Structural characterization and electrochemical performance of lithium trivanadate synthesized by microwave sol-gel method

The Li_1+xV₃O₈ material was successfully synthesized at 450 °C in short sintering duration by microwave sol-gel route. X-ray diffraction suggests oxygen defects in the lattice. Based on Randles-Sevcik formula, cyclic voltammograms measurements were conducted to measure Li⁺ ion diffusion coefficient. The material exhibits high discharge capacity of 250 mA g⁻¹ at 0.2 mA/cm² after 30 cycles in the range of 2.0-4.0 V. Alternating current impedance tests show that the growth of the charge transfer resistance at 0.4 mA/cm² is more rapid than that of at 0.2 mA/cm² as the galvanostatical charge-discharge continues.     

Synthesis and characterization of nano-sized calcium zincate powder and its application to Ni–Zn batteries

Nano-sized calcium zincate powders used as active materials for a secondary Zn electrode were prepared by a chemical co-precipitation method. The properties were studied by thermal gravimetric analysis (TGA), micro-Raman spectroscopy and nitrogen adsorption–desorption experiments. The secondary Zn electrodes using chemical co-precipitation calcium zincate powders (CP-ZnCa) and ball-milled calcium zincate powders (BM-ZnCa), were examined and compared. The electrochemical performance of the secondary Zn electrodes was systematically investigated by cyclic voltammetry and galvanostatic charge/discharge measurements. It was demonstrated that the electrochemical properties of the secondary Zn-pasted electrode using CP-ZnCa powders were greatly improved, as compared with conventional secondary ZnO electrodes. The results indicated that secondary Ni-Zn batteries using CP-ZnCa powders exhibited a better charge/discharge property and a longer life-cycle performance, compared with those based on ball-milled ZnO + Ca(OH)₂ (BM-ZnCa) powders.     

新型棒状碳材料的制备与表征

首次报告以松节油为碳源,利用化学气相沉积法在1150℃下获得直径大约微末级,而长度达数毫米的笔直的新型棒状碳材料,并采用X射线舒射仪、傅立叶红外仪、SEM以及热重分析仪对其进行了表征。热重分析发现其在氮气气氛中于10000℃下增重达1.1%。     

Voltammetric and electrochemical impedance spectroscopy characterization of a cathodic and anodic pre-treated boron doped diamond electrode

The effect of boron doped diamond (BDD) surface termination, immediately after cathodic and anodic electrochemical pre-treatments, on the electrochemical response of a BDD electrode in aqueous media and the influence of the different supporting electrolytes utilized in these pre-treatments on the final surface termination was investigated with [Fe(CN)₆]^4−/3−, as redox probe, by cyclic and differential pulse voltammetry and electrochemical impedance spectroscopy. The cyclic voltammetry results indicate that the electrochemical behavior for the redox couple [Fe(CN)₆]^4−/3− is very dependent on the state of the BDD surface, and a reversible response was observed after the cathodic electrochemical pre-treatment, whereas a quasi-reversible response occurred after anodic electrochemical pre-treatment. Differential pulse voltammetry in acetate buffer also showed that the potential window is very much influenced by the electrochemical pre-treatment of the BDD surface. Electroactivity of non-diamond carbon surface species (sp² inclusions) incorporated into the diamond structure was observed after cathodic and anodic pre-treatments. Electrochemical impedance spectroscopy confirmed the cyclic voltammetry results and indicates that the BDD surface resistance and capacitance vary significantly with the electrolyte and with the electrochemical pre-treatment, caused by different surface terminations of the BDD electrode surface.     

Structural and ferroelectric properties of hafnium substituted BiFeO3 multiferroics synthesized via auto combustion technique

A series of BiFe_1-xHf_(3/4)xO₃ ( 0%, 5%, 10%, 15% and 20%) nanoparticles were synthesized by simple auto combustion technique using citric acid as a fuel. Thermogravimetric (TGA), differential thermogravimetric (DTA), structural, magnetic, dielectric and ferroelectric analyses were investigated. Thermogravimetric analysis provides information of temperature at which phase develops (600?°C). DTA predicts ferroelectric to paraelectric transformation temperature which is found to be 822?°C. X-ray diffraction (XRD) results confirm formation of distorted rhombohedral structure for all compositions along with few traces of Bi₂₅FeO₄₀. The tolerance factor is increased from 0.845 to 0.853 due to larger ionic radius of Hf⁴⁺ substitution on Fe site. Crystallite size (D) is found in the range of 24.2–30.48?nm. Saturation magnetization (Ms) is increased to 16 times and remanent magnetization (Mr) is increased to 8 times than that of pure BiFeO₃. This increment in magnetic parameters is due to reduction of oxygen vacancies, small crystalline size (less than 62?nm), structural distortion and unbalancing condition for antiferromagnetic magnetic moments of Fe³⁺ ions. Dielectric parameters depict decrement behavior with increasing of applied field up to 3?GHz. For Fe_1-xHf_(3/4)xO₃, lower value of dielectric permittivity for all compositions is due to reduction of polarization and less growth of grains but more growth of grain boundaries because of mismatching of Hf and Fe³⁺ ions. P-E hysteresis loop changes from round shape to elliptical shape and it confirms less lossy nature of ferroelectric loops. Higher values of Ms as well as Mr but lower values of dielectric constant as well as remanent polarization for these nanoparticles make them useful for MeRAM (magnetoelectric random access memory) and high resonant applications.     

Structural and electrochemical characterization of Fe–Si/C composite anodes for Li-ion batteries synthesized by mechanical alloying

A Fe–Si (FeSi₂ + Si)/C composite was prepared by mechanical ball milling and investigated as a new inserting anode for use in Li-ion batteries. The composite so prepared has a sandwich structure with the alloy particles as middle cores and the graphite layer as outer shells. The charge-discharge measurements revealed that the Fe–Si/C composite not only had a quite high initial capacity of approximately 680 mAh g⁻¹, but also exhibited greatly improved capacity retention with a reversible capacity of approximately 500 mAh g⁻¹ after 15 cycles in comparison with pure Si and Fe–Si alloy. Based on XRD, XPS, SEM, Raman and EIS analysis of the composite electrode in different lithiated states, the mechanism for improved cycleability is found to be due to the effective buffering of the volumetric changes of the Fe–Si particles by the graphite shell.     

功能性碳酸钙材料的仿生合成及表征

根据生物矿化机理,利用碳化法,选用实验室自制的硬脂酸钠作为改性剂,原位合成出功能性梭形碳酸钙材料。产品的改性效果通过活化度、吸油值、接触角等性能测定。同时通过透射电子显微镜（TEM）和X射线衍射（XRD）等测试手段对产品结构和形貌进行表征,并对反应机理进行了初步探讨。实验结果表明,当硬脂酸钠用量达到2.0％（占碳酸钙理论值）时,产品活化度可达到99.9％,接触角为121.62°,从而为仿生矿化制备新材料提供了理论依据和合成手段。     

Synthesis and characterization of electrolyte substrate materials based on hyperbranched polyurethane elastomers for anodic bonding

A series of hyperbranched polyurethane elastomers (PEO-HBPUEs) as polymer electrolyte substrate materials was developed for anodic bonding with aluminum (Al) foil in micro-electro-mechanical system (MEMS) devices. The PEO-HBPUEs were prepared by pre-polymerization method with toluene-2,4-diisocyanate(TDI), polypropylene glycol (PPG), 1,4-butanediol(BDO), trimethylolpropane(TMP), lithium bis(trifluoromethanesulphonyl)imide (LiTFSI), and polyethylene oxide (PEO)-based electrolyte in varying proportions via solution casting technique at room temperature. All prepared PEO-HBPUEs exhibited low glass transition temperatures, good thermal stabilities, and suitable mechanical properties. The XRD results showed that PEO-HBPUEs are amorphous, and LiTFSI was well dissolved in the polymer matrix. The component of PEO-based electrolyte in PEO-HBPUEs contributed to increase the ionic conductivity, of which the highest value reached 1.23 × 10⁻³ S/cm at 75°C for PEO-HBPUE4. The anodic bonding of PEO-HBPUE substrate with Al foil was conducted by the coupling action of electric field, temperature field, and pressure field. A clear intermediate bonding layer between the substrate and Al foil was observed and the elements diffusion around bonding layer can be detected by SEM, indicating PEO-HBPUEs and Al foil have been jointed together successfully. The highest tensile strength of the bonding interface of PEO-HBPUE4/Al reached 1.88 MPa. All results demonstrated that the prepared PEO-HBPUEs materials would be promising substrates for flexible MEMS device that can be applied to flexible packaging by anodic bonding technology.     

On the electrochemical performance of anthracite-based graphite materials as anodes in lithium-ion batteries

The electrochemical performance as potential negative electrode in lithium-ion batteries of graphite materials that were prepared from two Spanish anthracites of different characteristics by heat treatment in the temperature interval 2400-2800 °C are investigated by galvanostatic cycling. The interlayer spacing, d₀₀₂, and crystallite sizes along the c axis, L_c, and the a axis, L_a, calculated from X-ray diffractometry (XRD) as well as the relative intensity of the Raman D-band, I_D/I_t, are used to assess the degree of structural order of the graphite materials. The galvanostatic cycling are carried out in the 2.1-0.003 V potential range at a constant current and C/10 rate during 50 cycles versus Li/Li⁺. Larger reversible lithium storage capacities are obtained from those anthracite-based graphite materials with higher structural order and crystal orientation. Reasonably good linear correlations were attained between the electrode reversible charge and the materials XRD and Raman crystal parameters. The graphite materials prepared show excellent cyclability as well as low irreversible charge; the reversible capacity being up to ∼250 mA h g⁻¹. From this study, the utilization of anthracite-based graphite materials as negative electrode in lithium-ion batteries appears feasible. Nevertheless, additional work should be done to improve the structural order of the graphite materials prepared and therefore, the reversible capacity.     

Chemical and electrochemical characterization of porous carbon materials

Chemical and electrochemical techniques have been used in order to asses surface functionalities of porous carbon materials. An anthracite has been chemically activated using both KOH and NaOH as activating agents. As a result, activated carbons with high micropore volume (higher than 1 cm³/g) have been obtained. These samples were oxidized with HNO₃ and thermally treated in N₂ flow at different temperatures in order to obtain porous carbon materials with different amounts of surface oxygen complexes. Thermal treatment in H₂ was also carried out. The sample treated with H₂ was subsequently treated in air flow at 450 °C. Thus, materials with very similar porous texture and widely different surface chemistry have been compared. The surface chemistry of the resulting materials was systematically characterized by TPD experiments and XPS measurements. Galvanostatic and voltammetric techniques were used to deepen into the characterization of the surface oxygen complexes. The combination of both, chemical and electrochemical methods provide unique information, regarding the key role of surface chemistry in improving carbon wettability in aqueous solution and the redox processes undergone by the surface oxygen groups. Both contributions are of relevance to understand the use of porous carbons as electrochemical capacitors.     

聚氨酯注浆堵水加固材料的制备

采用正交实验法,研究了聚醚多元醇配比、异氰酸酯指数和催化剂用量等对聚氨酯注浆材料冲击、压缩、拉伸性能的影响。结果表明,三种混合聚醚多元醇的配比为5∶2∶4,异氰酸酯指数为1.15,催化剂的用量为0.1%时制得的聚氨酯注浆材料性能最好,其冲击强度为4.4 kJ/m2,压缩强度为4.6 MPa,拉伸强度为2.810 MPa。此时硬质聚氨酯泡体为闭孔结构,其冲击断口形貌呈脆性断裂特征。     

Structural characterization and electrochemical properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> anode materials synthesized by a hydrothermal method

Cobalt oxide [Co₃O₄] anode materials were synthesized by a simple hydrothermal process, and the reaction conditions were optimized to provide good electrochemical properties. The effect of various synthetic reaction and heat treatment conditions on the structure and electrochemical properties of Co₃O₄ powder was also studied. Physical characterizations of Co₃O₄ are investigated by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller [BET] method. The BET surface area decreased with values at 131.8 m²/g, 76.1 m²/g, and 55.2 m²/g with the increasing calcination temperature at 200°C, 300°C, and 400°C, respectively. The Co₃O₄ particle calcinated at 200°C for 3 h has a higher surface area and uniform particle size distribution which may result in better sites to accommodate Li⁺ and electrical contact and to give a good electrochemical property. The cell composed of Super P as a carbon conductor shows better electrochemical properties than that composed of acetylene black. Among the samples prepared under different reaction conditions, Co₃O₄ prepared at 200°C for 10 h showed a better cycling performance than the other samples. It gave an initial discharge capacity of 1,330 mAh/g, decreased to 779 mAh/g after 10 cycles, and then showed a steady discharge capacity of 606 mAh/g after 60 cycles.     

Structural,magnetic and electrical properties of Y1-xScxFeO3 (x= 0, 0.5 & 1) nanoparticles synthesized by the sol-gel method

Nanoparticles exhibiting crystalline and single-phase characteristics with Y_1-xSc_xFeO₃ (x = 0, 0.5 & 1) nanoparticles synthesized by sol-gel method. The sizes of nanocrystals determined by X-Ray Diffractometry (XRD) were obtained between 30 and 39 nm. The shape of nanoparticles and the surface morphology of the samples were carried out using Field Emission Scanning Electron Microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The magnetic properties of Y_1-xSc_xFeO₃ samples were investigated by Vibrating Sample Magnetometry (VSM) and Field-Cooled (FC) and Zero-Field-Cooled (ZFC) measurements. The results showed antiferromagnetic and paramagnetic behaviors for these prepared perovskites. The electrical properties of the samples were investigated by measuring the polarization-electric loops, dielectric constant changes and dielectric loss through frequency and temperature. These measurements showed the T_N values of the samples to be 628 and 578 K for YFeO₃ and ScFeO₃ nanoparticles, respectively. In addition, diffuse reflectance spectroscopy analysis was used to calculate the band gap energy of the samples based on the Kubelka-Munk function. The achieved values showed the band gap energy of 2.97 and 3.07 eV for YFeO₃ and ScFeO₃.     

Structural,optical and electrochemical properties of TiO2 nanoparticles synthesized using medicinal plant leaf extract

The flower like TiO₂ nanoparticles have been identified as potential electrode material for efficient next generation electrochemical energy storage devices. The present work reports, a novel green approach to synthesize high surface area TiO₂ nanoparticles using medicinal plant leaf extracts namely Ocimum Tenuiflorum Plant and Calotropis Gigantea Plant. The TiO₂ nanoparticles synthesized using Calotropis Gigantea plant confirmed rutile phase from X-ray powder diffraction and Raman spectra. The fourier transform infrared spectroscopy spectra of the sample indicate the presence of TiO₂ vibrational bonds. The field emission scanning electron microscopy images revealed that the flower like shape of nano-granules with an average granule size of 200 nm. The presence of Ti and O elements qualitatively confirmed using energy dispersive spectroscopy spectra, which shows the good stoichiometry in the sample. The flower like shapes with nano petals were further disclosed with the help of high resolution transmission electron microscopy. The corresponding optical band gap was observed to be 3.0 eV. The electrochemical investigations of the sample exhibited a high specific capacitance of 224 F g^-1 at 0.5 A g^-1 with 71% of capacitive retention after 5000 cycles.     

MMA基混凝土修补材料的变形、强度及耐久性

MMA基混凝土修补材料是由甲基丙烯酸甲酯(MMA)和引发剂、增塑剂等合成的高分子聚合物,粘度小且可以通过聚合度的控制进行调整,适宜于细裂纹的修复与修补。研究表明,改性MMA基修补材料收缩接近为0;拉伸强度为46MPa,抗弯强度为90MPa,与砂浆的粘结强度为3 25～9 85MPa;紫外光照射一个月,修补材料的强度可以保持99%;经高温热震和低温热震循环300次后,修补材料的拉伸强度减小为21 56MPa和17 1MPa,弯曲强度减小为40 4MPa和32 5MPa,但仍然远远大于水泥混凝土的强度。     

Structural, chemical and electrochemical characterization of poly(3,4-ethylenedioxythiophene) (PEDOT) prepared with various counter-ions and heat treatments

Electrochemical deposition of the conjugated polymer poly(3,4-ethylenedioxythiophene) (PEDOT) forms thin, conductive films that are especially suitable for charge transfer at the tissue-electrode interface of neural implants. For this study, the effects of counter-ion choice and annealing parameters on the electrical and structural properties of PEDOT were investigated. Films were polymerized with various organic and inorganic counter-ions. Studies of crystalline order were conducted via X-ray diffraction (XRD). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to investigate the electrical properties of these films. X-ray photoelectron spectroscopy (XPS) was used to investigate surface chemistry of PEDOT films. The results of XRD experiments showed that films polymerized with certain small counter-ions have a regular structure with strong (100) edge-to-edge correlations of PEDOT chains at ∼1.3 nm. After annealing at 170 °C for 1 h, the XRD peaks attributed to PEDOT disappeared. PEDOT polymerized with LiClO₄ as a counter-ion showed improved impedance and charge storage capacity after annealing at 160 °C.     

Synthesis and characterization of poly(urethane‐ester)s based on calcium salt of mono(hydroxybutyl)phthalate

Calcium‐containing poly(urethane‐ester)s (PUEs) were prepared by reacting diisocyanate (HMDI or TDI) with a mixture of calcium salt of mono(hydroxybutyl)phthalate [Ca(HBP)₂] and hydroxyl‐terminated poly(1,4‐butylene glutarate) [HTPBG₁₀₀₀], using di‐n‐butyltin‐dilaurate as catalyst. About six calcium‐containing PUEs having different composition were synthesized by taking the mole ratio of Ca(HBP)₂:HTPBG₁₀₀₀:diisocyanate (HMDI or TDI) as 3:1:4, 2:2:4, and 1:3:4. Two blank PUEs were synthesized by the reaction of HTPBG₁₀₀₀ with diisocyanate (HMDI or TDI). The polymers were characterized by IR, ¹H NMR, Solid state ¹³C‐CP‐MAS NMR, TGA, DSC, XRD, solubility, and viscosity studies. The T_g value of PUEs increases with increase in the calcium content and decreases with increase in soft segment content. The viscosity of the calcium‐containing PUEs increases with increase in the soft segment content and decreases with increase in the calcium content. X‐ray diffraction patterns of the polymers show that the HMDI‐based polymers are partially crystalline and TDI‐based polymers are amorphous in nature. The dynamic mechanical analysis of the calcium‐containing PUEs based on HMDI shows that with increase in the calcium content of polymer, modulus (g′ and g″) increases at any given temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1720–1727, 2006     

Structural,magnetic and magnetocaloric properties of nanostructured Pr0.5Sr0.5MnO3 manganite synthesized by mechanical alloying

Nanostructure Pr_0.5Sr_0.5MnO₃ compounds were elaborated by mechanical milling in a planetary high energy ball mill at various milling times followed by high temperature sintering under air at 1400 °C for 20 h. The phase structure, the morphology, the magnetic and magnetocaloric properties of the powders were characterized by X-ray diffractometry, scanning electron microscopy and a vibrating sample magnetometer. Rietveld refinement of the X-ray diffraction patterns shows that all specimens crystallize in the tetragonal system with I4/mcm space group. Increasing the milling time up to 16 h, the average crystallites size decreases to the nanoscale (∼36 nm). During the intermediate stage of milling, significant changes occur in the morphology of the powder particles, due to the severe plastic deformation. Significant refinement in particle size was found evident at the final stage of milling (∼2 µm). From magnetic measurements, it was found that all samples present two magnetic transitions as a function of temperature. The Curie temperature T_C decreases with increasing milling time. Moreover, it was revealed that the antiferromagnetic domains fractions highly dependent on crystallites sizes. A large magnetocaloric effect and an important value of the relative cooling power around Neel temperature was observed in all samples. These characteristics may be related to the first-ordered nature of this transition. Moreover, the magnetic entropy change and the relative cooling power were increased with decreasing crystallites sizes.     

Synthesis and electrochemical characterization of nano-CeO2-coated nanostructure LiMn2O4 cathode materials for rechargeable lithium batteries

LiMn₂O₄ spinel cathode materials were coated with 0.5, 1.0, and 1.5 wt.% CeO₂ by a polymeric process, followed by calcination at 850 °C for 6 h in air. The surface-coated LiMn₂O₄ cathode materials were physically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron microscopy (XPS). XRD patterns of CeO₂-coated LiMn₂O₄ revealed that the coating did not affect the crystal structure or the Fd3m space group of the cathode materials compared to uncoated LiMn₂O₄. The surface morphology and particle agglomeration were investigated using SEM, TEM image showed a compact coating layer on the surface of the core materials that had average thickness of about 20 nm. The XPS data illustrated that the CeO₂ completely coated the surface of the LiMn₂O₄ core cathode materials. The galvanostatic charge and discharge of the uncoated and CeO₂-coated LiMn₂O₄ cathode materials were measured in the potential range of 3.0-4.5 V (0.5 C rate) at 30 °C and 60 °C. Among them, the 1.0 wt.% of CeO₂-coated spinel LiMn₂O₄ cathode satisfies the structural stability, high reversible capacity and excellent electrochemical performances of rechargeable lithium batteries.     

Structural and mechanical characterization of as-compacted powder mixtures of graphite and phenolic resin

The powder compaction of graphite and graphite–polymer mixtures was studied to produce dense structures. Different graphite powders were studied including: natural crystalline flake, synthetic isotropic and hybrid. The six graphite powders may be divided into three groups. Graphite powders of group 1 (Asbury 1645, 3610 and Timcal SFG-75) could be easily compacted. They produced textured XRD patterns and had the (0 0 2) family of planes oriented perpendicular to the compaction axis. Timcal graphite KS-150 was harder to compact and is alone in group 2. It produced parts with lower mechanical properties than graphite powders from group 1. X-ray diffraction patterns confirmed that graphite KS-150 did not produced parts with as much anisotropy as parts produced with graphite powders from group 1. The graphite powders of group 3 (Asbury 4956 and 4012) were difficult to compact and did not produce part with green strength sufficient to be handled. Parts made using these graphite powders exhibited diffraction patterns typical of a disordered polycrystalline structure. For compactable graphites, it was also possible to relate the transverse rupture strength and green density of compacted parts with their XRD patterns.