Catalytic packed bed non‐thermal plasma reactor for the extraction of hydrogen from hydrogen sulfide

The decomposition of hydrogen sulfide (H₂S) to hydrogen and sulfur with Al₂O₃, MoO_x/Al₂O₃, CoO_x/Al₂O₃ and NiO/Al₂O₃ packed non‐thermal plasma dielectric barrier discharge reactor was studied. The reaction was carried out with 5‐mm discharge gap during the decomposition of 5 vol.% H₂S at 150 ml/min (STP) flow rate. Typical results indicated the conversion of ~50% at a specific input energy of ~0.92 kJ/l H₂S and 10% (in length) packed reactor showed the best conversion. Among the catalysts studied, MoO_x and CoO_x supported on Al₂O₃ showed high performance, which may be caused by synergy between plasma excitation of the carrier gas molecules and catalytic behaviour of MoO_x and CoO_x. Copyright © 2012 John Wiley & Sons, Ltd.     

Materials issues in nuclear-waste management

In this article, materials issues in the management of nuclear waste, including its generation, processing, storage, transport, and disposal, are examined for low-level and high-level waste, with an emphasis on the aspects of their immobilization and long-term isolation. Selecting materials for low-level and high-level waste form and containers is reviewed, and the long-term performance issues with these materials as barriers to nuclide migration or release are discussed. Editor’s Note: A hypertext-enhanced version of this article is available on the web at www.tms.org/pubs/journals/JOM/0009/Yim-0009.html. For more information, contact M.-S. Yim, North Carolina State University, Department of Nuclear Engineering, Raleigh, North Carolina 27695-7909; (919) 515-1466; fax (919) 515-5115; e-mail yim@ncsu.edu.     

Creep deformation behavior of Sn–Zn solder alloys

Creep properties of three Sn–Zn solder alloys (Sn–9Zn, Sn–20Zn, and Sn–25Zn, wt%) were studied using the impression creep technique. Microstructural characteristics were examined using a scanning electron microscope. The alloys exhibited stress exponents of about 5.0. The activation energy for creep was calculated to be ~50–75 kJ/mol with a mean value of 66.3 kJ/mol. The likely creep mechanism was identified to be the low temperature viscous glide of dislocations.     

Transitions in creep mechanisms and creep anisotropy in Zr---1Nb---1Sn---0.2Fe sheet

The creep characteristics of a Zr---1Nb---1Sn---0.2Fe alloy sheet were investigated at temperatures from 773 to 923 K and at stresses ranging from 9 to 150 MPa along both the rolling and transverse directions. Transitions in creep mechanisms are noted, with diffusional viscous creep at low stresses, viscous-glide-controlled microcreep in the intermediate stress regime and the climb of edge dislocations at high stresses. The creep anisotropy decreases with a decrease in the stress exponent and the creep rates differ by only 30% in the viscous creep regime, while an order-of-magnitude difference is noted at high stresses. The solute-strengthening effect of Nb addition is evident in the stress regime where appropriate data are available. These transitions in creep mechansims clearly reveal the dangers in blind extrapolation of short-term high stress data to low stresses and long times relevant to in-reactor conditions. The creep behavior of these materials is similar to that noted in Class I alloys, while the transitions in deformation mechanisms in Zircaloy-4 resemble those found in pure metals or Class II alloys with no viscous glide mechanism.     

Tensile, creep, and ABI tests on sn5%sb solder for mechanical property evaluation

Sn5%Sb is one of the materials considered for replacing lead containing alloys for soldering in electronic packaging. We evaluated the tensile properties of the bulk material at varied strain-rates and temperatures (to 473K) to determine the underlying deformation mechanisms. Stress exponents of about three and seven were observed at low and high stresses, respectively, and very low activation energies for creep (about 16.7 and 37.7 kJ/mole) were noted. A maximum ductility of about 350% was noted at ambient temperature. Creep tests performed in the same temperature regime also showed two distinct regions, albeit with slightly different exponents (three and five) and activation energy (about 54.4 kJ/mole). Ball indentation tests were performed on the shoulder portions of the creep samples (prior to creep tests) using a Stress-Strain Microprobe^@ (Advanced Technology Corporation) at varied indentation rates (strain-rates). The automated ball indentation (ABI) data were at relatively high strain-rates; however, they were in excellent agreement with creep data, while both these results deviated from the tensile test data. Work is planned to perform creep at high stresses at ambient and extend ABI tests to elevated temperatures.     

Modified transform-based gamma correction for MRI tumor image denoising and segmentation by optimized histon-based elephant herding algorithm

Medical image processing is typically performed to diagnose a patient's brain tumor prior to surgery. In this study, a technique in denoising and segmentation was developed to improve medical image processing. The proposed approach employs multiple modules. In the first module, the noisy brain tumor image is transformed into multiple low- and high-pass tetrolet coefficients. In the second module, multiple low-pass tetrolet coefficients are applied through a modified transform-based gamma correction method. Generalized cross-validation is used on multiple high-pass tetrolet coefficients to obtain the best threshold value. In the third module, all enhanced coefficients are applied to the partial differential equation method. In the final module, the denoised image is applied to Atanassov's intuitionistic fuzzy set histon-based fuzzy clustering method with centroid optimization using an elephant herding method. Accordingly, the tumor part is segmented from the nontumor part in the magnetic resonance imaging brain images. The method was assessed in terms of peak signal-to-noise ratio, mean square error, specificity, sensitivity, and accuracy. The experimental results showed that the suggested method is superior to traditional methods.     

Electrical and magnetic properties of nanocrystalline BiFeO3 prepared by high energy ball milling and microwave sintering

A new synthesis route with high energy ball milling and microwave sintering is used to obtain nanocrystalline BiFeO3 with improved dielectric and magnetic properties. Electrical and magnetic properties are compared with a conventionally sintered microcrystalline BiFeO3. It is found that the dielectric constant is increased more than one order of magnitude, electrical resistivity by six orders of magnitude and remnant polarization value is increased by 4-5 times for nanocrystalline BiFeO3 in comparison to conventionally sintered microcrystalline BiFeO3. Nanocrystalline BiFeO3 is seen to have ferromagnetic behavior whereas microcrystalline BiFeO3 is known to be antiferromagnetic.     

Two-Stage Clathrate Hydrate/Membrane Process for Precombustion Capture of Carbon Dioxide and Hydrogen

A hybrid process for the capture of CO2 and H2 from a treated fuel gas mixture is presented. It consists of two hydrate crystallization stages operating at 273.7?K and 3.8 and 3.5?MPa, respectively. The CO2-lean stream from the first stage is directed to a membrane separation unit whereas the CO2-rich one is directed to the second hydrate stage. These operating pressures at the crystallization stages are possible by adding 2.5% by mole propane. Propane enables the reduction in the hydrate formation pressure and thus reduces the cost associated with the compression of the fuel gas. The two hydrate stages would operate at 7.5 and 3.5?MPa without adding propane. This work provides the relevant kinetic data, as well as the separation efficiency and recoveries achieved.