Synthesis,characterization and thermal properties of novel nanoencapsulated phase change materials for thermal energy storage

In this paper, nanocapsules containing n-octadecane with an average 50 nm thick shell of poly(ethyl methacrylate) (PEMA) and poly(methyl methacrylate) (PMMA), and a core/shell weight ratio of 80/20 were synthesized by the direct miniemulsion method, respectively. The average size of the capsules is 140 nm and 119 nm, respectively. The chemical structure of the sample was analyzed using Fourier Transformed Infrared Spectroscopy (FTIR). Crystallography of nanocapsules was investigated by X-ray diffractometer. The surface morphology was studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The thermal properties and thermal stability of the sample were obtained from Differential Scanning Calorimeter (DSC) and Thermal Gravimetric Analysis (TGA). The temperatures and latent heats of melting and crystallizing of PEMA nanocapsule were determined as 32.7 and 29.8 °C, 198.5 and ?197.1 kJ/kg, respectively. TGA analysis indicated that PEMA/octadecane nanocapsule had good thermal stability. The nanocapsules prepared in this work had a much higher encapsulation ratio (89.5%) and encapsulation efficiency (89.5%). Therefore, the findings of the work lead to the conclusion that the present work provides a novel method for fabricating nanoencapsulated phase change material, and it has a better potential for thermal energy storage.     

Activation characteristics and microstructure of composite hydrogen storage alloys prepared by two-step re-melting

In the present work, novel composites (x=0,5,10,30) for hydrogen storage were prepared by two-step re-melting and their activation characteristic and microstructure were investigated. The influence of Mg₂Ni content on the activation characteristics was analyzed by electrochemical method. With the increasing content of Mg₂Ni, activation characteristics and maximum discharge capacities of composites increase first and then decrease. The composite with 5% Mg₂Ni has the least cycle number for activation and the highest discharge capacity. It is activated after only 6 cycles (C_n=6) at room temperature and its maximum discharge capacity (C_max) reaches 274.4 mAh/g. However, the composite contained 30 wt% Mg₂Ni is difficult to be activated at room temperature. It is also found that it is easier to be activated for the composites at and than that at and , but their discharge capacity decay slightly at the condition of and . The XRD and SEM analysis show that, with the increasing Mg₂Ni content, the microstructure of the composites varies gradually from lamellar (x=5), acicular (x=10) to massive (x=30), and the activity of the composite declines as a result of the grain size of phase Mg₂Ni grows up.     

CuGa_2O_4光催化剂的制备、表征与光催化产氢性能研究

采用固相反应法合成了具有d~(10)电子构型的CuGa_2O_4光催化剂。采用XRD,UV-Vis和SEM等分析方法对CuGa_2O_4的物理化学性质进行了测试和表征。XRD和SEM的测试结果表明,CuGa_2O_4具有较纯的立方尖晶石结构并呈现不规则微颗粒状,UV-Vis分析结果显示对较宽的太阳光谱都有响应。以葡萄糖作为电子给体,考察了CuGa_2O_4负载RuO_2后的光催化产氢性能,结果显示葡萄糖能提高RuO_2/CuGa_2O_4的光催化产氢效率,同时自身也被很好地降解。经过最初几小时的诱导期后,RuO_2(1.0%)/CuGa_2O_4的平均产氢速率约为10.59μmol/h。     

Synthesis and characterization of rough electrochromic phosphotungstic acid films obtained by spray-gel process

Rough electrochromic phosphotungstic acid (PWA) films were fabricated by spraying a gel of phosphotungstate anions with a molar ratio of P:W=1:12 onto glass substrates. The substrates were coated with transparent and electrically conducting SnO₂:F at 300°C. Analysis by X-ray photoelectron spectroscopy determined that the P:W molar ratio in the films was approximately 1:14. Infrared spectroscopy and X-ray diffraction showed that the film is a form of polycrystalline phosphotungstic acid. SEM micrographs showed that the films have a rough morphology based on fiber-shape bridges. Optoelectrochemical measurements demonstrated pronounced electrochromism in the PWA films upon H⁺ intercalation/deintercalation with a high diffuse reflectance (R_d) and transmittance (T_d). We found for as-deposited films that R_d/total reflectance (R_t) and T_d/total transmittance (T_t) at 550 nm was around 0.83 and 0.68, respectively. This ratio decreases at bleached state to 0.74 and 0.41 for R_d/R_t and T_d/T_t, respectively.     

Synthesis and electrochemical characterization of carbon-coated nanocrystalline LiFePO4 prepared by polyacrylates-pyrolysis route

A carbon-coated nanocrystalline LiFePO₄ cathode material was synthesized by pyrolysis of polyacrylate precursor containing Li⁺, Fe³⁺ and PO₄⁻. The powder X-ray diffraction (XRD) and high-resolution TEM micrographs revealed that the LiFePO₄/C composite as prepared has a core-shell structure with pure olivine LiFePO₄ crystallites as cores and intimate carbon coating as a shell layer. Between the composite particulates, there exists a carbon matrix binding the nanocrystallites together into micrometer particles. The electrochemical measurements demonstrated that the LiFePO₄/C composite with an appropriate carbon content can deliver a very high discharge capacity of 157 mAh g⁻¹ (>92% of the theoretical capacity of LiFePO₄) with 95% of its initial capacity after 30 cycles. Since this preparation method uses less costly materials and operates in mild synthetic conditions, it may provide a feasible way for industrial production of the LiFePO₄/C cathode materials for the lithium-ion batteries.     

Tin–graphite materials prepared by reduction of SnCl4 in organic medium: Synthesis,characterization and electrochemical lithiation

Tin–graphite materials were prepared by chemical reduction of SnCl₄ by t-BuONa-activated NaH. TEM imaging showed that the crude material is composed of an amorphous organic matrix containing tin present either as nanosized particles deposited on the graphite surface or as free aggregates. Subsequent washings with ethanol and water allow removal of side products as well as most part of the organic matrix. Electrochemical insertion of lithium occurred in graphite and in tin. The initial reversible massic capacity of 630 mAh g⁻¹ decayed to a stable value of 415 mAh g⁻¹ after 12 cycles. This capacity value was lower than the expected maximum one of 650 mAh g⁻¹ corresponding to a Sn/12C molar composition and assuming the formation of LiC₆ and Li₂₂Sn₅. Even if this massic capacity is not much improved by comparison with that of graphite, it must be pointed out that the volume capacity of this graphite/Sn material is much larger (2137 mAh cm⁻³) than that corresponding to graphite (837 mAh cm⁻³). It was hypothesized that the part of tin bound to graphite could be responsible for the stable reversible capacity. To the contrary, graphite unsupported tin aggregates would contribute to the observed gradual decline in the storage capacity. Therefore, the improvement in cycleability, compared to that of massive metals, could be attributed both to the nanoscale dimension of the metal particles and to interactions between graphite and metal the nature of which remaining to be precised.     

Thermal property characterization of a low melting-temperature ternary nitrate salt mixture for thermal energy storage systems

Molten salts have better thermal properties than synthetic mineral oil, and hence they can be directly used as heat transfer fluids in solar power plants, but in practice their direct applications as heat transfer fluids are constrained due to their high freezing temperature points. In this paper, a class of ternary nitrate salt mixtures consisting of 50-80 wt% KNO₃, 0-25 wt% LiNO₃ and 10-45 wt% Ca(NO₃)₂ were processed and tested. Experimental results indicated that some mixtures within this range exhibited excellent thermal properties, such as a low melting point (<100 °C), robust reliability, high-temperature stability (upto 500 °C) and a low viscosity (e.g.,<5 cP at 190 °C). Apart from these desirable thermo-physical properties, the manufacturing cost of these novel inorganic salts HTFs (Heat Transfer Fluids) is considerably lower than those of the existing commercial heat transfer fluids (HTFs).     

Synthesis and characterization of aluminum-doped CdO thin films by sol–gel process

Aluminum-doped cadmium oxide (CdO:Al) thin films are deposited on glass substrates by the sol–gel dip-coating method, taking cadmium acetate dihydrate as the precursor material. Aluminum nitrate has been taken as a source of Al-dopant. XRD pattern reveals the good crystallinity of CdO thin films. SEM micrograph showed the presence of faceted crystallites. Optical study shows 40–85% transparency with a bandgap value lying in the range 2.76–2.52 eV, depending upon the Al content in the films. Optimum percentage of Al was 5.22 for a maximum room temperature conductivity of 2.81×10³ (Ω cm)⁻¹. Hall measurement confirmed that the material is of n-type, with mobility and carrier concentrations lying in the range 413–14.7 cm²/V s, and 3.4×10¹⁹–8.11×10²⁰ cm⁻³, when percentage of Al varies in the range 1.32–7.24.     

Analysis of thermal radiation,Joule heating,and viscous dissipation effects on blood-gold couple stress nanofluid flow driven by electroosmosis

Gold nanoparticles associated with DNA, RNA, proteins, oligonucleotides, and peptides are useful in therapies and drug delivery. The present article mainatins that gold nanoparticles play a tremendous role in remedying cancer and fatal diseases. A mathematical model is proposed for the two-dimensional motion of the couple stress nanofluid consisting of gold nanoparticles under the application of peristaltic propulsion and electroosmosis mechanisms in an asymmetric microchannel. The effects of radiation with slip boundary have been employed. The governing equations are simplified under the assumptions of low Reynolds number and long wavelength and the Poisson-Boltzmann equation is solved under Debye–Hückel linearization. Analytical solutions for the velocity of fluid motion, nanoparticle temperature, stream function, pressure gradient, are evaluated and analyzed graphically under the effects of various physical parameters. It is notable from the analysis that raising the Brinkman number boosts the nanoparticle temperature and heat transfer coefficient which validate the physical model and analysis. Moreover, it is noticed that sphere-shaped gold nanoparticles enhance the temperature as compared to other geometries of nanoparticles. The present study results may assist in developing the technology, smart micropumps, drugs, and device for hemodialysis and other health care applications.     

Efficient hydrogen gas production from cassava and food waste by a two-step process of dark fermentation and photo-fermentation

A two-step process of sequential anaerobic (dark) and photo-heterotrophic fermentation was employed to produce hydrogen from cassava and food waste. In dark fermentation, the average yield of hydrogen was approximately 199 ml H₂ g⁻¹ cassava and 220 ml H₂ g⁻¹ food waste. In subsequent photo-fermentation, the average yield of hydrogen from the effluent of dark fermentation was approximately 611 ml H₂ g⁻¹ cassava and 451 ml H₂ g⁻¹ food waste. The total hydrogen yield in the two-step process was estimated as 810 ml H₂ g⁻¹ cassava and 671 ml H₂ g⁻¹ food waste. Meanwhile, the COD decreased greatly with a removal efficiency of 84.3% in cassava batch and 80.2% in food waste batch. These results demonstrate that cassava and food waste could be ideal substrates for bio-hydrogen production. And a two-step process combining dark fermentation and photo-fermentation was highly improving both bio-hydrogen production and removal of substrates and fatty acids.     

Morphology, mechanical, thermal and rheological behavior of microcellular injection molded TPO-clay nanocomposites prepared by kneader

Thermoplastic olefin elastomers (TPO)/montmorillonite (MMT) nanocomposites prepared by kneader was used in this study. The organoclay TPO nanocomposites were then injection molded by conventional and microcellular methods. Nitrogen was used as the blowing agent. The effect of organoclay content on the mechanical/thermal/rheological properties of the TPO-clay nanocomposites was investigated. The results showed that the mechanical properties (tensile, impact, and wear resistance) increased as the clay content increased. Cell size decreased as the clay loading increased. The addition of MMT into TPO also improved the thermal stability of the TPO/clay nanocomposites. The XRD results showed that the nanocomposites having an intercalated layered structure. Rheological results showed the viscosity is clay loading dependent and shear thinning effect takes place at high shear rate.     

Structural,optical and electrochemical transient photoresponse properties of ZnO/Ga2O3 nanocomposites prepared by two-step CVD method

The influence of ZnO layer thickness on the structural, optical and electrochemical transient photoresponse properties of Ga₂O₃/ZnO heterostructured nanocomposites is evaluated. The increasing thickness of ZnO layer from 0 to 7.868 μm on the nanocomposites show an increase in the concentration of photogenerated electron-hole pairs, improve carrier separation and transportation to the electrolyte. This results to an enhanced photocurrent density from 164 to 833 μA/cm² at 1 V vs Ag/AgCl electrode. The unhybridized β-Ga₂O₃ film and the ZnO/Ga₂O₃ nanocomposites exhibit nanoblock-like and nanoplate-like morphologies, respectively. Structural studies reveal hexagonal ZnO and β-Ga₂O₃ crystalline phases for the nanocomposites. Optical bandgap of the reference β-Ga₂O₃ film is found to be 4.79 eV whereas, the nanocomposites exhibit two bandgaps: 3.30–3.25 eV belonging to the crystalline hexagonal ZnO phase, and 4.87–4.83 eV traced to the β-Ga₂O₃ phase. Photoluminescence spectroscopy exhibits blue-green emissions for the unhybridized film and ultraviolet-green emissions for the nanocomposites.     

Temperature Distributions in Power Series， Visualization and Measurement of a Thermal Wake

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Hydrogenolysis and hydrodeoxygenation of lignin in a two-step process to produce hydrocarbons and alkylphenols

Valuable fuels and chemicals production from biomass with high yields is always a big challenge in the energy utilization field. Herein, a two-step process for the catalytic conversion of lignin was proposed to form the fuels. In the first step, the depolymerization of lignin occurred efficiently via the hydrogenolysis reaction, resulting in 19.2% aromatic monomers under the catalysis of Pd/C and CrCl₃. The catalysts exhibited a synergistic effect on the cleavage of β-O-4 bonds and the hydrogenation procedure, which prevented the condensation of intermediate products remarkably. Afterwards, the aromatic monomers were extracted out with octane solvent successfully (extraction degree 89.7%) and then used as a substrate in a second hydrodeoxygenation (HDO) step. Product mixture composed of 26.5% hydrocarbons (increased from 5.5%) and 49.7% alkylphenols (increased from 42.9%) were obtained after the HDO upgrading, which exhibited high potential to be used as fuels. This two-step approach is very promising to be a practical chemical engineering process for the fuel production from lignin.     

Structure and electrochemical property of amorphous molybdenum selenide H2-evolving catalysts prepared by a solvothermal synthesis

Amorphous molybdenum selenide nanoparticles were synthesized by the solvothermal treatment of Mo(CO)₆ and Se in dimethylformamide. By varying the Mo(CO)₆ over Se molar ratio, we obtained a family of MoSe nanoparticles having comparable morphology but different chemical composition. Using a combination of experimental analyses (e.g. XRD, ICP-MS, Raman, XPS) and DFT theoretical calculation, we found that the structure of MoSe was close to that of the amorphous molybdenum sulfide analogous but not that of MoSe₂ layers. The MoSe was found to consist of [Mo₃Se₁₃]^2- cluster within its structure together with some structural defects. Thanks to its less ordered structure, the MoSe can be activated by several chemical and electrochemical treatment resulting in a catalytic enhancement. A treatment with fuming HCl resulted in generation of a novel catalyst displaying 1.4 time higher catalytic current. Remarkably, a treatment with reflux NaOH solution resulted in generation of a component being soluble in water and displaying catalytic H₂-evolving activity at a moderate onset overpotential of ca. 200 mV, being one of the most attractives homogeneous catalysts in water.     

Minority carrier lifetime and efficiency improvement of multicrystalline silicon solar cells by two-step process

Impurities and defects are of significant interest in multicrystalline silicon, due to the detrimental effect they can have on carrier lifetimes and electrical properties. In view of that, it is important to incorporate certain processing steps to decrease the recombination activities. In this study, a novel experiment was applied as a beneficial approach to improve the electronic quality of low-resistivity mc-Si substrates via a two-step process. Initially, the first step involves gettering multicrystalline substrates using sacrificial porous silicon layer on both sides, which was introduced as a simple sequence for efficient extrinsic gettering schemes. The gettering experiment was performed at 600–900 °C, and optimum results were obtained at 900 °C. Then, the second step involves coating the front surface of gettered mc-Si at 900 °C with vanadium oxide that serves as an excellent antireflection layer and leads to improve furthermore the electrical properties. Significant improvements were obtained after the deposition of vanadium oxide antireflection coating, in view of the fact that gettered mc-Si substrate at 900 °C provides the highest minority carrier lifetime and the lowest effective surface recombination velocity. An overall increase of the electrical properties was obtained after the described two-step process. The conversion efficiency increases from 6% (reference) and reached 13.7%.     

Preparation, physical property and thermal physical property of phase change microcapsule slurry and phase change emulsion

Phase change microcapsule slurry and phase change emulsion are two novel two-phase heat transfer fluids. Compared with a conventional single-phase heat transfer fluid such as water, their apparent specific heats in the phase change temperature range are greatly increased. Due to this, the heat transfer ability and energy transport ability can be obviously improved. Therefore, they have many potentially important applications in fields such as heating, ventilating, air-conditioning, refrigeration and heat exchangers. In this paper, a phase change emulsion was prepared by mixing film synthesis, and a phase change microcapsule slurry was prepared by in situ polymerization with polystyrene, polymethyl methacrylate, polyethyl methacrylate as encapsulation material, respectively. Physical properties, such as viscosity, diameter and its distribution of microcapsule and emulsion were investigated. The relationship between the concentration of tetradecane and physical properties have been discussed in detail. Meanwhile, the thermal physical properties of these two fluids were determined by DSC. Also, the influence of tetradecane concentration on phase change temperature and phase change heat has been discussed.     

Electrical and thermal characterization of a PV-CPC hybrid

Long term evaluation of an asymmetric CPC PV-thermal hybrid built for high latitudes, MaReCo (MaximumReflectorCollector), is performed in Lund, lat 55.7°, and this paper discusses output estimates and characteristics of the system. The output estimates are calculated using the MINSUN simulation program. To get the input for MINSUN, measurements were performed on two MaReCo prototypes. These measurements show that the front reflector collects most of the irradiation in the summer, and the back reflector in the spring and fall. Two different reflector materials were used, anodized aluminium and aluminium laminated steel. The steel based reflector was selected for its rigidness. The output estimates show no difference in yearly output between the two reflector materials, both back reflectors deliver 168 kW h/(m² cell area) of electricity compared to 136 kW h/m² cell area for cells without reflectors. The cells facing the front reflector deliver 205 kW h/(m² cell area) of electricity. The estimated output of thermal energy was 145 kW h/(m² glazed area) at 50 °C. The estimates show that the optimal placement of the photovoltaic cells is facing the front reflector, but having cells on both sides is in most cases the best option.