Physical and electrolytic properties of difluorinated dimethyl carbonate

The physical and electrolytic properties of difluorinated dimethyl carbonate (DFDMC) synthesized using F₂ gas (direct fluorination) were examined. The dielectric constant and viscosity of DFDMC are higher than those of monofluorinated dimethyl carbonate (MFDMC) and dimethyl carbonate (DMC). The oxidative decomposition voltage of DFDMC is higher than those of DMC and MFDMC. The specific conductivity in DFDMC solution is considerably lower than those in MFDMC and DMC solutions. The ethylene carbonate (EC)-DFDMC equimolar binary solution containing 1 mol dm⁻³ LiPF₆ shows a moderate conductivity of 6.91 mS cm⁻¹ at 25 °C. The lithium electrode cycling efficiency (charge-discharge coulombic cycling efficiency of lithium electrode) in EC-DFDMC equimolar binary solution containing 1 mol dm⁻³ LiPF₆ is higher than 80%. The EC-DFDMC solution is a good electrolyte for rechargeable lithium batteries.     

Polyvinylidenefluoride-hexafluoropropylene based nanocomposite polymer electrolytes (NCPE) complexed with LiPF3(CF3CF2)3

Merck KGaA, Germany recently tested a new electrolyte salt LiPF₃(CF₃CF₂)₃ (lithium fluoroalkyl phosphate (LiFAP)) for lithium ion power packs and suggested that it can be replaced with commercially used LiPF₆. LiFAP, for the first of its kind, was incorporated into polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP) matrix with ethylene carbonate and diethyl carbonate mixtures as plasticizing agents and SiO₂ nanoparticles as filler. Nanocomposite polymer electrolyte (NCPE) membranes were prepared by solvent casting technique. All NCPE membranes were subjected to a.c. impedance, fluorescence and morphological studies. NCPE membranes containing 2.5 wt% of SiO₂ exhibited enhanced conductivity of 1.13 mS cm⁻¹ at ambient temperature. Molecular motion in the polymeric media was supported by fluorescence studies. The percentage of crystallinity and activation energy has also been calculated.     

The solid state reaction between lanthanum oxide and strontium carbonate

The reaction between lanthanum oxide and strontium carbonate was studied non-isothermally between 350 and 1150 °C at different heating rates, intermediates and the final solid product were characterized by X-ray diffractometry (XRD). The reaction proceeds through formation of lanthanum oxycarbonate La₂O(CO₃)₂, lanthanum dioxycarbonate La₂O₂CO₃, and non-stoichiometric strontium lanthanum oxide La₂SrO_x (x = 4 + δ). La₄SrO₇ was found to be the final product which begins to form at ∼700 °C. Li⁺ doping enhances the formation of the final product as well as commencement of the reactions at lower temperatures.     

C80 Calorimeter Studies of the Thermal Behavior of LiPF 6 Solutions

The thermal behavior of several LiPF₆ solutions was studied using a C80 calorimeter. It was found that oxygen might react with the solvents and decrease their thermal stability. The dissolution of LiPF₆ influences the thermal behavior remarkably with more heat generation and a lower onset temperature. Furthermore, the exothermic peak of LiPF₆ based on an electrolyte containing diethyl carbonate (DEC) was found around 185 ^∘C, which is 9.5–13.6 ^∘C lower than that containing dimethyl carbonate (DMC), which may be due to the relative activity of C₂H₅— and CH₃— in DEC and DMC, respectively.     

Preparation and performances of nanosized Ta2O5 powder photocatalyst

Nanosized-Ta₂O₅ powder photocatalyst was successfully synthesized by using sol-gel method via TaCl₅ butanol solution as a precursor. Ta₂O₅ species can be formed under 500 °C via the decomposition of the precursor. The crystalline phase of Ta₂O₅ powder photocatalyst can be obtained after being calcined above 600 °C for 4 h. The crystal size and particle size of Ta₂O₅ powder photocatalyst was about 50 nm. A good photocatalytic performance for the degradation of gaseous formaldehyde was obtained for the nanosized-Ta₂O₅ powder. The Ta₂O₅ powder formed at 700 °C for 4 h and at 650 °C for 12 h showed the best performance. The calcination temperature and time play an important role in the crystallization and photocatalytical performance of nanosized-Ta₂O₅ powder.     

Electron-beam irradiation on poly(propylene carbonate) in the presence of polyfunctional monomers

Poly(propylene carbonate) (PPC) showed predominantly degradation under electron-beam irradiation, accompanied by deterioration of its mechanical performance due to sharp decrease of the molecular weight. Crosslinked PPC was prepared by addition of polyfunctional monomer (PFM) to enhance the mechanical performance of PPC. When 8 wt% of PFM like triallyl isocyanurate (TAIC) was added, crosslinked PPC with a gel fraction of 60.7% was prepared at 50 kGy irradiation dose, which showed a tensile strength at 20 °C of 45.5 MPa, whereas it was only 38.5 MPa for pure PPC. The onset degradation temperature (T_i) and glass transition temperature (T_g) of this crosslinked PPC was 246 °C and 45 °C, respectively, a significant increase related to pure PPC of 211 °C and 36 °C. Therefore, thermal and mechanical performances of PPC could be improved via electron-beam irradiation in the presence of suitable PFM.     

La0.6Sr1.4MnO4 layered perovskite anode material for intermediate temperature solid oxide fuel cells

La_0.6Sr_1.4MnO₄ (LSMO₄) layered perovskite with K₂NiF₄ structure was prepared and evaluated as anode material for La_0.8Sr_0.2Ga_0.83Mg_0.17O_3 − δ (LSGM) electrolyte supported intermediate temperature solid oxide fuel cells (IT-SOFCs). X-ray diffraction results show that LSMO₄ is redox stability. Thermal expansion coefficient of LSMO₄ is close to that of LSGM electrolyte. By adopting LSMO₄ as anode and La_0.6Sr_0.4Co_0.8Fe_0.2O₃ (LSCF) as cathode, maxium power densities of 146.6, 110.9 mW cm^− 2 with H₂ fuel at 850, 800 °C and 47.3 mW cm^− 2 with CH₄ fuel at 800 °C were obtained, respectively. Further, the cell demonstrated a reasonably stable performance under 180 mA cm^− 2 for over 40 h with H₂ fuel at 800 °C.     

Fluoroethylene carbonate as an important component in organic carbonate electrolyte solutions for lithium sulfur batteries

The benefits of fluoroethylene carbonate (FEC)-based electrolyte solution (1 M LiPF₆ in FEC/dimethyl carbonate (DMC)) over ethylene carbonate (EC)-based electrolyte solution (1 M LiPF₆ in EC/DMC) for the cycling of sulfur/carbon (S/C) composite cathodes were demonstrated for S/C composites prepared with two drastically different types of carbon hosts, micrometer-sized activated carbon powder (AC1) and carbonized polyacrylonitrile (PAN) cloth. The formation of solid electrolyte interphase (SEI) on the surface of the cycled S/C electrodes was demonstrated using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS).     

Thermal reactions of lithiated graphite anode in LiPF6-based electrolyte

The thermal reactions of a lithiated graphite anode with and without 1.3 M lithium hexafluorophosphate (LiPF₆) in a solvent mixture of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were investigated by means of differential scanning calorimetry (DSC). The products of the thermal decomposition occurring on the lithiated graphite anode were characterized by Fourier transform infrared (FT-IR) analysis. The lithiated graphite anode showed two broad exothermic peaks at 270 and 325 °C, respectively, in the absence of electrolyte. It was demonstrated that the first peak could be assigned to the thermal reactions of PF₅ with various linear alkyl carbonates in the solid electrolyte interphase (SEI) and that the second peak was closely related to the thermal decomposition of the polyvinylidene fluoride (PVdF) binder. In the presence of electrolyte, the lithiated graphite anode showed the onset of an additional exothermic peak at 90 °C associated with the thermal decomposition reactions of the SEI layer with the organic solvents.     

Microwave assisted volatilization of silicon as fluoride for the trace impurity determination in silicon nitride by dynamic reaction cell inductively coupled plasma-mass spectrometry

A low pressure microwave assisted vapor phase dissolution procedure for silicon nitride and volatilization of in situ generated SiF₄ has been developed using H₂SO₄, HF and HNO₃ for the determination of trace impurities present in silicon nitride. Sample was taken in minimum amount (0.5 mL for 100 mg) of H₂SO₄ and treated with vapors generated from HF and HNO₃ mixture in presence of microwaves in a closed container. An 80 psi pressure with ramp and hold times of 30 min and 60 min respectively, operated twice, resulted in 99.9% volatilization of Si. Matrix free solutions were analyzed for impurities using DRC-ICP-MS. The recoveries of Cr, Mn, Fe, Ni, Co, Cu, Zn, Sr, Y, Cd, Ba and Pb were between 80 and 100% after volatilization of Si. The blanks were in lower ng g⁻¹ with method detection limits in lower ng g⁻¹ to sub ng g⁻¹ range. The method was applied for the analysis of two silicon nitride samples.     

Complex formation equilibria between Ag(I) and thioureas in n-propanol

Complex formation equilibria between Ag(I) and thiourea or N-alkyl-substituted thioureas have been investigated in n-propanol by potentiometry at 10 °C intervals from 5 to 50 °C. Stepwise formation of tris-coordinated AgL_n (n = 1-3) complexes has been found for the majority of the ligands. ΔH and ΔS values for the complex formation reactions have been evaluated from the dependence of ln β_n on temperature. The alkyl-substituents affect the ligand affinities in different ways in relation with the coordination level n.The reactions are exothermic with few exceptions. Enthalpy favoured complex formation with negative dependence of ΔG on temperature (ΔS > 0) have been found.The enthalpy and entropy changes for the stepwise complex formation equilibria are correlated by two linear compensative relationships with the same isoequilibrium temperature 50-51 °C.     

Preparation and photocatalytic activity of ZnO/TiO2/SnO2 mixture

ZnO/TiO₂/SnO₂ mixture was prepared by mixing its component solid oxides ZnO, TiO₂ and SnO₂ in the molar ratio of 4?1?1, followed by calcining the solid mixture at 200-1300 °C. The products and solid-state reaction process during the calcinations were characterized with powder X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and Brunauer-Emmett-Teller measurement of specific surface area. Neither solid-state reaction nor change of crystal phase composition took place among the ZnO, TiO₂ and SnO₂ powders on the calcinations up to 600 °C. However, formation of the inverse spinel Zn₂TiO₄ and Zn₂SnO₄ was detected at 700-900 and 1100-1200 °C, respectively. Further increase of the calcination temperature enabled the mixture to form a single-phase solid solution Zn₂Ti_0.5Sn_0.5O₄ with an inverse spinel structure in the space group of . The ZnO/TiO₂/SnO₂ mixture was photocatalytically active for the degradation of methyl orange in water; its photocatalytic mass activity was 16.4 times that of SnO₂, 2.0 times that of TiO₂, and 0.92 times that of ZnO after calcination at 500 °C for 2 h. But, the mass activity of the mixture decreased with increasing the calcination temperature at above 700 °C because of the formation of the photoinactive Zn₂TiO₄, Zn₂SnO₄ and Zn₂Ti_0.5Sn_0.5O₄. The sample became completely inert for the photocatalysis after prolonged calcination at 1300 °C (42 h), since all of the active component oxides were reacted to form the solid solution Zn₂Ti_0.5Sn_0.5O₄ with no photocatalytic activity.     

Surface modification of carbon anodes for secondary lithium battery by fluorination

Recent results on the surface modification of petroleum cokes and their electrochemical properties as anodes of secondary lithium batteries are summarized. The surface of petroleum coke and those heat-treated at 1860-2800 °C were fluorinated by elemental fluorine (F₂), chlorine trifluoride (ClF₃) and nitrogen trifluoride (NF₃). No surface fluorine was found except only one sample when ClF₃ and NF₃ were used as fluorinating agents while surface region of petroleum coke was fluorinated when F₂ was used. Transmission electron microscopic (TEM) observation revealed that closed edge of graphitized petroleum coke was destroyed and opened by surface fluorination. Raman spectra showed that surface fluorination increased the surface disorder of petroleum cokes. Main effect of surface fluorination with F₂ is the increase in the first coulombic efficiencies of petroleum cokes graphitized at 2300-2800 °C by 12.1-18.2% at 60 mA/g and by 13.3-25.8% at 150 mA/g in 1 mol/dm³ LiClO₄-ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1, v/v). On the other hand, main effect of the fluorination with ClF₃ and NF₃ is the increase in the first discharge capacities of graphitized petroleum cokes by ∼63 mAh/g (∼29.5%) at 150 mA/g in 1 mol/dm³ LiClO₄-EC/DEC.     

Chemical analysis of acidic silicon etch solutions: I. Titrimetric determination of HNO3, HF, and H2SiF6

The chemical etching of silicon using HF-HNO₃ mixtures is a widely used process in the processing of silicon wafers for microelectronic or photovoltaic applications. The control of the etch bath composition is the necessary condition for an effective bath utilization, for the replenishment of the consumed acids, and to maintain a certain etch rate. The present paper describes two methods for the total analysis of the individual etch bath constituents HF, HNO₃, and H₂SiF₆. Both methods start with an aqueous acid-base titration determining the total acid concentration and the concentration of H₂SiF₆. The first method is an acid-base titration using a 0.1 mol L⁻¹ methanolic solution of cyclohexylamine (CHA) as non-aqueous titrant to determine the content of nitric acid. Then, the amount of hydrofluoric acid is calculated from the difference between the total acid and nitric acid content. The second method is based on the determination of the total fluoride concentration using a fluoride ion-selective electrode (F-ISE). The content of hydrofluoric acid is obtained from the difference between the total fluoride content and the amount of fluoride bound as H₂SiF₆. The amount of nitric acid results finally calculated as difference to the total acid content.     

A chemical route for the synthesis of cubic bismuth zinc niobate pyrochlore nanopowders

Cubic bismuth zinc niobate pyrochlore (base composition (Bi_1.5Zn_0.5)(Zn_0.5Nb_1.5)O₇) powders were successfully prepared by a chemical method. The formation mechanism of the pyrochlore phase was investigated by TG-DSC, FT-IR, Raman, and X-ray diffraction (XRD). The optical bandgap for the powders treated at temperatures ranging from 500 to 700 °C is 3.0-3.1 eV, indicating low crystallization temperature for the pyrochlore phase. No detectable intermediary phases as BiNbO₄ or a pseudo-orthorhombic pyrochlore were observed at any time and the cubic-BZN phase was already formed after thermal treatment at temperatures as low as 500 °C. The phase formation study reveals that a well-crystallized single-phased nanopowder is obtained after calcination at 700 °C, indicating that the chemical synthesis conferred a higher chemical homogeneity and reactivity on the powder, modifying the crystallization mechanism.     

Optimization of the photocatalytic activity of CdO + CdTiO3 coupled oxide thin films obtained by sol-gel technique

In the preparation of CdO + CdTiO₃ polycrystalline thin films by the sol-gel method, the optical, structural and crystalline properties, as well as the photocatalytic activity (PA) depends strongly on the sintering temperature (Ts) of the films and of the Ti/Cd ratio used in the precursor solution. In this work, CdO + CdTiO₃ thin films were prepared using a Ti/Cd constant ratio in the precursor solution. The films were sintered at six different Ts in the 450-550 °C range, in an open atmosphere. The structure of the films was characterized by X-ray diffraction and the PA was evaluated by the photobleaching of methylene blue in an aqueous solution using a UV-vis spectrometer. The relative intensity of the diffraction peaks associated with CdO and CdTiO₃, change with the Ts. The better photocatalytic activities were obtained for the films sintered at 490 °C and 550 °C. When the CdO was removed from the films by chemical etching the PA decreased, showing the importance of coupling both oxides.     

Synthesis of alkali-metal cobalt kambaldaite by precipitation method

Alkali-metal cobalt kambaldaite (alkali-metal cobalt carbonate hydroxide hydrate; ideal structure, M₂Co₈(CO₃)₆(OH)₆ · 6H₂O; M-CoKBL) was prepared by the addition of a cobalt nitrate solution into a solution containing a large excess of alkali-metal bicarbonate followed by aging at 50 °C for 2–3 h. Hydrated alkali-metal ions are present in the channels of the kambaldaite structure; therefore, we tried to ion-exchange the K-CoKBL sample with various metals. However, collapse of the kambaldaite structure took place easily because of low pH of the ion-exchange solution. The catalytic activity of Co₃O₄ obtained by the calcination of “ion-exchanged” K-CoKBL was dependent on the residual potassium content in the catalyst.     

Effect of the content of hydrogen fluoride in an etchant on the formation of nanopores in silicon during electrolytic etching

The effect of the HF content on the formation of nanopores in silicon during electrochemical etching was studied. Nanoporous silicon layers were established to be formed only when hydrogen fluoride content in etchants (initial HF content: 49 wt %) was higher than 10–12 vol %. The mass and charge balance of the electrolytic etching of silicon was calculated, and the change in charge number of reaction (effective silicon valence) was determined depending on the HF content. The obtained data were used to propose a silicon etching model with the formation of SiF₄ and nanoporous silicon (where nanopores were formed due to the action of predominantly (HF₂)^? ions).     

The reaction of MgCl2·4H2O with CCl2F2

A new reaction of MgCl₂·4H₂O with CCl₂F₂ is investigated by DTA and TG from room temperature to 350 °C. It is observed that MgF₂ was obtained between 252 and 350 °C, Below the temperature, MgCl₂·4H₂O dehydrates and hydrolyzes to MgCl₂ and Mg(OH)Cl, which are the real reactants of the reaction with CCl₂F₂. The formation of MgF₂ is ascribed to the reaction of MgCl₂ and Mg(OH)Cl with HF, which forms by decomposition of CCl₂F₂ with the taking part in of H₂O released from dehydration of hydrated magnesium chloride on the surface of MgCl₂ and Mg(OH)Cl, which catalyzes the decomposition of CCl₂F₂ in this case. Consequently, the reactions are tested in the fluid-bed condition. It is found that MgF₂ formed at temperatures down to 200 °C in a fluid-bed reactor. This reaction may be used as a method of disposing of the environmentally sensitive CCl₂F₂ (rather than release into the atmosphere). It is also a method for the preparation of MgF₂.     

Synthesis of nano-sized crystalline oxide ion conducting fluorite-type Y2O3-doped CeO2 using perovskite-like BaCe0.9Y0.1O2.95 (BCY) and study of CO2 capture properties of BCY

Formation of nano-sized Y₂O₃-doped CeO₂ (YCO) was observed in the chemical reaction between proton conducting Y₂O₃-doped BaCeO₃ (BCY) and CO₂ in the temperature range 700-1000 °C, which is generally prepared by wet-chemical methods that include sol-gel, hydrothermal, polymerization, combustion, and precipitation reactions. BCY can capture CO₂ of 0.13 g per ceramic gram at 700 °C, which is comparable to that of the well-known Li₂ZrO₃ (0.15 g per ceramic gram at 600 °C). Powder X-ray diffraction (PXRD), energy dispersive X-ray analysis (EDX), laser particle size analysis (LPSA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ac impedance spectroscopy were employed to characterize the reaction product obtained from reaction between BCY and CO₂ and subsequent acid washing. PXRD study reveals presence of fluorite-like CeO₂ (a=5.410 (1) Å) structure and BaCO₃ in reaction products. TEM investigation of the acid washed product showed the formation of nano-sized material with particle sizes of about 50 nm. The electrical conductivity of acid washed product (YCO) in air was found to be about an order higher than the undoped CeO₂ reported in the literature.