate temperature, and the full-widths at half-maximum (FWHMs) of X-ray rocking curves (XRC) for both symmetric and asymmetric planes of AlN layers grown at N₂ composition ratio of around 25%, became low. The FWHMs of XRC for (0002) diffraction of the AlN layers grown at 1080 °C, were less than 20 arcsec. The surface root-mean-square roughness of such highly c-axis oriented AlN layer was determined by atomic force microscopy, and was increased from 0.6 nm to 1.3 nm when AlN layer thickness was varied from 0.15 to 0.7 μm.     

Suppression of Potential Oscillations in PEFCs by Using Anode Catalyst Prepared by Polygonal Barrel‐Sputtering Method

In this study, we investigated the suppression of potential oscillations that occur while feeding H₂ gas including a large amount of CO to polymer electrolyte fuel cells. A carbon‐supported Pt–Ru alloy (Pt–Ru/C) sample was prepared by the polygonal barrel‐sputtering method. Electrochemical measurement was conducted in 1 N H₂SO₄ electrolyte solution saturated with H₂ gas including CO of 1,000 ppm. From the measurement, it was found that the prepared Pt–Ru/C sample showed higher CO tolerance than a commercially available sample, and therefore, potential oscillations in the case of the prepared sample occurred for slightly longer intervals. Additional samples were prepared by sputtering different amounts of Ru on the prepared Pt–Ru/C sample, and it was observed that the average interval of potential oscillations increased with the amount of Ru. This result suggests that in the case of the polygonal barrel‐sputtering method, Ru plays an important role in suppressing potential oscillations and influences the CO tolerance of Pt–Ru/C.     

Mitochondrial phospholipid hydroperoxide glutathione peroxidase plays a major role in preventing oxidative injury to cells

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is synthesized as a long form (L-form; 23 kDa) and a short form (S-form; 20 kDa). The L-form contains a leader sequence that is required for transport to mitochondria, whereas the S-form lacks the leader sequence. A construct encoding the leader sequence of PHGPx tagged with green fluorescent protein was used to transfect RBL-2H3 cells, and the fusion protein was transported to mitochondria. The L-form of PHGPx was identified as the mitochondrial form of PHGPx and the S-form as the non-mitochondrial form of PHGPx since preferential enrichment of mitochondria for PHGPx was detected in M15 cells that overexpressed the L-form of PHGPx, whereas no similar enrichment was detected in L9 cells that overexpressed the S-form. Cell death caused by mitochondrial injury due to potassium cyanide (KCN) or rotenone (chemical hypoxia) was considerably suppressed in the M15 cells, whereas the L9 cells and control RBL-2H3 cells (S1 cells, transfected with the vector alone) succumbed to the cytotoxic effects of KCN. Flow cytometric analysis showed that mitochondrial PHGPx suppressed the generation of hydroperoxide, the loss of mitochondrial membrane potential, and the loss of plasma membrane integrity that are induced by KCN. Mitochondrial PHGPx might prevent changes in mitochondrial functions and cell death by reducing intracellular hydroperoxides. Mitochondrial PHGPx failed to protect M15 cells from mitochondrial injury by carbonyl cyanide m-chlorophenylhydrazone, which directly reduces membrane potential without the generation of hydroperoxides. M15 cells were more resistant than L9 cells to cell death caused by direct damage to mitochondria and to extracellular oxidative stress. L9 cells were more resistant to tert-butylhydroperoxide than S1 cells, whereas resistance to t-butylhydroperoxide was even more pronounced in M15 cells than in L9 cells. These results suggest that mitochondria might be a target for intracellular and extracellular oxidative stress and that mitochondrial PHGPx, as distinct form non-mitochondrial PHGPx, might play a primary role in protecting cells from oxidative stress.