Multidisciplinary methods (co-precipitation,ultrasonic, microwave,reflux and hydrothermal) for synthesis and characterization of CaMn3O6 nanostructures and its photocatalytic water splitting performance

Production of hydrogen and oxygen from water splitting reaction under visible light is a simple method for conversion of solar-to-hydrogen energy and it is a hopeful clean and renewable method for H₂ fuel generation. However, there is still a lack of potential materials with significant activity under visible light. Because of safety, chemical inertness, low cost, stability and other characteristics, transition metal oxide semiconductors have been widely applied as photocatalysts for hydrogen generation. Albeit, wide usage of semiconductor photocatalysts were prevented by its inability to exploit solar energy of visible region. Here we show synthesis of a nano-sized mixed metal oxide (MMO) Ca₃MnO₆ through wet-chemistry methods such as co-precipitation, ultrasonic, microwave, reflux, and hydrothermal methods. The nano-sized Ca₃MnO₆ has initially selected based on morphology and respective particle diameters. The selected sample shows a well-defined single crystal, free from any impurities, complete structural formation, and a band gap energy (E_g) of around 5.3 eV. The best product synthesized in ultrasonic method which shows the best morphology, purity and the highest efficiency for splitting of water to hydrogen and oxygen. Irrespective of preparation methods and morphologies, all samples split water into hydrogen and oxygen, as confirmed from their respective photocatalytic analysis. When the selected sample combined with (NH₄)₂Ce(NO₃)₆, the single-crystal Ca₃MnO₆ nanoparticles split water into hydrogen and oxygen more efficiently under visible light. Our findings demonstrate the importance of nanostructured Ca₃MnO₆ single-crystal photocatalysts in solar water splitting.     

Quantitative Analysis of Work Hardening and Dynamic Softening Behavior of low carbon alloy Steel Based on the Flow Stress

In this study, the constitutive equation and DRX(Dynamic recrystallization) model of Nuclear Pressure Vessel Material 20MnNiMo steel were established to study the work hardening and dynamic softening behavior based on the flow behavior, which was investigated by hot compression experiment at temperature of 950 °C, 1050 °C, 1150 °C and 1250 °C with strain rate of 0.01 s⁻¹, 0.1 s⁻¹ and 10 s⁻¹ on a thermo-mechanical simulator THE RMECMASTOR-Z. The critical conditions for the occurence of dynamic recrystallization were determined based on the strain hardening rate curves of 20MnNiMo steel. Then the model of volume fraction of DRX was established to analyze the DRX behavior based on flow curves. At last, the strain rate sensitivity and activation volume V^* of 20MnNiMo steel were calculated to discuss the mechanisms of work hardening and dynamic softening during the hot forming process. The results show that the volume fraction of DRX is lower with the higher value of Z (Zener–Hollomon parameter), which indicated that the DRX fraction curves can accurately predicte the DRX behavior of 20MnNiMo steel. The storage and annihilation of dislocation at off-equilibrium saturation situation is the main reason that the strain has significant effects on SRS(Strain rate sensitivity) at the low strain rate of 0.01 s⁻¹ and 0.1 s⁻¹. While, the effects of temperature on the SRS are caused by the uniformity of microstructure distribution. And the cross-slip caused by dislocation piled up which beyond the grain boundaries or obstacles is related to the low activation volume under the high Z deformation conditions. Otherwise, the coarsening of DRX grains is the main reason for the high activation volume at low Z under the same strain conditions.     

AISI 316Ti (1.4571) steel—Mechanical,creep and fracture properties versus temperature

In this paper some useful, experimentally obtained, results regarding material properties of austenitic stainless steel 1.4571 are presented. Tests were performed at low and elevated temperatures. During uniaxial tests, mechanical properties such as ultimate tensile strength, 0.2% offset yield strength and short-time creep behaviour were determined. Charpy impact energy was also determined using the Charpy impact machine. Engineering stress-strain diagrams are shown at low and elevated temperatures, whereas creep curves for selected stress levels are presented at selected temperatures. Therefore, experimentally obtained data may be of importance for structure designers dealing with design of structures made of similar material and operating under similar environmental conditions.     

Eucalyptus and Populus short rotation woody crops for phosphate mined lands in Florida USA

Our short-rotation woody crops (SRWC) research in central and southern Florida is (1) developing superior Eucalyptus grandis (EG), E. amplifolia (EA), and cottonwood (Populus deltoides, PD) genotypes, (2) determining appropriate management practices for and associated productivities of these genotypes, and (3) assessing their economics and markets. Reclaimed clay settling areas (CSA) and overburden sites in phosphate mined areas in central Florida are a potential land base of over 80,000 ha for SRWC production. On CSAs, PD grows well in the absence of cogongrass (Imperata cylindrica) but is not as productive as the non-invasive EG and EA. SRWC establishment on CSAs requires strict implementation of the following cultural practices: thorough site preparation through herbiciding/disking and bedding, superior trees, watering/packing seedlings, fertilization with ammonium nitrate at planting and annually thereafter as feasible, high planting density possibly including double row planting, and winter harvesting so that coppice regeneration suppresses weeds. PD cultural requirements, that may require post-planting weed control to suppress herbaceous competition, exceed those of the eucalypts. EG SRWCs on CSAs are at risk of blowdown 3–4 years after planting or coppicing; younger PD, EG, and EA SRWCs appear much less susceptible to wind damage. Genetic improvement must continue if EG, EA, and PD are to increase in commercial feasibility. SRWC cost competitiveness will depend on establishment success, yield improvements, harvesting costs, and identifying/using incentives. Strong collaboration among public and private partners is necessary for commercializing SRWCs in Florida.     

Co-precipitation synthesis of CeVO4 nanoparticles for electrochemical hydrogen storage

Journal of Materials Science: Materials in Electronics - In this study, cerium vanadate (CeVO4) nanoparticles were synthesized using ammonium metavanadate and cerium (III) nitrate hexahydrate as...     

Effect of copper on improving the electrochemical storage of hydrogen in CeO2 nanostructure fabricated by a simple and surfactant-free sonochemical pathway

Introducing high-performance compounds for hydrogen sorption is of interest because of their advantages for substantial applications such as energy storage. Here, the role of copper addition on hydrogen storage capability and Coulombic efficiency of CeO₂ nanostructure (fabricated by an easy and surfactant-free sonochemical pathway) was examined, for the first time. Nanostructured oxides were fabricated with loading various percentages of copper (4 wt% and 40 wt%) inside CeO₂. Nanostructured copper-ceria binary oxides were checked by diverse analyses. The hydrogen storage performance as well as Coulombic efficiency of the nanostructured copper-ceria binary oxides and the net CeO₂ were checked through chronopotentiometry charge−discharge pathway in the alkaline medium. The outcomes exhibited that the hydrogen storage capacity of CeO₂ nanostructure could be enhanced with adding the proper dosage of copper as a beneficial low-cost solution. Self-assembled copper-doped CeO₂ hierarchical nanostructures could display the most appropriate performance than the net CeO₂ and nanostructured Cu₂O–CeO₂. The discharge capacity for the self-assembled copper-doped CeO₂ hierarchical nanostructures (fabricated by adding 4 wt% copper) could rise to 5070 mAh/g at 22nd cycle. Appropriate porosity, special architecture and unique morphology as well as convenient surface area of the self-assembled copper-doped CeO₂ hierarchical nanostructures render they can be very beneficial compounds in the energy storage.     

Preparation and corrosion resistance of nonstoichiometric lanthanum zirconate coatings

Lanthanum zirconate is a promising thermal barrier coating material owing to its excellent thermophysical properties and La plays the key role in its corrosion resistance. Here, an amorphous precursor is used as raw feedstock material so as to synthesize lanthanum zirconate coatings with tailorable composition by atmospheric plasma spray (APS). Three lanthanum zirconate coatings of La_1.7Zr_2.3O_7.15, La_2.0Zr_2.0O_7.0 and La_2.3Zr_1.7O_6.85 are fabricated. Furthermore, the corrosion resistance of the as-sprayed coatings against CaO-MgO-Al₂O₃-SiO₂ at 1250℃ is investigated. The increased La content promotes the formation of a sealing layer of the crystalline Ca₂La₈(SiO₄)₆O₂ apatite, which slows down the penetration of molten CaO-MgO-Al₂O₃-SiO₂. Therefore, the infiltration rate of the La_2.3Zr_1.7O_6.85 coating decreased up to 42.6 % compared with the other two coatings. This work develops a feasible preparation strategy to control the La composition for the improved corrosion resistance, which is expected to guide the future coating design and synthesis for the materials with big composition changes during the APS process.     

Gaussian orthogonal matrix transform approach for PAPR reduction of optical OFDM signals

Optical orthogonal frequency division multiplexing (O-OFDM) has been widely adopted as a high-speed data transmission technique in visible light communication systems. This technique usually suffers from high peak-to-average-power ratio (PAPR). In this paper, a new PAPR reduction technique is proposed for O-OFDM signals. At the transmitter, a matrix transformation with the Gaussian elements is applied to the time-domain O-OFDM signal and at the receiver, the inverse matrix is used to recover the original signal. We show that the Gaussian orthogonal matrices can reconstruct the original signals without degrading the bit error rate (BER) performance. Gram-Schmidt technique is used to orthogonalize the Gaussian matrices. Computer simulations are conducted for 16-QAM baseband modulated symbols and about 3 dB PAPR reduction gain is achieved by the proposed approach compared with conventional O-OFDM.     

A new post-coding approach for PAPR reduction in DC-biased optical OFDM systems

The high peak-to-average power ratio (PAPR) is one of the main drawbacks in orthogonal frequency division multiplexing (OFDM) communication systems, which also exists in the optical OFDM (O-OFDM) systems. In this letter, a new approach based on the discrete Hartley transform (DHT) post-coding technique is proposed to reduce PAPR of an O-OFDM signal in visible light communication systems. The proposed method is compared with Walsh-Hadamard transform (WHT) and discrete cosine transform (DCT) techniques in terms of PAPR reduction and bit error rate (BER) performance. Experimental results indicate that the proposed DHT post-coding method remarkably reduces the PAPR of an OFDM signal for optical intensity modulated direct detection systems without any corruption in the BER performance.     

Amino acid assisted-synthesis and characterization of magnetically retrievable ZnCo2O4–Co3O4 nanostructures as high activity visible-light-driven photocatalyst

A novel and environment-friendly way to fabricate ZnCo₂O₄–Co₃O₄ nanostructures (ZC–C NSs) as highly efficacious visible light photocatalyst was developed with the aid of the amino acids as new kinds of fuel and stabilizers, for the first time. Role of the efficacious parameters like kind of amino acid and its amount on the morphological characteristics and performance of ZC–C NSs as visible light photocatalyst was explored. The outcomes demonstrated that alteration in the kind of amino acid and its amount could be beneficial and determinative for control over dimension, performance and shape of ZC–C. Characteristics of as-produced ZC–C NSs were explored with the variant techniques. The estimated band gap demonstrates that ZC–C NSs are able to be activated by employing visible light for decomposition of contaminants. The performance of as-produced ZC–C NSs with variant morphologies were estimated from the destruction of organic contaminant, acid blue 92, illuminated with the aid of visible light. This is the first endeavor on the examination of efficiency of ZnCo₂O₄–Co₃O₄ nanostructures (produced with the aid of the various amino acids) as visible light photocatalyst for destruction of acid blue 92. The outcomes illustrate that ZC–C NSs produced with the aid of Phenylalanine are able to manifest superior performance to degrade the organic contaminant, acid blue 92. Besides, usage of new kind of fuel and stabilizing agent (amino acid) may be leading to fabricate ZC–C NSs, which are efficiently able to remove the undesirable contaminant, and eventuating to diminution in the environmental pollution.