Enhanced reduction of perchlorate by elemental iron at elevated temperatures

Kinetics of perchlorate reduction by elemental iron was examined at elevated temperatures using microwave heating and conventional block heating. It was hypothesized that increasing the solution temperature may accelerate the reduction of perchlorate by overcoming the high activation energy barrier. Results from microwave heating study showed that 98% of aqueous perchlorate was removed in 1 h at 200 degrees C. Similar results observed in control experiments with a block heater indicated that the enhancement in the extent and rate of perchlorate removal by elemental iron was mostly due to heat energy at high temperature. The rapid and complete reduction of perchlorate by elemental iron at elevated temperatures suggests that iron reduction process at elevated temperature may be an option to consider for complete removal of perchlorate from industrial discharges.     

Chemical denitrification of water by zero-valent magnesium powder

A laboratory-scale study was conducted in batch mode to investigate the feasibility of using zero-valent magnesium (Mg(0)), for removal of nitrate from aqueous solution. Reaction pH, dose of Mg(0), initial nitrate concentration and temperature were considered variable parameters during the study. Strong acidic condition enhanced nitrate reduction and in absence of external proton addition, reaction pH increased rapidly above ten and insignificant nitrate removal (7-16%) was achieved. At Mg(0):NO(3)(-)-N molar ratio of 5.8 and controlled reaction pH of 2, 84% denitrification efficiency was achieved (initial NO(3)(-)-N 50 mg/L) under ambient temperature and pressure and total nitrogen removal was 70% with 3.2% and 10% conversion of initial NO(3)(-)-N to NO(2)(-)-N and NH(4)(+)-N, respectively. The reaction was first order with respect to nitrate concentration. Nitrate removal rate decreased with solution pH and increased linearly with Mg(0) dose. Nitrate removal was coupled with 96-100% removal of dissolved oxygen and 85-90% generation of soluble Mg(2+) ion. An activation energy (E(a)) of nitrate reduction over the temperature range of 10-50 degrees C was observed as 17.7 kJ mol(-1).     

Hydroxyzine- and cetirizine-loaded liposomes: effect of duration of thin film hydration, freeze-thawing, and changing buffer pH on encapsulation and stability

PURPOSE: To assess the effect of the duration of film hydration, freeze-thawing, and changing buffer pH on the extent of entrapment of hydroxyzine and cetirizine, H1-antihistamines with different polarity, into liposomes, and the stability of these liposomes. METHODS: Multilamellar vesicles (MLV) were prepared by thin-lipid film hydration using L-alpha-phosphatidylcholine (PC) and buffer containing 80 mg hydroxyzine at pH 7. For MLV containing hydroxyzine, the liposomes were subjected to 1) hydration for 1 h, 24 h, or 48 h for the control batch, batch B, or batch D respectively; and 2) hydration for 1 h, 24 h, or 48 h with freeze-thawing for 5-cycles for batch A, batch C, or batch E, respectively. These formulations were stored at 10 +/- 2 degrees C and 37 +/- 0.1 degrees C. Small unilamellar vesicles (SUV) and MLV were prepared using L-alpha-phosphatidylcholine (PC), and buffer at pH 5.0, 5.5, 6.0, 6.5, and 7.0, containing 80 mg hydroxyzine or 82 mg cetirizine by the ethanol injection and thin-lipid film hydration methods, respectively. These formulations were stored at 10 +/- 2 degrees C. Liposomes were evaluated immediately after preparation and after storage by determining percent entrapment of hydroxyzine (PETH) or of cetirizine (PEC) and by observing changes in the physical appearance (PA). Particle size (PSA) of the liposomes freshly prepared at pH=6.5 was measured from transmission electron micrographs (TEM). RESULTS: Increasing thin-film hydration time or repeated freeze-thawing did not affect the initial PETH or long-term stability of control, A, B, C, D, and E batches of MLV containing hydroxyzine stored at 10 +/- 2 degrees C. At 37 +/- 0.1 degrees C, PETH of all MLV batches decreased considerably after 1 month. This was more evident in batches B, C, and E exposed to freeze-thawing. The PETH of SUV increased markedly from 53.0% to 84.0% when the pH of the buffer was increased from 5.0 to 5.5. As pH increased from 6.0 to 7.0, PETH continued to increase from 84% to 94%. The initial PETH of MLV increased slightly from 82.0% to 94.0% as the buffer pH values increased from 5.0 to 7.0. There was no effect of pH on initial PEC, and stability of SUV or initial PEC of MLV, which ranged from 92% to 94%, as buffer pH values increased from 5.0 to 6.5. After storage at 10 +/- 2 degrees C PEC in MLV decreased from 94% to 74%. CONCLUSIONS: The freeze-thawing processes had some effect on the stability of liposomes stored at temperatures higher than ambient temperature, 37 +/- 0.1 degrees C. The effect of changing the buffer pH from 5.5 to 7.0, and from 5.0 to 6.5 on initial PETH and PEC, respectively, was minimal. After 24 months at l0 +/- 2 degrees C, pH had no effects on PETH; however, PEC of MLV decreased.     

Short- and long-term effects of temperature on the Anammox process

The application of the Anammox process has been usually focused on the treatment of wastewater with temperatures around 30 degrees C in order to operate under optimum conditions. In this work, the feasibility of the application of the Anammox process at lower temperatures has been tested. First, the short-term effects of temperature on the Anammox biomass were studied using batch tests. An activation energy of 63 kJ mol(-1) was calculated and the maximum activity was found at 35-40 degrees C. Activity tests done at 45 degrees C showed an irreversible loss of the activity due to the biomass lysis. A SBR was operated at different temperatures (from 30 to 15 degrees C) to determine the long-term effects. The system was successfully operated at 18 degrees C but when temperature was decreased to 15 degrees C, nitrite started to accumulate and the system lost its stability. Adaptation of biomass to low temperatures was observed when the specific activities obtained during first batch tests are compared to those obtained during the operation of the SBR.     

Temperature-insensitive fiber Bragg grating tilt sensor

A temperature-insensitive optical fiber tilt sensor is presented. The sensor scheme uses a prestrained fiber Bragg grating to sense the strain, which depends on the tilt angle. To compensate for the temperature effect, materials that have different linear thermal expansion behaviors are used for implementation of the sensor body. The differentiation in the linear thermal expansion would then cause a counter effect to the original temperature effect. Experimental tests show an accuracy of +/-0.167 degrees in tilt angle measurement. A temperature stability better than +/-0.33 degrees over the temperature range from 27 degrees C to 75 degrees C is demonstrated. The resolution 0.0067 degrees in tilt angle measurement is achieved by using our preliminary sensor with a dimension of 1 6 x 5 x 5 cm(3).     

Gas-phase NMR technique for studying the thermolysis of materials: thermal decomposition of ammonium perfluorooctanoate

The kinetics of the thermal decomposition of ammonium perfluorooctanoate (APFO) has been studied by high-temperature gas-phase nuclear magnetic resonance spectroscopy over the temperature range 196-234 degrees C. We find that APFO cleanly decomposes by first-order kinetics to give the hydrofluorocarbon 1-H-perfluoroheptane and is completely decomposed (>99%) in a matter of minutes at the upper limit of this temperature range. Based on the temperature dependence of the measured rate constants, we find that the enthalpy and entropy of activation are DeltaH++ = 150 +/- 11 kJ mol(-1) and DeltaS++ = 3 +/- 23 J mol(-)(1) deg(-1). These activation parameters may be used to calculate the rate of APFO decomposition at the elevated temperatures (350-400 degrees C) at which fluoropolymers are processed; for example, at 350 degrees C the half-life for APFO is estimated to be less than 0.2 s. Our studies provide the fundamental parameters involved in the decomposition of the ammonium salt of perfluorooctanoic acid and indicate the utility of gas-phase NMR for thermolysis studies of a variety of materials that release compounds that are volatile at the temperature of decomposition and that contain an NMR-active nucleus.     

Atomic layer deposition of SiO2 thin films using tetrakis(ethylamino)silane and ozone

We examined the atomic layer deposition (ALD) of silicon dioxide thin films on a silicon wafer by alternating exposures to tetrakis(ethylamino)silane [Si(NHC2H5)4] and O3. The growth kinetics of silicon oxide films was examined at substrate temperatures ranging from 325 to 514 degrees C. The deposition was governed by a self-limiting surface reaction, and the growth rate at 478 degrees C was saturated at 0.17 nm/cycle for Si(NHC2H5)4 exposures of 2 x 10(6) L (1 L = 10(-6) Torr x s). The films deposited at 365-404 degrees C exhibited a higher deposition rate of 0.20-0.21 nm/cycle. However, they contained impurities, such as carbon and nitrogen, and showed poor film qualities. The concentration of impurities decreased with increasing substrate temperature. It was found that the films deposited in the high-temperature regime (478-514 degrees C) showed excellent physical and electrical properties equivalent to those of LPCVD films.     

Secondary electrospray ionization-ion mobility spectrometry for explosive vapor detection

The unique capability of secondary electrospray ionization (SESI) as a nonradioactive ionization source to detect analytes in both liquid and gaseous samples was evaluated using aqueous solutions of three common military explosives: cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), nitroglycerin (NG) and pentaerythritol tetranitrate (PETN). The adducts formed between the compounds and their respective dissociation product, RDX.NO(2)(-), NG.NO(3)(-), and PETN.NO(3)(-), gave the most intense signal for the individual compound but were more sensitive to temperature than other species. These autoadducts were identified as RDX.NO(2)(-), NG.NO(3)(-), and PETN.NO(3)(-) and had maximum signal intensity at 137, 100, and 125 degrees C, respectively. The reduced mobility values of the three compounds were constant over the temperature range from 75 to 225 degrees C. The signal-to-noise ratios for RDX, NG, and PETN at 50 mg L(-1) in methanol-water were 340, 270, and 170, respectively, with a nominal noise of 8 +/- 2 pA. In addition to the investigation of autoadduct formation, the concept of doping the ionization source with nonvolatile adduct-forming agents was investigated and described for the first time. The SESI-IMS detection limit for RDX was 116 microg L(-1) in the presence of a traditional volatile chloride dopant and 5.30 microg L(-1) in the presence of a nonvolatile nitrate dopant. In addition to a lower detection limit, the nitrate dopant also produced a greater response sensitivity and a higher limit of linearity than did the traditional volatile chloride dopant.     

Simultaneous determination of C1-C4 carboxylic acids and aldehydes using 2,4-dinitrophenylhydrazine-impregnated silica gel and high-performance liquid chromatography

A new method for the simultaneous determination of aliphatic carboxylic acids and aldehydes in air is described. In this work, carboxylic acids were allowed to react with 2,4-dinitrophenylhydrazine (DNPH) to form the corresponding carboxylic 2,4-dinitrophenylhydrazides. These derivatives have excellent thermal stability, with melting points higher than those of the corresponding hydrazones by 32-50 degrees C. C1-C4 carboxylic acid 2,4-dinitrophenylhydrazides exhibited maximum absorption wavelengths of 331-334 nm and molar absorption coefficients of 1.4 x 10(4) L/mol/cm. They were completely separated by high-performance liquid chromatography (HPLC) with an RP-Amide C16 column. Cartridges packed with DNPH-coated silica particles (DNPH cartridge) were used for sampling formic acid and aldehydes. Formic acid was physically adsorbed on the silica particles as the first step of the sampling mechanism. Gradual reaction with DNPH followed. Formic acid reacted very slowly with DNPH at room temperature (20 degrees C), but reacted completely at 80 degrees C over 4 h. In field measurements, the sample air was drawn through a DNPH cartridge. After sampling, the cartridges were heated at 80 degrees C for 5 h and extracted with acetonitrile for HPLC analysis. Under these optimized conditions, the LOD is 0.4 ug/m(3) for an air sample collected for 24 h at 100 mL/min (144 L).     

Measurement of association and dissociation rate constants for lead(II)/18-crown-6 using square wave voltammetry at a glassy carbon mercury film electrode

Understanding the rate parameters of metal ion-ligand complexes is necessary for sensing, separations, and responsive materials. The complexation between 18-crown-6 and lead(II) is of particular interest due to the potential use of this chemistry in sensors and separations. We have applied square wave voltammetry at a glassy carbon mercury film electrode to this problem. Lead(II) in aqueous solution containing an excess of 18-crown-6, studied with different experimental time scales, yields stoichiometry, binding constants, and rate constants (25 degrees C). For pulse times longer than 10 ms, the glassy carbon mercury film electrode acts as a planar electrode. For shorter pulse times, a roughness correction factor must be used to calculate dimensionless current because of the increase in effective area due to the droplike nature of the adsorbed mercury. Lead(II) forms a 1:1 complex with 18-crown-6 in both nitrate and perchlorate media. Log K for the complex with the nitrate counterion is 4.13 +/- 0.09 (SEM); in the presence of perchlorate it is 4.35 +/- 0.09 (SEM). The formation rate constants, kf, for the nitrate and perchlorate systems are (3.82 +/- 0.89) x 107 and (5.92 +/- 1.97) x 106 M-1 s-1, respectively. The dissociation rate constants, kd, are (2.83 +/- 0.66) x 103 s-1 with nitrate as the counterion and (2.64 +/- 0.88) x 102 s-1 with perchlorate as the counterion. The significant difference in rate constants for the two anions is probably caused by the ion pairing that occurs with lead(II) nitrate.     

Determination of vapor pressure of low-volatility compounds using a method to obtain saturated vapor with coated capillary columns

The vapor pressures of O-ethyl S-2-diisopropylaminoethyl methylphosphonothiolate (VX), O-isobutyl S-2-diethylaminoethyl methylphosphonothiolate (RVX), and 2,4-dinitrotoluene (2,4-DNT) were determined with the gas saturation method in temperatures ranging from -12 to 103 degrees C. The saturated vapor was generated using a fused-silica column coated with the compound. This column was placed in a gas chromatograph, and the vapor pressure was determined directly from the detector signal or by sampling on Tenax tubes that were subsequently analyzed. From the linear relationships obtained by plotting log P vs 1/T, the enthalpies of vaporization (deltaHvap) and the vapor pressures at selected temperatures were determined. The vapor pressure of VX at 25 degrees C was 0.110 Pa and the deltaHvap 77.9 kJ x mol(-1). The corresponding results for RVX were 0.082 Pa and 76.6 kJ x mol(-1). The vapor pressure of 2,4-DNT at 72 degrees C (melting point) was determined to 6.0 Pa, and the enthalpies of the solid and the liquid state were 94.2 and 75.3 kJ x mol(-1), respectively. Using capillary columns to generate saturated vapors has three major advantages: short equilibrium time, low consumption of sample, and safe handling of toxic compounds.     

Rapid synthesis and characterization of maghemite nanoparticles

Fe2O3-SiO2 nanocomposites were prepared by a sol-gel method using various evaporation surface to volume (S/V) ratios ranging from 0.03 to 0.2. The Fe2O3-SiO2 sols were gelated at various temperatures ranging from 50 degrees C to 70 degrees C, and subsequently they were calcined in air at 400 degrees C for 4 hours. The structure and the magnetic properties of the prepared Fe203-SiO2 nanocomposites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), and vibrating sample magnetometer (VSM) measurements. The gelation temperature of the Fe2O3-SiO2 sols influenced strongly the particle size and crystallinity of the maghemite nanoparticles. It was observed that the particle size of maghemite nanoparticles increased with the increasing of the gelation temperature of the sols, which may be due to the agglomeration of the maghemite particles at elevated temperatures inside the microporosity of the silica matrix during the gelation process, and the subsequent calcination of these gels at 400 degrees C resulted in the formation of large size iron oxide particles. Magnetization studies at temperatures of 10, 195, and 300 K showed superparamagnetic behavior for all the nanocomposites prepared using the evaporation surface to volume ratio (S/V) of 0.1, 0.2, 0.09, and 0.08. The saturation magnetization, Ms, values measured at 10 K were 5.5, 8.5, and 9.5 emu/g, for the samples gelated at 50, 60, and 70 degrees C, respectively. At the gelation temperature of 70 degrees C, gamma-Fe2O3 crystalline superparamagnetic nanoparticles with the particle size of 9 +/- 2 nm were formed in 12 hours for the samples prepared at the S/V ratio of 0.2.     

Nitrate removal efficiency of bacterial consortium (Pseudomonas sp. KW1 and Bacillus sp. YW4) in synthetic nitrate-rich water

The efficiency of bacterial isolates to reduce nitrate from synthetic nitrate-rich water was tested using a batch scale process. Two efficient nitrate reducing bacterial species were isolated from water samples collected from Kodaikanal and Yercaud lakes. Bacterial analysis of the samples revealed the presence of nitrate reducing bacteria belonging to the genera Pseudomonas, Bacillus, Micrococcus and Alcaligenes. Among the isolates, the consortium of Pseudomonas sp. KW1 and Bacillus sp. YW4 was found to be efficient in nitrate reduction. Influences of various carbon sources, incubation temperature and pH on nitrate reduction from synthetic wastewater were also studied. The results showed a rapid and efficient process of nitrate removal (99.4%) from synthetic wastewater supplemented with starch (1%), inoculated by bacterial consortium (Pseudomonas sp. KW1 and Bacillus sp. YW4) at incubation temperature of 30 degrees C at pH 7. This observation has led to the conclusion that the bacterial consortium was responsible for nitrate removal from synthetic nitrate-rich wastewater.     

THE HIGH STRAIN-RATE FRACTURE CHARACTERISTICS OF DUCTILE METALS AT ELEVATED AND SUB-AMBIENT TEMPERATURES

Abstract— High strain-rate tensile tests have been carried out on pre-notched specimens of OFHC copper and Remko iron at both elevated and cryogenic temperatures. When properly expressed as a function of stress triaxiality at the centre of the notch (as predicted by numerical simulations of the experiment), the ductility of copper was found to be independent of temperature over a range from —190°C to 300°C. The specially-processed Remko iron was found to undergo a ductile-to-brittle transition at a temperature dependent on the stress triaxiality and the particular batch of the material. Otherwise the fully ductile strains-to-failure (when expressed as a function of stress triaxiality) for iron were found to decrease with increasing temperature up to 400°C; this being the maximum temperature tested.     

Diffusion in Si(x)Ge(1-x)/Si nanowire heterostructures

Si0.48Ge0.52/Si tip/nanowire heterostructures were grown by pulsed laser vaporization (PLV) at a growth temperature of 1100 degrees C. Ge diffusion in [111]-growth Si nanowires was studied for different post-synthesis annealing temperatures from 200 degrees C to 800 degrees C. Ge composition profiles were quantified by energy-dispersive X-ray spectroscopy in a transmission electron microscope. The compositional profiles were modeled by a limited-source diffusion model to extract temperature-dependent diffusion coefficients. The Ge diffusion coefficients followed an Arrhenius relationship with an activation energy of 0.622 +/- 0.050 eV. This rather low activation energy barrier is similar to the previously reported activation energy barrier of 0.67 eV for Ge surface diffusion on Si, suggesting that surface diffusion may dominate in nanowires at this length scale.     

Characterization of low-k dielectric SiCOH films deposited with decamethylcyclopentasiloxane and cyclohexane

Ultra low-k dielectric SiCOH films were deposited with decamethylcyclopentasiloxane (DMCPSO, C10H30O5Si5) and cyclohexane (C6H12) precursors by plasma-enhanced chemical vapor deposition at the deposition temperature between 25 and 200 degrees C and their chemical composition and deposition kinetics were investigated in this work. Low dielectric constants of 1.9-2.4 were obtained due to intrinsic nanoscale pores originating from the relatively large ring structure of DMCPSO and to the relatively large fraction of carbon contents in cyclohexane. Three different deposition regions were identified in the temperature range. Deposition rates increased with temperature below 40 degrees C and decreased as temperature increased to 75 degrees C with apparent activation energies of 56 kJ/mol x K at < 40 degrees C, -26 kJ/mol x K at 40-100 degrees C, respectively. In the temperature region of 40-100 degrees C hydrocarbon deposition and decomposition process compete each other and decomposition becomes dominant, which results in apparent negative activation energy. Deposition rates remain relatively unaffected with further increases of temperature above 100 degrees C. FTIR analysis and deposition kinetic analysis showed that hydrocarbon deposition is the major factor determining chemical composition and deposition rate. The hydrocarbon deposition dominates especially at lower temperatures below 40 degrees C and Si-O fraction increases above 40 degrees C. We believe that dielectric constants of low-k films can be controlled by manipulating the fraction of deposited hydrocarbon through temperature control.     

Electrocatalytic behavior of calcium doped LaFeO3 as cathode material for solid oxide fuel cell

La(1-x)Ca(x)FeO3 (X = 0.0, 0.2, 0.4, abbreviated as LCF) as cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC) was synthesized by new route of glycine nitrate method. LCF materials were characterized by X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), electrical and electrochemical impedance spectroscopy (EIS). The powder LCFs exhibited single phase with orthorhombic structure, highly porous and small nanoparticles with average size of 200-300 nm. The electrical conductivities of LCFs increased as increasing the Ca content and achieved the maximum electrical conductivity of 148 Scm(-1) for La0.6Ca0.4FeO3 (X = 0.4) at 550 degrees C. The improved conductivity of LCFs could be a promising cathode material for IT-SOFCs. In the impedance analysis of fabricated symmetry cell with the optimized La0.6Ca0.4FeO3 cathode and Ce0.8Sm0.2O3 (SDC) electrolyte, the minimum area specific resistance (ASR) of 0.15 omegacm2 was observed at 850 degrees C, which may due to the lowest activation energy (1.55 eV), resulting from the reduction of oxygen molecules into oxygen ions. It was found that calcium doping was essential to increase the charge carrier concentration of lanthanum iron oxide materials, resulting in the high conductivity at intermediate temperature.     

Submicrosecond temperature measurement in liquid water with laser-induced thermal acoustics

Using laser-induced thermal acoustics, we demonstrate nonintrusive and remote sound-speed and temperature measurements in liquid water. Unsteady thermal gradients in the water sample produce fast, random laser beam misalignments, which are the primary source of uncertainty in these measurements. For water temperatures over the range 10 degrees C to 45 degrees C, the precision of a single 300-ns-duration measurement varies from +/-1 to +/-16.5 m/s for sound speed and from +/-0.3 degrees C to +/-9.5 degrees C for temperature. Averaging over 10 s (100 laser pulses) yields accuracies of +/-0.64 m/s and +/-0.45 degrees C for sound speed and temperature, respectively.     

Field-induced strain behavior for potassium sodium bismuth titanate ceramics

Data are reported for the dielectric, piezoelectric, electrostrictive, and ferroelectric properties of potassium-substituted sodium bismuth titanate, [(K(x)Na(1-x))(0.5)Bi(0.5)]TiO3. For the morphotropic phase boundary composition x = 0.2, relaxor-type behavior was observed at room temperature with piezoelectric (effective d(333) = 325 x 10(-12) m/V) and ferroelectric properties (P(R) = 25 microC/cm(2), E(C) = 30 kV/cm). A transition to a relatively frequency-independent, diffuse phase transformation region occurred with increasing temperature, with no remanent strain or coercive field. Above the transition temperature, the field-induced strain was consistent with contributions from electrostriction and field induced piezoelectricity (M(3333) = 1.9 x 10(-16) m2/V2 and d333 = 81 x 10(-12) m/V at 100 degrees C). Information is given for the temperature dependence of properties, e.g., 0.14% strain induced at 50 kV/cm at 200 degrees C. Higher potassium content x = 0.6 stabilized the ferroelectric piezoelectric region to temperatures above 200 degrees C, with a relatively stable d(333) = 150-145 x 10-12 m/V between 25 degrees C and 200 degrees C. Pb-free KNBT ceramics appear competitive with PZT, especially for higher temperature electromechanical applications.