Characterization of recent silicon carbide whiskers

SiC whisker surface chemistry and morphology can strongly impact composite processing and properties. We report here the surface chemistry and morphology of SiC whiskers received during late 1987 and 1988 from five sources. Comparisons are made with previously characterized whiskers.     

Anion effects on the electrochemical regeneration of Ce(IV) in nitric acid used for etching chromium

The anion impurities such as SO4(2-), Cl(-), and Cr2O7(2-) commonly present in the spent (hazardous) Cr-etch solutions from color filter manufacturing processes may influence the solutions' regeneration by the electrooxidation of Ce(III) to Ce(IV). This study, therefore, investigated the effects of these anions on Ce(III)/Ce(IV) redox reactions at glassy carbon in HNO3. In cyclic voltammetric tests, the presence of SO4(2-) decreased the formal potential but increased the peak potential separation (Delta Ep) of Ce(III)/Ce(IV) couple, and lowered the peak current for Ce(IV) reduction whereas Cl(-) did not change the formal potential and Delta Ep, but the peaks for Cl(-) and Ce(III) oxidation partially overlapped. Cr2O7(2-) slightly lowered the peak current for Ce(III) oxidation but significantly decreased that for Ce(IV) reduction. The Tafel slope for Ce(III) oxidation was approximately 65mVdecade(-1) in the absence of anion impurities. Increasing SO4(2-), Cl(-), or Cr2O7(2-) in solution raised the Tafel slope. The Ce(III)/Ce(IV) equilibrium potential decreased with the increase of SO4(2-) or Cl(-) but was hardly influenced by Cr2O7(2-) addition. These observations from individual anion species together well explained the anions' co-effect (kinetic hindrance) on the Ce(III) oxidation in HNO3, revealing that these anions are unfavorable for the electrooxidation of Ce(III) in the spent Cr-etch solutions.     

Dual high-frequency difference excitation for contrast detection

Stimulating high-frequency nonlinear oscillations of ultrasound contrast agents is helpful to distinguish microbubbles from background tissues. Nevertheless, inefficiency of such oscillations from most commercially available contrast agents and intense attenuation of the resultant high-frequency harmonics limit microbubble detection with high-frequency ultrasound. To avoid this high-frequency nature, we devised and explored a dual-frequency difference excitation technique to induce efficiently low-frequency, rather than high-frequency, nonlinear scattering from microbubbles by using high-frequency ultrasound. The proposed excitation pulse is comprised of 2 high-frequency sinusoids with frequency difference subject to the microbubble resonance frequency. Its envelope, with frequency being the difference between the 2 frequencies, is used to stimulate nonlinear oscillation of microbubbles for the consonant low-frequency harmonic generation, whereas high-imaging resolution is retained because of narrow high-frequency transmit beams. Hydrophone measurements and phantom experiments of speckle-generating flow phantoms were performed to demonstrate the efficacy of the proposed technique. The results show that, especially when the envelope frequency is near the microbubbleiquests resonance frequency, the envelope of the proposed excitation pulse can induce significant nonlinear scattering from microbubbles, the induced nonlinear responses tend to increase with the pulse pressures, and up to 26 dB and 36 dB contrast-to-tissue ratios with second- and fourth-order nonlinear responses, respectively, can be obtained. Potential applications of this method include microbubble fragmentation and cavitation with high-frequency ultrasound.     

Source characterization of total suspended particulate matter near a riverbed in Central Taiwan

Samples of total suspended particulate (TSP) matter were collected by using TSP samplers from certain areas representing the estuary of the Jhuoshuei River, Taiwan during monsoon and non-monsoon seasons in 2005. A total of 12 elements and nine inorganic ions were identified by inductively coupled plasma atomic emission spectrometry (ICP-AES) and ion chromatography (IC), respectively. Enrichment factors explaining a preponderance of the variance in the data were applied to the data sets. The results show that wind direction significantly affected the concentration of TSP during the monsoon season; moreover, these concentrations were also markedly higher during the monsoon than during the non-monsoon season. Low enrichment factor (EF) values (1.18-2.88) were observed during the monsoon for Ca, Fe, Na, Ba, Cd, Co, Li, Mn, and Sr, reflecting the importance of dust contribution by natural processes. Conversely, the EF values calculated for Ca, K, Ba, Co, Li, and Zn were relatively high (7.03-20.26) when observed during non-monsoon season, a phenomenon suggesting that they are mainly contributed from non-crustal sources. The observations of relatively enhanced EF values during monsoon indicate that the changes in wind direction between monsoon and non-monsoon seasons are associated with the different contribution sources. The high concentration of TSPs observed in the ambient air is believed to be primarily due to surface soil particle emission from the riverbeds.     

Thermostable variants constructed via the structure-guided consensus method also show increased stability in salts solutions and homogeneous aqueous-organic media

Enzyme instability is a major factor preventing widespread adoption of enzymes for catalysis. Stability at high temperatures and in the presence of high salt concentrations and organic solvents would allow enzymes to be employed for transformations of compounds not readily soluble in low temperature or in purely aqueous systems. Furthermore, many redox enzymes require costly cofactors for function and consequently a robust cofactor regeneration system. In this work, we demonstrate how thermostable variants developed via an amino acid sequence-based consensus method also showed improved stability in solutions with high concentrations of kosmotropic and chaotropic salts and water-miscible organic solvents. This is invaluable to protein engineers since deactivation in salt solutions and organic solvents is not well understood, rendering a priori design of enzyme stability in these media difficult. Variants of glucose 1-dehydrogenase (GDH) were studied in solutions of different salts along the Hofmeister series and in the presence of varying amounts of miscible organic solvent. Only the most stable variants showed little deactivation dependence on salt-type and salt concentration. Kinetic stability, expressed by the deactivation rate constant k(d,obs), did not always correlate with thermodynamic stability of variants, as measured by melting temperature T(m). However, a strong correlation (R(2) > 0.95) between temperature stability and organic solvent stability was found when plotting T(50)(60) versus C(50)(60) values. All GDH variants retained stability in homogeneous aqueous-organic solvents with >80% v/v of organic solvent.     

A new approximate solution for chlorine concentration decay in pipes

Biswas et al. (1993. A model for chlorine concentration decay in pipes. Water Res. 27(12), 1715-1724) presented an analytical solution of a two-dimensional (2-D) steady-state chlorine transport equation in a pipe under the turbulent condition and employed fractional error function and regression technique to develop an approximate solution. However, their approximate solution may not give a good result if the wall decay parameter is large. This paper provides a more accurate approximate solution of the 2-D steady-state chlorine transport equation under the turbulent condition. This new approximate solution has advantages of easy evaluation and good accuracy when compared with the approximate solution given by Biswas et al. (1993). In addition, this paper also develops a methodology that combines simulated annealing (SA) with this new approximate solution to determine the wall decay parameter. Two cases are chosen to demonstrate the application of the present approximate solution and methodology. The first case is to use this new approximate solution in simulating chlorine decay in pipes with the experiment-observed data given by Rossman (2006. The effect of advanced treatment on chlorine decay in metallic pipes. Water Res. 40(13), 2493-2502), while the second case presents the determination of the wall consumption at the end of the pipe network.     

Adsorption of Cu from water using raw and modified coal fly ashes

In this study, we found that both raw and modified coal fly ashes effectively adsorb Cu²⁺ from wastewater. The adsorption capacities followed the order CFA> CFA-600> CFA-NaOH. The adsorption isotherms for Cu²⁺ on the raw and modified coal fly ashes fit the Langmuir, Freundlich, and DKR isotherms quite well. These adsorptions were endothermic in nature; the values of E (between 1.3 and 9.6 kJ mol⁻¹) were consistent with an ion-exchange adsorption mechanism. The adsorptions of Cu²⁺ onto CFA, CFA-600, and CFA-NaOH followed pseudo-second-order kinetics.     

Negative air ions releasing properties of tourmaline contained ethylene propylene diene terpolymer/polypropylene thermoplastic elastomers

The releasing properties of negative air ions of tourmaline contained polypropylene (PP) and ethylene propylene diene terpolymer/polypropylene (EPDM/PP) composite films under varying testing conditions were investigated in this study. It is interesting to note that the C_ion− values of EPDM/PP/tourmaline specimens tested at varying conditions are significantly higher than those of the PP/tourmaline specimens with the same loadings of tourmaline powders. Moreover, all C_ion− values of PP/tourmaline and EPDM/PP/tourmaline film specimens tested at dynamic impact mode are significantly higher than those of the corresponding specimens tested at static mode but the same temperature. A beneficial temperature effect on C_ion− values of the PP/tourmaline and EPDM/PP/tourmaline film specimens tested at static and dynamic impact conditions was found. To understand these interesting negative air ion properties of PP/tourmaline and EPDM/PP/tourmaline film specimens, energy dispersive X-rays analysis of the tourmaline powders, scanning electron microscope morphology, and tensile property analysis of the PP/tourmaline and EPDM/PP/tourmaline film specimens were performed. Possible reasons account for the interesting negative air ion properties of the PP/tourmaline and EPDM/PP/tourmaline film specimens are discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of the ultradrawing behavior of gel films of ultrahigh‐molecular‐weight polyethylene and low‐molecular‐weight polyethylene blends on their physical properties

This study examined the effect of the ultradrawing behavior of gel film specimens of ultrahigh‐molecular‐weight polyethylene (UHMWPE) and UHMWPE/low‐molecular‐weight polyethylene (LMWPE) blends on their physical properties. The concentration of a gel film approximated its critical concentration at a fixed drawing temperature; its achievable draw ratio was higher than that of other blend specimens with various concentrations. Noticeably, when about 5 wt % LMWPE was added to a UHMWPE/LMWPE gel film specimen, the achievable draw ratio of the gel film increased, and this contributed to an apparent promoting effect on its anticreeping properties and thermal stability. Therefore, when UL_B?0.9 was drawn to a draw ratio of 300, the anticreeping behavior was improved to less than 0.026%/day. Moreover, with respect to the thermal stability, when the same specimen was drawn to a draw ratio of 300, the retention capability of its storage modulus could resist a high temperature of 150°C, which was obviously much higher than the temperature of an undrawn gel film specimen (70°C). To study these interesting behaviors further, this study systematically investigated the gel solution viscosities, anticreeping properties, dynamic mechanical properties, thermal properties, molecular orientations, and mechanical properties of undrawn and drawn UHMWPE/LMWPE gel film specimens. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Crystallization of poly(butylene terephthalate)/poly(ethylene octene) blends: Nonisothermal crystallization

Poly(ethylene octene) (POE), maleic anhydride grafted poly(ethylene octene) (mPOE), and a mixture of POE and mPOE were added to poly(butylene terephthalate) (PBT) to prepare PBT/POE (20 wt % POE), PBT/mPOE (20 wt % mPOE), and PBT/mPOE/POE (10 wt % mPOE and 10 wt % POE) blends with an extruder. The melting behavior of neat PBT and its blends nonisothermally crystallized from the melt was investigated with differential scanning calorimetry (DSC). Subsequent DSC scans exhibited two melting endotherms (T_mI and T_mII). T_mI was attributed to the melting of the crystals grown by normal primary crystallization, and T_mII was due to the melting of the more perfect crystals after reorganization during the DSC heating scan. The better dispersed second phases and higher cooling rate made the crystals that grew in normal primary crystallization less perfect and relatively prone to be organized during the DSC scan. The effects of POE and mPOE on the nonisothermal crystallization process were delineated by kinetic models. The dispersed phase hindered the crystallization; however, the well‐ dispersed phases of an even smaller size enhanced crystallization because of the higher nucleation density. The nucleation parameter, estimated from the modified Lauritzen–Hoffman equation, showed the same results. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008