Extent of oxidation of Cr(III) to Cr(VI) under various conditions pertaining to natural environment

Calculations show that oxidation of chromium oxide (Cr2O3) by oxygen and oxidation of chromium hydroxide (Cr(OH)3) by manganese dioxide (MnO2) are thermodynamically feasible in both aerobic and mildly anoxic environments. Experiments were carried out to determine the rate and extent of chromium oxidation under various conditions, i.e., when Cr2O3 was heated in the presence of oxygen, when Cr(OH)3 and MnO2 mixtures were suspended in aerobic or anoxic aqueous media at various pH values, when Cr(OH)3 and MnO2 mixtures interacted in moist aerobic conditions and when chromium assumed to be Cr(OH)3 and manganese assumed to be MnO2 interacted in the presence of competing electron donors/acceptors, as is the case in chromium-contaminated sludge. Results indicate that trivalent chromium in Cr2O3 could be readily converted to hexavalent chromium at a temperature range of 200-300 degrees C, with conversion rates of up to 50% in 12 h. In aqueous media, Cr(OH)3 was slowly converted to dissolved Cr(VI) in the presence of MnO2, both in aerobic and anoxic conditions, with conversion rates of up to 1% in 60 days. In moist aerobic conditions and in the presence of MnO2, Cr(OH)(3) slowly converted to hexavalent chromium, with up to 0.05% conversion observed in 90 days. Chromium oxidation also occurred in sludge samples, especially under aerobic conditions. However, such transformation was found to be transitory, with the Cr(VI) formed being ultimately reduced back to Cr(III) due to the presence of various reducing agents in the sludge. Nevertheless since up to 17% conversion of Cr(III) to Cr(VI) occurred in sludge under aerobic conditions by 30 days, there is real danger under field conditions of spreading Cr(VI) pollution due to possible intervening rainfall, runoff and percolation.     

Hydrogen Release from Magnesium Hydride Subjected to Uniaxial Pressing

Materials Science - We study the process of hydrogen release from magnesium hydride under the conditions of uniaxial pressing in a vacuum at room temperature up to pressures of about 2.4 ton/cm2....     

Procedure and Setup for the Investigation of Composite Materials in Torsion at Temperatures up to 3300 K

A procedure and a setup are proposed for the investigation of strength properties of composite materials under torsion at temperatures of up to 3300 K in vacuum and in an oxidizing or inert medium. The setup is fitted with a system for the program heating of specimens to realize conditions that are close to the working conditions of the material. This makes it possible to carry out tests at a heating rate of about 500 deg/s with a uniform temperature field maintained along the specimen length.     

Application of the embedded-atom method to liquid copper

A procedure for calculating the embedded-atom method (EAM) potential with the use of diffraction data for the metal near its melting point has been applied to copper at temperatures from 1423 to 7400 K. In optimizing the parameters of the EAM potential, we used the pair correlation functions of copper at 1423 and 1873 K, the thermodynamic properties of liquid copper under ordinary conditions, and flash heating and shock compression results. Molecular dynamics simulation with the EAM potential adequately represents the thermodynamic properties and structural characteristics of liquid copper up to 1873 K. The simulated 1423-K bulk modulus is close to the experimentally determined one. At low pressures, the self-diffusion coefficient rises as a power law function of temperature with an exponent close to 2.10. The simulated melting point of copper, 1384 ± 3 K, is close to the actual one. Simulations were performed at temperatures of up to 7400 K and densities a factor of 1.6 higher than the normal one. The melting point was evaluated at pressures of up to 50 GPa. The EAM potential obtained is suitable for the liquid phase but fails to accurately describe properties of crystalline copper.     

The Viscosity and Density of <Emphasis Type="Italic">n</Emphasis>-Dodecane and <Emphasis Type="Italic">n</Emphasis>-Octadecane at Pressures up to 200 MPa and Temperatures up to 473 K

A vibrating-wire instrument for simultaneous measurement of the density and viscosity of liquids under conditions of high pressure is described. The instrument is capable of operation at temperatures between 298.15 and 473.15 K at pressures up to 200 MPa. Calibration was performed by means of measurements in vacuum, air, and toluene at 298.15 K. For n-dodecane measurements were made along eight isotherms between 298.15 and 473.15 K at pressures up to 200 MPa while for n-octadecane measurements were measured along seven isotherms between 323.15 and 473.15 K at pressures up to 90 MPa. The estimated uncertainty of the results is 2% in viscosity and 0.2% in density. Comparisons with literature data are presented.     

CECILIA,a versatile research tool for cellular responses to gravity

We describe a centrifuge designed and constructed according to current demands for a versatile instrument in cellular gravitational research, in particular protists (ciliates, flagellates). The instrument (called CECILIA,centrifuge forciliates) is suited for videomonitoring, videorecording, and quantitative evaluation of data from large numbers of swimming cells in a ground-based laboratory or in a drop tower/drop shaft under microgravity conditions. The horizontal rotating platform holds up to six 8mm-camcorders and six chambers holding the experimental cells. Under hypergravity conditions (up to 15 g) chambers can be rotated about 2 axes to adjust the swimming space at right angles or parallel to the resulting gravity vector. Evaluations of cellular responses to central acceleration — in the presence of gravitational 1 g — are used for extrapolation of cellular behaviour under hypogravity conditions. CECILIA is operated and monitored by computer using a custom-made soft-ware. Times and slopes of rising and decreasing acceleration, values and quality of steady acceleration are supervised online. CECILIA can serve as an on-ground research instrument for precursor investigations of the behaviour of ciliates and flagellates under microgravity conditions such as long-term experiments in the International Space Station.     

CECILIA, a versatile research tool for cellular responses to gravity

We describe a centrifuge designed and constructed according to current demands for a versatile instrument in cellular gravitational research, in particular protists (ciliates, flagellates). The instrument (called CECILIA,centrifuge forciliates) is suited for videomonitoring, videorecording, and quantitative evaluation of data from large numbers of swimming cells in a ground-based laboratory or in a drop tower/drop shaft under microgravity conditions. The horizontal rotating platform holds up to six 8mm-camcorders and six chambers holding the experimental cells. Under hypergravity conditions (up to 15 g) chambers can be rotated about 2 axes to adjust the swimming space at right angles or parallel to the resulting gravity vector. Evaluations of cellular responses to central acceleration — in the presence of gravitational 1 g — are used for extrapolation of cellular behaviour under hypogravity conditions. CECILIA is operated and monitored by computer using a custom-made soft-ware. Times and slopes of rising and decreasing acceleration, values and quality of steady acceleration are supervised online. CECILIA can serve as an on-ground research instrument for precursor investigations of the behaviour of ciliates and flagellates under microgravity conditions such as long-term experiments in the International Space Station.     

Characterization of Failure Mechanisms of Duplex and Graded Thermal Barrier Coatings Exposed to Thermal Shock Test

The beginning of failure of a (ZrO2-7%Y2O3)/(Ni-22%Co-17%Cr-12.5%Al-0.6%Y) duplex andgraded coating systems on lnconel 617 and IN738LC in burner rig tests has been characterized.The test conditions are 40 s heating up to 75O℃ substrate temperature followed by 80 s aircooling. Failure is considered at the appearance of the first bright spot during heating period.Stresses due to thermal expansion mismatch strains on cooling are the probable cause of life-limiting in this conditions of testing.     

Specific Heat Capacity of Liquid Zirconium up to 4100 K

The temperature dependence of the specific heat capacity of liquid zirconium is investigated experimentally at atmospheric pressure and at temperatures from 2128 to 4100 K. Measured under conditions of pulsed (microseconds) electric heating of foil samples are the electric resistance, the specific energy input (equal to specific enthalpy E), and the temperature (with the aid of a high-speed pyrometer and solid-state light guide). Use is made of the specific enthalpy dependence of temperature, previously obtained [1] for two options of blackbody model, developed for investigation of liquid carbon. The first one of those models is a square tube made up of four zirconium strips, with the light guide introduced at the tube end. The second model is made up of two strips of zirconium, with the light guide introduced on the side into the gap between the two strips (two-strip blackbody model). The temperature dependence of the heat capacity of liquid zirconium up to 4100 K is given for both blackbody models. The random and systematic errors of the measured quantities are given. The values of specific heat capacity are compared with the available experimental data for the near melting stage of the liquid zirconium, obtained using a steady-state technique.     

Testing of strain-gauge pressure transducers up to 3.5 MPa at cryogenic temperatures and in magnetic fields up to 6 T

The characteristics of four commercial strain-gauge pressure transducers suitable for measurements in a temperature range from 4.2 to 293 K were determined in the presence of magnetic fields up to 6 T. The highest pressure measured was 3.5 MPa. Tests showed that if the transducers are used in these conditions and no corrections are made, uncertainties up to 19% of the transducer full scale may be inherent in measurements. When such high error levels are unacceptable, the transducers must be individually calibrated under the working conditions: in this way the uncertainties in pressure measurements can usually be kept below 1 % of the transducer full scale.     

Silicon coating treatment to improve high temperature corrosion resistance of 9%Cr steels

Abstract

A silicon coating process is described which confers good protection on 9% Cr steels and alloys in CO₂ based atmospheres at high temperatures and pressures. The coatings are formed by decomposition of silane at temperatures above 720 K. Protective layers are typically up to 1 μm thick. The optimum coating conditions are discussed. The chemical state of the coatings has been investigated by X-ray photoelectron spectroscopy and has demonstrated the importance of avoiding silicon oxide formation during processing. Corrosion testing has been carried out for extended periods, up to 20 000 h, at temperatures between 753 and 853 K, in a simulated advanced gas cooled reactor gas at 4 MPa pressure. Benefit factors of up to 60 times have been measured for 9% Cr steels. Even higher values have been measured for 9Cr–Fe binary alloy on which a 1 μm coating was sufficient to eliminate significant oxidation over 19 000 h except at the specimen edges. The mechanism of protection is discussed. It is suggested that a silicon surface coating for protecting steels from high temperature corrosion has some advantages over adding silicon to the bulk metal.

MST/1090     

A Fast Method to Calculate the Oil Droplet Velocity in Aero Engine Bearing Chambers

The oil droplet velocity in an aero engine bearing chamber can determine the initial film state which is the fundament for lubrication design and heat analysis. This paper studied the droplet motion in a respective aero engine bearing chamber and obtained a fast method to calculate the droplet velocity by an analytical method. Comparing the velocity results calculated by the fast method with those from the literatures by the numerical method under different operating conditions, the method proposed in this paper is confirmed to be fast and reliable. The effects of operating conditions on droplet velocity are obtained at the same time. This study contribute to follow-up research work on droplet deposition properties in aero engine bearing chambers     

Viscosity of Gaseous HFC-143a (1,1,1-trifluoroethane) Under High Pressures

The viscosity of gaseous HFC-143a(1,1,1-trifluoroethane) was measured with an oscillating-disk viscometer of the Maxwell type at temperatures from 298.15 to 423.15 K and at pressures up to the saturated vapor pressure at each temperature under subcritical conditions or up to 9 MPa under supercritical conditions. Intermolecular potential parameters of HFC-143a for the extended corresponding states were determined from the viscosity data at 0.1 MPa. An empirical viscosity equation as functions of temperature and density is proposed to interpolate the present experimental results.     

Photothermal properties of gold nanoparticles under exposure to high optical energies

Photothermal (PT) efficacy and damage thresholds of gold nanoparticles (NP)-spheres, rods and silica-gold shells-were experimentally studied during their excitation with nanosecond laser pulses at the fluence levels at and above the NP damage threshold. The maxima of PT efficacy of gold NPs with near-infrared (NIR) plasmon resonances (gold rods and shells) and the minima of their damage thresholds were found to be shifted from their plasmon resonance NIR wavelengths into non-resonant visible wavelengths. This suppression of PT efficacy of NIR plasmon resonances (bleaching) was found to be up to 18 times for the rods and up to 22 times for the shells. During laser-induced deterioration the NPs maintained their PT properties at least within 40-150?ns after exposure to laser pulses. PT properties of the gold NPs can be enhanced with the pulse train mode within the above time. The PT bubbles generated around superheated NPs were used as their optical markers and allowed us to quantify PT efficacy of plasmon resonance through the bubble parameters under the conditions when other methods of NP detection are not applicable.     

Ice loads on offshore structures: The transition from creep to fracture

During landfast winter ice conditions an offshore structure experiences loads due to static wind-driven sea ice. The load is generally not applied suddenly, but gradually increases as winds build up during the course of minutes or hours. Typical stress-rates for a structure 100 m wide are 0.02 kPa s⁻¹ and extreme stress-rates may be 1–5 kPa s⁻¹. Laboratory investigations by Sinha (1983) enable us to predict the onset of crack formation in ice as stress increases, using a delayed elastic strain criterion (Sinha, 1982). If we apply this criterion to realistic offshore cases, we find that first cracks in ice should typically occur at 0.4–0.7 MPa and in extreme conditions may occur at 0.8–1.8 MPa. We speculate that complete failure of the ice should occur soon afterwards. This would explain why existing measurements of winter ice forces on offshore structures seldom exceed 1 MPa. We cannot, however, exclude the possibility that higher stress-rates and higher stresses could, under different conditions, be achieved.     

Analytical solution to predict laser ablation rate in a graphitic target

Laser ablation is a process very useful to obtain many kinds of nanoparticles, included single wall carbon nanotubes (SWNTs). The control of the process, with the aim of determining the temperature conditions during ablation, is required to previously determine the formation and dynamic of growth of nanoparticles. An analytical method to predict the ablation rate is a starting point to set up the experimental conditions, to allow the predefinition of the nanoparticles produced with laser ablation. An ablation method using a pulsed Nd:YAG laser was carried out to ablate a target of graphite, which was irradiated with a laser energy density of 10 J/cm² at a temperature of 1,273 K under a controlled atmosphere of Ar. The ablation rate and the heat conduction in the target were studied through an appropriate heat balance method that offers an analytical solution and seems to be very appropriate to describe the ablation conditions. The predictions of ablation rate are in very good agreement with the experimental data.     

Comparative effects of humid tropical weathering and artificial ageing on a model composite properties from nano- to macro-scale

The effects of humid tropical conditions and artificial ageing tests on a UD glass-fibre/epoxy composite are compared at different scales. A modified network of 500 nm width around each fibre is identified by AFM force measurements. The evolution of this interphase is correlated to the composite embrittlement observed in transverse bending tests during ageing. DSC and DMA show up the matrix plasticization under tropical conditions and hygrothermal ageing. Chain scissions are also involved under artificial and natural UV exposure on surface layers and photoproducts are identified by FTIR analysis. The effects of artificial and natural hygrothermal conditions are emphasised inside interphases. The interfacial areas situated close to the composite surface are highly degraded by UV radiation. Cracks can then be initiated in these areas during bending tests. Finally, AFM force measurements highlight synergistic effects during natural weathering due to the combined effects of UV radiation and hygrothermal conditions.     

A Simple Method for Grain Refinement of Pure Aluminium

In order to produce the fully equiaxed and fine grained pure Al, a simple casting process that used cooling slope was examined and compared with conventional casting process under same casting conditions. By using cooling slope, grains over the whole section of castings were suddenly refined and ability of grain refinement kept up at very high mold temperature up to 550癈 in examined casting conditions.     

Application of Fenton oxidation to cosmetic wastewaters treatment

The removal of organic matter (TOC and COD) from a cosmetic wastewater by Fenton oxidation treatment has been evaluated. The operating conditions (temperature as well as ferrous ion and hydrogen peroxide dosage) have been optimized. Working at an initial pH equal to 3.0, a Fe(2+) concentration of 200 mg/L and a H(2)O(2) concentration to COD initial weight ratio corresponding to the theoretical stoichiometric value (2.12), a TOC conversion higher than 45% at 25 degrees C and 60% at 50 degrees C was achieved. Application of the Fenton oxidation process allows to reach the COD regional limit for industrial wastewaters discharges to the municipal sewer system. A simple kinetic analysis based on TOC was carried out. A second-order equation describes well the overall kinetics of the process within a wide TOC conversion range covering up to the 80-90% of the maximum achievable conversion.     

Supersensitivity due to uncertain boundary conditions

We study the viscous Burgers' equation subject to perturbations on the boundary conditions. Two kinds of perturbations are considered: deterministic and random. For deterministic perturbations, we show that small perturbations can result in O(1) changes in the location of the transition layer. For random perturbations, we solve the stochastic Burgers' equation using different approaches. First, we employ the Jacobi‐polynomial‐chaos, which is a subset of the generalized polynomial chaos for stochastic modeling. Converged numerical results are reported (up to seven significant digits), and we observe similar ‘stochastic supersensitivity’ for the mean location of the transition layer. Subsequently, we employ up to fourth‐order perturbation expansions. We show that even with small random inputs, the resolution of the perturbation method is relatively poor due to the larger stochastic responses in the output. Two types of distributions are considered: uniform distribution and a ‘truncated’ Gaussian distribution with no tails. Various solution statistics, including the spatial evolution of probability density function at steady state, are studied. Copyright © 2004 John Wiley & Sons, Ltd.