In-situ measurement of ethanol tolerance in an operating fuel cell

Ethanol is seen as an attractive option as a fuel for direct ethanol fuel cells and as a source for on-demand production of hydrogen in portable applications. While the effect of ethanol on in-situ electrode behavior has been studied previously, these efforts have mostly been limited to qualitative analysis. In alkaline fuel cells, several cathode catalysts, including Pt, Cu triazole, and Ag can be used. Here, we apply a methodology using a microfluidic fuel cell to analyze in-situ the performance of these cathodes as well as Pt anodes in the presence of ethanol and acetic acid, a common side product from ethanol oxidation. For a given concentration of ethanol (or acetic acid), the best cathode catalyst can be determined and the kinetic losses due to the presence of ethanol (or acetic acid) can be quantified. These experiments also yield information about power density losses from the presence of contaminants such as ethanol or acetic acid in an alkaline fuel cell. The methodology demonstrated in these experiments will enable in-situ screening of new cathodes with respect to contaminant tolerance and determining optimal operational conditions for alkaline ethanol fuel cells.     

Optimizing the overall configuration of a He-cooled W-alloy divertor for a power plant

A number of different He-cooled divertor configurations have been proposed for magnetic fusion energy (MFE) power plant application. They range in scale from a plate configuration with characteristic dimension of the order of 1 m, to the ARIES-CS T-tube configuration with characteristic dimension of the order of 10 cm, to the EU FZK finger concept with characteristic dimension of the order of 1.5 cm. All these designs utilize tungsten or tungsten alloy as structural material. This paper considers the characteristics of the different divertor configurations and proposes the possibility of optimizing the design by combining different configurations in an integrated design based on the anticipated divertor heat flux profile.     

Reactive ion etching of PECVD silicon nitride in SF6 plasma

The reactive ion etching of PECVD silicon nitride thin films has been investigated using SF₆ plasma. Effects of variations of process parameters such as pressure (50–350 mTorr), RF power (50–250 W), gas flow rate (3–130 sccm) and additions of O₂ and He (0–50%) in SF₆, on the PECVD silicon nitride etch rate and selectivity to the AZ 1350J photoresist were examined. An etch rate of 1 μm/min has been obtained under the condition of 150 mTorr, 100 W and 60 sccm. Experimental results also indicated a maximum etch rate at approximately 30% O₂ while addition of He showed only dilution effect. A nitride/photoresist selectivity ranging from 1 to 3:1 has been obtained.     

A finite element method for neutron transport—III. Two-dimensional one-group test problems

The even-parity transport equation for an isotropic scattering medium is applied using a maximum principle to determine the angular flux in a square lattice cell with a cylindrical fuel element, a square isotropic source in a corner of an absorbing shield and a dog-leg duct through an absorbing shield. The finite element solutions obtained are compared with an exact solution for the cell, and benchmark results for the square source and duct problem. The accuracies achieved for the fluxes in the cell problem are everywhere better than 0.75% and high accuracy is achieved for the other test problems. The linear elements, used for the spatial dependence of the angular flux in conjunction with a spherical harmonic expansion for the angular dependence, provide a flexible means of treating awkward geometries. At present the equations are assembled and solved using the UNCLE code, which uses direct Gaussian elimination. This process limits the speed of the finite element method to about 1/3 of the Fletcher finite difference spherical harmonics method for the square source problem. This latter method is, however, limited to systems with geometries defined by co-ordinate surfaces, whereas the finite element method can be used for any region that can be triangulated.     

Kinetics of initial stage of sintering of UO2 and UO2 with Nd2O3 addition

The kinetics of initial stage sintering of UO₂ powder were reinvestigated, using Ar-10% H₂ atmosphere. The effect of the addition of neodynium oxide was studied. The results revealed that surface and grain boundary diffusion mechanisms act simultaneously. The values of activation energies were found to be $\text{48.48 ± 3.51 kcal/mole}$ in the temperature range 870–942°C and $\text{89.88 ± 9.87 kcal/mole}$ in the temperature range of 942–1030°C for UO₂, and $\text{115.61 ± 7.77 kcal/mole}$ in the temperature range 1030–1150°C for UO₂ + Nd₂O₃. An important decrease in the calculated diffusion coefficient occurs by the addition of Nd₂O₃.     

Spontaneous fission activities

For several years, the Nuclear Data Project has been using a standard computer-readable format¹ to organize the results of data evaluations published in Nuclear Data Sheets. Adopted values for level energies, spins, half-lives, radiation properties, and spectroscopic factors are recorded in standard blocks of information, which are then filed onto indexed direct-access storage. The resulting Evaluated Nuclear Structure Data File (ENSDF) is then available as a standard source of nuclear structure information.² Computer organization of selected data into pages has been a feature of Nuclear Data Sheets since 1975.As an illustration of the power and potential usefulness of the ENSDF system, we present a collection of nuclear levels for which the spontaneous fission has been studied. The values tabulated have appeared in recent issues of Nuclear Data Sheets.³ The selection of values and arrangement into a table has been done completely automatically. We welcome comments and criticisms about the form or content of this table.     

Determination of deuterium in dead-sea water by nuclear methods

By using the D(d, p)³H nuclear reaction combined with the Rutherford-backscattering method, the amount of D₂O in relation to H₂O in water from the Dead Sea is measured. The amount of deuterium in the samples is determined from the integrated yield of the D(d, p)³H reaction in relation to the ¹⁶O(d, p₀)¹⁷O or ¹⁶O(d, p₁)¹⁷O reaction. For the low deuteron energies used (E 0.63 MeV), the differential cross section of the ¹⁶O(d, p₀)¹⁷O reaction was determined experimentally. No significant change of deuterium concentration in Dead-Sea water down to a depth of 36 m could be detected.     

Break opening times for axial rupture of a gas-pressurised pipe

The consequences of a major rupture of a pressurised pipe are strongly influenced by the break characteristics (i.e. fracture orientation, opening time and final breah area). For example, the amplitude of the blast wave generated in the external atmosphere is dictated by the rate at which energy is released through the developing breach and hence is a function of opening time. A pipe is assumed to be fully open when the breach area is twice the cross-sectional area of the pipe, thus allowing full flow from each leg of the pipe.This paper describes experiments where the development of an axial rupture in large gas-pressurised steel pipes was observed by high speed photography. The tests were performed on 610 mm diameter pipes, with wall thicknesses of either 6.2 mm or 9.3 mm, apart from the final test where a 915 mm diameter, 12.5 mm wall thickness pipe was ruptured. Rupture pressures ranged from 19 bar to 40 bar.Measured breach opening times are compared with data from earlier small scale tests (102 mm diameter pipes with 1.6 mm wall thickness) where rupture pressure ranged from 50 bar to 120 bar. Both sets of data are shown to be in general agreement with a theoretical model which combines an upper limit ductile fracture propagation velocity with a simple inertia model for the displacement of the free edges of the breach. For large pipes the measured and predicted opening times are significantly longer than the maximum of 1 ms specified in the current US design codes.     

Design of polymeric dispersants for waterborne coatings

Block and random copolymers of ammonium methacrylate and dimeth-ylaminoethyl methacrylate have been synthesized and tested as dispersants of various organic and inorganic pigments in formulations for waterborne paints. Blockiness of the co-monomer distribution is a prerequisite for good color characteristics in the final paint. It is however noteworthy that a tapered diblock (one-step anionic synthesis), a diblock copolymer with a regular change in composition from one block to the other one, has an interfacial activity quite comparable to the parent “pure” diblock copolymer (two-step anionic synthesis). The most interesting observation is that the poly(dimethylaminoethyl methacrylate) anchoring block can impart stability to dispersions of pigments as different as iron oxide, a blue Cu-phthalocyanine pigment, and a red organic pigment based on pyrrole in representative aqueous paint formulations. This type of diblock copolymer is promising for the design of universal dispersants. Center for Education and Research on Macromolecules (CERM), Sart-Tilman, B6, 4000 Liège, Belgium. Rijksstraatweg 31, P.O.Box 3, 2170 BA Sassenheim, The Netherlands.