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Ur Rehman, Zeeshan,Lee, Dong-Gun,Koo, Bon Heun Materials Research Society of Korea 2015 한국재료학회지 Vol.25 No.10
In this work, ceramic coatings were prepared on Al7075 aluminum alloy using microarc oxidation (MAO) process in a silicate-fluoride based electrolyte solution. The effect of $OH^-$ concentration, by adding NaOH to the solution on the microstructural and mechanical properties of the coating was investigated. Surface morphology and cross sectional view of the coating was analyzed using SEM while XRD was used to examine the phase compositions of the coatings. From XRD ${\alpha}-Al_2O_3$ phase was found to be increased by adding NaOH to the electrolyte. Thereby, the hardness and the wear properties of the MAO coatings were found to be superior to those of the coatings prepared without NaOH addition or with amount maximum than 2 g/l NaOH. Moreover, the morphology of the coatings was transformed form nodule-based cluster to crater based structure with the addition of NaOH to the MAO electrolyte solution.
Rehman, Saeed Ur,Shaur, Ahmad,Song, Rak-Hyun,Lim, Tak-Hyoung,Hong, Jong-Eun,Park, Seok-Joo,Lee, Seung-Bok Elsevier 2019 Journal of Power Sources Vol.429 No.-
<P><B>Abstract</B></P> <P>The cost-effective fabrication of nanostructured cathodes for solid oxide fuel cells (SOFCs) that catalyze the oxygen reduction reaction effectively is a milestone to be achieved. Infiltration being the conventional method for the fabrication of nanostructured SOFC cathodes requires many infiltration and calcination cycles due to the low catalyst loading per infiltration cycle. Chemically assisted electrodeposition (CAED), a new means of fabricating nanostructured SOFC cathodes in a single loading step, provides the advantage of the simultaneous deposition of multiple cations while using dilute aqueous solutions of readily available salts. In this study, CAED is demonstrated by fabricating a cobalt-free LaNiO<SUB>3</SUB>/GDC composite cathode. The LaNiO<SUB>3</SUB>/GDC composite cathode prepared by CAED exhibits superior electrochemical properties compared to LaNiO<SUB>3</SUB>/GDC composite cathodes fabricated by sintering or self-assembly (a recently introduced low-temperature SOFC cathode fabrication method) approaches. An anode-supported SOFC with a LaNiO<SUB>3</SUB>/GDC composite cathode fabricated by CAED shows a high power density of 974 mW cm<SUP>−2</SUP> at an intermediate operating temperature of 750 °C. Low-temperature nano-fabrication by CAED, producing a cathode with a high surface area while avoiding the formation of insulating phases, is believed to play an important role in achieving better SOFC performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> LaNiO<SUB>3</SUB> was successfully nanofabricated by chemically assisted electrodeposition. </LI> <LI> Chemically assisted electrodeposition enabled LaNiO<SUB>3</SUB> incorporation in a single step. </LI> <LI> LaNiO<SUB>3</SUB> showed a uniform morphology throughout the body of the cathode layer. </LI> <LI> Nanofabricated LaNiO<SUB>3</SUB> cathode showed a performance of 974 mWcm<SUP>−2</SUP> at 750 °C. </LI> <LI> Chemically assisted electrodeposition shows promise for SOFC electrode fabrication. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Rehman, Saeed Ur,Song, Rak-Hyun,Lim, Tak-Hyoung,Park, Seok-Joo,Hong, Jong-Eun,Lee, Jong-Won,Lee, Seung-Bok Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.16
<P>In this study, a new method is developed for the fabrication of nanofibrous LaCoO3 (LCO) perovskites as cathodes (oxygen electrodes) for solid oxide fuel cells (SOFCs). The proposed method involves chemically assisted electrodeposition (CAED) of mixed metal hydroxide onto a carbon nanotube (CNT) template, followed by a low-temperature heat-treatment process. The CNT template is first fabricated on porous zirconia-based ion-conducting scaffolds (ICS) by catalytic chemical vapor deposition (CCVD) of C2H4. Perovskite-type LCO is then fabricated on the CNT template by CAED process of mixed La-Co hydroxide combined with thermal conversion of hydroxide to perovskite oxide. The method proposed here allows for the fabrication of LCO perovskites with a unique nanofibrous structure at reduced temperatures (∼900 °C), while avoiding the formation of pyrochlore phases (<I>e.g.</I>, La2Zr2O7), which are typically observed during conventional high-temperature sintering processes of LaCoO3 with zirconia-based electrolytes. The new method also provides the precise control needed to achieve desired oxide loadings without the need for repeated deposition-annealing processes. The anode-supported SOFCs with nanofibrous LCO cathodes on zirconia and ceria scaffolds show high and stable electrochemical performance of 0.95 and 1.27 W cm<SUP>−2</SUP>, respectively, at 800 °C. In addition to the absence of insulating pyrochlore phases, the unique nanostructure of the LCO cathode is believed to play a beneficial role in improving the electrochemical properties by providing a large number of active reaction sites and by facilitating mass transport through the porous nanofibrous structure.</P>
Identities in a Prime Ideal of a Ring Involving Generalized Derivations
ur Rehman, Nadeem,Ali Alnoghashi, Hafedh Mohsen,Boua, Abdelkarim Department of Mathematics 2021 Kyungpook mathematical journal Vol.61 No.4
In this paper, we will study the structure of the quotient ring R/P of an arbitrary ring R by a prime ideal P. We do so using differential identities involving generalized derivations of R. We enrich our results with examples that show the necessity of their assumptions.
Rehman, Hafeez Ur,Noh, Heung-Ryoul,Kim, Jin-Tae Elsevier 2017 OPTICS COMMUNICATIONS - Vol.402 No.-
<P><B>Abstract</B></P> <P>We have investigated velocity selective spectral profile variations of probe beam transmittance at <SUB> F g </SUB> = 3 → <SUB> F e </SUB> = 2 , 3 , and 4 hyperfine manifolds of <SUP> 85 </SUP> Rb atoms along with coherence effects at the <SUB> F g </SUB> = 3 → <SUB> F e </SUB> = 4 transition with various coupling laser polarization configurations and a fixed probe polarization ( <SUP> σ + </SUP> ). Laser linewidth, atomic velocity distributions, frequency mixing of the coupling and probe laser beams between degenerate magnetic sublevels, and polarization variations of the coupling beam with the probe beam fixed at the <SUB> F g </SUB> = 3 → <SUB> F e </SUB> = 4 transition were used to simulate the line profiles. The calculated transmittance signals are in good agreement with observed signals for each coupling laser polarization configuration.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We investigate velocity selective optical pumping spectroscopy for <SUP> 85 </SUP> Rb atoms. </LI> <LI> We consider laser linewidth and frequency mixing of lasers in the calculation. </LI> <LI> The experimental results are compared with calculated results. </LI> </UL> </P>