Pseudocapacitive Properties of Isostructural Oxides Sr2LaBMnO7 (B=Co,Fe)

Pseudocapacitors promise to fill the gap between traditional capacitors and batteries by delivering reasonable energy densities and power densities. In this work, pseudocapacitive charge storage properties are demonstrated for two isostructural oxides, Sr₂LaFeMnO₇ and Sr₂LaCoMnO₇. These materials comprise spatially separated bilayer stacks of corner sharing BO₆ units (B=Fe, Co or Mn). The spaces between stacks accommodate the lanthanum and strontium ions, and the remaining empty spaces are available for oxide ion intercalation, leading to pseudocapacitive charge storage. Iodometric titrations indicate that these materials do not have oxygen-vacancies. Therefore, the oxide ion intercalation becomes possible due to their structural features and the availability of interstitial sites between the octahedral stacks. Electrochemical studies reveal that both materials show promising energy density and power density values. Further experiments through fabrication of a symmetric two-electrode cell indicate that these materials retain their pseudocapacitive performance over hundreds of galvanostatic charge-discharge cycles, with little degradation even after 1000 cycles.     

Sr3Mn2O6 and Sr3FeMnO6 for oxygen and hydrogen evolution electrocatalysis

Journal of Solid State Electrochemistry - Quasi-two-dimensional oxides Sr3Mn2O6 and Sr3FeMnO6 have been synthesized and their bifunctional electrocatalytic activity toward both half-reactions of...     

Current trends in direct transformation of waste printed circuit boards (WPCBs) into value-added materials and products

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High-accuracy measurement of specular spectral reflectance and transmittance

The realization of spectrophotometric quantities at the Helsinki University of Technology is based on our reference spectrometer. The reference spectrometer is a high-accuracy instrument developed for measuring spectral specular transmittance and reflectance in a wavelength range extending from ultraviolet to near-infrared. The relative uncertainty estimates for transmittance measurements of neutral-density filters are ca. 0.05%. For spectral reflectance the estimated uncertainties are between 0.14% and 0.34% depending on the sample reflectance and the measurement geometry. We have derived and verified equations that enable both the reflectance and transmittance of various samples to be predicted. Utilizing these equations, the reflectance and transmittance can be accurately calculated for samples with known refractive index. For precise calculations, the characteristics of the measurement beam must be taken into account.     

Crystal and magnetic structures of the brownmillerite compound Ca2Fe1.039(8)Mn0.962(8)O5

The crystal and magnetic structures of the brownmillerite material, Ca₂Fe_1.039(8)Mn_0.962(8)O₅ were investigated using powder X-ray and neutron diffraction methods, the latter from 3.8 to 700 K. The compound crystallizes in Pnma space group with unit cell parameters of a=5.3055(5) Å, b=15.322(2) Å, c=5.4587(6) Å at 300 K. The neutron diffraction study revealed the occupancies of Fe³⁺ and Mn³⁺ ions in both octahedral and tetrahedral sites and showed some intersite mixing and a small, ∼4%, Fe excess. While bulk magnetization data were inconclusive, variable temperature neutron diffraction measurements showed the magnetic transition temperature to be 407(2) K below which a long range antiferromagnetic ordering of spins occurs with ordering wave vector k=(000). The spins of each ion are coupled antiferromagnetically with the nearest neighbors within the same layer and coupled antiparallel to the closest ions from the neighboring layer. This combination of intra- and inter-layer antiparallel arrangement of spins forms a G-type magnetic structure. The ordered moments on the octahedral and tetrahedral sites at 3.8 K are 3.64(16) and 4.23(16) μ_B, respectively.     

Radar Absorption Properties of Ni0.5Zn0.5Fe2O4/PANI/epoxy Nanocomposites

A nitrate? citrate gel was prepared from metallic nitrates and citric acid by sol? gel process and was further used to synthesize Ni_0.5Zn_0.5Fe₂O₄ nanocrystalline powder by auto‐combustion. Then, two novel 15 and 35% (w/w) magnetic Ni_0.5Zn_0.5Fe₂O₄ containing polyaniline nanocomposites, named as PANI‐Ni15 and PANI‐Ni35, respectively, were prepared via in‐situ polymerization of aniline in an aqueous solution containing proper amount of Ni_0.5Zn_0.5Fe₂O₄ magnetic powder. The incorporation of the nanopowders to PANI matrix was confirmed by X‐ray diffraction (XRD), IR and SEM. Synthesized PANI‐NiZn ferrite composite particles were subsequently added to an epoxy resin matrix to produce related nanocomposites. The morphological properties of these nanocomposite materials were investigated by SEM and TEM. The electromagnetic‐absorbing properties were studied by measuring the reflection loss in the frequency range of 8.0 to 12.0 GHz. Results showed the reflection loss of the PANI‐Ni35 composite is higher than pure polyaniline and PANI‐Ni15. The good reflection loss of the nanocomposites suggests their potential applicability as radar absorber.     

Fabrication of Al/AlN nano‐composite layers by friction stir processing of 6061 Al‐T6 substrate

Friction stir processing was employed for the production of Al/AlN nano‐composite layers on a 6061 Al‐T6 substrate. Nano‐sized AlN powder was inserted in a groove in the middle length of the substrate. Defect‐free layers were achieved using tool rotation and substrate advancing speeds in the range of 900–1400 rpm and 63–310 mm/s, respectively. Subsequent passes were conducted to break‐up AlN clusters that formed in a non‐uniform fashion after initial pass. The grain size of aluminum matrix was found to decrease by the introduction of AlN powder. A nano‐composite layer with near uniform dispersion of nano‐sized AlN reinforcements with a ~9.6% volume fraction was achieved in a matrix of fine dynamically restorated Al grains with a mean size of ~2.5 µm after three subsequent passes. This layer showed an average micro hardness value of ~164 HV (much greater than ~103 HV of the underlying substrate). In addition, the nano‐composite layer exhibited superior dry sliding wear performance against hardened steel compared to that of 6061‐T6 substrate. Increasing tool rotation and substrate advancing speeds were found to decrease the AlN content of the processed layer possibly due to increasing in powder scattering by the pin tool. This was associated with a decrease and increase in hardness values and wear‐loss data, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

Zirconium(IV) chloride as versatile catalyst for the expeditious synthesis of quinoxalines and pyrido[2,3-<Emphasis Type="Italic">b</Emphasis>]pyrazines under ambient conditions

Abstract  

Among the various transition metal chlorides, zirconium(IV) chloride was found to be an efficient catalyst for the rapid synthesis of a wide range of 2,3-dialkyl- and 2,3-diaryl-quinoxaline and pyrido[2,3-b]pyrazine derivatives in excellent yields at room temperature. The remarkable features of this catalytic process are the mild reaction conditions, quantitative yields, short reaction times, high conversions, tolerability of various functional groups, clean reaction profiles, and operational simplicity.     

可重复使用的新型催化剂的合成、表征及在绿色条件下催化Suzuki和Heck反应:锚合在磁性纳米多孔的MCM-41上Pd(0)希夫碱络合物

将Pd希夫碱络合物固定在磁性的MCM-41表面上,做为环境友好且可循环使用的新型多相纳米催化剂,并采用红外光谱、振动探针式磁强计、能量散射谱、透射电镜、扫描电镜、热重、电感耦合等离子体发射光谱和X-射线衍射等对其进行了全面的表征.然后将该催化剂用于以PEG为绿色溶剂的一步法Suzuki和Heck合成反应中,均以较高收率得到目标产物.该法主要优点为反应时间短、反应条件绿色友好、操作简便、无需使用有毒的有机溶剂、催化剂使用量低,且底物适用性广.更为重要的是,通过外部磁场即可方便地将催化剂从反应混合物中分离出来,可重复使用数次而活性和稳定性未见明显下降.     

Microwave Assisted Mannich Reaction of Terminal Alkynes on Alumina

 Terminal alkynes, secondary amines, and formaldehyde undergo a Mannich reaction at room temperature in the presence of CuCl on Al₂O₃ without any organic solvent as reaction medium. The reaction can be promoted by microwave irradiation and is complete within one minute.